Sample records for kadavu high-mg adakite

  1. Origin of co-existing basalts, high-Mg andesites, and adakites in the SW Japan hot subduction system (United States)

    Kimura, J.; Kunikiyo, T.; Osaka, I.; Shimoshioiri, Y.; Katakuse, M.; Kakubuchi, S.; Nagao, T.; Furuyama, K.; Kamei, A.; Nakajima, J.; Stern, R. J.; Gill, J. B.


    In response to subduction of the young, hot Shikoku Basin of the Philippine Sea Plate (PSP) slab, arc magmas have been active throughout the late Cenozoic (high-Mg andesites (HMAs), and adakitic andesites and dacites. The OIB-type basalts preceded the arc-type magmas. Therefore, the transition from OIB- to arc-types was related to opening of the Japan of Sea back-arc basin and subsequent re-initiation of PSP subduction. However, both the origin and tectonic implications of this magmatism are debated. Consequently, we analyzed the bulk rock geochemistry of 340 lava samples from seven Quaternary volcanoes and investigated their sources and melting conditions using a geochemical mass balance model, Arc Basalt Simulator version 4 (ABS4). Comparison to basement granitoids precludes adakite genesis in the lower crust. Instead, the ABS4 model suggests that the adakites are mostly slab melts plus minor interaction with mantle wedge peridotite (PERID). Increasing involvement of PERID during slab melt-fluxed mantle melting explains fairly well the geochemical variations of the shoshonites, mildly alkalic to sub-alkalic basalts, and HMAs. We propose that the generation of various magma types in the late Cenozoic SW Japan arc originated simply by "slab melt-fluxed mantle melting" with large variations in melting conditions including depth, temperature, degree of melting, and flux fractions. Such volcanism has been continuous from 13 Ma (Setouchi HMA) to the present, so that the hot subduction system, involving subduction of the Shikoku Basin spreading ridge, should be continuous since 13 Ma beneath the SW Japan arc. Our results further suggest that this atypically hot system generated diverse primary arc magmas from various degrees of flux melting even though the slab source components and sub-arc mantle are fairly homogeneous.

  2. High-Mg adakitic rocks and their complementary cumulates formed by crystal fractionation of hydrous mafic magmas in a continental crustal magma chamber (United States)

    Ma, Qiang; Xu, Yi-Gang; Zheng, Jian-Ping; Sun, Min; Griffin, William L.; Wei, Ying; Ma, Liang; Yu, Xiaolu


    Understanding how adakitic magmas form is important for understanding the formation of the continental crust. Generating such high-Sr/Y rocks by crystal fractionation of basalts/basaltic andesites in magma chambers has been proposed in a wide range of tectonic settings. However, the complementary cumulates predicted by this scenario have rarely been observed. The late Triassic (~ 227 Ma) Ningcheng complex from the North China Craton is composed of a websterite - (Ol -/Hbl-) pyroxenite - gabbro unit and a quartz-diorite unit. They are interpreted as the products (cumulates and derivative melts, respectively) of fractionation from hydrous mafic magmas at mid- to lower-crustal pressures (4.9 ~ 8.3 kbar). The quartz diorites are high-Mg intermediate rocks with moderate SiO2 (57.0 ~ 62.9 wt%), high Mg# (> 49) and adakitic trace element signatures, such as high Sr (≥ 636 ppm) and light rare earth elements (REEs), low Y (≤ 17 ppm) and heavy REEs (Yb ≤ 1.8 ppm), lack of obvious Eu anomalies, and high Sr/Y (≥ 31) and La/Yb (≥ 24)). These adakitic signatures reflect differentiation of hydrous mantle-derived magmas in the deep crust, leaving behind a plagioclase-free residual solid assemblage in the early stages, which is represented by the coeval websterite-pyroxenite complex. This study therefore not only demonstrates that hydrous crystal fractionation is an important mechanism to form adakitic rocks, but also presents an example of a preserved fractionating system, i.e. high-Sr/Y rocks and their complementary cumulates. A geochemical comparison is made between representative adakitic rocks formed by fractionation of hydrous magmas and Archean TTGs. It is suggested that crystal fractionation is an efficient process for making Phanerozoic high Sr/Y rocks but was not responsible for the formation of Archean granitoids.

  3. Early Cretaceous continental delamination in the Yangtze Block: Evidence from high-Mg adakitic intrusions along the Tanlu fault, central Eastern China (United States)

    Jia, Liqiong; Mo, Xuanxue; Santosh, M.; Yang, Zhusen; Yang, Dan; Dong, Guochen; Wang, Liang; Wang, Xinchun; Wu, Xuan


    Early Cretaceous high-Mg adakitic rocks from central Eastern China provide important insights into the thinning mechanism of the over-thickened lithosphere in the Yangtze Block (YB) as well as the North China Block (NCB). The Tanlu fault (TLF), located between the North China and Yangtze Blocks, and has been considered as a prominent pathway of magmas and fluids that resulted in lithosphere thinning of the YB during the Mesozoic-Cenozoic. Here we report the petrology, whole-rock geochemistry, zircon U-Pb geochronology, in situ Hf isotopes, and whole-rock Sr-Nd-Pb isotopes of four high-Mg adakitic intrusions along the TLF in northeastern Langdai. These adakitic intrusions consist of monzodiorite, quartz monzonite porphyry, and quartz monzodiorite. Zircon LA-MC-ICPMS analyses of five samples yield weighted mean 206Pb/238U ages of 127.58 ± 0.80, 126.90 ± 0.81, 120.71 ± 0.64, 122.75 ± 0.57, and 129.2 ± 1.1 Ma, indicating their emplacement during the Early Cretaceous. The intrusions have intermediate SiO2 (53.18-65.48 wt%) and high potassium (K2O = 3.07-3.95 wt%; Na2O/K2O = 1.02-1.26) and are classified as shoshonitic to high-K calc-alkaline series. They are characterized by high MgO (1.80-7.35 wt%), Mg# (50-65), Sr (591-1183 ppm), Ni (20.3-143.0 ppm), and Cr (51.40-390.0 ppm) contents, high (La/Yb)N (11.60-28.33) and Sr/Y (27.9-113.5) ratios, and low Y (7.79-22.4 ppm) and Yb (0.60-2.01 ppm) contents, comparable with high-Mg adakites. The samples are enriched in light rare earth elements but depleted in heavy rare earth elements and high field strength elements with slightly negative to positive Eu anomalies (δEu = 0.81-1.30), resembling the features of high-Mg adakitic rocks. Their whole-rock εNd(t) = -16.2 to -15.0, initial (87Sr/86Sr)i = 0.7060-0.7074, low radiogenic Pb (206Pb/204Pb(t) = 16.208-16.509, 207Pb/204Pb(t) = 15.331-15.410, and 208Pb/204Pb(t) = 36.551-36.992), and zircon εHf(t) = -36.6 to -16.6 suggest magma derivation from a continental crustal

  4. 内蒙古林西早中生代O型高镁埃达克质安山岩的发现及其意义%Early Mesozoic O-type High-Mg Adakitic Andesites from Linxi Area, Inner Mongolia and Its Implication

    Institute of Scientific and Technical Information of China (English)

    王冬兵; 刘勇胜; 宗克清; 高长贵; 徐娟


    对内蒙古林西地区火山岩样品的地球化学研究表明,其具有大洋型(O型)高镁埃达克质安山岩的地球化学特征[w(SiO_2)=57.89%~63.97%、w(Al_2O_3)=15.39%~16.17%、w(Na_2O)/w(K_2O)=1.5~2.2(除一个为0.9)、A/CNK=0.83~0.97、Mg~#=49~64、w(Cr)=91~209 μg/g、w(Ni)=52.2~111.4 μg/g、w(Sr)=551~1 018 μg/g、w(Yb)=1.18~1.71 μg/g、w(Y)=12.6~17.7 μg/g、δ(Eu)=0.86~0.94]. 利用LA-ICP-MS对其锆石进行了U-Pb定年,得到~(206)Pb/~(238)U加权平均年龄为(244±2)Ma(MSWD=0.36).此时,区域内古亚洲洋已闭合,综合地球化学特征和区域地质环境说明,林西高镁埃达克质安山岩是由残余洋壳部分熔融并随后与地幔橄榄岩相互作用形成的.内蒙古林西早中生代高镁埃达克质安山岩的产出表明,洋壳来源的埃达克岩(O型埃达克岩)不仅可以随俯冲同时产生,而且也可以在非俯冲环境下由保存在古俯冲带地幔中的残余洋壳部分熔融产生.%This paper studies geochemical compositions of volcanic samples from Linxi area, Inner Mongolia. The results show that these samples have similar geochemical characteristics of ocean-type (O-type) high-Mg adakitic andesites[SiO~2 = 57.89%~63.97%,A1_2O_3= 15.39%~16.17%,Na_2O/K_2O=l.5~2.2 (except one of 0.9), A/CNK =0.83~0.97, Mg~#=49~64、Cr=91~209 μg/g, Ni = 52.2~111.4 μg/g, Sr=551~1 018 μg/g, Yb=l.18~1.71 μg/g, Y=12.6~17.7 μg/g, and δ(Eu)=0.86~0.94]. LA-ICP-MS zircon U-Pb dating results for the Linxi high-Mg adakitic andesites yield a weighted mean ~(206)Pb/~(238)U age of (244±2)Ma (MSWD=0.36), when the Paleo-Asian ocean was closed. The combination of geolog-ical setting and geochemical characteristics of the Linxi high-Mg adakitic andesites suggests that the Linxi high-Mg adakitic rocks were most probably derived from partial melting of the remnant of Paleo-Asian oce-anic crust and subsequently hybridized by mantle peridotite. Generation of the Linxi early

  5. An overview of adakite petrogenesis

    Institute of Scientific and Technical Information of China (English)

    Paterno R. Castillo


    The term adakite was originally proposed to define silica-rich, high Sr/Y and La/Yb volcanic and plutonic rocks derived from melting of the basaltic portion of oceanic crust subducted beneath volcanic arcs. It was also initially believed that adakite only occurs in convergent margins where young and thus still hot oceanic slabs are being subducted, but later studies have proposed that it also occurs in other arc settings where unusual tectonic conditions can lower the solidus of older slabs. Currently, adakite covers a range of arc rocks ranging from pristine slab melt, to adakite-peridotite hybrid melt, to melt derived from peridotite metasomatized by slab melt. Adakite studies have generated some confusions because (1) the definition of adakite combines com- positional criteria with a genetic interpretation (melt- ing of subducted basalt), (2) the definition is fairly broad and relies on chemistry as its distinguishing characteristic, (3) the use of high pressure melting experiment results on wet basalts as unequivocal proofs of slab melting and (4) the existence of ada- kitic rocks with chemical characteristics similar to adakites but are clearly unrelated to slab melting. Other studies have shown that adakitic rocks and a number of the previously reported adakites are pro- duced through melting of the mafic lower crust or ponded basaltic magma, high-pressure crystal frac- tionation of basaltic magma and low-pressure crystal fractionation of basaltic magma plus magma mixing processes in both arc or non-arc tectonic environ- ments. Despite the confusing interpretations on the petrogenesis of adakite and adakitic rocks, their in- vestigations have enriched our understanding of material recycling at subduction zones, crustal evolu- tionary processes and economic mineralization.

  6. Adakites from collision-modified lithosphere (United States)

    Haschke, M.; Ben-Avraham, Z.


    Adakitic melts from Papua New Guinea (PNG) show adakitic geochemical characteristics, yet their geodynamic context is unclear. Modern adakites are associated with hot-slab melting and/or remelting of orogenic mafic underplate at convergent margins. Rift-propagation over collision-modified lithosphere may explain the PNG adakite enigma, as PNG was influenced by rapid creation and subduction of oceanic microplates since Mesozoic times. In a new (rift) tectonic regime, decompressional rift melts encountered and melted remnant mafic eclogite and/or garnet-amphibolite slab fragments in arc collisional-modified mantle, and partially equilibrated with metasomatized mantle. Alternatively, hot-slab melting in a proposed newborn subduction zone along the Trobriand Trough could generate adakitic melts, but recent seismic P-wave tomographic models lack evidence for subducting oceanic lithosphere in the adakite melt region; however they do show deep subduction zone remnants as a number of high P-wave anomalies at lithospheric depths, which supports our proposed scenario.

  7. Adakitic magmas: modern analogues of Archaean granitoids (United States)

    Martin, Hervé


    Both geochemical and experimental petrological research indicate that Archaean continental crust was generated by partial melting of an Archaean tholeiite transformed into a garnet-bearing amphibolite or eclogite. The geodynamic context of tholeiite melting is the subject of controversy. It is assumed to be either (1) subduction (melting of a hot subducting slab), or (2) hot spot (melting of underplated basalts). These hypotheses are considered in the light of modern adakite genesis. Adakites are intermediate to felsic volcanic rocks, andesitic to rhyolitic in composition (basaltic members are lacking). They have trondhjemitic affinities (high-Na 2O contents and K 2O/Na 2O˜0.5) and their Mg no. (0.5), Ni (20-40 ppm) and Cr (30-50 ppm) contents are higher than in typical calc-alkaline magmas. Sr contents are high (>300 ppm, until 2000 ppm) and REE show strongly fractionated patterns with very low heavy REE (HREE) contents (Yb≤1.8 ppm, Y≤18 ppm). Consequently, high Sr/Y and La/Yb ratios are typical and discriminating features of adakitic magmas, indicative of melting of a mafic source where garnet and/or hornblende are residual phases. Adakitic magmas are only found in subduction zone environments, exclusively where the subduction and/or the subducted slab are young (situation is well-exemplified in Southern Chile where the Chile ridge is subducted and where the adakitic character of the lavas correlates well with the young age of the subducting oceanic lithosphere. In typical subduction zones, the subducted lithosphere is older than 20 Ma, it is cool and the geothermal gradient along the Benioff plane is low such that the oceanic crust dehydrates before it reaches the solidus temperature of hydrated tholeiite. Consequently, the basaltic slab cannot melt. The released large ion lithophile element (LILE)-rich fluids rise up into the mantle wedge, inducing both its metasomatism and partial melting. Afterwards, the residue is made up of olivine

  8. Experimental constraints on the origin of compositional variations in the adakite-TTG-sanukitoid-HMA family of granitoids (United States)

    Rapp, R. P.


    The current debate over whether or not Archean granitoids, including the TTG (tonalite-trondhjemite-granodiorite) and sanukitoid (high-Mg diorite) suites, are compositional analogues of modern day arc magmas related to "hot" subduction (adakites and high-Mg andesites, HMA), is for the most part an issue of semantics, the consequence of a definition for "adakite" that is too loose. That is not to say that the debate doesn't have important implications for the geodynamic setting in which growth of the Archean continental crust took place. Smithies (2000) and Martin (2002) both show that early-mid Archean (3.0--3.8 Ga) granitoids are generally restricted to low-Mg# TTG (with Mg# pressure interval of 1--4 GPa, have shown that low-moderate degrees of melting (˜10--40%) produces granitoid liquids with major- and trace-element characteristics comparable to both Archean TTG and low-Mg# adakite. These liquids are in equilibrium with garnet-bearing (garnet amphibolite or eclogite) crystalline residues; the mineral phases present in these residues (garnet, clinopyroxene, ± amphibole) impart to the melts the distinctive geochemical fingerprint that has come to be associated with both TTG and adakite. Experiments in which these "pristine" melts of garnet-bearing metabasalt are allowed to react with and assimilate mantle peridotite, simulating melt-rock reaction across the slab-wedge interface in modern subduction zones, or at the base of evolving Archean cratons, whatever the tectonic setting, produce hybridized granitoids resembling sanukitoids and HMAs. Assimilation of peridotite causes the Mg# of hybridizedTTG melts to increase, abundances of Cr and Ni to increase, SiO_2 to decrease, and the molar ratio [Al/(Ca+Na+K)] to decrease, but important trace element ratios (e.g., La/Yb, Sr/Y, Th/U) remain relatively unchanged, and primitive-mantle normalized abundance patterns of trace elements parallel those of the initial liquids. In terms of major- and trace-elements, therefore

  9. Episodic magmatism at 105 Ma in the Kinki district, SW Japan: Petrogenesis of Nb-rich lamprophyres and adakites, and geodynamic implications (United States)

    Imaoka, T.; Nakashima, K.; Kamei, A.; Itaya, T.; Ohira, T.; Nagashima, M.; Kono, N.; Kiji, M.


    Cretaceous episodic magmatism produced Nb-rich lamprophyres and adakitic granitoids in the Kinki district of SW Japan. K-Ar dating of minerals from the lamprophyres, adakites, and hornblende peridotite xenoliths yielded ages of 109-99 Ma, indicating a short-lived episodic magmatism. The lamprophyres generally display primitive high-Mg basaltic to basaltic andesite compositions with high Mg# and high Cr and Ni contents that preclude substantial differentiation. Some high-Nb basalt (HNB) and Nb-enriched basalt (NEB) compositions also occur. The lamprophyres have high large-ion lithophile element (LILE) and high field-strength element (HFSE) contents and variable (La/Yb)n ratios, and can be divided into high-(La/Yb)n (12.5-22.1) and low-(La/Yb)n (3.6-6.1) groups. The former contains nepheline-normative rocks with positive initial ɛNd(T) values, whereas the latter contains hypersthene-normative subalkaline rocks with negative initial ɛNd(T) values. The adakitic granitoids have relatively high TiO2, Nb, and Ta contents compared to more typical high-silica adakites elsewhere, indicating that they were produced by high temperatures (ca. 920 to 970 °C) during slab melting.

  10. Mesozoic adakitic rocks from the Xuzhou-Suzhou area, eastern China: Evidence for partial melting of delaminated lower continental crust (United States)

    Xu, Wen-Liang; Wang, Qing-Hai; Wang, Dong-Yan; Guo, Jing-Hui; Pei, Fu-Ping


    Adakitic rocks in the Xuzhou-Suzhou area, eastern China, consist of dioritic and monzodioritic porphyries and were dated at 131-132 Ma by the SHRIMP U-Pb zircon method. These rocks have high MgO content (1.47-5.73%), high Mg # values (0.49-0.61), and high La/Yb and Sr/Y ratios. These features are similar to rocks derived from partial melting of a subducted oceanic slab. However, their high initial 87Sr/ 86Sr (0.7053-0.7075) and low ɛNd( t) values (-4.43˜-13.14) are inconsistent with the origin from slab melting. These rocks often contain garnet residual crystals and eclogite, garnet clinopyroxenite, and garnet amphibolite xenoliths. Petrographical characteristics and estimated P- T conditions of these xenoliths indicate that they were once deeply subducted and subsequently underwent rapid exhumation in the early Mesozoic. Garnet residual crystals from the porphyries show similar chemical compositions to garnets from garnet clinopyroxenite and garnet amphibolite xenoliths. Ages of the inherited zircons of the xenoliths and their host rocks likely indicate that sources for the adakitic magma and protoliths of the eclogite and garnet clinopyroxenite xenoliths in the study area were from Precambrian basement of the North China Craton. The data also suggest that the lower continental crust in the eastern North China Craton was thickened during the early Mesozoic and delaminated in the early Cretaceous. The high-Mg adakitic magma resulted from partial melting of this delaminated lower continental crust and its subsequent interaction with the mantle during upward transport, leaving garnet as the residual phase.

  11. Mesozoic adakitic rocks from the Xuzhou Suzhou area, eastern China: Evidence for partial melting of delaminated lower continental crust (United States)

    Xu, Wen-Liang; Wang, Qing-Hai; Wang, Dong-Yan; Guo, Jing-Hui; Pei, Fu-Ping


    Adakitic rocks in the Xuzhou-Suzhou area, eastern China, consist of dioritic and monzodioritic porphyries and were dated at 131-132 Ma by the SHRIMP U-Pb zircon method. These rocks have high MgO content (1.47-5.73%), high Mg # values (0.49-0.61), and high La/Yb and Sr/Y ratios. These features are similar to rocks derived from partial melting of a subducted oceanic slab. However, their high initial 87Sr/ 86Sr (0.7053-0.7075) and low ɛNd( t) values (-4.43 to -13.14) are inconsistent with the origin from slab melting. These rocks often contain garnet residual crystals and eclogite, garnet clinopyroxenite, and garnet amphibolite xenoliths. Petrographical characteristics and estimated P-T conditions of these xenoliths indicate that they were once deeply subducted and subsequently underwent rapid exhumation in the early Mesozoic. Garnet residual crystals from the porphyries show similar chemical compositions to garnets from garnet clinopyroxenite and garnet amphibolite xenoliths. Ages of the inherited zircons of the xenoliths and their host rocks likely indicate that sources for the adakitic magma and protoliths of the eclogite and garnet clinopyroxenite xenoliths in the study area were from Precambrian basement of the North China Craton. The data also suggest that the lower continental crust in the eastern North China Craton was thickened during the early Mesozoic and delaminated in the early Cretaceous. The high-Mg adakitic magma resulted from partial melting of this delaminated lower continental crust and its subsequent interaction with the mantle during upward transport, leaving garnet as the residual phase.

  12. Early Cretaceous high-Mg diorites in the Yanji area, northeastern China: Petrogenesis and tectonic implications (United States)

    Ma, Xing-Hua; Cao, Rui; Zhou, Zhen-Hua; Zhu, Wen-Ping


    Mesozoic granitic rocks are widely distributed in northeast (NE) China. However, high-Mg dioritic rocks are considerably rare. Here, we report a newly recognized high-Mg diorite (the Xintun diorite) in the Yanji area, NE China, to constrain its origin and implications for the tectonic evolution of eastern Asian continental margin. Zircon U-Pb dating yields a crystallization age of 128 ± 1 Ma for the Xintun diorite. The diorites are characterized by high MgO (4.4-6.6 wt.%), Cr (119-239 ppm), Ba (419-514 ppm) and Sr (649-747 ppm) contents and Mg# values (59-64), but low FeOtotal/MgO ratios (1.2-1.4), with geochemical features similar to those of sanukitic high-Mg andesites (HMAs). They show moderate radiogenic Sr (ISr = 0.7047-0.7050) and Nd (εNd = 0.3-1.1), with high La/Sm ratios, which are indicative of contributions from sediment components. The mineral assemblage of euhedral hornblende, magnetite and titanite, implies a water-rich and oxidized signature for their primitive magmas. These features suggest that the Xintun high-Mg diorites were probably formed via partial melting of the subducting sediments and subsequent interaction of mantle peridotites with both melts and aqueous fluids. Geochemical modeling reveals that hornblende-dominated fractional crystallization under water-sufficient conditions enabled the evolved magmas to acquire adakitic signatures. We believe that the Paleo-Pacific subduction beneath eastern Asian continental margin caused large-scale back-arc extension of NE China in the Early Cretaceous, and, consequently, induced the asthenospheric flow toward the mantle wedge, reheating subducting sediments enough to cause melting. Therefore, the occurrence of the Xintun high-Mg diorites signifies the onset of extensive back-arc extension of eastern Asian continental margin at ca. 128 Ma.

  13. Generation of the Early Cenozoic adakitic volcanism by partial melting of mafic lower crust, Eastern Turkey: Implications for crustal thickening to delamination (United States)

    Karsli, Orhan; Dokuz, Abdurrahman; Uysal, İbrahim; Aydin, Faruk; Kandemir, Raif; Wijbrans, Jan


    Early Cenozoic (48-50 Ma) adakitic volcanic rocks from the Eastern Pontides, NE Turkey, consist of calc-alkaline and high-K calc-alkaline andesite and dacite, with SiO 2 contents ranging from 56.01 to 65.44 wt.%. This is the first time that Early Eocene volcanism and adakites have been reported from the region. The rocks are composed of plagioclase, amphibole, quartz, and Mg-rich biotite. They have high and low-Mg# values ranging from 55 to 62 and 13 to 42, respectively. High-Mg# rocks have higher Ni and Co contents than low-Mg# samples. The rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements, depletions in Nb, Ta and Ti and have high La/Yb and Sr/Y ratios. Their relative high ISr (0.70474-0.70640) and low ɛNd (50 Ma) values (- 2.3 to 0.8) are inconsistent with an origin as partial melts of a subducted oceanic slab. Combined major- and trace element and Sr-Nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region, where a transition from a collision to an extension stage has created thickening and delamination of the Pontide mafic lower crust at 50 Ma. The high-Mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle, and its subsequent interaction with the mantle peridotite during upward transport, leaving garnet as the residual phase, elevates the MgO content and Mg# of the magmas, whereas low-Mg# magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling, which supplies heat flux to the lower crust. The data also suggest that the mafic lower continental crust beneath the region was thickened between the Late Cretaceous and the Late Paleocene and delaminated during Late Paleocene to Early Eocene time, which coincides with the initial stage of crustal thinning caused by crustal extensional events in the Eastern Pontides and rules out the

  14. Two-types of Early Cretaceous adakitic porphyries from the Luxi terrane, eastern North China Block: Melting of subducted Paleo-Pacific slab and delaminated newly underplated lower crust (United States)

    Wang, Hao; Xu, Zhaowen; Lu, Xiancai; Fu, Bin; Lu, Jianjun; Yang, Xiaonan; Zhao, Zengxia


    The origin and tectonic setting of Early Cretaceous adakitic rocks from the Luxi terrane in the eastern North China Block (NCB) remain debated. To resolve this issue, we determined whole-rock geochemistry, zircon U-Pb ages, and in situ Hf-O isotopes of the Mengyin and Liujing adakitic porphyries from the Luxi terrane. Zircon U-Pb dating results reveal that both the Mengyin and Liujing plutons were emplaced during the Early Cretaceous, with weighted mean 206Pb/238U ages of 130 ± 1 Ma (2σ) and 131 ± 2 Ma (2σ), respectively. In addition, abundant Neoarchean-Paleoproterozoic inherited zircon cores are identified in the Mengyin adakitic porphyry with 207Pb/206Pb ages ranging from 2.53 to 2.42 Ga. Rocks of both plutons are silicic (SiO2 = 65.4-70.2 wt.%), metaluminous, and alkaline in composition, comprising mainly quartz syenite porphyries. Samples from both plutons are enriched in large ion lithophile elements (LILEs) (e.g., Rb, Sr, and Ba), and light rare earth elements (LREEs), depleted in high field strength elements (HFSEs) (e.g., Nb, Ta, and Ti), and heavy rare earth elements (HREEs), and have either positive or no Eu anomalies. In addition, both adakitic porphyries have high Mg# values (51-64), high Sr and La contents, low Y and Yb contents, and high Sr/Y (Mengyin = 149-264; Liujing = 58-110) and (La/Yb)N (Mengyin = 32.4-45.3; Liujing = 43.8-53.1) ratios, similar to adakitic rocks worldwide. The Mengyin adakitic porphyry has higher whole-rock εNd(t) values (-5.8 to - 4.1), more radiogenic Pb [(206Pb/204Pb)i = 18.35-18.39, (207Pb/204Pb)i = 15.55-15.56, (208Pb/204Pb)i = 38.20-38.23], higher zircon rim εHf(t) values (+ 3.3 to + 8.8) and δ18O values (+ 6.5‰ to + 7.9‰), and lower (87Sr/86Sr)i ratios (0.7049-0.7050) than the Liujing adakitic porphyry [εNd(t) = - 12.4 to - 12.2, (206Pb/204Pb)i = 17.63-17.72, (207Pb/204Pb)i = 15.56-15.58, (208Pb/204Pb)i = 37.76-37.94, εHf(t) = - 14.8 to - 11.2, δ18O = + 5.9‰ to + 7.1‰, (87Sr/86Sr)i = 0.7090-0.7091]. The

  15. Genesis of high-Mg andesites through shallow fractionation of primitive arc basalts at elevated oxygen fugacities (United States)

    Zellmer, G. F.; Shellnutt, J. G.


    The petrogenesis of high-Mg andesites has been linked to a variety of processes, including partial melting of hydrous mantle peridotite, re-equilibration of partial melts of the subducting slab with the mantle wedge, and assimilation of lower crustal cumulates into dacitic melts. Yet none of these processes can explain the recently identified association of adakitic andesites, many of which are high-Mg andesites, with regions of elevated surface heat flux that are likely related to unusually shallow magma ponding levels in the upper crust (Zellmer, 2009). Using MELTS modeling, we demonstrate here that at high oxygen fugacities (NNO+2, which based on whole-rock Fe3+/Fe2+ ratios is appropriate for the Western and Central Aleutians, the Trans-Mexican Volcanic Belt, and the Setouchi Volcanic Belt), shallow crustal pressures (0.7 kbar), and initial H2O contents between 0.5 and 4 wt%, iron-magnesium spinel will be fractionated from primitive arc basalts, producing andesitic residual melts with elevated Mg#. Subsequent assimilation of a few percent of autocrystic mafic phases makes typical high-Mg andesites with forsteritic olivines. Orthopyroxenes in equilibrium with these melts are Cr-rich due to increased uptake of Cr into orthopyroxene (Dopx/lq≥25) at lower temperatures (≤1130°C) and elevated oxygen fugacities (NNO+2). While arc magmas with high initial H2O contents will undergo early degassing induced crystallization and viscous stagnation, lower primary melt H2O contents will result in delayed crystallization and shallower magma ponding levels, accounting for elevated surface heat flux. Our findings are therefore consistent with the location of many high-Mg andesites in areas of high surface heat flux, and challenge the commonly accepted notion that these compositions are particularly hydrous primary melts generated in equilibrium with mantle peridotite. Reference: Zellmer G.F. (2009) Petrogenesis of Sr-rich adakitic rocks at volcanic arcs: insights from global

  16. Generation of continental adakitic rocks: Crystallization modeling with variable bulk partition coefficients (United States)

    Dai, Hong-Kun; Zheng, Jianping; Zhou, Xiang; Griffin, W. L.


    The geochemical signatures (i.e., high Sr/Y and La/Yb ratios) of adakitic rocks in continental settings, which are derived from the continental lower crust rather than from subducted slabs, may reflect high-pressure melting in the lower crust or may be inherited from their sources. The North China Craton (NCC) is an ideal place for investigation of this type of adakites due to its ubiquitous distribution. As an example, we explore the petrogenesis of the Jurassic ( 163 Ma) adakitic rocks in western Liaoning, in the NE part of the NCC, using elemental and Sr-Nd isotopic analysis and crystallization modeling based on Rhyolite-MELTS. The modeling demonstrates that adakitic signatures can be generated by fractional crystallization of magmas within crust of normal thickness (i.e., 33 km). Partial-melting modeling based on the composition of the lower continental crust shows that only the adakitic rocks from orogenic belts require a thickened crust (i.e., 45 km). We suggest that continental adakitic rocks are not necessarily linked to high-pressure processes and their use as an indicator of thickened/delaminated continental crust should be regarded with caution.

  17. Origin of adakite-like plutons in southern Korea (United States)

    Oh, Jeong-Im; Choi, Sung Hi; Yi, Keewook


    We present Sr-Nd-Pb isotopic compositions for two adakite-like intrusions in southern Korea (Jindong and Bongnae), including major and trace element concentrations, and the sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb age. Our aim is to constrain the origin and tectonomagmatic processes that gave rise to the plutons. A SHRIMP U-Pb zircon age of 88.7 ± 0.7 Ma was obtained from a Jindong granodiorite sample. The Jindong plutons belong to the medium-K calc-alkaline series, and have an overall enrichment in large ion lithophile elements (LILE), such as K, Rb, Ba, and Pb, and a relative depletion in high field strength elements, such as Nb, Ta, and Ti, compared with the neighboring elements in the primitive mantle-normalized multi-trace element variation diagram. It was found that (87Sr/86Sr)i = 0.70475-0.70596, (143Nd/144Nd)i = 0.512547-0.512604, [(εNd)i = + 0.4 to 2.2], and (206Pb/204Pb)i = 18.19-18.37, which fall within the field of the arc-type Cretaceous to Tertiary Bulguksa intrusive rocks in the Sr-Nd and Pb-Pb isotopic correlation diagrams. The elevated Sr/Y (17-40), but low La/Yb (3.7-8.8) ratios of the Jindong plutons, together with their coherent geochemical trends and U-shaped rare earth element (REE) patterns, indicate that they were not formed by slab melting, but by amphibole-dominated fractional crystallization of the Bulguksa-like arc magma. A SHRIMP U-Pb zircon age of 226.5 ± 2.5 Ma was obtained from a Bongnae tonalite sample. The Bongnae plutons belong to the shoshonitic series. Their trace element patterns resemble the Jindong samples, but are characterized by significantly negative U anomalies in mafic rocks. They also have elevated MgO, Ni, Co, Cr, Rb, Ba, Sr, and low Al2O3 and Na2O contents at a given SiO2 concentration compared with the Jindong plutons, and are typified by highly radiogenic Sr and unradiogenic Nd and Pb isotopic compositions: [(87Sr/86Sr)i = 0.71096-0.71290, (143Nd/144Nd)i = 0.511641-0.511681, (εNd)i = - 13

  18. Post-collisional plutonism with adakitic signatures: The Triassic Yangba granodiorite (Bikou terrane, northern Yangtze Block)

    Institute of Scientific and Technical Information of China (English)

    QIN Jiangfeng; LAI Shaocong; LI Yongfei


    The post-collisional Yangba granodiorite intruded into the Bikou metasedimentary-volcanic group, southern Mianlue Suture, central China. The host granodiorites contain many mafic microgranular enclaves which have acicular apatite, phenocrysts of host granodiorites, implying that the enclaves have been incorporated as magma globules into host granodioritic magma and undergone rapid cooling. The variation trends of major and trace elements between enclaves and host rocks suggest a mixing and mingling process with respect to their petrogenesis. The mafic microgranular enclaves are characterized by shoshonite with SiO2≤63%, σ (4.54-6.18)>3.3, high K2O content (4.22%-6.04%), K2O/Na2O>1; in the K2O-SiO2 diagram, all the samples plot in the shoshonite field, which are enriched in LILE and LREE, with obvious Nb, Ta negative anomalies, indicating a subducting fluid-metasomatised mantle source. Zircon LA-ICP-MS dating of the granodiorites yielded an age of 215.4±8.3 Ma, indicating they were formed during the late-orogenic or post-collisional stage (≤242±21 Ma) of the South Qinling Mountain Belt. The host granodiorites have many close compositional similarities to high-silica adakites from supra-subduction zone setting, but tend to have a higher concentration of K2O (3.22%-3.84%) and Mg#. Chondrite-normalized rare-earth element patterns are characterized by high ratios of (La/Yb)N, the extreme HREE depletion and a lack of significant Eu anomalies. In conjunction with the high abundances of Ba and Sr as well as the low abundances of Y and HREE, these patterns suggest a feldspar-poor, garnet ± amphibole-rich fractionation mineral assemblage. High Mg# values demonstrate that the host granodiorites were contaminated by enclave magma. On a whole, integrated geological and geochemical studies suggested the Yangba granodiorites and their mafic microgranular enclaves resulted from mixing of enriched mantle-derived shoshonitic magma and thickened lower crust-derived felsic

  19. Geochemical Characteristics and Petrogenesis of Adakites in Sikhote-Alin, Russian Far East (United States)

    Wu, Jeremy Tsung Jui; Jahn, Bor-ming; Nechaev, Victor; Chashchin, Alexander; Yokoyama, Kazumi; Tsutsumi, Yukiyasu


    The Sikhote-Alin orogenic belt and late Precambrian Khanka block are two major tectonic units in the southernmost Russian Far East. The Sikhote-Alin belt comprises several tectonostratigraphic terranes, including late Precambrian nappes, and Mesozoic accretionary prisms and turbidite basins. These terranes are overlain by Cretaceous to Paleocene felsic to intermediate volcanic rocks and intruded by granitoids. The magmatic rocks are collectively known as "the East Sikhote-Alin volcano-plutonic belt" (ESAVPB), and mainly characterized by acid-to-intermediate compositions. In this work we study the petrogenesis of adakitic rocks and discuss the possible tectonic implications. Adakitic rocks of the Sikhote-Alin orogen were emplaced in two main periods: Early Cretaceous (132-98 Ma) and Eocene (46-45 Ma). They mainly occur in the Khanka block, with a subordinate amount in the ESAVPB. The adakites show a large range of chemical composition: SiO2 = 57-74%, Al2O3 = 15-18%, Na2O = 3.5-6.1%, K2O = 0.7-3.2%, Na2O/K2O = 1.1-3.9, Sr/Y = 33-145, and (La/Yb)N = 11-53. HREE and HFSE are remarkably depleted. The Early Cretaceous adakites show eNd(T) = -1.0 to +3.2; ISr = 0.7040 - 0.7090, and the Eocene adakites have eNd(T) = -2.0 to +2.2; ISr = 0.7042 - 0.7058. Thus, the Cretaceous and Eocene adakites show rather similar Sr-Nd isotopic compositions, but their Nd isotopic signatures (slightly negative to positive eNd(T) values) may distinguish them from the granitoids of the ESAVPB (only negative eNd(T) values). Adakites may have different modes of generation, but partial melting of meta-basic rocks in a subduction zone is considered the most likely mode for the present case. The two periods of adakites have probably formed in the following scenario. The early Cretaceous emplacement ages for the adakites and the oldest granitoids of the ESAVPB, is considered as the time of initiation of the Paleo-Pacific subduction in NE Asia. The Eocene adakites were also generated in subduction

  20. Adakitic (tonalitic-trondhjemitic) magmas resulting from eclogite decompression and dehydration melting during exhumation in response to continental collision (United States)

    Song, Shuguang; Niu, Yaoling; Su, Li; Wei, Chunjing; Zhang, Lifei


    Modern adakite or adakitic rocks are thought to result from partial melting of younger and thus warmer subducting ocean crust in subduction zones, with the melt interacting with or without mantle wedge peridotite during ascent, or from melting of thickened mafic lower crust. Here we show that adakitic (tonalitic-trondhjemitic) melts can also be produced by eclogite decompression during exhumation of subducted and metamorphosed oceanic/continental crust in response to continental collision, as exemplified by the adakitic rocks genetically associated with the early Paleozoic North Qaidam ultra-high pressure metamorphic (UHPM) belt on the northern margin of the Greater Tibetan Plateau. We present field evidence for partial melting of eclogite and its products, including adakitic melt, volumetrically significant plutons evolved from the melt, cumulate rocks precipitated from the melt, and associated granulitic residues. This “adakitic assemblage” records a clear progression from eclogite decompression and heating to partial melting, to melt fractionation and ascent/percolation in response to exhumation of the UHPM package. The garnetite and garnet-rich layers in the adakitic assemblage are of cumulate origin from the adakitic melt at high pressure, and accommodate much of the Nb-Ta-Ti. Zircon SHRIMP U-Pb dating shows that partial melting of the eclogite took place at ∼435-410 Ma, which postdates the seafloor subduction (>440 Ma) and temporally overlaps the UHPM (∼440-425 Ma). While the geological context and the timing of adakite melt formation we observe differ from the prevailing models, our observations and documentations demonstrate that eclogite melting during UHPM exhumation may be important in contributing to crustal growth.

  1. Southern Tibetan Oligocene-Miocene adakites: A record of Indian slab tearing (United States)

    Zhang, Li-Yun; Ducea, Mihai N.; Ding, Lin; Pullen, Alex; Kapp, Paul; Hoffman, Derek


    Oligocene-Miocene granitoids exposed within the 1500-km-long Gangdese arc of southern Tibet exhibit adakitic compositions. Five plutonic samples from the southeastern Lhasa terrane near Namche Barwa area were analyzed to determine their geochemical characteristics and to better understand the geodynamic evolution of the eastern Himalayan syntaxis orogen. The samples, yielded U-Pb zircon ages in the range of 30-26 Ma, are intermediate to silicic in composition and have elevated K2O (1.5-8.9), Th/La ratios (0.14-1.10), low MgO (< 2%) and Mg# (< 50), as well as high initial 87Sr/86Sri (0.7062-0.7103) and low εNd(t) (- 10.9 to - 1.0) isotopic compositions. In addition, these granitic and granodioritic rocks have high Sr/Y (66-306) and La/Yb (25-312) ratios, a characteristic of adakitic rocks. In-situ zircon εHf(t) isotopic compositions are in the range of + 8.1 to - 1.9. Within the framework of the Tibetan-Himalayan orogenesis we attribute these rocks to represent partial melting and mixing products of two end-member components of the lower Tibetan crust: the roots of the relatively juvenile Gangdese arc crust and newly-underplated high-potassium mafic magmas. Adakitic magmatism initiated at 30-26 Ma near the eastern Himalayan syntaxis and systematically decreases in age to the west to 18-9 Ma near Shigatse. We attribute this temporal-spatial distribution of adakitic magmatism within the Gangdese arc, along with the regional Oligo-Miocene geology, to the progressive tearing of the Indian plate. Based on the decrease in age of adakitic magmatism from east to west we hypothesize that the tear initiated beneath the eastern Himalayan syntaxis and propagated westward.

  2. Genesis of high-Mg andesites (HMA) through shallow fractionation of primitive arc basalts at elevated oxygen fugacities (and low initial water contents) (United States)

    Zellmer, Georg; Shellnutt, Gregory


    The petrogenesis of high-Mg andesites has been linked to a variety of processes, including partial melting of hydrous mantle peridotite, re-equilibration of partial melts of the subducting slab with the mantle wedge, and assimilation of lower crustal cumulates into dacitic melts. Yet none of these processes can explain the recently identified association of adakitic andesites, many of which are high-Mg andesites, with regions of elevated surface heat flux that are related to unusually shallow magma ponding levels in the upper crust (Zellmer, 2009). Using MELTS modeling, we demonstrate here that at elevated oxygen fugacities (NNO+2, which based on whole-rock Fe3+/Fe2+ ratios is appropriate for the Western and Central Aleutians, the Trans-Mexican Volcanic Belt, and the Setouchi Volcanic Belt), shallow crustal pressures (0.7 kbar), and initial H2O contents between 0.5 and 4 wt%, iron-magnesium spinel will be fractionated from primitive arc basalts, producing andesitic residual melts with elevated Mg#. Subsequent assimilation of a few percent of autocrystic mafic phases makes typical high-Mg andesites with forsteritic olivines. Orthopyroxenes in equilibrium with these melts are Cr-rich due to increased uptake of Cr into orthopyroxene (Dopx-lq ≥25) at lower temperatures (≤1130° C) and elevated oxygen fugacities (NNO+2). While arc magmas with high initial H2O contents will undergo early degassing induced crystallization and viscous stagnation, lower primary melt H2O contents will result in delayed crystallization and shallower magma ponding levels, accounting for elevated surface heat flux. Our findings are therefore consistent with the location of many high-Mg andesites in areas of high surface heat flux, and challenge the commonly accepted notion that these compositions are particularly hydrous primary melts generated in equilibrium with mantle peridotite. Reference: Zellmer G.F. (2009) Petrogenesis of Sr-rich adakitic rocks at volcanic arcs: insights from global

  3. Geochemistry of the high-Mg andesites at Zhangwu, western Liaoning: Implication for delamination of newly formed lower crust

    Institute of Scientific and Technical Information of China (English)

    HUANG; Hua; GAO; Shan; HU; ZhaoChu; LIU; XiaoMing; YUAN; HongLing


    the thickening of the lower crust and formation of lower crustal eclogite, followed by foundering of the eclogitic lower crust into the asthenosphere. The foundered eclogite then melted and the resultant melts interacted with surrounding peridotite during their upward transport, which finally produced the high-Mg andesites. This well explains the high-Mg adakitic characters and absence of ancient inherited zircon in the Zhangwu lavas.

  4. Magmatic relationships and ages between adakites, magnesian andesites and Nb-enriched basalt-andesites from Hispaniola: Record of a major change in the Caribbean island arc magma sources (United States)

    Escuder Viruete, J.; Contreras, F.; Stein, G.; Urien, P.; Joubert, M.; Pérez-Estaún, A.; Friedman, R.; Ullrich, T.


    Located in the Cordillera Central of the Dominican Republic, the Late Cretaceous Tireo Fm (TF) records a major change of the magma sources in the Caribbean island arc. It comprises a > 3 km thick sequence of arc-related volcanic and volcano-sedimentary rocks with variable geochemical characteristics. Combined detailed mapping, stratigraphy, geochemistry and U-Pb/Ar-Ar geochronology show that the volcanic rocks of the Tireo Fm include two main volcanic sequences. The lower volcanic sequence is dominated by monotonous submarine vitric-lithic tuffs and volcanic breccias of andesite to basaltic andesite, with minor interbedded flows of basalts and andesites. Fossil and (U-Pb and 40Ar- 39Ar) geochronological data show that arc magmatism in the lower sequence began to accumulate before ˜ 90 Ma, from the Aptian to Turonian. These rocks constitute an island arc tholeiitic suite, derived from melting by fluxing of a mantle wedge with subduction-related hydrous fluids. The upper volcanic sequence is characterized by a spatial and temporal association of adakites, high-Mg andesites, and Nb-enriched basalts, which collectivelly define a shift in the composition of the subduction-related erupted lavas. A dacitic to rhyolitic explosive volcanism with subaerial and episodic aerial eruptions, and sub-volcanic emplacements of domes, characterize mainly this stratigraphic interval. The onset of this volcanism took place at Turonian-Coniacian boundary and continued in the Santonian to Lower Campanian, with minor events in the Late Campanian. Adakites represent melts of the subducting slab, magnesian andesites the product of hybridization of adakite liquids with mantle peridotite, and Nb-enriched basalts melts of the residue from hybridization. We propose a model of oblique ridge subduction at ˜ 90 Ma and possibly subsequent slab window formation, as principal cause of magmatic variations recorded in the Caribbean island arc, above a southwestern-dipping subduction zone.

  5. Adakites related to subduc- tion in the northern margin of Junggar arc for the Late Paleozoic: Products of slab melting

    Institute of Scientific and Technical Information of China (English)


    Volcanic rocks with adakitic compositional signature have been recognized in the northern margin of ancient Junggar island arc for the Late Paleozoic. These adakites for the early Devonian from the Tuoranggekudouke Group (D1t) are characteristic of high Sr, Sr/Y and (La/Yb)N but low Y, Yb and HREE. Their compositional characteristics are much similar to those of the typical adakites in the world but distinct from those of the normal arc volcanic rocks from the same Group. We conclude that these adakitic volcanic rocks were produced by slab melting during the early period of Paleoasia-ocean lithosphere subduction. This infers that the Paleoasia Ocean in the north Junggar area began a new subduction process in the early Devonian.

  6. 埃达克岩: 关于其成因的一些不同观点%Adakites: some variations on a theme

    Institute of Scientific and Technical Information of China (English)


    Adakites were proposed over a decade ago to be products of the melting of young subducted oceanic crust. In fact, several new localities have been discovered since the original work documented approximately ten localities in modern arcs (e.g., southwestern Japan, Trans Mexican Volcanic Belt, etc.). But work over the past ten years has also shown that adakites can be generated by other processes during subduction (e.g., along the edge of tears in the subducting slab, remnant slabs left in the upper mantle, etc.). In addition, adakites appear to be associated with a suite of rocks including high-Mg andesites resulting from either adakite interaction with the mantle (Adak-type) or melting of the mantle during adakite interaction (Piip-type), niobium enriched arc basalts (NEAB) that are believed to be derived from the partial melting of a mantle metasomatized extensively by adakites, and possibly boninites (several researchers have found an adakite component in boninites). A new rock suite, the adakite metasomatic volcanic series, has been proposed to account for the various associations. In addition, a large number of NEAB have been found to contain ultramafic mantle xenoliths with clear evidence of reaction between ultradepleted mantle and adakites.Several alternative hypotheses have been proposed for the generation of adakites primarily involving the melting of the lower crust rather than the subducting slab. One model proposes that the melting of the lower crust occurs when basaltic melts underplate the lower crust. There are many reasons that appear to rule this method out. The other model proposes that in areas where the continental crust is thick, the lower crust can become eclogitic and separate and sink into the mantle (delaminate). This delamination process will bring the lower sections of the lower crust or the upper part of the delaminated lower crust in contact with relatively hot mantle, which could initiate melting, and the production of adakites. This

  7. Partial melting of subducted paleo-Pacific plate during the early Cretaceous: Constraint from adakitic rocks in the Shaxi porphyry Cu-Au deposit, Lower Yangtze River Belt (United States)

    Deng, Jianghong; Yang, Xiaoyong; Li, Shuang; Gu, Huangling; Mastoi, Abdul Shakoor; Sun, Weidong


    A large porphyry Cu-Au deposit associated with early Cretaceous intrusive rocks has been discovered and explored in the Shaxi area, Lower Yangtze River Belt (LYRB), eastern China. We studied two types of intrusive rocks in the Shaxi area: Cu-Au mineralization related diorites and quartz-diorites (adakitic rocks), and newly found high Sr/Y ratio biotite-gabbros. They were formed almost simultaneously with crystallization ages of ca. 130 to 129 Ma, younger than the early stage shoshonitic rocks (Longmenyuan, Zhuanqiao and Shuangmiao Fm.) in the Luzong volcanic basin, ~ 10 km south of the Shaxi area. These intrusive rocks show similar distribution patterns of trace elements (enriched in LILEs and depleted in HFSEs) and REEs (enriched in LREEs and depleted in HREEs, no Eu negative anomaly, flat HREE patterns). The diorites and quartz-diorites are adakitic rocks with calc-alkaline affinity, distinguished from other adakitic rocks in the LYRB which are high-K calc-alkaline series. The biotite-gabbros are not adakitic rocks, although they are characterized by high Sr/Y ratios. Shaxi adakitic rocks show positive zircon εHf(t) values, which may be attributed to the contribution of subducted oceanic crust, while the εHf(t) values of the biotite-gabbros are mostly negative, indicating the involvement of old crustal materials. Although Sr-Nd-Pb isotopes of Shaxi adakitic rocks are more depleted than those of other adakitic rocks in the LYRB, they are still slightly enriched, similar to continental arc adakites in the Andean Austral Volcanic Zone. The Shaxi adakitic rocks are characterized by high Sr contents and Sr/Y ratios, medium (La/Yb)N, MgO contents and Mg#, and low K2O/Na2O ratios, decoupling of Sr/Y and (La/Yb)N, low Th/U values, exhibiting characteristics of slab-derived adakitic rocks. They were not produced by fractional crystallization of basaltic magmas like adakitic rocks in Edong-Jiurui and Tongling but originally generated from partial melting of subducted

  8. The genesis of early Carboniferous adakitic rocks at the southern margin of the Alxa Block, North China (United States)

    Xue, Shuo; Ling, Ming-Xing; Liu, Yu-Long; Zhang, Hong; Sun, Weidong


    Adakite is a highly debated petrologic term that was originally proposed to describe igneous rocks formed by slab melting. Subsequent studies reported other ways to generate adakitic signatures such as the melting of mafic lower continental crust and fractional crystallization of basaltic magma. We studied adakitic rocks from the Taohuala Mountain at the southern margin of the Alxa Block, North China. These rocks are characterized by high Sr concentrations (300-450 ppm), high Sr/Y (20-75 ppm) and (La/Yb)N (25-67 ppm) ratios, and low Y (diagram, combined with their high (87Sr/86Sr)i ratios (0.7113-0.7131) and low εNd(t) (- 15.8 to - 16.8) and εHf(t) (- 18 to - 10) values of zircon, indicates that the adakitic rocks formed by partial melting of thickened continental crust. U-Pb dating of zircons using LA-ICP-MS yields an early Carboniferous age of 330 ± 5 Ma. The ages and spatial distribution of magmatic rocks indicate that the Paleo-Asian oceanic crust subducted towards the Alxa Block in the late Paleozoic. Subsequently, northward slab rollback occurred during the Carboniferous. Therefore, we propose that the adakitic rocks from the Taohuala Mountain formed by partial melting of previously thickened lower continental crust, induced by the upwelling of asthenospheric mantle during slab rollback.

  9. Late Triassic syn-exhumation magmatism in central Qiangtang, Tibet: Evidence from the Sangehu adakitic rocks (United States)

    Liu, Han; Wang, Bao-di; Ma, Long; Gao, Rui; Chen, Li; Li, Xiao-bo; Wang, Li-quan


    The geodynamic setting of Late Triassic magmatic activity along the Longmu Co-Shuanghu suture zone (LSSZ) in central Qiangtang, Tibet is a matter of debate. This paper presents zircon LA-ICP-MS U-Pb ages, zircon Hf isotopic compositions, and whole-rock geochemical data for the Sangehu (SGH) granitic intrusion in central Qiangtang, and addresses the petrogenesis of Late Triassic magmatism, and the history of collision between the northern and southern Qiangtang terranes. The SGH pluton consists mainly of biotite adamellite with mafic microgranular enclaves (MMEs), and small amounts of K-feldspar granite. The biotite adamellite, MMEs, and K-feldspar granite give ages of 207.8 ± 3.0 Ma, 212.4 ± 31 Ma, and 211.6 ± 3.8 Ma, respectively. The MMEs show magmatic textures and acicular apatite, and are coeval with the host biotite adamellite, suggesting they were produced by magma mixing. All samples from the SGH pluton show high Sr and low Y contents, and positive Eu anomalies, similar to adakitic rocks. The high K2O contents and low Mg#, Cr, and Ni contents, and enriched Hf isotopic characteristics of the zircons indicate that these magmas were derived from the partial melting of thickened crust. However, the whole-rock geochemical data and zircon Hf isotopic compositions also reveal heterogeneity at the source. The combined magmatic and metamorphic records suggest that Triassic magmatic activity in central Qiangtang was closely related to the collision of the northern and southern Qiangtang terranes. The large-scale Late Triassic (225-200 Ma) magmatic event in central Qiangtang may have resulted from the breakoff of the Longmu Co-Shuanghu Tethys Ocean lithospheric slab in the early Late Triassic (236-230 Ma). The Late Triassic magmatic rocks, including adakitic rocks, are coeval with retrograde high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in central Qiangtang, and show characteristics of syn-exhumation magmatism. The early adakitic rocks (>220 Ma

  10. Mantle decarbonation and Archean high-Mg magmas (United States)

    Edwards, Garth R.


    Magnesium-rich mane to ultramafic extrusions were most common in the Archean and pose interesting petrological problems. The high Mg content of komatiites (>18 wt%, for example, is usually interpreted as indicating an origin at higher temperatures than exist in mantle melting zones in the modern Earth. Current contrasting models for the origin of komatiites in the mantle require either high degrees of melting or lower degrees of melting at great depth. A potential complementary mechanism for Mg enrichment in magmas involves the melting of magnesite-bearing garnet Iherxolite. In this model, the ascending primary mafic or ultramafic magma is enriched in MgO by the loss of some off the CO2 to the adjacent mantle at pressures of ˜2.2 GPa, where the magma becomes saturated with CO2. To generate komatiite in this way from a picritelike parent, for example, requires that the primary magma lose some of its major and trace element components to the adjacent mantle concurrently with the CO2. Production of magnesian magmas by magnesite breakdown may not have required the heat or depth of those produced by other means; this mechanism may help to explain some apparently low Archean geothermal gradients, as well as the contemporaneity of Archean diamonds and komatites. The mantle magnesite could have formed by direct reaction of primordial CO2 or CO with hot, protomantle material during Earth's accretionary period.

  11. Andean Adakites: Products of Slab Melting, Magma Evolution in Thickened Crust and Crustal Recycling by Forearc Subduction Erosion (United States)

    Kay, S. M.; Kay, R. W.; Goss, A.


    Adakites in the southern and central Andes show a residual garnet signature that can variously be related to local slab melting associated with subduction of hot oceanic crust at the Chile Triple Junction, widespread interaction of mafic magmas in regions of thickened crust, and episodic melting of crust removed by forearc subduction erosion, particularly at times of frontal arc migration. Among the most convincing slab-melt adakites on Earth are the late Miocene Cerro Pampa type dacitic adakites east of the Chile Triple Junction whose low 87Sr/86Sr ratios (0.7028-0.7033) and high Sr contents (up to 2300 ppm) are difficult to explain by any other mechanism. Elsewhere the appearance of transient extreme adakitic signatures at times of frontal arc migration can be explained by forearc subduction erosion and the evolution of magmas at deep crustal levels in a contractional regime provided the crust is thick. Transient steep adakitic-like REE patterns at times of arc migration fit with forearc crust being transported down the subduction channel, entering the tip of the asthenospheric wedge and being incorporated into the arc mantle source. Evidence for a genetic link for transient adakite signatures, arc migration and forearc subduction erosion comes from changing isotopic ratios in mafic magmas erupted before and after arc migration on the edges of the Chilean flat-slab near 27°S and 34°S (Kay et al 2005) where the arc front has migrated up to 50 km eastward in the last 8 Ma. The chemistry of these mafic magmas cannot be explained by enriched mantle or incorporation of subducted sediments or in situ crust. Sharp increases in 87Sr/86Sr ratios and transient steep REE patterns in Andean arc rocks erupted in the final stages of Cretaceous to early Tertiary magmatic cycles at 21°S to 26°S (see Haschke et al. 2002) can also be attributed to forearc subduction erosion. Forearc subduction erosion provides a better explanation for the formation of Aleutian and Central

  12. Post-collisional adakitic biotite plagiogranites from Guangtoushan pluton (Mianxian, central China): Petrogenesis and tectonic implication

    Institute of Scientific and Technical Information of China (English)

    QIN Jiangfeng; LAI Shaocong; LI Yongfei


    The post-collisional Guangtoushan pluton intruded into the Mianlue suture, Central China. Geochemi-cally, the Guangtoushan biotite plagiogranites show many close compositional similarities to high-silica adakites from the supra-subduction zone setting, but tend to have a higher concentration of K2O (3.22%-3.84%). Chondrite-normalized rare earth element pattems are characterized by high ratios of (La/Yb)N, concave-upward shapes of the heavy rare earth element (HREE), and a lack of significant Eu anomalies. In conjunction with high abundances of Ba and Sr, as well as low abundances of Y and HREE, these pattems suggest a feldspar-poor, garnet±amohibole-rich fractionation mineral assemblage. Coupled with previous studies, we suggest that the Guangtoushan biotite plagiogranites were likely to be caused by subducting slab break-off during the late orogenic stage in the West Qinling orogenic belt.

  13. Late Triassic high-Mg andesite/dacite suites from northern Hohxil, North Tibet: Geochronology, geochemical characteristics, petrogenetic processes and tectonic implications (United States)

    Wang, Qiang; Li, Zheng-Xiang; Chung, Sun-Lin; Wyman, Derek A.; Sun, Ya-Li; Zhao, Zhen-Hua; Zhu, Yin-Tang; Qiu, Hua-Ning


    This study reports age, petrologic and geochemical data for andesites and dacites from the Late Triassic sedimentary strata of northern Hohxil, in the Hohxil-Songpan-Ganzi Block (northern Tibet), which constitutes the most voluminous Triassic strata on Earth. LA-ICP-MS zircon U-Pb analysis of dacite (210.4 ± 1.9 Ma) and whole rock 40Ar- 39Ar analyses for both the andesites and dacites (211 ± 2 Ma and 210.9 ± 1.6 Ma) show that the rocks were almost contemporaneous. Both rock types are sodium-rich and calc-alkaline. The andesites, characterized by high MgO (up to 10 wt.%) or Mg # (~ 70), TiO 2, Al 2O 3, Cr, Ni, La/Yb and Th/La, but low Nb/Ta ratios, are geochemically similar to sanukitoids in southeastern Japan. The dacites are strongly peraluminous, and have high Al 2O 3 and La/Yb, low Y and Yb, coupled with negligible to positive Eu and Sr anomalies, comparable to slab-derived adakites in the circum Pacific arc system. Both rocks exhibit strongly fractionated platinum group element patterns, with Pt/Pt* (Pt anomaly), (Pt/Ir) N and Re/Os ratios higher than those of the primitive mantle. They have uniformly low ɛNd(t) values (- 7.57--9.59) and high ( 86Sr/ 87Sr) i ratios (0.7086-0.7106) that imply a continental rather than oceanic type magma source. We suggest that the northern Hohxil dacites were produced by partial melting of subducted sediments on the northward-subducting Songpan-Ganzi oceanic slab, and the high-Mg andesites were formed by subsequent interaction between the sediment-derived melts and mantle wedge peridotites. Taking into account the Triassic magmatic record from nearby regions, we suggest that the Late Triassic high-Mg andesite/dacite suites of northern Hohxil were generated in a forearc setting, and propose that double-sided subduction eventually closed the Songpan-Ganzi ocean during the Late Triassic.

  14. Potassic volcanic rocks and adakitic intrusions in southern Tibet: Insights into mantle-crust interaction and mass transfer from Indian plate (United States)

    Liu, Dong; Zhao, Zhidan; DePaolo, Donald J.; Zhu, Di-Cheng; Meng, Fan-Yi; Shi, Qingshang; Wang, Qing


    Elucidating geodynamic processes at depth relies on a correct interpretation of petrological and geochemical features in magmatic records. In southern Tibet, both potassic volcanic rocks and adakitic intrusions exhibit high Sr/Y and La/Yb, and low Y and Yb concentrations. But these two rock types have contrasting temporal-spatial distributions and isotopic variations. Here we present a systematic study on the postcollisional potassic and adakitic rocks in order to investigate their petrogenetic links with the coeval mantle-derived ultrapotassic rocks and shed light on the potential input from underthrusted Indian continental crust. We found that adakitic intrusions with higher K2O/Na2O tend to display lower Y and higher SiO2, suggesting that the mantle-derived ultrapotassic melts, showing relatively high Y and Yb concentrations, only played a minor role in adakitic magmatism. Therefore, the unradiogenic 143Nd/144Nd and the dramatic decrease of zircon εHf(t) values since 35 Ma shown by postcollisional adakites should be interpreted as reflecting the crustal input from Indian plate. Unlike adakitic intrusions in southern Lhasa subterrane, potassic volcanic rocks share similar spatial distributions with ultrapotassic rocks, and their isotopic discrepancy is diminishing with volcanic activity becomes younger and migrates eastward. Evidence from whole-rock Pb and zircon Hf isotopes further indicates that potassic volcanic rocks are more likely to originate from partial melting of the overthickened and isotopically heterogeneous Lhasa terrane crust rather than the underthrusted Indian continental crust. The elevated Rb/Sr and varying Sr/CaO in potassic volcanic rocks provide an argument for sanidine + plagioclase + clinopyroxene as the major fractionating phases during magmatic differentiation. These findings not only highlight the significance of potassic and adakitic rocks in providing constraints on the geodynamic processes beneath southern Tibet, but also imply that

  15. Cenozoic Adakite-type Volcanic Rocks in Qiangtang,Tibet and Its Significance

    Institute of Scientific and Technical Information of China (English)

    LIU Shen; HU Ruizhong; FENG Caixia; CHI Xiaoguo; LI Cai; YANG Rihong; WANG Tianwu; JIN Wei


    Volcanic rocks in the study area, including dacite, trachyandesite and mugearite, belong to the intermediate-acid, high-K calc-alkaline series, and possess the characteristics of adakite. The geochemistry of the rocks shows that therocks are characterized by SiO2>59%, enrichment in Al2O3 (15.09-15.64%) and Na2O (>3.6%), high Sr (649-885 μg/g)and Sc, low Y contents (<17 μg/g), depletion in HREE (Yb<1.22 μg/g), (La/Yb)N>25, Sr/Y>40, MgO<3% (Mg#<0.35),weak Eu anomaly (Eu/Eu*=0.84-0.94), and lack of the high field strength elements (HFSE) (Nb, Ta, Ti, etc.). The Nd andSr isotope data (87Sr/86Sr=0.7062-0.7079, 143Nd/144Nd=0.51166-0.51253, εNd= -18.61-0.02), show that the magmaresulted from partial melting (10%-40%) of newly underplated basaltic lower crust under high pressure (1-4 GPa), and thepetrogenesis is obviously affected by the crust's assimilation and fractional crystallization (AFC). This research will givean insight into the uplift mechanism of the Tibetan plateau.

  16. Using mineral geochemistry to decipher slab, mantle, and crustal inputs to the generation of high-Mg andesites from Mount Baker and Glacier Peak, northern Cascade arc (United States)

    Sas, M.; DeBari, S. M.; Clynne, M. A.; Rusk, B. G.


    A fundamental question in geology is whether subducting plates get hot enough to generate melt that contributes to magmatic output in volcanic arcs. Because the subducting plate beneath the Cascade arc is relatively young and hot, slab melt generation is considered possible. To better understand the role of slab melt in north Cascades magmas, this study focused on petrogenesis of high-Mg andesites (HMA) and basaltic andesites (HMBA) from Mt. Baker and Glacier Peak, Washington. HMA have unusually high Mg# relative to their SiO2 contents, as well as elevated La/Yb and Dy/Yb ratios that are interpreted to result from separation of melt from a garnet-bearing residuum. Debate centers on the garnet's origin as it could be present in mineral assemblages from the subducting slab, deep mantle, thick lower crust, or basalt fractionated at high pressure. Whole rock analyses were combined with major, minor, and trace element analyses to understand the origin of these HMA. In the Tarn Plateau (Mt. Baker) flow unit (51.8-54.0 wt.% SiO2, Mg# 68-70) Mg#s correlate positively with high La/Yb in clinopyroxene equilibrium liquids, suggesting an origin similar to that of Aleutian adakites, where slab-derived melts interact with the overlying mantle to become Mg-rich and subsequently mix with mantle-derived basalts. The source for high La/Yb in the Glacier Creek (Mt. Baker) flow unit (58.3-58.7 wt.% SiO2, Mg# 63-64) is more ambiguous. High whole rock Sr/P imply origin from a mantle that was hydrated by an enriched slab component (fluid ± melt). In the Lightning Creek (Glacier Peak) flow unit (54.8-57.9 SiO2, Mg# 69-72) Cr and Mg contents in Cr-spinel and olivine pairs suggest a depleted mantle source, and high whole rock Sr/P indicate hydration-induced mantle melting. Hence Lightning Creek is interpreted have originated from a refractory mantle source that interacted with a hydrous slab component (fluid ± melt). Our results indicate that in addition to slab-derived fluids, slab

  17. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, NE Iran

    Directory of Open Access Journals (Sweden)

    K. Jamshidi


    Full Text Available Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~ 350 (468–130 MPa, while amphiboles record both low pressures (~ 300 MPa and very high pressures (> 700 MPa of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa. The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process to intensify adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features, such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, imply final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  18. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, northeast Iran (United States)

    Jamshidi, K.; Ghasemi, H.; Troll, V. R.; Sadeghian, M.; Dahren, B.


    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, northeast Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~350 (130 to 468) MPa, while amphiboles record both low pressures (~300 MPa) and very high pressures (>700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process in intensifying adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, implies that final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  19. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, NE Iran (United States)

    Jamshidi, K.; Ghasemi, H.; Troll, V. R.; Sadeghian, M.; Dahren, B.


    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~ 350 (468-130) MPa, while amphiboles record both low pressures (~ 300 MPa) and very high pressures (> 700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process to intensify adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features, such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, imply final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  20. Petrogenesis of Cretaceous adakitic and shoshonitic igneous rocks in the Luzong area, Anhui Province (eastern China): Implications for geodynamics and Cu Au mineralization (United States)

    Wang, Qiang; Wyman, Derek A.; Xu, Ji-Feng; Zhao, Zhen-Hua; Jian, Ping; Xiong, Xiao-Lin; Bao, Zhi-Wei; Li, Chao-Feng; Bai, Zheng-Hua


    Both adakitic and shoshonitic igneous rocks in the Luzong area, Anhui Province, eastern China are associated with Cretaceous Cu-Au mineralization. The Shaxi quartz diorite porphyrites exhibit adakite-like geochemical features, such as light rare earth element (LREE) enrichment, heavy REE (HREE) depletion, high Al 2O 3, MgO, Sr, Sr / Y and La / Yb values, and low Y and Yb contents. They have low ɛNd( t) values (- 3.46 to - 6.28) and high ( 87Sr / 86Sr) i ratios (0.7051-0.7057). Sensitive High-Resolution Ion Microprobe (SHRIMP) zircon analyses indicate a crystallization age of 136 ± 3 Ma for the adakitic rocks. Most volcanic rocks and the majority of monzonites and syenites in the Luzong area are K-rich (or shoshonitic) and were also produced during the Cretaceous (140-125 Ma). They are enriched in LREE and large-ion lithophile elements, and depleted in Ti, and Nb and Ba and exhibit relatively lower ɛNd( t) values ranging from - 4.65 to - 7.03 and relatively higher ( 87Sr / 86Sr) i ratios varying between 0.7057 and 0.7062. The shoshonitic and adakitic rocks in the Luzong area have similar Pb isotopic compositions ( 206Pb / 204Pb = 17.90-18.83, 207Pb / 204Pb = 15.45-15.62 and 208Pb / 204Pb = 38.07-38.80). Geological data from the Luzong area suggest that the Cretaceous igneous rocks are distributed along NE fault zones (e.g., Tanlu and Yangtze River fault zones) in eastern China and were likely formed in an extensional setting within the Yangtze Block. The Shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of > 50 km (i.e., ˜1.5 GPa), possibly leaving rutile-bearing eclogitic residue. The shoshonitic magmas, in contrast, originated mainly from an enriched mantle metasomatized by subducted oceanic sediments. They underwent early high-pressure (> 1.5 GPa) fractional crystallization at the boundary between thickened (> 50 km) lower crust and lithospheric mantle and late low

  1. Using mineral geochemistry to decipher slab, mantle, and crustal input in the generation of high-Mg andesites and basaltic andesites from the northern Cascade Arc (United States)

    Sas, May; DeBari, Susan; Clynne, Michael A.; Rusk, Brian G.


    To better understand the role of slab melt in the petrogenesis of North Cascades magmas, this study focuses on petrogenesis of high-Mg lavas from the two northernmost active volcanoes in Washington. High-Mg andesites (HMA) and basaltic andesites (HMBA) in the Cascade Arc have high Mg# [molar Mg/(Mg+Fe2+)] relative to their SiO2 contents, elevated Nd/Yb, and are Ni- and Cr-enriched. The rock units examined here include the Tarn Plateau HMBA (51.8–54.0 wt% SiO2, Mg# 68–70) and Glacier Creek HMA (58.3–58.7 wt% SiO2, Mg# 63–64) from the Mount Baker Volcanic Field, and the Lightning Creek HMBA (54.8–54.6 SiO2, Mg# 69–73) from Glacier Peak. This study combines major and trace element compositions of minerals and whole rocks to test several petrogenetic hypotheses and to determine which, if any, are applicable to North Cascades HMA and HMBA. In the Tarn Plateau HMBA, rare earth element (REE) equilibrium liquids calculated from clinopyroxene compositions have high Nd/Yb that positively correlates with Mg#. This correlation suggests an origin similar to that proposed for Aleutian adakites, where intermediate, high Nd/Yb slab-derived melts interact with the overlying mantle to become Mg-rich, and subsequently mix with low Nd/Yb, mantle-derived mafic magmas with lower Mg#. In the Glacier Creek HMA, elevated whole-rock MgO and SiO2 contents resulted from accumulation of xenocrystic olivine and differentiation processes, respectively, but the cause of high Nd/Yb is less clear. However, high whole-rock Sr/P (fluid mobile/fluid immobile) values indicate a mantle source that was fluxed by an enriched, hydrous slab component, likely producing the observed high Nd/Yb REE signature. The Lightning Creek HMBA is a hybridized rock unit with at least three identifiable magmatic components, but only one of which has HMA characteristics. Cr and Mg contents in Cr-spinel and olivine pairs in this HMA component suggest that its source is a strongly depleted mantle, and high

  2. Geochemistry of high-Mg andesites from the early Cretaceous Yixian Formation, western Liaoning: Implications for lower crustal delamination and Sr/Y variations

    Institute of Scientific and Technical Information of China (English)

    WANG; Xiaorui; GAO; Shan; LIU; Xiaoming; YUAN; Honglin; HU; Zhaochu; ZHANG; Hong; WANG; Xuance


    85 volcanic rocks of the Yixian Formation from the Sihetun type section were collected and analyzed for geochemical and isotopic compositions. Major element compositions indicate that the Sihetun volcanic rocks are high magnesium andesites with some basalts occurring at the bottom of section. The Sihetun high magnesium andesites (SiO2 = 52.82-59.31wt%, Al2O3 = 14.15-16.35wt%)show many characteristics of adakites such as depletion in heavy rare-earth elements (HREE; Yb =1.03-1.88 μg/g) and Y(12-20 μg/g) and high Sr (620-1323 μg/g) and Sr/Y(32-88), with high LaN/YbN ratio (10-25). They share similar major and trace element characteristics to volcanic rocks from the Xinglonggou Formation except their lower Nd isotope ratios (143Nd/144Nd (130Ma) =0.5118-0.5119, εNd (130Ma) = -11.6--13.8, 87Sr/86Sr (130 Ma) = 0.7058-0.7064. They were interpreted in a way that eclogite that formed at the base of thickened Archean lower crust of the North China craton foundered into the convecting mantle and subsequently melted and interacted with peridotite. However, compared to the Xinglonggou volcanic rocks, the source of the Sihetun magma contained more ancient continental crustal material in order to explain its evolved Nd isotopes. The age of the Sihetun Formation was 120 to 130 Ma, and this indicates that delamination lasted to the early Cretaceous period. The Sr contents and Sr/Y ratios of the Sihetun high-Mg andesites show significant negative correlations with SiO2 for samples with SiO2 > 56%. These suggest that the Sr and Sr/Y values were reduced due to fractional crystallization of plagioclase. Accordingly, the effect of crystallization on volcanic Sr and Sr/Y ratio has to be taken into account.

  3. Paleozoic adakitic rocks in the northern Altyn Tagh, northwest China: Evidence for progressive crustal thickening beneath the Dunhuang Block (United States)

    Bao, Weihang; Long, Xiaoping; Yuan, Chao; Sun, Min; Zhao, Guochun; Wang, Yujing; Guan, Yili; Zhang, Yunying


    To constrain the Phanerozoic crustal evolution of the Dunhuang Block, new whole-rock geochemistry, zircon U-Pb ages and Hf isotopic data were determined for three Paleozoic granitic plutons in the northern Altyn Tagh, northwest China. Zircon U-Pb dating of these plutons, including gneissic granite, mylonitic granite and augen gneiss, yielded Middle Devonian to Early Carboniferous crystallization ages of 358 ± 4 Ma, 382 ± 4 Ma and 332 ± 2 Ma, respectively. The gneissic granites are characterized by a small SiO2 variation (69.11-70.33 wt.%) with moderate K2O (3.07-3.55 wt.%), Na2O (3.61-4.08 wt.%), low Fe2O3T (2.25-2.84 wt.%) and MgO (1.04-1.25 wt.%). The granites are weakly peraluminous with moderate aluminium saturation indexes (ASI = 1.02-1.08) and exhibit the geochemical features of high-K calc-alkaline igneous rocks. Although the major element contents of the mylonitic granites and the augen gneisses are different from those of the gneissic granites, all three plutons show similar REE patterns and trace element variations. Rocks from these plutons are all LREE-enriched and show relatively flat HREE patterns with pronounced depletions in Ba, Nb, Ta, Ti and negative Eu anomalies. Moreover, the rocks are characterized by high Sr (330.7-656 ppm), low Yb (0.513-1.521 ppm) and Y (5.199-13.73 ppm), and thus have high Sr/Y ratios (32-122), showing geochemical affinities of adakitic rocks. Their negative εHf(t) values, low MgO, Cr, Co and Ni contents indicate a continental crust origin without significant involvement of mantle-derived materials. The negative Eu anomalies, low Yb and Y contents of these granitic rocks reveal that plagioclase and garnet are major residue minerals in the magma source. All the geochemical characteristics demonstrate that these adakitic plutons were produced by partial melting of thickened lower crust at relatively shallow depths under high amphibolite or granulite facies and did not reach the eclogite facies. Combining this with the

  4. Repeated magmatism at 34 Ma and 23-20 Ma producing high magnesian adakitic andesites and transitional basalts on southern Okushiri Island, NE Japan arc (United States)

    Sato, Makoto; Shuto, Kenji; Nohara-Imanaka, Rikako; Takazawa, Eiichi; Osanai, Yasuhito; Nakano, Nobuhiko


    The southern part of Okushiri Island in the present-day back-arc margin of the NE Japan arc is one of the rare convergent plate boundaries where similar magma types (high-magnesian adakitic andesite (HMAA) and high-TiO2 basalt (HTB)) have been erupted concurrently at more than one time. Oligocene HMAA can be divided into two types: HMAA-I is characterized by high Sr/Y and low Y, and HMAA-II by relatively low Sr/Y and high Y. HMAA-I is primitive in terms of MgO (8.5 wt.%), Mg# (67), Ni (232 ppm) and Cr (613 ppm) contents, and the most Mg-rich olivine phenocrysts plot within the mantle olivine array in terms of Fo and NiO. The similar Cr versus Ni relations of types I and II HMAA indicate some interaction of slab-derived adakitic melts with mantle peridotite, whereas Ni contents are higher than those of most boninites derived by partial melting of mantle peridotite at a given Cr content. Types I and II HMAA have more enriched Sr and Nd isotopic compositions than N-MORB. The petrography and geochemistry of these rocks, combined with published results on the genesis of high-magnesian andesite (HMA) indicate that types I and II HMAA could be produced by interaction of slab (N-MORB and sediment)-derived adakitic melts with mantle peridotite. The comagmatism of HMAA and HTB is ascribed to the following model. A cool, less hydrous, adakite magma (spherical diapir) would rise from the subducting slab (Pacific Plate) and become more hydrous as a result of its interaction with overlying hydrous peridotite. This hydrated adakitic diapir further ascends and is heated on entering the overlying mantle wedge. Subsequently, the temperature and H2O gradients in the ascending adakitic diapir and surrounding mantle peridotite would have been established. The HTB magma segregated from the surrounding mantle peridotite region (high temperature and low H2O content) at a depth of 60 km or more, whereas the adakitic diapir (low temperature and high H2O content) continued to rise, with its

  5. Garnet-bearing tonalitic porphyry from East Kunlun, Northeast Tibetan Plateau: implications for adakite and magmas from the MASH Zone (United States)

    Yuan, Chao; Sun, Min; Xiao, Wenjiao; Wilde, Simon; Li, Xianhua; Liu, Xiaohan; Long, Xiaoping; Xia, Xiaoping; Ye, Kai; Li, Jiliang


    A garnet-bearing tonalitic porphyry from the Achiq Kol area, northeast Tibetan Plateau has been dated by SHRIMP U-Pb zircon techniques and gives a Late Triassic age of 213 ± 3 Ma. The porphyry contains phenocrysts of Ca-rich, Mn-poor garnet (CaO > 5 wt%; MnO 17 wt%) contents, and is metaluminous to slightly peraluminous (ACNK = 0.89-1.05). The rock samples are enriched in LILE and LREE but depleted in Nb and Ti, showing typical features of subduction-related magmas. The relatively high Sr/Y (~38) ratios and low HREE (Yb residual phase, while suppressed crystallization of plagioclase and lack of negative Eu anomalies indicate a high water fugacity in the magma. Nd-Sr isotope compositions of the rock (ɛNdT = -1.38 to -2.33; 87Sr/86Sri = 0.7065-0.7067) suggest that both mantle- and crust-derived materials were involved in the petrogenesis, which is consistent with the reverse compositional zoning of plagioclase, interpreted to indicate magma mixing. Both garnet phenocrysts and their ilmenite inclusions contain low MgO contents which, in combination with the oxygen isotope composition of garnet separates (+6.23‰), suggests that these minerals formed in a lower crust-derived felsic melt probably in the MASH zone. Although the rock samples are similar to adakitic rocks in many aspects, their moderate Sr contents (residual melt. It is suggested that extensive crystallization of apatite as an early phase may prevent some arc magmas from evolving into adakitic rocks even under high water fugacity.

  6. Adakitic-like magmatism in western Ossa-Morena Zone (Portugal): Geochemical and isotopic constraints of the Pavia pluton (United States)

    Lima, S. M.; Neiva, A. M. R.; Ramos, J. M. F.


    Granitic rocks are a major component of the Earth's continental crust and occur in a wide variety of tectonic settings. Their chemical and isotopic characterization is crucial to the recognition of the potential sources and mechanisms involved in their generation. In this study, we present the first whole rock chemical and isotopic (Sr-Nd-O) data for the Pavia pluton (328-317 Ma), located near the western border of the Ossa-Morena Zone (Évora Massif, Portugal). Major and trace element geochemistry suggests that the different granitic phases composing this intrusive body (enclaves, granites (s.l.) and crosscutting dikes) represent independent magma pulses and the majority is similar to TTGs and adakites. The little Sr-Nd-O isotopic variation, with (87Sr/86Sr)328 = 0.70428-0.70560, ɛNd328 ranging between - 3.4 and + 0.4 and δ18O varying from + 5.6‰ to + 8.4‰ implies an isotopically similar protolith for all phases. The most viable mechanism for the generation of the Pavia pluton adakitic-like magmatism is assimilation-fractional crystallization of a mantle-derived magma. This mechanism was also invoked to explain the genesis of other plutons within the Évora Massif but they have a distinct chemistry (typical arc calc-alkaline rocks). The chemical differences between them and the Pavia pluton granitic rocks are interpreted as the result of lower degrees of crustal assimilation and higher degrees of contamination of mantle-derived magmas by the sinking slab (after subduction blocking and subsequent slab break-off).

  7. Hot subduction: Magmatism along the Hunter Ridge, SW Pacific

    Energy Technology Data Exchange (ETDEWEB)

    Crawford, A.J.; Verbeeten, A.; Danyushevsky, L.V.; Sigurdsson, I.A. [SRC for Ore Deposit Research, Hobart, TAS (Australia); Maillet, P. [Australian National University, Canberra, ACT (Australia). Department of Geology; Maillet, P. [ORSTOM Centre de Brest, France, (France); Monzier, M. [ORSTOM Centre, Ecuador, (Ecuador)


    The Hunter `fracture zone` is generally regarded as a transform plate boundary linking the oppositely dipping Tongan and Vanuatu subduction systems. Dredging along the Hunter Ridge and sampling of its northernmost extent, exposed as the island of Kadavu in Fiji, has yielded a diversity of magmatic suites, including arc tholeiites and high-Ca boninites, high-Mg lavas with some affinities to boninites and some affinities to adakites, and true adakitic lavas associated with remarkable low-Fe, high-Na basalts with 8-16 ppm Nb (herein high-Nb basalts). Lavas which show clear evidence of slab melt involvement in their petrogenesis occur at either end of the Hunter Ridge, whereas the arc tholeiites and high-Ca boninites appear to be restricted to the south central part of the ridge. Mineralogical and whole rock geochemical data for each of these suites are summarized, and a tectono-magmatic model for their genesis and distribution is suggested. Trace element features and radiogenic isotope data for the Hunter Ridge lavas indicate compositions analogue to Pacific MORB-like mantle. Extended abstract. 6 refs., 2 figs.

  8. Adakite-type sodium-rich rocks in Awulale Mountain of west Tianshan: Significance for the vertical growth of continental crust

    Institute of Scientific and Technical Information of China (English)


    The sodium-rich dacites and albite porphyries of Permian in the Awulale Mountain of west Tianshan have unique chemical and trace element signatures identical to adakite. These intermediate-acidic igneous rocks are characterized by high Na2O, Al2O3 and Sr contents and high Sr/Y and La/Y ratios (>40 and >20, respectively), and low Y and Yb contents, and strong depletion in HREE, and posi- tive Eu anomaly. The (143Nd/144Nd)i is in the range from 0.51236 to 0.51248 and the e Nd(t) is positive value (+0.79- +3.11); the (87Sr/86Sr)i is in the range from 0.7052 to 0.7054. These Nd and Sr isotopic composition features indicate that the source rocks of these adakite-type rocks are from a weakly depleted mantle, or a depleted mantle, but was con-taminated by the crustal materials. These adakite-type rocks were most likely derived from the partial melting of new underplated basaltic rocks under the conditions of amphibo-lite to eclogite transition in the postcollisional environment of North Xinjiang during the Permian Period. They are not only the Phanerozoic juvenile crust materials, but also are probably animportant symbol of the underplating of mantle- derived basaltic magmas and the vertical growth of continen-tal crust in the west Tianshan area during the postcollision of Late Paleozoic.


    Institute of Scientific and Technical Information of China (English)

    王强; 许继锋; 赵振华


    Adakite is a kind of mediate and acid igneous Na-rich rock (andesite, dacite, sodiumic rhyolite and homologus intrusive rock ), with the sti ckup characteristics of SiO2≥56%, Al2O3≥15%,depletion in HREE and Y(Yb ≤1.9×10-6,Y≤18×10-6), high Sr(>400×10-6,rarely20.0~40.0), as well as positive Sr anomaly but absent or positive negative Eu anomaly. There are two types of adakites with different petrogenesis: one type is formed by the melting of subducting young ( ≤25~30 Ma) slab (Ⅰ-type adakite), and the other type is formed by the melting of basaltic lower crust under thickened setting (Ⅱtype adakite). Ⅰ-type adak ite has also these characteristics: sometimes associated with “high-Nb” or “Nb-enriched” basalt; usually reacting with the mantle during the adakitic ma gma uprising; closely related to high-pressure, ultra-pressure eclogite and sh allow earthquakes; sometimes associated with Au、Ag、Cu、Mo hydrotherm and porph yry deposit. In addition, Ⅰ-type adakite occurs when the age of subducted sla b is less than 25~30 Ma and the subducting slab reaches 70~80 km under the arc. The Mg#(Mg/(Mg+Fe)molar) of Ⅱtype adakite is generally less than 0.50. In the c ondition of aqua-undersaturation and the setting of thickened(>40 km) lower cru st, Ⅱtype adakite is apt to be formed by the melting of newly underplating basa ltic lower crust. Two types of adakites are very significative to studying geody namics, crust-mantle interaction, and the growth and evolution of continent cru st. We found the Ⅰ-type adakite in north Dabie and Qingling mountains and the Ⅱtype adakite in Shaxi region of Anhui province, and thought Shaxi porphyry Cu deposit could be related to Ⅱtype adakite.%埃达克岩(adakite)是一种中酸性富钠火成岩(安山岩、英安岩、钠质流纹岩及相应的侵入岩),其突出的地球化学特征就是SiO2≥56%,Al2O3≥15%,亏损重稀土元素(HREE)与Y(如Yb≤1.9×10-6,Y≤18×10

  10. Zircon U/Pb Dating of Cretaceous Adakitic Volcanic Rocks in the Eastern Part of North Dabie Mountains

    Institute of Scientific and Technical Information of China (English)

    薛怀民; 董树文; 刘晓春


    Mesozoic volcanic rocks in the eastern part of the North Dabie Mountains are rich inNa ( Na2O=4.03%, Na2O/K2O = 1.31 ), Sr (865μg/g) and Ba ( 1361μg/g) , and high inSr/Y ratio (66.1) but low in Nb, Y and HREE. They have experienced strong fractionation ofREE [ (La/Yb)N = 26.6 ], and are similar to adakite in geochemical characteristics. The U-Pbdating of zircon from the volcanic rocks is ( 129.2 + 2.6) Ma, belonging to Early Cretaceous.These rocks are similar to the volcanic rocks of North Huaiyang not only in age and rare-earth el-ement and trace element geochemistry, but also in the formation temperature and pressure of theminerals. The results indicated that the delamination of mountain root and underplating of mafic-ultramafic magma had happened in the Dabie orogen before Early Cretaceous. Mesozoic mag-matism was intense in the North Dabie Mountains, including the intrusion of mafic-ultramaficmagma, uplifting of gneiss dome, explosion of volcanic rocks and intrusion of granitic magma.The Mesozoic volcanic rocks in the eastern part of the North Dabie Mountains may be one part ofthe Mesozoic volcano-intrusive complex belt of North Huaiyang. The existence of Mesozoic vol-canic remnant cap means the denudation of the Dabie orogenic belt was not very strong sinceEarly Cretaceous.

  11. Primitive, high-Mg basaltic andesites: direct melts of the shallow, hot, wet mantle (United States)

    Andrews, A.; Grove, T. L.


    Direct mantle melts are rare in subduction zone settings. Such melts are identified by Mg #s (Mg # = Mg / (Mg+Fe)) greater than ~0.73, indicating chemical equilibrium with Fo90 mantle olivine. Most of these primitive arc melts are basaltic, characterized by SiO2 contents of ~48-50 wt % and MgO contents ranging from 8-10 wt %. However, primitive basaltic andesites with mantle-equilibrated Mg #s have also been found at subduction zones worldwide. These basaltic andesites have higher SiO2 contents (53-58 wt %) than typical primitive basalts as well as high MgO (8-10 wt %). Because these rocks have high SiO2 contents and yet retain evidence for chemical equilibrium with the mantle (Mg #s), their petrogenesis has sparked intense debate as researchers have tried to discern how these samples fit into the paradigm of mantle melting at subduction zones. Through an understanding of the conditions and processes that produce the SiO2 enrichment in these rocks, we also aim to understand the role of these melts in producing the observed andesitic compositional characteristics of the continental crust. To understand the petrogenesis of primitive, high-Mg basaltic andesites, this study investigates the experimental melts of undepleted mantle peridotite plus a slab component (Na-2O + K2O) from 1,205-1,470°C at 1.0-2.0 GPa under water-undersaturated conditions (0-5 wt % H2O). At 1.0 and 1.2 GPa, the experimental melts reproduce the compositions of natural primitive, high-Mg basaltic andesites in all major elements (SiO2, TiO2, Al2O3, FeO, MnO, MgO, and Na2O+K2O) except CaO. CaO contents are higher than the range of the natural samples by ~2 wt % at the highest silica contents of the experiments (54-56 wt% SiO2). This suggests that at 1.0-1.2 GPa, a higher percent of melting (30-35 %) with 3-5 wt % H2O is required to drive the chemical compositions of the experiments toward the representative compositions of the natural rocks. The experimental melts also show that mantle-wall rock

  12. Pomozdino - An anomalous, high-MgO/FeO, yet REE-rich eucrite (United States)

    Warren, P. H.; Jerde, E. A.; Migdisova, L. F.; Iaroshevskii, A. A.


    A new chemical analysis and petrographic data for the Pomozdino basaltic achondrite are presented. Earlier indications that Pomozdino is a eucrite and that it is a monomict breccia with an anomalous, REE-rich, yet high-MgO/FeO bulk composition, are confirmed. Characteristics such as texture, composition, and REE concentration are examined and compared to those in other publications. A model for the origin of this meteorite, as a partial cumulate with an uncommonly high content of trapped liquid, is found to be preferable. Two alternatives of the origin are suggested, one of which implies that the parent melt is roughly similar in composition to Stannern. The other considers Pomozdino as a possible primary partial melt, derived from a source region far more magnesian than generally envisaged for the sources of primary eucritic partial melts. It is concluded that at least some Stannern-like eucrites were involved in fractional crystallization, and thus do not represent primary partial melts.

  13. Sulfur passivation of surface electrons in highly Mg-doped InN

    Energy Technology Data Exchange (ETDEWEB)

    Linhart, W. M.; Veal, T. D. [Stephenson Institute for Renewable Energy and Department of Physics, University of Liverpool, Liverpool L69 4ZF (United Kingdom); Chai, J. [Department of Electrical and Computer Engineering, University of Canterbury, Christchurch 8140 (New Zealand); McConville, C. F. [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Durbin, S. M. [Department of Electrical and Computer Engineering, University of Canterbury, Christchurch 8140 (New Zealand); Department of Electrical and Computer Engineering, Western Michigan University, Kalamazoo, Michigan 49008 (United States)


    Electron accumulation with a sheet density greater than 10{sup 13} cm{sup −2} usually occurs at InN surfaces. Here, the effects of treatment with ammonium sulfide ((NH{sub 4}){sub 2}S{sub x}) on the surface electronic properties of highly Mg-doped InN (>4×10{sup 18} cm{sup −3}) have been investigated with high resolution x-ray photoemission spectroscopy. The valence band photoemission spectra show that the surface Fermi level decreases by approximately 0.08 eV with (NH{sub 4}){sub 2}S{sub x} treatment, resulting in a decrease of the downward band bending and up to a 70% reduction in the surface electron sheet density.

  14. High-Mg andesites petrogenesis by amphibole crystallization and ultramafic crust assimilation (United States)

    Tiepolo, M.; Tribuzio, R.; Langone, A.


    Mafic and ultramafic intrusives with high-Mg andesite (HMA) affinity are occasionally found in collisional settings. These amphibole-rich rocks preserve chemical and textural heterogeneities that are important records of the petrogenetic processes occurring in the deep portions of the arc crust. New insights on the origin of HMA are inferred from the Tertiary amphibole-rich ultramafic intrusives of the southern Adamello batholith (Italian Alps). These rocks consist of large amphibole grains with brown cores (Ti-pargasite) that progressively grade through brownish green (Mg-hornblende) and light green (edenite) rims. Brown amphibole has inclusions of olivine and clinopyroxene (±spinel) with irregular boundaries indicating disequilibrium with the host amphibole. Amphibole shows a marked chemical zoning. In particular, a decrease in Ti, HREE coupled to an increase in Mg, Ni, LREE, Th and U from the core to the rim is observed. Calculated equilibrium liquids for amphibole cores may be related to island arc basalts. On the other hand, liquids in equilibrium with amphibole rims share many compositional similarities to HMA (e.g. low HREE, strong LREE/HREE fractionation, high Th and U). According to the current knowledge of Amph/LD, a fractional crystallization process driven by amphibole may explain most of the observed elemental variations. However, the increase from core to rim of highly compatible elements in amphibole such as MgO and Ni contrasts with closed system fractional crystallization. The assimilation/resorption of olivine is considered the most efficient mechanism to supply or buffer MgO and Ni in the evolving system during amphibole crystallization. The textural disequilibrium of olivine with the host amphibole supports this process. In addition, clusters of olivine with triple junctions (Fo up to 85 mol%) and minor cpx were found in ultramafic rocks of the same complex. They probably represent fragments of older dunites/wehrlites dismembered by the

  15. An essential factor for high Mg2+ tolerance of Staphylococcus aureus

    Directory of Open Access Journals (Sweden)

    Joshua Armitano


    Full Text Available Internal bacterial concentration of Mg2+, the most abundant divalent cation in living cells, is estimated to be in the single millimolar range. However, many bacteria will thrive in media with only micromolars of Mg2+, by using a range of intensely studied and highly efficient import mechanisms, as well as in media with very high magnesium concentration, presumably mediated by currently unknown export mechanisms. Staphylococcus aureus has a particularly high Mg2+ tolerance for a pathogen, growing unimpaired in up to 770 mM Mg2+, and we here identify SA0657, a key factor in this tolerance. The predicted domain structure of SA0657 is shared with a large number of proteins in bacteria, archaea and even eukarya, for example CorB from Salmonella and the human CNNM protein family. One of the shared domains, a CBS pair potentially involved in Mg2+ sensing, contains the conserved Glycine326 which we establish to be a key residue for SA0657 function. In light of our findings, we propose the name MpfA, Magnesium Protection Factor A, for SA0657.

  16. Age and origin of earliest adakitic-like magmatism in Panama: Implications for the tectonic evolution of the Panamanian magmatic arc system (United States)

    Whattam, Scott A.; Montes, Camilo; McFadden, Rory R.; Cardona, Agustin; Ramirez, Diego; Valencia, Victor


    40-20 Ma marks a fundamental interval in the evolution of the 70-0 Ma Panamanian magmatic arc system. During this period, there is no evidence of Panamanian magmatic arc activity to the east of the Panama Canal Basin while to the west and in localized regions to the east of the Panama Canal Basin a phase of intrusive-only activity is recorded. Fundamentally, geochemical and geochronological evidence presented herein indicate that this intrusive activity was predominantly 'adakitic-like' and becomes younger from west to east along an approximately W-E striking lineament. Granodiorites of the Petaquilla batholith, western Panama yield LAM-ICP-MS 206Pb/238U zircon ages of 29.0 + 0.7, - 0.6 Ma, 28.5 + 0.7, - 0.5 Ma, 28.3 + 0.5, - 0.4 Ma and 26.2 + 0.5, - 0.9 Ma. To the east of the Panama Canal Basin zircons from a hypabyssal diorite of the mainly intermediate Majé subvolcanic suite, cedes a mean 206Pb/238U age of 18.9 + 0.4 Ma. Relative to other 70-5 Ma Panamanian magmatic arc lavas and intrusives, Majé and Petaquilla intrusives yield adakitic-like major and trace element abundances (e.g., > 15 wt.% Al2O3, generally > 3.5 wt.% Na2O, > 400 ppm Sr, 120) and strongly fractionated HREE patterns. These 30-26 Ma (Petaquilla) and 19 Ma (Majé) suites are also compositionally similar to a subvolcanic suite of rare, circa 25 Ma adakitic-like, andesitic intrusives which occur within the Panama Canal Basin midway between Petaquilla and Majé and at the same approximate latitude as Petaquilla and Majé. Collectively, the geochemical and geochronological data for the adakitic-like intrusives arc consistent with formation via partial melting of lowermost, mafic crust above a sub-horizontal slab tear that propagated from the west (Petaquilla) to the east (Majé) between 30 and 19 Ma. Our new tectonic model postulates that collision between the Panamanian magmatic arc system and an 'indentor' (e.g., a tract of thickened buoyant, oceanic crust or plateau) occurred at about 40 Ma, a

  17. New age and geochemical constraints on the origin of Quaternary adakite-like lavas in the Arabia-Eurasia collision zone (United States)

    Pang, Kwan-Nang; Chung, Sun-Lin; Zarrinkoub, Mohammad Hossein; Li, Xian-Hua; Lee, Hao-Yang; Lin, Te-Hsien; Chiu, Han-Yi


    Adakite-like lavas from the Iranian segment of the Arabia-Eurasia collision zone have been considered as partial melts derived from a subducted Neotethyan slab, a hypothesis that cannot be further evaluated due to the lack of systematic age and radiogenic isotopic data. Here, we revisit the Anar region, Iran where such lavas were reported by providing these data to examine their probable origin as slab melts. New SIMS zircon U-Pb ages attest to eruption at ca. 1 to 2 Ma, postdating the Arabia-Eurasia collision. The lavas are characterized by dacitic to rhyolitic, metaluminous to slightly peraluminous and trondhjemitic compositions, and incompatible element patterns similar to continental crustal rocks. Extreme depletion in Nb, Ta, Y and the heavy REE relative to the light and middle REEs reflects control by garnet and rutile. Except one sample presumably affected by secondary gain of radiogenic Sr, the depleted Sr-Nd-Hf isotopic compositions relative to the Bulk Silicate Earth [(87Sr/86Sr)i = 0.7040 to 0.7043; εNd(t) = + 3.2 to + 5.3; εHf(t) = + 10.5 to + 11.3] indicate magma genesis from juvenile source rocks. A slab melt origin for the Anar lavas is very unlikely and the reason is twofold. First, the Y and HREE of the source rocks estimated by inversed batch melting models assuming garnet pyroxenite residue are far too low compared with MORB-like lithologies and subducted sediments. Second, the low MgO, Ni and Cr of the lavas point to limited interaction with peridotites in a mantle wedge. Fractionation-related models are also unlikely due to the apparent lack of broadly coeval, mafic precursor magmas without adakitic signature. The low-Y and low-HREE source rocks revealed by the melting models, together with the low MgO, Ni and Cr of the Anar lavas, can be explained by lower crustal melting under eclogite-facies conditions. These source rocks were most likely high-pressure cumulates in the root of the Urumieh-Dokhtar magmatic arc, a Neotethyan arc that was

  18. A Review on Forearc Ophiolite Obduction, Adakite-Like Generation, and Slab Window Development at the Chile Triple Junction Area: Uniformitarian Framework for Spreading-Ridge Subduction (United States)

    Bourgois, Jacques; Lagabrielle, Yves; Martin, Hervé; Dyment, Jérôme; Frutos, Jose; Cisternas, Maria Eugenia


    This paper aggregates the main basic data acquired along the Chile Triple Junction (CTJ) area (45°-48°S), where an active spreading center is presently subducting beneath the Andean continental margin. Updated sea-floor kinematics associated with a comprehensive review of geologic, geochemical, and geophysical data provide new constraints on the geodynamics of this puzzling area. We discuss: (1) the emplacement mode for the Pleistocene Taitao Ridge and the Pliocene Taitao Peninsula ophiolite bodies. (2) The occurrence of these ophiolitic complexes in association with five adakite-like plutonic and volcanic centers of similar ages at the same restricted locations. (3) The inferences from the co-occurrence of these sub-coeval rocks originating from the same subducting oceanic lithosphere evolving through drastically different temperature-pressure ( P- T) path: low-grade greenschist facies overprint and amphibolite-eclogite transition, respectively. (4) The evidences that document ridge-jump events and associated microplate individualization during subduction of the SCR1 and SCR-1 segments: the Chonos and Cabo Elena microplates, respectively. The ridge-jump process associated with the occurrence of several closely spaced transform faults entering subduction is controlling slab fragmentation, ophiolite emplacement, and adakite-like production and location in the CTJ area. Kinematic inconsistencies in the development of the Patagonia slab window document an 11- km westward jump for the SCR-1 spreading segment at ~6.5-to-6.8 Ma. The SCR-1 spreading center is relocated beneath the North Patagonia Icefield (NPI). We argue that the deep-seated difference in the dynamically sustained origin of the high reliefs of the North and South Patagonia Icefield (NPI and SPI) is asthenospheric convection and slab melting, respectively. The Chile Triple Junction area provides the basic constraints to define the basic signatures for spreading-ridge subduction beneath an Andean

  19. A Review on Forearc Ophiolite Obduction, Adakite-Like Generation, and Slab Window Development at the Chile Triple Junction Area: Uniformitarian Framework for Spreading-Ridge Subduction (United States)

    Bourgois, Jacques; Lagabrielle, Yves; Martin, Hervé; Dyment, Jérôme; Frutos, Jose; Cisternas, Maria Eugenia


    This paper aggregates the main basic data acquired along the Chile Triple Junction (CTJ) area (45°-48°S), where an active spreading center is presently subducting beneath the Andean continental margin. Updated sea-floor kinematics associated with a comprehensive review of geologic, geochemical, and geophysical data provide new constraints on the geodynamics of this puzzling area. We discuss: (1) the emplacement mode for the Pleistocene Taitao Ridge and the Pliocene Taitao Peninsula ophiolite bodies. (2) The occurrence of these ophiolitic complexes in association with five adakite-like plutonic and volcanic centers of similar ages at the same restricted locations. (3) The inferences from the co-occurrence of these sub-coeval rocks originating from the same subducting oceanic lithosphere evolving through drastically different temperature-pressure (P-T) path: low-grade greenschist facies overprint and amphibolite-eclogite transition, respectively. (4) The evidences that document ridge-jump events and associated microplate individualization during subduction of the SCR1 and SCR-1 segments: the Chonos and Cabo Elena microplates, respectively. The ridge-jump process associated with the occurrence of several closely spaced transform faults entering subduction is controlling slab fragmentation, ophiolite emplacement, and adakite-like production and location in the CTJ area. Kinematic inconsistencies in the development of the Patagonia slab window document an 11- km westward jump for the SCR-1 spreading segment at ~6.5-to-6.8 Ma. The SCR-1 spreading center is relocated beneath the North Patagonia Icefield (NPI). We argue that the deep-seated difference in the dynamically sustained origin of the high reliefs of the North and South Patagonia Icefield (NPI and SPI) is asthenospheric convection and slab melting, respectively. The Chile Triple Junction area provides the basic constraints to define the basic signatures for spreading-ridge subduction beneath an Andean

  20. Geochronology and geochemistry of the high Mg dioritic dikes in Eastern Tianshan, NW China: Geochemical features, petrogenesis and tectonic implications (United States)

    Li, Deng-Feng; Zhang, Li; Chen, Hua-Yong; Hollings, Pete; Cao, Ming-Jian; Fang, Jing; Wang, Cheng-Ming; Lu, Wan-Jian


    Zircon U-Pb ages of high Mg dioritic dikes in the Mesoproterozoic Kawabulake Group in the Eastern Tianshan area, NW China indicate that they were emplaced in the Early Carboniferous at 353-348 Ma. The dikes consist of medium-grained plagioclase and hornblende with minor clinopyroxene and trace quartz. They are characterized by intermediate SiO2 (60-62 wt.%), low TiO2 (0.63-0.71 wt.%), relatively high Al2O3 (15.1-15.8 wt.%) and MgO contents (3.45-4.15 wt.%) with Mg# generally higher than 56 (56-59). The geochemistry of the high Mg diorites suggest they were formed by similar magmatic processes to sanukitoid high Mg Andesites such as those of the Setouchi volcanic belt, Japan. Zircons from the high Mg dioritic dikes have εHf(t) values of -6.8 to +14.5. The dominantly positive values suggest a juvenile source, whereas the small number of negative values suggests mature components were also incorporated into the source. Similarly, the positive εNd(t) values (0 to +2.2) are interpreted to reflect a juvenile source whereas the negative values of (-5.2 to 0) suggest participation of old crustal rocks in the petrogenesis of the diorites. The variable εHf(t) and εNd(t) values suggest that the mature material was assimilated during magma ascent rather than in the mantle wedge which would result in more uniform values. Mass balance calculations suggest that the dioritic dikes were derived from sources composed of approximately 97% juvenile mantle-derived material and 3% sediment. Petrographic, elemental, and isotopic evidence suggest that the dioritic dikes were generated by partial melting of depleted mantle that migrated into the shallow crust where it assimilated older sedimentary rocks of the Mesoproterozoic Kawabulake Group.

  1. Evolving volcanism at the tip of a propagating arc: The earliest high-Mg andesites in northern New Zealand (United States)

    Booden, Mathijs A.; Smith, Ian E. M.; Mauk, Jeffrey L.; Black, Philippa M.


    A NNW-striking string of isolated volcanic centers, the Kiwitahi chain, erupted between 15 and 5.5 Ma in northern New Zealand. Prior to 6.2 Ma, the erupted rocks were plagioclase- and hornblende-dominated andesites, which are geochemically comparable to coeval andesites erupted in the nearby, much larger Coromandel Volcanic Zone (CVZ). Compared to CVZ andesites, however, the Kiwitahi andesites show more subdued incompatible element enrichments, and they generally have relatively unradiogenic Sr isotope compositions. These features, and the small eruption volumes involved, suggest that the Kiwitahi centers formed over the edge of a magmatic system that was centered on the CVZ. The Kiwitahi centers progressively become younger towards the SSE representing the migration over the time of the edge of this magmatic system. Between 6.2 and 5.5 Ma, four centers at the southern end of the chain erupted pyroxene-dominated, high-magnesium andesites that are geochemically unlike coeval andesites in the CVZ, but similar to Quaternary high-Mg andesites erupted along the western edge of the Taupo Volcanic Zone. These are the earliest known high-Mg andesites in northern New Zealand; their appearance may mark the inception of the current configuration where high-Mg andesite eruptions precede regular andesitic volcanism at the leading edge of the arc.

  2. Experimental Insights Into the Formation of High-Mg Andesites in the Trans-Mexican Volcanic Belt (United States)

    Weber, R. M.; Wallace, P. J.; Johnston, A.


    High-Mg basaltic andesites and andesites occur in the central Trans-Mexican Volcanic Belt, primarily in the Chichinautzin Volcanic Field south of Mexico City, and their primitive chemical characteristics suggest equilibration with mantle peridotite. These lavas may represent either slab melts that re-equilibrated with peridotite during ascent or hydrous partial melts of a peridotite source. We have experimentally mapped the liquidus mineralogy for a high-Mg basaltic andesite (9.6 wt% MgO, 54.4 wt% SiO2) from the Pelagatos cinder cone as a function of temperature and water content over a range of mantle wedge pressures. We chose this primitive composition rather than a true andesite because samples from the Chichinautzin region with >55 wt% SiO2 and relatively high MgO and Mg# contain textural evidence for contamination in the form of quartz xenocrysts or reaction products. Our experimental results show that the Pelagatos composition could be in equilibrium with a harzburgite residue (with Fo90 olivine) at relatively high water contents (>7 wt%) and low temperatures (1080-1150°C) at pressures ranging from 11 to 14 kbar. These results agree well with a published thermobarometer for peridotite melting, so we use this thermobarometer to estimate equilibration conditions for other primitive magmas in the region. In contrast to the high Ni contents found in olivine phenocrysts in many high-Mg basaltic andesites and andesites produced in Chichinautzin, the olivine phenocrysts in the Pelagatos lava contain Ni contents typical of lherzolite or harzburgite melts that have subsequently fractionated a small amount of olivine after segregating from their mantle source. Because the refractory mantle source for Pelagatos may have had Fo>90 olivine, we estimate formation conditions for the composition recalculated to be in equilibrium with Fo92 olivine. This calculation shifts equilibration conditions to higher temperatures (1190-1270°C) at mantle wedge pressures (11-14 kbar

  3. Extreme high field strength element (HFSE) depletion and near-chondritic Nb/Ta ratios in Central Andean adakite-like lavas (~ 28°S, ~ 68°W) (United States)

    Goss, A. R.; Kay, S. M.


    The eruption of andesites with steep REE patterns and high Sr concentrations (adakite-like) in the northernmost Chilean flatslab region of the Central Andes spatially and temporally corresponds with the appearance of a marked HFSE (high field strength element) depletion in these lavas (La/Ta up to 95). Known as the Dos Hermanos and Pircas Negras andesites, these lavas erupted at the beginning (˜ 8 Ma), during (7-3 Ma), and immediately following (3-2 Ma) a period of tectonic instability characterized by eastward migration of the frontal volcanic arc. ICP-MS analyses of the HFSE reveal a range of chondritic (20-18) to subchondritic (18-11) Nb/Ta ratios in these lavas. Evident temporal trace element trends support a change from a rutile-bearing to an amphibole-bearing eclogitic residual assemblage in equilibrium with the mafic precursor magmas of these andesites. This change in residual mineralogy is contemporaneous with the onset of frontal arc migration in the region. Potential eclogitic sources for the Dos Hermanos and Pircas Negras adakitic andesites include mafic Andean lower crust and an additional flux of forearc crust transported to the sub-arc mantle via subduction erosion during the height of arc migration and Pircas Negras magmatism. Batch melting models of rutile- or amphibole-bearing eclogitic arc basalt in tandem with magma mixing calculations generate the observed adakitic signatures and near-chondritic Nb/Ta ratios of these Central Andean andesites.

  4. Early Carboniferous adakitic rocks in the area of the Tuwu deposit, eastern Tianshan, NW China: Slab melting and implications for porphyry copper mineralization (United States)

    Wang, Yin-Hong; Xue, Chun-Ji; Liu, Jia-Jun; Wang, Jian-Ping; Yang, Jun-Tao; Zhang, Fang-Fang; Zhao, Ze-Nan; Zhao, Yun-Jiang; Liu, Bin


    Existing geochronological and geochemical data for the Early Carboniferous magmatic rocks in the eastern Tianshan, Xinjiang, have been interpreted in a variety of theories regarding petrogenesis and geodynamic setting. The proposed settings include rift, back-arc basin, passive continental margin, island arc, ridge subduction, and post-collisional environment. To evaluate these possibilities, we present new SHRIMP zircon U-Pb geochronology and geochemical data, whole-rock geochemical, Hf isotope, and S isotope data for tonalitic rocks and ores associated with the Tuwu porphyry copper deposit located in the center of the late Paleozoic Dananhu-Tousuquan arc, eastern Tianshan. SHRIMP zircon U-Pb dating indicates that the magmatic activity and thus associated copper mineralization occurred ca.332 Ma. The tonalitic rocks are calc-alkaline granites with A/CNK values ranging from 1.16 to 1.58; are enriched in K, Rb, Sr, and Ba; and are markedly depleted in Nb, Ta, Ti, and Th. They show geochemical affinities similar to adakites, with high Sr, Al2O3, and Na2O contents and La/Yb ratios; low Y and Yb contents; and slight positive Eu anomalies. In situ Hf isotopic analyses of zircons yielded positive initial εHf(t) values ranging from 6.9 to 17.2. The δ34S values of the ore sulfides range from -3.0‰ to +1.7‰, reflecting a deep sulfur source. Our results indicate that the paleo-Tianshan oceanic slab was being simultaneously subducted northward beneath the Dananhu-Tousuquan arc, and southward beneath the Aqishan-Yamansu arc during the Early Carboniferous. The Tuwu adakitic tonalitic rocks were derived from the partial melting of the subducted paleo-Tianshan oceanic slab, which was subsequently hybridized by mantle wedge peridotites. The slab-derived magmas have considerably high copper contents and are highly oxidized, thus leading to porphyry copper mineralization. Such Early Carboniferous tonalitic rocks that are widespread in the eastern Tianshan define a province

  5. Extreme High Field Strength Element Depletion and Chondritic Nb/Ta in Central Andean Adakite-like Lavas (~27° S, ~68° W) (United States)

    Goss, A. R.; Kay, S. M.


    We present new high precision ICP-MS HFSE data on ~30 samples from the adakite-like Pircas Negras (SiO2 =57-62 %; La/Yb= 20-60; Sr = 600-900 ppm, Cr to 200 ppm) and Dos Hermanos (SiO2 =56-59 %; La/Yb= 57-61; Sr = 1200-1500 ppm, Cr to 60 ppm) andesites from the southernmost Andean Central Volcanic Zone (CVZ). These andesites erupted in a broadened arc as the volcanic front was displaced about 50 km to the east between 8 and 3 Ma and likely reflect melting of a garnet bearing crustal source. Our data reveal a discrete change from chondritic Nb/Ta ratios (19-21) and low Zr/Sm (25-30) in older 8-7 Ma Dos Hermanos lavas to dominantly subchondritic Nb/Ta ratios (11-18) and higher Zr/Sm (30-45) in Hermanos (La/Ta= 90-100) lavas are best explained as hydrous and oxidizing conditions within the mantle wedge initially stabilized Ti-oxides (i.e. rutile) as the arc front migrated. These steeper REE patterns and high La/Ta are a transient feature measured in lavas erupting during the peak of arc migration, as mafic <2 Ma CVZ lavas to the north (~26° S) have lower La/Yb (< 20) and La/Ta (< 40). The observed temporal shift in Nb/Ta coupled with a general increase in Zr/Sm suggests a change from residual rutile to low-Mg amphibole within an eclogitic/granulitic crustal residue during the course of arc migration. A potential factor in explaining these data is that a transient period of increased subduction erosion associated with the migration of the frontal arc transported forearc crustal material into the progressively dehydrating mantle wedge. Partial melting of this eclogitized forearc material contributed to the transient adakite-like nature of the magmas erupted along the margin.

  6. Slab-derived adakites and subslab asthenosphere-derived OIB-type rocks at 156 ± 2 Ma from the north of Gerze, central Tibet: Records of the Bangong-Nujiang oceanic ridge subduction during the Late Jurassic (United States)

    Li, Shi-Min; Zhu, Di-Cheng; Wang, Qing; Zhao, Zhidan; Zhang, Liang-Liang; Liu, Sheng-Ao; Chang, Qing-Song; Lu, Ying-Huai; Dai, Jin-Gen; Zheng, Yuan-Chuan


    This paper reports zircon U-Pb age and Hf isotope, whole-rock major and trace element, and whole-rock Sr-Nd-Hf isotope data of the dacites from Rena Tso and mafic rocks (diabases and basalts) from Duobuza, north of Gerze, central Tibet. These data reveal the presence of a distinct rock association of slab-derived adakites (154 ± 1 Ma) and subslab asthenosphere-derived OIB-type (oceanic island basalt) mafic rocks (157.6 ± 1.4 Ma). The medium-K calc-alkaline dacites (SiO2 = 66-69 wt.%) from Rena Tso are enriched in Sr (520-1083 ppm) and depleted in heavy rare earth elements (HREEs) and Y (9.8-10.8 ppm), resembling adakites. These adakitic dacites have low whole-rock initial 87Sr/86Sr ratios of 0.7043-0.7046, positive εNd(t) (+ 1.0 to + 3.4), εHf(t) (+ 6.4 to + 7.0), and zircon εHf(t) (+ 1.9 to + 7.6) values, indicating an oceanic slab origin (crust and sediment). Considering the low Mg# (32-53) and (La/Yb)N (19-23), the adakitic dacites are most likely derived from the partial melting of the subducting slab at shallow depths and the subsequent interaction with peridotite in a thin mantle wedge during magma ascent. The diabases and basalts (SiO2 = 49-53 wt.%) from Duobuza show an alkali signature with enrichment of high field strength elements (HFSEs) (e.g., Zr = 213-285 ppm) and exhibit positive Nb-Ta-Ti anomalies that are geochemically comparable to those of OIB. These samples show positive whole-rock εNd(t) values of + 3.3 to + 3.7, εHf(t) values of + 4.7 to + 5.7, and negative to positive zircon εHf(t) values of - 1.5 to + 5.2. These OIB-type mafic samples are interpreted as the products of low-degree decompression melting of the upwelling subslab asthenosphere with a minor contribution from the sub-continental lithospheric mantle (SCLM). Our new data indicate the presence of a distinct rock association of coeval slab-derived adakites and subslab asthenosphere-derived OIB-type rocks. Such an association along with the normal arc rocks further to the north

  7. Basicity for blast furnace-type slag containing B2O3 and high MgO

    Institute of Scientific and Technical Information of China (English)

    黄振奇; 蔡亚旻; 朱文非; 杨祖磐


    There is quite abundant resource of ludwigite ore in Liaoning Province of China. Content of MgO in the slag of pyrometallurgical separation of boron from iron is much higher than that in the ordinary slags. Through the equilibrium partition ratio of sulfur LS between the metal and the slag in an atmosphere of CO-N2, the acidic coefficients for B2O3 and the basic coefficients for MgO were estimated. The basic formulae were given for the blast furnace-type slag containing B2O3 and high MgO.

  8. Experimental constraints on the origin of potassium-rich adakites in eastern China%中国东部富钾埃达克岩成因的实验约束

    Institute of Scientific and Technical Information of China (English)

    RobertP.PAPP; 肖龙; 等


    Adakites are geochemically distinct volcanic and plutonic granitoid rocks found in intraoceanic island arc settings where relatively young, hot oceanic lithosphere has been subducted and melted (termed "slab melting"), and in continental arcs, such as the Andes, where melting has taken place at the base of tectonically- or magmatically-thickened lower crust (termed "lower crustal melting"). In both settings, the distinctive geochemical signature of adakitic granitoids is attributed to an origin by partial melting of a variably-hydrated metabasaltic protolith at sufficient depths for garnet to be stable within the residual crystalline assemblage (I.e., residues of garnet-amphibolite and/or eclogite). Once generated, "pristine" or "parental" adakite melts may have their composition subsequently modified by processes of assimilation (of either mantle or continental material) and crystal fractionation during transport to and emplacement in the middle-upper crust. Late Mesozoic (early-mid Cretaceous, ~160-110 Ma) adakites in eastern China are unusually rich in potassium (K2O) and other large-ion lithophile elements (e.g., Ba, Th, U), with low Na2O/ K2O ratios (~1.0-1.1), in contrast to sodic adakites, found in eastern China and elsewhere, which resemble experimental adakite liquids produced by dehydration melting of basalt in the garnet-amphibolite to eclogite facies. And which formed by either slab melting of oceanic crust, or by partial melting of broadly basaltic, lower crustal protoliths. Despite these compositional differences, their overall geochemical character defines the potassic granitoids of eastern China as adakites. We attribute the unique chemistry of these potassium-rich adakites to either peculiarities in the composition of their source, or to the processes, including assimiliation and fractional crystallization (AFC), that subsequently modified parental adakite magmas. Although the apparent lack of proximity to a subduction zone suggests that

  9. Growth of high Mg content wurtzite MgZnO epitaxial films via pulsed metal organic chemical vapor deposition (United States)

    Alema, Fikadu; Ledyaev, Oleg; Miller, Ross; Beletsky, Valeria; Osinsky, Andrei; Schoenfeld, Winston V.


    We report on the growth of high Mg content, high quality, wurtzite MgxZn1-xO (MgZnO) epitaxial films using a pulsed metal organic chemical vapor deposition (PMOCVD) method. Series of MgZnO films with variable Mg concentration were deposited on bare and AlN coated sapphire substrates. The band gap of the films estimated using UV-visible transmission spectra ranges from 3.24 eV to 4.49 eV, corresponding to fraction of Mg between x=0.0 and x=0.51, as determined by Rutherford backscattering spectroscopy. The cathodoluminescence (CL) measurement has shown a blue-shift in the peak position of MgZnO with an increasing Mg content. No multi-absorption edges and CL band splitting were observed, suggesting the absence of phase segregation in the as grown films. The crystal structure and phase purity of the films were also confirmed by XRD analysis. Hall effect measurement in van der Pauw configuration was employed to evaluate the electrical properties of the films. With a rise in Mg incorporation into the ZnO lattice, the films became very resistive, consistent with the widening of the band gap. The AFM measurement on the films has shown a decreasing surface roughness with an Mg content. To the best of our knowledge, the current result shows the highest Mg content (x=0.51), high quality, wurtzite MgZnO epitaxial film ever grown by MOCVD. The high Mg incorporation without phase separation is believed to be due to the non-equilibrium behavior of the PMOCVD in which the kinetic processes dominate the thermodynamic one.

  10. Experimental insights into the formation of high-Mg basaltic andesites in the trans-Mexican volcanic belt (United States)

    Weber, Rachel M.; Wallace, Paul J.; Dana Johnston, A.


    High-Mg basaltic andesites and andesites occur in the central trans-Mexican volcanic belt, and their primitive geochemical characteristics suggest equilibration with mantle peridotite. These lavas may represent slab melts that reequilibrated with overlying peridotite or hydrous partial melts of a peridotite source. Here, we experimentally map the liquidus mineralogy for a high-Mg basaltic andesite (9.6 wt% MgO, 54.4 wt% SiO2, Mg# = 75.3) as a function of temperature and H2O content over a range of mantle wedge pressures. Our results permit equilibration of this composition with a harzburgite residue at relatively high water contents (>7 wt%) and low temperatures (1,080-1,150°C) at 11-14 kbar. However, in contrast to the high Ni contents characteristic of olivine phenocrysts in many such samples from central Mexico, those of olivine phenocrysts in our sample are more typical of mantle melts that have fractionated a small amount of olivine. To account for this and the possibility that the refractory mantle source may have had olivine more Fo-rich than Fo90, we numerically evaluated alternative equilibration conditions, using our starting bulk composition adjusted to be in equilibrium with Fo92 olivine. This shifts equilibration conditions to higher temperatures (1,180-1,250°C) at mantle wedge pressures (11-15 kbar) for H2O contents (>3 wt%) comparable to those analyzed in olivine-hosted melt inclusions from this region. Comparison with geodynamic models shows that final equilibration occurred shallower than the peak temperature of the mantle wedge, suggesting that basaltic melts from the hottest part of the wedge reequilibrated with shallower mantle as they approached the Moho.

  11. Ultramafic lavas and pyroxene-spinifex high-Mg basaltic dykes from the Othris ophiolite complex, Greece (United States)

    Baziotis, Ioannis; Economou-Eliopoulos, Maria; Asimow, Paul


    This study aims to constrain the physico-chemical conditions and processes associated with the origin of ultramafic lavas of the Agrilia formation and high-Mg basaltic dykes in the Pournari area within the Othris ophiolite complex, a supra-subduction zone ophiolite of Mesozoic age (Paraskevopoulos & Economou, 1986; Barth et al., 2008). Hand-sample-scale spinifex texture is lacking from the ultramafic lavas and, despite whole-rock MgO contents greater than 31 wt.%, we infer an upper bound of 17 wt.% MgO for the erupted liquid, and thus identify these lavas as picrites containing accumulated olivine. We use textural and compositional criteria to divide the crystals within the Agrilia lavas between pre-eruptive and post-eruptive growth phases. The high-Mg basaltic dyke margins display a distinctive thin-section-scale micro-spinifex texture of skeletal and plumose Al- and Fe-rich clinopyroxene surrounded by large crystals of orthopyroxene. Normally zoned clinopyroxene in the Agrilia lavas and clinopyroxene of various textures (skeletal, needle- and dendritic-like) and sizes in the Pournari dykes display anomalous enrichment in Al2O3 and FeO* with decreasing MgO that require rapid, disequilibrium growth. Quantitative characteristics of the micro-spinifex pyroxene textures (Journal of Petrology 29, 305-331. Barth et al., 2008. Lithos, 100(1), 234-254. Faure et al., 2006. Journal of Petrology 47, 1591- 1610. Paraskevopoulos, G., Economou, M., 1986. Ofioliti 11 (3), 293 - 304. Roeder et al., 2001. The Canadian Mineralogist, 39(2), 397-416. Welsch et al., 2016. Contributions to Mineralogy and Petrology 171(1), 1-19.

  12. Fluxed-melting of shallow and hot high-grade metamorphic rocks in the Namcha Barwa Massif: A new mechanism for the generation of adakitic melts (United States)

    Zeng, L.; Liu, J.; Hou, Z.; Gao, L.; Xie, K.


    Extremely rapid exhumation has been a major factor leading to rapid advection of relatively hot crustal rocks into shallow crustal levels in the Namcha Barwa massif. In such a hot tectonic regime, it is conceivable that hot crustal material can undergo partial melting assisted by excessive water. Previous studies indeed have documented extremely young Na-rich granitic rocks (63.5 and up to 237.1), consistent with garnet either as a non-reactant phase or as a residue phase; (2) these leucosomes have similar Sr isotope compositions to their host rocks, but some of them have Nd isotope compositions significantly deviated from their host by ~4-5 epsilon units. Since high-grade metamorphic rocks in the Namcha Barwa were already shallower than 10 km in the past 5 million years, these data is best explained by water- fluxed melting of granitic components in the source rocks. This interpretation is also consistent with at water- present and relatively lower temperature conditions, both apatite and garnet behaves as non-reactant phases during a partial melting event, which could lead to depletion of garnet-compatible elements as well as negative shift in Nd isotope compositions in the amphibolite- or metapelite-derived melts. Our data emphasize that at rapidly exhumed and relatively hot tectonic regimes (e.g. the Nanga Parbat and Namcha Barwa areas), fluxed-melting of high-graded metamorphic rocks at relatively shallower crustal levels could be another important mechanism to produced adakitic magma and associated porphyritic Cu-Au deposits.


    Langone, A.; Tiepolo, M.; Morishita, T.; Tribuzio, R.


    High-Mg andesites (HMA) are a group of arc products, usually rich in amphibole, whose origin is still debated. High-Mg diorites (HMD) are intrusive counterparts of HMA and are locally found in exhumed arc sections. In places, HMD are closely associated with ultramafic amphibole-rich rocks and may provide further constrains on the role of amphibole in the origin of HMA and in the petrogenesis of arc related-magmas. Small bodies of Cretaceous amph-rich mafic and ultramafic intrusives with similar petrographic features and HMA affinity (e.g. Kamei et al., 2004) are exhumed together with granitoid rocks along the Japan arc. These rocks, originated during the Cretaceous subduction of the Pacific plate under Asia, give the opportunity to investigate modifications in the composition of melts with HMA affinity as a function of the along-margin position and time. Mafic and ultramafic intrusives were sampled in different localities of the Honshu (NE Japan arc) and Kyushu Island (SW Japan arc). In situ U-Pb zircon geochronology by laser ablation ICPMS was carried out to constrain the time relationships among the different intrusive bodies. U-Pb concordia ages show that the HMD were mostly emplaced from ca. 100 Ma up to 118 Ma. In only one case (Honshu Island) U-Pb concordia ages as young as 70 Ma were obtained. High modal proportions of amphibole (40-60 vol%) with pargasite cores (mg# = 0.66-0.77) characterize all studied samples. In ultramafic rocks (Ol-hornblendites and Cpx-hornblendites), pargasitic amphibole is poikilitic on sub-rounded clinopyroxene (mg# up to 88) and olivine (Fo61-78). In mafic rocks (amph-gabbros and amph-diorites), large amphibole grains are dispersed in a fine-grained matrix defining a porphyritic texture. The matrix consists mainly of Mg-hornblende, plagioclase and clinopyroxene. The cores of pargasitic amphibole from mafic rocks have clinopyroxene inclusions with mg# up to 88, similar to what found in ultramafic rocks. Independently from the age

  14. 甘肃北祁连毛藏寺埃达克岩及其成因类型%Adakite granite of Maozangsi and its origin in the north of Qilian area in Gansu

    Institute of Scientific and Technical Information of China (English)



    The specificity and its scientific and practical significance of Adakite deeply attracted scientists on Earth. The Qilian Early Paleozoic orogenic belt,which located in the northeastern margin of Qinghai-Tibet Plateau, is cradle of Chinese scientists to study the plate tectonics. By contrast,the characteristics of intrusive rocks in Lianhuashan of the north Qilian orogenic belt were studied. The results is: intermediate-acid intrusive rocks of Caledonian in Lianhuashan have high SiO2 、 A12O3、Na2O content, Na2O/K2O ratio is high, while MgO is lower, LREE enrichment strong,HREE apparent loss,the majority of L/H ratio>15 ; Th,Sr,Ba is an obvious positive anomalies,of which Sr content is more than 507×10-6 , Sr/Y、La/Yb(21. 39 -41. 72) ratio is high and the Cr、Ni. Σ values of the rock are 1. 45 ~ 2. 76,A/CNK were 0. 83 ~ 1. 15 , the majority < 1. 0, the main rocks are calc-alkaline granitoids series aluminum side. Rock eigenvalue are pointing to Adakite. In the( La/Yb) N-YbN and Sr/Y-Y discriminant diagram, samples fall into the scope of the Adakite. In the SiO2-Mg# diagram,the rock fall "slab origin Adakite" region,content of the rock, also in line with the "0" type Adakite characteristics. These show that Adakite of Lianhuashan region originated in the subduction of the partial melting of oceanic crust, which is "O" type Adakite. The geodynamic background is the subduction of the north Qilian oceanic crust to the north China plate during Early Paleozoic. Discovery of the " O" type Adakite in the region confirms previous understanding of Qilian orogenic belt and its tectonic evolution, and puts forward new ideas of mineral resources exploration in the region.%埃达克岩( Adakite)的特殊性及其科学和现实意义广泛地吸引着地球科学工作者.位于青藏高原东北缘的祁连山早古生代造山带是新中国地学界认识板块构造的摇篮.本文研究了北祁连造山带中段毛藏寺地区侵入岩的岩石学和地球化学特

  15. Trace element abundances of high-MgO glasses from Kilauea, Mauna Loa and Haleakala volcanoes, Hawaii (United States)

    Wagner, T.P.; Clague, D.A.; Hauri, E.H.; Grove, T.L.


    We performed an ion-microprobe study of eleven high-MgO (6.7-14.8 wt%) tholeiite glasses from the Hawaiian volcanoes Kilauea, Mauna Loa and Haleakala. We determined the rare earth (RE), high field strength, and other selected trace element abundances of these glasses, and used the data to establish their relationship to typical Hawaiian shield tholeiite and to infer characteristics of their source. The glasses have trace element abundance characteristics generally similar to those of typical shield tholeiites, e.g. L(light)REE/H(heavy)REE(C1) > 1. The Kilauea and Mauna Loa glasses, however, display trace and major element characteristics that cross geochemical discriminants observed between Kilauea and Mauna Loa shield lavas. The glasses contain a blend of these discriminating chemical characteristics, and are not exactly like the typical shield lavas from either volcano. The production of these hybrid magmas likely requires a complexly zoned source, rather than two unique sources. When corrected for olivine fractionation, the glass data show correlations between CaO concentration and incompatible trace element abundances, indicating that CaO may behave incompatibly during melting of the tholeiite source. Furthermore, the tholeiite source must contain residual garnet and clinopyroxene to account for the variation in trace element abundances of the Kilauea glasses. Inversion modeling indicates that the Kilauea source is flat relative to C1 chondrites, and has a higher bulk distribution coefficient for the HREE than the LREE.

  16. Formation of the adakite-like granitoid complex and porphyry copper-gold deposit in Shaxi from southern Tancheng-Lujiang fault belt: A clue to the West Pacific plate subduction

    Institute of Scientific and Technical Information of China (English)

    LAN Xianghua; YANG Xiaoyong; YU Liangfan; ZHANG Qianming


    On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geo-logical background of the deposit in detail and presented significant proofs for the conditions of formation of the Shaxi porphyry copper-gold deposit. Compared with other large and supper-large porphyry copper deposits in China and the adjacent Cu-Au mineralized areas, the ore-forming processes and conditions were analyzed; and the possibil-ity of forming large porphyry copper deposits in the Shaxi area was discussed. The present study indicated that the ore-forming fluid and material were mainly of magmatic origin, while meteoric water played a certain role in the ore-forming processes. Interactions between subducting and overriding plates provided a major driving force for the formation of igneous rocks and the deposition of metal elements in East China since Jurassic. Based on the geo-chemical data of the Shaxi intrusive, it is found that the copper (gold) mineralization is closely related to the genesis of adakite-like intrusive in the Shaxi area. This adakite-like intrusive was formed in the subduction environment as a result of the subduction of the West Pacific plate toward the East China continent, where there is a great potential-ity to form a large porphyry copper deposit.

  17. Early Paleozoic accretionary orogenesis along northern margin of Gondwana constrained by high-Mg metaigneous rocks, SW Yunnan (United States)

    Xing, Xiaowan; Wang, Yuejun; Cawood, Peter A.; Zhang, Yuzhi


    SW Yunnan of China constituted part of the northern margin of Gondwana facing the proto-Tethys ocean in the early Paleozoic. However, the evolution of the region and its relationship with the accretionary orogenism have been poorly established. This paper reports a set of new zircon U-Pb age data and whole-rock major oxides, elemental and Sr-Nd isotopic data for early Paleozoic metavolcanic rocks from the previously defined Lancang Group and reveals the development of an Ordovician suprasubduction zone in SW Yunnan. Zircon U-Pb ages of 462 ± 6 and 454 ± 27 Ma for two representative samples indicate eruption of the volcanic rocks in the Late Ordovician. Geochemical data for the metavolcanic rocks together with other available data indicate a calc-alkaline affinity with high Al2O3 (13.04-18.77 wt%) and low TiO2 (0.64-1.00 wt%). They have Mg-numbers ranging from 62 to 50 with SiO2 of 53.57-69.10 wt%, compositionally corresponding to the high-Mg andesitic rocks. They display enrichments in LREEs and LILEs with significant Eu negative anomalies (δEu = 0.20-0.33), and depletions in HFSEs, similar to arc volcanic rocks. Their initial 87Sr/86Sr ratios range from 0.721356 to 0.722521 and ɛNd(t) values from -7.63 to -7.62 with Nd model ages of 2.06-2.10 Ga. Integration of ages and geochemical data with available geological observations, we propose the presence of Ordovician magmatism related to proto-Tethyan evolution in SW Yunnan and the metaigneous rocks formed in an island-arc setting. They were part of a regional accretionary orogen that extended along the northern margin of Gondwana during Neoproterozoic to early Paleozoic period.

  18. Syn-convergence extension in the southern Lhasa terrane: Evidence from late Cretaceous adakitic granodiorite and coeval gabbroic-dioritic dykes (United States)

    Ma, Xuxuan; Xu, Zhiqin; Meert, Joseph G.


    Late Cretaceous (∼100-80 Ma) magmatism in the Gangdese magmatic belt plays a pivotal role in understanding the evolutionary history and tectonic regime of the southern Lhasa terrane. The geodynamic process for the formation of the early Late Cretaceous magmatism has long been an issue of hot debates. Here, petrology, geochronology and geochemistry of early Late Cretaceous granodiorite and coeval gabbroic-dioritic dykes in the Caina region, southern Lhasa, were investigated in an effort to ascertain their petrogenesis, age of intrusion, magma mixing and tectonic setting. Zircon U-Pb dating of granodiorite yields 206Pb/238U ages of 85.8 ± 1.7 and 86.4 ± 1.1 Ma, whilst that of the E-W trending dykes yields ages of 82.7 ± 2.6 and 83.5 ± 3.5 Ma. Within error, the crystallization ages of the dykes and the granodiorite are indistinguishable. Field observations and mineralogical microstructures are suggestive of a magma mixing process during the formation of the dykes and the granodiorite. The granodiorite exhibits geochemical features that are in agreement with those of subduction-related high-SiO2 adakites. The granodiorite and dykes have relatively constant εNd(t) values of +2.2 to +4.9 and initial 87Sr/86Sr ratios (0.7045-0.7047). These similar characteristics are herein interpreted as an evolutionary series from the dykes to granodiorite, consistent with magma mixing process. Ti-in-zircon thermometer and Al-in-hornblende barometer indicate that the granodiorite and the dioritic dyke crystallized at temperatures of ca. 750 and 800 °C, depths of ca. 6-10 and 5-9 km, respectively. Taking into account the synchronous magmatic rocks in the Gangdese Belt and the coeval rifted basin within the Lhasa terrane, the granodiorite and dykes reveal an early Late Cretaceous syn-convergence extensional regime in the southern Lhasa terrane, triggered by slab rollback of the Neotethyan oceanic lithosphere.

  19. High-Mg# andesitic lavas of the Shisheisky Complex, Northern Kamchatka: implications for primitive calc-alkaline magmatism (United States)

    Bryant, J. A.; Yogodzinski, G. M.; Churikova, T. G.


    Primitive arc magmatism and mantle wedge processes are investigated through a petrologic and geochemical study of high-Mg# (Mg/Mg + Fe > 0.65) basalts, basaltic andesites and andesites from the Kurile-Kamchatka subduction system. Primitive andesitic samples are from the Shisheisky Complex, a field of Quaternary-age, monogenetic cones located in the Aleutian-Kamchatka junction, north of Shiveluch Volcano, the northernmost active composite volcano in Kamchatka. The Shisheisky lavas have Mg# of 0.66-0.73 at intermediate SiO2 (54-58 wt%) with low CaO (3.0 wt%) and K2O (>1.0 wt%). Olivine phenocryst core compositions of Fo90 appear to be in equilibrium with whole-rock `melts', consistent with the sparsely phyric nature of the lavas. Compared to the Shisheisky andesites, primitive basalts from the region (Kuriles, Tolbachik, Kharchinsky) have higher CaO (>9.9 wt%) and CaO/Al2O3 (>0.60), and lower whole-rock Na2O (andesites. The absence of plagioclase phenocrysts from the primitive andesitic lavas contrasts the plagioclase-phyric basalts, indicating relatively high pre-eruptive water contents for the primitive andesitic magmas compared to basalts. Estimated temperature and water contents for primitive basaltic andesites and andesites are 984-1,143°C and 4-7 wt% H2O. For primitive basalts they are 1,149-1,227°C and 2 wt% H2O. Petrographic and mineral compositions suggest that the primitive andesitic lavas were liquids in equilibrium with mantle peridotite and were not produced by mixing between basalts and felsic crustal melts, contamination by xenocrystic olivine, or crystal fractionation of basalt. Key geochemical features of the Shisheisky primitive lavas (high Ni/MgO, Na2O, Ni/Yb and Mg# at intermediate SiO2) combined with the location of the volcanic field above the edge of the subducting Pacific Plate support a genetic model that involves melting of eclogite or pyroxenite at or near the surface of the subducting plate, followed by interaction of that melt with

  20. Neoproterozoic chromite-bearing high-Mg diorites in the western part of the Jiangnan orogen, southern China: Geochemistry, petrogenesis and tectonic implications (United States)

    Chen, Xin; Wang, Di; Wang, Xiao-Lei; Gao, Jian-Feng; Shu, Xu-Jie; Zhou, Jin-Cheng; Qi, Liang


    High-Mg diorites were discovered in the southern part of the ca. 830 Ma Dongma Pluton, northern Guangxi Province of southern China. The diorites (SiO2 = 59-65 wt%) are characterized by high MgO (6.7-8.9 wt%) contents and Mg-number [Mg# = 100 × Mg/(Mg + Fe)] (69-73), in contrary to the associated medium-Mg (MgO = 3.4-3.8 wt%, Mg# = 59-63) granodiorites in the Dongma main body and the low-Mg (MgO = 1.4-1.9 wt%, Mg# = 46-51) granodiorites in the Bendong Pluton to the north. Moreover, the high-Mg diorites show surprisingly high Cr (595-640 ppm) and Ni (171-194 ppm) concentrations, which are beyond the ranges of most coeval mafic rocks in the study area. Correspondingly, chromite crystals were separated from the high-Mg diorites and some of the medium-Mg granodiorites, and they show high Cr# [100 × Cr/(Cr + Al)] (average of 75), but low Mg# (0.34-2.51) and low Fe3 +. The decoupling of Cr# and Mg# and the existence of quartz + apatite mineral inclusion in chromites suggest Mg-Fe exchange that may be facilitated by the disequilibrium resulted from magma mixing. The high-Mg diorites show low La/Yb (6.8-8.5) and Sr/Y (2.1-3.1) ratios, significant negative anomalies of Nb and Ti and positive anomaly of Pb, resembling the Setouchi high-Mg andesites, despite of their relatively low Sr (71-100 ppm). All of the studied diorites and granodiorites show enriched Nd isotope compositions, with εNd(t) values (- 3.2 to - 5.9) a bit higher than some of the associated mafic rocks. Some of the high-Mg diorites show whole-rock εHf(t) (- 6.0 to - 6.2) coupled with Nd isotopes, similar to the associated mafic-ultramafic rocks in northern Guangxi, suggesting the metasomatism by melts of subducting sediments in the mantle source. Whereas, others show decoupled Nd-Hf isotopes that are similar to the medium- and low-Mg granodiorites [εHf(t) = - 1.8 to + 0.05], probably indicating the late magma mixing with granitic magmas at a crustal level for the dioritic magmas. We propose a two

  1. Las adakitas de la Cordillera Patagónica: Nuevas evidencias geoquímicas y geocronológicas The adakites of the Patagonian Cordillera: new geochemical and geochronological evidences

    Directory of Open Access Journals (Sweden)

    V.A. Ramos


    (~50°15'S, que no tienen características adakíticas, a pesar que se hallan ubicadas al este de donde la dorsal de Chile chocó alrrededor de los 14 Ma. En esta última región no hay importantes lavas basálticas miocenas de meseta relacionadas con ventanas astenosféricas entre la placa Antártica y la de Nazca. Los estudios de campo y las consideraciones petrológicas señalan que la fusión de corteza oceánica miocena en Patagonia requirió un aporte térmico desde el manto astenosférico tanto como de la subducción de una placa joven y caliente. Un caso similar puede ser observado entre las adakitas de arco de la Zona Volcánica Austral y los basaltos pliocenos a recientes del sector extrandino.The origin of many adakites ascribed to slab melting has been questioned with their formation being attributed to melting of thickened continental crust or forearc subduction erosion. Some of the best remaining candidates for a slab-melt origin are the Cerro Pampa adakites (47°55'SL in Patagonia that erupted east of the inactive volcanic arc as the Chile Ridge collided with the Chile Trench at ca. 12 Ma. Support for a slab-melt origin for these hornblende-bearing dacites comes from high Sr concentrations (1330-2300 ppm at 63-68% SiO2, MORB-like 87Sr/86Sr (0.7028-0.7031, 143Nd/144Nd > 0.5129, and steep (heavy depleted REE pattern (La/Yb = 30-37 in an area of thin crust. Two other adakite localities to the southwest that are also east of where the Chile ridge collided at ~ 12 Ma, have been recognized more recently (65-66% SiO2, 1370-1440 ppm Sr, 87Sr/86Sr = 0.7032-7033, 143Nd/144Nd ~ 0.51289, La/Yb 28-30. These Puesto Nuevo (48°59'°S and Chaltén adakites (~49°25'°S adakites are to the east of the Pleistocene to Recent adakites in the Austral Volcanic Zone arc. New 40Ar/39Ar plateau ages obtained via laser incremental heating of hornblendes show that the Chaltén, Puesto Nuevo, and Cerro Pampa adakites decrease nortwards in age (14.50 ± 0.29, 13.12 ± 0.55, 11.39

  2. Carboniferous magmatism in the Evora Massif (southwest Portugal, Ossa-Morena Zone): from typical arc calc-alkaline to adakitic-like magmatism (United States)

    Lima, Selma M.; Neiva, Ana M. R.; Ramos, Joao M. F.


    the PP and the neighboring plutons are observed. First, the PP has the most primitive Sr-Nd isotopic signature; second, several chemical features (like high Na2O [3.86-5.87 %], Sr [278-939 ppm] and Sr/Y [12.4-192.5], low Y [2.4-19.5 ppm] and K2O/Na2O [0.19-0.75], strongly fractionated REE patterns [LaCN/YbCN = 18-43] and lack of pronounced Eu anomaly) suggest that the PP is chemically distinct from typical calc-alkaline arc rocks and is more similar to Archean TTGs and modern adakites. Using the compositional criteria of [6], an evolution towards 'slab-melts' compositions is observed within the PP, whereas the other Evora Massif plutons clearly represent 'non-slab melts'. Given their close spatial and temporal relation, we believe that the link between these granitic bodies deserves further investigation. [1] Silva and Pereira (2004) Geologische Rundschau 93, 886-896; [2] Moita et al. (2005) Geogaceta 37, 55-58; [3] Antunes et al. (2011) Estudios Geologicos 66, 25-34; [4] Antunes et al. (2011) Hutton Symposium Abstracts 9-10; [5] Lima et al. (2012) Journal of Petrology 53, 1887-1911; [6] Defant and Drummond (1990) Nature 347, 662-665.

  3. Pan-African adakitic rocks of the north Arabian-Nubian Shield: petrological and geochemical constraints on the evolution of the Dokhan volcanics in the north Eastern Desert of Egypt (United States)

    Obeid, Mohamed A.; Azer, Mokhles K.


    The Precambrian basement of Egypt is part of the Red Sea Mountains and represents the north-western part of the Arabian-Nubian Shield (ANS). Five volcanic sections are exposed in the Egyptian basement complex, namely El Kharaza, Monqul, Abu Had, Mellaha and Abu Marwa. They are located in the north Eastern Desert (ED) of Egypt and were selected for petrological and geochemical studies as they represent the Dokhan volcanics. The volcanics divide into two main pulses, and each pulse was frequently accompanied by deposition of immature molasse type sediments, which represent a thick sequence of the Hammamat group in the north ED. Compositionally, the rocks form a continuum from basaltic andesite, andesite, dacite (lower succession) to rhyodacite and rhyolite (upper succession), with no apparent compositional gaps. These high-K calc-alkaline rocks have strong affinities to subduction-related rocks with enriched LILEs (Rb, Ba, K, Th, Ce) relative to high field strength elements (Nb, Zr, P, Ti) and negative Nb anomalies relative to NMORB. The lower succession displays geochemical characteristics of adakitic rocks with SiO2 >53 wt%, Al2O3 >15 wt%, MgO >2.5 wt%, Mg# >49, Sr >650 ppm, Y 25 ppm, Cr >50 ppm and Sr/Y >42.4. They also have low Nb, Rb and Zr compared to the coexisting calc-alkaline rhyodacites and rhyolites. The highly fractionated rhyolitic rocks have strong negative Eu anomalies and possess the geochemical characteristics of A-type suites. Trace element geochemical signatures indicate a magma source consistent with post-collisional suites that retain destructive plate signatures associated with subduction zones. The adakitic rocks in the northern ANS are generated through partial melting of delaminated mafic lower crust interacting with overlying mantle-derived magma. The Dokhan volcanics were likely generated by a combination of processes, including partial melting, crystal fractionation and assimilation.

  4. Carboniferous adakite-high-Mg andesite-Nb-enriched basaltic rock suites in the Northern Tianshan area: Implications for Phanerozoic crustal growth in the Central Asia Orogenic Belt and Cu-Au mineralization%天山北部石炭纪埃达克岩-高镁安山岩-富Nb岛弧玄武质岩:对中亚造山带显生宙地壳增生与铜金成矿的意义

    Institute of Scientific and Technical Information of China (English)

    王强; 赵振华; 许继峰; Derek; A.WYMAN; 熊小林; 资峰; 白正华



  5. Lithospheric contributions to high-MgO basanites from the Cumbre Vieja Volcano, La Palma, Canary Islands and evidence for temporal variation in plume influence (United States)

    Prægel, N.-O.; Holm, P. M.


    New geochemical and isotopic data are presented from the oldest part of the Cumbre Vieja volcano, La Palma (Canary Islands), located near the assumed emergence of the Canary mantle plume. The volcanics comprise a suite dominated by basanite flows with subordinate amounts of phono-tephrite, tephri-phonolite and phonolite flows and intrusives. Two compositionally different basanite groups have been identified, both with HIMU (high-μ)-type incompatible trace element characteristics: Primitive high-MgO basanites (10.7-12.1% MgO), found only at the base of a stratigraphic profile near Fuencaliente on the south coast, and intermediate-MgO basanites (6.0-7.3% MgO), exposed in the upper part of the profile and widespread on the east coast of La Palma. The high-MgO basanites are interpreted as near-primary mantle melts (primary composition 14-15% MgO) derived by progressive melting (2.9% to 4.5%) of a common lithospheric mantle source. Model calculations indicate that it is not possible to generate the intermediate-MgO basanites from the high-MgO group by crystal fractionation of observed phenocrysts. Relative to intermediate-MgO basanites, the high-MgO flows have lower concentrations of LIL and HFS elements, except for Ti, which is markedly enriched in the primitive rocks (3.7-4.7% TiO 2 vs 3.4-3.9% TiO 2). Fuencaliente volcanics display limited temporal isotopic variations suggested to be a result of mixing of melts originating from the rising plume and the metazomatized lithospheric mantle. 87Sr / 86Sr and 143Nd / 144Nd ratios range 0.70305-0.70311 and 0.51285-0.51291, respectively, while the corresponding ranges in Pb-isotope ratios are 206Pb / 204Pb = 19.46-19.64, 207Pb / 204Pb = 15.55-15.61, and 208Pb / 204Pb = 39.16-39.53. The overall variation of the Cumbre Vieja isotopic data can be accounted for by mixtures of three mantle components in the proportions 72-79% plume source (LVC = low velocity component), 9-16% depleted mantle (DM) and up to 12% enriched mantle

  6. Rare Earths, Trace Element Characteristics of High-Mg Volcanic Rocks of Yixian Formation in Sihetun West Liaoning Province and Its Apocalypse

    Institute of Scientific and Technical Information of China (English)

    Zhang Hong; Zhang Qi


    The high-Mg volcanic rocks of the Yixian Formation in the Sihetun area have the obvious characteristics of mantle-derived lava in rare earth, trace element characteristics with high Mg# (62~70) and high content of compatible elements. In the meantime, the volcanic rocks also have the obvious characteristics of Crust-source material in rare earth, trace element characteristics with high ∑REE (158.78×10-6~359.66×10-6), high (La/Yb)N (14.61~29.60), high La/Nb(2.37~7.52) and high Ba/Nb(67.58~205.96), obvious positive anomaly of Pb and negative anomaly of Nb, Ta in trace element spider-gram. In Sr-Nd-Pb isotope the (87Sr/86Sr)i ratio is higher than 0.706 and the εNd(t) ratio is from -3.4 to -13, both reflect enriched Mantle characteristics. The characteristics above of the volcanic rocks combined with the content of Sr, Ba, Y, Yb and the ratio of Sr/Y show that the volcanic rocks have the property of the Sanukite rocks in Setouchi Japan beside subduction zone, and illuminate that the Sanukite rocks can be formed not only in island-arc near subduction zone but also in intro-plate. The analysis indicates that the high-Mg volcanic rocks in the Sihetun area result from the collective function of mantle-derived lava and crust-source materials. The result illuminates that the West Liaoning region is very special in tectonic geochemical background in Cretaceous in East China, and is an ideal region for us to further study the characteristics of magmatic activity as well as the process of Crust-Mantle interaction in Eastern China.

  7. Zircon LA-ICP MS U-Pb Age, Sr-Nd-Pb Isotopic Compositions and Geochemistry of the Triassic Post-collisional Wulong Adakitic Granodiorite in the South Qinling, Central China, and Its Petrogenesis

    Institute of Scientific and Technical Information of China (English)

    QIN Jiangfeng; LAI Shaocong; WANG Juan; LI Yongfei


    The Indosinian post-collisional Wulong pluton intruded into the Mesoproterozoic Fuping Group, South Qinling, central China. In the southern part of the pluton, some mafic enclaves have sharp or gradational contact relationships with the host biotite granodiorite. Geochemistry, zircon LA-ICP MS (laser ablation inductively-coupled plasma mass spectrometry) U-Pb chronology and Sr- Nd-Pb isotope geochemistry of the pluton are reported in this paper. The biotite granodiorite shows close compositional similarities to high-silica adakite. Its chondrite-normalized REE patterns are characterized by strong HREE depletion (Yb = 0.33-0.96 10-6 and Y = 4.77-11.19×10-6), enrichment of Ba (775-1386×10-6) and Sr (643-1115×10-6) and high Sr/Y (57.83-159.99) and Y/Yb (10.99-14.32) ratios, as well as insignificant Eu anomalies (δEu = 0.70-0.83), suggesting a feldspar-poor, garnet±amphibole-rich residual mineral assemblage. The mafic enclaves have higher MgO (4.15- 8.13%), Cr (14.79-371.31×10-6), Ni (20.00-224.24×10-6) and Nb/Ta (15.42-21.91) than the host granodiorite, implying that they are mantle-derived and might represent underplated mafic magma. Zircon LA-ICP MS dating of the granodiorite yields a 20.6Pb/238U weighted mean age of 208±2 Ma (MSWD=0.50, 1σ), which is the age of emplacement of the host biotite granodiorite. This age indicates that the Wulong pluton formed during the late-orogenic or post-collisional stage (≤242±21 Ma) of the South Qinling belt. The host biotite granodiorite displays 87Sr/86Sr = 0.7059-0.7062, Isr = 0.7044-0.7050,143Nd/144Nd = 0.51236-0.51238, εNd(t)=-2.26 to-2.66,2.6Pb/2.4pb=18.099-18.209,207Pb/2.4pb=15.873-15.979 and 2.8Pb/204pb=38.973-39.430. Those ratios are similar to those of the Mesoproterozoic Yaolinghe Group in the South Qinling. Furthermore, its Nd isotopic model age(~1.02 Ga) is consistent with the age (~1.1 Ga) of the Yaolinghe Group. Based on the integrated geological and geochemical studies, coupled with previous

  8. Post-collisional high-Mg granitoids from the Paleoproterozoic East Sarmatian Orogen (East European Craton): Evidence for crust-mantle interaction (United States)

    Terentiev, R. A.; Santosh, M.


    The East Sarmatian Orogen (ESO) is located along the southwestern domain of the East European Craton and occupies a key tectonic link between the Sarmatian and Volgo-Uralian domains. Here we investigate the Paleoproterozoic Novaya Melovatka pluton and its mafic-ultramafic xenoliths to gain insights into the role of interaction between intermediate-felsic crustal melt with mantle rocks as a mechanism for the generation of high-Mg granitoids at crustal pressures. The pluton is composed of biotite-orthopyroxene quartz dioritic and monzodioritic porphyrites (Phase 1) and medium-grained biotite-amphibole quartz diorite, tonalite and granodiorite and commingled Phase 1 mafic magmatic enclaves (MME) (Phase 2). The general geochemical characteristics of these rocks are similar to those of Late-Archean high-Mg sanukitoids. The TDM (model) ages for intermediate Phase 1 and granitoid Phase 2 are similar and show a range of 2324-2439 and 2284-2519 M, respectively. The εNd(t) values are grouped around subchondritic values (=+1.4-+1.9 and + 1.1-+2.2) and the initial 87Sr/86Sr ratios are in the range of 0.70202-0.70390. The complex compositional zoning of minerals suggests that the rocks crystallized as synchronous but discrete magma pulses, with limited to significant mixing. Based on the geochemical features we infer that the Phase 1 rocks formed from partial melting of a mantle wedge metasomatized to different degrees by fluids/melts. The presence of MMEs, compositional zoning of minerals including reversely zoned amphiboles, plagioclases with thin calcic overgrowths, and acicular apatite, as well as the whole-rock geochemical features are consistent with a hybrid origin of the high-Mg granitoids belonging to Phase 2. Geobarometry indicates crystallization at upper-crustal depths (i.e. 1.7-2.4 kbar). The igneous suite evolved by fractional crystallization of orthopyroxene, hornblende, plagioclase and biotite. Here we propose a tectonic model involving partial melting of the

  9. Neoproterozoic granitoids associated with the Bou-Azzer ophiolitic melange (Anti-Atlas, Morocco): evidence of adakitic magmatism in an arc segment at the NW edge of the West-African craton (United States)

    Beraaouz, E. H.; Ikenne, M.; Mortaji, A.; Madi, A.; Lahmam, M.; Gasquet, D.


    The Neoproterozoic intrusions of the Bou-Azzer El Graara inlier consist of metaluminous, medium to high-K, I-type granitoids. Two groups of granitoids can be distinguished based on chemistry and isotopic signature: (1) the early (≈670 Ma) medium-K calc-alkaline, pre-collisional diorites of Ousdrat, Bou-Azzer, Bou-Izbane, and Ait-Hmane, with less fractionated REE patterns (2.6 Bleida characterized by relatively more fractionated REE patterns (8.9 15%, 3 < %Na 2O < 6.4, Yb < 1.8 ppm, Y < 20 ppm and isotopic ratios of Sr and Nd similar to the ophiolitic rocks). However their La/Yb and Sr/Y are relatively low in most of the samples. The origin of these arc magmas is not completely understood. In this paper we argue that some of these rocks probably contain components of adakitic melts. The early group was produced by partial melting of subducted oceanic crust followed by interaction of the melt with the overlying mantle wedge, and the late group by dehydration melting of underplated basalts in the lower crust in the garnet stability field.

  10. 印尼苏门答腊岛巴东地区埃达克质岩地球化学特征和构造环境%Geochemical characteristics and its significance of tectonic setting for Adakite-like rocks in Padang area, Sumatra (Indonesia)

    Institute of Scientific and Technical Information of China (English)

    朱章显; 杨振强; 胡鹏


    Based on composition of chemical analyses of rocks in Padong Area ,Sumatra (Indonesia) comparing with the data of the typical adakitic rocks ,this paper discusses the geochemical characteristics and their significance of tectonic setting .The comparative results shows that the trace element composition of the adakite-like rocks have the characteristics of low Sr contents (general 3 .88 × 10-6 ~83 .6 × 10-6 ) ,low Y contents(≤20 × 10-6 ) ,low Yb contents(≤1 .9 × 10-6 )of HREE ,and lower Sr/Y ratio (1 .09~18 .55) .On the chondrite-normalized spider diagram of trace element ,there are positive peak of Th ,Ba and strongly negative anomaly of Nb、Ta、Ti elements .The La/Yb ratio of REE are within the range of 1 .28~35 .46 ,and there are two types of chondrite-nomalized rare earth elements pattern:enriched and no enriched model , belonging to C-and O-type adakite respectively .The tectonic setting of theses adakite-like rocks are located at the volcano-arc of active continental margin near ocean-continent collision zone .The igneous magma derived from the areas of partly melting of seduction ocean slab plus partly molting and assimilation o f mantle wedge(MASH) .The distribution of adakite-like rocks in this area is in perfect accord with Cu-Au deposits of skarn type and iron deposits as well as hypothermal hot-spring Au zone .That meams the adakite-like rocks have a big significance in exploration .%根据苏门答腊岛巴东地区的岩石化学分析数据与典型埃达克岩进行对比,本文讨论其地球化学特征及其大地构造环境意义。对比结果表明:该地区的埃达克质岩微量元素特征为低Sr含量(一般为3.88×10-6~83.6×10-6),低重稀土元素Y含量(≤20×10-6)和低Yb含量(≤1.9×10-6),低Sr/Y比值(1.09~18.55)。在微量元素蛛网图上有 Th、Ba正异常峰和强烈的 Nb、Ta、Ti等元素负异常。稀土元素La/Yb比值为1.28~35.46,在REE元素

  11. Metallogeny and Origin for Two Types of Cenozoic Adakites:Southeastern Asia Region Versus East Pacific Zone%两类埃达克岩的含矿性和成因:东南亚地区与东太平洋带对比

    Institute of Scientific and Technical Information of China (English)

    朱章显; 杨振强; 向文帅; 胡鹏


    新生代埃达克岩是一种新型的火成岩(Sr/Y≥20),多产出于大洋岛弧、大陆边缘造山带(东南亚地区)和陆缘火山弧环境(东太平洋带),依据REE配分模式可将其划分为2种成因类型:大洋型(O型)和大陆型(C型).埃这克岩分别广泛分布于东南亚地区的菲律宾群岛、苏拉威西、中加里曼丹、印度尼西亚几内亚岛、巴布亚新几内亚至所罗门群岛一带,及东太平洋带的北美洲、墨西哥、中美洲、南美洲的北部至南部.研究表明:不同成因类型的埃达克岩具有不同的含矿性,反映各自岩浆源区不同.C型埃达克岩(La/Yb> 12)是俯冲海洋板块部分熔融叠加增厚的地壳底部部分熔融MASH(熔融-混染-储存-均一化)和AFC(混染-分异-结晶)作用的产物,多半与世界级斑岩铜金矿床共生;O型埃达克岩(La/Yb≤12)则与平缓俯冲的海洋板片部分熔融作用有关,在东南亚地区主要与浅成热泉金矿有成因联系.%The Cenozoic adakite, usually located at the oceanic island arcs, continental margin orogenic zone (in southeastern Asia) and volcanic arcs of continental margin (around eastern circura-Pacific zone) , is a new kind of igneous rock ( Sr/Y ratio ≥ 20) , which can be subdivided into two kinds of origin types: oceanic type (O-type) and continental type (C-type) based on their REE distribution patterns. The adakites in southeastern Asia are widely distributed within Philippines archipelago, Sulawesi (Indonesia), Central Kalimantan, Guinea Island (both Indonesia and New Papua Guinea) to Solomon Islands, but relatively rare in Sumatra, western Java, and Banda island arc; adakites around eastern circum-Pacific zone include North America, Mexico, Central America, and South America. According to the research results, the two subtypes of adakite show different metallogenic features, reflecting that they derived from diffe-rent magmatic sources. C-type adakites ( La/Yb ratio > 12) formed from

  12. Revisiting the compositions and volatile contents of olivine-hosted melt inclusions from the Mount Shasta region: implications for the formation of high-Mg andesites (United States)

    Ruscitto, D. M.; Wallace, P. J.; Kent, A. J. R.


    Primitive chemical characteristics of high-Mg andesites (HMA) suggest equilibration with mantle wedge peridotite, and they may form through either shallow, wet partial melting of the mantle or re-equilibration of slab melts migrating through the wedge. We have re-examined a well-studied example of HMA from near Mt. Shasta, CA, because petrographic evidence for magma mixing has stimulated a recent debate over whether HMA magmas have a mantle origin. We examined naturally quenched, glassy, olivine-hosted (Fo87-94) melt inclusions from this locality and analyzed the samples by FTIR, LA-ICPMS, and electron probe. Compositions (uncorrected for post-entrapment modification) are highly variable and can be divided into high-CaO (>10 wt%) melts only found in Fo > 91 olivines and low-CaO ( 90 olivines. Restored low-CaO melt inclusions are HMAs (57-61 wt% SiO2; 4.9-10.9 wt% MgO), whereas high-CaO inclusions are primitive basaltic andesites (PBA) (51-56 wt% SiO2; 9.8-15.1 wt% MgO). HMA and PBA inclusions have distinct trace element characteristics. Importantly, both types of inclusions are volatile-rich, with maximum values in HMA and PBA melt inclusions of 3.5 and 5.6 wt% H2O, 830 and 2,900 ppm S, 1,590 and 2,580 ppm Cl, and 500 and 820 ppm CO2, respectively. PBA melts are comparable to experimental hydrous melts in equilibrium with harzburgite. Two-component mixing between PBA and dacitic magma (59:41) is able to produce a primitive HMA composition, but the predicted mixture shows some small but significant major and trace element discrepancies from published whole-rock analyses from the Shasta locality. An alternative model that involves incorporation of xenocrysts (high-Mg olivine from PBA and pyroxenes from dacite) into a primary (mantle-derived) HMA magma can explain the phenocryst and melt inclusion compositions but is difficult to evaluate quantitatively because of the complex crystal populations. Our results suggest that a spectrum of mantle-derived melts, including

  13. Late Jurassic adakitic granodiorite in the Dong Co area, northern Tibet: Implications for subduction of the Bangong-Nujiang oceanic lithosphere and related accretion of the Southern Qiangtang terrane (United States)

    Fan, Jian-Jun; Li, Cai; Wu, Hao; Zhang, Tian-Yu; Wang, Ming; Chen, Jing-Wen; Xu, Jian-Xin


    In this paper we present new major and trace element chemical data, zircon U-Pb age data, and zircon Hf isotopic compositions for the Dong Co granodiorites (DGs) that were emplaced directly in the Dong Co ophiolites (DOs) in the middle segment of the Bangong-Nujiang suture zone (BNSZ), northern Tibet. We use these new data to discuss the genesis of the DGs and implications for the evolution of the region. The DGs have high contents of SiO2, Al2O3, Na2O, and Sr, high values of Mg#, low contents of Yb and Y, and markedly high Sr/Y ratios, indicating an adakitic affinity, and we show that they were derived from the partial melting of subducted oceanic crust. The DGs contain large numbers of inherited zircons that have similar shapes and peak ages to the detrital zircons in the accretionary wedge graywackes that surround the DGs, suggesting that many of these sediments were assimilated during the formation of the DGs. Five DG samples yield the youngest zircon U-Pb ages of 155-160 Ma, indicating that the DGs formed during the Late Jurassic. Based on the present results and regional geological data, we infer that the Bangong-Nujiang oceanic lithosphere was subducted northwards beneath the Southern Qiangtang terrane during the formation of a continental arc system during the Late Jurassic. The Bangong-Nujiang oceanic lithosphere retreated rapidly after its initial subduction, and the Southern Qiangtang terrane to the north of the Bangong-Nujiang Ocean acquired a massive amount of new oceanic material in the form of an accretionary wedge. This wedge, which included the DOs and the Mugagangri Group, became sufficiently large (both in size and width) for arc-type magmas (DGs) to develop within it during the Late Jurassic.

  14. Petrology of the Motaghairat mafic-ultramafic complex, Eastern Desert, Egypt: A high-Mg post-collisional extension-related layered intrusion (United States)

    Abdel Halim, Ali H.; Helmy, Hassan M.; Abd El-Rahman, Yasser M.; Shibata, Tomoyuki; El Mahallawi, Mahmoud M.; Yoshikawa, Masako; Arai, Shoji


    The geodynamic settings of the Precambrian mafic-ultramafic complexes in the Eastern Desert of Egypt have important bearing on understanding the geotectonic evolution of the Arabian Nubian Shield. We present a detailed petrological study on a layered mafic-ultramafic intrusion that is located at the contact between the Precambrian continental crust and the Miocene Red Sea oceanic crust. The Motaghairat layered intrusion consists of basal lherzolite, orthopyroxenite, troctolite, olivine gabbro and anorthosite on the top. Variations in modal mineralogy and mineral chemistry along with the chemical composition of these units suggest their derivation from a common high-Mg tholeiitic parent melt through fractional crystallization processes. The parental magma was derived from a metasomatised mantle source. The primitive mantle-normalized patterns of the calculated melts exhibit enrichment in U relative to Th and Ba relative LREE which indicate that the enriched lithospheric mantle source was metasomatised by fluids derived from a subducted oceanic crust rather than by a sediment melt. Geological and petrological evidences suggest that the layered Motaghairat intrusion was emplaced during post-orogenic extension following subduction break-off and lithospheric delamination after the collision between the amalgamated island arc terranes and the Saharan Metacraton. The heat source required to melt the metasomatised lithospheric mantle was derived from the upwelling of hot asthenosphere after the subduction-break-off.

  15. Zircon U-Pb age, Lu-Hf isotope, mineral chemistry and geochemistry of Sundamalai peralkaline pluton from the Salem Block, southern India: Implications for Cryogenian adakite-like magmatism in an aborted-rift (United States)

    Renjith, M. L.; Santosh, M.; Li, Tang; Satyanarayanan, M.; Korakoppa, M. M.; Tsunogae, T.; Subba Rao, D. V.; Kesav Krishna, A.; Nirmal Charan, S.


    The Sundamalai peralkaline pluton is one among the Cryogenian alkaline plutons occurring in the Dharmapuri Rift Zone (DRZ) of the Salem Block in the Southern Granulite Terrane (SGT) of India. Here we present zircon U-Pb age and Lu-Hf isotopic composition, mineral chemistry and geochemistry of the pluton to explore the petrogenesis and geodynamic implications. Systematic modal variation of orthoclase, Na-plagioclase, Ca-amphibole (ferro-edenite and hastingsite) and quartz developed quartz-monzonite and granite litho units in the Sundamalai pluton. Thermometry based on amphibole-plagioclase pair suggests that the pluton was emplaced and solidified at around 4.6 kbar pressure with crystallization of the major phases between 748 and 661 °C. Estimated saturation temperature of zircon (712-698 °C) is also well within this range. However, apatite saturation occurred at higher temperatures between 835 and 870 °C, in contrast with monazite saturation (718-613 °C) that continued up to the late stage of crystallization. Estimated oxygen fugacity values (log fO2: -14 to -17) indicate high oxidation state for the magma that stabilized titanite and magnetite. The magmatic zircons from Sundamalai pluton yielded a weighted mean 206Pb/238U age of 832.6 ± 3.2 Ma. Geochemically, the Sundamalai rocks are high-K to shoshonitic, persodic (Na2O/K2O ratio > 1), silica-saturated (SiO2:65-72 wt.%), and peralkaline in composition (aluminum saturation index, ASI effect) controlled differentiation between quartz-monzonite and granite. Both rock types have high content of Na2O (5.1-6.3 wt.%), Ba (350-2589 ppm) and Sr (264-1036 ppm); low content of Y (8.7-17 ppm) and Yb (0.96-1.69 ppm); elevated ratios of La/Yb (11-46) and Sr/Y (46-69) and are depleted in Ti, with a positive Sr anomaly suggesting an adakite-like composition and garnet controlled melting of a plagioclase-poor source. The low content of MgO (aborted rifting along the DRZ generating the magma that crystallized the Sundamalai

  16. Post-kinematic lithospheric delamination of the Wuyi-Yunkai orogen in South China: Evidence from ca. 435 Ma high-Mg basalts (United States)

    Yao, Wei-Hua; Li, Zheng-Xiang; Li, Wu-Xian; Wang, Xuan-Ce; Li, Xian-Hua; Yang, Jin-Hui


    Understanding the processes responsible for the intra-plate early Paleozoic Wuyi-Yunkai orogeny (> 460 Ma to 420-415 Ma) in the South China Block (SCB) is important for deducing the interactions of this block with other continents at that time, as well as the tectonic evolution of East Asia. One salient feature of the orogen is that despite the wide occurrence of syn- to late-orogenic (440 Ma to 420-415 Ma) granites in the orogen, neither syn- to late-orogenic volcanic rocks nor mafic rocks of any type have been reported. Such mafic rocks could shed clues about any mantle-crust interaction during such a major orogeny, thus help to understand the dynamics of the orogenic event. We present here, for the first time, geochronological, isotopic and geochemical data for a mafic-intermediate volcanic succession in northern Guangdong, near the edge of the metamorphic core of the orogen. The volcanic rocks unconformably overlie strongly deformed Cambro-Ordovician strata, but are in low-angle unconformable contact with overlying post-orogenic mid-Devonian strata. LA-ICP-MS and SHRIMP U-Pb dating of zircons from two andesitic and dacitic samples gives a consistent crystallization age of ca. 435 Ma, younger than the 460-445 Ma peak metamorphism of the orogeny but synchronous with the widespread late-orogenic (ca. 440-415 Ma) granitic intrusions. Nine least crustally-contaminated basaltic samples are characterized by high MgO (12.3-19.2 wt.%), Ni (214-715 ppm) and Cr (724-1107 ppm), but low TiO2 (0.6-0.8 wt.%), Al2O3 (10.2-12.8 wt.%) and Fe2O3T (total Fe as Fe2O3) (8.7-11.4 wt.%) contents. The basalts also exhibit low Nb/La ratios (0.4-0.8) and constant ɛNd(t) values (- 8.0 to - 8.4) with variable SiO2 (44.8-51.5 wt.%) contents, suggesting a likely sub-continental lithospheric mantle origin. These high-magnesian basalts have chemical compositions similar to their primary magma, which was estimated using geochemical modeling at SiO2 ≈ 50 wt.%, MgO ≈ 14 wt.% and FeOT ≈ 9

  17. Formation and Significance of Adakitic Rocks in Datong Pluton of Early Paleozoic Magmatic Arc of Western Kunlun Orogen%西昆仑早古生代岩浆弧大同岩体中埃达克质岩石的成因及地质意义

    Institute of Scientific and Technical Information of China (English)

    曹颖; 王建; 刘建国; 包真艳; 宋樾; 李爱


    大同岩体位于西昆仑柯冈库地其曼于特和麻扎康西瓦两条蛇绿混杂岩带之间。为进一步了解西昆仑早古生代岩浆弧中某些具体岩石类型、岩浆产生机理、地质意义及成因联系,本文从岩相学、主微量元素地球化学、锆石U Pb年龄和Hf同位素等方面,对大同岩体中和外围新发现的埃达克质岩石进行了研究。埃达克质岩石由石英二长花岗岩和黑云母二长花岗岩两种岩性组成,呈独立的岩体和大同主岩体中的脉体两种产状,高硅(w(SiO2)≥60.34%)、高铝(w(Al2O3)≥14.73%)、富碱(w(K2O+Na2O)≥6.40%)、低镁(w(MgO)≤2.35%),以及高锶(w(Sr)≥504×10-6)、低钇(w(Y)≤17.20×10-6)和高Sr/Y(平均为70.88),富集轻稀土元素和大离子亲石元素,亏损重稀土元素和高场强元素,不同程度负Eu异常及Ta、Nb、P和Ti亏损。锆石U Pb测年显示,埃达克质岩石年龄为(443.6±1.4)~(462.0±1.0)Ma ,与大同主岩体的形成年龄相当。锆石εHf (t)为-7.28~4.56(平均-0.84),我们认为埃达克质岩石是由原特提斯洋洋壳及部分洋壳之上的陆源沉积物向南俯冲过程中,发生部分熔融形成的熔体上升过程中与地幔楔橄榄岩反应,最后定位于地壳浅层的结果。通过与大同岩体主岩体对比,对早古生代岩浆弧的形成和演化有了更深入的了解。%Datong pluton is located between Kegang Kudi Qimanyute ophiolite belt and Mazha Kangxiwa ophiolite belt in the western Kunlun orogen .This paper presents the study of petrography , major and trace elements ,geochemistry ,zircon U Pb chronology ,and Hf isotopic data of the adakitic rocks ,which are in and surround Datong pluton .The adakitic rocks consist of biotite monzonitic granite and quartz monzonitic granite ,occurring in small isolated plutons and dykes in the


    Institute of Scientific and Technical Information of China (English)

    李永飞; 孙守亮; 郜晓勇


    A detailed study is carried out on petrology,laser 40Ar/39Ar dating and geochemistry of the high-Mg# volcanic rocks from Tuquan Basin in Central Daxinganling region on the ground of their genesis,magmatic origin and geological implication.It is concluded that the volcanic rocks comprise a series of the acid-medium rocks (namely,andesite and dacite) with the age of 136.0 ±2.0 Ma by the method of laser 40Ar/39Ar dating,identical to early Early-Cretaceous.Geochemically,these rocks show a close affinity to adakitic rocks,with SiO2 ≥57.50%,high Al2O3 (≥ 16.66%),MgO<3.31%,Mg#>45,low Y (averagely 17.53×10-6,<18×10-6) and Yb (averagely 1.84×10-6,<1.90×10-6),high Sr (>534×10-6)and Ba (789×10-6-925×10-6),Sr/Y=22.71-73.54,Y/Yb=8.32-11.32,enriched LREE,depleted HREE and without significant Eu anomaly (average Eu/Eu*=0.94).The features listed above imply that the original magma for the studied rocks is most likely resulted from partial melting of the thickened lower crust and in turn contaminated by the basaltic magma.Combined with the tectonic evolution characteristics in this region in Mesozoic,the volcanics from the Tuquan Basin should be derived from partial melting of the thickened lower crust as the result of the collision of Mongol-Okhotsk (Paleo-Pacific) orogenic belt.%对大兴安岭中段突泉盆地中出露的高Mg#火山岩进行了详细的岩石学、激光全熔40Ar/39Ar测年及地球化学研究,讨论了该组火山岩成因、岩石物质来源及其地质意义.突泉盆地高Mg#火山岩为一套中酸性岩石,化学成分显示其主要为安山岩与英安岩.岩石激光全熔40Ar/39Ar测年结果显示火山岩年龄为136.0±2.0 Ma,形成于早白垩世早期.火山岩地球化学特征总体表现出了埃达克质岩石的地球化学特征:SiO2≥57.50%,A12O3≥16.66%,MgO<3.31%,Mg#>45,贫Y(平均值17.53×10-6),贫Yb(平均值1.84×10-6),高Sr(>534×10-6),高Ba(789× 10-6~925×10-6);Sr/Y=22.71~73.54,Y

  19. Middle Jurassic MORB-type gabbro, high-Mg diorite, calc-alkaline diorite and granodiorite in the Ando area, central Tibet: Evidence for a slab roll-back of the Bangong-Nujiang Ocean (United States)

    Yan, Haoyu; Long, Xiaoping; Wang, Xuan-Ce; Li, Jie; Wang, Qiang; Yuan, Chao; Sun, Min


    Mesozoic intrusions, including MORB-type gabbros, high-Mg diorites, calc-alkaline diorites and granodiorites, were exposed in the Ando microcontinent that is bounded between the Qiangtang and Lhasa terranes. Discoveries of these Mesozoic intrusions have provided new petrogenetic constraints on our understanding of Bangong-Nujiang ocean evolution. Zircon U-Pb dating shows that these intrusions formed in the early-middle Jurassic (174-177 Ma). The gabbros have relatively flat REE distribution patterns, which is analogous to the geochemical features of MORB. Their positive εNd(t) values (εNd(t) = 4.4-5.5) are consistent with those of ophiolites along the Bangong-Nujiang suture zone. These gabbros are also characterized by enrichments of fluid-sensitive elements and negative to positive Nb anomalies, indicative of the influence of subduction-related compositions in their mantle source. These features suggest that the gabbros were most likely originated from asthenosphere-derived melts metasomatized by enriched lithospheric mantle during the upwelling. The high-Mg diorites are characterized by typical features of high compatible elements (MgO = 8.3-10.24 wt%, Cr = 400-547 ppm, Ni = 120-152 ppm), high Mg# (70-74) and low Sr/Y ratios. Their high initial 87Sr/86Sr isotopic ratios and negative εNd(t) values (- 10.5 to - 10.8), together with their sanukitic characteristics, imply that the high-Mg diorites were probably produced by partial melting of mantle peridotites metasomatized by slab-derived melts and aqueous fluids. The calc-alkaline diorites have relatively high MgO (4.04-5.50 wt%), Cr, Ni contents and Mg# (56-59), as well as high (86Sr/87Sr)i ratios and negative εNd(t) values (- 7.5 to - 7.3), suggesting that they were most likely formed by partial melting of the Ando basement rocks with significant input of mantle components. The granodiorites are peraluminous and have higher (86Sr/87Sr)i ratios and more negative εNd(t) values (- 10.6 to - 10.8), similar to

  20. Geochemical characteristics of Permian adakitic granodiorite in Bayinwula of Sonid Left Banner, Inner Mongolia%内蒙古苏尼特左旗巴音乌拉二叠纪埃达克质花岗闪长岩类地球化学特征及其地质意义

    Institute of Scientific and Technical Information of China (English)



    内蒙古苏尼特左旗巴音乌拉二叠纪花岗闪长岩、石英闪长岩分布于二连-贺根山蛇绿岩带的北侧,1∶20万区域地质调查将其归于华力西晚期侵入体(γδ4(3)).经研究,该岩体具高铝(Al2O3=13.69%~16.48%)、富钠(Na2O=3.53%~4.58%)、贫钾(K2O=2.12%~4.10%)、高锶(Sr=425.1×10-6~645.2×10-6)的特点,SiO2=62.13%~72.87%,Y<18×10-6(7.23×10-6~14.29×10-6),δEu=0.71~0.83,轻重稀土元素分馏强烈,稀土元素配分曲线为右倾斜型,铕异常不明显,为典型的埃达克质岩.在微量元素原始地幔标准化蛛网图中具明显Sr高峰和Nb低谷,有与埃达克岩一致的曲线,与岛弧安山岩-英安岩-流纹岩及大陆弧安山岩-英安岩-流纹岩有明显差异.花岗闪长岩锆石U-Pb年龄为256.1±0.9 Ma,为早二叠世岩浆活动的产物.Mg#值很高(>50),表明晚古生代洋壳向北俯冲时在75~85 km深度(角闪岩相与榴辉岩相过渡相)发生部分熔融形成埃达克质熔体,侵入地壳形成埃达克岩.%Permian adakitic granodiorite and quartz-diorite in Bayinwula of Sonid Left Banner are distributed on the northern side of the Erlian-Hegen Mountain ophiolite zone. The 1∶200 000 regional geological survey has assigned it to Late Variscan intrusive mass (γδ4(3)). Studies show that the rocks have characteristics of high aluminum (Al2O3=13.69%~16.48%), higher sodium(Na2O=3.53%~4.58%), lower potassium(K2O=2.12%~4.10%)and higher strontium(Sr=425.1×10-6~645.2×10-6),SiO2=62.13%~72.87%, Y<18×10-6(7.23×10-6~14.29×10-6), δEu=0.71~0.83. The fractionation of light-weight thulium is sharp and the partition curve of thulium forms a right-oblique model. Europium anomaly is not conspicuous, suggesting typical adakitic rock. The spidergram of traced elements relative to the original mantle obviously shows a Sr peak and a Nb valley, and the original earth mantle standard curve is in accordance with that of adakites but obviously

  1. Late Permian high-Mg andesite and basalt association from northern Liaoning, North China: Insights into the final closure of the Paleo-Asian ocean and the orogen-craton boundary (United States)

    Yuan, Lingling; Zhang, Xiaohui; Xue, Fuhong; Lu, Yinghuai; Zong, Keqing


    High-Mg andesites (HMAs) and related basalts constitute a volumetrically minor, but genetically important occurrence along most convergent plate margins of various ages on Earth. The details of their petrogenesis can contain critical information for resolving essential geodynamic and crustal evolutionary issues. This zircon U-Pb dating and geochemical study documents the late Permian metamorphosed high-Mg basaltic to andesitic suite from Kaiyuan of northern Liaoning, North China. These rocks feature SiO2 contents ranging from 48.7 to 63.2 wt.%, high Mg# values of 63-75, an enrichment in large-ion lithophile elements (LILE), and depletion in high field strength elements (HFSE). They possess whole-rock initial 87Sr/86Sr ratios of 0.70417-0.70457, εNd(t) values from - 0.4 to 5.0, and εHf(t) values from 5.1 to 11, as well as zircon εHf(t) values from - 9.4 to 0.4. These features indicate that their petrogenesis most likely involved precursory metasomatism of mantle peridotites by melts from subduction-related sediments, and subsequent partial melting. With a depleted mantle source and possible tectonic link to post-subduction slab break-off, the Kaiyuan suite could present a spatial reference not only for defining the demarcation line between the North China craton (NCC) and the Central Asian Orogenic belt (CAOB) in the region, but also for tracing the final location of the cryptic suturing zone of the Paleo-Asian Ocean. Synthesizing the suite with coeval igneous episodes as well as concomitant metamorphic events along the Solonker-Xra Moron-Changchun zone leads to the characterization of the eventual closure of the Paleo-Asian Ocean within a double-sided subduction system during late Permian-Early Triassic.

  2. 吉南新太古代高镁安山岩及其地质意义%Neoarchean High-Mg Andesi tes and Its Geological Significance in Southern Jilin Province

    Institute of Scientific and Technical Information of China (English)

    李承东; 许雅雯; 张庆红; 周红英; 彭树华; 陈军强; 张阔; 赵利刚; 李省印


    The high-Mg andesite occurring in the Zhangsangou and Jinyinbie Formation-Complex in southern Jilin Province is dated at (2 493 ± 12) Ma by the SHRIMP zircon U Pb method ,which indicates that it was generated in the Neoarchean period . The high-Mg andesite belongs to the cal-calkaline series .It is geochemically characterized by SiO2 content of 53 .93% 57 .90% ,high MgO (6 .54% 8 .82 % ) and high Mg# (0 .68 0 .71 ,avg .0 .69) ,associated with enrichments of Cr (270 .66 × 10-6 1 117 .30 × 10 -6 ,avg .443 .62 × 10 -6 ) and Ni (141 .74 × 10 -6 542 .98 × 10 -6 ,avg .250 .50 × 10-6 ) .According to its high MgO ,Cr and Ni ,the high-Mg andesite is relate to the partial melting of mantle peridotites in genesis .On the other hand ,the andesite is strongly enriched in light rare earth elements (Ce:38 .34 × 10-6 59 .34 × 10-6 ) and large-ion-lithophile elements (such as Sr ,Cs ,K ,Pb ,Rb and Ba) ,and is also characterized by depletion of high-field-strength elements (such as Nb ,Ta ,Ti and P) and heavy rare earth elements (Yb:1 .38 × 10-6 1 .57 × 10 -6 ) ,which demonstrates geochemical characteristic of the arc volcanic rock .The high-Mg andesite was most likely derived from the products of interaction of slab-derived fluid or melt with mantle peridotites .It can thus be concluded that the high-Mg andesite was derived from the subduction zone and there occurred the modern plate tectonics in the Neoarchean period .%吉南张三沟岩组和金银别岩组发育一套高镁安山岩类,S H RIM P锆石 U Pb定年为(2493±12)Ma ,形成于新太古代。高镁安山岩类属于钙碱性系列,w (SiO2)为53.93%~57.90%,富 MgO (w(MgO)为6.54%~8.82%),高Mg#值(0.68~0.71,平均0.69),高铬(w(Cr)为(270.66~1117.30)×10-6,平均443.62×10-6),高镍(w(Ni)为(141.74~542.98)×10-6,平均250.50×10-6),这种高MgO、Cr、Ni的特征表明其成因与地幔部分熔融

  3. A Study of Characteristics and Origins of Stars of Ultra High Mg Abundances%Mg 超丰恒星的性质及其起源的研究

    Institute of Scientific and Technical Information of China (English)

    李响; 赵刚; 陈玉琴


    Mg超丰恒星([ Mg/Fe]>1.0)的特殊丰度模式无法用普通恒星的Mg元素起源和银河系化学演化机制解释。对这类特殊天体的起源和演化及化学丰度性质的研究,有助于深化理解恒星核合成及星系演化中一些特殊过程。首先介绍了目前文献中由高分辨率光谱证认的Mg超丰恒星,并对这些恒星的大气参数、运动学参数和化学丰度特征等性质及其起源机制进行了分析。其次统计了在斯隆巡天数据中系统搜寻的Mg超丰恒星候选体的大气参数和运动学分布特征,并且筛选了其中C超丰的候选体。研究发现绝大部分Mg超丰恒星表现了C超丰;在Mg超丰恒星中,存在中子俘获元素超丰的那些恒星都存在于双星系统中,其演化过程受到了AGB伴星的影响;而没有表现中子俘获元素超丰的那些恒星极有可能起源于第一代低能量超新星,部分恒星具有很高的空间速度,这类空间速度大于300 km/s的Mg超丰恒星可能是搜寻第一代恒星([ Fe/H]<-5.0)的最好样本。%Chemical abundances of stars of ultra high Mg abundances are rather different from those of the vast majority“normal” stars.Their typical abundance pattern cannot be completely explained by current models of stellar origin and evolution.Therefore, detailed studies of chemical abundances of a sufficient amount of such stars can improve our understanding of some special processes of stellar nuclear syntheses and related issues of galaxy evolution.In this paper we first describe stars of ultra high Mg abundances that have been identified in previous research and are suitable for abundance analyses.These stars were identified through High Resolution Spectra (HRS);their chemical-abundance patterns and kinetics have been well studied.We then present our statistical analyses of characteristics of stellar parameters and kinetics of certain candidates for stars of ultra high Mg

  4. High temperature uniaxial deformation experiment of bubble-free highly crystalline magmas; a case study for the high-Mg andesite from Goshiki-dai lava plateau, southwest Japan (Invited) (United States)

    Ishibashi, H.


    Rheological property of magma is a key factor for understanding various volcanic processes. Natural magmas commonly have crystals of various volume fraction and such suspended crystals strongly affect on magma rheology. For dilute to intermediately crystalline magmas, previous studies (e.g., Ishibashi, 2009JVGR; Vona et al. 2011ChemGeol) experimentally investigated the effects of suspended crystals on apparent viscosities and the model predicting the effects of crystals is proposed by Mader et al. (2013JVGR). However, for highly crystalline magmas, our knowledge on their complex rheological behaviors is still not enough even for bubble-free system whereas several experimental studies have been done (e.g., Carrichi et al., 2007EPSL; Picard et al., 2013JGR). Understanding rheological property in the crystal-melt two phase system is important for considering magma dynamics in deep magma chambers and dykes and also for investigating the property in bubble-crystal-melt three phase system. In this study, uniaxial compression deformation experiments were done for bubble-free, highly crystalline natural lava under high temperature, 1atm pressure conditions to investigate the effects of suspended crystals on rheology of bubble-free magma. The high-Mg andesite erupted at ca. 15 Ma from Goshiki-dai lava plateau, southwest Japan, was used for starting materials. The lava is aphyric, bubble-free, and composed of fine-grained elongated plagioclase, pyroxenes, and magnetite crystals and unaltered silicate glass. Crystal volume fraction is ca. 0.65. Samples were cut into rectangular with 15mm length, 15mm width, and 30 mm high from massive portion of lava without any visible fracture. The samples were deformed by using the high temperature uniaxial compression apparatus, installed at Earthquake Research Institute, the University of Tokyo, under conditions of temperature from 1292 to 1133 K, log strain rate from -5.5 to -2.5, and 1 atm pressure. Total strains of the samples are

  5. 赣东北蛇绿岩带新元古代(~800 Ma)高镁安山岩的发现及其意义%Recognition and Significance of Neoproterozoic (ca.800 Ma) High-Mg Andesites in the NE Jiangxi Ophiolite Belt

    Institute of Scientific and Technical Information of China (English)

    王存智; 余明刚; 黄志忠; 洪文涛; 赵希林; 姜杨; 周效华; 段政; 邢光福


    The newly discovered Neoproterozoic high-Mg andesites are located at Zhangshudun of the NE Jiangxi ophiolite belt and are dated at a zircon U-Pb age of 794.8 ±6.0 Ma.They have variable SiO2(54.90%~58.45%),CaO (2.46%~6.73%),relatively consistent Al2O3 (15.31%~16.77%,mostly less than 16%) and FeOT/MgO values (0.87~1.20),and show relatively high MgO contents (6.22~8.47%),high Mg#(64~7 1 ),which clearly exhibits the diagnostic features of typical high-Mg andesites.The study samples are enriched in LREE and have slightly negative Eu anomalies.In spider diagram,they show enrichment of LILE (eg.Rb,Ba) while depleted in Nb and Sr elements.These andesites have relatively low Sr abundance and Sr/Y ratios (4.1 1 ~7.29),similar to Sanukitoids of the Setouchi volcanic belt in Japan.The zircon Hf isotopes show positive initial epsilon Hf values ranging from +10.3 to +17.8.These geochemical data indicate Zhangshudun high-Mg andesites should derived from the deplted mantle wedge metasomatized by fluids released from the subducted slab,within an oceanic arc setting.Therefore,it is inferred that the Shuangxiwu arc was away from the southeastern margin of the Yangtze Block,and the Yangtze and Cathaysia blocks had not collided at least at ca.800Ma.%在赣东北蛇绿岩带中的樟树墩地区新发现新元古代高镁安山岩,其LA-ICP-MS锆石U-Pb法年龄为794.8±6.0 Ma。它们的 SiO2介于54.90%~58.45%,Al2O3介于15.31%~16.77%(平均小于16%);CaO 为2.46%~6.73%,FeOT/MgO变化于0.87~1.20,具有高MgO(6.39%~8.76%)、高Mg#(64~71)特点;富集轻稀土元素且具弱负Eu异常,明显富集LILE而亏损HFSE,Sr含量(普遍<200×10-6)和Sr/Y比值(4.11~7.29)均较低,具有典型高镁安山岩的地球化学特征,类似于日本Setouchi火山带的Sanukitoids。锆石εHf(t)值介于10.23~17.79之间,反映它们起源于亏损地幔。主、微量及同位素特征均表明,本区

  6. Study on technologic conditions for production of P-Mg compound fertilizer with high Mg phosphate gangue in mixed phosphoric acid and sulfuric acid%硫磷混酸分解高镁尾矿渣制取磷镁复合肥的工艺条件研究

    Institute of Scientific and Technical Information of China (English)

    胡宏; 徐德龙; 段永华; 解田


    介绍了以硫磷混酸和高镁磷尾矿粉为原料制备磷镁复合肥的工艺条件,研究了硫酸用量、磷酸用量、反应时间和反应温度对五氧化二磷、氧化镁转化率的影响.通过单因素实验得到最佳的工艺条件:磷酸用量为110 g、硫酸用量为15g、反应时间为20 min、反应温度为50℃.在此条件下,磷尾矿渣中五氧化二磷的转化率大于90%,氧化镁转化率大于80%.%Technologic conditions for production P-Mg compound fertilizer with mixed phosphoric acid and sulfuric acid and high Mg phosphate gangue as raw materials were introduced.Influences of factors,such as sulfuric acid dosage,phosphoric acid dosage,reaction time,and reaction temperature on conversion percents of P2O5 and MgO were studied.Through single factor experiment optimum technology conditions were obtained:phosphoric acid was 110 g,sulfuric acid was 15g,reaction time was 20 min.and reaction temperature was 50℃.Under the optimum conditions,conversion percent of P2O5 was more than 90% and conversion percent of MgO was over 80%.

  7. The Late Jurassic high-Mg andesites in the Daru Tso area, Tibet:Evidence for the subduction of the Bangong Co-Nujiang River oceanic lithosphere%西藏达如错地区晚侏罗世高镁安山岩--班公湖-怒江洋壳俯冲消减的证据

    Institute of Scientific and Technical Information of China (English)

    李小波; 王保弟; 刘函; 王立全; 陈莉


    对出露于拉萨地块北部的达如错接奴群安山岩进行了年代学、元素地球化学和锆石原位Hf同位素研究。用LA-ICP-MS技术测得的安山岩锆石206Pb/238U年龄为163.3±1.7Ma,即火山活动时限为晚侏罗世早期。安山岩地球化学研究结果表明,其具有典型高镁安山岩的地球化学特征,所有样品均具有较高的MgO、Mg#值,低的TFeO/MgO值(小于1.5);所有样品都显示轻稀土元素富集,具有Eu负异常,富集大离子亲石元素、亏损高场强元素的特征;锆石εHf(t)值为较均一的负值(εHf(t)=-8.5~-6.7)。研究表明,达如错高镁安山岩很可能是班公湖—怒江洋壳在俯冲消减背景下,由俯冲沉积物熔融产生的熔体与地幔橄榄岩发生交代作用的产物,形成于与班公湖—怒江洋壳俯冲消减有关的活动大陆边缘(安第斯型)的构造环境。由此认为,晚侏罗世接奴群火山岩是班公湖—怒江洋壳俯冲消减的产物,从而为班公湖—怒江洋壳的俯冲消减提供了直接的火山岩证据。%This paper reports zircon U-Pb and Hf isotopic data of major and trace elements for the andesites of Jienu Group from the Daru Tso area in the northern Lhasa block. LA-ICP-MS U-Pb zircon analyses suggest that the andesite were formed at 163.3 ± 1.7Ma, and that the volcanic rocks were formed in early Late Jurassic period. Geochemical studies show Daru Tso andesites have typi⁃cal geochemical characteristics similar to the high-Mg andesite (HMA). They are characterized by high MgO content, Mg # values, and low TFeO/MgO ratios. They are enriched in LREE in the chondrite-normalized REE patterns with negative Eu anomalies, and are enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs). Zircon εHf(t) values are from-8.5 to-6.7. Geochemical features of the Daru Tso high-Mg andesites are considered to have been generated by the subduc

  8. 江南中段慈化地区新元古代高镁安山岩的厘定及其构造意义%Geochronology and Geochemistry of Cihua Neoproterozoic High-Mg Andesites in Jiangnan Orogen and Their Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    张玉芝; 王岳军; 郭小飞; 甘成势; 邢晓婉; 宋菁菁


    江南造山带被普遍认为是扬子与华夏陆块在新元古代的拼合带,其拼合机制及精细时代却一直备受争议.在江南造山带中段湘赣交界慈化地区识别出新元古代火山岩,并对其进行了锆石 U-Pb 年代学及主微量地球化学研究.该火山岩发育于冷家溪群地层中,其锆石 LA-ICP-MS 年代学测试得到了832±12 Ma 的206 Pb/238 U 加权平均年龄(n=16,MSWD=0.12),代表其喷发年龄.主量元素结果显示,SiO2和 MgO 含量分别为57.67%~61.33%和3.51%~4.29%,Mg#为52~57,高于正常弧火山岩,属高镁安山岩.微量元素富集轻稀土元素和大离子亲石元素,亏损高场强元素,其 Nb-Ta、Ti 亏损,具“弧型”地球化学特征,可能来源于受板片熔体/流体或者俯冲再循环沉积物交代的难熔地幔源区.上述资料表明,慈化高镁安山岩是江南造山带中段楔形地幔源区受消减组分交代作用的产物,暗示此时江南造山带中段仍在消减,扬子和华夏陆块尚未完全拼合.结合前人研究成果,江南造山带不同区段的闭合时间可能存在差异.%It is generally accepted that the Jiangnan orogenic belt led to the amalgamation of the Yangtze with Cathaysia blocks during the Neoproterozoic period.However,its tectonic evolution and amalgamation timing are still in debate.This paper pres-ents a set of new geochronological and geochemical data for the newly-identified Neoproterozoic high-Mg volcanics from Cihua (Jiangxi).LA-ICP-MS zircon U-Pb dating of the representative sample yields a weighted mean age of 832±12 Ma (n=16, MSWD=0.12),representing the eruption age of the andesite.Geochemical results indicate that they can be classified as high-Mg andesites with SiO2 ranging from 57.67% to 61.33%,MgO from 3.51% to 4.29% and Mg-number from 52 to 57.Their chondrite-normalized REE patterns exhibit a left-sloping pattern with enriched LREEs

  9. Early Cretaceous high Mg# and high Sr/Y clinopyroxene-bearing diorite in the southeast Gangdese batholith, Southern Tibet%藏南冈底斯岩基东南缘早白垩世高镁-高Sr/Y含单斜辉石闪长岩

    Institute of Scientific and Technical Information of China (English)

    王莉; 曾令森; 高利娥; 陈振宇


    Field investigations and SHRIMP zircon U-Pb dating indicate that a suite diorite that intruded into gneisses of granodioritic composition north of Langxian of the southern Gangdese belt,formed at 121.8 ± 1.5Ma.This Early Cretaceous suite contains magmatic epidote and clinopyroxene.Whole rock geochemical data and zircon Hf isotope data of this suite of diorite show the following characteristics:(1) low SiO2 (54.9% ~ 55.4%),high Al2O3 (17.7% ~ 17.9%) and high Mg# (65.3 ~ 66.1) ; (2) relatively high Na2O/K2O (>2.5),indicating that they were of granite rich in sodium; (3) enriched in LREE,depleted in HREE,nearly flat distribution patterns for elements from Ho to Yb with (Ho/Yb)N =0.93 ~ 1.07,and weak negative Eu anomalies with Eu/Eu* =0.88 ~ 0.91 ; (4) relatively high Sr (488 × 10-6 ~ 500 × 10-6) and Ba (176 × 10-6 ~ 181 × 10-6),high Sr/Y (37.5 ~41.7) and low La/Yb (7.6 ~ 9.8) ; (5) relatively high zircon εHf (t) values (+ 3.4 ~ + 6.9) ; and (6) depleted in the HFSE,but relatively enriched in garnet compatible elements (Sc,Y and HREE) as well as mantle compatible elements (Cr,Ni and Co).These geochemical features and mineral assemblages indicate that they were hydrous magma derived from the partial melting of fluid metasomatised mantle wedge during the northward subduction of the Neo-Tethyan slab.Emplace depths for the Early Cretaceous diorite as well as the Early Carboniferous granodiorite estimated by M-in-hornblende geobarometer indicate that they were emplaced at ~ 13km and ~ 21km,respectively,which in turn yields a long term exhumation rate of ~0.04mm/yr.%野外地质调查和SHRIMP锆石U-Pb定年表明,在冈底斯南缘朗县北部发育一套年龄为121.8±1.5Ma的闪长岩,侵入到一套年龄为360.8±3.5Ma弱片麻理化的花岗闪长岩中.除了典型的闪长岩矿物组合外,这套早白垩世闪长岩不仅含岩浆型绿帘石,而且含单斜辉石.朗县早白垩世闪长岩

  10. Petrogenesis and metallogenesis of the Yanshanian adakite-like rocks in the Eastern Yangtze Block

    Institute of Scientific and Technical Information of China (English)

    WANG; Qiang(


    Among the Sinian to Triassic strata in South China, the stratiform, quasi-stratiform and lenticular metallic deposits in association with hydrothermal sedimentation mainly occur in the four periods: (1) the Sinian Datangpo interglacial period, (2) the early period of Early Cambrian, (3) the late period of Middle Devonian to early period of Late Devonian,and (4) the late period of Early Permian. The four mineralization periods all happened around the maximum flooding period in the third-order seal-level cycle during the ascending stage in the first-order sea-level cycle. The deep seawater layer, starved and non-compensatory basin, low sedimentary rate, and low energy and anoxic environment during the maximum flooding period are very suitable for the formation and preservation of large to superlarge hydrothermal sedimentary deposits. The maximum flooding period also coincided with the intensified regional tectonism, extensive deep magmatism and hydrothermal sedimentation, which provide, for the formation of large to superlarge hydrothermal sedimentary deposits through the rapid accumulation of hydrothermal sediments, the needed dynamics, ore-forming materials and favorable passway for hydrothermal fluids to enter the basin.

  11. High-Temperature CO2 Sorption on Hydrotalcite Having a High Mg/Al Molar Ratio. (United States)

    Kim, Suji; Jeon, Sang Goo; Lee, Ki Bong


    Hydrotalcites having a Mg/Al molar ratio between 3 and 30 have been synthesized as promising high-temperature CO2 sorbents. The existence of NaNO3 in the hydrotalcite structure, which originates from excess magnesium nitrate in the precursor, markedly increases CO2 sorption uptake by hydrotalcite up to the record high value of 9.27 mol kg(-1) at 240 °C and 1 atm CO2.

  12. Geochemical and Sr-Pb-Nd isotopic characteristics of the Shakhtama porphyry Mo-Cu system (Eastern Transbaikalia, Russia) (United States)

    Berzina, A. P.; Berzina, A. N.; Gimon, V. O.


    The Shakhtama Mo-Cu porphyry deposit is located within the eastern segment of the Central Asian Orogenic Belt, bordering the southern margin of the Mongol-Okhotsk suture zone. The deposit includes rocks of two magmatic complexes: the precursor plutonic (J2) and ore-bearing porphyry (J3) complexes. The plutonic complex was emplaced at the final stages of the collisional regime in the region; the formation of the porphyry complex may have overlapped with a transition to extension. The Shakhtama rocks are predominantly metaluminous, I-type high K calc-alkaline to shoshonitic in composition, with relatively high Mg#, Ni, Cr and V. They are characterized by crustal-like ISr (0.70741-0.70782), relatively radiogenic Pb isotopic compositions, ɛNd(T) values close to CHUR (-2.7 to +2.1) and Nd model ages from 0.8 to 1.2 Ga. Both complexes are composed of rocks with K-adakitic features and rocks without adakite trace element signatures. The regional geological setting together with geochemical and isotopic data indicate that both juvenile and old continental crust contributed to their origin. High-Mg# K-adakitic Shakhtama magmas were most likely generated by partial melting of thickened lower crust during delamination and interaction with mantle material, while magmas lacking adakite-like signatures were probably generated at shallower levels of lower crust. The derivation of melts, related to the formation of plutonic and porphyry complexes involved variable amounts of old Precambrian lower crust and juvenile Phanerozoic crust. Isotopic data imply stronger contribution of juvenile mantle-derived material to the fertile magmas of the porphyry complex. Juvenile crust is proposed as an important source of fluids and metals for the Shakhtama ore-magmatic system.

  13. Origin of primitive andesites by melt-rock reaction in the sub-arc mantle (Invited) (United States)

    Rapp, R. P.


    The genetic relationship between primitive granitoids, including high-Mg andesites (HMAs) and bajaites, and primary granitoids, or "pristine" adakites, has been vigorously debated since Defant and Drummond (1991; henceforth D&D) first applied the term "adakite" to refer to Cenozoic arc magmas (andesites and dacites) "associated with young subducting lithosphere", with low Y and Yb, low high-field strength elements (HFSEs), high Sr, and high Sr/Y and (La/Yb)N ratios "relative to island arc andesite-dacite-rhyolite". These characteristics were attributed to an origin for adakites by partial melting of basaltic crust within the subducting slab (hence "slab melts"). That such a process can produce melts with the characteristics described by D&D has since been largely confirmed by dehydration melting experiments on hydrous metabasalt at ~1-4 GPa. Attention was also drawn to the geochemical similarities between "adakites" and large-ion lithophile element (LILE)-enriched, high-field strength element (HFSE) depleted magnesian andesites (HMAs) from Adak Island in the western Aleutians, first described by Kay (1978), implying a genetic relationship between primary granitoid (adakites) formed by partial melting of basaltic ocean crust in the subducting slab, transformed to garnet-amphibolite or eclogite, and primitive magnesian andesites (HMAs) with high Mg-numbers (Mg# = molar Mg/(Mg+Fe)x100) and high concentrations of Ni and Cr. What then is the true origin of these enigmatic arc magmas, with both crustal and mantle, derivative and primitive, geochemical signatures? Kay (1978) suggested a "hybrid" model, in which "hydrous melting of eclogite (slab melting) results in a small volume of dacitic melt ("pristine adakite"), which rises into the hotter overlying peridotite wedge and equilibrates with olivine and orthopyroxene, reacting with olivine until it becomes andesitic". In this paper, I will discuss the results of melt-rock reaction experiments modelling this peridotite

  14. Slab melting, adakite differentiation and emplacement in a fossile subduction channel: the late Paleocene Sabzevar magmatism (NE Iran) (United States)

    Rossetti, Federico; Nasrabady, Mohsen; Gerdes, Axel; Moniè, Patrick; Theye, Thomas; Lucci, Federico; Vignaroli, Gianluca


    This study describes the structural setting, petrogenesis, and geochronology of a suite of acidic magmatic rocks that are intruded in the metamorphic core of the Tertiary ophiolitic suture zone of the Sabzevar Range, NE central Iran. This ophiolitic complex consists of a ductile-to-brittle, S/SE-verging orogenic domain, where a frontal nonmetamorphic and an inner metamorphic sector can be identified in the field. The metamorphic domain consists of a major ophiolitic tectonic mélange, where variably sized, foliated metabasic rocks (blueschists, greenschists, and amphibolites) occur dispersed as centimetre- to kilometre-size blocks into a highly sheared serpentinite matrix. The granitoids occur as leucocratic tabular bodies, with variably developed contact metamorphic zones that are typically gradational in the field and concordant with the regional country rock foliation. The field relations with the host rocks and the internal (magmatic to solid state) fabrics in the Sabzevar granitoids document a syntectonic magma emplacement scenario, based on: (1) concordance of pluton shapes and internal structures with regional structures (S-L fabrics); (2) the existence of a continuum of magmatic through solid-state noncoaxial flow consistent with the regional sense of shear (top-to-the-SSE); and (3) occurrence of foliated wall-rock xenoliths, incorporated by flowing magma into the marginal sectors of the intrusive bodies. These points, together with the evidence that magma preferentially migrated along flats, attest that the Sabzevar granitoids intruded into rocks that were actively deforming during compressional shearing. In the TAS diagram, the granitoid compositions define a medium-K calc-alkaline suite, spanning from basaltic andesite to the dacite and rhyolite fields. They show characteristic low MgO (0.15-0.60 wt%) and Ni (

  15. Arc magmatic activity of Qingbaikou Period along the southeastern margin of Yangtze Block:Implications from the zircon U-Pb age and geochemical characteristics of Nb-enriched gabbro and high-Mg diorite in the Jinhua plutonic complex%扬子陆块东南缘浙江金华地区青白口纪晚期岛弧岩浆活动--来自富铌辉长岩和高镁闪长岩锆石U-Pb年龄和地球化学证据

    Institute of Scientific and Technical Information of China (English)

    姜杨; 赵希林; 邢光福; 李龙明; 段政


    In order to probe into the Neoproterozoic magmatic activity along the southeastern margin of Yangtze Block, the authors conducted petrographic, geochemical and chronologic studies of the first-discovered Nb-enriched gabbros (NEGs) and high-Mg di⁃orites (HMDs) in the Jinhua plutonic complex, Zhejiang Province. The NEGs show relatively high P 2O5, TiO2 and Nb values with (La/Nb)N less than 1.3, similar to features of Archean and Palaeozoic Nb-enriched basalts. The HMDs have relatively higher MgO content with Mg# higher than 62.5 and lower TiO2 content, and are enriched in Cr but depleted in Sr, Y and HREE, consistent with features of Miocene high-Mg andesites of Setouchi volcanic belt in Japan and Piip-type HMAs in west Aleutian. The enrichment of LILE (e.g., Rb, Ba, K and Pb) and depletion of HFSE (e.g., Nb, Ta and Ti) with dataεNd(t)>+2.92 and ISr=0.70308~0.70474, proba⁃bly indicate that the NEGs and the HMDs were formed by partial melting of mantle wedge peridotite with slab fluid metasomatism. The HMD yielded a weighted mean 206Pb/238U age of 848 ± 10Ma (measured by LA-ICP-MS). Based on the regional geology and previous studies, the authors hold that obvious island arc magmatic activity still existed along the southeast margin of Yangtze Block at Ca.848Ma, and hence the Precambrian geotectonic evolution history of south China should be reconsidered.%为探讨扬子陆块东南缘新元古代岩浆活动的性质,选择浙江金华罗店深成杂岩中的中基性岩石,开展了系统的岩石学、地球化学、同位素地球化学和年代学研究,发现该深成杂岩中存在富铌辉长岩和高镁闪长岩等典型的岛弧地区岩浆岩。富铌辉长岩相对富P2O5、TiO2和Nb,原始地幔标准化La/Nb62.5,富Cr而贫Sr、Y和重稀土元素,接近于日本Setouchi火山岩带的中新世高镁安山岩和阿留申西部的Piip型高镁安山岩。而且,二者均富集Rb、Ba、K、Pb等大离子亲石元素,亏损Nb、Ta

  16. Tectono-metamorphic evolution of high-P/T and low-P/T metamorphic rocks in the Tia Complex, southern New England Fold Belt, eastern Australia: Insights from K-Ar chronology (United States)

    Fukui, Shiro; Tsujimori, Tatsuki; Watanabe, Teruo; Itaya, Tetsumaru


    The Tia Complex in the southern New England Fold Belt is a poly-metamorphosed Late Paleozoic accretionary complex. It consists mainly of high-P/low-T type pumpellyite-actinolite facies (rare blueschist facies) schists, phyllite and serpentinite (T = 300 °C and P = 5 kbar), and low-P/high-T type amphibolite facies schist and gneiss (T = 600 °C and P high-Mg andesite and adakite might explain formation of S-type granitoids (Hillgrove suite) and coeval low-P/high-T type metamorphism in the Tia Complex.

  17. Low p-type contact resistance by field-emission tunneling in highly Mg-doped GaN (United States)

    Okumura, Hironori; Martin, Denis; Grandjean, Nicolas


    Mg-doped GaN with a net acceptor concentration (NA-ND) in the high 1019 cm-3 range was grown using ammonia molecular-beam epitaxy. Electrical properties of NiO contact on this heavily doped p-type GaN were investigated. A potential-barrier height of 0.24 eV was extracted from the relationship between NA-ND and the specific contact resistivity (ρc). We found that there is an optimum NA-ND value of 5 × 1019 cm-3 for which ρc is as low as 2 × 10-5 Ω cm2. This low ρc is ascribed to hole tunneling through the potential barrier at the NiO/p+-GaN interface, which is well accounted for by the field-emission model.


    Institute of Scientific and Technical Information of China (English)

    R.Z. Wu; B.D. Sun; H.J. Ni; Y.B. Wu; H.S. Wu; J.G. Ge


    40% Mg-content cored-wire was used to desulphurize and spheroidize ductile iron melt in industrial experiments. The optimal feeding speed and suitable treatment temperature were determined in the experiments. And cored-wire method and pouring method were compared.Conclusions have been drawn that, under these conditions in the experiments, the optimal feeding speed is 15m/min, treatment temperature should be as low as possible, 1400-1450℃ generally; and cored-wire method can act more effective in ductile iron melt desulphurization and spheroid than pouring method.

  19. Inhibitory effect of high [Mg2+] on the vasopressin-stimulated hydroosmotic permeability of the isolated perfused cortical collecting duct

    Directory of Open Access Journals (Sweden)

    Falkenstein D.


    Full Text Available High magnesium concentration inhibits the effect of arginine vasopressin (AVP on smooth muscle contraction and platelet aggregation and also influences hepatocyte AVP receptor binding. The aim of this study was to determine the role of magnesium concentration [Mg2+] in AVP-stimulated water transport in the kidney collecting duct. The effect of low and high peritubular [Mg2+] on the AVP-stimulated osmotic water permeability coefficient (Pf was evaluated in the isolated perfused rabbit cortical collecting duct (CCD. Control tubules bathed and perfused with standard Ringer bicarbonate solution containing 1 mM Mg2+ presented a Pf of 223.9 ± 27.2 µm/s. When Mg2+ was not added to the bathing solution, an increase in the AVP-stimulated Pf to 363.1 ± 57.2 µm/s (P<0.05 was observed. An elevation of Mg2+ to 5 mM resulted in a decrease in Pf to 202.9 ± 12.6 µm/s (P<0.05. This decrease in the AVP-stimulated Pf at 5 mM Mg2+ persisted when the CCDs were returned to 1 mM Mg2+, Pf = 130.2 ± 20.3 µm/s, and was not normalized by the addition of 8-[4-chlorophenylthio]-adenosine 3',5'-cyclic monophosphate, a cAMP analogue, to the preparation. These data indicate that magnesium may play a modulatory role in the action of AVP on CCD osmotic water permeability, as observed in other tissues.

  20. Geochemistry and U-Pb zircon geochronology of Late-Mesozoic lavas from Xishan, Beijing

    Institute of Scientific and Technical Information of China (English)

    YUAN; Honglin; LIU; Xiaoming; LIU; Yongsheng; GAO; Shan; LING; Wenli


    Zircon U-Pb dating by both SHRIMP and LA-ICP-MS and geochemical study of the Tiaojishan Formation and the Donglintai Formation from Xishan, Beijing, reveal that ages of upper lavas of Tiaojishan Formation and Middle of Donglintai Formation are 137.1±4.5 Ma(2σ) and 130-134 Ma, respectively. The fomer is slightly older than the latter and the age difference between these two formations is less than 5 Ma. These lines of evidence prove that the two volcanoes erupted within a short time. The age of the Tiaojishan Formation from Xishan, Beijing is distinctively different from that of the Chende Basin. This indicated that the ages of Tiaojishan lavas varied in different regions. The Tiaojishan Formation consists of typical adakite (SiO2=56%, Na2O = 3.99-6.17, Na2O/K2O = 2.2-3.1, Sr = 680-1074×10-6, Y = 13.2-16.3×10-6, Yb = 1.13-1.52×10-6, Sr/Y = 43-66), high-Mg adakite and high-Mg andesite (Mg# = 54-55). Features of continental crust of adakite from the Tiaojishan Formation and its syngeneric middle silicic vocanic rocks, such as typical Nd-Ta negative abnormality and Pb possive abnormality, indicate that these lavas are originated from partial melts of continental crust. These results suggest that the adakite from the Tiaojishan Formation of Xishan, Beijing derived from thickened eclogitic lower crust and lithosphere beneath the North China craton at mesozoic that was foundered into the aesthenosphere, and subsequenctly partially melted and interacted with mantle olivine during melts upward migration. The age of lavas from the Tiaojishan Formation restrained the foundation which should last at least until 137 Ma. Lavas of the Donglintai Formation are rhyolith and andesite with normal Mg# and thus they did not interact with the mantle. These lavas represent remobilized melts of lower crust material caused by mantle aesthenosphere upwelling migration induced by foundation.

  1. Sr, Nd and Pb isotope and geochemical data from the Quaternary Nevado de Toluca volcano, a source of recent adakitic magmatism, and the Tenango Volcanic Field, Mexico (United States)

    Martínez-Serrano, Raymundo G.; Schaaf, Peter; Solís-Pichardo, Gabriela; Hernández-Bernal, Ma. del Sol; Hernández-Treviño, Teodoro; Julio Morales-Contreras, Juan; Macías, José Luis


    Volcanic activity at Nevado de Toluca (NT) volcano began 2.6 Ma ago with the emission of andesitic lavas, but over the past 40 ka, eruptions have produced mainly lava flows and pyroclastic deposits of predominantly orthopyroxene-hornblende dacitic composition. In the nearby Tenango Volcanic Field (TVF) pyroclastic products and lava flows ranging in composition from basaltic andesite to andesite were erupted at most of 40 monogenetic volcanic centers and were coeval with the last stages of NT. All volcanic rocks in the study area are characterized by a calc-alkaline affinity that is consistent with a subduction setting. Relatively high concentrations of Sr (>460 ppm) coupled with low Y (45 km) that underlies the volcanoes of the study area, the geochemical and isotopic patterns of these rocks indicate low interaction with this crust. NT volcano was constructed at the intersection of three fault systems, and it seems that the Plio-Quaternary E-W system played an important role in the ascent and storage of magmas during the recent volcanic activity in the two regions. Chemical and textural features of orthopyroxene, amphibole and Fe-Ti oxides from NT suggest that crystallization of magmas occurred at polybaric conditions, confirming the rapid upwelling of magmas.

  2. Geochemistry and zircon U-Pb geochronology of granitoids in the East Kunlun Orogenic Belt, northern Tibetan Plateau: origin and tectonic implications (United States)

    Zhou, Bo; Dong, Yunpeng; Zhang, Feifei; Yang, Zhao; Sun, Shengsi; He, Dengfeng


    The East Kunlun Orogenic Belt (EKOB) in the northern margin of the Tibet Plateau is characterized by widespread granitic plutons, which are keys to understanding the tectonic evolution of the EKOB. The Zhiyu pluton, newly recognized in the central part of the EKOB, mainly consists of monzogranites, biotite granites and quartz diorites. Their LA-ICPMS zircon U-Pb results show formation ages of 447 ± 1.6 Ma, 448 ± 2.5 Ma and 408 ± 1.8 Ma. The monzogranites and biotite granites are characterized by relatively high Sr (208-631 ppm), low Y (4.28-15.82 ppm) and Yb (0.44-1.59 ppm) contents, thus resulting in elevated Sr/Y (30-105) and (La/Yb)N (4-79) ratios, indicating geochemical features of adakitic rocks. These adakitic granites are medium- to high-K, calcic or calc-alkaline in composition, and display a weak peraluminous character. They have low MgO (0.57-1.84 wt.%, average 1.01 wt.%), Mg# (40-53, average 45), as well as low Cr (3.67-17.98 ppm, average 7.19 ppm) and Ni (2.59-9.30 ppm, average 4.71 ppm) contents. These rocks are enriched in LREE, and show negligible or variable positive Eu anomalies (Eu/Eu∗ = 0.61-3.80, average 1.45) and significant negative Nb and Ta anomalies. Majority of the zircon grains from these adakitic granitic rocks have positive εHf(t) values of 0.09-5.21 with two-stage model ages ranging from 1.1 Ga to 1.6 Ga. These features are compatible with those of adakitic rocks derived from a thickened lower crust in the garnet stability field. Their formation is mainly controlled by the process of crust thickening following the closure of the Qimantag Ocean. The younger quartz diorites belong to medium- to high-K, calc-alkalic or alkali-calcic and metaluminous series, and exhibit a relatively high MgO (2.23-5.18 wt.%) and Mg# (40-56, average 50.11), with significant LREE enrichment and negative Eu anomalies, as well as depletion of Nb, Ta. In addition, the quartz diorites have an enriched εHf(t) values ranging from -5.25 to -3.19. Combining

  3. Deep levels in a-plane, high Mg-content Mg{sub x}Zn{sub 1-x}O epitaxial layers grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Guer, Emre [Department of Physics, Faculty of Science, Atatuerk University, Erzurum 25240 (Turkey); 205 Dreese Laboratory, Department of Electrical and Computer Engineering, The Ohio State University, 2015 Neil Avenue, Columbus, Ohio 43210-1272 (United States); Tabares, G.; Hierro, A. [Dpto. Ingenieria Electronica and ISOM, Universidad Politecnica de Madrid, Ciudad Universitaria s/n, 28040 Madrid (Spain); Arehart, A.; Ringel, S. A. [205 Dreese Laboratory, Department of Electrical and Computer Engineering, Ohio State University, 2015 Neil Avenue, Columbus, Ohio 43210-1272 (United States); Chauveau, J. M. [CRHEA-CNRS, 06560 Valbonne (France); University of Nice Sophia Antipolis, ParcValrose, 06102 Nice Cedex 2 (France)


    Deep level defects in n-type unintentionally doped a-plane Mg{sub x}Zn{sub 1-x}O, grown by molecular beam epitaxy on r-plane sapphire were fully characterized using deep level optical spectroscopy (DLOS) and related methods. Four compositions of Mg{sub x}Zn{sub 1-x}O were examined with x = 0.31, 0.44, 0.52, and 0.56 together with a control ZnO sample. DLOS measurements revealed the presence of five deep levels in each Mg-containing sample, having energy levels of E{sub c} - 1.4 eV, 2.1 eV, 2.6 V, and E{sub v} + 0.3 eV and 0.6 eV. For all Mg compositions, the activation energies of the first three states were constant with respect to the conduction band edge, whereas the latter two revealed constant activation energies with respect to the valence band edge. In contrast to the ternary materials, only three levels, at E{sub c} - 2.1 eV, E{sub v} + 0.3 eV, and 0.6 eV, were observed for the ZnO control sample in this systematically grown series of samples. Substantially higher concentrations of the deep levels at E{sub v} + 0.3 eV and E{sub c} - 2.1 eV were observed in ZnO compared to the Mg alloyed samples. Moreover, there is a general invariance of trap concentration of the E{sub v} + 0.3 eV and 0.6 eV levels on Mg content, while at least and order of magnitude dependency of the E{sub c} - 1.4 eV and E{sub c} - 2.6 eV levels in Mg alloyed samples.

  4. Practice and Result of Improving the Proportion Scheme of High-MgO Clinker%高MgO熟料配料方案的改进

    Institute of Scientific and Technical Information of China (English)




  5. Deep Fractionation of Ciinopyroxene in the East Pacific Rise 13°N: Evidence from High MgO MORB and Melt Inclusions

    Institute of Scientific and Technical Information of China (English)

    ZHANG Guoliang; ZENG Zhigang; YIN Xuebo; WANG Xiaoyuan; CHEN Daigeng


    Mid-ocean ridge basalts (MORBs) from East Pacific Rise (EPR) 13°N are analysed for major and trace elements, both of which show a continuous evolving trend. Positive MgO-Al2O3 and negative MgO-Sc relationships manifest the cotectic crystallization of plagioclase and olivine, which exist with the presence of plagioclase and olivine phenocrysts and the absence of clinopyroxene phenocrysts. However, the fractionation of clinopyroxene is proven by the positive correlation of MgO and CaO. Thus, MORB samples are believed to show a "clinopyroxene paradox". The highest magnesium.bearing MORB sample E13-3B (MGO=9.52%) is modelled for isobaric crystallization with COMAGMAT at different pressures. Observed CaO/Al2O3 ratios can be derived from E13-3B only by fractional crystallization at pressure >4±1 kbar, which necessitates clinopyroxene crystallization and is not consistent with cotectic crystallization of olivine plus plagioclase in the magma chamber (at pressure~1 kbar). The initial compositions of the melt inclusions, which could represent potential parental magmas, are reconstructed by correcting for post-entrapment crystallization (PEC). The simulated crystallization of initial melt inclusions also produce observed CaO/Al2O3 ratios only at >4±1 kbar, in which clinopyroxene takes part in crystallization. It is suggested that MORB magmas have experienced clinopyroxene fractionation in the lower crust, in and below the Moho transition zone. The MORB magmas have experienced transition from clinopyroxene+plagioclase+olivine crystallization at >4±1 kbar to mainly olivine+plagioclase crystallization at <1 kbar, which contributes to the explanation of the "clinopyroxene paradox".

  6. High-Mg andesites and their geodynamic implications%高镁安山岩及其地球动力学意义

    Institute of Scientific and Technical Information of China (English)

    唐功建; 王强



  7. Early Paleozoic ridge subduction in the Chinese Altai: Insight from the abrupt change in zircon Hf isotopic compositions

    Institute of Scientific and Technical Information of China (English)


    Zircons were separated from granitoids, gneisses, and sedimentary rocks of the Chinese Altai. Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma, recording a long history of magmatic activity in the region. Zircon Hf isotopic compositions show an abrupt change at ~420 Ma, indicating that prior to that time the magmas came from both ancient and juvenile sources, whereas younger magmas were derived mainly from juvenile material. This may imply that the lithosphere was signifi- cantly modified in composition by a rapid addition of melt from the mantle. We suggest that this dramatic change was due to the onset of ridge subduction, which can account not only for the formation of voluminous granitoids, mafic rocks with complex compositions, and the association of adakite + high-Mg andesite + boninite + Nb-enriched basalt, but also for the coeval high-T, low-P metamorphism.

  8. Early Paleozoic ridge subduction in the Chinese Altai:Insight from the abrupt change in zircon Hf isotopic compositions

    Institute of Scientific and Technical Information of China (English)

    SUN Min; LONG XiaoPing; CAI KeDa; JIANG YingDe; WANG BuYun; YUAN Chao; ZHAO GuoChun; XIAO WenJiao; WU FuYuan


    Zircons were separated from granitoids,gneisses,and sedimentary rocks of the Chinese Altai.Those with igneous characteristics yielded U-Pb ages of 280-2800 Ma,recording a long history of magmatic activity in the region.Zircon Hf isotopic compositions show an abrupt change at ~420 Ma,indicating that prior to that time the magmas came from both ancient and juvenile sources,whereas younger magmas were derived mainly from juvenile material.This may imply that the lithosphere was significantly modified in composition by a rapid addition of melt from the mantle.We suggest that this dramatic change was due to the onset of ridge subduction,which can account not only for the formation of voluminous granitoids,mafic rocks with complex compositions,and the association of adakite + high-Mg andesite+boninite + Nb-enriched basalt,but also for the coeval high-T,Iow-P metamorphism.

  9. 天山石炭纪火山岩系中含有富Nb岛弧玄武岩吗?%Do the Tianshan Carboniferous volcanic successions contain Nb-enriched arc basalts?

    Institute of Scientific and Technical Information of China (English)

    夏林圻; 夏祖春; 徐学义; 李向民; 马中平


    中国西北部天山石炭纪-早二叠世裂谷火山作用代表了一个新近被认可的大火成岩省.有人认为,在天山石炭纪火山岩系中发育有富Nb岛弧玄武岩、埃达克岩和高镁安山岩组合.然而,该岩石组合具有与典型富Nb岛弧玄武岩、埃达克岩和高镁安山岩不同的化学和同位素特点,表明其并非是岛弧岩石组合.这一推断的岛弧岩石组合实际上是大陆板内火山岩组合,由未遭受地壳混染、受到地壳轻微混染和遭受地壳强烈混染的大陆火山岩组成.%The Tianshan Carboniferous-Early Permian rift-related volcanism in northwestern China represents a newly recognized large igneous province. It has been deemed that an assemblage of Nb-enriched arc basalt, adakite and high-Mg andesite occurred in the Tianshan Carboniferous volcanic successions. Divergent chemical and isotopic characteristics between this rock assemblage and the typical Nb-enriched arc basalts, adakites and high-Mg andesites reveal that the former is not arc related. This postulated arc-related assemblage is indeed an intracontinental volcanic assemblage that consists of crustally uncontaminated, less-contaminated and strongly contaminated continental volcanic rocks.

  10. Cenozoic Adakites in Papua New Guinea and Metallogetic Significance%巴布亚新几内亚新生代埃达克岩及成矿意义

    Institute of Scientific and Technical Information of China (English)

    朱章显; 杨振强


    根据巴布亚新几内亚地区埃达克岩地球化学特征,讨论了埃达克岩的构造环境意义.巴布亚新几内亚埃达克岩微量元素特征为高锶(一般大于596.80×10-6),在微量元素蛛网图上具有正Sr异常(Sr/Y比值平均>41.7)和明显的Nb、Th负异常.Y和重稀土元素Yb含量很低(分别为≤20×10-6和≤1.9×10-6).Mg#值>0.45;87Sr/86Sr一般小于0.704 5.巴布亚新几内亚埃达克岩主要形成于弧-陆碰撞环境的大洋岛弧和大陆边缘造山带.埃达克岩的分布区与世界级斑岩铜-金矿和浅成热泉金矿成矿带分布一致.

  11. A primary discussion on geochemical evidence and significance of Cenozoic adakites,Papua New Guinea%巴布亚新几内亚新生代埃达克岩的地球化学证据

    Institute of Scientific and Technical Information of China (English)

    朱章显; 杨振强



  12. The origin of high-Mg magmas in Mt Shasta and Medicine Lake volcanoes, Cascade Arc (California): higher and lower than mantle oxygen isotope signatures attributed to current and past subduction (United States)

    Martin, E.; Bindeman, I.; Grove, T. L.


    We report the oxygen isotope composition of olivine and orthopyroxene phenocrysts in lavas from the main magma types at Mt Shasta and Medicine Lake Volcanoes: primitive high-alumina olivine tholeiite (HAOT), basaltic andesites (BA), primitive magnesian andesites (PMA), and dacites. The most primitive HAOT (MgO > 9 wt%) from Mt. Shasta has olivine δ18O (δ18OOl) values of 5.9-6.1‰, which are about 1‰ higher than those observed in olivine from normal mantle-derived magmas. In contrast, HAOT lavas from Medicine Lake have δ18OOl values ranging from 4.7 to 5.5‰, which are similar to or lower than values for olivine in equilibrium with mantle-derived magmas. Other magma types from both volcanoes show intermediate δ18OOl values. The oxygen isotope composition of the most magnesian lavas cannot be explained by crustal contamination and the trace element composition of olivine phenocrysts precludes a pyroxenitic mantle source. Therefore, the high and variable δ18OOl signature of the most magnesian samples studied (HAOT and BA) comes from the peridotitic mantle wedge itself. As HAOT magma is generated by anhydrous adiabatic partial melting of the shallow mantle, its 1.4‰ range in δ18OOl reflects a heterogeneous composition of the shallow mantle source that has been influenced by subduction fluids and/or melts sometime in the past. Magmas generated in the mantle wedge by flux melting due to modern subduction fluids, as exemplified by BA and probably PMA, display more homogeneous composition with only 0.5‰ variation. The high-δ18O values observed in magnesian lavas, and principally in the HAOT, are difficult to explain by a single-stage flux-melting process in the mantle wedge above the modern subduction zone and require a mantle source enriched in 18O. It is here explained by flow of older, pre-enriched portions of the mantle through the slab window beneath the South Cascades.

  13. Technique for Separating Magnesium and Lithium from Salt Lake Brine with High Mg/Li Ratio%高镁锂比盐湖卤水镁锂分离工艺

    Institute of Scientific and Technical Information of China (English)

    张丽芬; 张大义; 欧阳红勇; 汪全义; 宁顺明; 万洪强


    以酸化提硼后卤水为原料,采用饱和氯化钾溶液作为沉镁剂,使用三步结晶法进行了沉淀镁并富集锂的研究。结果表明,通过3段蒸发结晶析出光卤石,可以有效地实现镁锂分离:添加95%理论用量的氯化钾可以把原卤水中的镁锂质量比由10.1∶1降低到0.39∶1,锂在滤液中总回收率为77.90%,并使锂浓度从10 g/L富集到49.30 g/L。%With the salt lake brine after boron recovery as raw material and saturated solution of potassium chloride for magnesium precipitation, research was carried out on separating lithium from magnesium by the process of three⁃step evaporation crystallization. The experimental results show that the separation between lithium and magnesium could be attained after carnallite precipitation through three⁃step evaporation crystallization. The mass ratio of magnesium to lithium was reduced from 10.1∶1 to 0.39∶1 with the addition of potassium chloride at 95% of theoretical amount, resulting in the total Li+ recovery from the filtrate reaching 77.90%, and Li+ concentration enriched from 10 g/L to 49.30 g/L.

  14. Important role of magma mixing in generating the Mesozoic monzodioritic-granodioritic intrusions related to Cu mineralization, Tongling, East China: Evidence from petrological and in situ Sr-Hf isotopic data (United States)

    Chen, C. J.; Chen, B.; Li, Z.; Wang, Z. Q.


    The Mesozoic ore-bearing high-Mg monzodioritic-granodioritic rocks in the Tongling mining district (East China) have been described as having adakitic affinities, and their origin has been attributed to partial melting of delaminated eclogite at depth in the mantle, followed by interaction of the resultant granitic magma with mantle peridotite. Here we present petrological data and in situ Sr isotopic data for zoned plagioclase that are inconsistent with the eclogite-derived model and instead propose a model that involves magma mixing of siliceous crustal melts and basaltic magma that was derived from metasomatized mantle in a back-arc extensional regime. The principal geochemical signatures of these Mesozoic rocks include a high-K calc-alkaline affinity, high values of Mg#, high Sr-Ba abundances, high Sr/Y and La/Yb ratios, εNd(t) = - 13.1 to - 9.0, and ISr = 0.70707-0.70824. The magma mixing model is supported by (1) the common existence of mafic microgranular enclaves (MMEs) and the disequilibrium textures of plagioclase and amphibole, (2) the 87Sr/86Sr ratios of embayed high-Ca cores of plagioclase that are distinctly lower than in the euhedral low-Ca overgrowth rims, (3) the negative correlations between whole-rock Nd and Sr isotopic ratios, and (4) the significant differences in the values of εHf(t) (- 9.5 to - 26) within different zircons from the same intrusion.

  15. Timing and geochemical characters of the Sanchazi magmatic arc in Mianlüe tectonic zone, South Qinling

    Institute of Scientific and Technical Information of China (English)


    The Sanchazi mafic-ultramafic complex in Mianlue tectonic zone, South Qinling can be subdivided into two blocks, i.e. Sanchazi paleo-magmatic arc and Zhuangkegou paleo-oceanic crust fragment (ophiolite). The Sanchazi paleo-magmatic arc is mainly composed of andesite, basaltic and basalt-andesitic gabbro (or diorite), andesitic dyke, plagiogranite and minor ultramafic rocks, which have typical geochemical features of island arc volcanic rocks, such as high field strength element (e.g. Nb, Ti) depletions and lower Cr, Ni contents. The Light rare earth element (LREE) and K enrichments of these rocks and zircon xenocrystals of 900 Ma from plagiogranite suggest that this magmatic arc was developed on the South active continental margin of the South Qinling micro-continent. The U-Pb age of (300 ± 61)Ma for zircons from plagiogranite indicates that the Mianlue paleo-oceanic crust was probably subducted underneath the South Qinling micro-continent in Carboniferous. This is consistent with the formation time (309Ma) of the Huwan eclogite originating from oceanic subduction in Dabie Mountains, suggesting that the Mianlue paleo-ocean probably extended eastward to the Dabie Mountains in Carboniferous. The high-Mg adakitic rocks in Sanchazi paleo-magmatic arc suggest that the subducted oceanic crust was relatively young (<25Ma) and hot.

  16. Diverse magmatic effects of subducting a hot slab in SW Japan: Results from forward modeling (United States)

    Kimura, Jun-Ichi; Gill, James B.; Kunikiyo, Tomoyuki; Osaka, Isaku; Shimoshioiri, Yusuke; Katakuse, Maiko; Kakubuchi, Susumu; Nagao, Takashi; Furuyama, Katsuhiko; Kamei, Atsushi; Kawabata, Hiroshi; Nakajima, Junichi; van Keken, Peter E.; Stern, Robert J.


    response to the subduction of the young Shikoku Basin of the Philippine Sea Plate, arc magmas erupted in SW Japan throughout the late Cenozoic. Many magma types are present including ocean island basalt (OIB), shoshonite (SHO), arc-type alkali basalt (AB), typical subalkalic arc basalt (SAB), high-Mg andesite (HMA), and adakite (ADK). OIB erupted since the Japan Sea back-arc basin opened, whereas subsequent arc magmas accompanied subduction of the Shikoku Basin. However, there the origin of the magmas in relation to hot subduction is debated. Using new major and trace element and Sr-Nd-Pb-Hf isotope analyses of 324 lava samples from seven Quaternary volcanoes, we investigated the genetic conditions of the magma suites using a geochemical mass balance model, Arc Basalt Simulator version 4 (ABS4), that uses these data to solve for the parameters such as pressure/temperature of slab dehydration/melting and slab flux fraction, pressure, and temperature of mantle melting. The calculations suggest that those magmas originated from slab melts that induced flux melting of mantle peridotite. The suites differ mostly in the mass fraction of slab-melt flux, increasing from SHO through AB, SAB, HMA, to ADK. The pressure and temperature of mantle melting decreases in the same order. The suites differ secondarily in the ratio of altered oceanic crust to sediment in the source of the slab melt. The atypical suites associated with hot subduction result from unusually large mass fractions of slab melt and unusually cool mantle temperatures.

  17. Can slabs melt beneath forearcs in hot subduction zones? (United States)

    Ribeiro, J.; Maury, R.; Gregoire, M.


    At subduction zones, thermal modeling predict that the shallow part of the downgoing oceanic crust (test the hypothesis that adakites are pristine slab melts. We find that adakites from Baja California and Philippines formed by two distinct petrogenetic scenarios. In Baja California, hydrous mantle melts mixed/mingled with high-pressure (HP) adakite-type, slab melts within a lower crustal (~30 km depth) magma storage region before stalling into the upper arc crust (~7-15 km depth). In contrast, in the Philippines, primitive mantle melts stalled and crystallized within lower and upper crustal magma storage regions to produce silica-rich melts with an adakitic signature. Thereby, slab melting is not required to produce an adakitic geochemical fingerprint in hot subduction zones. However, our results also suggest that the downgoing crust potentially melted beneath Baja California.

  18. A Late Carboniferous-Early Permian slab window in the West Junggar of NW China: Geochronological and geochemical evidence from mafic to intermediate dikes (United States)

    Yin, Jiyuan; Long, Xiaoping; Yuan, Chao; Sun, Min; Zhao, Guochun; Geng, Hongyan


    The Late Carboniferous to Early Permian is a critical period for the formation of particular high-temperature magmatic associations in West Junggar, NW China and the geodynamic processes of ridge subduction and related slab windows in the Central Asian Orogenic Belt. Mafic to intermediate dikes, exposed in the central and southeastern West Junggar extensively, mainly consist of Nb-enriched and magnesian suites. The Nb-enriched dikes (305 Ma) are characterized by high Nb contents (5.63-9.08 ppm) and large variations of major element contents, exhibiting high-K to medium-K calc-alkaline characteristics with high Na2O/K2O (1.33-3.85) and low Sr/Y (9-32) ratios. The dikes have moderate Mg# (44.6-52.9), LREE-rich and sub-horizontal HREE patterns ((La/Yb)N = 3.05-7.18; (Gd/Yb)N = 1.43-1.78) with weak Eu anomalies (Eu*/Eu = 0.81-1.10) and positive εNd (t) values (+ 5.2 to + 8.0), and likely originate from partial melting of mantle peridotite that was metasomatized by subducted sediment-derived melts and slab fluids. The medium-K magnesian dikes (305 Ma) are characterized by high MgO (3.05-7.28 wt.%), Cr (22.3-311 ppm) and Ni (32.6-199 ppm) contents and all plot in the field of high-Mg andesite. Some have very high Mg numbers (Mg# > 60), suggesting a primitive melt composition. These samples display positive Ba, Sr, K and negative Nb-Ta-Ti anomalies as well as strongly-depleted HREE patterns with weak positive Eu anomalies. They have high Sr/Y (27-126) and relatively high εNd (t) values (+ 6.0 to + 8.3), which suggest a similar petrogenesis as the Nb-enriched dikes, but were metasomatized by adakitic melts. The high-K magnesian dikes (284 Ma) are high-K calc-alkaline and have lower MgO (3.63-5.57 wt.%) compared with the medium-K suite. They have high Sr (422-819 ppm), Sr/Y (26-62) ratios and εNd (t) values (+ 7.0 to + 7.1) with relatively flat REE patterns ((La/Yb)N = 2.4-5.5), probably originating from partial melting of K-enriched mantle wedge peridotite metasomatized

  19. Geochemical evidence for the melting of subducting oceanic lithosphere at plate edges. (United States)

    Yogodzinski, G M; Lees, J M; Churikova, T G; Dorendorf, F; Wöerner, G; Volynets, O N


    Most island-arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust. Volcanic rocks interpreted to contain a component of melt (not just a fluid) from the subducting slab itself are uncommon, but possible examples have been recognized in the Aleutian islands, Baja California, Patagonia and elsewhere. The geochemically distinctive rocks from these areas, termed 'adakites, are often associated with subducting plates that are young and warm, and therefore thought to be more prone to melting. But the subducting lithosphere in some adakite locations (such as the Aleutian islands) appears to be too old and hence too cold to melt. This implies either that our interpretation of adakite geochemistry is incorrect, or that our understanding of the tectonic context of adakites is incomplete. Here we present geochemical data from the Kamchatka peninsula and the Aleutian islands that reaffirms the slab-melt interpretation of adakites, but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate. We conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow. The use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction-zone environments.

  20. Possible early Neoproterozoic magmatism associated with slab window in the Pingshui segment of the Jiangshan-Shaoxing suture zone: Evidence from zircon LA-ICP-MS U-Pb geochronology and geochemistry

    Institute of Scientific and Technical Information of China (English)


    We report here geochemical data, U-Pb zircon ages, and Hf isotopes for the high-Mg diorites (HMDs), Nb-enriched basaltic porphyrys (NEBPs) and plagiogranites (PLAGs) in the Pingshui segment of the Jiangshan-Shaoxing suture zone. The HMDs are characterized by high Mg# (>60), high Na and LREE contents, depletion of HREE and HFSE, and pronounced positive εNd(t) values of 7.0 to 7.7, similar to some adakitic high-Mg andesites. The NEBPs are relatively Na-rich (Na2O/K2O>6) and display high abundances of P2O5 (~1.00%), TiO2 (~3.08%) and HFSE (e.g., Nb=9.53-10.27 ppm). Their Nd isotopic compositions (εNd(t)=6.8-8.0) are comparable to those of the HMDs. The PLAGs are metaluminous (A/CNK=0.84-0.89) and sodic (Na2O/K2O>10). Their depletion in HFSE (e.g., Nb, Ta) is consistent with "SSZ-type" plagiogranite. Zircon LA-ICP-MS U-Pb dating yields an age of 932±7 Ma for the HMD, 916±6 Ma for the NEBP, and 902±5 Ma for the PLAG, respectively, indicating that they were products of early Neoproterozoic magmatism. The PLAGs exhibit relatively high zircon Hf isotopes and positive εHf(t) values of 11.0 to 16.2, consistent with their Nd isotopic data (εNd(t)=7.5-8.4). Such features are similar to those of oceanic plagiogranites in ophiolites and distinct from those of crust-derived granites. The PLAGs were most likely derived from partial melting of subducted oceanic crust in an active continental margin. Considering these results in the context of the regional geology, we suggest that a slab window in the subducting oceanic crust between the Yangtze Block and Cathaysia Block was possibly the principal cause for the unique arc magmatism in the area. The upwelling asthenosphere below the slab window may have provided significant thermodynamic conditions.

  1. Possible early Neoproterozoic magmatism associated with slab window in the Pingshui segment of the Jiangshan-Shaoxing suture zone: Evidence from zircon LA-ICP-MS U-Pb geochronology and geochemistry

    Institute of Scientific and Technical Information of China (English)

    CHEN ZhiHong; GUO KunYi; DONG YongGuan; CHEN Rong; LI LongMing; LIANG YiHong; LI ChunHai; YU XiMing; ZHAO Ling; XING GuangFui


    We report here geochemical data, U-Pb zircon ages, and Hf Isotopes for the high-Mg diorites (HMDs), Nb-enriched basaltic porphyrys (NEBPs) and plagiogranitee (PLAGs) in the Pingshui segment of the Jiangshan-Shaoxing suture zone. The HMDs are characterized by high Mg# (>60), high Na and LREE contents, depletion of HREE and HFSE, and pronounced positive εNd(t) values of 7.0 to 7.7, similar to some adakitic high-Mg andesites. The NEBPs are relatively Na-rich (Na2O/K2O>6) and display high abundances of P2Os5(~1.00%), TiO2(~3.08%) and HFSE (e.g., Nb=9.53-10.27 ppm). Their Nd isotopic compositions (εNd(t)=6.8-8.0) are comparable to those of the HMDs. The PLAGs are metaluminous (AJCNK=0.84-0.89) and sodic (Na2O/K2O>10). Their depletion in HFSE (e.g., Nb, Ta) Is consistent with "SSZ-type" plagiogrenite. Zircon LA-ICP-MS U-Pb dating yields an age of 932±7 Ma for the HMD, 916±6 Ma for the NEBP, and 902±5 Ma for the PLAG, respectively, indicating that they were products of early Neoproterozoic magmatism. The PLAGs exhibit relatively high zircon Hf isotopes and positive εHf(t) values of 11.0 to 16.2, consistent with their Nd isotopic data (trod(f)=7.5-8.4). Such features are similar to those of oceanic plagiogranites in ophiolites and distinct from those of crust-derived granites. The PLAGs were most likely derived from partial melting of subducted oceanic crust in an active conUnen- tal margin. Considering these results in the context of the regional geology, we suggest that a slab window in the subducting oceanic crust between the Yangtze Block and Cathaysia Block was possibly the principal cause for the unique arc magmatism in the area. The upwelling aathenosphere below the slab window may have provided significant thermodynamic conditions.

  2. A Primary Discussion on Tectonnical Enviroment Significance of Two-type of Adakites,Papua New Guinea%巴布亚新几内亚新生代两类埃达克岩的构造环境意义

    Institute of Scientific and Technical Information of China (English)

    朱章显; 杨振强; 姚华舟


    本文根据新几内亚安山岩的化学分析数据与典型埃达克岩进行对比,讨论了巴布亚新几内亚埃达克岩的地球化学特征及其大地构造环境意义.对比结果表明:巴布亚新几内亚埃达克岩微量元素特征为高锶(一般>于400×10-6),Sr/Y比值平均>41.7,重稀土元素Y和Yb含量很低(分别为≤20×10-6和1.9×10-6).在微量元素蛛网图上有Sr,Ba正异常峰和明显的Nb,Th负异常.稀土元素表现为LREE富集模式,(La/Yb)N比值平均为2.19~18.69.巴布亚新几内亚埃达克岩的Mg#值>0.45,87Sr/86Sr值一般<0.7045与典型埃达克岩一相致.巴布亚新几内亚埃达克岩分别位于弧 - 陆碰撞带大地构造环境中的大洋岛弧和大陆边缘造山带中.埃达克岩的分布区域与世界级斑岩铜 - 金矿和浅成热泉金矿的成矿带的分布相一致.

  3. Initial subduction of the Paleo-Pacific Oceanic plate in NE China: Constraints from whole-rock geochemistry and zircon U-Pb and Lu-Hf isotopes of the Khanka Lake granitoids (United States)

    Liu, Kai; Zhang, Jinjiang; Wilde, Simon A.; Zhou, Jianbo; Wang, Meng; Ge, Maohui; Wang, Jiamin; Ling, Yiyun


    Northeast China is located in the eastern part of the Central Asian Orogenic Belt (CAOB) and was influenced by Paleo-Pacific subduction during the Mesozoic. Abundant granitoids from the late Paleozoic to early Mesozoic in NE China record this process, including the Khanka Lake granitoids, which resulted in extensive growth of continental crust in the area. However, the question of how and when the Paleo-Pacific tectonic system began to affect NE China is still highly controversial. The Khanka Lake granitoids can be subdivided into two main components based on their geochemical characteristics, namely granodiorite and syenogranite. The granodiorite has a U-Pb age of 249 Ma and is adakite-like (enriched in LREE and LILEs with high Mg#, Sr, La/Yb, Sr/Y and Na2O/K2O), with zircon εHf(t) values of - 0.65 to 1.61, produced by the magma mixing between melting of the lower continental crust and juvenile basaltic magma. The syenogranite has zircon U-Pb ages of 209 to 199 Ma and geochemical features of highly fractionated I-type granites, with high SiO2, total alkalis and low Mg (and Mg#), Fe, Cr and Ni, and positive zircon εHf(t) of 1.72 to 5.12, indicating an origin from remelting of juvenile crust. The granitoids were intruded by felsic veins between 195 and 184 Ma with positive zircon εHf(t) from 0.57 to 5.32. The εHf(t) values of the granitoids become more positive as the zircon U-Pb ages become younger, suggesting continuous melting of juvenile crust during subduction. It is concluded that the Khanka Lake granitoids record the early stage of subduction of the Paleo-Pacific Oceanic plate, which commenced at least ca. 250 Ma ago.

  4. Caribbean island-arc rifting and back-arc basin development in the Late Cretaceous: Geochemical, isotopic and geochronological evidence from Central Hispaniola (United States)

    Escuder Viruete, J.; Joubert, M.; Urien, P.; Friedman, R.; Weis, D.; Ullrich, T.; Pérez-Estaún, A.


    We present new regional petrologic, geochemical, Sr-Nd isotopic, and U-Pb geochronological data on the Turonian-Campanian mafic igneous rocks of Central Hispaniola that provide important clues on the development of the Caribbean island-arc. Central Hispaniola is made up of three main tectonic blocks—Jicomé, Jarabacoa and Bonao—that include four broad geochemical groups of Late Cretaceous mafic igneous rocks: group I, tholeiitic to calc-alkaline basalts and andesites; group II, low-Ti high-Mg andesites and basalts; group III, tholeiitic basalts and gabbros/dolerites; and group IV, tholeiitic to transitional and alkalic basalts. These igneous rocks show significant differences in time and space, from arc-like to non-arc-like characteristics, suggesting that they were derived from different mantle sources. We interpret these groups as the record of Caribbean arc-rifting and back-arc basin development in the Late Cretaceous. The> 90 Ma group I volcanic rocks and associated cumulate complexes preserved in the Jicomé and Jarabacoa blocks represent the Albian to Cenomanian Caribbean island-arc material. The arc rift stage magmatism in these blocks took place during the deposition of the Restauración Formation from the Turonian-Coniacian transition (~ 90 Ma) to Santonian/Lower Campanian, particularly in its lower part with extrusion at 90-88 Ma of group II low-Ti, high-Mg andesites/basalts. During this time or slightly afterwards adakitic rhyolites erupted in the Jarabacoa block. Group III tholeiitic lavas represent the initiation of Coniacian-Lower Campanian back-arc spreading. In the Bonao block, this stage is represented by back-arc basin-like basalts, gabbros and dolerite/diorite dykes intruded into the Loma Caribe peridotite, as well as the Peralvillo Sur Formation basalts, capped by tuffs, shales and Campanian cherts. This dismembered ophiolitic stratigraphy indicates that the Bonao block is a fragment of an ensimatic back-arc basin. In the Jicomé and

  5. Zircon U-Pb age, Hf isotope and geochemistry of Carboniferous intrusions from the Langshan area, Inner Mongolia: Petrogenesis and tectonic implications (United States)

    Liu, Min; Zhang, Da; Xiong, Guangqiang; Zhao, Hongtao; Di, Yongjun; Wang, Zhong; Zhou, Zhiguang


    Late Paleozoic was a critical period for the tectonic evolution of the northern margin of the Alxa-North China craton, but the evolutionary history is not well constrained. The Carboniferous intrusions in the Langshan area in the western part of the northern margin of the Alxa-North China craton are mainly composed of tonalite, quartz diorite, olivine gabbro and pyroxene peridotite. Zircon LA-ICP-MS U-Pb dating indicates that the Langshan Carboniferous intrusions were emplaced at ca. 338-324 Ma. The quartz diorites are characterized by high amounts of compatible trace elements (Cr, Ni and V) and high Mg# values, which may suggest a significant mantle source. The positive Pb and negative Nb-Ta-Ti anomalies, the variable εHf(t) (-6.9 to 2.0) values and the old Hf model ages (1218-1783 Ma) imply some involvement of ancient continental materials in its petrogenesis. The tonalite has relatively high Sr/Y ratios, low Mg#, Yb and Y contents, features of adakite-like rocks, negative εHf(t) values (-9.8 to -0.1) and older Hf model ages (1344-1953 Ma), which suggest significant involvement of ancient crust materials and mantle-derived basaltic component in its petrogenesis. The high Mg# values, high Cr and Ni contents, and low Zr and Hf contents of the mafic-ultramafic rocks show evidence of a mantle source, and the relatively low zircon εHf(t) values (-5.9 to 3.2) might point to an enriched mantle. The trace element characteristics indicate the influence of subducted sediments and slab-derived fluids. In the tectonic discrimination diagrams, all the rocks plot in subduction-related environment, such as volcanic arc and continental arc. Considering the regional geology, we suggest that the Carboniferous intrusions in the Langshan area were likely emplaced during the late stage of the southward subduction of the Paleo-Asian Ocean plate, which formed a continental arc along the northern margin of the Alxa-North China craton.

  6. 右江盆地晚侏罗世钾玄质高镁安山岩的厘定及其构造意义%The identification and implications of the Late Jurassic shoshonitic high-Mg andesite from the Youjiang basin

    Institute of Scientific and Technical Information of China (English)

    甘成势; 王岳军; 张玉芝; 刘汇川; 张立敏


    右江盆地在大地构造上处于特提斯和滨太平洋构造域的结合部位.本文报道了该盆地东部杨屯安山岩的岩相学、年代学和地球化学特征.杨屯安山岩具斑状结构和气孔状构造,斑晶主要为辉石,基质以针状斜长石微晶为主,含少量辉石.LA-ICP-MS锆石U-Pb定年结果表明杨屯安山岩的喷发时代为159.3±2.8Ma,即晚侏罗世.样品的SiO2含量为53.13%~55.71%,具高MgO(6.74%~8.85%)、Mg#值(63~72)、Cr(416×10-6~565×10-6)和Ni (207×10-6~246×10-6),低FeOT/MgO (0.83~1.23)等特征,与典型高镁安山岩的特征相似.所有样品具高K2O (3.39%~4.77%)和K2O/Na2O(1.31~2.33),同时也具钾玄质岩石的地球化学特征.样品强烈富集大离子亲石元素和轻稀土元素,而亏损高场强元素,具较高的Rb/Sr (0.20~0.46)和较低的Ba/Rb (7.17 ~9.30),富集的Sr-Nd同位素组成((87Sr/86 Sr)i=0.70738~0.70739,εNd (t)=-3.6~-3.4).元素和同位素特征表明杨屯钾玄质高镁安山岩是含金云母的富集岩石圈地幔部分熔融的产物,形成于板内伸展环境而不是岛弧环境.晚侏罗世杨屯钾玄质高镁安山岩的厘定,反映了该时期右江地区处于岩石圈伸展-减薄阶段.

  7. Early Paleozoic subduction of the Paleo-Asian Ocean: Zircon U-Pb geochronological and geochemical evidence from the Kalatag high-Mg andesites, East Tianshan%早古生代古亚洲洋俯冲记录:来自东天山卡拉塔格高镁安山岩的年代学、地球化学证据

    Institute of Scientific and Technical Information of China (English)

    李玮; 陈隽璐; 董云鹏; 徐学义; 李智佩; 柳小明; 何登峰


    吐哈盆地南缘荒草坡群大柳沟组火山岩出露于大草滩断裂以北的彩霞山、土屋铜矿北和卡拉塔格地区.该组火山岩主要为基性、中酸性熔岩及火山碎屑岩组合.LA-ICP MS锆石U-Pb分析获得安山岩和英安岩的年龄分别为434.8±3.8Ma和438.4 ±4.9Ma,表明大柳沟组火山岩形成于早志留世.安山岩SiO2含量为54.35%~60.70%;Al2O3含量为11.8%~16.3%,MgO含量为4.94%~8.27%,TiO2含量为0.38% ~0.52%,Na2O和K2O的含量分别为0.50%~3.83%和0.08%~1.26%,铝饱和指数(A/CNK)为0.77 ~ 1.37,低∑REE(43×10-6 ~70×10-6),为具有亏损源区特征的高镁安山岩.英安岩较安山岩SiO2含量高(63.74% ~75.35%),具有相似的Al2O3(12.3% ~ 16.0%%)和TiO2(0.32% ~0.52%)含量;Na2O和K2O含量分别为2.01% ~5.53%和0.16% ~2.19%,∑REE含量较安山岩略高(61×10-6 ~84×10-6),铝饱和指数(A/CNK)为0.77 ~5.74.安山岩和英安岩均轻重稀土分异明显,具有中等的Eu负异常;富集大离子亲石元素(LILE),亏损高场强元素(HFSE),具有明显的Nb-Ta-Ti负异常.相似的岩石地球化学特征表明安山岩和英安岩可能为同源岩浆,英安岩是安山质岩浆经过角闪石等矿物结晶分异作用形成的,安山岩的母岩岩浆很可能来自亏损大洋岩石圈地幔.基于该组岩石组合、地球化学特征和区域地质资料,推测研究区高镁安山岩可能形成于洋内弧环境,这表明东天山吐哈盆地南缘卡拉塔格地区在早古生代已经存在古亚洲洋的俯冲.

  8. Zircon SHRIMP geochronology and geochemistry of Late Permian high-Mg andesites in Seluohe area, Jilin province, China%吉林色洛河晚二叠世高镁安山岩SHRIMP锆石年代学及其地球化学特征

    Institute of Scientific and Technical Information of China (English)

    李承东; 张福勤; 苗来成; 颉航强; 许雅雯


    吉林色洛河地区发育高镁安山岩类,SHRIMP锆石U-Pb定年结果表明它们形成于晚二叠世(252±5Ma).色洛河高镁安山岩类(SiO259.08%~65.67%)具有富MgO(3.68%~5.30%),高Mg#值(0.62~0.68,平均0.66),高Cr(203.17×10-6~379.70×10-6,平均258.79×10-6)、Ni(98.13×10-6~249.35×10-6,平均137.00×10-6)含量;富集大离子亲石元素(如Cs、K、Pb、Rb和Ba),亏损高场强元素(如Ta、Ti、Nb、P);富集LREE(Ce39.14×10-6~48.74×10-6),强烈亏损HREE(Yb 0.95×10-6~1.27×10-6,Y 10.80×10-6~13.13×10-6,(La/Yb)N13.27~16.66);但它们含有较低的Sr(158.62×10-6~369.77×10-6,平均258.52×10-6).它们属于中钾、钙碱性系列,具有明显的结晶分异和同化混染特征.上述地球化学特征表明它可能与消减沉积物流体交代形成富集地幔的部分熔融有关,其后又经历了分异和混染作用.这揭示它们形成于活动陆缘的构造背景,表明晚古生代末期古亚洲洋板块仍在消减,华北地块和佳木斯-兴凯地块(中亚造山带)最终的拼合时间可能在二叠纪之后.

  9. Reaction experiments between tonalitic melt and mantle olivine and their implications for genesis of high-Mg andesites within cratons%英云闪长质熔体与地幔橄榄石反应的实验研究——对克拉通内部高镁安山岩成因的约束

    Institute of Scientific and Technical Information of China (English)

    王明梁; 唐红峰


    产于克拉通内部的高镁(Mg#>45)安山岩受到地学界的高度关注,目前对于高镁安山岩的成因仍然存在明显的争议.为了对已有基于岩石学和地球化学研究推断的克拉通内部高镁安山岩成因认识进行检验并提供直接的证据,我们在六面顶压机上开展了1250~1400℃,2.0~5.0 GPa条件下英云闪长质熔体与地幔橄榄石反应的高温高压实验,模拟研究拆沉到地幔的榴辉岩化下地壳部分熔融产生的熔体与地幔橄榄岩的反应.实验结果显示,反应后熔体的化学组成与华北克拉通内部高镁安山岩有很相似的变化.因此,榴辉岩化下地壳部分熔融产生的英云闪长质熔体与地幔橄榄岩的反应可能是形成克拉通内部高镁安山岩的重要机制之一.

  10. The Lonchaeidae of fiji (Diptera: schizophora) . (United States)

    Macgowan, Iain


    The status of the family Lonchaeidae on the islands of the Fiji group is reviewed. Data are provided from trapping undertaken as part of the NSF-Fiji Terrestrial Arthropod Survey and from Fijian Lonchaeidae in the collections of the Bishop Museum, Hawaii and the Natural History Museum, London. Five new species, Lonchaea fiji sp. nov., Lonchaea melanesia sp. nov., Lonchaea vanua sp. nov., Silba kadavu sp. nov. and Silba setiphallus sp. nov. are described. Two species new to Fiji, Dasiops ruidifrons McAlpine, 1964 amd Lamprolonchaea lustrata McAlpine, 1964, are recorded. Five species previously recorded, Lamprolonchaea brouniana (Bezzi, 1919), Lamprolonchaea smaragdi (Walker, 1849), Lonchaea cyaneoneitens Kertész, 1901, Silba calva (Bezzi, 1913) and Silba setifera (de Meijere, 1910) are re-evaluated and are removed from the checklist. The fauna is now considered to comprise of 11 species in 4 genera. A key is provided to the Lonchaeidae present on the islands.

  11. Archaean associations of volcanics, granulites and eclogites of the Belomorian province, Fennoscandian Shield and its geodynamic interpretation (United States)

    Slabunov, Alexander


    An assembly of igneous (TTG-granitoids and S-type leucogranites and calc-alkaline-, tholeiite-, kometiite-, boninite- and adakite-series metavolcanics) and metamorphic (eclogite-, moderate-pressure (MP) granulite- and MP amphibolite-facies rocks) complexes, strikingly complete for Archaean structures, is preserved in the Belomorian province of the Fennoscandian Shield. At least four Meso-Neoarchaean different-aged (2.88-2.82; 2.81-2.78; ca. 2.75 and 2.735-2.72 Ga) calc-alkaline and adakitic subduction-type volcanics were identified as part of greenstone belts in the Belomorian province (Slabunov, 2008). 2.88-2.82 and ca. 2.78 Ga fore-arc type graywacke units were identified in this province too (Bibikova et al., 2001; Mil'kevich et al., 2007). Ca.2.7 Ga volcanics were generated in extension structures which arose upon the collapse of an orogen. The occurrence of basalt-komatiite complexes, formed in most greenstone belts in oceanic plateau settings under the influence of mantle plumes, shows the abundance of these rocks in subducting oceanic slabs. Multiple (2.82-2.79; 2.78-2.76; 2.73-2.72; 2.69-2.64 Ga) granulite-facies moderate-pressure metamorphic events were identified in the Belomorian province (Volodichev, 1990; Slabunov et al., 2006). The earliest (2.82-2.79 Ga) event is presumably associated with accretionary processes upon the formation of an old continental crust block. Two other events (2.78-2.76; 2.73-2.72 Ga) are understood as metamorphic processes in suprasubduction setting. Late locally active metamorphism is attributed to the emplacement of mafic intrusions upon orogen collapse. Three groups of crustal eclogites with different age were identified in the Belomorian province: Mesoarchaean (2.88-2.86 and 2.82-2.80 Ga) eclogites formed from MORB and oceanic plateau type basalts and oceanic high-Mg rocks (Mints et al., 2011; Shchipansky at al., 2012); Neoarchaean (2.72 Ga) eclogites formed from MORB and oceanic plateau type basalts. The formation of

  12. “三江”地区中旬弧普朗成矿斑岩地球化学特征及其成因%Geochemistry and petrogenesis of Pulang porphyries in Sanjiang region

    Institute of Scientific and Technical Information of China (English)

    任江波; 许继峰; 陈建林; 张世权; 梁华英


    Located in Zhongdian island arc belt in northwestern Yunnan Province, the Pulang super large porphyry copper deposit was formed in late Triassic during the westward subduction of the Ganzi-Litang ocean plate below Zhongdian microplate. The mineralized rocks of the Pulang porphyry copper deposit mainly include quartz dioritic porphyries and quartz monzonitic porphyries in a complex pluton, and economic ores are mainly preserved in the quartz monzonitic porphyries. The quartz dioritic porphyrites were intruded by later quartz monzonitic porphyries, but the two kinds of rocks display similar geochemical characteristics, such as similar REE patterns, incompatible trace element patterns and initial 87Sr/86Sr and Nd/144Nd ratios, suggesting that they were coge-netic products or were derived from similar sources. Geochemically, both kinds of rocks are akin to adakite, as evidenced by such characteristics as high Sr content (289×10-6~l 200×10-6), high La/Yb and Sr/Yb ratios, relatively high MgO and Mg# (>59), depleted Y and Yb, slightly negative Eu anomalies and positive Sranomalies Moreover, the radiogenic Sr [0.705 60 61.0%) and K2O (2.2%~4.4%), while the latter have high SiQ2(> 65.9%) and K2O (3.5%~8.1%). Therefore, the authors hold that the Pulang porphyry copper deposit was probably related to the westward subduction of Ganzhi-Litang oceanic plate during late Triassic. At the early stage of subduction, the quartz dioritic porphyries with subduction-related origin were formed firstly, then increasing adakitic magmas of slab melting were mixed with melts from subducted sediments or arc materials, producing more acid and high oxygen fugacity adakitic magmas, which finally intruded the upper crust below Pulang and promoted the mineralization of the Pulang porphyry copper deposit at the shallow level.%普朗斑岩铜矿床是中国西南“三江”地区新发现的具超大规模的印支期斑岩铜矿床,其成矿岩体的斑岩具有高的Sr含量(289×10-6~1 200

  13. Important role of magma mixing in generating the Mesozoic monzodioritic-granodioritic intrusions related to Cu mineralization, Tongling, East China: evidence from petrological and in situ Sr-Hf isotopic data (United States)

    Chen, Bin; Chen, ChangJian


    The Mesozoic ore-bearing high-Mg monzodioritic-granodioritic rocks in the Tongling mining district (East China) have been described as having adakitic affinities, and their origin has been attributed to partial melting of delaminated eclogite at depth in the mantle, followed by interaction of the resultant granitic magma with mantle peridotite. Here we present petrological data and in situ Sr isotopic data for zoned plagioclase that are inconsistent with the eclogite-derived model, and instead propose a model that involves magma mixing of siliceous crustal melts and basaltic magma that was derived from metasomatized mantle by subduction zone fluids in an extensional regime. The principal geochemical signatures of these Mesozoic rocks include a hydrous and high-K calc-alkaline affinity, high values of Mg#, high Sr abundances, high Sr/Y and La/Yb ratios, ɛNd(t)=-13.1 to -9.0, and ISr=0.70707-0.70824. The magma mixing model is supported by (1) the common existence of mafic microgranular enclaves (MMEs) and the disequilibrium textures of plagioclase and hornblende, (2) the increase in Ti and Al(IV) from hornblende cores to rims, and the overgrowths of high-Ca pyroxene around hornblende grains as well, indicative of episode of heating and rejuvenation of the magma chamber as a result of recharge of mafic magma, (3) the 87Sr/86Sr ratios of embayed high-Ca cores of plagioclase that are distinctly lower than in the euhedral low-Ca overgrowth rims, (4) negative correlations between whole-rock Nd and Sr isotopic ratios, and (5) the significant differences in the values of ɛHf(t) (-9.5 to -26) within different zircons from the same intrusion. We propose that underplating of hydrous basaltic magma from the metasomatized lithospheric mantle in the lower crust resulted in partial melting of the lower crustal rocks (Precambrian TTG gneisses and amphibolite/granulite) under water-saturated conditions, during which plagioclase decomposed, leaving hornblende-rich restites and

  14. K-Ar age and geochemistry of the SW Japan Paleogene cauldron cluster: Implications for Eocene-Oligocene thermo-tectonic reactivation (United States)

    Imaoka, T.; Kiminami, K.; Nishida, K.; Takemoto, M.; Ikawa, T.; Itaya, T.; Kagami, H.; Iizumi, S.


    Systematic K-Ar dating and geochemical analyses of Paleogene cauldrons in the Sanin Belt of SW Japan have been made to explore the relationship between the timing of their formation and the Paleogene subduction history of SW Japan documented in the Shimanto accretionary complex. We also examine the magma sources and tectonics beneath the backarc region of SW Japan at the eastern plate boundary of Eurasia. Fifty-eight new K-Ar ages and 19 previously reported radiometric age data show that the cauldrons formed during Middle Eocene to Early Oligocene time (43-30 Ma), following a period of magmatic hiatus from 52 to 43 Ma. The hiatus coincides with absence of an accretionary prism in the Shimanto Belt. Resumption of the magmatism that formed the cauldron cluster in the backarc was concurrent with voluminous influx of terrigenous detritus to the trench, as a common tectono-thermal event within a subduction system. The cauldrons are composed of medium-K calc-alkaline basalts to rhyolites and their plutonic equivalents. These rocks are characterized by lower concentrations of large ion lithophile elements (LILE) including K 2O, Ba, Rb, Th, U and Li, lower (La/Yb) n ratios, lower initial Sr isotopic ratios (0.7037-0.7052) and higher ɛNd( T) values (-0.5 to +3.5) relative to Late Cretaceous to Early Paleogene equivalents. There are clear trends from enriched to depleted signatures with decreasing age, from the Late Cretaceous to the Paleogene. The same isotopic shift is also confirmed in lower crust-derived xenoliths, and is interpreted as mobilization of pre-existing enriched lithospheric mantle by upwelling depleted asthenosphere. Relatively elevated geothermal gradients are presumed to have prevailed over wide areas of the backarc and forearc of the SW Japan arc-trench system during the Eocene to Oligocene. Newly identified Late Eocene low silica adakites and high-Mg andesites in the Sanin Belt and Early Eocene A-type granites in the SW Korea Peninsula probably formed

  15. In-situ U-Pb, Hf and Re-Os isotopic analyses of the Xiangshan Ni-Cu-Co deposit in Eastern Tianshan (Xinjiang), Central Asia Orogenic Belt: Constraints on the timing and genesis of the mineralization (United States)

    Han, Chunming; Xiao, Wenjiao; Zhao, Guochun; Ao, Songjian; Zhang, Jien; Qu, Wenjun; Du, Andao


    The timing and genesis of the major Ni-Cu-Co sulfide deposit in the Xiangshan intrusion have been studied based on newly obtained in-situ U-Pb, Hf and Re-Os isotopic analyses. The SIMS U-Pb zircon ages of the gabbro hosting the Ni-Cu-Co sulfide deposit indicate that the Xiangshan intrusion was emplaced at 279.6 ± 1.1 Ma (95% confidence level, MSWD = 1.30, n = 15). On the basis of combined geological and geochronological evidence, we suggest that the Xiangshan and other adjacent Ni-Cu deposits were formed in the same period. Sulphides have low common Os concentrations and high Re/Os ratios, similar to sulphide ores from the Duluth, Sally Malay and Voisey Bay complexes. The Re-Os isotopic data from the disseminated and massive ores from the Xiangshan intrusion do not form a single isochron, as they have different initial Os ratios. The Hf and Os isotopic data suggest that the Xiangshan intrusion and associated Ni-Cu-Co mineralization were derived from crustally contaminated mantle melts. The geochemical data show a tholeiitic affinity and a strong suprasubduction zone signature with negative Nb, Sr, and Ti anomalies similar to N-MORB and E-MORB. We suggest that the mafic-ultramafic rocks and associated Ni-Cu mineralization of the Eastern Tianshan orogen formed in an Alaska-type subduction zone-arc setting. Some diagnostic features of ridge-trench interaction are present in the Chinese East Tianshan orogen (e.g. granites, adakites, high-Mg andesites, near-trench magmatism, Alaskan-type mafic-ultramafic complexes, high-temperature metamorphic belts that prograde rapidly from low-grade belts, and orogenic gold deposits). The above distinctive rock groups are probably related to the same thermal event, ridge subduction, as in the Cenozoic orogen of Alaska. We suggest that ridge subduction is the most plausible mechanism to provide the necessary heat. Ridge subduction provides an important promising model for understanding many aspects of the evolution of the Chinese

  16. A Devonian to Carboniferous intra-oceanic subduction system in Western Junggar, NW China (United States)

    Zhang, Ji'en; Xiao, Wenjiao; Han, Chunming; Mao, Qigui; Ao, Songjian; Guo, Qianqian; Ma, Chong


    The Devonian and Carboniferous rock assemblages in Western Junggar, southern Altaids, include ophiolitic mélanges and coherent units. At Baijiantan, Yeyagou and Dagun Devonian gabbros and one group of volcanic rocks (type I lava) generally crop out as blocks in a matrix of ultramafic rocks and/or mudstone. They have a depleted light rare earth element (LREE) and mid-oceanic ridge basalt (MORB)-like signature with a small negative Nb anomaly, suggesting formation in a back-arc basin. Another group of volcanic rocks (type II lava) from Baijiantan, Yeyagou, Western Karamay and Maliya includes alkaline basalt, basanite, andesite, dacite and trachyte that contain microphenocrysts of clinopyroxene-plagioclase, amygdales filled with chalcedony and calcite, and accessory pyrite and ilmenite. The type II lavas are further subdivided into five sub-types: (1) Type II1 lava is strongly enriched in LREE with incompatible trace element ratios similar to oceanic island basalt (OIB), suggesting derivation from enriched mantle. (2) Type II2 lava and tuff are slightly LREE-enriched, with a marked negative Nb anomaly and Th/Yb-enrichment indicating that they were generated in a supra-subduction zone (SSZ). (3) Type II3 lava is also moderately enriched in LREE suggesting derivation from a more-enriched MORB mantle. (4) Type II4 lava is enriched in LREE and has high Nb/Yb values close to those of OIB. It is extensively depleted in Nb suggesting a source containing a mixture of enriched and SSZ mantle. (5) Type II5 lava has MORB-like REE patterns, and Nb/Yb and Th/Yb ratios. Based on field structural data, and the contemporaneity of the Baogutu adakite, a high-Mg diorite dike and the Miaoergou charnockite, these enriched and depleted magmatic features suggest generation in an intra-oceanic subduction zone influenced by ridge-trench interaction. The Altaids in Western Junggar are characterized by multiple intra-oceanic subduction systems, which may have continued to operate to the late

  17. Role of the subduction filter in mantle recycling (United States)

    Kimura, J. I.; Skora, S. E.; Gill, J.; Van Keken, P. E.


    Subduction modifies the descending basaltic and sedimentary oceanic crust and generates felsic arc materials and continental crust. Studies of element mass balances in the subduction zone therefore reveal the evolution of the Earth's two major geochemical reservoirs: the continent crust and mantle. We use the Arc Basalt Simulator ver.4 (ABS4) to model the geochemical mass balance during dehydration by prograde metamorphism and melting of the slab followed by subsequent flux melting of the wedge mantle caused by the addition of slab-derived liquids. The geochemistry of high-Mg andesite or adakite formed in a hot subduction zone is akin to the present-day bulk continental crust and to the Archean (>2 Ga) Tonalite-Trondjhemite-Granodiorite composition. Therefore, the residual slab and the metasomatized mantle wedge at hot subduction zones should be the most plausible sources for materials recycled back into the deep mantle. Model calculations of isotopic growth in the residual slab and mantle formed in hot subduction zones reproduce fairly well the EM1-FOZO-HIMU isotope arrays found in ocean island basalts (OIBs) of deep mantle plume origin, although FOZO with high 3He/4He is not generated by this slab recycling process. The recycled materials are bulk igneous ocean crust for HIMU and metasomatized mantle wedge peridotite for EM1. In contrast, the EM2-FOZO array can be generated in a cold subduction zone with igneous oceanic crust for FOZO and sediment for EM2 sources. Necessary residence time are ~2 Ga to form HIMU-FOZO-EM1 and ~1 Ga to form EM2-FOZO. The subducted oceanic crust (forming HIMU) and mantle wedge peridotite (forming EM1) may have travelled in the mantle together. They then melted together in an upwelling mantle plume to form the EM1-FOZO-HIMU isotopic variations found frequently in OIBs. In contrast, the less frequent EM2-FOZO array suggests a separate source and recycling path. These recycling ages are consistent with the change in the mantle potential

  18. Apatite trace element and halogen compositions as petrogenetic-metallogenic indicators: Examples from four granite plutons in the Sanjiang region, SW China (United States)

    Pan, Li-Chuan; Hu, Rui-Zhong; Wang, Xin-Song; Bi, Xian-Wu; Zhu, Jing-Jing; Li, Chusi


    The abundances of trace elements including Sr, Ga and rare earth elements (REE) and halogens in apatite crystals from four intermediate-felsic plutons in the Zhongdian terrane in the Sanjiang region have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometry to evaluate the potential of apatite as a petrogenic-metallogenic indicator. The selected plutons include one that is not mineralized (the Triassic Xiuwacu pluton, or the TXWC pluton), one that hosts a porphyry-type Cu deposit (the Pulang pluton, or the PL pluton), one that hosts a porphyry-type Mo deposit (the Tongchanggou pluton, or the TCG pluton), and one that hosts a vein-type Mo deposit (the Cretaceous Xiuwacu pluton, or the CXWC pluton). Except for the CXWC pluton, the other three plutons have adakite-like trace element signatures in whole rocks. The results from this study show that REE, Sr and halogens in apatite can be used to track magma compositions, oxidation states and crystallization history. Apatite crystals from the adakite-like plutons are characterized by much higher Sr/Y and δEu than the non-adakite-type pluton. This means that apatite, which is not susceptible to alteration, is a useful tool for identifying the adakite-like plutons that no longer preserve the initial Sr/Y ratios in whole rocks due to weathering and hydrothermal alteration. Based on apatite Ga contents and δEu values, it is inferred that the parental magmas for the two adakite-like plutons containing porphyry-type Cu and Mo mineralization are more oxidized than that for the non-adakite-type pluton containing vein-type Mo mineralization. Apatite crystals from the vein-type Mo deposit have much lower Cl/F ratios than those from the porphyry-type Cu and Mo deposits. Apatite crystals from the adakite-like pluton without Cu or Mo mineralization is characterized by much lower Cl/F ratios than those from the adakite-like plutons that host the porphyry-type Cu and Mo deposits. The

  19. The Role of Philippine Sea Plate to the Genesis of Quaternary Magmas of Northern Kyushu Island, Japan, Inferred from Along-Arc Geochemical Variations (United States)

    Shibata, T.; Yoshikawa, M.; Itoh, J.; Ujike, O.; Miyoshi, M.; Takemura, K.


    Quaternary volcanoes on Kyushu Island comprise volcanoes Himeshima, Futagoyama, Yufu-Tsurumi, Kuju, Aso, Kirishima and Sakurajima from north to south alongstrike the volcanic front. Adakitic lavas are observed from Yufu-Tsurumi and Kuju volcanoes in northern Kyushu (Kita et al., 2001; Sugimoto et al., 2007), whereas no Quaternary adakites were observed at Aso (e.g., Hunter, 1998) and the volcanoes south of Aso along the entire Ryukyu arc. Sugimoto et al. (2007) suggested that the trace element and Sr, Nd, and Pb isotopic compositions of adakitic magmas from Yufu-Tsurumi volcano indicate derivation of the magmas by partial melting of the subducting PSP. In contrast, Zellmer et al. (2012) suggested that these adakites may have formed by fractional crystallization of mantle-derived mafic magmas within the garnet stability field in the crust. The Honshu-Kyushu arc transition is a particular favorable setting to address these controversial models for the origin of the adakitic lavas, because of the potential relationship between the PSP materials and the alongstrike variation of the lava chemistry. The Palau-Kyushu ridge divides the oceanic crust of the PSP into northeastern and southwestern segments with ages of 26-15 (Shikoku Basin) and 60-40 Ma (West Philippine Basin), respectively (Mahony et al., 2011). Although there are no clear plate images beneath northern Kyushu, the northern extension of the Palau-Kyushu ridge potentially corresponds to the boundary between the SW Japan and Ryukyu arcs. If adakite genesis was related to the subducted slab rather than the overlying crust, then the spatial distribution of Quaternary adakites should correlate with the age of the subducted PSP. In order to test such correlation and elucidate the petrogenesis of the northern Kyushu adakites, we compiled major and trace elements and Sr-Nd-Pb isotope ratios from volcanoes along the arc front that includes the transition from adakitic to non-adakitic arc volcanism. Comprehensive

  20. Petrogenesis of Late Mesozoic granitoids and coeval mafic rocks from the Jiurui district in the Middle-Lower Yangtze metallogenic belt of Eastern China: Geochemical and Sr-Nd-Pb-Hf isotopic evidence (United States)

    Xu, Yao-Ming; Jiang, Shao-Yong; Zhu, Zhi-Yong; Yang, Shui-Yuan; Zhou, Wei


    Large-scale Cu-Au mineralization is associated with the Late Mesozoic granitoids in the Jiurui district of the Middle-Lower Yangtze Mineralization Belt in Eastern China. To constrain the petrogenesis of these granitoids and coeval mafic rocks, a detailed geochemical and Sr-Nd-Pb-Hf isotopic study was performed. The Jiurui granitoids are made up primarily of granodiorite porphyry and quartz diorite porphyry. These granitoids are characterized by SiO2 and K2O contents of 58.8 wt.% to 68.6 wt.% and 1.9 wt.% to 5.7 wt.%, respectively. These granitoids show relatively high MgO contents (1.0 wt.% to 3.1 wt.%, average 2.1 wt.%) and high Mg# values (39 to 70, average 54). The Jiurui granitoids are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE), and compatible trace elements (Cr, Ni and V) but are relatively depleted in Nb, Ta, Y and Yb. These rocks show a negligible negative Eu anomaly (Eu/Eu* = 0.76-1.13, average 0.91) and nearly no negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7060 to 0.7092, and the ɛNd(t) values vary from - 5.4 to - 2.0. The granitoids show radiogenic Pb isotopic ratios with values of 206Pb/204Pb (17.93-18.21), 207Pb/204Pb (15.55-15.58), and 208Pb/204Pb (38.16-38.56) for the plagioclases. The zircon Hf isotopic compositions show ɛHf(t) values from - 11.8 to 2.4. The coeval mafic rocks consist of lamprophyre, diabase and fine-grained mafic dyke. These rocks are characterized by SiO2 contents ranging from 47.6 wt.% to 54.8 wt.%, with a negative Eu anomaly and a positive to negative Sr anomaly. The whole-rock initial 87Sr/86Sr ratios range from 0.7059 to 0.7071, and the ɛNd(t) values vary from - 3.8 to - 1.4. By comparing the geochemical and isotopic compositions of the Jiurui granitoids and the coeval mafic rocks, we conclude that the granitoids are similar to adakites that were likely related to the delamination processes, and the coeval mafic rocks may have originated directly from

  1. Petrogenesis of the Mesozoic intrusive rocks in the Tongling area, Anhui Province, China and their constraint on geodynamic process

    Institute of Scientific and Technical Information of China (English)

    王强; 许继峰; 赵振华; 熊小林; 包志伟


    Petrology, element and isotopic geochemistry of the Mesozoic intrusive rocks in the Tongling area were systematically investigated in this study. The intrusive rocks can be divided into two groups, one contains shoshonitic rocks with SiO2≤55%, the other consists mainly of high-potassic calc-alkaline rocks with SiO2>55%. The shoshonitic rocks (SiO2≤55%) were generated by the fractional crystallization of the primary basaltic magma sourced from an enriched mantle, then the evolved basaltic magma likely experienced low-degree contamination with the lower crust materials when they ascended. On the other hand, although the intrusive rocks with SiO2>55% show most elemental geochemical characteristics similar to an adakite, such as high Na2O, Al2O3, Sr contents, high Sr/Y and La/Yb ratios, they have isotopic compositions much different from an adakite, such as low εNd(t) (-9.16-16.55) and high (87Sr/86Sr)i(0.7068-0.7105), and some of them show relatively high Y and Yb contents than those of an adakite. We propose that the intrusive rocks with SiO2>55% were most probably produced by mixing of the mantle-derived basaltic magma and adakite-like magma derived from the melting of basaltic lower crust that was heated by the underplating mantle-derived shoshonitic magmas. The delamination of lower crust likely took place after or during the formation of these adakite-like rocks in the Tongling area.

  2. Multiple rifting and alkaline magmatism in southern India during Paleoproterozoic and Neoproterozoic (United States)

    Renjith, M. L.; Santosh, M.; Satyanarayanan, M.; Rao, D. V. Subba; Tang, Li


    The Southern Granulite Terrane (SGT) in India preserves the history of tectonothermal events ranging from Paleoarchean to latest Neoproterozoic-Cambrian. Here we investigate alkaline magmatism possibly associated with rifting events in Paleoproterozoic and Neoproterozoic based on petrological, geochemical and zircon U-Pb and Lu-Hf isotopic studies on the alkaline complexes of Korangani (KGAC) and Kambamettu (KAC) in the Madurai Block of SGT. The mica pyroxenite which represents the first intrusive phase at KGAC crystallized from a mildly alkaline hydrous magma derived from a metasomatized mantle. The younger shoshonitic syenite was emplaced at 2533 ± 16 Ma, carries mafic microgranular enclaves, and shows trace-elements ratios consistent with magma mixing trend, and zircon εHf(t) values display mixed positive and negative values - 2.6 to 3.6 suggesting the mixing of adakite-like felsic crustal melt and non-adakitic mantle derived melt. In KAC, four distinct magmatic intrusions are identified: i) quartz-monzonite (emplaced at 2498 ± 16 Ma), an ultrapotassic adakitic rock derived from a carbonated alkali-rich lower crustal source with negative zircons εHf(t) values in zircon (- 8.0 to - 0.8); Y/Nb (> 1.2) and Th/Ce (0.03-0.8) ratios; lower Ni (< 30 ppm) and Cr (< 14 ppm) contents; ii) phlogopite-rich pyroxenite, crystallized from an alkali-rich basaltic parental magma derived from carbonate metasomatized mantle; iii) mantle derived high Ba-Sr carbonatite (emplaced at 2470 ± 15 Ma); and iv) shoshonitic peralkaline syenite rock (emplaced at 608 ± 6 Ma) with strong adakitic signature, low MgO (< 1 wt.%), Ni (12-5 ppm) and Cr (49-35 ppm) contents and negative zircon εHf(t) values (- 30.3 to - 27.3) and trough of Zr-Hf in spidergrams suggesting a carbonated alkali-rich garnet-bearing crustal source. The geochemical features and petrogenetic considerations of the felsic shoshonitic-ultrapotassic adakite-like rocks (syenite, quartz monzonite), mica-pyroxenites and

  3. 岩浆弧火成岩构造组合与洋陆转换%Magmatic Arc and Ocean-Continent Transition:Discussion

    Institute of Scientific and Technical Information of China (English)

    邓晋福; 姚图; 冯艳芳; 狄永军; 刘翠; 肖庆辉; 苏尚国; 赵国春; 孟斐; 马帅


    This paper discusses the ocean—continent transition of the magmatic arc and its processes in terms of the igneous petrotectonic assemblage,the geologic characteristics,and the arc maturity.The major igneous petrotectonic assemblages characterized the oceanic subduction may be tonalite—trondhjemite—granodiorite (TTG),high-Mg andesitic,Mg andesitic,adakitic and Nb-enriched arc basaltic assemblages.Based on the disposition of the petrotectonic assemblages,four possible models of oceanic subducted crust—mantle structure are discussed:(1 )the warm young subducted oceanic crust and the above-situated cool mantle-wedge lithosphere;(2)both the cool older subducted oceanic crust and the mantle-wedge lithosphere;(3)the cool older subducted oceanic crust and the above-situated warm mantle-wedge asthenosphere;(4)both the warm oceanic crust and the mantle-wedge asthenosphere.The tectonic indications of the arc magmatic front as the structure markers and the special compositional polarity are also discussed.A model of two-layered arc crust is suggested,the lower arc crust may be composed of the mafic granulites and amphibolites,and the upper crust consists of the felsic TTG gneisses. The petrologic structure of the arc crust may have a typical transitional character between the ocean crust and the continental crust or may be regarded as the first stage of the continental crust,the juvenile continental crust.The magmatic arc and the transitional character of the arc crust are regarded as the most important record for the ocean—continent transitional belts (or the accretional orogenic belts)derived by the oceanic subduction.%本文从岩浆弧的火成岩构造组合、主要地质特征和弧地壳成熟度几个方面,讨论洋陆转换作用及其过程。表征洋俯冲环境的火成岩构造组合主要有英云闪长岩—奥长花岗岩—花岗闪长岩(TTG)组合,高镁安山岩组合,镁安山岩组合,Adakite 组合(即高锶低钇中酸性岩

  4. 安徽滁县琅琊山一带燕山期岩浆岩成因及区域找矿方向%Study on the Yanshanian Intrusions in Langyashan Area of Chuxian County: Petrogenesis and Regional Ore Prospection

    Institute of Scientific and Technical Information of China (English)

    段留安; 杨晓勇; 孙卫东; 孙健; 洪长春; 胡俊杰


    intrusion was analyzed.The results show that these Yanshanian intrusive rocks have geochemical characteristics similar to those of adakite,with features of SiO2 >56% ,high Al content (Al2O3≥ 15% ) ,rich in Sr,Ba and Cr,Ni,high inSr/Y(145-181) and (La/Yb)NS≥21 ratios; with low Y(7.5 ~9.1 μg/g) and Yb (0.68-0.71 μg/g) contents,and no significant Eu anomalies (8Eu =0.96-1.04).The high MgO contents (3.15% -3.36%),Mg(56~66) and Sr/La(56 ~67) ,display characteristics of seawater alteration of MORB.The Yanshanian magmatic rocks in this region are the typical adakites which were derived from subducted oceanic crust,During the emplacement of the rocks,the ore-forming materials were enriched and mineralized in the suitable position.The Shangyaopu magmatic intrusion nearby has similar geochemical features,and thus,should have similar genetic and mineralization background like that of the Chuxian intrusion.Moreover,we found a pulse of silicified shattered dolomite belt with micron pyrite on the north-west side of the Chouxian magmatic body occurring as siliceous vein and polymetallic mineralization around the Shangyaopu magmatic body.Comparing the silicified belt and siliceous vein to the Langyashan copper mineralization skarn,we deduced that they are closely related to the Yanshanian intrusive rocks,the Shangyaopu magmatic body and surrounding areas can be prospective area for copper associated with gold deposit.In conclusion,the authors propose that regional ore exploration should not be limited to the present skarn-type copper-gold deposit while the new type of siliceous veins with polymetallic mineralization be ignored.

  5. Neoarchean orogenic, magmatic and hydrothermal events in the Kalgoorlie-Kambalda area, Western Australia: constraints on gold mineralization in the Boulder Lefroy-Golden Mile fault system (United States)

    Mueller, Andreas G.; Hagemann, Steffen G.; McNaughton, Neal J.


    The Boulder Lefroy-Golden Mile (BLF-GMF) fault system is the most intensely mineralized structure (>2150 t Au to 2015) in the Archean Yilgarn Craton, Western Australia. The fault system links the Kalgoorlie and Kambalda mining districts in the Eastern Goldfields Province, a continental-margin orogen subdivided into the western Kalgoorlie ensialic rift and the eastern Kurnalpi volcanic arc. After rifting, the 2.73-2.66 Ga greenstone-greywacke succession in the Kalgoorlie-Kambalda area underwent five phases of orogenic deformation, predominantly during ENE-WSW shortening: D1 upright folding at ca. 2680 Ma, D2 sinistral strike-slip faulting at 2678-2663 Ma, D3 folding of late conglomerate-turbidite successions at 2665-2655 Ma, D4 dextral strike-slip faulting at 2655-2640 Ma and D5 east-northeast-striking normal faulting. Regional prehnite-pumpellyite to greenschist facies burial metamorphism took place during D1 and D3 crustal thickening, and amphibolite facies aureoles formed around granite batholiths during and after D3 at 400 ± 100 MPa pressure. The D2 BLF offsets D1 folds by 12 km SW-side south and contains a porphyry dyke (2676 ± 7 Ma) boudinaged by transtensional oblique-slip along a line pitching 21° southeast. The BLF is linked by transverse D2 thrusts to other sinistral faults recording strike-slip until 2663 ± 7 Ma. Late D2 strike-slip movement alternated with early D3 shortening. D3 thrusts accommodated strain in fault blocks of rigid mafic-ultramafic volcanic rocks consolidated during D1, while the sedimentary rocks in D3 synclines were foliated at high strain. Biotite-sericite alteration and gold-pyrite mineralization in the BLF-GMF system took place at 11 ± 4 km burial depth in faults active during D2 and D3. The Golden Mile (1708 t Au) and other deposits are associated with stocks and dykes of high-Mg monzodiorite-tonalite porphyry, part of a late-orogenic (2665-2645 Ma) mantle-derived suite of adakitic affinity. Hornblende and apatite compositions

  6. The giant Dexing porphyry Cu-Mo-Au deposit in east China: product of melting of juvenile lower crust in an intracontinental setting (United States)

    Hou, Zengqian; Pan, Xiaofei; Li, Qiuyun; Yang, Zhiming; Song, Yucai


    The Dexing porphyry Cu-Mo-Au deposit in east China (1,168 Mt at 0.45 % Cu) is located in the interior of the South China Craton (SCC), made up of two lithospheric blocks, the Yangtze and Cathaysia blocks. The Cu-Mo-Au mineralization is associated with mid-Jurassic granodioritic porphyries with three high-level intrusive centers, controlled by a series of lineaments at the southeastern edge of the Yangtze block. Available age data define a short duration (172-170 Ma) of the felsic magmatism and the mineralization (171 ± 1 Ma). The deposit shows broad similarities with deposits in volcanoplutonic arcs, although it was formed in an intracontinental setting. Porphyries associated with mineralization are mainly granodiorites, which contain abundant phenocrysts (40-60 %) and carry contemporaneous microgranular mafic enclaves (MMEs). They are mainly high-K calc-alkaline and show geochemical affinities with adakite, characterized by relatively high MgO, Cr, Ni, Th, and Th/Ce ratios. The least-altered porphyries yielded relatively uniform ɛ Nd( t) values from -0.9 to +0.6, and wide (87Sr/86Sr)i range between 0.7046 and 0.7058 partially overlapping with the Sr-Nd isotopic compositions of the MMEs and mid-Jurassic mafic rocks in the SCC. Zircons from the porphyries have positive ɛ Hf( t) values (3.4 to 6.9), and low δ18O values (4.7 to 6.3 ‰), generally close to those of depleted mantle. All data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components (e.g., Neoproterozoic mafic arc magmas), triggered by invasion of contemporaneous mafic melts at Dexing. The MMEs show textural, mineralogical, and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas. These MMEs usually contain magmatic chalcopyrite, and have original, variable contents of Cu (up to 500 ppm). Their geochemical characteristics suggest that they were derived from an enriched mantle source, metasomatized by

  7. Evolution of a Permian intraoceanic arc-trench system in the Solonker suture zone, Central Asian Orogenic Belt, China and Mongolia (United States)

    Jian, Ping; Liu, Dunyi; Kröner, Alfred; Windley, Brian F.; Shi, Yuruo; Zhang, Wei; Zhang, Fuqin; Miao, Laicheng; Zhang, Liqao; Tomurhuu, Dondov


    The identification of a fossil arc-trench system from the ophiolite-decorated Solonker suture zone in the southernmost Central Asian Orogenic Belt (CAOB) enables us to constrain the timing of pre-subduction extension (ca. 299-290 Ma), subduction initiation (ca. 294-280 Ma), ridge-trench collision (ca. 281-273 Ma) and slab break-off (ca. 255-248 Ma) in the Permian. A fraction of proto-arc crust (ca. 45 km long, up to 8 km wide) is preserved as a volcanic-plutonic sequence and is juxtaposed against a wide (ca. 30-80 km) forearc mélange. This proto-arc crust comprises two distinct magma series, island arc tholeiite (IAT) and mid-ocean ridge basalt (MORB), both of which have strong supra-subduction zone (SSZ) geochemical signatures. Zircons from a gabbro and a plagiogranite yielded weighted mean 206Pb/ 238U ages of 284.0 ± 4.0 and 288.0 ± 6.0 Ma. The forearc mélange consists of numerous ophiolite fragments and continental margin-derived olistoliths/blocks that predate the ophiolite. The olistoliths are best represented by a gabbroic block (291.8 ± 2.3 Ma) that contains granite xenoliths (312.6 ± 1.8 and 313.6 ± 3.1 Ma). Other dated blocks include a trondhjemite (323.9 ± 2.7 Ma), a gabbro (296.6 ± 1.7 Ma) and a tonalite (294.9 ± 2.4 Ma). Small bodies of diabase, andesite and diorite in the forearc mélange exhibit a wide variety of geochemical signatures. We dated zircons from an N-MORB-like diabase (274.4 ± 2.5 Ma), an E-MORB-like diabase (252.5 ± 2.3 Ma), a transitional sanukitoid/adakite (andesite, 250.2 ± 2.4 Ma), a sanukitoid (high-Mg diorite; 251.8 ± 1.1 Ma) and an anorthosite (252.2 ± 1.7 Ma). The N-MORB-like diabase contains ca. 301-394 Ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench. The other dated rocks simultaneously formed near the Permian/Triassic boundary and captured abundant zircon xenocrysts (ca. 269-295 Ma; ca. 301-495 Ma; and ca. 923-2501 Ma). Our new formation ages constrain

  8. Appinite suites: A record of the role of water in the genesis, transport, emplacement and crystallization of magma (United States)

    Murphy, J. Brendan


    The appinite suite of rocks offers a unique opportunity to study the effect of water on the generation, emplacement and crystallization history of mafic to felsic magma. The suite consists of a group of coeval plutonic and/or hypabyssal rocks, ranging from ultramafic to felsic in composition in which hornblende is the dominant mafic mineral, and typically occurs both as large prismatic phenocrysts and in the finer grained matrix. The suite is also characterized by abundant evidence for mixing and mingling between diverse magma types and variable degrees of contamination by host rock. Field observations corroborate experimental and theoretical studies that the hornblende stability field expands at the expense of olivine and pyroxene with increasing pH2O in the magma. Textures characteristic of appinites are consistent with rapid growth and with experimental evidence for the reduced viscosity of melts allowing efficient migration of ions to the sites of mineral growth. The appinite suite was originally defined in the Paleozoic Caledonide orogen in Scotland, where it occurs as a number of small shallow crustal bodies that were emplaced after the cessation of subduction and in the immediate aftermath of terrane collision and closure of the Iapetus Ocean. The mafic component is thought to have been triggered by asthenospheric upwelling following stab break-off, and magmas produced have both juvenile and sub-continental lithospheric mantle components. Its compositions have affinities with shoshonites. The felsic components include large batholiths that were probably derived by fractional crystallization. Other appinite suites share some, but not all of these characteristics. Appinite suites apparently range in age from Neo-Archean to Recent, and occur at all crustal levels, at depths of up to 40 km. In addition to shoshonites, appinite suites share some similar geochemical features with high-Mg andesites, sanukitoids and adakites. Some common tectonic traits include a

  9. The geodynamic characteristics of Cretaceous (Paleogene) magmatic belts between the southeastern coast of China and Japan: Implication from ductile deformations time and diagenetic manner (United States)

    Mao, J.; Takahashi, Y.; Ye, H.; Zhao, X.; Li, Z.; Kee, W.; Liu, K.; Hu, Q.


    1.Introduction It is generally believed that the Yanshanian orogeny outlined the present-day geological configuration that has developed since the Jurassic (Li 2000), by which the Early Yanshanian (J3) dominated the Cathaysia interior, whereas the Late Yanshanian (K1) dominated the southeast coastal area. Basically, products of the early Cretaceous magmatism are more restricted in a NE-SW trending zone-the Southeast Coast of China Magmatic Belt (SECMB) in China. Previous investigations have revealed that volcano-intrusive rock assemblages are mainly shallow-level, calc-alkaline, I-type felsic rocks ranging from granodioritic to alkali feldspar granitic, and succeeding A-type granites(Chen et al. 2000). The Cretaceous to Paleogene volcano-intrusive complex rocks are extensively distributed in the WS Japan Magmatic Belt (WSJMB). Note that the majority of granitic intrusions were emplaced in the Cretaceous, and they intruded into the pre-Cretaceous accretionary complexes which include regional metamorphic rocks. The intrusive granitoids are associated with coeval gabbros, diorites, rhyolites and ignimbrites.The formation of the Japanese Islands has been taken as the classic model for accretionary orogeny and often serves as an example for understanding the crustal evolution of the CAOB and other accretionary orogens (Sengor and Natal'in, 1996; Condie, 2007; Cawood and others, 2009). 2. Correlation with two Cretaceous magmatic belts 2.1 The beginning and end times for magmatic activity as well as dynamics deformation time. 2.2 Beginning of high-Mg andesite and adakite produced by melting of subducting oceanic slab in Japan. 2.3 The finishing marks of magmatic activity. 2.4 Approximatively resembling diagenetic manner. 3. Geodynamic characteristics of two magmatic belts The WSJMB is a plutonic-metamorphic terrane that comprises unmetamorphosed pre-Cretaceous accretionary complexes with shallow-level, calc-alkaline, I-type granites-rhyolites, metasediments with

  10. Composition and Thermal History of the Lower Crust Beneath the Tanzania Craton and the Adjacent Mozambique Belt (United States)

    Mansur, A. T.; Manya, S.; Rudnick, R. L.


    The Tanzanian craton has undergone little deformation since its formation 2.6 Ga ago, but Archaean crust of the adjacent Mozambique Belt (MB) has been reworked by at least two high-grade metamorphic events. An old, thick (~~200-km) lithospheric keel appears to have stabilized the craton during these deformational events. Although a thick keel appears to be absent beneath the MB today, ancient mantle lithosphere is preserved beneath much of the MB and the original thickness of this lithosphere is uncertain. Studies of the present-day lower crust can help to constrain the compositional and thermal evolution of this region. Granulite xenoliths from the Labait volcano (craton margin) are exclusively mafic and are mostly two pyroxene granulites, but also include gt-opx granulites and a gt-cpx-spinel-corundum anorthosite. Most samples also have orthoclase as a major phase. Two-pyroxene thermometry yields temperatures of 710 to 810°C for an estimated lower crustal pressure of 1 GPa; whereas the anorthosite appears to have equilibrated at a somewhat hotter temperature (gt-cpx T = 970°C). All Labait xenoliths exhibit high K2O (0.8 to 2.6 wt., excluding the anorthosite), Ba (530 to 6730 ppm), Sr (440 to 1040 ppm) and Ni contents (100 to 400 ppm) and relatively high Mg# (47 to 63). The combined high Ni, Mg# and alkali and alkaline-earth elements may reflect an unusual igneous protolith (e.g., adakitic magma) or mafic cumulates that have been metasomatically enriched in the lower crust. Granulite xenoliths from Lashaine (MB) are also exclusively mafic and form two groups: 1) anorthositic, high Al2O3 (17 to 23 wt. %) and Mg#, plag-ky-cpx-gt granulites, which are enriched in Sr and have positive Eu anomalies and 2) lower Al2O3 (13 wt. %), two pyroxene ± gt granulites, which are enriched in Ti, K, P and Ni. The latter may be meta-cumulates from alkaline magmas. Temperatures for Lashaine granulites range from 770 to 980°C. Unlike Labait and Lashaine, the Naibor Soito

  11. Geochemistry and petrogenesis of Early Cretaceous volcanic rocks from Mengyin basin%蒙阴盆地早白垩世火山岩地球化学特征及其岩石成因

    Institute of Scientific and Technical Information of China (English)

    牛漫兰; 傅朋远; 吴齐; 朱光; 夏文静


    rare earth element (LREE) enrichment and high field strength element ( HFSE) depletion ( Nb, Ta, P and Ti) as well as enriched Sr-Nd-Pb compositions (87Sr/86Sr(t) =0.7051 to 0. 711,εNd(t) = -5.16~-16.4). Base on MgO contents and Mg# values, andesitic rocks can be furtherly subdivided into high-Mg ( Mg#> 60) and low-Mg ( Mg#< 60) suites. Compared with the low-Mg andesite, the high-Mg andesite possesses higher MgO, Cr, Ni contents, incompatible element contents, 87Sr/86Sr(t) , and lower εNd(t) with a tendency to the EM Ⅱ -type enrichment mantle end member. The low-Mg andesitic rocks have similar geochemical characteristics to adakites, display isotopic features between the EM Ⅰ -type mantle and the granulite facies lower crust of the North China Craton ( NCC) . However, the rhyolite is characterized by lower MgO, Cr, Ni contents, evident negative Eu and Sr anomalies relative to andesitic rocks. Its isotopic composition is similar to the upper-middle crust of the Yangtze Craton (YC). Studies indicate that the Mengyin high-Mg andesitic rocks were derived from the partial melting of the NCC lithospheric mantle which had previously experienced a reconstruction of subducted Yangtze crustal melts. Meanwhile, melting magmas could suffer from the NCC lower crustal assimilation or contamination during magmas ascent. The low-Mg andesitic rocks mainly came from partial melting of the NCC lower crust. The rhyolite was related to the partial melting of subducted YC middle-upper crust under the lithospheric extension and thinning setting. Geological phenomena imply that the Tan-Lu fault zone controlled the Mengyin downfaulted basins, had a close relation with petrogenesis of Early Cretaceous volcanic rocks, and played an important role in the NCC destruction.

  12. Zircon U-Pb ages, Hf-O isotopes and trace elements of Mesozoic high Sr/Y porphyries from Ningzhen, eastern China: Constraints on their petrogenesis, tectonic implications and Cu mineralization (United States)

    Wang, Fangyue; Liu, Sheng-Ao; Li, Shuguang; Akhtar, Shamim; He, Yongsheng


    The relationship between high Sr/Y (adakitic) rocks and Cu mineralization has been long recognized but the mechanism remains unclear. The Cretaceous high Sr/Y porphyries in the Ningzhen area host major Cu polymetallic deposits in the Lower Yangtze River Belt (LYRB) of eastern China. These rocks exhibit some geochemical characteristics (e.g., non-radiogenic Pb isotope ratios) that differ from adakitic rocks from adjacent locations in the LYRB. In this study, we present a study of the zircon U-Pb-Hf-O isotope and trace element compositions for five porphyries from Ningzhen to reveal their petrogenesis and how that correlates with Cu-Fe-Mo mineralization. Zircon U-Pb ages of Anjishan (Cu deposit), Tongshan (Cu-Mo deposit) and Xiangshan (Fe deposit) plutons in the Ningzhen area are 108.8 ± 1.5 Ma, 105-107 Ma and 100-105 Ma, respectively, which are significantly younger than the ore-bearing adakites (140 ± 5 Ma) in the western part of the LYRB. Zircon εHf(t) and δ18O values range from - 23.4 to - 10.6 and from 5.7 to 7.0‰, respectively, falling between subduction-related adakites from the other regions in the LYRB and delamination-related adakitic rocks from the adjacent South Tan-Lu Fault Zone. The similarities of Ce4 +/Ce3 + and Eu/Eu* ratios in zircons from Ningzhen and those from the western LYRB indicate higher oxygen fugacity in their magma sources. Ti-in-zircon thermometer yields magma temperatures of 550 to 700 °C (with an average of ~ 650 °C) for the Ningzhen porphyries, which are significantly lower than those of the South Tan-Lu Fault adakites (> 750 °C), but similar to those for the LYRB adakites ( 50), non-radiogenic Pb, enriched Sr-Nd isotopic compositions, negative zircon εHf(t), mantle-like δ18O values, high oxygen fugacities and low magma temperatures. Mafic rocks that co-exist with ore-bearing porphyries or occur as xenoliths in porphyries are widespread. We proposed that the Ningzhen high Sr/Y porphyries originated from mixing of magmas

  13. The Solodamu Surveys: determining fossil fuel use and sea transport need in a coastal village in Fiji

    Directory of Open Access Journals (Sweden)

    Alison Patricia Newell


    Full Text Available Domestic sea transport is critical to all aspects of life in the Pacific, providing access to markets and health and education services, as well as enabling cultural and social connectivity. Current sea transport services are entirely dependent upon use of increasingly expensive fossil fuels. Whilst there has been increasing research on international shipping, very little focus has been given to date to domestic shipping in the Pacific, and in particular at the local, village level. Recent studies have highlighted lack of data, particularly at a village level, as being a major impediment to progressing a shift to more sustainable transport.The importance of transport in achieving sustainable development and green growth is being increasingly highlighted by Pacific Leaders as a key priority, and particularly the need to find alternatives to reduce the region’s crippling dependency on imported fossil fuels. Small Island Developing States (SIDS in other regions also face similar challenges.This paper provides a summary of the findings of a village-based assessment of transport and fossil fuel use in Solodamu Village, Kadavu, Fiji carried out in 2009 and 2011. The objectives of the surveys were to gauge the overall sea, land and air transport use by the village and the fossil fuel footprint of the village by collecting data on a household by household basis. We then go on to outline how this assessment methodology has been expanded for an island group and highlight the potential of using this in other SIDS, so building the data sets available for more accurate analysis of both transport need and fossil fuel use to better address the issues of fossil fuel dependency and sustainable transport for the Pacific.

  14. Magmatism of the Shuteen Complex and Carboniferous subduction of the Gurvansaikhan terrane, South Mongolia (United States)

    Batkhishig, Bayaraa; Noriyoshi, Tsuchiya; Greg, Bignall


    The Carboniferous Shuteen Complex, a volcano-plutonic ring complex associated with Cu-Au porphyry mineralization, is located in the Gurvansaikhan island arc terrane of South Mongolia. This paper presents new data on the petrography, major and trace element chemistry, and Sr-Nd isotopic chemistry of the Shuteen Complex. We discuss the relationship between volcanic and plutonic rocks of the complex, and consider their similarity to high-Al 2O 3 trondhjemite-tonalite-granodiorite and adakites. We also consider the origin, magma source, and dynamic processes of the Shuteen Complex; propose a petrogenetic model; and investigate the composition of the subducting slab and the features of arc volcanism at the time. We assess some of the magmatic processes likely to have occurred within the Shuteen Complex, such as Carboniferous slab subduction and partial melting, and examine their influence on magma composition. The Shuteen Complex is geochemically similar to adakite-type rocks. The complex is silica-saturated (SiO 2 ⩾ 56%), rich in Al 2O 3 (⩾15%), MgO (400 ppm), and depleted in high field strength elements. It also has a high Sr/Y value, and ( 87Sr/ 86Sr) I arc setting, and partial melting was the dominant process during petrogenesis. The primary Shuteen magma had an adakitic composition and was probably derived from the partial melting of subducting oceanic crust, possibly with minor local interaction with mantle material. The results of quantitative modelling of mass balance and partial melt equilibrium for the magma source indicate that the subducting slab contained oceanic basalt and a minor component of oceanic sediment, which together with a restite eclogite phase formed the source of the Shuteen magma. The conclusive results of this study provide new insights into the magmatic evolution of the Shuteen Complex.

  15. Rapid transition to long-lived deep crustal magmatic maturation and the formation of giant porphyry-related mineralization (Yanacocha, Peru) (United States)

    Chiaradia, Massimo; Merino, Daniel; Spikings, Richard


    The Yanacocha magmatic field (northern Peru) hosts the largest high sulfidation gold deposit on Earth. Mineralization is associated with porphyritic intrusions distributed along a NE-trending magmatic structural corridor. Eight of these intrusions investigated in this study range in age from 12.4 to 8.4 Ma and show systematic chemical and isotopic changes through time. They are interpreted to derive from hydrous mafic magmas evolving through amphibole-clinopyroxene ± garnet fractionation and lower crust melting (leaving a garnet residue) at deeper levels, which led to variably strong adakite-like signatures, and through plagioclase-amphibole fractionation at shallower levels, both accompanied by crustal assimilation and recharge (recharge assimilation fractional crystallization, RAFC, processes). Systematic geochemical and isotopic changes with intrusion ages, coupled with plagioclase zoning and amphibole geobarometry, suggest that the evolution of the magmatic system occurred through interaction of mantle-derived melts with an increasing length of the crustal column and propagation from deep towards shallower crustal levels through time. This was probably the result of a steadily increasing compression that has progressively slowed down magma ascent forcing magmas to evolve at a series of intermediate level chambers between the lower and upper crust. Increased compression might have been related to the onset of subduction of the buoyant Inca oceanic plateau, estimated to occur at ˜ 12 Ma, i.e., the same time of the onset of the rapid transition from "normal" to adakite-like signatures. The giant Yanacocha ore system developed in coincidence with the ˜ 3.6-4.0 Ma-long intrusion of the adakite-like magmas (12.4/12.0-8.4 Ma) formed by the above processes into a small upper crustal volume and peaked during the last ˜ 2.4 Ma (10.8-8.4 Ma) of magmatic activity after a ˜ 1.4 Ma long (12.4-11.0 Ma) maturation of magmas at deep crustal levels. Further investigation is

  16. Geodynamic characteristics of Cretaceous-Paleogene volcano-intrusive belts between in Southeast China Coast and Southwest Japan%中国东南沿海与西南日本白垩纪-古近纪火山-侵入岩带的地球动力学特征

    Institute of Scientific and Technical Information of China (English)

    毛建仁; 叶海敏; Yutaka Takahashi; 厉子龙; Weon-Seo KEE; 赵希林; 刘凯


    those in the SWJMB .The high-Mg andesites and adakites (120~105 Ma) in Southwest Japan were formed by partial melting of subducting oceanic slab under high temperature environment during the early period of voluminous Cretaceous magmatism .The termination marks of magmatic activities in the SECCMB are the within-plate setting miarolitic A-type granites and rhyolite-dominated bimodal volcanic ;w hereas the magmatic activities in the SECCMB are shown by the S-type strong peralumious garnet/muscovite granites and rhyolites formed by compression remelting of the younger crust in an absence of the crust-derived S-type granites w hich are developed in South China .In the SECCMB there have arc magmatic rocks resulted from the subduction of oceanic crust .The source regions of the igneous rocks in the two magmatic belts were dominantly originated from the mantle-derived rocks with the involvement of recycled Precambrian crust . The Sr-Nd isotopic data show that ,with the passage of time ,the mantle-derived components increased in volcano-intrusive rocks of the SECCMB but decreased in those of the SWJMB .The large-scale Mesozoic magmatic activity (170 ± 5 Ma) in South China was resulted from the continental lithospheric thinning and reactivation of intraconti-nental deep fault under the background of oblique subduction of paleo-Pacific Ocean Plate .Asian continent margin during late Yanshanian (<120 Ma) ,the eastern Asian continental margin was belonged to paleo-Pacific Ocean orthogonal subduction-related tectonic system ,but the geodynamic indications varied in dif-ferent segments .

  17. Petrochemistry and mineralogy of Dongyuan tungsten-bearing pluton in eastern Jiangnan Orogen%江南造山带东段东源含钨岩体的岩石化学、矿物学特征研究

    Institute of Scientific and Technical Information of China (English)

    周洁; 葛伟亚; 姜耀辉; 徐生发; 傅建真


    Dongyuan pluton, geographically located in south Anhui Province, is a part of eastern Jiangnan orogen. It is composed of granodiorite, monzogranite, syenogranite, showing obvious formation of sericite and carbonate in feldspar, and formation of muscovite and chlorite in biotite. Zircon LA-ICP-MS U-Pb dating results show that the pluton was emplaced at 146.7 Ma. In addition, abundant inherited zircons are identified in the granite, showing the average age of the Neoproterozoic zircon is (770.2±9.7) Ma. Biotite in Dongyuan pluton can be classified as high-Mg type, and is plotted in the crust-mantle zone on the material source discrimination diagram. The Dongyuan pluton belongs to the high potassium calc alkaline and shoshonitic series, being metaluminous-peraluminous, showing relatively high Sr and Ba, low Y and Yb, and weak negative Eu anomalies (δEu =0.74~0.83). It is enriched in light rare earth elements (LREE) and light ion lithophile elements (LILE) but is depleted in high field strength elements (HFSE), exhibiting strongly fractionated REE pattern. The pluton exhibits high initial 87Sr/86Sr ratios (0.7124), low εNd(t) (–5.53), and variable zircon εHf(t) (–13.0~ –7.0) values. The elemental and isotopic data suggests that the Dongyuan granite shows some affinities with adakite, so can be postulated to be most likely derived from partial melting of thickened lower crust with little contribution from mantle components.%东源岩体主要由花岗闪长岩、二长花岗岩、正长花岗岩构成。长石绢云母化、碳酸盐化作用较强,黑云母发生白云母化和轻微绿泥石化蚀变。锆石LA-ICP-MS U-Pb定年获得岩体的成岩年龄为晚侏罗世-早白垩世((146.7±4.1) Ma);含有大量新元古代的继承锆石,加权平均年龄为(770.2±9.7) Ma。岩体中黑云母为镁质黑云母,显示寄主岩为壳幔混合来源。岩石地球化学特征总体表现为高钾钙碱性系列-橄榄粗玄岩系列,准铝质-过铝质,

  18. Ridge subduction and porphyry copper-gold mineralization:An overview

    Institute of Scientific and Technical Information of China (English)


    Many large porphyry Cu-Au deposits are connected to adakitic rocks known to be closely associated with ridge subduction. For example, there are several subducting ridges along the east Pacific margin, e.g., in Chile, Peru, and South America, most of which are associated with large porphyry Cu-Au deposits. In contrast, there are much fewer ridge subductions on the west Pacific margin and porphyry Cu-Au deposits are much less there, both in terms of tonnage and the number of deposits. Given that Cu and Au are moderately incompatible elements, oceanic crust has much higher Cu-Au concentrations than the mantle and the continental crust, and thus slab melts with their diagnostic adakitic chemistry have systematically higher Cu and Au, which is favorable for mineralization. Considering the geotherm of subducting slabs in the Phanerozoic, ridge subduction is the most favorable tectonic setting for this. Therefore, slab melting is the likely link in the spatial association between ridge subduction and Cu-Au deposits. Geochemical signatures of slab melting and hence maybe ridge subduction in less eroded regions in eastern China, the central Asian orogenic belt etc. may indicate important exploration targets for large porphyry Cu-Au deposits.

  19. The genesis of the slab window-related Arzular low-sulfidation epithermal gold mineralization (eastern Pontides, NE Turkey

    Directory of Open Access Journals (Sweden)

    Enver Akaryalı


    Full Text Available The Arzular mineralization is one of the best examples of epithermal gold deposits in the eastern Pontides orogenic belt. The mineralization is hosted by the subduction-related basaltic andesites and is mainly controlled by E–W and NE–SW trending fracture zones. The main ore minerals are galena, sphalerite, pyrite, chalcopyrite, tetrahedrite and gold. Homogenization temperatures of fluid inclusions are between 130 and 295 °C for quartz and between 90 and 133 °C for sphalerite. Sulphur isotope values obtained from pyrite, galena and sphalerite vary between −1.2‰ and 3‰, indicating that sulphur belongs to magmatic origin and was derived from the Lutetian non-adakitic granitic intrusions in the region. Oxygen isotope values are between 15.0‰ and 16.7‰, and hydrogen isotope values are between −87‰ and −91‰. The sulphur isotope thermometer yielded temperatures in the range of 244–291 °C for the ore formation. Our results support the hypothesis that the Arzular mineralization is a low-sulfidation epithermal gold deposit associated with non-adakitic subduction-related granitic magmas that were generated by slab window-related processes in a south-dipping subduction zone during the Lutetian.

  20. Plume-subduction interaction in southern Central America: Mantle upwelling and slab melting (United States)

    Gazel, Esteban; Hoernle, Kaj; Carr, Michael J.; Herzberg, Claude; Saginor, Ian; den Bogaard, Paul van; Hauff, Folkmar; Feigenson, Mark; Swisher, Carl


    The volcanic front in southern Central America is well known for its Galapagos OIB-like geochemical signature. A comprehensive set of geochemical, isotopic and geochronological data collected on volumetrically minor alkaline basalts and adakites were used to better constrain the mantle and subduction magma components and to test the different models that explain this OIB signature in an arc setting. We report a migration of back-arc alkaline volcanism towards the northwest, consistent with arc-parallel mantle flow models, and a migration towards the southeast in the adakites possibly tracking the eastward movement of the triple junction where the Panama Fracture Zone intersects the Middle America Trench. The adakites major and trace element compositions are consistent with magmas produced by melting a mantle-wedge source metasomatized by slab derived melts. The alkaline magmas are restricted to areas that have no seismic evidence of a subducting slab. The geochemical signature of the alkaline magmas is mostly controlled by upwelling asthenosphere with minor contributions from subduction components. Mantle potential temperatures calculated from the alkaline basalt primary magmas increased from close to ambient mantle (~ 1380-1410 °C) in the Pliocene to ~ 1450 °C in the younger units. The calculated initial melting pressures for these primary magmas are in the garnet stability field (3.0-2.7 GPa). The average final melting pressures range between 2.7 and 2.5 GPa, which is interpreted as the lithosphere-asthenosphere boundary at ~ 85-90 km. We provide a geotectonic model that integrates the diverse observations presented here. The slab detached after the collision of the Galapagos tracks with the arc (~ 10-8 Ma). The detachment allowed hotter asthenosphere to flow into the mantle wedge. This influx of hotter asthenosphere explains the increase in mantle potential temperatures, the northwest migration in the back-arc alkaline lavas that tracks the passage of the

  1. The Influence of Ridge Geometry at the Ultraslow-Spreading Southwest Indiean Ridge (9 deg - 25 deg E): Basalt Composition Sensitivity to Variations in Source and Process (United States)


    Along-strike variation in lavas of the Aleutian island arc: implications for the genesis of high Mg # andesite and the continental crust, in Inside the...entire Atlantis II FZ peridotite suite. Harzburgites (red triangles) generally have low Cr # and high Mg #, which is indicative of low degrees of melting...and high Mg #, suggesting a lower degree of compositions (Figures 4 and 6). Upon first glance, melting and thus a less depleted residual peridotite

  2. Biogenic and synthetic high magnesium calcite - a review. (United States)

    Long, Xia; Ma, Yurong; Qi, Limin


    Systematic studies on the Mg distributions, the crystal orientations, the formation mechanisms and the mechanical properties of biogenic high-Mg calcites in different marine organisms were summarized in detail in this review. The high-Mg calcites in the hard tissues of marine organisms mentioned generally own a few common features as follows. Firstly, the Mg distribution is not uniform in most of the minerals. Secondly, high-Mg calcite biominerals are usually composed of nanoparticles that own almost the same crystallographic orientations and thus they behave like single crystals or mesocrystals. Thirdly, the formation of thermodynamically unstable high-Mg calcites in marine organisms under mild conditions is affected by three key factors, that is, the formation of amorphous calcium (magnesium) carbonate precursor, the control of polymorph via biomolecules and the high Mg/Ca ratios in modern sea. Lastly, the existence of Mg ions in the Mg-containing calcite may improve the mechanical properties of biogenic minerals. Furthermore, the key progress in the synthesis of high-Mg calcites in the laboratory based on the formation mechanisms of the biogenic high-Mg calcites was reviewed. Many researchers have realized the synthesis of high-Mg calcites in the laboratory under ambient conditions with the help of intermediate amorphous phase, mixed solvents, organic/inorganic surfaces and soluble additives. Studies on the structural analysis and formation mechanisms of thermodynamically unstable biogenic high-Mg calcite minerals may shed light on the preparation of functional materials with enhanced mechanical properties.

  3. Niobium-tantalum Fractionation During Slab Subduction:Implications for the Formation of Continental Crust

    Institute of Scientific and Technical Information of China (English)

    Yilin Xiao; Weidong Sun; Jochen Hoefs; Klaus Simon; Zeming Zhang; Shuguang Li; Albrecht W. Hofmann


    @@ Compared with the oceanic crust, knowledge about the formation of the continental crust (CC) is relatively poor. Although melting of subducted slabs in the early history of the Earth has been considered as the major way that shaped the chemical characteristics of the CC by most geologists, as the CC shares many characteristics with modern adakites, some geologists argued that Archean TTG was formed in the same way as modern arcs rather than slab melting, whereas others proposed that melting at the bottom of the thickened oceanic crust was more important. Recently,the debate is mainly focused on the unique subchondritic Nb/Ta value of the CC, and particularly, how Nb and Ta fractionated from each other and consequently how, in detail, the CC was built.

  4. Magma Evolution of the Late Jurassic Volcanic Rocks and Its Genesis of the Lanqi Formation, Beipiao Area, Western Liaoning Province%辽西北票晚侏罗世蓝旗组火山岩的岩浆演化及其岩石成因

    Institute of Scientific and Technical Information of China (English)



    % in SiQ2, high Al2O3 (>15%), high MgO (≤4. 22%, 0. 44 to 0. 49 in Mg# )and low K2O (<2. 2%) characterizes by high Sr (<500 μg/g), Cr (>125 μg/g), Ni (>47 μg/g) contents and higher Sr/Y ratio (> 28) and low REE ?112 μ/g), U ?0. 3 μ/g) ,Th ?2 μg/g) and HREE (Y16. 6%) and K2O (>2%), low MgO(≥2. 64%, 0. 08 to 0. 38 in Mg# ) characterizes by high REE (>180 μg/g), U (≥0. 80 μg/g), Th (>4 μg/g) and Sr (>350 μg/g) contents, and low Cr (<28 μg/g), Ni (<19 μg/g) contents and low Sr/Y ratio (≤23) and by strongly fractionated LREE (10. 22 to 16. 28 in (La/Yb)N) and distinct negative Eu and Sr anomalies, which differ from those of the adakitic rock. All the volcanic rocks also show positive Pb and Ba anomalies, and negative Nb-Ta anomalies, and have moderate esr(t) (20. 15 to 23. 34), TDm(1. 45 to 1. 50 Ga) and lowεNd(t) (―7. 69 to ―8. 62), which are similar to the features of the Eml-like component and of the ancient continental lower crust of the North China craton and the Late Jurassic-Early Cretaceous volcanic rocks in Yanshan orogen belt. In this paper,author thinks that andesitic magmas of Lanqi Formation are derived partial melting of foundered lower continental basaltic crust near the transition between the crust-mantle and occur the interaction of the mantle and crust, and trachyandesitic magmas from partial melting o'l foundered lower continental basaltic crust. The magma evolution of Lanqi Formation indicates that the process of the crust thinning from the thicken crust, it is an important significance to understand the deep process for the litho-spheric thinning of the North China Craton during the Mesozoic era.

  5. U-Pb geochronology and geochemistry of Bibi-Maryam pluton, eastern Iran: Implication for the late stage of the tectonic evolution of the Sistan Ocean (United States)

    Delavari, Morteza; Amini, Sadraddin; Schmitt, Axel K.; McKeegan, Kevin D.; Mark Harrison, T.


    The Bibi-Maryam pluton crops out in the Sistan suture zone, eastern Iran. This pluton is a 1.5 × 2 km stock composed of leucocratic tonalite, granodiorite and granite. U-Pb zircon geochronology of a leucogranite indicates an emplacement age of 58.6 ± 2.1 Ma (95% confidence). The Bibi-Maryam rock suite is sodic with elevated Na2O/K2O (2.9 to 5.5), Sr/Y (15.6-62.2), La/Yb (13.3-22.2), and low MgO (0.86-1.81) abundances. It lacks significant Eu anomalies. Because of these geochemical characteristics, Bibi-Maryam rocks are similar to high-SiO2 adakites. Trace element modeling indicates that the Bibi-Maryam adakitic rocks could be produced by 5-8% non-modal batch partial melting from a source with composition of 95% N-MORB + 5% sediment in the presence of 35-40% amphibole + 5-10% garnet + 55-60% clinopyroxene + 1% apatite + 1% rutile. This source mineralogy is similar to hornblende eclogite or garnet amphibolites. Collectively, these data provide new constraints for the evolution of the Sistan suture zone and suggest that the Bibi-Maryam pluton formed via slab melting in an oceanic arc and pre-plate collision tectonic setting. This implies that the closure of the Sistan Ocean and Lut-Afghan continental blocks collision happened after the Bibi-Maryam emplacement at 58.6 ± 2.1 Ma.

  6. Petrogenesis batuan vulkanik daerah tambang emas Lebong Tandai, Provinsi Bengkulu, berdasarkan karakter geokimianya

    Directory of Open Access Journals (Sweden)

    Iskandar ZulkarnaIn


    Full Text Available Tandai is a village in the Napal Putih Sub-regency, North Bengkulu Regency, that can be accessed only through the local people train called “molek”. The area is well known as a gold mine since the Dutch time. Volcanic rocks in the area belong to the Hulusimpang Formation that are dominated by andesitic rocks with small amount of dacite and basalt. They show an affinity as a transition between calc-alkaline and tholeiite. Its trace elements and REE patterns show that they are derived from “magma one”, one of the two magma sources producing volcanic rocks in Bengkulu. “Magma one” is derived from a magma source with adakitic composition due to the most primitive sample among the “magma one” samples. The Lebong Tandai magma activity has occurred since more than 30 million years ago in a back-arc side tectonical environment, and they were enriched on incompatible elements during an upper crust penetration. The occurrence of gold mineralization in this area indicates that the “magma one” is a gold bearing mineralized magma in this region. It seems to be reasonable when it is corresponded with an investigation result reported from the Phillippine that adakitic rocks contain higher gold concentration than calc-alkaline rocks. This paper is written using a geochemical approach based on major elements, trace elements and rare earth elements (REE that are plotted into general and specific classifications in a petrological discussion.  

  7. Petrogenesis batuan vulkanik daerah tambang emas Lebong Tandai, Provinsi Bengkulu, berdasarkan karakter geokimianya

    Directory of Open Access Journals (Sweden)

    Iskandar ZulkarnaIn


    Full Text Available Tandai is a village in the Napal Putih Sub-regency, North Bengkulu Regency, that can be accessed only through the local people train called “molek”. The area is well known as a gold mine since the Dutch time. Volcanic rocks in the area belong to the Hulusimpang Formation that are dominated by andesitic rocks with small amount of dacite and basalt. They show an affinity as a transition between calc-alkaline and tholeiite. Its trace elements and REE patterns show that they are derived from “magma one”, one of the two magma sources producing volcanic rocks in Bengkulu. “Magma one” is derived from a magma source with adakitic composition due to the most primitive sample among the “magma one” samples. The Lebong Tandai magma activity has occurred since more than 30 million years ago in a back-arc side tectonical environment, and they were enriched on incompatible elements during an upper crust penetration. The occurrence of gold mineralization in this area indicates that the “magma one” is a gold bearing mineralized magma in this region. It seems to be reasonable when it is corresponded with an investigation result reported from the Phillippine that adakitic rocks contain higher gold concentration than calc-alkaline rocks. This paper is written using a geochemical approach based on major elements, trace elements and rare earth elements (REE that are plotted into general and specific classifications in a petrological discussion.  

  8. Crustal thickening prior to 220 Ma in the East Kunlun Orogenic Belt: Insights from the Late Triassic granitoids in the Xiao-Nuomuhong pluton (United States)

    Xia, Rui; Wang, Changming; Deng, Jun; Carranza, Emmanuel John M.; Li, Wenliang; Qing, Min


    The East Kunlun Orogenic Belt (EKOB) played an important role in plate tectonics, magma generation, and crustal evolution. Late Triassic granodiorites and their mafic micro-granular enclaves (MMEs) from Xiao-Nuomuhong in the EKOB were studied for geochemistry and geochronology to constrain their petrogenesis. Zircon LA-ICP-MS dating indicates that the Xiao-Nuomuhong granodiorites are coeval with their MMEs (∼222 Ma). The granodiorites are high-K calc-alkaline rocks that are enriched in Rb, Th, U and LREE, and depleted in Cr, Ni and HFSE, with high Sr/Y ratios (82.2-85.3) and geochemically resemble the lower crust-derived adakites. The MMEs are also high-K calc-alkaline rocks, with high Al2O3 (16.8-18.8 wt.%), low Mg# (30-40), Nb, Zr and Hf, with weak negative Eu anomalies (Eu/Eu# = 0.8-0.9). We suggest the MMEs are mafic magmatic globules that were injected into the felsic host magma. The adakitic rocks from the Xiao-Nuomuhong pluton were generated by partial melting of thickened crust, while the primitive compositions of the MMEs were most likely from the lithospheric mantle beneath the EKOB. The Late Triassic Xiao-Nuomuhong pluton is important evidence that crustal thickening in the EKOB occurred prior to 220 Ma. The pluton is interpreted as the result of mixing between thickened lower crust-derived melts and lithospheric mantle-derived mafic melts and the protracted magmatic response to the break-off of the Paleo-Tethys oceanic slab at ∼232 Ma.

  9. Impacts of tropical cyclones on Fiji and Samoa (United States)

    Kuleshov, Yuriy; Prakash, Bipendra; Atalifo, Terry; Waqaicelua, Alipate; Seuseu, Sunny; Ausetalia Titimaea, Mulipola


    Weather and climate hazards have significant impacts on Pacific Island Countries. Costs of hazards such as tropical cyclones can be astronomical making enormous negative economic impacts on developing countries. We highlight examples of extreme weather events which have occurred in Fiji and Samoa in the last few decades and have caused major economic and social disruption in the countries. Destructive winds and torrential rain associated with tropical cyclones can bring the most damaging weather conditions to the region causing economic and social hardship, affecting agricultural productivity, infrastructure and economic development which can persist for many years after the initial impact. Analysing historical data, we describe the impacts of tropical cyclones Bebe and Kina on Fiji. Cyclone Bebe (October 1972) affected the whole Fiji especially the Yasawa Islands, Viti Levu and Kadavu where hurricane force winds have been recorded. Nineteen deaths were reported and damage costs caused by cyclone Bebe were estimated as exceeding F20 million (F 1972). Tropical cyclone Kina passed between Fiji's two main islands of Viti Levu and Vanua Levu, and directly over Levuka on the night of 2 January 1993 with hurricane force winds causing extensive damage. Twenty three deaths have been reported making Kina one of the deadliest hurricanes in Fiji's recent history. Severe flooding on Viti Levu, combined with high tide and heavy seas led to destruction of the Sigatoka and Ba bridges, as well as almost complete loss of crops in Sigatoka and Navua deltas. Overall, damage caused by cyclone Kina was estimated as F170 million. In Samoa, we describe devastation to the country caused by tropical cyclones Ofa (February 1990) and Val (December 1991) which were considered to be the worst cyclones to affect the Samoan islands since the 1889 Apia cyclone. In Samoa, seven people were killed due to cyclone Ofa, thousands of people were left homeless and entire villages were destroyed. Damage

  10. Magmatism evolution on the last Neoproterozoic development stage of the western Siberian active continental margin (United States)

    Vernikovskaya, Antonina E.; Vernikovsky, Valery A.; Matushkin, Nikolay Yu.; Kadilnikov, Pavel I.; Romanova, Irina V.


    Rocks from active continental margin complexes are characterized by a wide variety of chemical compositions from depleted in alkali to alkali differentiates. When addressing issues of geodynamic settings in which such rocks form, it is important to understand the evolution of the host tectonic structure, as well as the chemical affiliation of the various rocks composing it. The Yenisey Ridge orogen located in the south-western framing of Siberia is one of the more studied regions with a long history of Neoproterozoic magmatic events. This orogen was formed during the collision of the Central Angara terrane with Siberia, which took place 761-718 Ma. Subsequent subduction-related events in the orogen have been recorded in the coeval magmatism (711-629 Ma) of two complexes: one is the active continental margin complex (Nb enriched igneous rocks - gabbroids, trachybasalts, A-type granites and carbonatites, including contact metasomatites zones with Nb mineralization), and the other one is an island arc complex (differentiated series volcanics, gabbroids and plagiogranites). The rocks of these complexes are respectively located in two suture zones: the Tatarka-Ishimba zone that formed due to the collision mentioned above, and the Yenisei suture marking the subduction zone [Vernikovsky et al., 2003; 2008]. The final Neoproterozoic stage in the evolution of the active margin of Siberia is manifested as adakite-gabbro-anorthosite magmatism in the 576-546 Ma interval. Our results indicate a genetic relationship between the adakites and their host NEB-type metabasites of the Zimovey massif. These Neoproterozoic adakites could have formed in a setting of transform-strike-slip drift of lithospheric plates after the subduction stopped, both from a crustal and mantle-crustal source, similarly to the Cenozoic magmatic complexes of the transform margin in the eastern framing of Eurasia [Khanchuk et al., 2016]. Vernikovsky V.A., Vernikovskaya A.E., Kotov A.B., Sal'nikova E

  11. Crystallization conditions and petrogenesis of the lava dome from the ˜900 years BP eruption of Cerro Machín Volcano, Colombia (United States)

    Laeger, Kathrin; Halama, Ralf; Hansteen, Thor; Savov, Ivan P.; Murcia, Hugo F.; Cortés, Gloria P.; Garbe-Schönberg, Dieter


    The last known eruption at Cerro Machín Volcano (CMV) in the Central Cordillera of Colombia occurred ˜900 years BP and ended with the formation of a dacitic lava dome. The dome rocks contain both normally and reversely zoned plagioclase (An24-54), unzoned and reversely zoned amphiboles of dominantly tschermakite and pargasite/magnesio-hastingsite composition and olivine xenocrysts (Fo = 85-88) with amphibole/clinopyroxene overgrowth, all suggesting interaction with mafic magma at depth. Plagioclase additionally exhibits complex oscillatory zoning patterns reflecting repeated replenishment, fractionation and changes in intrinsic conditions in the magma reservoir. Unzoned amphiboles and cores of the reversely zoned amphiboles give identical crystallization conditions of 910 ± 30 °C and 360 ± 70 MPa, corresponding to a depth of about 13 ± 2 km, at moderately oxidized conditions (f = +0.5 ± 0.2 ΔNNO). The water content in the melt, calculated based on amphibole chemistry, is 7.1 ± 0.4 wt.%. Rims of the reversely zoned amphiboles are relatively enriched in MgO and yield higher crystallization temperatures (T = 970 ± 25 °C), slightly lower melt H2O contents (6.1 ± 0.7 wt.%) and overlapping pressures (410 ± 100 MPa). We suggest that these rims crystallized following an influx of mafic melt into a resident magma reservoir at mid-crustal depths, further supported by the occurrence of xenocrystic olivine. Crystallization of biotite, albite-rich plagioclase and quartz occurred at comparatively low temperatures (probably rock chemistry of the CMV lava dome dacites is homogenous. They have elevated (La/Nb)N ratios of 3.8-4.5, typical for convergent margin magmas, and display several geochemical characteristics of adakites. Both Sr and Nd isotope compositions (87Sr/86Sr ˜0.70497, 143Nd/144Nd ˜0.51267) are among the most radiogenic observed for the Northern Volcanic Zone of the Andes. They are distinct from oceanic crust that has been subducted in the region

  12. Ore-forming mechanism for the Xiaoxinancha Au-rich Cu deposit in Yanbian,Jilin Province,China:Evidence from noble gas isotope geochemistry of fluid inclusions in minerals

    Institute of Scientific and Technical Information of China (English)

    KEISUKE; Nagao; HIROCHIKA; Sumino


    : (1) formation of fluidand ore substance-bearing Adakitic magma by degassing, dewatering and partial melting during subduction of the Izanagi plate; (2) separation and formation of ore fluids from the Adakitic magma; and (3) success-sive ascending of the ore fluids and final formation of the Au-rich Cu deposit of veinlet-dissemination and vein types by secondary boiling.

  13. Triassic granitoids in the eastern Songpan Ganzi Fold Belt, SW China: Magmatic response to geodynamics of the deep lithosphere (United States)

    Yuan, Chao; Zhou, Mei-Fu; Sun, Min; Zhao, Yongjiu; Wilde, Simon; Long, Xiaoping; Yan, Danping


    The Songpan Ganzi Fold Belt (SGFB), SW China, was developed from a passive continental margin into an orogenic belt with the consumption of the Paleo-Tethys. During the evolution of the SGFB, numerous Late Triassic granitic plutons formed and exhibited a progressive development from adakite/I-type granite, high Ba-Sr granite, A-type granite and monzonite. Representative Late Triassic plutons were studied to unravel the bewildering evolution of the eastern SGFB. The Menggu Pluton (224 ± 3 Ma) consists of granites with high alkali (K 2O+Na 2O = 7.85-10.4 wt.%) and adakitic characteristics (Sr/Y = 19-38). The ɛNd T values (- 2.77 to - 5.03), initial 87Sr/ 86Sr ratios (0.7050-0.7063) and low Nb/Ta ratios (8-10) are indicative of an origin by partial melting of amphibolitic lower crust. Rocks from the Niuxingou Pluton (215 ± 3 Ma) are richer in K than Na (K 2O/Na 2O = 1.1-1.5) and contain high Sr (1006-1662 ppm) and Ba (1277-2009 ppm), typical of shoshonite and high Ba-Sr granite. They have less enriched ɛNd T values (+ 0.08 to - 2.04) and less radiogenic 87Sr/ 86Sr i ratios (0.7047-0.7048), and formed from a mixed melt derived from upwelling asthenosphere and the overlying metasomatised lithospheric mantle. The Taiyanghe Pluton (205 ± 3 Ma) consists of monzonites, with high Al 2O 3 (> 20 wt.%), but low MgO (0.94-1.39 wt.%). The rocks are richer in Na than K (K 2O/Na 2O shoshonitic plutons reflect thickening in response to an arc-continental collision accompanied by fracturing of the lithosphere and an extensional regime in the deep lithosphere in the Late Triassic. The 205 Ma Taiyanghe Pluton was emplaced simultaneously with a rapid uplift of the lithosphere, when surface deposits changed from deep-water turbidite to tidal flat sediments. It was therefore generated during decompression, probably related to the rapid removal of the overthickened lithospheric mantle. The Triassic magmatism in the eastern SGFB is therefore important for probing geodynamic processes

  14. The nature of magmatism at Palinpinon geothermal field, Negros Island, Philippines: implications for geothermal activity and regional tectonics (United States)

    Rae, Andrew J.; Cooke, David R.; Phillips, David; Zaide-Delfin, Maribel


    The Palinpinon geothermal field, Negros Island, Philippines is a high-temperature, liquid-dominated geothermal system in an active island-arc volcanic setting. This paper presents a regional context for the Palinpinon geology, discusses the petrogenetic evolution of magmatism in the district and assesses the genetic relationships between intrusion and geothermal circulation. The oldest rock formation, the Lower Puhagan Volcanic Formation (Middle Miocene), is part of a volcanic sequence that is traceable throughout the Visayas region and is related to subduction of the Sulu Sea oceanic basin in a southeasterly direction beneath the Sulu arc. Late Miocene to Early Pliocene times mark a period of regional subsidence and marine sedimentation. A thick sequence of calcareous sediments (Okoy Formation) was deposited during this period. Magmatism in Early Pliocene to Recent times coincided with commencement of subduction at the Negros-Sulu Arc. This produced basaltic andesites and andesites belonging to the Southern Negros and Cuernos Volcanic Formations. During this time the Puhagan dikes and the Nasuji Pluton intruded Middle Miocene, Late Miocene and Early-Late Pliocene formations. Based on radiogenic ( 40Ar/ 39Ar) dating of hornblende, the Puhagan dikes are 4.1-4.2 Ma and the Nasuji Pluton 0.3-0.7 Ma. This age difference confirms these intrusions are not genetically related. The Early Pliocene age of the Puhagan dikes also confirms they are not the heat source for the current geothermal system and that a much younger intrusion is situated beyond drill depths. Igneous rock formations in southern Negros are the products of regional island-arc magmatism with medium K, calc-alkaline, basaltic to dacitic compositions. Their adakitic affinity implies that the melting of subducted oceanic basalt has influenced magmatism in this region. Considering the regional tectonic history the most likely scenarios for the generation of slab melts are: (1) during the Middle Miocene, by the

  15. Geochemical characteristics of the Shujiadian Cu deposit related intrusion in Tongling: Petrogenesis and implications for the formation of porphyry Cu systems in the Middle-Lower Yangtze River Valley metallogenic belt, eastern China (United States)

    Wang, Shiwei; Zhou, Taofa; Yuan, Feng; Fan, Yu; Cooke, David R.; Zhang, Lejun; Fu, Bin; White, Noel C.


    Porphyry Cu deposits can form in intracontinental or post-collision settings; however, both the genesis of fertile magmas and the mechanism of metal enrichment remain controversial. The Shujiadian porphyry Cu deposit is located in the Tongling area of the Middle-Lower Yangtze River Valley metallogenic belt. It is hosted by the Shujiadian complex, which mainly consists of quartz diorite porphyry (143.7 ± 1.7 Ma) and pyroxene diorite (139.8 ± 1.6 Ma). They both belong to the calc-alkaline series, with enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in high field-strength elements (HFSE) and heavy rare earth elements (HREE), and slightly negative Eu anomalies. Both quartz diorite porphyry and pyroxene diorite have geochemical affinities with adakite, and their low MgO (1.5-3.7 wt%), and Ni (3.7-6.9 ppm), Cr (2.0-44 ppm), and Th/Ce contents (0.06-0.11) indicate that the intrusive rocks have some characteristics of adakite-like rocks derived from thickened lower crust and melts from metabasaltic rocks and eclogites. Plagioclases from the quartz diorite porphyry are andesine (An value = 31.8-40.5) and from the pyroxene diorite are felsic albite and oligoclase with large-scale zones and variable An value (An value = 8.9-18.3), Fe and Sr contents, which indicate that mixing of mafic and felsic magma may have occurred in the shallow magma chamber. Compared to the barren quartz diorite porphyry, relatively lower SiO2 contents (49.5-55.2 wt.%), higher εNd(t) values (- 7.4 to - 6.9), εHf(t) values (- 11.0 to - 9.1) compositions, Ti-in-zircon temperatures (714-785 °C), and variations of HREE contents of the mineralization-related pyroxene diorite suggest mixing with high-temperature mafic magma. Calculated Ce4 +/Ce3 + values of pyroxene diorite plot between the Ni-NiO buffer (NNO) and magnetite-hematite buffer (MH), and barren quartz diorite porphyry samples plot below the Ni-NiO buffer (NNO). Geochemical features of

  16. Ore-forming mechanism for the Xiaoxinancha Au-rich Cu deposit in Yanbian, Jilin Province, China: Evidence from noble gas isotope geochemistry of fluid inclusions in minerals

    Institute of Scientific and Technical Information of China (English)

    SUN JingGui; ZHAO JunKang; CHEN JunQiang; KEISUKE Nagao; HIROCHiKA Sumino; SHEN Kun; MEN LanJing; CHEN Lei


    ) formation of fluid- and ore substance-bearing Adakitic magma by degassing, dewatering and partial melting during subduction of the Izanagi plate; (2) separation and formation of ore fluids from the Adakitic magma; and (3) success- sive ascending of the ore fluids and final formation of the Au-rich Cu deposit of veinlet-dissemination and vein types by secondary boiling.

  17. Spatial and temporal evolution of a back-arc Plio-pleistocene magmatic series: an example of Auca Mahuida and El Tromen volcanoes from Payenia Basaltic Province, Argentina (United States)

    Pallares, C.; Quidelleur, X.; Debreil, J. A.; Gillot, P. Y.; Tchilinguirian, P.


    The Auca Mahuida and El Tromen volcanoes are located in southern Payenia Basaltic Province (PBP), within a back-arc zone. New K-Ar ages and geochemistry analysis confirm that during the Plio-pleistocene epoch they erupted mainly basaltic and andesitic lavas. Normative minerals (Ol: 17.61, Ne: 3.86 and Ab: 23.57) of shield Auca Mahuida lavas characterize these rocks in the boundary between alkali basalts and basanites. Compatible elements (Ni: 227.30 ppm, Co: 50.75 ppm) and MgO values (9.70 %) reveal their primitive origin (OIB type). On the contrary, major and trace elements data from El Tromen volcano expose typical characteristics of more evolved laves. The Auca Mahuida magmas plotted in incompatible multi-element diagram [normalised to the primitive mantle (MP) of Sun & Mcdonough,1989] show moderately fractioned patterns (50 to 100 times the MP), a slight depletion in heavy REE and Y and a very slight depletion in Nb (signature of subduction?). However, the lavas of El Tromen show spidergrams similar to calc-alkaline or Low Silica Adakites patters: moderate enrichment in the most incompatible elements, negative anomaly in Nb, positive anomalies in K, Pb, Sr and depletion in heavy REE and Y. Furthermore, the Ba/La and La/Ta ratios of El Tromen lavas confirm an arc signature (20 and 29 respectively). The geochemical affinity of El Tromen volcano could be due to geographical proximity of the Andes arc. The very slight arc signature exposed by the shield Auca Mahuida volcano could be due to this volcano location (130 km SE of El Tromen) within a intersection between the PBP and Tromen-Domuyo belt, thus the alkaline source was only slightly modified. Finally, we think that in this region magmatic mantle sources were probably modified by subduction-related fluids; this metasomatism would generate the lavas of El Tromen volcano, while magmatic mantle sources of the shield Auca Mahuida were not considerably influenced by this metasomatism. Finally, our new K-Ar ages

  18. 3D Numeric modeling of slab-plume interaction in Kamchatka (United States)

    Constantin Manea, Vlad; Portnyagin, Maxim; Manea, Marina


    Volcanic rocks located in the central segment of the Eastern Volcanic Belt of Kamchatka show a high variability, both in age as well as in the geochemical composition. Three principal groups have been identified, an older group (7-12 my) represented by rich alkaline and transitional basalts, a 7-8 my group exemplified by alkaline basalts of extreme plume type, and a younger group (3-8 my) characterized by calc-alkaline andesites and dacites rocks. Moreover, the younger group shows an adakitic signature. The magmas are assumed to originate from two principle sources: from a subduction modified Pacific MORB-type and from plume-type mantle. In this paper we study the interaction of a cold subducting slab and a hot plume by means of 3D numeric modeling integrated 30 my back in time. Our preliminary modeling results show a short episode of plume material inflowing into the mantle wedge at ~10 my consistent with the second rocks group (plume like). Also our models predict slab edge melting consistent with the youngest group.

  19. Ar-Ar geochronology of Late Mesozoic volcanic rocks from the Yanji area,NE China and tectonic implications

    Institute of Scientific and Technical Information of China (English)

    LI ChaoWen; GUO Feng; FAN WeiMing; GAO XiaoFeng


    Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined "Triassic-Jurassic" volcanic rocks(including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.)were erupted during 118-106Ma,corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage(130-120 Ma)of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. Were extruded at ca.55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as:Tuopangou Fm., Sanxianling/Tuntianying Fm.(118-115 Ma),Malugou/Tianqiaoling Fm.(K1),Huoshanyan/Jingouling Fm.(108-106 Ma),Changcai Fm.(K2),Quanshuicun Fm.(~55 Ma)and Dalazi Fm. Our results suggest that subduction of the Palaeo-Pacific Ocean beneath the East Asian continental margin occurred during 106to 55 Ma. Consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95-65 Ma.

  20. Ar-Ar geochronology of Late Mesozoic volcanic rocks from the Yanji area, NE China and tectonic implications

    Institute of Scientific and Technical Information of China (English)


    Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined “Triassic-Jurassic” volcanic rocks (including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.) were erupted during 118―106 Ma, corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage (130―120 Ma) of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. were extruded at ca. 55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as: Tuopangou Fm., Sanxianling/Tuntianying Fm. (118―115 Ma), Malugou/Tianqiaoling Fm. (K1), Huoshanyan/Jingouling Fm. (108―106 Ma), Changcai Fm. (K2), Quanshuicun Fm. (~55 Ma) and Dalazi Fm. Our results suggest that subduction of the Pa- laeo-Pacific Ocean beneath the East Asian continental margin occurred during 106 to 55 Ma, consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95―65 Ma.

  1. Paleogene volcanism in Central Afghanistan: Possible far-field effect of the India-Eurasia collision (United States)

    Motuza, Gediminas; Šliaupa, Saulius


    A volcanic-sedimentary succession of Paleogene age is exposed in isolated patches at the southern margin of the Tajik block in the Ghor province of Central Afghanistan. The volcanic rocks range from basalts and andesites to dacites, including adakites. They are intercalated with sedimentary rocks deposited in shallow marine environments, dated biostratigraphically as Paleocene-Eocene. This age corresponds to the age of the Asyābēd andesites located in the western Ghor province estimated by the 40Ar/39Ar method as 54 Ma. The magmatism post-dates the Cimmerian collision between the Tajik block (including the Band-e-Bayan block) and the Farah Rod block located to the south. While the investigated volcanic rocks apparently bear geochemical signatures typical to an active continental margin environment, it is presumed that the magmatism was related to rifting processes most likely initiated by far-field tectonics caused by the terminal collision of the Indian plate with Eurasia (Najman et al., 2017). This event led to the dextral movement of the Farah Rod block, particularly along Hari Rod (Herat) fault system, resulting in the development of a transtensional regime in the proximal southern margin of the Tajik block and giving rise to a rift basin where marine sediments were interbedded with pillow lavas intruded by sheeted dyke series.

  2. The Galapagos-OIB signature of the central Costa Rican volcanic front: arc-hotspot interaction (United States)

    Gazel, E.; Carr, M. J.; Hoernle, K.; Feigenson, M. D.; Hauff, F.; Szymanski, D.; van den Bogaard, P.


    Although most Central American magmas have a typical arc geochemical signature, magmas in southern Central America have isotopic and trace element compositions with an OIB affinity, similar to the Galapagos hotspot lavas. Our new data for Costa Rica suggest that this signature, unusual for a convergent margin, has a relatively recent origin (Late Miocene-Pliocene ca. 6 Ma). We also show that there was a transition from typical arc magmas (analogous to the modern Nicaraguan volcanic front) to OIB-like magmas. The geographic distribution of the Galapagos signature in recent lavas from southern Central America is present landward from the subduction of the Galapagos hotspot tracks (the Seamount Province and the Cocos/Coiba Ridges) at the Middle American Trench. The higher Pb isotopic ratios, relatively low Nd isotopic ratios and enriched geochemical signature of central Costa Rican magmas can be explained by arc-hotspot interaction. The isotopic ratios of central Costa Rican lavas require the subducting Seamount Province (Northern Galapagos Domain) component, whereas the isotopic ratios of the adakites and alkaline basalts from southern Costa Rica and Panama are in the geochemical range of the subducting Cocos/Coiba Ridges (Central Galapagos Domain). Geological, geochemical, and isotopic evidence collectively indicate that the relatively recent Galapagos-OIB signature in southern Central America represents a geochemical signal from subducting Galapagos hotspot tracks, which started to collide with the margin ~8 Ma ago. The Galapagos hotspot contribution decreases systematically along the volcanic front from central Costa Rica to NW Nicaragua.

  3. Petrogenesis and significance of the Mesozoic North Taihang complex: Major and trace element evidence

    Institute of Scientific and Technical Information of China (English)

    CHEN; Bin(陈斌); ZHAI; Mingguo(翟明国); SHAO; Ji'an(邵济安)


    The Mesozoic North Taihang complex consists mainly of intermediate rocks and leucogranites as well as minor, synplutonic enriched-mantle derived mafic rocks. The intermediate rocks show high-K calc-alkaline affinity, and high Sr (and Ba) and La/Yb ratios with negligible Eu anomalies, but are low in Y; these signatures are shared by the mafic rocks. The intermediate rocks were probably produced by magma mixing between the evolved enriched-mantle derived mafic magma and a crustal granitic magma, followed by fractional crystallization. The leucogranites show high SiO2 and low ferromagnesian contents; they probably represent residual melts produced from fractional crystallization of the intermediate rocks. Therefore, the North Taihang complex represents significant addition of juvenile crust in the Mesozoic. Mobilized by an upwelling asthenosphere, enriched portions of subcontinental lithospheric mantle experienced partial melting and were consumed significantly, resulting in the intensive magmatism within the North China Craton (NCC). This process is possibly an important mechanism responsible for the lithosphere thinning beneath the NCC. Although the Taihang (and the whole eastern China) granites display rare earth patterns similar to adakites, they appear to have no genetic link with the latter. The model of "eastern plateau" proposed by some authors is not supported by our new data for the Taihang rocks.

  4. 青藏高原冈底斯带南缘泽当多金属矿田多期岩浆活动及年代意义%Multistage Magmatism of the Zetang Polymetallic Orefield on the Southern Margin of the Gangdise Belt in the Tibetan Plateau and Its Chronological Significance

    Institute of Scientific and Technical Information of China (English)

    赵珍; 吴珍汉; 胡道功; 陆露


    Five-phase acidic magmatism was identified though nearly three years’ field observation, test analysis and study in the Zetang orefield on the southern margin of the Gangdise belt. The LA-MC-ICPMS (laser probes) method was used to determine the zircon U-Pb isotope magma formation age and analyze the magma-forming tectonic background and the effects of natural resources. The zircon U-Pb isotope age of trondhjemites in the west of Zetang County is (156±1.0)~(152.5±1.3) Ma. The rocks are adakites, suggesting that the Paleo-Tethy ocean plate subducted northward and formed an intra-oceanic arc tectonic setting in Jurassic. The zircon U-Pb isotope age of host granodiorite rocks (adakites) of the Sangbujiala deposit located in the north of Zetang County is (94.1±0.96) Ma. The magma probably originated from melting of subduction block, and was contaminated by mantle wedge material. Magmatic evolution was closely related to the intra-oceanic subduction of Sangri Island Arc. There existed two phases of magmatic activities in the east of Zetang County, with the zircon isotope age of granodiorite being (63.0±1.0) Ma and (50.2±1.3)~(45.93±0.21) Ma respectively, both of them exhibited continental margin arc features, which indicates initial India-Asian collision. The zircon isotope age of adamellite in the east of Zetang Country is (31.64±0.47)~(29.88±0.39) Ma, and the petrogeochemistry of these two kinds of rocks shows different characteristics. The Chongmuda granites are adakitic rocks, while the Mingze granites are potassium-rich rocks. It is estimated that the adakitic magma came from the melting of India plate underneath the Lhasa Block. However, the two intrusive rocks are probably exotic blocks or are not original magma, whose geochemistry can not represent the tectonic and magmatic evolution of the Zetang polymetallic orefield. Based on the zircon isotope ages, petrology and geochemistry, the authors have reached the conclusion that the first four phases of

  5. First insights on the molybdenum-copper Bled M'Dena complex (Eglab massif, Algeria) (United States)

    Lagraa, Karima; Salvi, Stefano; Béziat, Didier; Debat, Pierre; Kolli, Omar


    Molybdenum-Copper showings in the Eglab massif (eastern part of the Reguibat rise of Algeria), are found in quartz-monzodiorite and granodiorite of the Bled M'Dena complex, a Paleoproterozoic circular structure of ∼5 km in diameter, comprising volcanic and intrusive suites. The latter consist of quartz-diorite, quartz-monzodiorite and granodiorite with a metaluminous normative composition. They display an "adakitic character" with moderate light rare-earth element (LREE) enrichment, minor Eu anomalies, high Sr/Y ratio and low Yb concentration, suggestive of a hydrous, arc magma of volcanic-arc affinity. The mineralization occurs mostly in quartz + molybdenite + chalcopyrite stockwork veins marked by widespread propylitic alteration along the selvages. Molybdenite and chalcopyrite are commonly associated with calcite, which precipitated at relatively late stages of the hydrothermal alteration. Fluid inclusions related to the mineralization stage, range from aqueous to aqueous-carbonic to solid bearing. The latter inclusions have the highest homogenization temperature (up to ∼400 °C), are salt saturated, and commonly contain molybdenite and/or chalcopyrite crystals. The petrology and geochemistry of the host rocks, the style of the hydrothermal alteration, the ore mineral associations, and the characteristics of the fluid inclusions, are all coherent in indicating that the Bled M'Dena represents a Paleoproterozoic porphyry style Mo mineralization, which is far unreported in the African continent.

  6. Linking magmatism with collision in an accretionary orogen. (United States)

    Li, Shan; Chung, Sun-Lin; Wilde, Simon A; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian


    A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251-245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen.

  7. 886-857 Ma granites from Yenisey Ridge formed long before their collision with the western margin of the Siberian Craton (United States)

    Vernikovskiy, V. A.; Vernikovskaya, A. E.; Metelkin, D. V.; Kazansky, A. Y.; Matushkin, N. Y.; Kadilnikov, P. I.; Romanova, I.; Larionov, A. N.; Wingate, M. T. D.


    Yenisei Ridge represents the key geological structure in the western framing of the Siberian Craton, playing a significant role in regional and global geodynamic paleoreconstructions. This Late Precambrian orogenic belt stretches along the Yenisei River and is built of terranes of different nature (Vernikovsky et al., 2003). The largest structure of the Yenisei Ridge is the Central Angara terrane enclosing 886-857 Ma Yeruda granites. Origin and age of Yeruda granites along with paleogeographic position of the Central Angara terrane at the time of their formation were investigated using combined petrological, geochemical, geochronological and paleomagnetic approach. Yeruda granites were emplaced 886-857 Ma and are characterized by fractionated compositions, transitional between I- and S-types. The final stage of 859-857 Ma marks the formation of leucocratic granites, including high-K adakites or continental type (C-type), which could be formed during post-orogenic phase following extreme crustal thickening as described in (Xiao, Clemens, 2007). The calculated apparent movement of polar wonder (APWP) for Yeruda granites is significantly different from the trajectory of Siberia during Early Neoproterozoic, corresponding to paleolatitude difference of more than 8.6°. This clearly indicates that the Central Angara terrane was thousands of kilometers away from Siberia at the time of Yeruda granites emplacement.

  8. Abnormal seismological and magmatic processes controlled by the tearing South American flat slabs (United States)

    Hu, Jiashun; Liu, Lijun


    The influence of flat slab subduction on the formation of intra-slab earthquakes, volcanic activities and mantle seismic velocity anomalies remains unclear. We attempt to better understand these processes by simulating the two flat slabs in Peru and Chile using data-orientated geodynamic models. Our results successfully reproduce the observed flat slabs as mainly due to two subducting aseismic ridges. In contrast to the traditional view of flat-slab subduction, we find that these slabs are internally torn, as is due to the 3D nature of the subducting buoyancy features. This broken slab configuration, confirmed by regional tomography, naturally explains the abnormal distribution of and stress regimes associated with the intermediate-depth earthquakes. We further show that the slab tearing process could also better explain the formation of adakitic and ore-forming magmatism, the evolution of the magmatic arc, and the enigmatic mantle seismic structures beneath these regions. We propose that slab tearing may represent a common result of buoyancy feature subduction and that the resulting mantle processes could affect the long-term geodynamic evolution of continents.

  9. Mapping of magnesium and of different protein fragments in sea urchin teeth via secondary ion mass spectroscopy. (United States)

    Robach, J S; Stock, S R; Veis, A


    Mature portions of sea urchin are comprised of a complex array of reinforcing elements yet are single crystals of high and very high Mg calcite. How a relatively poor structural material (calcite) can produce mechanically competent structures is of great interest. In teeth of the sea urchin Lytechinus variegatus, we recorded high-resolution secondary ion mass spectrometry (SIMS) maps of Mg, Ca ,and specific amino acid fragments of mineral-related proteins including aspartic acid (Asp). SIMS revealed strong colocalization of Asp residues with very high Mg. Demineralized specimens showed serine localization on membranes between crystal elements and reduced Mg and aspartic acid signals, further emphasizing colocalization of very high Mg with ready soluble Asp-rich protein(s). The association of Asp with nonequilibrium, very high magnesium calcite provides insight to the makeup of the macromolecules involved in the growth of two different composition calcites and the fundamental process of biomineralization.

  10. <研究報告>長崎県西彼杵半島南部の高Mg安山岩と玄武岩



    The late Cenozoic volcanic rocks in the southern Nishisonogi Peninsula, which are characterized by dominance of undifferentiated, primitive rocks, show a large variation in chemical composition ranging from high-Mg andesite (HMA) through tholeiitic basalt to alkali basalt and from high-Mg basalt to rhyolite. Most HMA is cpx-HMA crystallized clinopyroxene with the highest Mg# and Cr_2O_3 of 87.4 and 1.24%, respectively, following olivine with the highest Fo of 92.1 and NiO of 0.48%. An orthopy...

  11. Geochemistry and fluid characteristics of the Dalli porphyry Cu-Au deposit, Central Iran (United States)

    Zarasvandi, Alireza; Rezaei, Mohsen; Raith, Johann; Lentz, David; Azimzadeh, Amir-Mortaza; Pourkaseb, Hooshang


    The Miocene Dalli porphyry Cu-Au deposit in the central part of Urumieh-Dokhtar magmatic arc is the first reported Au-rich porphyry Cu deposit in the Zagros orogenic belt. The Cu-Au mineralization is mainly hosted in diorite and quartz diorite intrusions, presenting as numerous veinlets in the altered wall rocks, with potassic, phyllic, and propylitic alteration developed. Based on the mineral assemblages and crosscutting relations of veinlets, hydrothermal mineralization-alteration occurred in at least three stages, characterized by veinlets of (1) Qtz + Kfs + Mag ± Ccp, (2) Qtz + Py + Ccp ± Bn ± Cv ± Cc and, (3) Qtz + Chl + Bt. The ore-bearing intrusions exhibit typical geochemical characteristics of subduction zone magmas, including LREE fractionated pattern, strong enrichment in LILE (Cs, Rb, Ba, Pb, and U), and depletion of HFSE, with marked negative Ti and Nb anomalies. The adakite-like ore-hosting porphyry intrusions are characterized by a systematic gradual decreasing and increasing of Y and Eu/Eu∗ with increasing SiO2 content, respectively. Moreover, they exhibit a significant increasing trend of Sr/Y with decreasing of Y, which indicates progressive hornblende fractionation and suppression of plagioclase fractionation during the evolution toward high water content of parental magma. A relatively flat HREE pattern with low Dyn/Ybn and Nb/Ta values may represent that amphibole played a more important role than garnet in the generation of the adakitic melts in the thickened lower crust. Based on the phase assemblages confirmed by detailed laser Raman spectroscopy analyses and proportion of solid, liquid, and gaseous components, five types of fluid inclusions were recognized, which are categorized as; (1) liquid-rich two phase (liquidH2O + vaporH2O) (IIA), (2) vapor-rich two phase (vaporH2O/CO2 + liquidH2O) (IIB), (3) high saline simple fluids (IIIA; liquidH2O + vaporH2O + Hl), (4) high saline opaque mineral-bearing fluids (IIIB; liquidH2O + vaporH2O

  12. Geochemical constraints on the nature of magma sources for Triassic granitoids from South Qinling in central China (United States)

    Lu, Ying-Hui; Zhao, Zi-Fu; Zheng, Yong-Fei


    A combined study of zircon U-Pb ages and Lu-Hf isotopes, whole-rock major-trace elements and Sr-Nd isotopes as well as mineral chemistry and O isotopes was carried out for Triassic granitoids from the South Qinling orogen in central China. Model calculations were also performed to examine the trace element fractionation during partial melting of crustal rocks. The results provide insights into the nature of magma sources for these granitoids. LA-ICPMS zircon U-Pb dating yields concordant ages of 208 ± 2 to 216 ± 3 Ma for these granitoids from the Shahewan (SHW), Caoping (CP) and Zhashui (ZS) plutons, and no relict zircon cores are identified by the CL imaging and U-Pb dating. The SHW and CP granitoids contain hornblende and are metaluminous with A/CNK ratios of 0.84 to 0.93. They exhibit relatively low SiO2 contents (62.88-69.04 wt.%) but high contents of FeOT, MgO and TiO2, and slightly to negligibly negative Eu anomalies (δEu = 0.79-0.89). Zircons from them show mantle-like δ18O values of 4.71 to 5.72‰. In contrast, the ZS granites contain no hornblende and are metaluminous to weakly peraluminous with A/CNK ratios of 0.99 to 1.03. They show relatively high SiO2 contents (69.32-75.94 wt.%) but low FeOT, MgO and TiO2 contents, and moderate negative Eu anomalies (δEu = 0.63-0.81). They have slightly low zircon δ18O values of 4.60 to 4.83‰. All of these granitoids show arc-like trace element distribution patterns with enrichment in LREE and LILE (e.g., Rb, K and Pb) but depletion in HFSE (e.g., Nb, Ta and Ti). Geochemical comparison and modeling indicate that these granitoids are different from adakitic rocks originating from the thickened lower continental crust. Compared with the composition of felsic melts produced by petrological experiments of various lithologies, it appears that these granitoids are derived from dehydration melting of metabasaltic sources at normal lower crustal depths, and experienced varying degrees of fractional crystallization

  13. 长江中下游贵池矿集区燕山期岩浆作用及其地质意义:年代学、地球化学及Sr-Nd-Hf同位素证据%Zircon U-Pb age, element and Sr-Nd-Hf isotope geochemistry of Late Mesozoic magmatism from the Guichi metallogenic district in the Middle and Lower Reaches of the Yangtze River Region

    Institute of Scientific and Technical Information of China (English)

    刘园园; 马昌前; 吕昭英; 黄卫平


    长江中下游贵池地区燕山期侵入岩发育,与成矿关系密切.本文对该区侵入岩开展了详细的锆石U-Pb年代学、地球化学及Sr-Nd-Hf同位素研究.结果表明,马头花岗闪长斑岩形成于147±2Ma,而花园巩石英二长岩形成于127±1Ma,比花岗闪长斑岩晚约20Ma.早期的花岗闪长斑岩(147 ~ 145Ma)为高钾钙碱性系列,具有高Al2O3、Sr含量和Sr/Y、La/Yb比值,以及低的Y、Yb含量,与埃达克质岩的地球化学特征一致;而晚期石英二长岩(127Ma)和石英正长岩为钾玄岩系列,具有高的(Na2O+ K2O)、Zr、Nb、Y含量和Y/Nb、Yb/Ta比值,与造山带A2型花岗岩地球化学特征相似;碱长花岗岩(125~124Ma)同样具有A型花岗岩的地球化学特征,但与石英二长岩、石英正长岩相比,碱长花岗岩的Y/Nb、Yb/Ta比值相对较低,具板内环境A1型花岗岩的地球化学特征.因此,贵池地区岩浆岩从早期的埃达克质岩变为晚期的A型花岗岩,反应了晚中生代时期长江中下游地区的构造环境由大陆边缘环境向伸展环境的转变.%Zircon U-Pb ages, elemental and Sr-Nd-Hf isotopic data are reported for Late Mesozoic plutons in the Guichi metallogenic district in the Middle and Lower Reaches of the Yangtze River Region, attempting to constrain their age, petrogenesis, and tectonic implications. The Matou granodiorite porphyry and the Huayuangong quartz monzonite were dated at 147 ±2Ma and 127 ± 1Ma, respectively. The early Matou and Tongshan granodiorite porphyries are high-K calc-alkaline, and exhibit adakite-like geochemical features, such as high A12O3, Sr, Sr/Y and La/Yb values, and low Y and Yb contents. The 127Ma Huayuangong quartz monzonites and quartz syenites are shoshonitic, and characterized by high ( Na2O + K2O), Zr, Nb, Y, Y/Nb and Yb/Ta values, indicating A2-type granite affinity at convergent margins. The 125 ~ 124Ma Huangyuangong alkali feldspar granites also exhibit A-type granite geochemical


    Institute of Scientific and Technical Information of China (English)

    赵丽君; 吕晓瑜; 王岐


    The Neoarchean rocks in Eastern Liaoning form the basement of North China landmass, which is divided by the Paleoproterozoic Liaoning-Jilin rift into two micro-landmasses in north and south. The northern micro-]andmass is composed of Fujiapuzi gneiss complex (U-Pb 2730 Ma), Huzhuang gneiss (U-Pb 2524.85 Ma) and Lianshanguan granite (U-Pb 2563 Ma). The southern micro-landmass consists of Desheng gneiss complex (U-Pb 2591 Ma). The northern micro-landmass geochemically presents the characteristics of shoshonite series-sodic calc-alkaline series, belonging to LREE enriched type with positive to negative Eu anomalies. The magma evolved from sodic calc-alkaline to potassic calc-alkaline series. The tectonic setting is active continental margin, with crustal evolution from extension in early orogenic period to compression in major orogenic period. The geochemistry of the rocks in the southern micro-landmass is characterized by high Al and Mg, which is similar to that of adakite, with low total REE, belonging to LREE enriched type with negative Eu anomaly. The magmatic evolution shows sodic trend. The existence of adakite in the southern micro-landmass suggests that the southern micro-landmass subducted northward around 2500 Ma, forming the united Archean continent in Eastern Liaoning region.%辽东地区新太古代构成了华北陆块重要结晶基底.以辽吉古元古代裂谷为界,分为南北两个微陆块.北部微陆块由新太古代付家堡子片麻杂岩(U-Pb法2730 Ma)、虎庄片麻岩(U-Pb法2524.85 Ma)、连山关花岗岩(U-Pb法2563 Ma)组成,南部微陆块由得胜片麻杂岩(U-Pb法2519 Ma)组成.北部微陆块岩石地球化学显示钾玄岩系列-钠质钙碱系列,正铕异常-负铕异常轻稀土富集型特征.岩浆演化由钠质钙碱系列→钾质钙碱系列.源区性质为地壳深熔,相当于变质泥岩、变质杂砂岩部分熔融.构造背景为活动大陆边缘,由造山早期构造拉张环境上侵就位(付家堡子片

  15. Petrologic Consequences of the Magmatic Death of a Continental Arc: Vanda Dike Swarm, Dry Valleys, Antarctica (United States)

    Harpp, K. S.; Christensen, B. C.; Geist, D. J.; Garcia, M. O.


    The Dry Valleys of southern Victoria Land, Antarctica, are notable for the presence of the Vanda dikes, prominent NE-trending swarms that crosscut a sequence of granitoid plutons. These older plutons are regional in extent and comprise 3 Cambro-Ordovician groups, including: a) calc-alkaline granitoids formed at an active plate margin during the Ross Orogeny (c. 505 Ma); b) adakitic granitoids, likely marking the conclusion of Ross Orogeny subduction-related activity (c. 490 Ma); and c) younger monzonitic plutons, probably generated in an intraplate extensional setting (Cox et al., 2000). The Vanda dikes crosscut the younger plutons, possibly between c. 490 and 477 Ma (Allibone et al., 1993; Encarnacion and Grunow, 1996). Dikes from the east wall of Bull Pass and the south wall of the Wright Valley range from 0.5-25 m wide with nearly vertical dips, are usually several km long, and, in the center of the swarms, occur with a frequency of ~18 dikes/km. Most have chilled margins and are surrounded by brittle fractures, indicative of shallow intrusion into cold country rock. Dike compositions are bimodal, most defining a trend at the boundary between the high-K calc-alkaline and shoshonite series in SiO2-K2O space; some Wright Valley dikes have slightly lower K2O and are calc-alkaline. Granite porphyry dikes are relatively homogeneous (69-73 wt.% SiO2), whereas the mafic dikes exhibit a wider range of compositions (49-57 wt.% SiO2). The felsic and mafic dikes have distinct trace element abundances but similar normalized distribution patterns, including fractionated heavy rare earth elements and negative Eu and high field-strength element anomalies. Average Sr/Y ratios of both the felsic and mafic dikes cluster around 20, well below a typical adakite signature. Major and trace element variations suggest that the felsic dikes may be differentiates of the mafic magmas. Field relations further indicate that the felsic lavas may represent, on average, a later phase of dike

  16. Petrogenesis of Granitoids, U-Pb zircon geochronology, Sr-Nd Petrogenesis of granitoids, U-Pb zircon geochronology, Sr-Nd isotopic characteristics, and important occurrence of Tertiary mineralization within the Lut block, eastern Iran

    Directory of Open Access Journals (Sweden)

    M.H. Karimpour


    Full Text Available Tertiary intrusive granitoids within the Lut block in the Khorasan Razavi and South Khorasan provinces are mainly sub-volcanic with porphyry texture and their composition varies from granite to diorite but monzonite is dominant. With the exception of Hired, these are classified as belonging to the magnetite-series of I-type granitoids. Chemically, these rocks are meta-aluminous. Those with mineralization are K-rich and those without mineralization such as Najmabad are Na-rich. All intrusive rocks plot in the field of calc-alkaline to adakite except Najmabad that plot in the adakite field. Based on low content of Nb (30, low initial 87Sr/86Sr (17 ppm, low ratio of Zr/Nb (0.707 and low initial εNd value (-3, magmas in the Kaybar-Kuh were more contaminated in the continental crust. Based on depletion in HREE and high ratio of (La/YbN (17-23, magma in Najmabad originated in the deep region in which garnet was present. Based on REE pattern and ration of Eu/Eu* (0.8-1, intrusive rocks within Maherabad, Khoopik, Chah-Shaljami, Kuh Shah and Dehsalm are calc-alkaline and their magma formed in an oxidant condition whereas Kaybar Kuh magma with low ratio of Eu/Eu* (<0.8 was contaminated in the continental crust under reduced conditions. The age of these granitoids is between Middle Eocene and Lower Oligocene. Kaybar-Kuh (43.3 Ma is situated in the north and Chah-Shaljami (33.3 Ma in the south. The initial 87Sr/86Sr ratios decrease from north (0.7077 to south (0.7047 as the age decreases. εNd of Maherabad, Khoopik, Dehsalm, and Chah-Shaljami granitoids is between +0.5 and +2.49 and the initial 87Sr/86Sr ratio is less than 0.7055. The age of the source rock (TDM, which was calculated based on Sm-Nd isotopes indicates that these magma originated from oceanic crust with different ages. Kaybar-Kuh originated from the oldest oceanic crust (840 Ma and was contaminated more in continental crust, but Najmabad originated from a younger oceanic crust (360 Ma with

  17. Remelting of Neoproterozoic relict volcanic arcs in the Middle Jurassic: Implication for the formation of the Dexing porphyry copper deposit, Southeastern China (United States)

    Liu, Xuan; Fan, Hong-Rui; Santosh, M.; Hu, Fang-Fang; Yang, Kui-Feng; Li, Qiu-Li; Yang, Yue-Heng; Liu, Yongsheng


    The Dexing copper deposit in southeastern China is a typical non-arc porphyry deposit, the origin of which has been a topic of debate for several decades. Here we present new results from U-Pb geochronology, whole-rock chemistry and Sr-Nd-Hf-O isotopic investigations on the ore-forming granodioritic porphyry. LA-ICPMS zircon U-Pb data suggest that the granodioritic porphyry was formed in the Middle Jurassic (ca. 172.5 Ma) probably associated with lithospheric thinning driven by either sub-continental lithospheric mantle delamination or asthenospheric upwelling. The porphyry displays both arc-like and adakitic trace element signatures. The adakitic features suggest that HREE (heavy rare earth elements)-rich minerals such as garnet and hornblende, in the absence of plagioclase resided in the source region. The arc-like signatures are broadly comparable with those of the proximal Neoproterozoic island arc rocks including the keratophyre from Shuangxiwu Group and associated granitoids indicating a potential genetic relationship. The porphyry has chondritic ɛNd(t) of - 0.28 to 0.25 and radiogenic ɛHf(t) of 2 to 7, and correspondingly, uniform two stage depleted mantle Nd model ages of 940-980 Ma and Hf model ages of 800-1100 Ma (mean ~ 920 Ma). On Nd and Hf isotopic evolution diagrams, these values are markedly similar to those of the adjacent Neoproterozoic arc rocks when calculated forward to the Mid-Jurassic. Zircons of the porphyry show mantle-like oxygen isotope characters with δ18O values clustering in the range of 4.7-5.9‰, similar to the values for the Neoproterozoic arc rocks mentioned above. The geochemical and isotopic features recorded in our study suggest mantle-derived magmas with no significant supracrustal input for the source of the porphyry. With regard to the source of the Cu ore, we consider a model involving the remelting of sulfide-bearing arc-related lower crustal source. Furthermore, the occurrence of a Neoproterozoic VMS (volcanic massive

  18. Syntectonic emplacement of the Triassic biotite-syenogranite intrusions in the Taili area, western Liaoning, NE China: Insights from petrogenesis, rheology and geochronology (United States)

    Li, Weimin; Liu, Yongjiang; Jin, Wei; Neubauer, Franz; Zhao, Yingli; Liang, Chenyue; Wen, Quanbo; Feng, Zhiqiang; Li, Jing; Liu, Qing


    The North China Craton (NCC) is one of the oldest cratons in the world, and it recently becomes a hot study area because of large volumes of Mesozoic intrusions associated with lithospheric thinning contributing to cratonic destruction in late Mesozoic times. However, the timing of initial thinning and destruction is still controversial. The Taili area, western Liaoning Province, in the northeastern part of the NCC well exposes the Archean basement rocks and the Mesozoic magmatic rocks with variable plastic deformation. This study focuses on the syntectonic emplacement of the Triassic biotite-syenogranite intrusions, in order to understand their petrogenesis, timing as well as the geological significance. Zircon LA-ICP-MS U-Pb ages reveal that the biotite-syenogranites formed between 246 and 191 Ma, and contain many ancient (2564-2317 Ma) zircon xenocrysts. Geochemical data suggests that the biotite-syenogranites display an adakitic affinity with high Sr/Y = 135-167 and (La/Yb)N = 48-69, as well as negligible Eu anomalies (δEu = 0.87-0.94), high negative zircon εHf(t) values (-15.5 to -21.5) and ancient TDM2 ages (2246-2598 Ma). This data suggests that the parent magmas were generated from partial melting of thickened Archean lower crustal rocks probably due to the bidirectional amalgamation of the NCC with the NE China micro-blocks and the Yangtze Craton in its north and south, respectively. In the middle part of the Taili area, magmatic fabrics are well preserved in the biotite-syenogranite intrusion characterized by the strong preferred orientation of biotite and hornblende crystals, which parallel to the intrusion margin and are slightly oblique to the gneissosity of the sheared host Neoarchean granitic gneisses. The quartz grain size piezometer suggests that the paleo-differential stresses weaken toward to the central part of the intrusion, ranging from 21.40-22.22 MPa to 16.74-19.34 MPa, during quartz crystallization in the emplacement stage. This allow

  19. Geochemistry and petrogenesis of Mashhad granitoids: An insight into the geodynamic history of the Paleo-Tethys in northeast of Iran (United States)

    Mirnejad, H.; Lalonde, A. E.; Obeid, M.; Hassanzadeh, J.


    Mashhad granitoids in northeast Iran are part of the so-called Silk Road arc that extended for 8300 km along the entire southern margin of Eurasia from North China to Europe and formed as the result of a north-dipping subduction of the Paleo-Tethys. The exact timing of the final coalescence of the Iran and Turan plates in the Silk Road arc is poorly constrained and thus the study of the Mashhad granitoids provides valuable information on the geodynamic history of the Paleo-Tethys. Three distinct granitoid suites are developed in space and time (ca. 217-200 Ma) during evolution of the Paleo-Tethys in the Mashhad area. They are: 1) the quartz diorite-tonalite-granodiorite, 2) the granodiorite, and 3) the monzogranite. Quartz diorite-tonalite-granodiorite stock from Dehnow-Vakilabad (217 ± 4-215 ± 4 Ma) intruded the pre-Late Triassic metamorphosed rocks. Large granodiorite and monzogranite intrusions, comprising the Mashhad batholith, were emplaced at 212 ± 5.2 Ma and 199.8 ± 3.7 Ma, respectively. The high initial 87Sr/86Sr ratios (0.708042-0.708368), low initial 143Nd/144Nd ratios (0.512044-0.51078) and low ɛNd(t) values (- 5.5 to - 6.1) of quartz diorite-tonalite-granodiorite stock along with its metaluminous to mildly peraluminous character (Al2O3/(CaO + Na2O + K2O) Mol. = 0.94-1.15) is consistent with geochemical features of I-type granitoid magma. This magma was derived from a mafic mantle source that was enriched by subducted slab materials. The granodiorite suite has low contents of Y (≤ 18 ppm) and heavy REE (HREE) (Yb 594 ppm) and high ratio of Sr/Y (> 35) that resemble geochemical characteristics of adakite intrusions. The metaluminous to mildly peraluminous nature of granodiorite from Mashhad batholiths as well as its initial 87Sr/86Sr ratios (0.705469-0.706356), initial 143Nd/144Nd ratios (0.512204-0.512225) and ɛNd(t) values (- 2.7 to - 3.2) are typical of adakitic magmas generated by partial melting of a subducted slab. These magmas were then

  20. Geochemistry and petrogenesis of the K-rich 'Bongo-type' granitoids in the Paleoproterozoic Bole-Nangodi greenstone belt of Ghana (United States)

    Abitty, Emmanuel K.; Dampare, Samuel B.; Nude, Prosper M.; Asiedu, Daniel K.


    The 'Bongo-type' granitoids intrude the northern portion (where it cross cuts the Tarkwaian), central and south-central portions of the Bole-Nangodi greenstone belt in Ghana. The non-foliated, porphyritic granitoids are characterised by microcline (5-18 mm), often set in a medium to fine grained matrix of quartz and plagioclase, contains granular quartz and show incipient development of mymerkites under thin section. The major mafic phases are a brownish-green variety of hornblende ± biotite, with sphene, epidote and apatite occurring as accessory minerals. The pink looking 'Bongo-type' granitoids are classified as granites with subordinate granodiorites and quartz monzonites. Whole-rock geochemical analyses show that the granitoids are magnesian and metaluminous to weakly peraluminous. On the basis of their Th-Co-K2O and SiO2 contents, the granitoids classified as high-K calc-alkaline and shoshonite series rocks. They show enriched LILE trends, decoupled LILE-HFSE patterns, negative Ta-Nb anomaly, pronounced negative Ti anomaly and variable positive and negative Sr anomalies. The K-rich granitoids from the middle and south-central portions of the Bole-Nangodi belt show the lowest concentrations of LILE and some HFSE with the most prominent negative Ti and Si anomalies. The 'Bongo-type' granitoids show I-type characteristics. Based on Ba-U-Th concentrations, they are interpreted to have had some interaction with crustal materials or some influence of subducted sediments. The granitoids unequivocally show subduction-related signatures and mimic high silica adakites (HSA). They show evidence of being emplaced in a volcanic arc geotectonic environment. Their geochemical similarities to A-type granitoids, however, suggest an arc-back-arc tectonic setting.

  1. Galapagos-OIB signature in southern Central America: Mantle refertilization by arc-hot spot interaction (United States)

    Gazel, Esteban; Carr, Michael J.; Hoernle, Kaj; Feigenson, Mark D.; Szymanski, David; Hauff, Folkmar; van den Bogaard, Paul


    Although most Central American magmas have a typical arc geochemical signature, magmas in southern Central America (central Costa Rica and Panama) have isotopic and trace element compositions with an ocean island basalt (OIB) affinity, similar to the Galapagos-OIB lavas (e.g., Ba/La 10, 206Pb/204Pb > 18.8). Our new data for Costa Rica suggest that this signature, unusual for a convergent margin, has a relatively recent origin (Late Miocene ˜6 Ma). We also show that there was a transition from typical arc magmas (analogous to the modern Nicaraguan volcanic front) to OIB-like magmas similar to the Galapagos hot spot. The geographic distribution of the Galapagos signature in recent lavas from southern Central America is present landward from the subduction of the Galapagos hot spot tracks (the Seamount Province and the Cocos/Coiba Ridge) at the Middle American Trench. The higher Pb isotopic ratios, relatively lower Sr and Nd isotopic ratios, and enriched incompatible-element signature of central Costa Rican magmas can be explained by arc-hot spot interaction. The isotopic ratios of central Costa Rican lavas require the subducting Seamount Province (Northern Galapagos Domain) component, whereas the isotopic ratios of the adakites and alkaline basalts from southern Costa Rica and Panama are in the geochemical range of the subducting Cocos/Coiba Ridge (Central Galapagos Domain). Geological and geochemical evidence collectively indicate that the relatively recent Galapagos-OIB signature in southern Central America represents a geochemical signal from subducting Galapagos hot spot tracks, which started to collide with the margin ˜8 Ma ago. The Galapagos hot spot contribution decreases systematically along the volcanic front from central Costa Rica to NW Nicaragua.

  2. Inverse modeling of Central American lavas: old lithospheric and young asthenospheric heterogeneities (United States)

    Feigenson, M.; Gazel, E.; Carr, M. J.


    In recent years, there have been a number of models proposed to account for the OIB-like geochemical characteristics of lavas from central Costa Rica. The source for most basalts of the Central American volcanic front (ranging from Guatemala to northern Costa Rica) is dominantly DM (depleted MORB-source mantle) fluxed by subduction-derived fluids. In contrast, central Costa Rican basalts display striking isotopic similarities to the Galapagos hotspot. How the Galapagos signature is introduced into the Central American source is at the heart of the conflicting theories. Several models incorporate asthenospheric flow of this enriched mantle, either around the Central American arc via South America, or through a slab window, which may have opened about 5 my ago beneath central Costa Rica. Alternatively, passage of the Caribbean plate over the Galapagos hotspot may have left veins of unerupted melt within the sub-Caribbean lithosphere. These veins may be preferentially tapped during later superimposed arc volcanism. Although these models yield identical isotopic systematics, it may be possible to distinguish between them by a geochemical technique that can indicate the presence of garnet in the source region. This method, developed by Hofmann and coworkers in the 1980s, is termed inverse modeling, and uses the variation of REEs in lavas to assess the relative importance of garnet vs. clinopyroxene during partial melting. We have applied this method to new REE data from back arc lavas throughout Central America, and preliminary results indicate that garnet is not present in their sources. In contrast, direct slab melts (adakites) from Central America, as well as volcanic front lavas and alkaline basalt (with minimal slab signature) from central Costa Rica and Panama, require a source with garnet. Therefore, enriched mantle in the back arc is likely stored in the shallow lithosphere rather than introduced through asthenospheric flow. Enriched material in the volcanic

  3. The distribution, geochronology and geochemistry of early Paleozoic granitoid plutons in the North Altun orogenic belt, NW China: Implications for the petrogenesis and tectonic evolution (United States)

    Meng, Ling-Tong; Chen, Bai-Lin; Zhao, Ni-Na; Wu, Yu; Zhang, Wen-Gao; He, Jiang-Tao; Wang, Bin; Han, Mei-Mei


    Abundant early Paleozoic granitoid plutons are widely distributed in the North Altun orogenic belt. These rocks provide clues to the tectonic evolution of the North Altun orogenic belt and adjacent areas. In this paper, we report an integrated study of petrological features, U-Pb zircon dating, in situ zircon Hf isotope and whole-rock geochemical compositions for the Abei, 4337 Highland and Kaladawan Plutons from north to south in the North Altun orogenic belt. The dating yielded magma crystallization ages of 514 Ma for the Abei Pluton, 494 Ma for the 4337 Highland Pluton and 480-460 Ma for the Kaladawan Pluton, suggesting that they are all products of oceanic slab subduction because of the age constraint. The Abei monzogranites derived from the recycle of Paleoproterozoic continental crust under low-pressure and high-temperature conditions are products of subduction initiation. The 4337 Highland granodiorites have some adakitic geochemical signatures and are sourced from partial melting of thickened mafic lower continental crust. The Kaladawan quartz diorites are produced by partial melting of mantle wedge according to the positive εHf(t) values, and the Kaladawan monzogranite-syenogranite are derived from partial melting of Neoproterozoic continental crust mixing the juvenile underplated mafic material from the depleted mantle. These results, together with existing data, provide significant information about the evolution history of oceanic crust subduction during the 520-460 Ma. The initiation of subduction occurred during 520-500 Ma with formation of Abei Pluton; subsequent transition from steep-angle to flat-slab subduction at ca.500 Ma due to the arrival of buoyant oceanic plateaus, which induces the formation of 4337 Highland Pluton. With ongoing subduction, the steep-angle subduction system is reestablished to cause the formation of 480-460 Ma Kaladawan Pluton. Meanwhile, it is this model that account for the temporal-spatial distribution of these early

  4. The Origin of Graphic Granite: New Insights from Electron Backscatter Diffraction (EBSD) Analyses (United States)

    Xu, H.; Wu, Y.


    Graphic granite, found predominantly in granitic pegmatite, is a leucocratic granitic rock consisting of an intimate intergrowth of alkali feldspar and quartz with a distinctive texture as ancient cuneiform writing when viewed in certain cross sections. Deciphering the graphic texture is important for understanding its origin and the crystallization process of granitic rocks. In this study, we present investigations on petrology, mineral composition, crystallographic relationship and topotaxy of quartz and alkali feldspar in graphic granites from the Fangshan adakitic pluton, Beijing, north China and the Luotian dome in the Northern Dabie Mountains, central China. The euhedral to subhedral coarse-grained feldspar host in graphic granite can be alkali feldspar or plagioclase. Microscopically, the feldspar host is usually a perthite, which is decomposed into irregular intergrowth of sodic and potassic feldspar. The volume content of quartz usually ranges from 20% to 45%, and the composition of feldspar in graphic granite depends greatly on the formation conditions. However, the quartz-feldspar ratio and the composition of feldspar in graphic granite are relatively stable in coeval graphic granites in the same area. The majority of the quartz grains undergrown with host feldspar are in the form of sub-parallel tabular, long rods and unconnected dendritic crystals, which only shows a distinctive graphic texture in certain cross sections. Under cross polarized light microscopy, multiple domains of quartz grains exhibit a nearly simultaneous extinction within a single crystal of feldspar. The crystallographic orientations of the quartz grains and the host feldspar were measured using the electron backscatter diffraction (EBSD) technique. Statistical analyses indicate a definite crystallographic orientation relationship between the majority of graphic quartz grains and the host feldspar in that [11-23]Quartz parallel to [001]Feldspar. Moreover, Dauphiné twin of quartz

  5. Magma associations in Ediacaran granitoids of the Cachoeirinha‒Salgueiro and Alto Pajeú terranes, northeastern Brazil: Forty years of studies (United States)

    Sial, Alcides N.; Ferreira, Valderez P.


    Granitic magmatism in the Cachoeirinha‒Salgueiro and Alto Pajeú terranes in the Transversal Zone Domain of the Borborema Province, northeastern Brazil, occurred in three main time intervals: 650-620 Ma, 590-560 Ma and 545-520 Ma. The oldest one is characterized by intrusions of magmatic-epidote (mEp) bearing calc-alkalic (some with trondhjemitic affinities) and high-K calc-alkalic plutons, synkinematic to the main regional foliation, under contractional tectonic regime, and exhibits TDM plutons is compatible with partial fusion of subducted oceanic basaltic crust (mEp-bearing calc-alkalic tonalites/granodiorites, equivalent to adakites). Voluminous intrusions in the 590-560 Ma interval are represented by abundant mEp-free high-K calc-alkalic, peralkalic, ultrapotassic, mEp-bearing high-K calc-alkalic, and less abundant shoshonitic magmas. Nd-model ages for this group of plutons vary from 1.5 to 2.5 Ga and ƐNd (0.6 Ga) ranges from -8 to -20; δ18O (zircon) varies from 6.4 to 7.9‰VSMOW. Values of δ18O (zircon) for the 590‒560 Ma old group of plutons coupled with Nd isotope data are compatible with remelting of crustal (negative ƐNd, 1.6 to 2.0 Ga old) source rocks. O- and Nd-isotope data for this group of plutons are compatible with underplating of basaltic magma in the base of the lower crust for the high-K calc-alkalic granitoids, coeval to transcurrent movements along sigmoidal shear zones. Intrusion of one shoshonitic (Serrote do Arapuá), one calc-alkalic (Riacho do Icó) plutons besides the peralkalic Manaíra-Princeza Isabel dike set have witnessed this transition from contractional to transcurrent movements along shear zones, around 610‒600 Ma.

  6. Timing of subduction and exhumation in a subduction channel: Evidence from slab melts from La Corea Mélange (eastern Cuba) (United States)

    Blanco-Quintero, I. F.; Rojas-Agramonte, Y.; García-Casco, A.; Kröner, A.; Mertz, D. F.; Lázaro, C.; Blanco-Moreno, J.; Renne, P. R.


    High pressure igneous rocks (tonalites), generated by partial melting of subducted basaltic rocks accreted to the mantle wedge, are present in the La Corea serpentinite-matrix mélange (eastern Cuba) as centimeter- to meter-sized blocks and as concordant to crosscutting veins within high-pressure parent amphibolite blocks. The slab melts have adakitic signatures, in agreement with formation after partial melting of metabasite. Thermobarometric calculations indicate 620-680 °C and 13-15 kbar during crystallization of tonalites and down to 250-300 °C, 6 kbar during retrogression, indicating counter-clockwise P-T paths (hot subduction-cool exhumation). Free water required for melting of amphibolite at moderate temperature (700-750 °C) and moderate pressure (13-16 kbar) close to the wet basaltic solidus is inferred to have been provided after dehydration of sediments, altered basaltic crust and serpentinite of the subducting Proto-Caribbean lithosphere. Single zircon (SHRIMP) and phengite 40Ar/39Ar age data constrain the P-T-t evolution of the mélange from the timing of crystallization of melts at ~ 110-105 Ma to cooling at ~ 87-84 Ma, ca. 350 °C, ca. 9 kbar. These figures are consistent with subduction of an oblique ridge, shortly before 115 Ma. Furthermore, our data indicate very slow exhumation (ca. 1 mm/yr) in the subduction channel during the oceanic convergence stage (120-70 Ma) until final fast exhumation to the surface occurred at 70-65 Ma during a regional arc-platform collision event.

  7. Metamorphic complexes in accretionary orogens: Insights from the Beishan collage, southern Central Asian Orogenic Belt (United States)

    Song, Dongfang; Xiao, Wenjiao; Windley, Brian F.; Han, Chunming; Yang, Lei


    The sources of ancient zircons and the tectonic attributions and origins of metamorphic complexes in Phanerozoic accretionary orogens have long been difficult issues. Situated between the Tianshan and Inner Mongolia orogens, the Beishan orogenic collage (BOC) plays a pivotal role in understanding the accretionary processes of the southern Central Asian Orogenic Belt (CAOB), particularly the extensive metamorphic and high-strained complexes on the southern margin. Despite their importance in understanding the basic architecture of the southern CAOB, little consensus has been reached on their ages and origins. Our new structural, LA-ICP-MS zircon U-Pb and Hf isotopic data from the Baidunzi, Shibandun, Qiaowan and Wutongjing metamorphic complexes resolve current controversial relations. The metamorphic complexes have varied lithologies and structures. Detrital zircons from five para-metamorphic rocks yield predominantly Phanerozoic ages with single major peaks at ca. 276 Ma, 286 Ma, 427 Ma, 428 Ma and 461 Ma. Two orthogneisses have weighted mean ages of 294 ± 2 Ma and 304 ± 2 Ma with no Precambrian inherited zircons. Most Phanerozoic zircons show positive εHf(t) values indicating significant crustal growth in the Ordovician, Silurian and Permian. The imbricated fold-thrust deformation style combined with diagnostic zircon U-Pb-Hf isotopic data demonstrate that the metamorphic rocks developed in a subduction-accretion setting on an arc or active continental margin. This setting and conclusion are supported by the nearby occurrence of Ordovician-Silurian adakites, Nb-rich basalts, Carboniferous-Permian ophiolitic mélanges, and trench-type turbidites. Current data do not support the presence of a widespread Precambrian basement in the evolution of the BOC; the accretionary processes may have continued to the early Permian in this part of the CAOB. These relationships have meaningful implications for the interpretation of the tectonic attributions and origins of other

  8. Monzonitoid magmatism of the copper-porphyritic Lazurnoe deposit (South Primor'e): U-Pb and K-Ar geochronology and peculiarities of ore-bearing magma genesis by the data of isotopic-geochemical studies (United States)

    Sakhno, V. G.; Kovalenko, S. V.; Alenicheva, A. A.


    Magmatic rocks from the copper-porphyritic Lazurnoe deposit (Central Primor'e) have been studied. It has been found that rocks from the Lazurnyi massif are referred to gabbro-monzodiorites, monzodiorites, and monzo-granodiorites formed during two magmatic phases of different ages. The earlier phase is represented by gabbro-monzodiorites and diorites of the North Stock, and the later one, by gabbro-monzodiorites and monzo-grano-diorites of the South Stock. On the basis of isotopic dating by the U-Pb (SHRIMP) method for zircon and by the K-Ar method for hornblendes and biotites, the age of magmatic rocks is determined at 110 ± 4 for the earlier phase and at 103.5 ± 1.5 for the later one. Examination of the isotopic composition for Nd, Sr, Pb, Hf, δ18O, and REE spectra has shown that melts of the first phase are contaminated with crustal rocks and they are typical for a high degree of secondary alterations. Potassiumfeldspar, biotite, propylitic alterations, and sulfidization are manifested in these rocks. The rocks of the later stage of magmatism are characteristic for a primitive composition of isotopes and the absence of secondary alterations. They carry the features of adakite specifics that allows us to consider them derivatives of mantle generation under high fluid pressure. The intrusion of fluid-saturated melts of the second phase into the magmatic source of the first phase caused both an alteration pattern of rocks and copper-porphyritic mineralization. Isotopes of sulfur and oxygen allow us to consider the ore component to be of magmatic origin.

  9. 3D crustal velocity structure beneath the broadband seismic array in the Gyeongju area of Korea by receiver function analyses (United States)

    Lee, Dong Hun; Lee, Jung Mo; Cho, Hyun-Moo; Kang, Tae-Seob


    A temporary seismic array was in operation between October 2010 and March 2013 in the Gyeongju area of Korea. Teleseismic records of the seismic array appropriate for receiver function analysis were collected, and selected seismograms were split into five groups based on epicenters-the Banda-Molucca, Sumatra, Iran, Aleutian, and Vanuatu groups. 1D velocity structures beneath each seismic station were estimated by inverting the stacked receiver functions for possible groups. The inversion was done by applying a genetic algorithm, whereas surface wave dispersion data were used as constraints to avoid non-uniqueness in the inversion. The composite velocity structure was constructed by averaging the velocity structures weighted by the number of receiver functions used in stacking. The uncertainty analysis for the velocity structures showed that the average of 95% confidence intervals was ± 0.1 km/s. The 3D velocity structure was modeled through interpolation of 1D composite velocity structures. Moho depths were determined in each composite velocity structure based on the AK135-F S-wave velocity model, and the depths were similar to the H-κ analysis results. The deepest Moho depth in the study area was found to be 31.9 km, and the shallowest, was 25.9 km. The Moho discontinuity dips in a southwestward direction beneath the area. A low velocity layer was also detected between 4 and 14 km depth. Adakitic intrusions and/or a high geothermal gradient appear to be the causes of this low velocity layer. The 3D velocity structure can be used to reliably assess seismic hazards in this area.

  10. Subduction of young oceanic plates: A numerical study with application to aborted thermal-chemical plumes (United States)

    Blanco-Quintero, Idael Francisco; Gerya, Taras V.; GarcíA-Casco, Antonio; Castro, Antonio


    We investigated numerical models of initiation and subsequent evolution of subduction of young (10-30 Myr) oceanic lithosphere. Systematic numerical experiments were carried out by varying the age of the subducting plate (10, 12.5, 15, 17.5, 20, 25 and 30 Myr), the rate of induced convergence (2, 4 and 5 cm/yr) and the degree of hydration (0 and 2 wt% H2O) of the pre-existing weak oceanic fracture zone along which subduction is initiated. Despite the prescribed plate forcing, spontaneously retreating oceanic subduction with a pronounced magmatic arc and a backarc basin was obtained in a majority of the experiments. It was also found that the younger age of oceanic lithosphere results in more intense dehydration and partial melting of the slab during and after the induced subduction initiation due to the shallow dispositions of the isotherms. Partial melting of the subducted young crust may create thermal-chemical instabilities (cold plumes) that ascend along the slab-mantle interface until they either freeze at depth or detach from the slab and penetrate the upper plate lithosphere contributing to the nucleation and growth of a volcanic arc. Freezing of the plumes in the slab-mantle interface is favored by subduction of very young lithosphere (i.e., 10 Myr) at moderate rate (4 cm/yr) of convergence. Such aborted plumes may correspond to Cretaceous partially melted MORB-derived slab material and associated adakitic tonalitic-trondhjemitic rocks crystallized at ca. 50 km depth in the slab-mantle interface and exhumed in a subduction channel (serpentinite mélanges) in eastern Cuba.

  11. Petro-geochemical constraints on the source and evolution of magmas at El Misti volcano (Peru) (United States)

    Rivera, Marco; Martin, Hervé; Le Pennec, Jean-Luc; Thouret, Jean-Claude; Gourgaud, Alain; Gerbe, Marie-Christine


    El Misti volcano, a large and hazardous edifice of the Andean Central Volcanic Zone (CVZ) of southern Peru, consists of four main growth stages. Misti 1 (> 112 ka) is an old stratovolcano partly concealed by two younger stratocones (Misti 2, 112-40 ka; Misti 3, 38-11 ka), capped in turn by a recent summit cone (Misti 4, processes during their evolution, likely due to the presence of thick (65-70 km) continental crust beneath the CVZ in southern Peru. Geochemical evidence indicates that magmatic evolution is mostly controlled by Assimilation-Fractional Crystallisation (AFC) mechanisms. Modelling reveals a mass-assimilated/mass-fractionated ratio (ρ) ≤ 2.2, which suggests an assimilated crust fraction below 14 wt.% on average. Our isotopic data clearly identify the Proterozoic "Charcani gneiss" basement as the main contaminant. Both contamination and assimilation processes peaked at 30 wt.%, during the Misti 3 stage when rhyolites were generated. We ascribe the general depletion in HREE and Y and elevated La/Yb and Sr/Y ratios in El Misti samples to the enrichment of the mantle wedge source of the parental magmas by a felsic melt of adakitic composition and hydrous fluids. Our work highlights that El Misti's magmatic system has remained relatively homogeneous since at least 0.12 Ma, with a marked influence of the contaminating crust in the Late Pleistocene Misti 3 stage, which resulted in highly explosive eruptions. Andesitic-dacitic compositions are dominant in the Holocene and historical Misti 4 stage, and are expected for future volcanic events at El Misti.

  12. Genesis and open-system evolution of Quaternary magmas beneath southeastern margin of Tibet: Constraints from Sr-Nd-Pb-Hf isotope systematics (United States)

    Zou, Haibo; Ma, Mingjia; Fan, Qicheng; Xu, Bei; Li, Shuang-Qing; Zhao, Yongwei; King, David T.


    Post-collisional volcanic rocks on the Tibetan Plateau and its margins contain valuable information about the geodynamic processes associated with this Cenozoic continent-continent collision. The Quaternary Tengchong volcanic field at the southeastern margin of the Tibetan Plateau formed high-potassium calc-alkaline volcanic rocks. Herein, we present comprehensive Nd-Sr-Pb-Hf isotopic and elemental data for trachybasalts, basaltic trachyandesites, and trachyandesites from four Quaternary Tengchong volcanoes (Maanshan, Dayingshan, Heikongshan, and Laoguipo) in order to understand their magma genesis and evolution as well as tectonic significance. Good correlations between SiO2 content and the ratios 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, and 177Hf/176Hf for these Quaternary volcanics strongly suggest that the combined assimilation and fractional crystallization (AFC) was an important process in the origin of basaltic trachyandesites and trachyandesites. High Y and Yb contents and low Sr/Y ratios of these basaltic trachyandesites and trachyandesites are uncharacteristic of adakites that formed by partial melting of eclogitic lower crust or partial melting of basaltic oceanic crust with eclogite as a restite. A combined assimilation-fractional crystallization model is proposed for these basaltic trachyandesites and trachyandesites. Nd-Sr-Pb-Hf isotopes for the uncontaminated Tengchong magma (trachybasalts with SiO2 5.5% wt.%) reflect a heterogeneous enriched mantle source. High Th/U, Th/Ta, and Rb/Nb ratios and Nd-Sr-Pb-Hf isotope characteristics of the uncontaminated magmas suggest that the enriched mantle beneath Tengchong formed as a result of subduction of clay-rich sediments, which probably came from the Indian continental plate. Partial melting of the enriched mantle was generated by deep continental subduction coupled with recent regional extension in the Tengchong area.

  13. Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa Terrane (United States)

    Wei, Youqing; Zhao, Zhidan; Niu, Yaoling; Zhu, Di-Cheng; Liu, Dong; Wang, Qing; Hou, Zengqian; Mo, Xuanxue; Wei, Jiuchuan


    Understanding the geological history of the Lhasa Terrane prior to the India-Asia collision ( 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene ( 18-10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183-174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr-Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I-S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane.

  14. Zircon U-Pb dating and geochemical study of the Xianggou granite in the Ma’anqiao gold deposit and its relationship with gold mineralization

    Institute of Scientific and Technical Information of China (English)

    LEE; Ben


    Single zircon LA-ICP-MS U-Pb dating and lithogeochemical studies have been performed on the Xianggou monzonitic granitic porphyry outcropped in the Ma’anqiao gold deposit.A weighted average U-Pb age of 242.0±0.8 Ma for Xianggou monzonitic porphyry has been obtained.This corresponds with the conclusions of previous studies indicating a syn-orogenic age (242±21 Ma) of the Qinling Orogenic Belt,suggesting that the formation of the Xianggou granite should be associated with the collisional event of the North China Plate and the Yangtze Plate in the Indosinian period.The Xianggou granite is characterized by the high silicon and alkali of high K calc-alkaline series granites.It is rich in Al (Al2O3=14.49%-15.61%) and Sr (457.10-630.82 ppm),poor in Y (<16 ppm) and HREE (Yb<0.45 ppm),and exhibits high ratios of Sr/Y (76.24-97.34) and (La/Yb)N (29.65-46.10),as well as strongly fractionated REE patterns.These geochemical characteristics suggest the Xianggou granite can be classified as C-type adakitic rock.The initial Sr isotope ratios for the Xianggou granite vary from 0.70642 to 0.70668,εNd(t) values from -4.54 to -3.98,and TDM values from 1152 Ma to 1220 Ma.The low εNd(t) and ISr and high TDM values,as well as Na2O/K2O ratios of the Xianggou granite are close to 1 (Na2O/K2O=0.95-1.10),indicating that it is not an I-type adakite formed by partial melting of the subducting oceanic crust,nor adakitic rock formed by melting of the underplated basaltic lower crust,but the product of partial melting of the nonunderplated basaltic thickened lower crust.Zircons from the Xianggou pluton have a homogeneous Hf isotopic composition with negative εHf(t) values (between -9.7 and -5.9,with an average of -6.9),indicating that the rock-forming materials were mostly extracted from the ancient crust,not from the depleted mantle.The Xianggou monzonitic granitic porphyry is rich in LILE and LREE and depleted in HSFE,HREE and Y;the composition of trace element and REE are similar to

  15. The Origin of ‘OIB-Type’ Magmas in the Central Mexican Volcanic Belt (United States)

    Straub, S. M.; Gomez-Tuena, A.; Zellmer, G. F.; Cai, Y.; Stuart, F. M.; Espinasa-Perena, R.; Langmuir, C. H.; Goldstein, S. L.


    Many models consider a primary mantle origin of high-Mg andesites, but the subarc mantle of arcs producing high-Mg andesites remains poorly defined. In the monogenetic volcanic field of Sierra Chichinautzin (central Mexican Volcanic Belt), high-Mg andesites are spatially and temporally intimately associated with mildly alkaline basalts and basaltic andesites, variously referred to as ‘OIB-type’, ‘intraplate’ or ‘high-Nb arc basalts’ (Wallace and Carmichael 1999, Contrib Mineral Petrol; Schaaf et al. 2005, J Petrol). ‘OIB-type’ magmas and high-Mg andesites have erupted within a few hundreds to thousands of years from vents only a few kilometers apart, or may even have erupted jointly from single vents. It has been suggested that these ‘OIB-type’ magmas were melts from subarc mantle yet unmodified by subduction fluxes while high-Mg andesites were produced from mantle sources residual to the ‘OIB-type’ magmas. In order to test this model, we investigated ‘OIB-type’ magmas erupting from three young and closely spaced monogenetic volcanoes in the Sierra Chichinautzin Volcanic Field (V. Chichinautzin, V. Suchiooc, Cuescomates vent). The primitive olivine-phyric alkaline basalts and basaltic andesites (SiO2 = 49.6-53.5 wt%; Mg#=62-68 and MgO= 6.5-8.3 wt%) have high Ni (97-179 ppm), Nb (18-34 ppm), Nb/La (0.9-1.2) and 3He/4He ratios (R/Ra = 7.3-8.0) typical of near-primary mantle magmas unaffected by the passage through the ~47 km thick continental crust. However, all ‘OIB-type’ magmas contain high-Ni olivines that are indicative of siliceous slab melts infiltrating and reacting with peridotite mantle (Straub et al., 2008, G-cubed; Wang & Gaetani 2008, Contrib Mineral Petrol). Significant slab additions to the mantle source of the ‘OIB-type’ magmas are further confirmed by Sr-Nd-Pb systematics. We suggest that ‘OIB-type’ arc magmas reflect fertilization of a pre-existing MORB-type subarc mantle by enriched, little fractionated slab

  16. Geochemistry of komatiites and basalts from the Rio das Velhas and Pitangui greenstone belts, São Francisco Craton, Brazil: Implications for the origin, evolution, and tectonic setting (United States)

    Verma, Sanjeet K.; Oliveira, Elson P.; Silva, Paola M.; Moreno, Juan A.; Amaral, Wagner S.


    The Neoarchean Rio das Velhas and Pitangui greenstone belts are situated in the southern São Francisco Craton, Minas Gerais, Brazil. These greenstone belts were formed between ca. 2.79-2.73 Ga, and consist mostly of mafic to ultramafic volcanics and clastic sediments, with minor chemical sediments and felsic volcanics that were metamorphosed under greenschist facies. Komatiites are found only in the Rio das Velhas greenstone belt, which is composed of high-MgO volcanic rocks that have been identified as komatiites and high-Mg basalts, based on their distinctive geochemical characteristics. The Rio das Velhas komatiites are composed of tremolite + actinolite + serpentine + albite with a relict spinifex-texture. The Rio das Velhas komatiites have a high magnesium content ((MgO)adj ≥ 28 wt.%), an Al-undepleted Munro-type [(Al2O3/TiO2)adj and (CaO/Al2O3)adj] ratio ranging from 27 to 47 and 0.48 to 0.89, relatively low abundances of incompatible elements, a depletion of light rare earth elements (LREE), a pattern of non-fractionated heavy rare- earth elements (HREE), and a low (Gd/Yb)PM ratio (≤ 1.0). Negative Ce anomalies suggest that alteration occurred during greenschist facies metamorphism for the komatiites and high-Mg basalts. The low [(Gd/Yb)PM 18] and high HREE, Y, and Zr content suggest that the Rio das Velhas komatiites were derived from the shallow upper mantle without garnet involvement in the residue. The chemical compositions [(Al2O3/TiO2)adj, (FeO)adj, (MgO)adj, (CaO/Al2O3)adj, Na, Th, Ta, Ni, Cr, Zr, Y, Hf, and REE] indicate that the formation of the komatiites, high-Mg basalts and basalts occurred at different depths and temperatures in a heterogeneous mantle. The komatiites and high-Mg basalts melted at liquidus temperatures of 1450-1550 °C. The Pitangui basalts are enriched in the highly incompatible LILE (large-ion lithophile elements) relative to the moderately incompatible HFS (high field strength) elements. The Zr/Th ratio ranging from 76 to

  17. SHRIMP U-Pb dating and geochemistry of the Cretaceous plutonic rocks in the Korean Peninsula: A new tectonic model of the Cretaceous Korean Peninsula (United States)

    Kim, Sung Won; Kwon, Sanghoon; Park, Seung-Ik; Lee, Changyeol; Cho, Deung-Lyong; Lee, Hong-Jin; Ko, Kyoungtae; Kim, Sook Ju


    The Cretaceous tectonomagmatism of the Korean Peninsula was examined based on geochemical and geochronological data of the Cretaceous plutonic rocks, along with distribution of volcano-sedimentary nonmarine N- to NE-trending fault bounded sedimentary basins. We conducted sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages and whole-rock geochemical compositions of 21 Cretaceous plutonic rocks, together with previously published data, from the central to southern Korean Peninsula. Four age groups of plutonic rocks were identified: Group I (ca. 119-106 Ma) in the northern to central area, Group II (ca. 99-87 Ma) in the central southern area, Group III (ca. 85-82 Ma) in the central to southern area, and Group IV (ca. 76-67 Ma) in the southernmost area. These results indicate a sporadic trenchward-younging trend of the Cretaceous magmatism in the Korean Peninsula. The Group I, II, and III rocks are dominated by high-K calc-alkaline I-type rocks with rift-related A-type granitoids. In contrast, the Group IV rocks are high-K calc-alkaline I-type plutonic rocks with no A-type rocks. The geochemical signatures of the entire groups indicated LREEs (light rare earth elements) enrichments and negative Nb, Ta, and Ti anomalies, indicating normal arc magmatism. A new tectonic model of the Cretaceous Korean Peninsula was proposed based on temporal and spatial distribution of the Cretaceous plutons represented by four age groups; 1) magmatic quiescence throughout the Korean Peninsula from ca. 160 to 120 Ma, 2) intrusions of the I- and A-type granitoids in the northern and central Korean Peninsula (Group I plutonic rocks from ca. 120 to 100 Ma) resulted from the partial melting of the lower continental crust due to the rollback of the Izanagi plate expressed as the conversion from flat-lying subduction to normal subduction. The Gyeongsang nonmarine sedimentary rift basin in the Korean Peninsula and adakite magmatism preserved in the present-day Japanese Islands

  18. Sr-Nd-Pb isotopic compositions of the lower crust beneath northern Tarim: insights from igneous rocks in the Kuluketage area, NW China (United States)

    Zhang, Yan; Wei, Xun; Xu, Yi-Gang; Long, Xiao-Ping; Shi, Xue-Fa; Zhao, Jian-Xin; Feng, Yue-Xing


    The composition of lower crust of the Tarim Craton in NW China is essential to understand the petrogenesis of the ~290-275 Ma Tarim basalts and associated intermediate-felsic rocks. However, it remains poorly constrained because extremely sparse granulite terrains or granulite xenoliths have been found in the Tarim Craton. New trace element and Sr-Nd-Pb isotopic data are reported for the Neoarchean and Neoproterozoic igneous rocks widely distributed in the northern margin of the Tarim Craton. The Neoarchean granitic gneisses show fractionated REE (rare earth element) patterns [(La/Yb) N = 12-58, YbN = 10.6-36] with pronounced negative Nb-Ta and Ti anomalies. These features, together with negative ɛNdi (-0.7 to -3.2) suggest that they were derived from melting of mafic lower crust. The Neoproterozoic biotite granodiorites are strongly depleted in HREE with (La/Yb) N up to 55. They are characterized by high Sr (671-789 ppm) but very low Y (7.10-8.06 ppm) and Yb contents (0.47-0.58 ppm), showing typical features of adakitic rocks. The samples with different SiO2 contents display identical 87Sr/86Sri (0.7101-0.7103), ɛNdi (-14.1 to -15.7) and Pb isotopes (208Pb/204Pbi = 36.94-37.07). These features together with arc-like trace element patterns suggest that they were derived from melting of thickened lower crust. In comparison, the Neoproterozoic hornblende-biotite granodiorites have similar trace element compositions except for weaker depletion in HREE and have lower 87Sr/86Sri (0.7078) and initial Pb isotopes, and higher ɛNdi (-12.3 to -12.7). This suggests that they were formed by melting of old lower continental crust at a shallower depth than the biotite granodiorites. These rocks were derived from the lower crust, thus providing valuable information on the nature of the lower crust beneath northern Tarim. Combined with published data, the 87Sr/86Sri, ɛNdi, 206Pb/204Pbi and ɛHfi of the northern Tarim lower crust ranges from 0.7055 to 0.7103, from -12 to -17

  19. Reconciling evidence for Tethyan intra-oceanic subduction and a two-stage collision between India and Eurasia (United States)

    Gibbons, Ana D.; Zahirovic, Sabin; Dietmar Müller, R.; Whittaker, Joanne M.; Yatheesh, Vadakkeyakath


    We present a plate tectonic model for the India-Eurasia collision that includes a time-dependent network of evolving plate boundaries with synthetic plates constructed for now-subducted Tethyan ocean floor, including back-arc basins that formed on the southern Eurasian margin. Southern Eurasia and Southeast Asia are riddled with dismembered oceanic arcs indicating long-lived intra-oceanic subduction. This intra-oceanic subduction may have extended further west into the India-Eurasia convergence zone in the NeoTethys, which was consumed during Greater India's northward trajectory towards Eurasia from the Early Cretaceous. Fragments of obducted oceanic crust within the Himalayan Yarlung-Tsangpo Suture Zone, between India and Eurasia, cluster around two age groups, the Late Jurassic and mid Cretaceous (Barremian-Aptian). The adakitic, boninitic and MORB-affinities of the various ophiolites along strike suggest that there was at least one generation of intra-oceanic subduction, whose plate boundary configuration remains uncertain, though it is best preserved in the Kohistan-Ladakh Arc. Paleomagnetic and magmatic characterisation studies from the ophiolites suggest that the intra-oceanic arc was as far south as the equator during the Early Cretaceous before subduction resumed further north beneath the southern Eurasian margin (Lhasa terrane) to consume the back-arc basin. During ~80-65 Ma, a hiatus in subduction-related magmatism along the southern Lhasa terrane may indicate the approach of the back-arc spreading centre towards the active Andean-style margin. We incorporate these observations into a regional, self-consistent plate tectonic model for the dispersal of East Gondwana, simultaneously considering geophysical data and seafloor spreading histories from abyssal plains offshore West Australia and East Antarctica, including Jurassic seafloor age data from offshore NW Australia that limits northern Greater India to a maximum of ~1000 km. This Greater India collided

  20. Contamination of the Convecting Mantle in Eastern Tethyan 'Subduction Factories' (United States)

    Flower, M. F.; Nguyen, T. H.


    Fe- and HFSE-rich MORB and OIB. 3) LILE and, presumably, LREE variation is less constrained by solid-melt equilibria and plausibly attributed to metasomatism. We therefore suggest that refractory mantle wedge sources represent 'pods' of lithospheric mantle rheologically changed by slab-derived, hydrous contamination, and, in response to downward drag from subducting slabs (or slab fragments), incorporated by the convecting asthenosphere. Partial melting at higher pressures of slab-entrained sediment or eclogitized oceanic crust will contribute granitic and adakitic melt fractions, respectively, to convecting slab-contiguous mantle. The combined effects of relative buoyancy and decreased viscosity following pressure-induced dehydration predispose refractory mantle 'pods' to decompression thereby yielding 'low-pressure' primitive magmas with 'inherited' LILE, HFSE, LILE (etc.) attributes. On this basis, we propose a testable model for mantle wedge evolution during the closing stages of a typical Wilson cycle.

  1. Geochemical features of the mantle source beneath Irazú and Turrialba volcanoes, Costa Rica (United States)

    Rizzo, A. L.; Di Piazza, A.; Alvarado-Induni, G.; Carapezza, M. L.; de Moor, M. J.; Martinez, M.


    Irazú and Turrialba are active arc volcanoes located at the southeastern terminus of the Central American Volcanic Arc (CAVA). These volcanoes have been considered in literature as "twin volcanoes" or as a linked volcanic system. Effectively their proximity may lead to the assumption that they share a common plumbing system, but geochemical data on rocks and fluids reveal a more complicated framework. In this study, we analyzed the rock chemistry of a selected suite of eruptive products emitted in the last 50ka from Irazú volcano, including products from the 1963-1965 eruption. We also analyzed He-Ne-Ar isotopes in fluid inclusions hosted in olivines and pyroxenes hand-picked from these products, and we compared our results with those available for Irazú and the neighboring Turrialba. Rock samples from Irazú are basalts to andesites with MgO content ranging between 3 and 8 wt%, with a variability that follows typical trends of fractional crystallization. The pattern of trace elements is subduction-related with an OIB-like component, testified by an unusual enrichment (e.g., K, REE; e.g., Benjamin et al., 2007 and references therein), associated with the subduction of the Galapagos seamounts. In addition, Turrialba volcano shows the presence of andesites with adakite-like affinity (Di Piazza et al., 2015) which is not observed in rocks from Irazú . The 3He/4He ratio measured in olivine crystals from Irazú varies from 7.1 to 7.5 Ra, overlapping the measurements performed in surface gases (7.2 Ra; Fischer et al., 2002). This range is also comprised in the measurements carried out in gases and rocks from Turrialba (7.0-8.1 Ra; Di Piazza et al., 2015), which showed the presence of a MORB- and OIB-like component at the mantle source. Based on these evidences, we propose that the mantle beneath Irazú reflects an intermediate composition respect to the extreme components recognized at Turrialba. Irazú shows more typical arc-like geochemical signatures, whereas

  2. Post-collisional granitoids from the Dabie orogen: New evidence for partial melting of a thickened continental crust (United States)

    He, Yongsheng; Li, Shuguang; Hoefs, Jochen; Huang, Fang; Liu, Sheng-Ao; Hou, Zhenhui


    The geological implications of granitoid magmas with high Sr/Y and La/Yb are debated because these signatures can be produced by multiple processes. This study presents comprehensive major and trace element compositions and zircon SHRIMP U-Pb age data of 81 early Cretaceous granitoids and 4 mafic enclaves from the Dabie orogen to investigate partial melting of the thickened lower continental crust (LCC). On the basis of Sr/Y ratios, granitoids can be grouped into two magma series: (i) high Sr/Y granitoids (HSG) and (ii) normal granitoids with low Sr/Y. Relative to normal granitoids, HSG display the following distinct chemical features: (1) at given SiO 2 and CaO contents, the HSG have significantly higher Sr than normal granitoids, defining two different trends in Sr versus SiO 2, CaO diagrams; (2) highly depleted heavy rare earth element (REE) relative to middle and light REE with (Dy/Yb) N and (La/Yb) N up to 3.2 and 151, respectively; (3) variable and higher Nb/Ta; and (4) positive correlations among Sr/Y, (Dy/Yb) N, (La/Yb) N, and Nb/Ta. High Sr/Y, (La/Yb) N, (Dy/Yb) N, and Sr/CaO of HSG do not correlate with major elements (e.g., SiO 2). Large variations in these ratios at a given SiO 2 content indicate that these features do not reflect magma mixing or fractionation. HSG have higher Sr at a given CaO content and larger variation of (Dy/Yb) N than old crustal rocks (including exposed basement, global mafic LCC xenoliths, high Sr/Y TTG suites, and adakites in modern arcs). This precludes inheritance of the HSG chemical features from these source rocks. Instead, the chemical features of the HSG are best explained by partial melting of the thickened LCC with garnet-dominant, plagioclase-poor, and rutile-present residual lithologies. The coupled chemical features of the HSG are not observed in post-collisional granitoids younger than ca.130 Ma, indicating removal of the eclogitic source and/or residuum of HSG underneath the orogen. These characteristic chemical

  3. Early Earth melt production in a subduction zone, a petrological model (United States)

    Magni, V.; Bouilhol, P.; Van Hunen, J.; Moyen, J.


    A large part of the Archean continental crust is made of a composite rock assemblage dominated by granitoids belonging to the TTG series (tonalite-trondhejmeite-granodiorite). The modus operandi of this sodic granitoids still disputed. If the modern processes leading to continental crust formation at convergent margins are well constrained, the extrapolation to early Earth conditions is hazardous, because the composition of Earth's early crust can be achieved through several processes. However, an 'arc' signature seems to be present in TTGs, suggesting a formation of continental crust in subduction zone settings. Moreover, they show strong similarities with modern adakites, which are thought to be formed by melting of the oceanic subducting crust. We present the results of a study where numerical models of subduction are integrated with a thermodynamic database. Our goal is to investigate under which conditions slab melting can be achieved if at all. We particularly focus our attention on the fate of water, since it is a component that is essential to the formation of TTG series, independently of the petrogenetical scenario preferred. The amount and composition of water bearing fluids in a subduction zone is controlled by slab devolatilization, and influence both the melting regime and the melt composition. Our reference model of an early Earth regime, with a high mantle potential temperature, show that the slab dehydrates early, ending up being composed of a dry eclogites. Importantly, our models show that dehydration melting is not achieved in the slab crust; yet, water-present melting of the 'dry' eclogites can be achieved if a dehydration reaction occurs in the deeper portion of the slab, fuelling the melting reaction with water. Moreover, the dehydration reactions that occurred within the slab are able to metasomatize the overlying mantle wedge, forming hydrated peridotites, that becomes a melt source when dragged down by corner-flow. Our results show the

  4. Mesozoic magmatism and copper polymetallic mineralization processes in the Shanghang-Datian region,Fujian Province,Southeast China

    Institute of Scientific and Technical Information of China (English)

    MAO Jianren; HU Qing; XU Naizheng; CHEN Rong; YE Haimin; ZHAO Xilin


    Various isotopic ages were reported for four granite plutons in the area studied, i. e. , the Tangquan pluton (185-158 Ma); the Zijinshan pluton (157-145 Ma); the Caixi pluton (133 Ma);and the Sifang pluton (108-105 Ma). The Tangquan and Zijinshan plutons belong to Early-Middle Jurassic and Late Jurassic of Early-Mesozoic respectively, and the Caixi and Sifang plutons belong to EarlyCretaceous of Late Mesozoic. Both the Tangquan and Sifang plutons, which are the metaluminous granites with A/CNK < 1.0, are considered to possess the geochemical characteristics of adakite rich in Sr, Ba and poor in HREE, Y, Yb, and are regarded as the most potential host rocks of copper ores. The Zijinshan pluton is regarded as a peraluminous granite with A/CNK > 1.1, and possesses the geochemical features of crust-derived muddy materials resultant from partial melting with enrichments in K, Rb, Th, Y, HREE and depletions in Sr, Ba, and Ti. The Caixi pluton is a weakly peraluminous granite with A/CNK = 1.0-1.1, and its geochemical characteristics are intermediate between the Zijinshan pluton and the Sifang pluton. The Tangquan pluton with higher Na2O contents, which resulted from partial melting of Proterozoic thick lower-crust derived basic rocks in response to underplating of mantle-derived basic magma, is one of the major host rocks of the metallogenic series of copper, iron and polymetallic deposits. The Sifang pluton with higher K2O contents, which was mixed between middle-lower crust-derived granite magma by partial melting and mantle-derived high-K basic magma, giving rise to the increment of K2O in the melt, and extracted large amounts of copper and other metals, as well as sulphur, is one of the major host rocks of the metallogenic series of porphyry copper, gold and polymetallic deposits. Petrological records have shown that there has occurred lithosphere extension since the Early-Middle Jurassic ( 180 Ma) in the region, and the formation of Zijinshan peraluminous

  5. Early Cretaceous volcanic mechanism in Jianshan of Xingcheng area,Liaoning and its lithogeochemical characteristics%辽宁兴城尖山早白垩世火山机构及岩石地球化学特征

    Institute of Scientific and Technical Information of China (English)

    王睿; 李世超; 刘正宏; 秦硕; 黄鸿琨; 杨进益; 苗立志


    The petrology and petrography of Jianshan volcanic mecganism in Xingcheng,Liaoning have been analyzed,and the geochemistry of hornblende andesites were studied.The results show that the hornblende andes-ites are characterized by SiO2 =58. 42%~60. 42%,MgO=1 . 39%~3. 08%,Mg#=31 ~50,Al2 O3 =1 6. 1 7%~1 7. 5%,Sr=(387~1 325) ×1 0 -6,Yb=(1 . 1 5 ~1 . 57) ×1 0 -6,Y=(1 2. 1 ~1 6. 8) ×1 0 -6,respec-tively.In addition,the volcanic rocks are enrichment in LREE and LILE and depletion in HREE,with high Sr and Sr/Y values and low Y and Yb values,showing the geochemical characteristics of adakite.However,they are low in Mg#,indicating the volcanic rocks may originate by partial melting of the thickened mafic lower crust,and could be related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.%对辽宁兴城尖山火山机构的岩性-岩相学特征进行了分析,并对角闪安山岩进行了岩石地球化学研究。结果表明角闪安山岩SiO2=58.42%~60.42%,Al2 O3=16.17%~17.5%,MgO=1.39%~3.08%,Mg#=31~50,Sr=(387~1325)×10-6,Yb =(1.15~1.57)×10-6,Y =(12.1~16.8)×10-6。岩石富集轻稀土元素及大离子亲石元素,亏损高场强元素,高Sr和Sr/Y比值,低Y和Yb,显示出埃达克岩的地球化学特征,但其Mg#较低,表明该类火山岩可能是加厚的基性下地壳部分熔融的产物,可能与早白垩世太平洋板块的俯冲构造背景有关。

  6. How many sutures in the southern Central Asian Orogenic Belt: Insights from East Xinjiang–West Gansu (NW China?

    Directory of Open Access Journals (Sweden)

    Wenjiao Xiao


    Full Text Available How ophiolitic mélanges can be defined as sutures is controversial with regard to accretionary orogenesis and continental growth. The Chinese Altay, East Junggar, Tianshan, and Beishan belts of the southern Central Asian Orogenic Belt (CAOB in Northwest China, offer a special natural laboratory to resolve this puzzle. In the Chinese Altay, the Erqis unit consists of ophiolitic mélanges and coherent assemblages, forming a Paleozoic accretionary complex. At least two ophiolitic mélanges (Armantai, and Kelameili in East Junggar, characterized by imbricated ophiolitic mélanges, Nb-enriched basalts, adakitic rocks and volcanic rocks, belong to a Devonian–Carboniferous intra-oceanic island arc with some Paleozoic ophiolites, superimposed by Permian arc volcanism. In the Tianshan, ophiolitic mélanges like Kanggurtag, North Tianshan, and South Tianshan occur as part of some Paleozoic accretionary complexes related to amalgamation of arc terranes. In the Beishan there are also several ophiolitic mélanges, including the Hongshishan, Xingxingxia–Shibangjing, Hongliuhe–Xichangjing, and Liuyuan ophiolitic units. Most ophiolitic mélanges in the study area are characterized by ultramafic, mafic and other components, which are juxtaposed, or even emplaced as lenses and knockers in a matrix of some coherent units. The tectonic settings of various components are different, and some adjacent units in the same mélange show contrasting different tectonic settings. The formation ages of these various components are in a wide spectrum, varying from Neoproterozoic to Permian. Therefore we cannot assume that these ophiolitic mélanges always form in linear sutures as a result of the closure of specific oceans. Often the ophiolitic components formed either as the substrate of intra-oceanic arcs, or were accreted as lenses or knockers in subduction-accretion complexes. Using published age and paleogeographic constraints, we propose the presence of (1 a major

  7. LA--ICP--MS zircon U--Pb age of Dongliang pluton in Balinyouqi,Inner Mongolia and its geochemical characteristics%内蒙古巴林右旗东梁岩体 LA--ICP--MS 锆石 U--Pb 定年及地球化学特征

    Institute of Scientific and Technical Information of China (English)

    王璐; 赵庆英; 李鹏川; 李子昊; 邱士龙; 田子龙


    The study of the petrologic,chronological and geochemical characteristics of Dongliang pluton in Balinyouqi,Inner Mongolia shows that the lithology of Dongliang pluton is of quartz diorite,while the LA--ICP--MS zircon U --Pb dating shows the weighted average age as (251.9 ±4.4) Ma,representing the Dongliang pluton formed in the Early Triassic.The geochemical characteristics indicate that the rocks are enriched in Si,Al,Na, and depleted in Mg,K.The A /CNK is 0.98 ~1.11,showing the pluton is of calc-alkalic metaluminous-weakly peraluminous rocks.The quartz diorite is rich in LREE,depleted in HREE and without Eu,Ce anomaly,which shows the characteristics of high Sr,low Y and Yb,belonging to adakite rocks.Combined with previous resear-ches,the authors believe that the magma of Dongliang pluton may be originated from the partial melting of juvenile crust caused by the collision and suturing of Siberian Plate and North China Plate.%本文对内蒙古巴林右旗东梁岩体进行的岩石学、年代学和地球化学研究显示,东梁岩体岩性为石英闪长岩,LA-ICP-MS 锆石 U-Pb 定年加权平均年龄为(251.9±4.4)Ma,指示东梁岩体形成于早三叠世。地球化学特征表明岩石富硅、铝、钠,贫镁、钾,A /CNK =0.98~1.11,属于钙碱性准铝质-弱过铝质岩石,轻稀土富集,重稀土亏损,不具 Eu 和 Ce 异常,具有高 Sr、低 Y、低 Yb 的特征,属于埃达克岩。结合区域已有研究成果,认为东梁岩体的岩浆可能来源于西伯利亚板块和华北板块碰撞拼合所导致的新生地壳部分熔融。

  8. How many sutures in the southern Central Asian Orogenic Belt:Insights from East XinjiangeWest Gansu (NW China)?

    Institute of Scientific and Technical Information of China (English)

    Wenjiao Xiao; Jun Luo; Chunming Han; Wei Liu; Bo Wan; Ji’en Zhang; Songjian Ao; Zhiyong Zhang; Dongfang Song; Zhonghua Tian


    How ophiolitic mélanges can be defined as sutures is controversial with regard to accretionary orogenesis and continental growth. The Chinese Altay, East Junggar, Tianshan, and Beishan belts of the southern Central Asian Orogenic Belt (CAOB) in Northwest China, offer a special natural laboratory to resolve this puzzle. In the Chinese Altay, the Erqis unit consists of ophiolitic mélanges and coherent assemblages, forming a Paleozoic accretionary complex. At least two ophiolitic mélanges (Armantai, and Kelameili) in East Junggar, characterized by imbricated ophiolitic mélanges, Nb-enriched basalts, adakitic rocks and volcanic rocks, belong to a DevonianeCarboniferous intra-oceanic island arc with some Paleozoic ophiolites, superimposed by Permian arc volcanism. In the Tianshan, ophiolitic mélanges like Kanggurtag, North Tianshan, and South Tianshan occur as part of some Paleozoic accretionary complexes related to amalgamation of arc terranes. In the Beishan there are also several ophiolitic mélanges, including the Hongshishan, XingxingxiaeShibangjing, HongliuheeXichangjing, and Liuyuan ophiolitic units. Most ophiolitic mélanges in the study area are characterized by ultramafic, mafic and other components, which are juxtaposed, or even emplaced as lenses and knockers in a matrix of some coherent units. The tectonic settings of various components are different, and some adjacent units in the same mélange show contrasting different tectonic settings. The formation ages of these various com-ponents are in a wide spectrum, varying from Neoproterozoic to Permian. Therefore we cannot assume that these ophiolitic mélanges always form in linear sutures as a result of the closure of specific oceans. Often the ophiolitic components formed either as the substrate of intra-oceanic arcs, or were accreted as lenses or knockers in subduction-accretion complexes. Using published age and paleogeographic con-straints, we propose the presence of (1) a major early Paleozoic

  9. Ridge Subduction Beneath the Americas: Synthesis and New Research on Anomalous Tectonism and Magmatism (United States)

    Thorkelson, D. J.; Madsen, J. K.; Breitsprecher, K.; Groome, W. G.; Sluggett, C.


    The west coast of the Americas has been repeatedly affected by ridge-trench interactions from Mesozoic to Recent time. Beneath North America, subduction of the Kula-Farallon, Kula-Resurrection and Farallon- Resurrection spreading ridges resulted in anomalous and time-transgressive forearc to backarc magmatism and related tectonism from the Late Cretaceous to the Eocene. Following consumption and redistribution of the Kula and Resurrection plates, the Neogene Farallon-Pacific ridge system intersected the North American trench in two locations - western Canada and northwestern Mexico / southwestern United States - causing pronounced magmatic and tectonic effects that continue to the present. Beneath Central America, divergent subduction of the Nazca and Cocos plates led to development of a slab window, with a present location beneath Panama and a probable pre-Pliocene position beneath Columbia or Ecuador. Patagonia has been the site of localized ridge subduction from the Eocene to the Recent, with the Phoenix-Farallon ridge subducting from the Eocene to the early Miocene, and the Nazca-Antarctic ridge from the Miocene to the present. Antarctica experienced diverging Antarctic-Phoenix plate subduction from the Eocene to the Pliocene. In all cases, normal arc magmatism was interrupted or eliminated by anomalous igneous activity ranging in signature from adakitic to intraplate. Our current research involves geochemical, tectonic, and thermal modeling of slab window environments. A new geochemical analysis on the effects of Miocene to Recent subduction of the northern segment of the Farallon (Juan de Fuca)-Pacific ridge is underway. A symmetrical arc-intraplate-arc geochemical pattern is evident in a transect from the northern Cascade Arc, through the volcanic fields of British Columbia, Yukon and eastern Alaska, and into the Aleutian Arc. This pattern can be explained by Neogene displacement of the arc-metasomatized mantle wedge caused by upwelling oceanic

  10. Source variation for Mesozoic granitoid plutons in the White-Inyo Range, California, and implications for changes in the lithospheric structure (United States)

    Gammel, E.; Nabelek, P. I.; Phillips, E. H. W.; Scott, S. R.; Sims, K. W. W.


    The White-Inyo Range (WIR) of eastern California lies to the east of Owen's Valley and the Sierra Nevada batholith (SNB). Over twenty recognized Mesozoic, granitic to gabbroic plutons intruded into Precambrian and Cambrian sedimentary units that were previously metamorphosed to the greenschist facies. These plutons represent intrusive equivalents of volcanics erupted during two magmatic events at ca. 180-167 Ma and 102-86 Ma (Coleman et al, 2003). The motivation of this study is to understand changes in magma sources over this time period. We propose there is a time-transgressive change in source material in the WIR. Preliminary trace element data suggest that Jurassic plutons were sourced from deep crustal material, whereas later Cretaceous plutons may have had a shallower origin. This is supported by high Sr/Y ratios in the Jurassic plutons (up to 300) and relatively lower ratios in Cretaceous plutons (down to 14). Chiaradia (2015) suggests elevated Sr/Y ratios are directly linked to increasing crustal thickness, therefore the WIR plutons may record the period of crustal thinning in this region or maturation of the crust that allowed shallower melting in the Cretaceous. The highest values also suggest possible adakitic source material. REE patterns suggest that the youngest plutons (e.g. Sage Hen Flat) are more similar to samples collected from the eastern Sierra Nevada batholith than older plutons with higher La/Yb ratios. Relatively flat patterns REE patterns of Tertiary basalts and a late diabase dike in the WIR are also similar to SNB samples. Another goal of this study is to determine the degree of mixing as a function of time during the emplacement of plutons in the range. Field and petrographic analyses suggest that older plutons represent more mafic materials and younger plutons are more granitic with mafic enclaves. We propose either (1) older plutons represent initial lower lithosphere melting, and with time, there is an increase of incorporation of

  11. Andesite Petrogenesis in Nevado de Toluca Stratovolcano, Central Mexico (United States)

    Gomez-Tuena, A.; Capra, L.; Cai, Y.; Goldstein, S. L.


    A popular model for andesite petrogenesis in continental arcs involves a hydrous parental basalt that fractionates and probably assimilates continental crust during ascent. Nevertheless, andesites erupted from polygenetic volcanoes in the Trans-Mexican Volcanic Belt are not entirely consistent with this scenario because: (1) they display a shift to higher SiO2 contents at similar Mg# than true basalts, (2) they trend to lower HREE and HFSE contents with increasing SiO2, and (3) they often show correlated isotopic compositions with proxies for slab inputs but not with fractionation indexes. Young andesites from Toluca stratovolcano (1-0.042 Ma) also display modest adakite-like features (Sr/YToluca rock-suite revealed that some other andesites (2.6-1 Ma) also exhibit very strong negative Ce (Ce/Ce~0.25) anomalies, fractionated HREE patterns (Gd/Yb~4.2), as well as low Zr/Sm (~12.6), and Sr/Y (~12) ratios. These features are not easily explained by low or even high pressure differentiation from a common primitive magma, unless enormous quantities of fractionating accessory minerals are taken into account. And yet these geochemical signals are almost identical to those observed in the pelagic sedimentary horizon of the subducted Cocos plate sampled at DSDP site 487, and thus provide strong evidence for slab-derived sediment contributions to the petrogenesis of Toluca andesites. Since sediment transfer to the Toluca source must have occurred in the form of a silicate melt, the new evidence brings further support to the slab melting hypothesis in the Mexican subduction zone. Interestingly, Ce/Pb ratios of the Toluca rocks display a linear positive correlation with Pb isotopes, that departs from the pelagic sediment values, and extends to the enriched Pb isotopic compositions of intraplate-type volcanic rocks from the Chichinautzin volcanic field. Thus the Toluca rocks likely represent discrete slab-derived melts coming from different portions of the subducted slab that

  12. Origin of the ca. 90 Ma magnesia-rich volcanic rocks in SE Nyima, central Tibet: Products of lithospheric delamination beneath the Lhasa-Qiangtang collision zone (United States)

    Wang, Qing; Zhu, Di-Cheng; Zhao, Zhi-Dan; Liu, Sheng-Ao; Chung, Sun-Lin; Li, Shi-Min; Liu, Dong; Dai, Jin-Gen; Wang, Li-Quan; Mo, Xuan-Xue


    Bulk-rock major and trace element, Sr-Nd-Hf isotope, zircon U-Pb age, and zircon Hf isotopic data of the Late Cretaceous Zhuogapu volcanic rocks in the northern Lhasa subterrane provide a new insight into tectonic processes following the collision of the terrane with the Qiangtang zone. SHRIMP zircon U-Pb dating reveals that the Zhuogapu volcanic rocks crystallized at ca. 91 Ma, postdating the development of a regional angular unconformity between the Upper Cretaceous and the underlying strata in the Lhasa-Qiangtang collision zone. Compared to the Andean arc-type andesites and dacites, the Zhuogapu volcanic rocks are characterized by higher MgO of 2.78-5.86 wt.% and Mg# of 54-64 for andesites and MgO of 2.30-2.61 wt.% and Mg# of 55-58 for dacites. Eight andesite samples have whole-rock (87Sr/86Sr)i of 0.7054-0.7065, εNd(t) of - 3.2 to - 1.7, and εHf(t) of + 3.8-+ 6.4, similar to those of the three dacite samples with (87Sr/86Sr)i = 0.7056-0.7060, εNd(t) of - 2.7 to - 2.2, and εHf(t) of + 5.6-+ 7.0. Thirteen analyses from a dacite sample give positive zircon εHf(t) of + 5.6 to + 8.7. These signatures indicate that the Zhuogapu Mg-rich andesites were most likely derived from partial melting of a delaminated mafic lower crust (including the lowermost crust straddling the northern and central Lhasa subterranes) that led to the generation of the Zhuogapu primary melts with adakitic signatures and small negative εNd(t). Such melts subsequently experienced interaction of melt-asthenospheric mantle peridotite followed by the modification of highly fractionated magmas in shallow crustal magma chamber. Hornblende-controlled fractionation results in the change of geochemical composition from Mg-rich andesitic to Mg-rich dacitic magmas. Field observations, together with geochronological and geochemical data, indicate that the Zhuogapu Mg-rich volcanic rocks and coeval magmatism in the northern Lhasa subterrane may be the result of thickened lithospheric delamination

  13. The pre-Kos Plateau Tuff Volcanic Rocks on Kefalos Peninsula (Kos Island, Dodecanese, Greece): Crescendo to the Largest Eruption of the Modern Aegean Arc (United States)

    Bachmann, O.; Schnyder, C.


    Young volcanic rocks (K-Ar ages of 3 to 0.5 Ma) from the Kefalos Peninsula (Kos Island, Dodecanese, Greece) erupted prior to the voluminous (>60 km\\ 3) Kos Plateau Tuff (KPT; Ar-Ar age of 0.16 Ma) were studied in order to better define the conditions that led to the paroxysmal eruption of the modern Aegean Arc. Two different whole-rock compositions were sampled on Kefalos peninsula; dacites (63-65 wt% SiO2) and rhyolites (75-77 wt% SiO2). Kefalos dacites are crystal-rich (>40% crystals), show high Sr-Ba contents compared to other continental arcs, and have "adakitic" Sr/Y ratios (>40). Kefalos rhyolites are typical high- SiO2 arc magmas, similar in composition and mineralogy to the KPT, but displaying lower crystallinities (30% in most of the KPT). The high Sr/Y ratios of the dacites is surprising in an area where the subducting slab is not particularly hot and the continental crust relatively thin (~30 km). If the low Y and high Sr-Ba contents result from the fact that magma formed deep enough to supress plagioclase and have garnet present, dacite magma generation must have occurred in the mantle. There is geochemical and mineralogical evidence for the Kefalos and KPT rhyolites being generated by fractional crystallization from magmas similar to the Kefalos dacites. However, the few distinctions between KPT and Kefalos rhyolites (KPT is more voluminous, contains more crystals, has lower whole-rock U and Th contents, and lower MgO-SiO2, but higher Al2O3-FeOtot in biotite) suggest slightly different conditions in the magma chambers. These observations, together with increasing explosivity of the volcanic products from ~3 Ma to 0.16 Ma, may indicate that the build-up to the large KPT eruption could be the result of an increase in magmatic water input in the system through time.

  14. Late Eocene-Early Oligocene two-mica granites in NW Turkey (the Uludağ Massif): Water-fluxed melting products of a mafic metagreywacke (United States)

    Topuz, Gültekin; Okay, Aral I.


    This paper deals with the petrogenesis of two-mica granites within the amphibolite-facies metamorphic rocks in the Uludağ Massif (NW Turkey). The two-mica granites are represented by three different types (i) a 17 km long and 1.5 km-wide strongly foliated and lineated metagranite, (ii) a relatively younger circular granite, 11 km by 6.5 km, free of any penetrative fabric, and (iii) up to 5 m thick dikes of unfoliated granite-porphyries. Mineral constituents include quartz, plagioclase, microcline, biotite, muscovite and minor apatite, zircon, ilmenite and monazite. U-Pb zircon dating indicates that the metagranite was emplaced at 35 ± 1 Ma (2σ, latest Eocene) and the unfoliated granite at 28 ± 1 Ma (2σ) (Early-Late Oligocene boundary). Overall, the two-mica granites are characterized by (i) a restricted bulk composition (SiO2 70-76 wt.%), (ii) near-linear to linear inter-element variations, (iii) high concentrations of Al2O3, Sr, Ba, LREEs, and low abundances of Rb, Y, Sc and HREEs, comparable with adakitic rocks, (iv) variably pronounced concave-upward shape of HREEs and absent to feeble Eu anomaly, (v) relatively high Na2O, CaO and Sr, and lower K2O and Rb contents at identical silica contents relative to the classical S-type granites. 87Sr/86Sr(i) and εNd(i) values range from 0.7052 to 0.7080, and 0.7 to - 3.6, respectively. The 206Pb/204Pb(i) values range from 18.23 to 18.69, 207Pb/204Pb(i) from 15.63 to 15.70 and 208Pb/204Pb(i) from 38.48 to 38.77. 87Sr/86Sr(i) and εNd(i), and εNd(i) and 207Pb/204Pb(i) values are negatively correlated. Isotopic variation and negative correlations can best be explained by a heterogeneous source, including an older crustal component and a more juvenile basic component. Magma temperatures are estimated as 754-790 °C based on zircon and monazite saturation. All these features such as (i) relatively Na-, Ca- and Sr-rich compositions, (ii) isotopically heterogeneous source with inferred residual phases such as garnet and

  15. Early Paleozoic magmatism and metallogeny in Northeast China: a record from the Tongshan porphyry Cu deposit (United States)

    Hu, Xinlu; Yao, Shuzhen; Ding, Zhenju; He, Mouchun


    The Tongshan Cu deposit is located in the northern segment of the Great Xing'an Range and represents one of the few early Paleozoic porphyry Cu deposits in northeastern China. The granitic rocks in the Tongshan Cu deposit include concealed granodiorite and exposed tonalite, which yield LA-ICP-MS zircon U-Pb ages of 478 ± 3 Ma and 214 ± 3 Ma, respectively. The granodiorite has relatively high SiO2 (60.5-63.5 wt%) and Sr (596-786 ppm) contents, low Yb (1.21-1.53 ppm) and Y (9.81-13.0 ppm) contents, and initial 87Sr/86Sr ratios (0.7038-0.7040), suggesting adakitic affinity. Combined with its positive ɛNd( t) values (3.5-5.4), low Mg# values (41-50), and low contents of Cr (18.6-29.0 ppm) and Ni (7.3-9.1 ppm), we propose an origin by partial melting of a juvenile mafic lower crust in a post-collisional setting after the amalgamation of the Erguna and Xing'an Blocks. The tonalite is characterized by high SiO2 (63.1-65.9 wt%) and Al2O3 (16.0-16.3 wt%) contents, low (87Sr/86Sr) i ratios (0.7041-0.7042), positive ɛNd( t) values (2.6-3.0), along with LILE and LREE enrichments and Nb-Ta-Ti depletions, suggesting an origin by partial melting of juvenile mafic lower crust, coupled with fractional crystallization, in a post-orogenic setting after the collision between the Xing'an and Songnen Blocks. The δD values of ore-forming fluids range from -100 to -93 ‰, and the δ18O values calculated from hydrothermal quartz are between -3 and 10 ‰. The δ34S values of sulfides vary from -2.6 to -1.1 ‰. Field observations, as well as the geochronological and H-O-S isotopic data, suggest that the Cu mineralization at Tongshan was genetically linked with the granodiorite.

  16. Age, tectonic setting, and metallogenic implication of Phanerozoic granitic magmatism at the eastern margin of the Xing'an-Mongolian Orogenic Belt, NE China (United States)

    Chen, Cong; Ren, Yunsheng; Zhao, Hualei; Yang, Qun; Shang, Qingqing


    The eastern margin of the Xing'an-Mongolian Orogenic Belt is characterised by widespread Phanerozoic granitic magmatism, some of which is closely related to significant ore mineralisation. This paper presents new geochronological, petrogenetic, and tectonic data for selected intrusions. Zircon U-Pb geochronology for five granitoid plutons indicates they were emplaced during the middle-late Permian (264-255 Ma) and Cretaceous (106-94 Ma), and thus granitic magmatism occurred throughout the Phanerozoic, Permian (268-252 Ma), Early-Middle Triassic (248-240 Ma), Early Jurassic (183 Ma), and Cretaceous (112-94 Ma). The Permian granitoids consist of monzogranite, granodiorite, tonalite, and quartz diorite, characterised by enrichment in Na2O (3.60-4.72 wt.%), depletion in K2O (0.97-2.66 wt.%), and a negative correlation between P2O5 and SiO2. Together with the presence of hornblende, these geochemical features are indicative of an I-type affinity. The Permian granitic magmatism is associated with quartz-vein-type tungsten deposits (252 Ma; unpublished Sm-Nd isochron age), which formed in an active continental margin setting related to subduction of the Palaeo-Asian Ocean. The Cretaceous quartz diorites have an adakitic affinity, having relatively high Sr (374-502 ppm), low Yb (0.51-0.67 ppm) and Y (8.7-10.7 ppm), and high Sr/Y (39.4-46.8) and (La/Yb)N values (16.2-34.7), suggesting that they were related to the partial melting of subducted oceanic crust. In addition, they are associated with porphyry Au-Cu deposits. We conclude that the Cretaceous granitic rocks and associated porphyry Au-Cu mineralisation occurred in an extensional tectonic setting related to the subduction of the Palaeo-Pacific Plate beneath the Eurasian Plate. In addition, the large-scale Early-Middle Triassic syn-collisional granite belt at the eastern margin of the Xing'an-Mongolian Orogenic Belt extends from the middle of Jilin Province to the Wangqing-Hunchun region, constraining the timing of the

  17. Geochemistry and Sr-Nd-Pb isotopic characteristics of the Mugouriwang Cenozoic volcanic rocks from Tibetan Plateau: Constraints on mantle source of the underplated basic magma

    Institute of Scientific and Technical Information of China (English)

    LAI ShaoCong; QIN JiangFeng; LI YongFei; LONG Ping


    The Mugouriwang Cenozoic volcanic rocks exposed in the north Qiangtang Block of Tibetan Plateau are mainly composed of basalt and andesitic-basalt, both characterized by the lower SiO2 (51%-54%), high refractory elements (i.e. Mg, Cr, Ni) as well as the moderate enrichment in light rare earth elements (LREE) relative to a slight depleted in Eu and high strength field elements (HFSE, i.e. Nb, Ta, Ti). Besides, the fairly low Sm/Yb value (3.07-4.35) could signify that the rocks should be derived directly from partial melting of the spinel lherzolite at the upper part of the asthenosphere. These rocks have radiogenic Sr and Pb (87Sr/86Sr = 0.705339 to 0.705667; 208Pb/204Pb = 38.8192 to 38.8937; 207Pb/204Pb = 15.6093 to 15.6245; 206Pb/204Pb = 18.6246 to 18.6383), and non-radiogenic Nd (143Nd/144Nd = 0.512604 to 0.512639; εNd = +0.02 to-0.66) in agreement with those values of the BSE mantle reservoir. The DUPAL anomaly of the rocks can be evidently attested by the △8/4Pb = 66.82 to 74.53 , △7/4Pb = 9.88 to 11.42, △Sr>50, implying that the Mugouriwang volcanic rock is likely to be generated by partial melting of a Gondwana-bearing asthenospheric mantle ever matasomatised by the fluid from subduction zone. Depending on the previous study on the high-K calc-alkaline intermediate-felsic volcanics in the study area, this paper proposed that the fluids derived from the subducted Lhasa Block metasomatised the asthenosphere beneath the Qiangtang Block, and induced its partial melting, and then the melt underplated the thickened Qiangtang lithosphere and caused the generation of the Cenozoic adakite-like felsic magmas in the Qiangtang region.

  18. Geochemistry and Sr-Nd-Pb isotopic characteristics of the Mugouriwang Cenozoic volcanic rocks from Tibetan Plateau:Constraints on mantle source of the underplated basic magma

    Institute of Scientific and Technical Information of China (English)


    The Mugouriwang Cenozoic volcanic rocks exposed in the north Qiangtang Block of Tibetan Plateau are mainly composed of basalt and andesitic-basalt,both characterized by the lower SiO2 (51%―54%),high refractory elements (i.e. Mg,Cr,Ni) as well as the moderate enrichment in light rare earth elements (LREE) relative to a slight depleted in Eu and high strength field elements (HFSE,i.e. Nb,Ta,Ti). Be-sides,the fairly low Sm/Yb value (3.07―4.35) could signify that the rocks should be derived directly from partial melting of the spinel lherzolite at the upper part of the asthenosphere. These rocks have radiogenic Sr and Pb (87Sr/86Sr = 0.705339 to 0.705667; 208Pb/204Pb = 38.8192 to 38.8937; 207Pb/204Pb = 15.6093 to 15.6245; 206Pb/204Pb = 18.6246 to 18.6383),and non-radiogenic Nd (143Nd/144Nd = 0.512604 to 0.512639; εNd = +0.02 to -0.66) in agreement with those values of the BSE mantle reservoir. The DUPAL anomaly of the rocks can be evidently attested by the △8/4Pb = 66.82 to 74.53 ,△7/4Pb = 9.88 to 11.42,△Sr>50,implying that the Mugouriwang volcanic rock is likely to be generated by partial melting of a Gondwana-bearing asthenospheric mantle ever matasomatised by the fluid from subduction zone. Depending on the previous study on the high-K calc-alkaline intermediate-felsic volcanics in the study area,this paper proposed that the fluids derived from the subducted Lhasa Block metasomatised the asthenosphere beneath the Qiangtang Block,and induced its partial melting,and then the melt under-plated the thickened Qiangtang lithosphere and caused the generation of the Cenozoic adakite-like felsic magmas in the Qiangtang region.

  19. Discovery of dunite and pyroxenite xenoliths in Mesozoic diorite at Jinling, western Shandong and its significance

    Institute of Scientific and Technical Information of China (English)

    XU Wenliang; WANG Dongyan; GAO Shan; LIN Jingqian


    Abundant deeply-derived xenoliths are discovered in a Mesozoic diorite at Jinling, Zibo, western Shandong, which mainly consist of dunite and pyroxenite. The dunite can be further subdivided into two subtypes. The first type shows tabular texture and high Mg# values (93-94) in olivines. The second type is characterized by the metamorphic-deformation texture superimposed by later metasomatism and relatively low olivine Mg# values (86-87). The mineral chemical data indicate that the former could be derived from ancient lithospheric mantle and the latter could have resulted from silica-rich melt metasomatism. The exsolution texture and the high Mg# value in clinopyroxenes, together with the rather high equilibrium temperature, imply that the pyroxenite xenoliths could be the cumulates of mantle-derived magma in the uppermost mantle or near the crust-mantle boundary in the Mesozoic.

  20. Geology, composition, and physicochemical model of sparry magnesite deposits of the Southern Urals (United States)

    Krupenin, M. T.; Kol'tsov, A. B.


    The metasomatic nature of magnesite formation, sequence and timing of geological processes, and solution sources have been established by comprehensive geological and geochemical study of the typical Satka and Ismakaevo deposits of sparry magnesite in the South Ural province. The hydrothermal metasomatic formation of magnesite is related to injection of high-Mg evaporite brine into heated carbonate rocks within permeable rift zones. The numerical physicochemical simulation of solution-rock interaction allowed us to determine the necessary prerequisites for sparry magnesite formation: the occurrence of marine salt solutions with a high Mg/Ca ratio and heating of solutions before or during their interaction with host carbonate rocks. The contribution of compositionally various solution sources, the temperature variation regime, proportions of CO2 and H2S concentrations in solution created specific features of particular deposits.

  1. Boninitic metavolcanic rocks and island arc tholeiites from the Older Metamorphic Group (OMG) of Singhbhum Craton, eastern India: Geochemical evidence for Archean subduction processes

    Digital Repository Service at National Institute of Oceanography (India)

    Manikyamba, C.; Ray, J.; Ganguly, S.; Singh, M.R.; Santosh, M.; Saha, A.; Satyanarayanan, M.

    . Major, trace and rare earth element compositions of these rocks are characterized by high Mg# (80–82), MgO (30.6–32.9 wt.%), Ni (490–1262 ppm) and Cr (2404–4385 ppm) contents, high Al2O3/TiO2 (49–67), Zr/Hf (10...

  2. Microbial and Chemical Characterization of Underwater Fresh Water Springs in the Dead Sea


    Danny Ionescu; Christian Siebert; Lubos Polerecky; Yaniv Y Munwes; Christian Lott; Stefan Häusler; Mina Bižić-Ionescu; Christian Quast; Jörg Peplies; Frank Oliver Glöckner; Alban Ramette; Tino Rödiger; Thorsten Dittmar; Aharon Oren; Stefan Geyer


    Due to its extreme salinity and high Mg concentration the Dead Sea is characterized by a very low density of cells most of which are Archaea. We discovered several underwater fresh to brackish water springs in the Dead Sea harboring dense microbial communities. We provide the first characterization of these communities, discuss their possible origin, hydrochemical environment, energetic resources and the putative biogeochemical pathways they are mediating. Pyrosequencing of the 16...

  3. Crustal contamination versus an enriched mantle source for intracontinental mafic rocks: Insights from early Paleozoic mafic rocks of the South China Block (United States)

    Xu, Wenjing; Xu, Xisheng; Zeng, Gang


    Several recent studies have documented that the silicic rocks (SiO2 > 65 wt.%) comprising Silicic Large Igneous Provinces are derived from partial melting of the crust facilitated by underplating/intraplating of ;hidden; large igneous province-scale basaltic magmas. The early Paleozoic intracontinental magmatic rocks in the South China Block (SCB) are dominantly granitoids, which cover a combined area of 22,000 km2. In contrast, exposures of mafic rocks total only 45 km2. These mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched (whole rock initial 87Sr/86Sr = 0.7041-0.7102; εNd(t) = - 8.4 to + 1.8; weighted mean zircon εHf(t) = - 7.4 to + 5.2), show low Ce/Pb and Nb/U ratios (0.59-13.1 and 3.5-20.9, respectively), and variable Th/La ratios (0.11-0.51). The high-MgO mafic rocks (MgO > 10 wt.%) tend to have lower εNd(t) values (- 4) and Sm/Nd ratios (> 0.255). The differences in geochemistry between the high-MgO and low-MgO mafic rocks indicate greater modification of the compositions of high-MgO mafic magmas by crustal material. In addition, generally good negative correlations between εNd(t) and initial 87Sr/86Sr ratios, MgO, and K2O, along with the presence of inherited zircons in some plutons, indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination, rather than an enriched mantle source. The results show that high-MgO mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source, and it is more likely that the lithospheric mantle beneath the SCB during the early Paleozoic was moderately depleted than enriched by ancient subduction processes.

  4. I-Xe Ages and the Thermal History of the Toluca IAB Meteorite (United States)

    Pravdivtseva, O.; Meshik, A. P.; Petaev, M. I.; Hohenberg, C. M.


    The I-Xe system in Toluca silicates seems to survive catastrophic impact and breakup of the IAB parent body. As a result of cooling at about 40 +/- 20 K/Ma, the I-Xe system in the high-Mg pyroxenes in Toluca nodules closed at about 4559.7 Ma, in low-Mg pyroxenes at 4553.6-4548.9 Ma.

  5. Extensive occurrence and genesis of authigenic carbonates from Krishna-Godavari offshore basin (Bay of Bengal): Possible influence of methane hydrates occurrences.

    Digital Repository Service at National Institute of Oceanography (India)

    Kocherla, M.; Pillai, S.; Patil, D.J.

    .2 1.3 6 3.8 0.2 3.8 1 3 6 0.3 0.2 3.5 0.3 0.5 5 10.6 0.2 3.7 12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 0 2 4 6 8 10 12 A u t h i g e n i c C a r b o n a t e s T h i c k n e s s ( c m ) MD-161 Site ID Low-Mg Calcite High-Mg Calcite Siderite ...-rich friable siderite nodules vary from -16.38 to 6.42 ‰ VPDB and from -50.22 to -26.77 ‰ VPDB for high-Mg calcites. The δ18O values for high-Mg calcites range from -0.31 to +8.12 ‰ VPDB and -15.70 to 8.80 ‰ VPDB for siderites. Interestingly in one...

  6. Mid-Miocene thermal Impact on the Lithosphere of Asia by sub-lithospheric convective Mantle Material: Temporal Transition from high- to moderate-Mg Magmatism beneath Vitim Plateau, Southern Siberia (United States)

    Chuvashova, Irina; Rasskazov, Sergei


    In Inner Asia, high-Mg lavas is characteristic of the Middle Miocene volcanism. In the Vitim plateau, we studied the high- and moderate-Mg volcanics, erupted at 16-14 and 14-13 Ma, respectively. In the former (small volume) unit, initial basaltic melts, contaminated by crustal material, were followed by uncontaminated high-Mg basanites and basalts of transitional (K-Na-K) compositions and afterwards by picrobasalts and basalts of K series. In the latter (high-volume) unit, initial basalts and basaltic andesites of transitional (Na-K-Na) compositions and basalts of Na series were overlain by basalts and trachybasalts of K-Na series. From pressure estimates after equation [Scarrow, Cox, 1995], we infer that the high-Mg melts were derived from the sub-lithospheric mantle as deep as 115-150 km, unlike the moderate-Mg ones that were produced by melting of the shallow lithospheric mantle. We suggest that the studied transition from high- and moderate-Mg magmatism reflected the mid-Miocene thermal impact on the lithosphere by a hot sub-lithospheric mantle material from the Transbaikalian low-velocity domain with potential temperature estimates up to 1510 oC. This thermal impact triggered rifting in the lithosphere of the Baikal Rift System. The study is supported by the Russian Foundation for Basic Research (Grant 14-05-31328).

  7. Interpreting the I-Xe system in individual silicate grains from Toluca IAB (United States)

    Pravdivtseva, O. V.; Meshik, A. P.; Hohenberg, C. M.; Petaev, M.


    Detailed isotopic and mineralogical studies of silicate inclusions separated from a troilite nodule of the Toluca IAB iron meteorite reveal the presence of radiogenic 129Xe in chlorapatite, plagioclase, perryite, and pyroxene grains. Subsequent I-Xe studies of 32 neutron-irradiated pyroxene grains indicate that high-Mg and low-Mg pyroxenes have distinctive I-Xe signatures. The I-Xe system in high-Mg pyroxenes closed at 4560.5 ± 2.4 Ma, probably reflecting exsolution of silicates from the melt, while the low-Mg pyroxenes closed at 4552.0 ± 3.7 Ma, 8.5 Ma later, providing a means for determining the cooling rate at the time of exsolution. If the host Toluca graphite-troiliterich inclusion formed after the breakup and reassembly of the IAB parent body as has been suggested, the I-Xe ages of the high-Mg pyroxenes separated from this inclusions indicate that this catastrophic impact occurred not later than 4560.5 Ma, 6.7 Ma after formation of CAIs. The cooling rate at the time of silicates exsolution in Toluca is 14.5 ± 10.0 °C/Ma.

  8. Barren Miocene granitoids in the Central Andean metallogenic belt, Chile: Geochemistry and Nd-Hf and U-Pb isotope systematics Granitoides estériles del Mioceno en la franja metalogénica de los Andes Centrales, Chile: geoquímica e isotopía de Nd-Hf y U-Pb

    Directory of Open Access Journals (Sweden)

    Katja Deckart


    Full Text Available Four Middle-to-Late Miocene barren plutonic complexes that occur between the giant porphyry copper deposits of the central Chilean Andes were selected for U-Pb LA-ICPMS geochronology and Hf-isotope systematics on single zircon grains. Major and trace elements and Sr-Nd-Hf isotope whole rock geochemical studies were under-taken to compare with slightly younger or coeval barren and fertile intrusive rocks between 32° and 34°S. The studied granitoids yield resolvable crystallization ages of 11.3±0.1 Ma (Cerro Mesón Alto massif, 10.3±0.2 Ma (La Gloria pluton, 14.9±0.2 Ma/14.9±0.1 Ma (Yerba Loca stock and 11.2±0.1 Ma/14.7±0.1 Ma (San Francisco Batholith. Major and trace elements discard an adakitic signature as suggested for coeval porphyric intrusions at 32°S, slightly younger mineralized porphyries at Río Blanco-Los Bronces deposit and other Cenozoic adakites. Volcanic host rocks are less fractionated than the intrusive rock units. The same observation can be made for the unmineralized northern plutons compared to the southern ones. Initial Sr-Nd isotope data show insignificant variation (0.703761-0.704118 and 0.512758-0.512882, plotting in the mantle array. Trace element enrichment can be explained by addition of subducted-slab fluids and/or terrigenous sediments to the mantle wedge prior to and/or slight crustal input during magma ascent. Zircon grains separated from these barren intrusives share a similar initial εHf i-data variation for the younger age group (10-12 Ma; 7.04-9.54 and show a more scattered range for the older one (14-15 Ma; 8.50-15.34; both sets plot between the DM and CLTUR evolution lines. There is evidence that magma evolution was slightly distinct through time from older to younger barren magmatism, compared to a few fertile porphyritic rocks from Río Blanco-Los Bronces porphyry copper deposit. It is suggested that chronological inconsistencies within these complexes might be related to differential shortening

  9. Petrogenesis of metamorphosed Paleoproterozoic, arc-related tonalites, granodiorites and coeval basic to intermediate rocks from southernmost Brazil, based on elemental and isotope geochemistry (United States)

    Gregory, Tiago Rafael; Bitencourt, Maria de Fátima; Nardi, Lauro Valentim Stoll; Florisbal, Luana Moreira


    In southern Brazil, three associations of metamorphosed tonalites and granodiorites that are compositionally similar to tonalite-trondhjemite-granodiorite (TTG) or adakitic associations have been identified in the Arroio dos Ratos Complex (ARC) Paleoproterozoic magmatism. The metatonalites of Association 1 (A1; 2148 ± 33 Ma) have a well-developed fabric, compatible with strong solid-state deformation. The metatonalites and metagranodiorites of Association 2 (A2; 2150 ± 28 Ma) are intrusive in A1 and have a similar composition, but are less deformed, and their primary structures are partly preserved. Both associations display contemporaneity relations with basic to intermediate magmas. Association 3 (A3; 2077 ± 13 Ma) is represented by tonalitic to granodioritic gneisses, without any associated basic to intermediate magmatism, and its main characteristic is the banding that resulted from strong solid-state deformation. Partial melting features are locally present in A3. The geochemical compositions of the three associations are similar and indicate sources related to a continental magmatic arc environment. The 87Sr/86Sr(i) ratios (between 0.701 and 0.703), positive ƐNd(t) values (+ 1.45 to + 5.19), and TDM ages close to the crystallization ages indicate juvenile sources for the A1 and A2 associations. The A3 rocks have a 87Sr/86Sr(i) ratio of 0.715, an ƐNd(t) value of + 0.47 and a TDM age that is close to the crystallization age, indicating a source composition different from those of the other associations. The Pb isotope ratios of A1 and A2 are similar and compatible with the evolution of mantle and orogen (208Pb/204Pb = 37.3-37.6; 207Pb/204Pb = 15.62-15.65; 206Pb/204Pb = 18.0-18.2). The Pb isotope ratios of A3 differ from A1 and A2, indicating a more Th-poor source (208Pb/204Pb = 37.1; 207Pb/204Pb = 15.64; 206Pb/204Pb = 18.5). The geochemistry of associations A1 and A2 suggests a juvenile source with contamination by crustal material. However, the Sr

  10. Silicic Arc Magmas And Silicic Slab Melts: The Melt-Rock Reaction Link (United States)

    Straub, S. M.; Gomez-Tuena, A.; Bolge, L. L.; Espinasa-Perena, R.; Bindeman, I. N.; Stuart, F. M.; Zellmer, G. F.


    While a genetic link between silicic arc magmas and silicic melts from the subducted slab has long been proposed, this hypothesis is commonly refuted because most arc magmas lack a 'garnet-signature' which such slab melts must have. A comprehensive geochemical study of high-Mg# arc magmas from the Quaternary central Mexican Volcanic Belt (MVB), however, shows that this conflict can be reconciled if melt-rock reaction processes in the mantle wedge were essential to arc magma formation. In the central MVB, monogenetic and composite volcanoes erupt high-Mg# basalts to andesites with highly variable trace element patterns. These magmas contain high-Ni olivines (olivine Ni higher than permissible for olivines in partial peridotite melts) with high 3He/4He = 7-8 Ra that provide strong evidence for silicic slab components that infiltrate the subarc mantle to produce olivine-free segregations of 'reaction pyroxenite' in the sources of individual volcanoes. Melting of silica-excess and silica-deficient reaction pyroxenites can then produce high-Mg# basaltic and dacitic primary melts that mix during ascent through mantle and crust to form high-Mg# andesites. Mass balance requires that reaction pyroxenites contain at least >15-18 wt%, and likely more, of slab component. However, because the HREE of the slab component are efficiently retained in the eclogitic slab, elements Ho to Lu in partial melts from reaction pyroxenites remain controlled by the mantle and maintain MORB-normalized Ho/Lun ˜1.15 close to unity. In contrast, the MREE to LREE and fluid mobile LILE of the arc magmas are either controlled, or strongly influenced, by slab-contributions. The origin from hybrid sources also shows in the major elements that are blends of mantle-derived elements (Mg, Ca, Mn, Fe, Ti) and elements augmented by slab contributions (Si, Na, K, P, and possibly Al). Moreover, strong correlations between bulk rock SiO2, 87Sr/86Sr and δ18O (olivines) can be interpreted as mixtures of subarc

  11. The Global Array of Primitve Arc Melts (United States)

    Schmidt, M. W.; Jagoutz, O. E.


    A longstanding question concerns the nature of the melts forming in the subarc mantle and giving rise to arc magmatism. The global array of primitive arc melts (1180 volcanic rocks in 25 arcs extracted from the georoc database, calculated to be in equilibrium with mantle olivine) yields five principal melt types: calc-alkaline basalts and high-Mg andesites, tholeiitic basalts and high-Mg andesites, and shoshonitic or alkaline arc melts; many arcs have more than one type. Primitive calc-alkaline basalts occur in 11 arcs but most strikingly, 8 continental arcs (incl. Aleutians, Cascades, Japan, Mexico, Kamtschatka) have a continuous range of calc-alkaline basalts to high-Mg andesites with mostly 48-58 wt% SiO2. In each arc, these are spatially congruent, trace element patterns overlap, and major elements form a continuum. Their Ca-Mg-Si systematics suggests saturation in olivine+opx+cpx. We hence interpret the large majority of high-Mg andesites as derived from primitive calc-alkaline basalts through fractionation and reaction in the shallower mantle. Removal of anhydrous mantle phases at lower pressures increases SiO2 and H2O-contents while Mg# and Ni remain buffered to mantle values. Primitive tholeiitic basalts (Cascades, Kermadec, Marianas, Izu-Bonin, Japan, Palau, Sunda) have a much lesser subduction signal (e.g. in LILE) than the calc-alkaline suite. These tholeiites have been interpreted to form through decompression melting, but also characterize young intraoceanic arcs. In the two continental arcs with both tholeiitic and calc-alkaline primitive basalts (clearly distinct in trace patterns), there is no clear spatial segregation (Casacades, Japan). Three intraoceanic arcs (Marianas, Izu-Bonin, Tonga) have primitive tholeiitic, highly depleted high-Mg andesites (boninites) with HFSE and HREE slightly above primitive mantle values. These deviate in majors from the array formed by the basalts and calc-alkaline andesites suggesting that only these formed from a

  12. Liquid Immiscibility of Boninite in Xiangcheng, Southwestern China, and Its implication to Genetic Relationship between Boninite and Komatiitic Basalt

    Institute of Scientific and Technical Information of China (English)


    Boninitic rocks and associated high-magnesian basalt and high-iron tholeiite in the Xiangcheng area constitute the basal horizon of the arc volcanic sequence in the Triassic Yidun Island-Arc, southwestern China. The boninite occurs as pillow, massive and ocellar lavas; the last one possesses well-developed globular structure and alternates with the former two. The boninite is characterized by the absence of phenocrysts of olivine and low-Ca pyroxenes and by low CaO/Al2O3 ratios (1000 ppm) and Ni (>250 ppm). The normalized abundance patterns (NAP) of trace elements to primitive mantle are similar to the NAP of low-Ca modern boninites and SHMB in the Archaean and Proterozoic. As a mechanism of ocellar texture, liquid immiscibility in boninite is supported by the following lines of evidence: (a) sharp contact between ocelli and matrix, (b) constant volumetric ratios of ocelli/matrix and common coalescence of ocelli in ocellar rocks, (c) identical micro-spinifex textures and mineral assemblages with different modal mineral contents in ocelli-matrix pairs, (d) bubbles and acicular clinopyroxene crystal strand over the boundary between ocelli and matrix, and (e) chemical compositions of ocelli and matrix corresponding to high-Mg andesite and komatiitic basalt, respectively. The close association and geochemical similarities between ocellar boninites and pillow boninite/massive boninite suggest that these are comagmatic rocks. The primary features of the ocellar boninite indicated by high Mg/(Mg+Fe2+) ratio and high Cr and Ni abundance show that liquid immiscibility took place in the early evolution stage of the boninitic magma. The miscibility gap in boninite which is smaller than that in tholeiite is likely to be due to the low FeO*/MgO+FeO* ratio and high MgO content of the boninitic magma. The association of komatiite-komatiitic basalt-boninite (or SHMB) and the immiscibility phenomenon in high-Mg lavas in some Archaean greenstone belts and ophiolites is also

  13. Underplating in the middle-lower Yangtze Valley and model of geodynamic evolution: Constraints from geophysical data

    Institute of Scientific and Technical Information of China (English)

    Lü; Qingtian


    [1]Chang, Y. F., Liu, X. P., Wu, Y. C., The Copper-Iron Belt of the Lower and Middle Reaches of the Changjiang River (in Chinese),Beijing: Geological Publishing House, 1991, 1-379.[2]Rudnick, R., Growing from below, Nature, 1990, 347(25): 711.[3]Drummond, B. J., Collins, C. D. N., Seismic evidence for underplating of the lower continental crust of Australia, Earth and Planetary Science Letters, 1986, 79: 361-372.[4]Yang, W. C., Hu, Z. Y., Cheng, Z. Y. et al., Long profile of geophysical investigation from Tanchen to Lianshui, East-central China, Acta Geophysica Sinica (in Chinese), 1999, 42(2):206-217.[5]Yang, W. C., Wang, J. Y., Geophysical evidences for magmatic underplating in the Sulu area, Acta Geologica Sinica (in Chinese),2002, 76(2): 173-179.[6]Lu, Q. T., Hou, Z. Q., Zhao, J. H. et al., Deep seismic reflection profiling revealing the complex crustal structure of the Tongling ore district, Science in China, Series D, 2004, 47(3): 193-200.[7]Wang, Q., Zhao, Z. H., Xiong, X. L. et al., Melting of the underplated basaltic lower crust: Evidence from the Shaxi adakite sodic quartz diorite-porphyrites, Anhui Province, China, Geochimica (in Chinese), 2001, 30(4): 353-362.[8]Wang, Q., Zhao, Z. H., Xu, J. F. et al., Yanshanian adakite-like rock and its metallogenesis on the east part of Yangtze block,Science in China, Series D, 2002, 32(Suppl.): 127-136.[9]Xu, J. F., Wang, Q., Xu, Y. al., Geochemistry of Anjishan intermediate-acid intrusive rocks in Ningzhen area: Constraint on origin of the magma with HREE and Y depletion, Acta Petrologica Sinica (in Chinese), 2001, 17(4): 576-584.[10]Xu, J. F., Shinjo, R., Defant, M. J. et al., Origin of Mesozoic adakitic intrusive rocks in the Ningzhen area of east China: Partial melting of delaminated lower continental crust? Geology, 2002,30: 1111-1114.[11]Brown, L. D., A new map of crustal terranes in the United States from COCORP deep seismic reflection profiling, Geophys. J. Int.,1991, 105: 3-13.[12]Deemer, S. J., Hurich

  14. Experimental Evidence for Polybaric Intracrustal Differentiation of Primitive Arc Basalt beneath St. Vincent, Lesser Antilles (United States)

    Blundy, Jon; Melekhova, Lena; Robertson, Richard


    We present experimental phase equilibria for a primitive, high-Mg basalt from St. Vincent, Lesser Antilles. Experimental details were presented in Melekhova et al (Nature Geosci, 2013); the objective here is to compare experimental phase compositions to those of erupted lavas and cumulates from St. Vincent. Starting material with 4.5 wt% H2O is multiply-saturated with a lherzolite assemblage at 1.3 GPa and 1180 ° C, consistent with mantle wedge derivation. Experimental glasses from our study, in addition to those of Pichavant et al (GCA, 2002) and Pichavant & Macdonald (CMP 2007) on a similar high-Mg basalt, encompass a compositional range from high-magnesian basalt to dacite, with a systematic dependence on H2O content, temperature and pressure. We are able to match the glasses from individual experiments to different lava types, so as to constrain the differentiation depths at which these magmas could be generated from a high-Mg parent, as follows: Composition wt% H2OP (GPa) T (° C) High-Mg basalt 3.9-4.8 1.45-1.751180-1200 Low-Mg basalt 2.3-4.5 1.0-1.3 1065-1150 High alumina basalt 3.0-4.5 0.4 1050-1080 Basaltic andesite 0.6-4.5 0.7-1.0 1050-1130 Andesite 0.6 1.0 1060-1080 The fact that St. Vincent andesites (and some basaltic andesites) appear to derive from a low-H2O (0.6 wt%) parent suggest that they are products of partial melting of older, high-Mg gabbroic rocks, as 0.6 wt% H2O is approximately the amount that can be stored in amphibole-bearing gabbros. The higher H2O contents of parents for the other lava compositions is consistent with derivation by crystallization of basalts with H2O contents that accord with those of olivine-hosted melt inclusions from St. Vincent (Bouvier et al, J Petrol, 2008). The generation of evolved melts both by basalt crystallization and gabbro melting is consistent with the hot zone concept of Annen et al (J Petrol, 2006) wherein repeated intrusion of mantle-derived basalt simultaneously crystallize by cooling and melt

  15. The role of amphibole in the evolution of arc magmas and crust: the case from the Jurassic Bonanza arc section, Vancouver Island, Canada (United States)

    Larocque, Jeff; Canil, Dante


    The Jurassic Bonanza arc, on Vancouver Island, British Columbia, represents an exhumed island arc crustal section of broadly diorite composition. We studied bodies of mafic and ultramafic cumulates within deeper levels of the arc to constrain the conditions and fractionation pathways leading from high-Mg basalt to andesite and dacite. Major element trends coupled with textural information show the intercumulus crystallization of amphibole, as large oikocrysts enclosing olivine in primitive cumulates controls the compositions of liquids until the onset of plagioclase crystallization. This process is cryptic, occurring only in the plutonic section, and explains the paucity of amphibole in mafic arc volcanics and the change in the Dy/Yb ratios in many arc suites with differentiation. The correlation of octahedral Al in hornblende with pressure in liquidus experiments on high-Mg basalts is applied as an empirical barometer to hornblendes from the Bonanza arc. It shows that crystallization took place at 470-880 MPa in H2O-saturated primitive basaltic magmas. There are no magmatic equivalents to bulk continental crust in the Bonanza arc; no amount of delamination of ultramafic cumulates will shift the bulk arc composition to the high-Mg# andesite composition of bulk continental crust. Garnet removal from wet magmas appears to be the key factor in producing continental crust, requiring high pressures and thick crust. Because oceanic island arcs are built on thinner crust, the long-term process generating the bulk continental crust is the accretion of island arcs to continental margins with attendant tectonic thickening.

  16. Chemical compositions of aqueous fluid, silicate melt, and supercritical fluid in the vicinity of the second critical endpoint in the system peridotite-H2O (United States)

    Mibe, K.; Kawamoto, T.; Ono, S.


    Knowing the chemical compositions of fluid and melt is fundamental in understanding the magma genesis and chemical differentiation in the Earth's interior. We investigated the stability fields of aqueous fluid, silicate melt, and supercritical fluid magma using in-situ x-ray radiography and the second critical endpoint in the system peridotite-H2O was determined to be around 3.8 GPa (Mibe et al., 2007, JGR). Using the quenched recovered samples obtained by Mibe et al. (2007), we determined the chemical compositions of aqueous fluid, silicate melt, and supercritical fluid in the vicinity of the second critical endpoint in the system peridotite-H2O by EPMA analyses. A 10- to 30-μm diameter electron beam was used to obtain the composition of quenched materials from aqueous fluid, silicate melt, and supercritical fluid. The compositions of coexisting aqueous fluid and silicate melt were determined at 3.3 GPa and 3.6 GPa and 1180°C. In both samples, olivine coexists with aqueous fluid and silicate melt. In the run at 3.3 GPa, the composition of aqueous fluid was high-Mg dacitic, whereas the composition of silicate melt was hydrous peridotite. In the run at 3.6 GPa, the composition of aqueous fluid was high-Mg andesitic, whereas the composition of silicate melt was hydrous komatiitic. Although aqueous fluids in both runs are high-Mg, both MgO and FeO preferentially enters into silicate melt compared to aqueous fluid.

  17. Ice-sheet control of continental erosion in central and southern Chile (36°-41°S) over the last 30,000 years (United States)

    Muratli, Jesse M.; Chase, Zanna; McManus, James; Mix, Alan


    Bulk sediment chemistry from three Chilean continental margin Ocean Drilling Program sites constrains regional continental erosion over the past 30,000 years. Sediments from thirteen rivers that drain the (mostly igneous) Andes and the (mostly metamorphic) Coast Range, along with existing rock chemistry datasets, define terrestrial provenance for the continental margin sediments. Andean river sediments have high Mg/Al relative to Coast-Range river sediments. Near 36°S, marine sediments have high-Mg/Al (i.e. more Andean) sources during the last glacial period, and lower-Mg/Al (less Andean) sources during the Holocene. Near 41°S a Ti-rich source, likely from coast-range igneous intrusions, is prevalent during Holocene time, whereas high-Mg/Al Andean sources are more prevalent during the last glacial period. We infer that there is a dominant ice-sheet control of sediment sources. At 36°S, Andean-sourced sediment decreased as Andean mountain glaciers retreated after ˜17.6 ka, coincident with local oceanic warming and southward retreat of the Patagonian Forest and, by inference, westerly winds. At 41°S Andean sediment dominance peaks and then rapidly declines at ˜19 ka, coincident with local oceanic warming and the earliest deglacial sea-level rise. We hypothesize that this decreased flux of Andean material in the south is related to rapid retreat of the marine-based portion of the Patagonian Ice Sheet in response to global sea-level rise, as the resulting flooding of the southern portion of the Central Valley created a sink for Andean sediments in this region. Reversal of the decreasing deglacial Mg/Al trend at 41°S from 14.5 to 13.0 ka is consistent with a brief re-advance of the Patagonian ice sheet coincident with the Antarctic Cold Reversal.

  18. Periodical mixing of MORB magmas near East Pacific Rise 13°N: Evidence from modeling and zoned plagioclase phenocrysts

    Institute of Scientific and Technical Information of China (English)


    Thirty-six basalt samples from near East Pacific Rise 13°N are analyzed for major and trace elements. Different types of zoned plagioclase phenocrysts in basalts are also backscatter imaged, and major element profiles scanned and analyzed for microprobe. Basalts dredged from a restricted area have evolved to different extents (MgO=9.38wt%—6.76wt%). High MgO basalts are modeled for crystalliza-tion to MgO of about 7wt%, and resulted in the Ni contents (≈28 ppm) that are generally lower than that in observed basalts (>60 ppm). It suggests that low MgO basalts may have experienced more intensive magma mixing. High MgO (9.38wt%) basalt is modeled for self-"mixing-crystallization", and the high Ni contents in low MgO basalts can be generated in small scale and periodical self-mixing of new magma (high MgO). "Mixing-crystallization" processes that low MgO magmas experienced accord with recent 226Ra/230Th disequilibria studies for magma residence time, in which low MgO magmas have experi-enced more circles of "mixing-crystallization" in relatively longer residence time. Magma mixing is not homogeneous in magma chamber, however, low MgO magmas are closer to stable composition pro-duced by periodical "mixing-crystallization", which is also an important reason for magma diversity in East Pacific Rise. Zoned plagioclase phenocrysts can be divided into two types: with and without high An# cores, both of which have multiple reversed An# zones, suggesting periodical mixing of their host magmas. Cores of zoned plagioclase in low MgO (7.45wt%) basalt differ significantly with their mantle in An#, but are similar in An# with microlite cores (products of equilibrium crystallization) in high MgO (9.38wt%) basalt, which further shows that plagioclase phenocryst cores in low MgO basalts may have formed in their parental magmas before entering into the magma chamber.

  19. High dietary zinc supplementation increases the occurrence of tetracycline and sulfonamide resistance genes in the intestine of weaned pigs



    Background Dietary zinc oxide is used in pig nutrition to combat post weaning diarrhoea. Recent data suggests that high doses (2.5 g/kg feed) increase the bacterial antibiotic resistance development in weaned pigs. Therefore, the aim of this study was to investigate the development of enterobacterial antibiotic resistance genes in the intestinal tract of weaned pigs. Findings Weaned pigs were fed diets for 4 weeks containing 57 (low), 164 (intermediate) or 2425 (high) mg kg−1 analytical grade...

  20. Petrogenesis of the Miocene volcanism along the İzmir-Balıkesir Transfer Zone in western Anatolia, Turkey: Implications for origin and evolution of potassic volcanism in post-collisional areas (United States)

    Ersoy, Yalçın E.; Helvacı, Cahit; Uysal, İbrahim; Karaoğlu, Özgür; Palmer, Martin R.; Dindi, Fulya


    The Miocene volcanic rocks along the İzmir-Balıkesir Transfer Zone along the western margin of the Menderes Core Complex (MCC) in western Anatolian Volcanic Province (WAVP), where strike-slip deformation is dominant, comprise: (Group 1) early-middle Miocene high-K to shoshonitic rocks with high-Mg# and relatively low SiO2, (Group 2) middle Miocene phonolitic rocks with low-Mg# and intermediate SiO2, (Group 3) early-middle Miocene medium- to high-K series from andesites to rhyolites, (Group 4) middle Miocene rhyolites with distinct trace element compositions; and (Group 5) late Miocene high-MgO basalts, K-trachybasalts and (Group 6) late Miocene high-MgO basaltic andesites. The geochemical features of these rocks are comparable with the other Oligocene to Miocene volcanic rocks, but differ from the Eocene volcanic rocks in WAVP. The geochemical features of the most primitive early-middle Miocene Group 1 rocks indicate that they were derived from an anomalously metasomatized lithospheric mantle. The mineralogical and geochemical properties of garnet-amphibole peridotite from the Ulten Zone (UZP), Eastern Alps, which is thought to represent a fossil metasomatic mantle wedge contaminated by continental subduction, is similar to the model mantle composition previously proposed for the genesis of the mafic rocks. Together with the presence of Eocene to early Miocene continental subduction beneath the Aegean-west Anatolia region, this strongly suggests that continental subduction was an important factor in the genesis of the high-MgO shoshonitic to ultrapotassic volcanism in this post-collisional area. The origin of the Group 3 andesitic to rhyolitic rocks includes; (1) lower crustal melting, (2) mixing between lower crustally-derived and mantle-derived melts, and (3) FC-AFC processes. The late Miocene Group 5 and 6 rocks, however, derived from a more depleted mantle source, indicating that the mantle became depleted over time. The rhyolites of Group 4 are most probably

  1. Platinum-alloy and sulfur saturation in an arc-related basalt to rhyolite suite: Evidence from the Pual Ridge lavas, the Eastern Manus Basin (United States)

    Park, Jung-Woo; Campbell, Ian H.; Arculus, Richard J.


    We have measured the platinum group element (PGE) and Re concentrations of arc-type lavas from the Pual Ridge and the surrounding area in the Eastern Manus Basin. These magmas followed an Fe-enrichment trend to produce a wide range of compositions with MgO varying between 8 and 0.1 wt.%. We found distinct differences in the PGE geochemistry of the high (>3 wt.% MgO) and the low-Mg lavas (high-Mg lavas suggest that the depletion of these elements is due to Pt-rich alloy saturation. This is consistent with the high Pt contents in the high-Mg lavas, which is close to the solubility of Pt in the basaltic melt at similar conditions. In contrast, the concentrations of all PGE and Re drop rapidly in the low-Mg lavas (except for Ru and Ir), with the PGE concentrations falling at a rate that is appreciably faster than Cu, which we attribute to sulfide saturation. As a consequence, there is a marked decline in Pd/Cu in the low-Mg lavas and we suggest that this ratio is the best indicator of sulfide saturation in an evolving magmatic system. A feature of the data is that duplicate analyses of the same sample often do not agree within error. We attribute this scatter to the nugget effect, with nuggets of a Pt-rich alloy in the high-Mg lavas and sulfide blebs in the low-Mg lavas. The PGE concentrations of phenocryst-bearing high-Mg lavas are higher than in the associated glassy lavas, and scatter on MgO variation diagrams is significantly reduced if only glassy lavas are considered, which indicates that the micron scale Pt-rich alloy grains are intimately associated with the phenocrysts. Our results provide strong evidence that Pt-rich alloys can crystallize from a basaltic-andesitic magma, along with the silicate minerals, and fractionate Pt from Pd during magmatic differentiation. As a consequence, Pd/Pt increases during Pt alloy fractionation and this ratio can be used to identify Pt-rich metal saturation. The Pual Ridge alloys are Pt-rich because the primary magmas are Pt

  2. Compositional variations in the Mesoarchean chromites of the Nuggihalli schist belt, Western Dharwar Craton (India)

    DEFF Research Database (Denmark)

    Mukherjee, Ria; Mondal, Sisir Kanti; Rosing, Minik Thorleif


    -98)) and pyroxene grains (Mg-numbers = 97-99). Compositional variability on the scale of a single chromite grain occurs in the form of zoning, and it is common in the accessory chromite grains in serpentinite and in the altered grains in chromitite. In the zoned grains, the composition of the core is modified...... has been used to compute the nature of the parental melt. The parental melt calculations indicate derivation from a high-Mg komatiitic basalt that is similar to the composition of the komatiitic rocks reported from the greenstone sequences of the Western Dharwar Craton. Tectonic discrimination...

  3. Temporal source evolution and crustal contamination at Lopevi Volcano, Vanuatu Island Arc



    Here we present a new geochemical study of Lopevi volcano, one the most active volcanoes in the Vanuatu island arc. We focus on the temporally well-defined sequence of lava flows emitted since 1960, and for the first time, on pre-1960 volcanic products, including high-MgO basalts and felsic andesites, the most evolved lavas sampled so far on this island. This work reports the first Pb and Hf isotopic study of lavas from Lopevi island. These lavas display correlations between differentiation i...

  4. Influence of Mg Content on Deformability of AlMg Alloys during Extrusion

    Directory of Open Access Journals (Sweden)

    Leśniak D.


    Full Text Available In this study the research on deformability of AlMg alloys with high Mg contents in extrusion was carried out. The different shapes from AlMg alloys containing 3.5%, 4.5% and 5.5% of Mg were extruded on 500 T semi-industrial press by using one-hole and multi-hole flat dies. The extrudates surface quality was under investigations in relation with the temperature-speed parameters of the extrusion process. The metal exit speed was estimated depending on the extrudates shape, wall thickness and Mg content. The alloy’s border solidus and liquidus temperatures were also determined.

  5. Petrogenesis and tectonic implications of Early Jurassic volcanic rocks of the Raohe accretionary complex, NE China (United States)

    Wang, Zhi-Hui; Ge, Wen-Chun; Yang, Hao; Bi, Jun-Hui; Ji, Zheng; Dong, Yu; Xu, Wen-Liang


    The Raohe accretionary complex, located at the border between the Russian Far East and Northeastern China, is a significant part of the western Pacific Oceanic tectonic regime. Due to lack of precise age and geochemical constraints, the tectonic setting and petrogenesis of the magmatic rocks in this area remain undefined, resulting in debate about crustal growth mechanisms and subduction-related accretionary processes in Northeastern China. Here, we report whole-rock major and trace element and Sr-Nd isotope data, together with zircon U-Pb ages and in situ zircon Hf isotope data for calc-alkaline andesites, dacites, rhyolites, rhyolitic crystal tuffs, Nb-enriched andesites and basaltic andesites, and high-Mg andesites of the Raohe accretionary complex in NE China. Samples were collected from Late Triassic to Early Jurassic strata. However, geochronological results in this study indicated that the studied magmatism occurred in the Early Jurassic (187-174 Ma). The calc-alkaline volcanic rocks possess geochemical characteristics typical of arc magmas that form at active continental margins, such as moderate enrichments in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depletions in high field strength elements (HFSEs). They have positive εHf(t) values of +3.4 to +10.6 and relatively high (87Sr/86Sr)i values of 0.7047-0.7102. While the Nb-enriched andesites and basaltic andesites have higher TiO2, Hf, Nb, and Zr contents and higher Nb/Ta (24.0-87.6), Nb/U (11.9-75.9), (Nb/Th)PM (0.67-2.70), and (Nb/La)PM (1.95-5.00) ratios than typical arc basalts. They have negative εNd(t) values (-5.5 to -6.0) and relatively variable (87Sr/86Sr)i values of 0.7047-0.7114, suggesting an origin via the partial melting of mantle wedge peridotite that had been metasomatized by slab-derived melt. The high-Mg volcanic rocks, characterized by high MgO and Mg#, TiO2, Al2O3, Cr, Ni, (La/Yb)N and (La/Sm)N, but low Ba/Th ratios, are geochemically similar to

  6. Generation of continental crust in the northern part of the Borborema Province, northeastern Brazil, from Archaean to Neoproterozoic (United States)

    de Souza, Zorano Sérgio; Kalsbeek, Feiko; Deng, Xiao-Dong; Frei, Robert; Kokfelt, Thomas Find; Dantas, Elton Luiz; Li, Jian-Wei; Pimentel, Márcio Martins; Galindo, Antonio Carlos


    This work deals with the origin and evolution of the magmatic rocks in the area north of the Patos Lineament in the Borborema Province (BP). This northeastern segment of NE Brazil is composed of at least six different tectonic blocks with ages varying from late-Archaean to late-Palaeoproterozoic. Archaean rocks cover ca. 5% of the region. They were emplaced over a period of 700 Ma, with at least seven events of magma generation, at 3.41, 3.36, 3.25, 3.18, 3.12, 3.03, and 2.69 Ga. The rocks are subalkaline to slightly alkaline, with affinity to I- and M-type magmas; they follow trondhjemitic or potassium calc-alkaline differentiation trends. They have epsilon Nd(t) of +1.4 to -4.2 and negative anomalies for Ta-Nb, P and Ti, consistent with a convergent tectonic setting. Both subducted oceanic crust and upper mantle (depleted or metasomatised) served as sources of the magmas. After a time lapse of about 350 m y., large-scale emplacement of Paleoproterozoic units took place. These rocks cover about 50% of the region. Their geochemistry indicates juvenile magmatism with a minor contribution from crustal sources. These rocks also exhibit potassic calc-alkaline differentiation trends, again akin to I- and M-type magmas, and show negative anomalies for Ta-Nb, Ti and P. Depleted and metasomatised mantle, resulting from interaction with adakitic or trondhjemitic melts in a subduction zone setting, is interpreted to be the main source of the magmas, predominanting over crustal recycling. U-Pb ages indicate generation of plutonic rocks at 2.24-2.22 Ga (in some places at about 2.4-2.3 Ga) and 2.13-2.11 Ga, and andesitic volcanism at 2.15 Ga. Isotopic evidence indicates juvenile magmatism (epsilon Nd(t) of +2.9 to -2.9). After a time lapse of about 200 m y. a period of within-plate magmatic activity followed, with acidic volcanism (1.79 Ga) in Orós, granitic plutonism (1.74 Ga) in the Seridó region, anorthosites (1.70 Ga) and A-type granites (1.6 Ga) in the Transverse Zone

  7. Petrochemistry of igneous rocks of the California-Vetas mining district, Santander, Colombia: Implications for northern Andean tectonics and porphyry Cu (-Mo, Au) metallogeny (United States)

    Bissig, Thomas; Mantilla Figueroa, Luis Carlos; Hart, Craig J. R.


    Porphyry Mo and Cu mineralization in the California-Vetas mining district is contemporaneous with 10.9 to 8.4 Ma granodiorite porphyry stocks and overprinted by Au-Ag mineralization of epithermal affinity. Mineralization is hosted by Grenvillian aged paragneisses (Bucaramanga Gneiss of the Santander Massif) and late Triassic to early Jurassic granitic rocks. All intrusive rocks are high-K calc-alkaline. Late Triassic to early Jurassic rocks include peraluminous granites with more than 70 wt.% SiO2 as well as metaluminous diorites, tonalites and granodiorites with SiO2 between 54.9 and 60.4 wt.%. Late Miocene rocks are weakly peraluminous granodiorite porphyries with SiO2 between 61 and 67 wt.% SiO2. Late Miocene rocks share some characteristics with adakite-like rocks which are widely associated with porphyry and epithermal style mineralization elsewhere in the Andes. They have high Ba (930 to 1500 ppm) and high Ba/La (28 to 50), high Sr (850 to 1100 ppm) and Sr/Y (48-78) and depleted middle rare earth elements (MREE) compared to the Mesozoic granites, which have 400 to 700 ppm Ba (Ba/La 14 to 25) and 80 to 150 ppm Sr (Sr/Y 2.5 to 14), and Mesozoic diorites and tonalites, which have ~ 900 to 1200 ppm Ba (Ba/La 20 to 32) and ~ 610 to 750 ppm Sr (Sr/Y 22 to 25). Miocene granodiorite porphyries, in contrast to Mesozoic intrusive rocks have only weak negative Eu anomalies. The Miocene rocks have 87Sr/86Sr ratios of 0.7052 to 0.7067 and εNd of - 1.9 to - 5.4 and are significantly more isotopically primitive than all other rocks in the study area including the Mesozoic diorites to tonalites (87Sr/86Sr = 0.7082 and 0.7092; εNd = - 6.7 and - 7.2), granites (87Sr/86Sr = 0.730 (n = 2); εNd = - 8.2 and - 8.3) and Bucaramanga Gneiss (0.718 to 0.743; εNd = - 10.8 to - 14.1). Lead isotope data are broadly consistent with the Sr and Nd isotope data and the Miocene porphyries have the lowest 207Pb/204Pb ratios but overlap with the Mesozoic diorites to tonalites in their 206Pb

  8. Age and geochemistry of host rocks of the Cobre Panama porphyry Cu-Au deposit, central Panama: Implications for the Paleogene evolution of the Panamanian magmatic arc (United States)

    Baker, Michael J.; Hollings, Peter; Thompson, Jennifer A.; Thompson, Jay M.; Burge, Colin


    The Cobre Panama porphyry Cu-Au deposit, located in the Petaquilla district of central Panama, is hosted by a sequence of medium- to high-K calc-alkaline volcanic and sub-volcanic rocks. New crystallisation ages obtained from a granodiorite Petaquilla batholith and associated mineralised diorite to granodiorite porphyry stocks and dikes at Cobre Panama indicate that the batholith was emplaced as a multi-phase intrusion, over a period of ~ 4 million years from 32.20 ± 0.76 Ma to 28.26 ± 0.61 Ma, while the porphyritic rocks were emplaced over a ~ 2 million year period from 28.96 ± 0.62 Ma to 27.48 ± 0.68 Ma. Both the volcanic to sub-volcanic host rocks and intrusive rocks of the Cobre Panama deposit evolved via fractional crystallisation processes, as demonstrated by the major elements (e.g. Al2O3, Fe2O3, TiO2 and MgO) displaying negative trends with increasing SiO2. The Petaquilla intrusive rocks, including the diorite-granodiorite porphyries and granodiorite batholith, are geochemically evolved and appear to have formed from more hydrous magmas than the preceding host volcanic rocks, as evidenced by the presence of hornblende phenocrysts, higher degrees of large-ion lithophile element (LILE) and light rare earth element (LREE) enrichment and heavy rare earth element (HREE) depletion, and higher Sr/Y and La/Yb values. However, the degree of LREE enrichment, HREE depletion and La/Yb values are insufficient for the intrusive rocks to be considered as adakites. Collectively, the volcanic and intrusive rocks have LILE, REE and mobile trace element concentrations similar to enriched Miocene-age Cordilleran arc magmatism found throughout central and western Panama. Both the Petaquilla and Cordilleran arc magmatic suites are geochemically more evolved than the late Cretaceous to Eocene Chagres-Bayano arc magmas from northeastern Panama, as they display higher degrees of LILE and LREE enrichment. The geochemical similarities between the Petaquilla and Cordilleran arc

  9. Geology, Geochemistry and Geochronology of the Upper Cretaceous high-K volcanics in the southern Part of the Eastern Pontides: Implications for Mesozoic Geodynamic Evolution of NE Turkey (United States)

    Eyuboglu, Y.


    The Eastern Pontide Orogenic Belt is one of the most complex geodynamic settings in the Alpine-Mediterranean region. Its geodynamic evolution is very controversial due to lack of systematic, quantitative structural, geochemical and geochronological data. This belt is divided into three subgroups: northern, southern and axial zones, distinguished from north to south by different lithological units, facies changes and tectonic characteristics. Especially, the southern zone is very attractive with its numerous rock associations such as alaskan-type mafic-ultramafic intrusions, shoshonitic and ultrapotassic volcanics, adakitic magmatics, glaucophane-bearing gabbros, metamorphic and ultramafic massifes. This study focuses on the petrology, geotectonic setting and evidence for subduction polarity of the Upper Cretaceous shoshonitic and ultrapotassic volcanics exposed in the most southerly part of the eastern Pontide magmatic arc. Geological, geochemical and isotopic data indicate that there were two distinct cycles of high-K volcanic activity in the southern part of the eastern Pontide magmatic arc during the Late Cretaceous. The first cycle (Early Campanian), represented by shoshonitic trachyandesites and associated pyroclastics, containing high K2O (2.74-4.81 wt %) and Na2O (3.60-5.51 wt %), overlies the Middle-Cretaceous ophiolitic-olistostromal melange formed during the rifting stage of a back-arc basin (Neotethys). The second cycle of high-K volcanism is characterized by potassic or ultrapotassic analcime-bearing volcanics, erupted in a lagoonal environment during the Maastrichtian. Progressive shallowing of the basin indicates that Upper Cretaceous high-K volcanism developed during the final stage of pull-apart basin development in the southern zone of the eastern Pontides. These volcanic rocks, intercalated with continental detritus, are characterized by high Na2O (3.22-7.16 wt %) concentrated in secondary analcime crystals. Their K2O contents also range between 0

  10. 苏门答腊岛(印尼)成矿带的岩浆作用和源区及其对比%Magmatism and provenances of mineralization zones in Sumatra (Indonesia)and their comparisons to adjacent terrains

    Institute of Scientific and Technical Information of China (English)

    高小卫; 吴秀荣; 杨振强


    This paper introduces the mineral distribution, igneous rock types and their geochemical characteris-tics within two mineralization zones (i.e. Cu-Au- and Sn-mineralization zones). Based on the litho-chemical data taken from our research project, the authors summary the geochemical characteristics of ore-bearing igneous par-ent rock and discuses the magmatic origin and source area in Cu-Au-mineralization zone. Meanwhile, a compari-son of rock types of magma and geochemistry-tectonic setting for Sn-mineralization zones in Sumatra Island to the adjacent Terrains is made here. The results of this study indicate that the ore-bearing parent rocks of Cu-Au mineralization zones in the West Sumatra Terrain are adakitic granitoids (SI-Type) were formed in the tectonic setting of volcano-arc in active continental margin(ACM)and the igneous matter came from partly melting of sub-ducted ocean-slab plus weakly melting-assimilation within mantle wedge(MASH),Whereas the ore-bearing ig-neous parent rock in tin mineralization zones within the‘tin island’of East Sumatra Terrain as well as“Sibumasu Terrain”are peraluminum granitoids(S-Type) belonging to tectonic setting of backed arc basin or rift within con-tinent after collision zone and were derived from the re-melting of crust and igneous fraction crystal. The geo-chemical data show that the East Sumatra Terrain and the West Sumatra Terrain may have the same deep igneous source area.%本文介绍了苏门答腊岛上两个成矿带(即铜-金矿成矿带和锡矿成矿带)的矿产分布,岩浆岩的岩石类型和地球化学特征。根据本研究课题在巴东地区岩石化学资料,本文总结了铜-金矿成矿带含矿母岩的地球化学特征,探讨其岩浆岩成因和源区。同时,将其锡矿成矿带岩浆岩的岩石类型和地球化学-大地构造环境与其相邻地体进行对比。研究结果表明:西苏门答腊地体的铜-金矿成矿带的含矿母岩为SI-型埃达克质花

  11. 太古宙TTG岩石是什么含义?%What is the Archean TTG?

    Institute of Scientific and Technical Information of China (English)

    张旗; 翟明国


    太古宙TTG岩石的成因是一个热门话题,它与太古宙麻粒岩地体并称为太古宙两大疑案.TTG岩石关系到地球早期陆壳是如何形成、生长和演化的.现在流行的观点是,太古宙TTG要么产于板块消减带,要么来自加厚的下地壳,这两种说法孰对孰错?笔者认为二者证据都不充分.上述认识是将太古宙TTG与现代埃达克岩简单对比得出来的,而这种对比忽略了地质时代和构造背景的差异,正确的对比应当是在太古宙不同类型花岗质岩石之间进行.太古宙地壳异常的热,什么时候开始出现板块构造至今没有得到明确的结论.太古宙TTG是太古宙地壳的主要成分,太古宙TTG地体反映的是太古宙地壳的平均厚度,加厚是相对于正常地壳厚度而言的.太古宙地质研究存在一个明显的误区,即不恰当地运用“将今论古”的原则,“将今论古”只适合显生宙或中-新元古代.研究TTG岩石意义十分重大,对我们理解前板块构造以及板块构造何时开始的是很关键的.%The Archean granulite massif and Archean TTG are two big mystery in Archean. Archean TTG has long been a hot topic. It is related to how the early continental crust formed grew and evolved. It has been widely acknowledged that Archean TTG formed either in a subduction zone or a product of melting thickened lower continental crust. However, these understandings were based on a simple comparison between Archean TTG and modern adakite. Instead, the correct comparison should be made between various types of Archean granites. And the Archean crust was abnormally hot and the presence of plate tectonics in Archean is still questioned. As the major component of the Archean crust, Archean TTG reflects the average thickness of the Archean crust. But, thickened crust is a concept compared to normal crust thickness. Consequently, there is a significant misunderstanding in the studies on Archean geology and improper usage

  12. Geochronology, geochemistry, and mineralization of the granodiorite porphyry hosting the Matou Cu-Mo (±W) deposit, Lower Yangtze River metallogenic belt, eastern China (United States)

    Zhu, Zhi-Yong; Jiang, Shao-Yong; Hu, Jian; Gu, Lian-Xing; Li, Jianwei


    Porphyry and skarn Cu-Fe-Au-Mo deposits are widespread in the Middle and Lower Yangtze River metallogenic belt (MLYMB), eastern China. The Matou deposit has long been regarded as a typical Cu-Mo porphyry deposit within Lower Yangtze part of the belt. Recently, we identified scheelite and wolframite in quartz veins in the Matou deposit, which is uncommon in other porphyry and skarn deposits in the MLYMB. We carried out detailed zircon U-Pb dating and geochemical and Sr-Nd-Hf isotopic studies of the granodiorite porphyry at Matou to define any differences from other ore-related granitoids. The porphyry shows a SiO2 content ranging from 61.85 wt.% to 65.74 wt.%, K2O from 1.99 wt.% to 3.74 wt.%, and MgO from 1.74 wt.% to 2.19 wt.% (Mg# value ranging from 45 to 55). It is enriched in light rare earth elements and large ion lithophile elements, but relatively depleted in Nb, Ta, Y, Yb and compatible trace elements (such as Cr, Ni, and V), with slight negative Eu anomalies (Eu/Eu* = 0.88-0.98) and almost no negative Sr anomalies. Results of electron microprobe analysis of rock-forming silicate minerals indicate that the Matou porphyry has been altered by an oxidized fluid that is rich in Mg, Cl, and K. The samples show relatively low ɛNd(t) values from -7.4 to -7.1, slightly high initial 87Sr/86Sr values from 0.708223 to 0.709088, and low ɛHf(t) values of zircon from -9.0 to -6.5, when compared with the other Cu-Mo porphyry deposits in the MLYMB. Zircon U-Pb dating suggests the Matou granodiorite porphyry was emplaced at 139.5 ± 1.5 Ma (MSWD = 1.8, n = 15), which is within the age range of the other porphyries in the MLYMB. Although geochemical characteristics of the Matou and other porphyries in the MLYMB are similar and all adakitic, the detrital zircons in the samples from Matou suggest that Archean lower crust (2543 ± 29 Ma, MSWD = 0.25, n = 5) was involved with the generation of Matou magma, which is different from the other porphyries in the belt. Our study

  13. Is gold solubility subject to pressure variations in ascending arc magmas? (United States)

    Jégo, Sébastien; Nakamura, Michihiko; Kimura, Jun-Ichi; Iizuka, Yoshiyuki; Chang, Qing; Zellmer, Georg F.


    Magmas play a key role in the genesis of epithermal and porphyry ore deposits, notably by providing the bulk of ore metals to the hydrothermal fluid phase. It has been long shown that the formation of major deposits requires a multi-stage process, including the concentration of metals in silicate melts at depth and their transfer into the exsolved ore fluid in more superficial environments. Both aspects have been intensively studied for most of noble metals in subsurface conditions, whereas the effect of pressure on the concentration (i.e., solubility) of those metals in magmas ascending from the sublithospheric mantle to the shallow arc crust has been quite neglected. Here, we present new experimental data aiming to constrain the processes of gold (Au) dissolution in subduction-linked magmas along a range of depth. We have conducted hydrous melting experiments on two dacitic/adakitic magmas at 0.9 and 1.4 GPa and ∼1000 °C in an end-loaded piston cylinder apparatus, under fO2 conditions close to NNO as measured by solid Co-Pd-O sensors. Experimental charges were carried out in pure Au containers, the latter serving as the source of gold, in presence of variable amounts of H2O and, for half of the charges, with elemental sulfur (S) so as to reach sulfide saturation. Au concentrations in melt quenched to glass were determined by LA-ICPMS. When compared to previous data obtained at lower pressures and variable redox conditions, our results show that in both S-free and sulfide-saturated systems pressure has no direct, detectable effect on melt Au solubility. Nevertheless, pressure has a strong, negative effect on sulfur solubility. Since gold dissolution is closely related to the behavior of sulfur in reducing and moderately oxidizing conditions, pressure has therefore a significant but indirect effect on Au solubility. The present study confirms that Au dissolution is mainly controlled by fO2 in S-free melts and by a complex interplay of fO2 and melt S2

  14. Paleozoic intrusive rocks from the Dunhuang tectonic belt, NW China: Constraints on the tectonic evolution of the southernmost Central Asian Orogenic Belt (United States)

    Zhao, Yan; Sun, Yong; Diwu, Chunrong; Zhu, Tao; Ao, Wenhao; Zhang, Hong; Yan, Jianghao


    The Dunhuang tectonic belt (DTB) is of great importance for understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt (CAOB). In this study, the temporal-spatial distribution, petrogenesis and tectonic setting of the Paleozoic representative intrusive rocks from the DTB were systematically investigated to discuss crustal evolution history and tectonic regime of the DTB during Paleozoic. Our results reveal that the Paleozoic magmatism within the DTB can be broadly divided into two distinct episodes of early Paleozoic and late Paleozoic. The early Paleozoic intrusive rocks, represented by a suite metaluminous-slight peraluminous and medium- to high-K calc-alkaline I-type granitoids crystallized at Silurian (ca. 430-410 Ma), are predominantly distributed along the northern part of the DTB. They were probably produced with mineral assemblage of eclogite or garnet + amphibole + rutile in the residue, and were derived from magma mixing source of depleted mantle materials with various proportions of Archean-Mesoproterozoic continental crust. The late Paleozoic intrusive rocks can be further subdivided into two stages of late Devonian stage (ca. 370-360 Ma) and middle Carboniferous stage (ca. 335-315 Ma). The former stage is predominated by metaluminous to slight peraluminous and low-K tholeiite to high-K calc-alkaline I-type granitic rocks distributed in the central part of the DTB. They were also generated with mineral assemblage of amphibolite- to eclogite-facies in the residue, and originated from magma source of depleted mantle materials mixed with different degrees of old continental crust. The later stage is represented by adakite and alkali-rich granite exposed in the southern part of the DTB. The alkali-rich granites studied in this paper were possibly produced with mineral assemblage of granulite-facies in the residue and were generated by partial melting of thickened lower continental crust. Zircon Hf isotopes and field distribution of

  15. The nature and history of the Qilian Block in the context of the development of the Greater Tibetan Plateau (United States)

    Huang, Hui; Niu, Yaoling; Nowell, Geoff; Zhao, Zhidan; Yu, Xuehui; Mo, Xuanxue


    The Greater Tibetan Plateau is a geological amalgamation formed by several continental collision events from northeast in the Early Palaeozoic towards southwest in the Cenozoic. Compared to the youngest India-Asia collision event (~ 55 Ma), the earlier events to the north are not well understood, especially the earliest Qilian-Qaidam system at the northern margin. Understanding the petrogenesis of the Paleozoic granitoids in the Qilian Block (QB) helps understand the nature and history of the block, while also offering new perspectives on its sutures to the north (the North Qilian Orogenic Belt) and to the South (the North Qaidam Ultra-High Pressure Metamorphic Belt). Granitoids in the QB were sampled from several intrusions in two areas: Huangyuan (HY) and Gangcha (GC). All the samples are calc-alkaline varying from mafic-diorite to granite. Most of the HY samples are peraluminous containing Al-rich phases. The GC samples can be divided into two groups (fine-grained group with amphibole and coarse-grained without amphibole). Most HY samples are enriched in LREEs with flat HREE patterns (Group A). A garnet-bearing HY sample has elevated HREEs. Another three adakitic samples are depleted in HREEs with negative ?Hf(t) (-12~-11), indicating a deep crustal origin. The coarse-grained GC samples have similar REE patterns to HY group A while fine-grained samples have flat REE patterns with a stronger negative Eu anomaly. Zircons in all these samples are of magmatic origin but age data scatter along the Concordia and do not give "well-constrained" crystallization ages within a single sample. We adopt the histogram and identify the crystallization age with a peak at ~450 Ma. The ages of inherited zircons range from ~ 500 Ma to ~ 2600 Ma. The more peraluminous samples tend to have older inherited zircons, pointing to the greater old crust contribution. The older Proterozoic and Archean ages recorded in inherited zircons reveal the complex histories of the QB, which is likely

  16. Petrogenesis and geodynamic setting of Early Cretaceous mafic-ultramafic intrusions, South China: A case study from the Gan-Hang tectonic belt (United States)

    Qi, Youqiang; Hu, Ruizhong; Liu, Shen; Coulson, Ian M.; Qi, Huawen; Tian, Jianji; Zhu, Jingjing


    metasomatized by adakitic and felsic melts under a subducted oceanic crust-lithospheric mantle in Neoproterozoic. During the subduction of the oceanic crust, the juvenile SCLM can be sandwiched by the ancient SCLM above and the pyroxenites below and stored for hundreds of millions of years until Late Mesozoic. Then partial melting of the pyroxenites was triggered during the peak of extension in response to the tectonic reactivation of the GHTB in Early Cretaceous. It is clear that fault reactivation and structural constraints within the GHTB had played an important role in its magmatic evolution.

  17. Geology, zircon geochronology, and petrogenesis of Sabalan volcano (northwestern Iran) (United States)

    Ghalamghash, J.; Mousavi, S. Z.; Hassanzadeh, J.; Schmitt, A. K.


    Sabalan Volcano (NW Iran) is an isolated voluminous (4821 m elevation; > 800 km2) composite volcano that is located within the Arabia-Eurasia collision zone. Its edifice was assembled by recurrent eruptions of trachyandesite and dacite magma falling into a relatively restricted compositional range (56-67% SiO2) with high-K calc-alkaline and adakitic trace element (Sr/Y) signatures. Previous K-Ar dating suggested protracted eruptive activity between 5.6 and 1.4 Ma, and a two stage evolution which resulted in the construction of the Paleo- and Neo-Sabalan edifices, respectively. The presence of a topographic moat surrounding Neo-Sabalan and volcanic breccias with locally intense hydrothermal alteration are indicative of intermittent caldera collapse of the central part of Paleo-Sabalan. Volcanic debris-flow and debris-avalanche deposits indicate earlier episodes of volcanic edifice collapse during the Paleo-Sabalan stage. In the Neo-Sabalan stage, three dacitic domes extruded to form the summits of Sabalan (Soltan, Heram, and Kasra). Ignimbrites and minor pumice fall-out deposits are exposed in strongly dissected drainages that in part have breached the caldera depression. Lavas and pyroclastic rocks are varyingly porphyritic with Paleo-Sabalan rocks being trachyandesites carrying abundant phenocrysts (plagioclase + amphibole + pyroxene + biotite). The Neo-Sabalan rocks are slightly more evolved and include dacitic compositions with phenocrysts of plagioclase + amphibole ± alkali-feldspar ± quartz. All Sabalan rock types share a common accessory assemblage (oxides + apatite + zircon). High spatial resolution and sensitivity U-Pb geochronology using Secondary Ionization Mass Spectrometry yielded two clusters of zircon ages which range from 4.5 to 1.3 Ma and 545 to 149 ka, respectively (all ages are averages of multiple determinations per sample). U-Th zircon geochronology for selected Neo-Sabalan rocks agrees with the U-Pb ages, with the youngest zircon rims dating

  18. The Pliocene-Quaternary South Harghita (Romania) volcanic chain-ending segment - a review (United States)

    Seghedi, Ioan; Szakács, Alexandru


    South Harghita, the chain terminus segment of the Cǎlimani-Gurghiu-Harghita volcanic range is notorious for its specific characteristics. It consist of different and unique volcanological and petrological features, as compared with the rest of the range, including lowest erupted magma volumes and eruption rates, which originate from changes of the geodynamic setting along with magma generation processes. The Pliocene-Quaternary calc- alkaline volcanism developed in the 5.3 - 0.3 Ma time interval with two gaps at 3.9-2.8 and 1.6-1.0 Ma, respectively, but the volcanoes partially overlap each other along the NW-SE direction, crosscutting the Carpathian internal folded units. At 1.6 - 1.4 Ma K-alkalic volcanism developed at Bicsad/Malnaş at the southward extension of the South Harghita chain, whereas Na-alkalic volcanism (1.2-0.6 Ma) developed 40 km to the west in the Perşani Mountains. There are four major volcanic edifices recognized in this chain segment: Luci-Lazul, Cucu, Pilişca and Ciomadul. Luci-Lazu, the northernmost andesitic volcano shows a typical shield morphology. The Cucu andesite-dacite volcano displays a multiple-crater edifice topped by lava domes. Inside the craterial area there is a complex intrusive assemblage. The next volcano in the row, Pilişca is an andesitic composite volcano topped by steep dacitic lava dome complexes. The south-easternmost dacitic Ciomadul volcanic complex is most well-preserved consisting of a lava dome and flow complex and twin-crater pyroclastic cones developed during several explosive eruptions between 55.9 - 32.6 Ka. According to the recent studies Ciomadul can be viewed as having some residual magma in its crustal magma chamber whose future eruption potential is unclear. The compositional changes from calc-alkaline (Luci-Lazul) to adakite-like calc-alkaline (Cucu-Ciomadul) may be connected to the sinking of the block/slab beneath the active Vrancea seismic zone and coeval with the tearing along the Trotuş fault

  19. New Progresses in 1:50 000 Regional Geological Survey of Diaoluoshan Area, Southeastern Hainan Island%海南吊罗山一带1:5万区调主要成果与进展

    Institute of Scientific and Technical Information of China (English)

    魏昌欣; 李孙雄; 云平; 周进波; 官军; 王超; 袁勤敏; 朱耀河; 莫位任


    在海南岛东南部吊罗山.陵水县地区完成的1:5万区域地质调查,通过地层学的综合研究,将区域地层划分为5个岩石地层单位(包括1个非正式地层单位);新获得9件侵入岩LA—ICP—MS锆石U—Pb年龄,为建立区域岩浆岩的时空格架和反演演化过程提供了新的资料;通过地球化学对比,首次将调查区内早白垩世保亭杂岩体确定为C型埃达克质岩石,为区内燕山晚期花岗岩找矿提供基础地质资料;首次发现和厘定出北东向芒三水库.长丰韧性变形带,并对变形带的岩石学特征、变形特征、运动学特征等进行了初步研究;新发现稀土矿床l处、矿化点10个,圈定4个成矿预测区,为下一步开展地质找矿提供了靶区;调查了区内地质灾害类型及分布特征,探讨了地质灾害的形成条件和诱发因素;对区内旅游资源进行了概略调查。%During 1:50 000 regional survey in Diaoluoshan area, Lingshui County, southeastern Hainan province, we subdivided the regional stratigraphic system into five lithostratigraphic units (include one informal lithostratigraphic unit) through integrated study of stratigraphy. Obtainment of nine new zircon LA-ICP-MS U-Pb ages of intrusions offered new information for establishing the evolving process and spa- tio-temporal fi'amework of the magrnatic rocks. Early Cretaceous Baoting complex is defined as C-type adakite by geochemical research, which provides basic geological information to search for mineral deposits in Late Yanshanian granite in this area. The petrological, deformation and kinematic features of deformable zone of newly discovered NE-trending Mangsan Reservior-Changfeng ductile shear zone are studied in detail. One rare earth deposit and ten ore occurrences are discovered in this geological survey, and four metallogenic prog- nosis areas are pointed out for further geologic prospecting. The types and distributing

  20. Geochemistry of Garibaldi Lake andesites and dacites indicates crustal contamination involved in formation of Northern Cascade arc lavas (United States)

    Martindale, M.; Mullen, E.; Weis, D.


    The Cascade Arc presents a unique setting for studying the controls on andesite genesis and the implications for growth and evolution of the continental crust. It is the type-locality for a ';hot' subduction zone, where the downgoing slab is young and subduction is relatively slow. The northern segment of the Cascade arc, the Garibaldi Volcanic Belt (GVB), hosts the youngest subducting crust in Cascadia and the termination of the subducting slab. These conditions may affect magma generation processes by reducing the amount of water reaching the area of melt generation [1,2] and imparting an adakitic signature to magmas generated there if the slab edge melts [3]. We provide insights on the origin of andesites and dacites from the Garibaldi Lake area using new high-precision Pb, Sr, Nd, Hf isotope ratios and trace element data. Andesites and dacites from the Garibaldi Lake area (The Black Tusk, Mt. Price, and The Table) are calc-alkaline and show evidence for crustal contamination such as positive correlations between Ba/Nb and SiO2. Silica variation diagrams show no systematic trend for any of the volcanic centres, suggesting the presence of distinct magma batches. Garibaldi Lake andesites and dacites have among the least radiogenic Pb isotope ratios of all Cascade arc lavas, and define a linear array in Pb-isotope space. This most likely reflects mixing between MORB-source mantle (similar to Gorda and Explorer plate sources) and locally subducting sediments [4]. However, relative to GVB basalts and lavas from the rest of the Cascades (High Cascades), the andesites and dacites have higher 207Pb/204Pb (15.55-15.56) for a given 206Pb/204Pb (18.66-18.74). The Garibaldi Lake lavas also have higher 87Sr/86Sr (0.7033-0.7036) and lower ɛNd (5.8-7.9) at a given 206Pb/204Pb than GVB basalts and High Cascades lavas but among the highest ɛNd for a given SiO2 for the whole of the Cascades. ɛHf values (10.5-13.5) are higher at a given SiO2 value for Garibaldi Lake evolved

  1. A Cambrian intra-oceanic subduction system in the Bozshakol area, Kazakhstan (United States)

    Shen, Ping; Pan, Hongdi; Seitmuratova, Eleonora; Yuan, Feng; Jakupova, Sholpan


    adakites. Therefore, Bozshakol intrusive rocks were also derived from the mantle wedge and minor slab melts. We propose a model of intra-oceanic subduction for the Middle to Late Cambrian magmatic evolution of magmatic arcs in northwestern central Kazakhstan.

  2. Age and geochemistry of western Hoh-Xil-Songpan-Ganzi granitoids, northern Tibet: Implications for the Mesozoic closure of the Paleo-Tethys ocean (United States)

    Zhang, Li-Yun; Ding, Lin; Pullen, Alex; Xu, Qiang; Liu, De-Liang; Cai, Fu-Long; Yue, Ya-Hui; Lai, Qing-Zhou; Shi, Ren-Deng; Ducea, Mihai N.; Kapp, Paul; Chapman, Alan


    A geologic investigation was undertaken in the Hoh-Xil-Songpan-Ganzi (HXSG) complex, northern Tibet in order to better understand magma genesis and evolution during the late stages of Paleo-Tethys ocean closure. The HXSG complex is composed of vast accumulations of Middle-Upper Triassic marine gravity flow deposits that were extensively intruded by igneous rocks. These early Mesozoic rocks exposed in this area record a rich history of accretionary tectonics during the amalgamation of the Tibetan Plateau terranes. Eight plutons sampled from the western HXSG complex yield zircon U-Pb ages that range from 225 to 193 Ma. Muscovite 40Ar/39Ar ages for the Hudongliang and Zhuonai Lake plutons yield ages of 210.7 ± 2.5 Ma and 212.7 ± 2.5 Ma, respectively. These plutonic rocks can be subdivided into two geochemically distinct groups. Group 1 (221-212 Ma: Dapeng Lake, Changhong Lake and Heishibei Lake plutons) is composed of high-K calc-alkaline rocks that have strongly fractionated REE patterns with high (La/Yb)N ratios (91-18) and generally lack Eu anomalies (Eu*/Eu = 1.02-0.68). Rocks in Group 1 display pronounced negative Nb-Ta and Ti anomalies on primitive mantle-normalized spidergrams. Group 1 rocks exhibit high Sr (782-240 ppm) and low Y (6.3-16.0 ppm) contents with high Sr/Y ratios (84-20). Based on Sr-Nd-Hf isotopic data (87Sr/86Sri = 0.7079-0.7090, ɛNd(t) = - 7.7-- 4.7, ɛHf(t) = - 5.7-- 0.8) and low MgO contents (MgO = 1.10-2.18%), Group 1 rocks are geochemically similar to adakitic rocks and were probably derived from partial melting of the downgoing Paleo-Tethys oceanic slab and overlying marine sediments. Group 2 plutons (225-193 Ma: Daheishan, Yunwuling, Zhuonai Lake, Malanshan and Hudongliang plutons) display lower P2O5 with increasing SiO2 and are medium-K to high-K I-type calc-alkaline bodies with low Sr (14-549 ppm) and high Y (22.3-10.5 ppm) contents. Group 2 rocks have variable fractionated REE patterns ((La/Yb)N = 3-38) and negative Eu anomalies (Eu

  3. Geochemical characteristics and their implications of peraluminous granite in the Jiama deposit, Tibet%西藏甲玛过铝质花岗岩的地球化学特征及成因意义

    Institute of Scientific and Technical Information of China (English)

    秦志鹏; 汪雄武; 唐菊兴; 唐晓倩; 周云; 彭慧娟


    探讨了西藏甲玛中新世花岗斑岩的地球化学特征及意义.通过对岩体(脉)进行的野外地质调查、岩相学研究、全岩地球化学分析及同位素分析,结果表明甲玛花岗斑岩表现过铝质花岗岩的特征,整体表现为:Na2O/K2O1.1,刚玉标准分子(w(C-norm))>1%;轻稀土元素富集,重稀土元素亏损,负Eu、Ce异常不明显,高Sr,低Y、Yb,但Sr/Y值相对较低,不具有埃达克岩的地球化学特征;此外,富集大离子亲石元素,尤其是Rb、Cs、Th、U、K等元素,而高场强元素,尤其是Sc、Ti则强烈亏损;Pb-Sr-Nd同位素均显示其下地壳的物质来源,并受到地幔物质(EMⅡ)的混染.甲玛过铝质花岗斑岩形成于亚洲-印度大陆"后碰撞"造山运动早期阶段的构造活动.%This paper studies the geochemical characteristics and their implications of the Miocene granite porphyry in the Jiama deposit, Tibet. The results are obtained by means of field geological investigations, petrographic study, bulk rock analysis and isotopic analysis. These results indicate that the Jiama granite porphyry has the characteristics of peraluminous granite. Na2O/K2O is less than 1 and A/CNK is more than 1. 1. Corundum standard molecule(w(C-norm)) is more than 1%. Light REE are rich, while heavy REE are scarce. Negative Eu and Ce are extremely inconspicuous. Sr is high, Y and Yb are low, and Sr/Y value is relatively low. It doesnot possess the geochemical characteristics of adakite rock. It is rich in LILE, especially Rb, Cs, Th, U and K, while its HFSE are scarce, especially Sc and Ti. The Pb-Sr-Nd isotopes reveal about the source of materials from the lower crust, which is mixed with the mantle materials (EM Ⅱ ). It is concluded that the Jiama peraluminous granite porphyry is a product of tectonic movements in the early period of the “post-collision” orogenesis of Asia-India Continent.

  4. Geochronology, geochemistry, and Sr-Nd-Hf isotopes of the early Paleozoic igneous rocks in the Duobaoshan area, NE China, and their geological significance (United States)

    Wu, Guang; Chen, Yuchuan; Sun, Fengyue; Liu, Jun; Wang, Guorui; Xu, Bei


    The Duobaoshan area of northwestern Heilongjiang Province is the most important copper resource concentration region in NE China. To date, the Duobaoshan superlarge Cu-Mo deposit and the Tongshan large Cu-Mo deposit have been discovered in the Duobaoshan area. Both the deposits are hosted by granodiorites and volcanic rocks. Zircon LA-ICP-MS U-Pb dating indicates that these granodiorites emplaced approximately 479 Ma ago and that those volcanic rocks erupted between 447 and 450 Ma. The early Ordovicain granodiorites belong to the high-K to medium-K calc-alkaline series and are characterized by high Al2O3 and Sr contents, low Yb and Y contents, and relatively low Mg# values and Na2O/K2O ratios, with positive Eu or slight negative Eu anomalies (averaging 1.18). All of these geochemical characters are similar to those of the adakites generated by partial melting of a thickened lower crust in the world. Moreover, the granodiorites have low initial 87Sr/86Sr ratios (varying from 0.703474 to 0.704436), very high zircon εHf(t) and whole-rock εNd(t) values (varying from 13.0 to 16.8 and 5.27 to 5.46, respectively), and young zircon Hf and whole-rock Nd single-stage and two-stage model ages. Taking these geochemical characteristics and Sr-Nd-Hf isotope compositions together, we suggest that the early Ordovician granodiorites in the Duobaoshan area occurred in a post-collision environment and were formed by partial melting of a juvenile thickened lower crust dominated by depleted mantle-derived material. These late Ordovician volcanic rocks, which are composed of basalt, basaltic andesite, and andesite, belong to the tholeiitic or calc-alkaline series. They are generally enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Zr, Hf, P, and Ti), consistent with the geochemistry of igneous rocks from island arcs or active continental margins. Compared with the early Ordovician granodiorites, these volcanic rocks

  5. Mo-mineralized porphyries are relatively hydrous and differentiated: insights from the Permian-Triassic granitic complex in the Baituyingzi Mo-Cu district, eastern Inner Mongolia, NE China (United States)

    Sun, Yan; Liu, Jianming; Zeng, Qingdong; Wang, Jingbin; Wang, Yuwang; Hu, Ruizhong; Zhou, Lingli; Wu, Guanbin


    Mo-Cu mineralization in the Baituyingzi district of eastern Inner Mongolia occurs within a granitic complex. This paper presents and discusses zircon U-Pb ages and whole-rock geochemical and Sr-Nd-Pb isotopic data from the granitic complex as potential indicators for porphyry Mo fertility. The U-Pb ages indicate that five units of the granitic complex were emplaced between 265.2 ± 0.7 and 246.5 ± 1.0 Ma. Constrained by crosscutting dikes, Mo-Cu mineralization was probably related to the Baituyingzi monzogranite porphyry dated at 248.2 ± 0.64 Ma. The intrusions belong to high-K calc-alkaline to shoshonitic series that are characterized by highly fractionated rare earth element (REE) patterns and strong enrichments of large ion lithophile elements, relative to high-field strength elements. Apart from the ˜246-Ma dike that shows negative ɛNd (t) values (-14.9 to -13.1), the intrusions have ɛNd(t) values ranging from -3.9 to 1.0, relatively young depleted mantle model ages (811 to 1183 Ma), 206Pb/204Pb of 18.137-18.335, and 207Pb/204Pb of 15.591-15.625, which are consistent with a juvenile lower crustal origin. Among the intrusions, the ˜248-Ma porphyry and the ˜246-Ma dike show adakite-like characteristics (e.g., Sr/Y = 44.9-185) and listric-shaped REE patterns that indicate amphibole fractionation and a hydrous magma source. However, the porphyry exhibits a higher differentiation index (81.4-91.5) and a steeper REE profile (e.g., LaN/YbN = 25.6-87.0) than those of the ˜246-Ma dike, which suggests that it is highly differentiated. We propose that the complex was generated by the partial melting of juvenile mafic lower crust (containing minor old crustal relicts) that was triggered by collision between the North China Craton and Siberian Craton. As indicated by the Th/Nb, Th/Yb, Ba/Th, and Ba/La ratios of the intrusions, the crust may have been derived from the melting of the fertile mantle wedge that was metasomatized by various amounts of slab-derived fluids

  6. Rare earth elements exploitation, geopolitical implications and raw materials trading (United States)

    Chemin, Marie-Charlotte


    Rare earth elements (REE) correspond to seventeen elements of the periodic table. They are used in high technology, cracking, electric cars' magnet, metal alloy for batteries, and also in phone construction or ceramics for electronic card. REEs are an important resource for high technology. This project targets 16 years old students in the subject "personalized aid" and will last six weeks. The purpose of this project is to develop autonomy and research in groups for a transdisciplinary work. This project gathers knowledge in geology, geography and economics. During the first session students analyze the geology applications of the REE. They begin the analysis with learning the composition in different rocks such as basalt and diorite to make the link with crystallization. Then they compare it with adakite to understand the formation of these rocks. In the second session, they study REE exploitation. We can find them as oxides in many deposits. The principal concentrations of rare earth elements are associated with uncommon varieties of igneous rocks, such as carbonatites. They can use Qgis, to localize this high concentration. In the third session, they study the environmental costs of REE exploitation. Indeed, the exploitation produces thorium and carcinogenic toxins: sulphates, ammonia and hydrochloric acid. Processing one ton of rare earths produces 2,000 tons of toxic waste. This session focuses, first, on Baotou's region, and then on an example they are free to choose. In the fourth session, they study the geopolitical issues of REE with a focus on China. In fact this country is the largest producer of REE, and is providing 95% of the overall production. REE in China are at the center of a geopolitical strategy. In fact, China implements a sort of protectionism. Indeed, the export tax on REE is very high so, as a foreign company, it is financially attractive to establish a manufacturing subsidiary in China in order to use REE. As a matter of fact

  7. Mo-mineralized porphyries are relatively hydrous and differentiated: insights from the Permian-Triassic granitic complex in the Baituyingzi Mo-Cu district, eastern Inner Mongolia, NE China (United States)

    Sun, Yan; Liu, Jianming; Zeng, Qingdong; Wang, Jingbin; Wang, Yuwang; Hu, Ruizhong; Zhou, Lingli; Wu, Guanbin


    Mo-Cu mineralization in the Baituyingzi district of eastern Inner Mongolia occurs within a granitic complex. This paper presents and discusses zircon U-Pb ages and whole-rock geochemical and Sr-Nd-Pb isotopic data from the granitic complex as potential indicators for porphyry Mo fertility. The U-Pb ages indicate that five units of the granitic complex were emplaced between 265.2 ± 0.7 and 246.5 ± 1.0 Ma. Constrained by crosscutting dikes, Mo-Cu mineralization was probably related to the Baituyingzi monzogranite porphyry dated at 248.2 ± 0.64 Ma. The intrusions belong to high-K calc-alkaline to shoshonitic series that are characterized by highly fractionated rare earth element (REE) patterns and strong enrichments of large ion lithophile elements, relative to high-field strength elements. Apart from the ˜246-Ma dike that shows negative ɛNd ( t) values (-14.9 to -13.1), the intrusions have ɛNd( t) values ranging from -3.9 to 1.0, relatively young depleted mantle model ages (811 to 1183 Ma), 206Pb/204Pb of 18.137-18.335, and 207Pb/204Pb of 15.591-15.625, which are consistent with a juvenile lower crustal origin. Among the intrusions, the ˜248-Ma porphyry and the ˜246-Ma dike show adakite-like characteristics (e.g., Sr/Y = 44.9-185) and listric-shaped REE patterns that indicate amphibole fractionation and a hydrous magma source. However, the porphyry exhibits a higher differentiation index (81.4-91.5) and a steeper REE profile (e.g., LaN/YbN = 25.6-87.0) than those of the ˜246-Ma dike, which suggests that it is highly differentiated. We propose that the complex was generated by the partial melting of juvenile mafic lower crust (containing minor old crustal relicts) that was triggered by collision between the North China Craton and Siberian Craton. As indicated by the Th/Nb, Th/Yb, Ba/Th, and Ba/La ratios of the intrusions, the crust may have been derived from the melting of the fertile mantle wedge that was metasomatized by various amounts of slab

  8. Ca2+ involvement in the action potential generation of myenteric neurones in the rat oesophagus. (United States)

    De Laet, A; Cornelissen, W; Adriaensen, D; Van Bogaert, P-P; Scheuermann, D W; Timmermans, J-P


    Intracellular recordings were used to study the physiological behaviour of rat oesophageal myenteric neurones, which are embedded in striated muscle. Injection of depolarizing pulses evoked action potentials with a clear 'shoulder' in all neurones. This shoulder disappeared under low Ca2+/high Mg2+ conditions. Tetrodotoxin (TTX; 1 micromol L-1) did not impede spike firing, whereas under combined TTX and low Ca2+/high Mg2+ conditions the action potentials were completely abolished, indicating that TTX- resistant action potentials are mediated by a Ca2+ current. Further experiments with omega-conotoxin GVIA (100 nmol L-1) revealed that these Ca2+ currents enter the cell via N-type voltage-activated Ca2+ channels (see also accompanying paper). Tetraethylammonium (10 mmol L-1) caused broadening of the action potentials, which probably resulted from prolonged Ca2+ influx due to blockade of the delayed rectifier K+ channel. Although Ca2+ appears to be involved in the spike generation of all rat oesophageal myenteric neurones, only a minority (14%) shows a slow afterhyperpolarization. Thus, no strict correlation exists between the presence of a shoulder and a slow afterhyperpolarization. Furthermore, morphological identification of 25 of the impaled neurones revealed that there was no strict correlation between morphology and electrophysiological behaviour. Consequently, rat oesophageal myenteric neurones appear to differ in several aspects from myenteric neurones in smooth muscle regions of the gastrointestinal tract.

  9. Impact of high CO2 on the geochemistry of the coralline algae Lithothamnion glaciale (United States)

    Ragazzola, F.; Foster, L. C.; Jones, C. J.; Scott, T. B.; Fietzke, J.; Kilburn, M. R.; Schmidt, D. N.


    Coralline algae are a significant component of the benthic ecosystem. Their ability to withstand physical stresses in high energy environments relies on their skeletal structure which is composed of high Mg-calcite. High Mg-calcite is, however, the most soluble form of calcium carbonate and therefore potentially vulnerable to the change in carbonate chemistry resulting from the absorption of anthropogenic CO2 by the ocean. We examine the geochemistry of the cold water coralline alga Lithothamnion glaciale grown under predicted future (year 2050) high pCO2 (589 μatm) using Electron microprobe and NanoSIMS analysis. In the natural and control material, higher Mg calcite forms clear concentric bands around the algal cells. As expected, summer growth has a higher Mg content compared to the winter growth. In contrast, under elevated CO2 no banding of Mg is recognisable and overall Mg concentrations are lower. This reduction in Mg in the carbonate undermines the accuracy of the Mg/Ca ratio as proxy for past temperatures in time intervals with significantly different carbonate chemistry. Fundamentally, the loss of Mg in the calcite may reduce elasticity thereby changing the structural properties, which may affect the ability of L. glaciale to efficiently function as a habitat former in the future ocean.

  10. Impact of pulsed electric field on electrodialysis process performance and membrane fouling during consecutive demineralization of a model salt solution containing a high magnesium/calcium ratio. (United States)

    Cifuentes-Araya, Nicolás; Pourcelly, Gérald; Bazinet, Laurent


    Pulsed electric fields (PEFs), hashed modes of current consisting in the application of a constant current density during a fixed time (Ton) followed by a pause lapse (Toff), were recently demonstrated as an effective alternative for mineral fouling mitigation and process intensification during electrodialysis (ED) treatments. Recent ED studies have continuously reported a considerable mineral fouling formation on ion-exchange membranes, especially during the demineralization of solutions containing a high Mg/Ca ratio and a basified concentrate solution. The aim of this study was to evaluate the process performance under two different PEF conditions on a mineral solution containing a mineral mixture giving a high Mg(2+)/Ca(2+) ratio of 2/5. Two different pause-lapse durations (PEF ratio 1 (Ton/Toff 10s/10s); PEF ratio 0.3 (Ton/Toff 10s/33.3 s)) during consecutive ED treatments and their comparison with dc current were evaluated at a current density of 40 mA/cm(2). Our results showed that PEFs resulted in an intensification of ED process, enhancing the demineralization rates (DRs), reducing the system resistance (SR), and reducing the fouling and energy consumption (EC). PEF ratio 1 was the most optimal condition among the current regimes applied, leading to faster and higher demineralization rates due to a lower fouling and with low energy consumption during all consecutive runs.

  11. Mantle olivine xenocrysts entrained in Mesozoic basalts from the North China craton:Implication for replacement process of lithospheric mantle

    Institute of Scientific and Technical Information of China (English)

    ZHANG Hongfu; YING Jifeng; XU Ping; MA Yuguang


    Mesoxzoic(125 Ma) Fangcheng basalts from Shandong Province contain clearly zoned olivines that are rare in terrestrial samples and provide first evidence for the replacement of lithospheric mantle from high-Mg peridotites to low-Mg peridotites through peridotite-melt reaction. Zoned olivines have compostions in the core(Mg#=87.2-90.7)similar to those olivines from the mantle peridotitic xenoliths entrained in Cenozoic basalts from the North China craton and in the rim (Mg#=76.8-83.9)close to olivine phenocrysts of the host basalts (75.7-79.0).These compositional features as well as rounded crystal shapes and smaller grain sizes (300-800μm)demonstrate that these zoned olivines are mantle xenocrysts , important type of the replacement of lithospheric mantle.The reaction resulted in the transformation of the Paleozoic refractory (high-Mg)peridotites to the late Mesozoic fertile (low-Mg) and radiogenic isotope-enriched peridotites,leading to the loss of old lithospheric mantle.

  12. Eclogite-melt/peridotite reaction: Experimental constrains on the destruction mechanism of the North China Craton

    Institute of Scientific and Technical Information of China (English)


    To study the mechanism of melt-peridotite reaction pertinent to the destruction of the North China Craton (NCC) lithosphere, a series of experiments were performed at a pressure of 2.0 GPa and temperatures from 1250 to 1400°C using Bixiling eclogite and Damaping peridotite as starting materials. The experimental results show that the reaction between eclogite melt and peridotite causes dissolution of olivine and orthopyroxene and precipitation of clinopyroxene in the melt. The experimental run products, characterized by a lherzolite/pyroxenite/garnet-pyroxenite sequence, are consistent with the mantle xenoliths in the Neogene Hannuoba basalt of the NCC found by Liu et al. (2005). It suggests that the mafic lower continental crust was probably recycled into the mantle during the Mesozoic Era. In the experiments conducted at 1300 and 1350°C, the resulting melts have a high Mg# andesite signature, indicating that the melt-peridotite reaction may have played a major role in the generation of high Mg# andesite. Our experimental results support the hypothesis that melts derived from foundered eclogite in the asthenosphere will consume the lithospheric peridotites. Therefore, melt-peridotite reaction is an important mechanism for the destruction/thinning of the lithosphere.

  13. 印度与欧亚板块东部碰撞边界——腾冲火山岩的Nd-Sr同位素与微量元素研究

    Institute of Scientific and Technical Information of China (English)

    朱炳泉; 毛存孝


    The Tengchong volcanies in western Yunnan Province, China, are located in the eastern part of the collision margin between Indian and Eurasian Plates. Alternating extention and compression controlled the eruption, from late Tertiary to Holeeno, of at least 5 groups of volcanics consisting of a Major series of hlgh-Al basalts (3 groups), a high-K andesite-dacite group and a high-Mg basalt group. The Major series has a range of GNd from +0.7 to-6.7 and Sr87/Sr86 from 0.70595 to 0.70881, exhibiting good linear correlations between Zr/Ni and Zr as well as between Nd. and both Sm/Nd and 1/Nd and similar chondrite-normalized incompatible element patterns. This suggests an ecologitic source metasomatized with fluids derived from parts of thesubducted Indian plate.The high-K andesite-dacite group shows a more extreme isotopic composition of GNd=-12.3, Sr87/Sr66=0.71124. It is chemically comparable to the calc-alkaline lavas in Xizang and could be resulted from mixing between shallow mantle zones and lower crust. The high-Mg basalt group has Sr87/Sr86-0.708 and slightly negative GNd (-2). They are similar, in chemical composition and possibly also in source, to the intraplate basalts in east China. A partial melting model of isotopic tmequilibrium system has been proposed to explain the isotope and trace element correlations of Tengchong volcanics.

  14. Sulfur in foraminiferal calcite as a potential proxy for seawater carbonate ion concentration (United States)

    van Dijk, I.; de Nooijer, L. J.; Boer, W.; Reichart, G.-J.


    Sulfur (S) incorporation in foraminiferal shells is hypothesized to change with carbonate ion concentration [CO32-], due to substitution of sulfate for carbonate ions in the calcite crystal lattice. Hence S/Ca values of foraminiferal carbonate shells are expected to reflect sea water carbonate chemistry. To generate a proxy calibration linking the incorporation of S into foraminiferal calcite to carbonate chemistry, we cultured juvenile clones of the larger benthic species Amphistegina gibbosa and Sorites marginalis over a 350-1200 ppm range of pCO2 values, corresponding to a range in [CO32-] of 93 to 211 μmol/kg. We also investigated the potential effect of salinity on S incorporation by culturing juvenile Amphistegina lessonii over a large salinity gradient (25-45). Results show S/CaCALCITE is not impacted by salinity, but increases with increasing pCO2 (and thus decreasing [CO32-] and pH), indicating S incorporation may be used as a proxy for [CO32-]. Higher S incorporation in high-Mg species S. marginalis suggests a superimposed biomineralization effect on the incorporation of S. Microprobe imaging reveals co-occurring banding of Mg and S in Amphistegina lessonii, which is in line with a strong biological control and might explain higher S incorporation in high Mg species. Provided a species-specific calibration is available, foraminiferal S/Ca values might add a valuable new tool for reconstructing past ocean carbonate chemistry.

  15. Role of calcium in the regulation of acetylcholine receptor synthese in cultured muscle cells*. (United States)

    Birnbaum, M; Reis, M A; Shainberg, A


    Embroyonic muscles differentiated in vitro were used to study the effects of intracellular Ca2+ ([Ca2+1]i) variations on the amount of acetylcholine receptors ([AChR]) in the cell membrane. 2. Increased Ca2+ concentration in the growth medium ([Ca2+]o) caused a marked elevation of AChR levels, apparently through de novo synthesis. 3. Agents known to increase [Ca2+]i and its accumulation in the sarcoplasmic reticulum (SR), such as ionophore A23187, sodium dantrolene (DaNa), or high [Mg2+]o all enhanced alpha-bungarotoxin (alpha-BGT) binding after 48 h of treatment. 4. Electrical stimulation or caffeine, both affectors of SR calcium release, brought about a decrease in [AChR] probably by suppressing its synthesis. 5. The effects of simultaneous treatment with two AChR-inducing agents, namely, high [Ca2+]o in the presence of tetrodotoxin (TTX) or high [Mg2+]o were not additive, thus suggesting action via a common saturable mediator. 6. Intermediate AChR levels obtained following simultaneous treatments with opposing effects, e.g., electrical stimulation in the presence of high [Ca2+]o or DaNa, suggest contradictory actions on a common mediator. 7. All these observations indicate a strong correlation between SR calcium levels and [AChR] on myotubes; while calcium accumulation in the Sr was followed by increased AChR synthesis, calcium release was accompanied by suppression of receptor synthesis.

  16. Skeletal structures and habitats of Recent and fossil Acanthochaetetes (subclass Tetractinomorpha, Demospongiae, Porifera) (United States)

    Reitner, J.; Engeser, T. S.


    The investigation of the habitats, the spicular skeletons, and the structure and chemistry of the nonspicular high-Mg calcite skeletons of a fossil Acanthochaetetes from the Late Albian (Cretaceous) of Northern Spain and the extant Acanthochaetetes wellsi from Pacific reefs demonstrates an astonishing correspondence. The skeletons of both species are hemispherical or pyriform with the lower part containing an epitheca. They are built up of single calicles which are subdivided by tabulae. Spines protrude from the walls into the calicles. Scanning electron microscopy and thin sections reveal that the high-Mg calcite skeleton consists of two different microstructures: a irregular ssensu Wendt 1979 or microlamellar (sensu Cuif et al. 1979) and a completely irregular structure. AAS and EDAX analysis of the calcite skeletons produce roughly the same Mg and Sr contents. Tylostyle megascleres and aster-like microscleres are observed in the spicular skeletons of both species. The only difference between the two species is the greater variability of the microscleres in the extant species. Moreover, the fossil species incorporates the scleres in the non-spicular skeleton, while the extant species does not. Both species live/lived in the same niches of tropical reefs: the cryptic habitats of submarine caves in the reef core and the dimly lighted habitats of the deeper fore-reef.

  17. Impact of high CO2 on the geochemistry of the coralline algae Lithothamnion glaciale. (United States)

    Ragazzola, F; Foster, L C; Jones, C J; Scott, T B; Fietzke, J; Kilburn, M R; Schmidt, D N


    Coralline algae are a significant component of the benthic ecosystem. Their ability to withstand physical stresses in high energy environments relies on their skeletal structure which is composed of high Mg-calcite. High Mg-calcite is, however, the most soluble form of calcium carbonate and therefore potentially vulnerable to the change in carbonate chemistry resulting from the absorption of anthropogenic CO2 by the ocean. We examine the geochemistry of the cold water coralline alga Lithothamnion glaciale grown under predicted future (year 2050) high pCO2 (589 μatm) using Electron microprobe and NanoSIMS analysis. In the natural and control material, higher Mg calcite forms clear concentric bands around the algal cells. As expected, summer growth has a higher Mg content compared to the winter growth. In contrast, under elevated CO2 no banding of Mg is recognisable and overall Mg concentrations are lower. This reduction in Mg in the carbonate undermines the accuracy of the Mg/Ca ratio as proxy for past temperatures in time intervals with significantly different carbonate chemistry. Fundamentally, the loss of Mg in the calcite may reduce elasticity thereby changing the structural properties, which may affect the ability of L. glaciale to efficiently function as a habitat former in the future ocean.

  18. Petrogenesis of Neoarchean metavolcanic rocks in Changyukou, Northwestern Hebei: Implications for the transition stage from a compressional to an extensional regime for the North China Craton (United States)

    Liou, Peng; Shan, Houxiang; Liu, Fu; Guo, Jinghui


    The 2.5 Ga metavolcanic rocks in Changyukou, Northwestern Hebei, can be classified into three groups based on major and trace elements: high-Mg basalts, tholeiitic basalts, and the calc-alkaline series (basaltic andesites-andesites and dacites-rhyolites). Both high-Mg basalts and tholeiitic basalts have negative anomalies of Nb, Zr, Ti and Heavy Rare Earth Elements (HREE) as well as enrichments of Sr, K, Pb, Ba and Light Rare Earth Elements (LREE) and show typical subduction zone affinities. The petrogenesis of high-Mg basalts can be ascribed to high-degree partial melting of an enriched mantle source in the spinel stability field that was previously enriched in Large Ion Lithophile Elements (LILE) and LREE by slab-derived hydrous fluids/melts/supercritical fluids, as well as the subsequent magma mixing processes of different sources at different source depths, with little or no influence of polybaric fractional crystallization. The flat HREE of tholeiitic basalts indicates they may also originate from the spinel stability field, but from obviously shallower depths than the source of high-Mg basalts. They may form at a later stage of the subduction process when rapid slab rollback leads to extension and seafloor spreading in the upper plate. We obtain the compositions of the Archean lower crust of the North China Craton based on the Archean Wutai-Jining section by compiling the average tonalite-trondhjemite-granodiorite (TTG) components, average mafic granulite components, and average sedimentary rock components. The modeling results show that the generation of high-Al basalts, basaltic andesites and andesites can be attributed to assimilation by high-Mg basalts (primary basalts) of relatively high-Al2O3 thickened lower crust and the subsequent crystallization of prevailing mafic mineral phases, while Al2O3-rich plagioclase crystallization is suppressed under high-pressure and nearly water-saturated conditions. Dacites and rhyolites may be the result of further

  19. Paleoproterozoic crustal evolution in the East Sarmatian Orogen: Petrology, geochemistry, Sr-Nd isotopes and zircon U-Pb geochronology of andesites from the Voronezh massif, Western Russia (United States)

    Terentiev, R. A.; Savko, K. A.; Santosh, M.


    Andesites and related plutonic rocks are major contributors to continental growth and provide insights into the interaction between the mantle and crust. Paleoproterozoic volcanic rocks are important components of the East Sarmatian Orogen (ESO) belonging to the East European Craton, although their petrogenesis and tectonic setting remain controversial. Here we present petrology, mineral chemistry, bulk chemistry, Sr-Nd isotopes, and zircon U-Pb geochronological data from andesites and related rocks in the Losevo and Vorontsovka blocks of the ESO. Clinopyroxene phenocrysts in the andesites are depleted in LREE, and enriched in HFSE (Th, Nb, Zr, Hf, Ti) and LILE (Ba, Sr). Based on the chemistry of pyroxenes and whole rocks, as well as Fe-Ti oxides, we estimate a temperature range of 1179 to 1262 °C, pressures of 11.3 to 13.0 kbar, H2O content of 1-5 wt.%, and oxygen fu gacity close to the MH buffer for the melts of the Kalach graben (KG) and the Baygora area (BA) andesites. Our zircon U-Pb geochronological data indicate new zircon growth during the middle Paleoproterozoic as displayed by weighted mean 207Pb/206Pb ages of 2047 ± 17 Ma and 2040 ± 16 Ma for andesite and dacite-porphyry of the BA, and 2050 ± 16 Ma from high-Mg basaltic andesite of the KG. The andesites and related rocks of the KG and BA are characterized by high magnesium contents (Mg # up to 0.68). All these volcanic rocks are depleted in LREE and HFSE, and display negative Nb and Ti anomalies relative to primitive mantle. The high-Mg bulk composition, and the presence of clinopyroxene phenocrysts suggests that the parent melts of the KG and BA suite were in equilibrium with the mantle rocks. The rocks show positive εNd(T) values and low initial 87Sr/86Sr, suggesting that the magmas were mostly derived from metasomatized mantle source. The geochemical differences between the two andesite types are attributed to: the predominance of fractional crystallization, and minor role of contamination in the

  20. The 3.1 Ga Nuggihalli chromite deposits, Western Dhawar craton (India)

    DEFF Research Database (Denmark)

    Mukherjee, Ria; Mondal, Sisir K.; Frei, Robert


    , therefore melting and mixing of the eclogite component with depleted mantle melts resulted in distinct HFSE enrichment in the Nuggihalli rocks. Alternatively, melting of a HFSE-enriched eclogitic slab and the surrounding depleted mantle within an active subduction zone is another possible mechanism, however......The Nuggihalli greenstone belt is part of the older greenstone belts (3.4 - 3.0 Ga) in the Western Dharwar Craton, southern India. This greenstone sequence consists of conformable metavolcanic and metasedimentary supracrustal rock assemblages that belong to the Sargur Group. Sill-like ultramafic......-mafic plutonic bodies are present within these supracrustal rocks (schist rocks) which are in turn enclosed by tonalite-trondhjemite-granodiorite gneiss (TTG). The sill-like ultramafic-mafic rocks are cumulates derived from a high-Mg parental magma that are represented by chromitite-hosted serpentinite...

  1. Collaboration between primitive cell membranes and soluble catalysts. (United States)

    Adamala, Katarzyna P; Engelhart, Aaron E; Szostak, Jack W


    One widely held model of early life suggests primitive cells consisted of simple RNA-based catalysts within lipid compartments. One possible selective advantage conferred by an encapsulated catalyst is stabilization of the compartment, resulting from catalyst-promoted synthesis of key membrane components. Here we show model protocell vesicles containing an encapsulated enzyme that promotes the synthesis of simple fatty acid derivatives become stabilized to Mg(2+), which is required for ribozyme activity and RNA synthesis. Thus, protocells capable of such catalytic transformations would have enjoyed a selective advantage over other protocells in high Mg(2+) environments. The synthetic transformation requires both the catalyst and vesicles that solubilize the water-insoluble precursor lipid. We suggest that similar modified lipids could have played a key role in early life, and that primitive lipid membranes and encapsulated catalysts, such as ribozymes, may have acted in conjunction with each other, enabling otherwise-impossible chemical transformations within primordial cells.

  2. Geochemistry of Archaean supracrustal belts in SW Greenland

    DEFF Research Database (Denmark)

    Szilas, Kristoffer

    . (3) The Nunatak 1390 area contains ultramafic rocks with geochemical characteristics similar to high-Ti komatiites, but they show geochemical signs of a juvenile slab melt contribution. Their high MgO contents may thus reflect flux-melting of a refractory mantle source, as is the case for boninites......This PhD-thesis investigates the geological formation environment of c. 3200-3000 million-year-old volcanic rocks from SW Greenland, using whole-rock geochemical data in combination with U-Pb, Sm-Nd and Lu-Hf isotope data. The following three supracrustal areas were studied: (1) The Tartoq Group...... geochemical mixing trends between juvenile felsic and mafic end-members. This suggests that partial melting and magma mixing by mafic underplating and slab melt metasomatism of the mantle source region were important in forming rocks of andesitic composition, which is also observed in some modern island arcs...

  3. Fish as major carbonate mud producers and missing components of the tropical carbonate factory (United States)

    Perry, Chris T.; Salter, Michael A.; Harborne, Alastair R.; Crowley, Stephen F.; Jelks, Howard L.; Wilson, Rod W.


    Carbonate mud is a major constituent of recent marine carbonate sediments and of ancient limestones, which contain unique records of changes in ocean chemistry and climate shifts in the geological past. However, the origin of carbonate mud is controversial and often problematic to resolve. Here we show that tropical marine fish produce and excrete various forms of precipitated (nonskeletal) calcium carbonate from their guts ("low" and "high" Mg-calcite and aragonite), but that very fine-grained (mostly 4 mole % MgCO3) are their dominant excretory product. Crystallites from fish are morphologically diverse and species-specific, but all are unique relative to previously known biogenic and abiotic sources of carbonate within open marine systems. Using site specific fish biomass and carbonate excretion rate data we estimate that fish produce ~6.1 x 106 kg CaCO3/year across the Bahamian archipelago, all as mud-grade (the factories function both today and in the past.

  4. Effect of magnesium content on the semi solid cast microstructure of hypereutectic aluminum-silicon alloys (United States)

    Hekmat-Ardakan, Alireza


    A comprehensive study of microstructural evolution of A390 hypereutectic aluminum-silicon alloy (Al-17%Si-4.5%Cu-0.5%Mg) with addition of Mg contents up to 10% was carried out during semi solid metal processing as well as conventional casting. As a first step, the FACTSAGE thermodynamic databank and software was applied in order to investigate the phase diagram, the solidification behavior as well as the identification of the components that are formed during the solidification of A390 alloy with different Mg contents for equilibrium and non-equilibrium (Schiel) conditions. With higher Mg content between 4.2 - 7.2 %, the Mg2Si intermetallic phase is solidified in the eutectic network according to the ternary reaction together the primary silicon due to the binary reaction of Liq → Si + Mg2Si. However the primary silicon is still the first solidified phase in this critical Mg zone. For Mg contents greater than 7.2%, the Mg2Si solidifies first as a primary phase. In fact, the Mg2Si is solidified during the primary, the binary and the ternary reactions and can be observed in the microstructure as a eutectic phase and a pro-eutectic phase with different morphology. In the next stage, the experimental tests were carried out in order to verify the accuracy of the results obtained by the FACTSAGE software. The microstructures of the A390 and the 6 and 10 wt% Mg alloys were investigated using conventional casting and rheocasting (stir casting) processes with continuous cooling solidification. The results showed that, for both processes, the microstructure of the eutectic network for high Mg alloys, specifically the eutectic Si phase is modified compared to the eutectic Si in the microstructure of A390 alloy. However the alloys with 6% and 10% Mg have a similar eutectic morphology. The eutectic formation temperature was measured by placing the thermocouple into the melt for determination of the cooling curves. DSC (Differential Scanning Calorimeter) test were also carried

  5. How to Determine the Environmental Exposure of PAHs Originating from Biochar

    DEFF Research Database (Denmark)

    Mayer, Philipp; Hilber, Isabel; Gouliarmou, Varvara


    Biochars are obtained by pyrolyzing biomass materials and are increasingly used within the agricultural sector. Owing to the production process, biochars can contain polycyclic aromatic hydrocarbons (PAHs) in the high mg/kg range, which makes the determination of the environmental exposure of PAHs...... originating from biochars relevant. However, PAH sorption to biochar is characterized by very high (104–106 L/kg) or extreme distribution coefficients (KD) (>106 L/kg), which makes the determination of exposure scientifically and technically challenging. Cyclodextrin extractions, sorptive bioaccessibility...... extractions, Tenax extractions, contaminant traps, and equilibrium sampling were assessed and selected methods used for the determination of bioavailability parameters for PAHs in two model biochars. Results showed that: (1) the KD values of typically 106–109 L/kg made the biochars often act as sinks, rather...

  6. Contrasting geochemistry of the Cretaceous volcanic suites in Shandong province and its implications for the Mesozoic lower crust delamination in the eastern North China craton (United States)

    Ling, Wen-Li; Duan, Rui-Chun; Xie, Xian-Jun; Zhang, Yong-Qing; Zhang, Jun-Bo; Cheng, Jian-Ping; Liu, Xiao-Ming; Yang, Hong-Mei


    The Qingshan volcanic sequences occur in the Mengyin and Jiaozhou basins, west and east of the Tan-Lu fault zone, respectively, were formed at 128 ± 2 and 106 - 98 Ma. Lithologically the Mengyin succession comprises unimodal andesite (53 - 65 wt.% SiO 2), whereas the Jiaozhou succession consists of bimodal andesite (56-59 wt.% SiO 2) and rhyolite (69-77 wt.% SiO 2). High-Mg (Mg# >60) and low-Mg (Mg# andesitic suites are recognized in the Mengyin volcanic rocks. They show tholeiitic and calc-alkaline trends, respectively. Though the two suites share common trace element features of LILE enrichment and HFSE depletion, higher incompatible element contents in the high-Mg andesite relative to the low-Mg andesite rule out their genetic connection by magmatic differentiation. Similarly, the Jiaozhou andesites also possess higher incompatible element contents compared to their interbedded rhyolites, suggesting their distinct source rocks. The Qingshan mafic volcanic suites are characterized by radiogenic Sr and unradiogenic Nd isotopic compositions, of which the Mengyin high-Mg andesitic rocks display the lowest ɛ Nd(t) and highest initial Sr ratio. By contrast, the Jiaozhou rhyolites possess a positive correlation between Sr-Nd isotopes and relatively unradiogenic Sr isotopic ratios. The Qingshan mafic rocks exhibit geochemical characteristics distinct from those of mantle peridotite- or pyroxenite-derived melt as well as from Fangcheng basalts, the only basalts documented in the Cretaceous volcanic suites in Shandong province. They are inferred to be crust-derived melts. However, a clear decreasing trend in ACNK with Mg# increasing and the elevated MgO, Cr and Ni contents relative to basalt-derived melts indicate assimilation with mantle peridotite during their pristine magmatic evolution. Such a two-step process can be best explained by the Archean lower crust delamination of the North China craton with a ~35% partial melting followed by a variable extent of

  7. Evidence for crustal recycling during the Archean: The parental magmas of the stillwater complex (United States)

    Mccallum, I. S.


    The petrology and geochemistry of the Stillwater Complex, an Archean (2.7 Ga) layered mafic intrusion in the Beartooth Mountains of Montana is discussed. Efforts to reconstruct the compositions of possible parental magmas and thereby place some constraints on the composition and history of their mantle source regions was studied. A high-Mg andesite or boninite magma best matches the crystallization sequences and mineral compositions of Stillwater cumulates, and represents either a primary magma composition or a secondary magma formed, for example, by assimilation of crustal material by a very Mg-rich melt such as komatiite. Isotopic data do not support the extensive amounts of assimilation required by the komatiite parent hypothesis, and it is argued that the Stillwater magma was generated from a mantle source that had been enriched by recycling and homogenization of older crustal material over a large area.

  8. Subduction initiation, recycling of Alboran lower crust, and intracrustal emplacement of subcontinental lithospheric mantle in the Westernmost Mediterranean (United States)

    Varas-Reus, María Isabel; Garrido, Carlos J.; Bosch, Delphine; Marchesi, Claudio; Hidas, Károly; Booth-Rea, Guillermo; Acosta-Vigil, Antonio


    largest outcrop (> 300 km2) of subcontinental lithospheric mantle peridotite in westernmost Mediterranean -- occurs at the basal units of the western Alpujarride. Late, intrusive mantle, high-Mg pyroxenite dykes in the Ronda peridotite (Betic Cordillera, S. Spain) show geochemical signature akin to high-pressure (> 1 GPa) segregates of high-Mg andesite and boninite found in island arc terrains and ophiolite, where they usually witness nascent subduction and/or oceanic accretion in a forearc setting. These pyroxenites point to a suprasubduction environment prior to the intracrustal emplacement of subcontinental peridotites drawing some parallels between the crustal emplacement environment of some ophiolites and that of sublithospheric mantle in the westernmost Mediterranean. Here, we present new Sr-Nd-Pb-isotopic data from a variety of crustal rocks that might account for the crustal components seen in high-Mg Ronda pyroxenites. This data allows the origin of this crustal component to be unveiled, providing fundamentally constraints on the processes involved in the emplacement of large massifs of subcontinental mantle lithosphere in the westernmost Mediterranean. In order to test the hypothesis that the crustal component in Ronda high-Mg pyroxenites was acquired during the Alpine evolution of the Betic-Rif orogen, we selected samples from crustal sections that might have been underthrusted beneath the Alboran lithospheric mantle before the putative Miocene intra-crustal emplacement of peridotites. Samples are from the western Betics and comprise sediments from the Gibraltar Arc Flysch Trough units, which forms a fold-and-thrust belt between the Iberian paleomargin and the allochthonous Alboran domain, and metasedimentary rocks from the Jubrique and Blanca units of the Alpujarride complex, which underlie and overlie the Ronda peridotite and constitute the crustal section of the Alboran lithosphere domain to which the Ronda peridotite pertains. Sr-Nd-Pb systematic of

  9. Contrasting compositional trends of rocks and olivine-hosted melt inclusions from Cerro Negro volcano (Central America): implications for decompression-driven fractionation of hydrous magmas (United States)

    Portnyagin, Maxim V.; Hoernle, Kaj; Mironov, Nikita L.


    Melt inclusions in olivine Fo83-72 from tephras of 1867, 1971 and 1992 eruptions of Cerro Negro volcano represent a series of basaltic to andesitic melts of narrow range of MgO (5.6-8 wt %) formed by ~46 wt % fractional crystallization of olivine (~6 wt %), plagioclase (~27 wt %), pyroxene (~13 wt %) and magnetite (high-Mg basalts reflects the process of phenocryst re-distribution in progressively evolving melt. The crystallization scenario is anticipated to operate everywhere in dykes feeding basaltic volcanoes and can explain the predominance of plagioclase-rich high-Al basalts in island arc as well as typical compositional variations of magmas during single eruptions.

  10. Early Devonian suprasubduction ophiolites of the southern Urals (United States)

    Belova, A. A.; Ryazantsev, A. V.; Razumovsky, A. A.; Degtyarev, K. E.


    The composition of ophiolites widespread in the southern Urals shows that they were formed in a suprasubduction setting. Low-Ti and high-Mg sheeted dikes and volcanic rocks vary from basalt to andesite, and many varieties belong to boninite series. The rocks of this type extend as a 600-km tract. The volcanic rocks contain chert interbeds with Emsian conodonts. Plagiogranites localized at the level of the sheeted dike complex and related to this complex genetically are dated at 400 Ma. The ophiolites make up a base of thick islandarc volcanic sequence. The composition of the igneous rocks and the parameters of their metamorphism indicate that subduction and ascent of a mantle plume participated in their formation. The nonstationary subduction at the intraoceanic convergent plate boundary developed, at least, from the Middle Ordovician.

  11. The major-element composition of Mercury's surface from MESSENGER X-ray spectrometry. (United States)

    Nittler, Larry R; Starr, Richard D; Weider, Shoshana Z; McCoy, Timothy J; Boynton, William V; Ebel, Denton S; Ernst, Carolyn M; Evans, Larry G; Goldsten, John O; Hamara, David K; Lawrence, David J; McNutt, Ralph L; Schlemm, Charles E; Solomon, Sean C; Sprague, Ann L


    X-ray fluorescence spectra obtained by the MESSENGER spacecraft orbiting Mercury indicate that the planet's surface differs in composition from those of other terrestrial planets. Relatively high Mg/Si and low Al/Si and Ca/Si ratios rule out a lunarlike feldspar-rich crust. The sulfur abundance is at least 10 times higher than that of the silicate portion of Earth or the Moon, and this observation, together with a low surface Fe abundance, supports the view that Mercury formed from highly reduced precursor materials, perhaps akin to enstatite chondrite meteorites or anhydrous cometary dust particles. Low Fe and Ti abundances do not support the proposal that opaque oxides of these elements contribute substantially to Mercury's low and variable surface reflectance.

  12. [Electron microscopy of alpha-latrotoxin from the venom of the black widow spider Latrodectus mactans tredecimguttatus]. (United States)

    Lunev, A V; Demin, V V; Zaĭtsev, O I; Spadir, S I; Grishin, E V


    Two-dimensional crystals of alpha-latrotoxin from the venom of black widow spider (Latrodectus mactans tredecimguttatus) were studied by the negative staining electron microscopy. Two-dimensional crystals were obtained by adsorption of the protein solution with a high Mg2+ concentration on carbon-coated electron microscopy grids. The crystals were about 0.4 mkm in size, had the unit cell parameters: a = b = 15.55 nm, gamma = 90 degrees, p4 plane group symmetry. The contour map of a stain-excluding region of such crystals was calculated by the Fourier-filtering procedure at about 4 nm resolution. The calculation of molecular weight of the unit cell, with the symmetry p4 taken into account, showed that alpha-latrotoxin particles, revealed by negative staining, consisted of 4 or 8 protomers.

  13. [Vibrational spectra of Corallium elatius]. (United States)

    Fan, Lu-wei; Zhang, Yan; Hu, Yang


    Corallium elatius, which has unique color distribution characteristic, is the most important species of Taiwan precious corals. EPMA, XRD, FTIR and Laser Raman detective methods were used to study the chemical, mineral composition and spectra characteristics of Corallium elatius. The result of EPMA, XRD and FTIR shows the high-Mg calcite mineral componentand the stable minor chemical constituents of the samples. Meanwhile, the cell parameter indicates the lattice distortion and the preferred orientation of calcite grain caused by organic matter. The red part of the samples shows a different Raman spectrum from that of the white part, located at 1517/1128 cm(-1) and 1296/1016 cm(-1). Raman scattering measurement reveals the relationship between the organic matter and color.

  14. Apollo 15 yellow-brown volcanic glass: Chemistry and petrogenetic relations to green volcanic glass and olivine-normative mare basalts

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, S.S.; Schmitt, R.A.; (Oregon State Univ., Corvallis (USA)); Delano, J.W. (State Univ. of New York, Albany (USA))


    Apollo 15 yellow-brown glass is one of twenty-five, high Mg, primary magmas emplaced on the lunar surface in pyroclastic eruptions. Forty spherules of this glass were individually analyzed by electron microprobe and INAA for major- and trace-elements. The abundances demonstrate that this primary magma was produced by partial melting of differentiated cumulates in the lunar mantle. Models are developed to explain the possible source-regions of several Apollo 15 and Apollo 12 low-Ti mare magmas as being products of hybridization involving three ancient differentiated components of a primordial lunar magma ocean: (a) early olivine {plus minus} orthopyroxene cumulates; (b) late-stage clinopyroxene + pigeonite + ilmenite + plagioclase cumulates; and (c) late-stage inter-cumulus liquid.

  15. Interface Induced Carbonate Mineralization: A Fundamental Geochemical Process Relevant to Carbon Sequestration

    Energy Technology Data Exchange (ETDEWEB)

    Teng, H. Henry [PI, The George Washington University; Xu, Huifang [Co-PI, University of Wisconsin-Madison


    We have approached the long-standing geochemical question why anhydrous high-Mg carbonate minerals (i.e., magnesite and dolomite) cannot be formed at ambient conditions from a new perspective by exploring the formation of MgCO{sub 3} and Mg{sub x}Ca{sub (1-x)}CO{sub 3} in non-aqueous solutions. Data collected from our experiments in this funding period suggest that a fundamental barrier, other than cation hydration, exists that prevents Mg{sup 2+} and CO{sub 3}{sup 2-} ions from forming long-range ordered structures. We propose that this barrier mainly stems from the lattice limitation on the spatial configuration of CO{sub 3} groups in magnesite crystals. On the other hand, the measured higher distribution coefficients of Mg between magnesian calcites formed in the absence and presence of water give us a first direct proof to support and quantify the cation hydration effect.

  16. Mg/Si Mineralogical Ratio of Low-Mass Planet Hosts. Correction for the NLTE Effects (United States)

    Adibekyan, V.; Gonçalves da Silva, H. M.; Sousa, S. G.; Santos, N. C.; Delgado Mena, E.; Hakobyan, A. A.


    Mg/Si and Fe/Si ratios are important parameters that control the composition of rocky planets. In this work we applied non-LTE correction to the Mg and Si abundances of stars with and without planets to confirm/reject our previous findings that [Mg/Si] atmospheric abundance is systematically higher for Super-Earth/Neptune-mass planet hosts than stars without planets. Our results show that the small differences of stellar parameters observed in these two groups of stars are not responsible for the already reported difference in the [Mg/Si] ratio. Thus, the high [Mg/Si] ratio of Neptunian hosts is probably related to the formation efficiency of these planets in such environments.

  17. Platinum Group Elements (PGE) geochemistry of komatiites and boninites from Dharwar Craton, India: Implications for mantle melting processes (United States)

    Saha, Abhishek; Manikyamba, C.; Santosh, M.; Ganguly, Sohini; Khelen, Arubam C.; Subramanyam, K. S. V.


    High MgO volcanic rocks having elevated concentrations of Ni and Cr are potential hosts for platinum group elements (PGE) owing to their primitive mantle origin and eruption at high temperatures. Though their higher PGE abundance is economically significant in mineral exploration studies, their lower concentrations are also valuable geochemical tools to evaluate petrogenetic processes. In this paper an attempt has been made to evaluate the PGE geochemistry of high MgO volcanic rocks from two greenstone belts of western and eastern Dharwar Craton and to discuss different mantle processes operative at diverse geodynamic settings during the Neoarchean time. The Bababudan greenstone belt of western and Gadwal greenstone belt of eastern Dharwar Cratons are dominantly composed of high MgO volcanic rocks which, based on distinct geochemical characteristics, have been identified as komatiites and boninites respectively. The Bababudan komatiites are essentially composed of olivine and clinopyroxene with rare plagioclase tending towards komatiitic basalts. The Gadwal boninites contain clinopyroxene, recrystallized hornblende with minor orthopyroxene, plagioclase and sulphide minerals. The Bababudan komatiites are Al-undepleted type (Al2O3/TiO2 = 23-59) with distinctly high MgO (27.4-35.8 wt.%), Ni (509-1066 ppm) and Cr (136-3036 ppm) contents. These rocks have low ΣPGE (9-42 ppb) contents with 0.2-2.4 ppb Iridium (Ir), 0.2-1.4 ppb Osmium (Os) and 0.4-4.4 ppb Ruthenium (Ru) among Iridium group PGE (IPGE); and 1.4-16.2 ppb Platinum (Pt), 2.8-19 ppb Palladium (Pd) and 0.2-9.8 ppb Rhodium (Rh) among Platinum group PGE (PPGE). The Gadwal boninites are high-Ca boninites with CaO/Al2O3 ratios varying between 0.8 and 1.0, with 12-24 wt.% MgO, 821-1168 ppm Ni and 2307-2765 ppm Cr. They show higher concentration of total PGE (82-207 ppb) with Pt concentration ranging from 13 to 19 ppb, Pd between 65 and 180 ppb and Rh in the range of 1.4-3 ppb compared to the Bababudan komatiites. Ir

  18. Diversity and food web structure of nematode communities under high soil salinity and alkaline pH. (United States)

    Salamún, Peter; Kucanová, Eva; Brázová, Tímea; Miklisová, Dana; Renčo, Marek; Hanzelová, Vladimíra


    A long-term and intensive magnesium (Mg) ore processing in Slovenské Magnezitové Závody a.s. in Jelšava has resulted in a high Mg content and alkaline pH of the soil environment, noticeable mainly in the close vicinity of the smelter. Nematode communities strongly reacted to the contamination mostly by a decrease in abundance of the sensitive groups. Nematodes from c-p 1 group and bacterivores, tolerant to pollution played a significant role in establishing the dominance at all sites. With increasing distance from the pollution source, the nematode communities were more structured and complex, with an increase in proportion of sensitive c-p 4 and 5 nematodes, composed mainly of carnivores and omnivores. Various ecological indices (e.g. MI2-5, SI, H') indicated similar improvement of farther soil ecosystems.

  19. The volcanic and geochemical development of São Nicolau, Cape Verde Islands

    DEFF Research Database (Denmark)

    Duprat, Helene Inga; Holm, Paul Martin; Sherson, Jacob Friis;


    We present 34 new age results from 40 Ar/39 Ar incremental heating analyses of groundmass separates from volcanic rocks from São Nicolau, Cape Verde. Combining the age results with field observations, we show that the volcanic activity that formed the island occurred in four separate stages: 1: >6...... of 207 volcanic rocks representing all volcanic activity stages is presented. The rocks are alkaline and mostly primitive (MgO >8 wt.%) basic to ultrabasic ranging from nephelinites through basanites to picrobasalts. Evolved rocks range to phonolites. During all four volcanic stages predominantly high Mg...... assumed. With more ages of only around 50 ka the youngest volcanic rocks found on the island indicate that stage 4 may still be active. The cyclieity of São Nico volcanism suggests that mantle plume material arrived under São Nicolau in batches separated by nonfertile material....

  20. O efeito facilitatório do óxido nítrico sobre a transmissão neuromuscular de preparações nervo frênico- diafragma isolado de ratos é Ca++ dependente - DOI: 10.4025/actascibiolsci.v26i4.1528 NO- induced neuromuscular facilitation in the phrenic nerve diaphragm preparation of rats is Ca++ dependent - DOI: 10.4025/actascibiolsci.v26i4.1528

    Directory of Open Access Journals (Sweden)

    Heraldo Esheveria Borges


    Full Text Available A pesquisa foi conduzida para verificar se os efeitos neuromusculares induzidos por óxido nítrico (NO poderiam depender dos níveis extracelulares de Ca++. O doador de NO, nitroprussiato de sódio (NPS, e o análogo de GMPc, 8-Br-cGMP, aumentaram a amplitude das contrações musculares (ACM em preparações indiretamente estimuladas a 0.2 Hz, mas não produziram efeitos quando a solução nutriente (Krebs normal foi trocada por Krebs com baixo Ca++/ alto Mg++. NPS e 8-Br-cGMP reduziram a ACM quando as preparações foram diretamente estimuladas, mas tal efeito não foi observado com o uso de Krebs com baixo Ca++/ alto Mg++. Dados sugerem que os efeitos neuromusculares induzidos por NO dependem dos níveis extracelulares de Ca++The research was carried out to verify whether the neuromuscular effects induced by nitric oxide (NO might depend on extracellular level of Ca++. The donor of NO, sodium nitroprusside (SNP, and the analogue of cGMP, 8-Br-cGMP, increased the muscular contraction amplitude (MCA in preparations indirectly stimulated at 0.2 Hz, but did not produce any effect when the nutrient solution was exchanged by Krebs buffer low Ca++/ high Mg++. SNP and 8-Br-cGMP reduced the MCA in preparations directly stimulated. Such effect was not recorded in Krebs buffer low Ca++/ high Mg++. Data suggest that the neuromuscular effects induced by NO or cGMP depend on extracellular level of Ca++

  1. The 1.88 Ga Kotalahti and Vammala nickel belts, Finland: geochemistry of the mafic and ultramafic metavolcanic rocks

    Directory of Open Access Journals (Sweden)

    Stephen J. Barnes


    Full Text Available The mafic and ultramafic volcanic rocks within the Svecofennian (1.88 Ga Kotalahti and Vammala Nickel Belts, Finland, are spatially associated and coeval with a suite of mineralized mafic–ultramafic intrusions. They have been divided into five suites based on major element geochemistry and spatial distribution: the Rantasalmi high- and low-Mg suites, the Vammala high-Mg suite, and the Rantasalmi, Kestilä and Pielavesi low-Mg suites. The Rantasalmi and Vammala high-Mg suites are very similar and probably comagmatic, and the Kestilä and Rantasalmi low-Mg suites are derived from them by a combination of fractionation and crustal assimilation. The Pielavesi suite is interpreted as an unrelated suite of island-arc affinity.On the basis of their trace element contents, the Kotalahti Belt intrusions are comagmatic with part of the analyzed volcanic rocks. In the Vammala Belt it is likely that the parent magmas to the intrusions and picrite magmas have a common mantle source but have evolved along distinct paths, and the picrites probably do not represent parent magmas tapped directly from the intrusions. Platinum-group element data show localised evidence for depletionby sulfide extraction. Vammala picrites are predominantly S-undersaturated, with the exception of lavas in the Stormi area. In the Kotalahti Belt the volcanic rocks are predominantlyS-undersaturated, while the volcanic rocks in the more northern part of the Belt are predominantly S-saturated. These spatial differences imply that the PGE contents of the metavolcanic rocks can be used as regional area selection criteria for intrusive nickel-copper-(PGE deposits within the Finnish Svecofennian.

  2. The mineralogical responses of marine calcifiers to CO2-induced ocean acidification (United States)

    Ries, J. B.; Cohen, A. L.; McCorkle, D. C.


    We have conducted 6-month laboratory experiments to investigate the effect of pCO2-induced reductions in seawater CaCO3 saturation state on biocalcification by 18 aragonitic and calcitic (low-high Mg) taxa representing eight of the major marine calcifying groups: Chlorophyta; Rhodophyta; Crustacea; Bivalvia; Gastropoda; Annelida; Cnidaria; and Echinodermata. The CaCO3 saturation states of the experimental seawaters, constrained by intercalibrated determinations of pH, alkalinity, and DIC, were attained with bubbled air-CO2 mixtures of 400 (ambient), 600, 900, and 2850 ppm pCO2, yielding Ωarag of 2.5 (ambient), 2.0, 1.5, 0.7, respectively. We previously showed that while rates of net calcification obtained from buoyant weighing declined with increasing pCO2 for nearly half of the species investigated, a nearly equal number exhibited constant or, in some cases, increased calcification under moderately (600 ppm) or extremely (900 or 2850 ppm) elevated pCO2. The organisms' investigated in this study secrete various forms of CaCO3, which differ in crystallographic structure and therefore solubility: aragonite and high-Mg are generally more soluble than low-Mg calcite. We have employed powder x-ray diffraction, Raman spectroscopy, inductively-coupled-plasma mass-spectrometry, and scanning electron microscopy to quantify changes in the organisms' skeletal mineralogy (aragonite:calcite ratio) and Mg-content (MgCO3:CaCO3 ratio) that occurred in response to the prescribed reductions in seawater CaCO3 saturation state. We will compare calcification and mineralogical response patterns amongst the organisms to elucidate the role of mineral lability in driving species-specific responses to CO2-induced ocean acidification.

  3. The petrology, geochronology and geochemistry of Hauhungatahi volcano, S.W. Taupo Volcanic Zone (United States)

    Cameron, Errol; Gamble, John; Price, Richard; Smith, Ian; McIntosh, William; Gardner, Mairi


    Hauhungatahi volcano is an eroded andesitic edifice 10 km west of Ruapehu volcano constructed on an upfaulted block of Mesozoic marine sediments. Hauhungatahi andesites are distinctively clinopyroxene-phyric with high ratios of clinopyroxene:plagioclase. This contrasts with the plagioclase-phyric dominated assemblages in the stratovolcanoes such as Ruapehu and Tongariro. Hauhungatahi andesites show high MgO (> 8.0% wt), Sr (> 400 ppm), Ni (> 100 ppm) and Cr (> 400 ppm) and low Si, Rb, Ba and Zr relative to andesites from Ruapehu volcano, with fractionated LREE (Ce/Sm) n ~ 2 and flat HREE (Dy/Yb) n ~ 1. Sr-isotope ratios are lower at equivalent Nd isotope ratios than Ruapehu andesites of the (oldest) Te Herenga Formation. 40Ar/ 39Ar step-heating experiments of groundmass concentrates of 4 samples have yielded ages between 881 ± 83 ka and 961 ± 59 ka, with a weighted mean age of 933 ± 46 ka, indicating that Hauhungatahi is significantly older than Ruapehu Volcano where volcanism commenced ~ 250-300 ka. Hauhungatahi is therefore similar in age to the older andesitic edifices that are marginal to the TVZ (eg Titiraupenga, Pureora and Rolles Peak). We suggest that these high-Mg andesites hold clues to the early conditioning of the lithosphere beneath TVZ, prior to the establishment of the large andesite stratovolcanoes that presently dominate the skyline at the southern end of TVZ. The relatively low abundance of plagioclase in the phenocryst assemblages hints at high P H 2O and possible involvement of amphibole in the source.

  4. Formation of hybrid arc andesites beneath thick continental crust (United States)

    Straub, Susanne M.; Gomez-Tuena, Arturo; Stuart, Finlay M.; Zellmer, Georg F.; Espinasa-Perena, Ramon; Cai, Yue; Iizuka, Yoshiyuki


    Andesite magmatism at convergent margins is essential for the differentiation of silicate Earth, but no consensus exists as to andesite petrogenesis. Models proposing origin of primary andesite melts from mantle and/or slab materials remain in deadlock with the seemingly irrefutable petrographic and chemical evidence for andesite formation through mixing of basaltic mantle melts with silicic components from the overlying crust. Here we use 3He/4He ratios of high-Ni olivines to demonstrate the mantle origin of basaltic to andesitic arc magmas in the central Mexican Volcanic Belt (MVB) that is constructed on ~ 50 km thick continental crust. We propose that the central MVB arc magmas are hybrids of high-Mg# > 70 basaltic and dacitic initial mantle melts which were produced by melting of a peridotite subarc mantle interspersed with silica-deficient and silica-excess pyroxenite veins. These veins formed by infiltration of reactive silicic components from the subducting slab. Partial melts from pyroxenites, and minor component melts from peridotite, mix in variable proportions to produce high-Mg# basaltic, andesitic and dacitic magmas. Moderate fractional crystallization and recharge melt mixing in the overlying crust produces then the lower-Mg# magmas erupted. Our model accounts for the contrast between the arc-typical SiO2 variability at a given Mg# and the strong correlation between major element oxides SiO2, MgO and FeO which is not reproduced by mantle-crust mixing models. Our data further indicate that viscous high-silica mantle magmas may preferentially be emplaced as intrusive silicic plutonic rocks in the crust rather than erupt. Ultimately, our results imply a stronger turnover of slab and mantle materials in subduction zones with a negligible, or lesser dilution, by materials from the overlying crust.

  5. Subduction-related oceanic crust in the Khantaishir ophiolite (western Mongolia). (United States)

    Gianola, O.; Schmidt, M. W.; Jagoutz, O. E.


    Most of the oceanic crust is generated at mid oceanic ridges and only a minor portion results from magmatism related to subduction zones (i.e. back-arc basins or in incipient arcs). However it has been observed that several ophiolites preserve an oceanic crust displaying a subduction zone signature. Such a signature is also found in the Khantaishir ophiolite located in western Mongolia. This ~570 m.y. old ophiolite is ~480 km2 in size and displays a complete sequence, tectonically slightly dismembered during the emplacement process. The ophiolite exposes ~130 km2 of highly refractory harzburgitic mantle with local dunite channels and lenses. Towards its top the mantle is replaced by sub-horizontal km-wide discrete zones of pyroxenites situated either in the mantle or forming a crust-mantle transition zone overlain by gabbros. The crust is then composed of various gabbros and minor gabbronorite (both in part replaced by pyroxenites and/or cut by intermediate dykes), by a dyke/sill-complex and by pillow lavas. The entire ophiolite is re-equilibrated at lower greenschist facies conditions. Major and trace elements of the crustal rocks of the Khantaishir ophiolite show trends similar to those observed for the Izu-Bonin-Mariana subduction system. Mafic dykes/sills and pillow lavas of the Khantaishir ophiolite have overall basaltic-andesite compositions, resembling high-Mg andesites with an average SiO2 of 57 wt%. Their low TiO2 (high-Mg andesites and boninites from modern island arcs. This evidence suggests that the Kantaishir crust might represent the submarine initial stage of an incipient arc, probably when the preexisting oceanic crust is spread and incipient island arc crust is formed.

  6. Self-compensation due to point defects in Mg-doped GaN (United States)

    Miceli, Giacomo; Pasquarello, Alfredo


    Using hybrid density functional theory, we address point defects susceptible to cause charge compensation upon Mg doping of GaN. We determine the free energy of formation of the nitrogen vacancy and of several Mg-related defects. The entropic contribution as a function of temperature is determined within the quasiharmonic approximation. We find that the Mg interstitial shows a noticeably lower free energy of formation than the Mg substitutional to Ga in p -type conditions. Therefore, the Mg impurity is amphoteric behaving like an acceptor when substitutional to Ga and like a double donor when accommodated in an interstitial position. The hybrid-functional results are then linked to experimental observations by solving the charge neutrality equations for semiconductor dominated by impurities. We show that a thermodynamic equilibrium model is unable to account for the experimental hole concentration as a function of Mg doping density, due to nitrogen vacancies and Mg interstitials acting as compensating donors. To explain the experimental result, which includes a dropoff of the hole concentration at high Mg densities, we thus resort to nonequilibrium models. We show that either nitrogen vacancies or Mg interstitials could be at the origin of the self-compensation mechanism. However, only the model based on interstitial Mg donors provides a natural mechanism to account for the sudden appearance of self-compensation. Indeed, the amphoteric nature of the Mg impurity leads to Fermi-level pinning and accounts for the observed dropoff of the hole concentration of GaN samples at high Mg doping. Our work suggests that current limitations in p -type doping of GaN could be overcome by extrinsically controlling the Fermi energy during growth.

  7. Petrogenesis and tectonic settings of volcanic rocks of the Ashele Cu-Zn deposit in southern Altay, Xinjiang, Northwest China: Insights from zircon U-Pb geochronology, geochemistry and Sr-Nd isotopes (United States)

    Wu, Yufeng; Yang, Fuquan; Liu, Feng; Geng, Xinxia; Li, Qiang; Zheng, Jiahao


    The Early-Mid-Devonian Ashele Formation of the southern margin of the Chinese Altay hosts the Ashele Cu-Zn volcanogenic massive sulfide (VMS) deposit and consists of intercalated volcanic and sedimentary rocks that have experienced regional greenschist-facies metamorphism. We studied the petrography, zircon U-Pb geochronology, geochemistry, and Sr-Nd isotopes of dacites and basalts in order to understand the petrogenesis of these rocks and the regional tectonic evolution. Two dacites yielded LA-MC-ICP-MS zircon U-Pb ages of 402 ± 6 Ma and 403 ± 2 Ma. The dacites are calc-alkaline, and characterized by high Na2O/K2O ratios (3.6-9.3), and high Mg# values (47-63), enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in Nb, Ta, Ti, and P, and relatively positive εNd(t) values (+3.6 to +7.5), collectively suggesting a sanukitic magma affinity. The variations in the major and trace elements of the dacites indicate that Fe-Ti oxide, plagioclase, and apatite were fractionated during their petrogenesis. The basalts are tholeiitic, and are characterized by high Mg# values (66-73), and negative Nb and Ta anomalies. The geochemical characteristics of the basalts are similar to those of N-MORB. Those characteristics together with the positive εNd(t) values (+6.8 to +9.2) of the basalts, indicate that the precursor magma was derived mainly from an N-MORB-type depleted asthenospheric mantle in an island arc setting. The geochemical similarities between the basalts and dacites indicate that they both originated from a similar depleted mantle source via partial melting under different magmatic conditions in each case, possibly related to ridge subduction.

  8. Geochronology, geochemistry and metallogenic implications of the Lamasu intrusion in western Tianshan, NW China%西天山喇嘛苏岩体年代学、地球化学及成矿意义

    Institute of Scientific and Technical Information of China (English)

    解洪晶; 武广; 朱明田; 晋建平; 钟伟; 刘军; 糜梅


    The zircon U-Pb geochronology , major and trace elements and Sr-Nd isotopes determination of the Lamasu intrusion in western Chinese Tianshan were conducted to understand its petrogenesis and geodynamic setting. The Lamasu intrusion is mainly composed of quartz monzodiorite,granodiorite porphyry and tonalite porphyry. Among them the quartz monzodiorite was formed in 394. 8 + 4. 9 Ma, while the granodiorite porphyry and tonalite porphyry were intruded in 380, 9 + 3. 9 Ma. The rocks display the adakitic affinity and show a calc-alkaline and high-K calc-alkaline differentiation trend. They display REE patterns characterized by relative enrichment of LREE ((La/Yb)N: 3. 55 - 15. 52) with slightly negative or positive Eu anomalies (δEu: 0. 53 - 1. 12). They have high Sr ((322 - 808) × 10-6) and low Y contents ((12. 90 - 18. 86) ×10-6) and also enriched in LILE but depleted in HFSE with negative Nb, Ta and Ti anomalies. Initial Sr-Nd isotopic compositions are εNd(t) = -4. 29 to 0. 75 and Isr = 0. 706052 to 0. 708263. The Nd model ages vary from 1. 03 to 1. 46 Ga. The Pb isotopic ratios of granodiorite porphyry and tonalite porphyry are 206Pb/204Pb=18. 500 -19. 044,207Pb/204 Pb= 15. 575 - 15. 626,208Pb/204 Pb= 38. 443 - 38. 864, while the quartz monzodiorite are 206Pb/204Pb=18. 694 - 18. 711,207Pb/204Pb=15. 622 - 15. 630,208Pb/204 Pb = 38. 648 - 38. 660. All these geochemical data demonstrate that the Lamasu intrusion is likely derived from the partial melting of oceanic crust, with the subsequent melts interacted during their uplift with the overlying mantle wedge metasomatized by the subducted sediments and subordinately contaminated by ancient crust. The Lamasu intrusion was emplaced in a continental arc setting during the southward subduction of the Junggar Remnant Ocean Basin in the Late Devonian and are closely related with Cu (Au) mineralization of that region.%文中主要对西天山喇嘛苏岩体进行SHRIMP锆石U-Pb年龄、主微量及Sr-Nd-Pb同位素

  9. 班公湖-怒江缝合带中段东巧地区早白垩世岩浆作用--对大洋演化和地壳增厚的指示%Early Cretaceous magmatism in Dongqiao, Tibet:Implications for the evolution of the Bangong-Nujiang Ocean and crustal growth in a continent-continent collision zone

    Institute of Scientific and Technical Information of China (English)

    强巴扎西; 吴浩; 格桑旺堆; 次仁欧珠; 巴桑顿珠; 琼达; 女达娃


    rhyolites can be divided into two types of high Sr and low Sr rhyolites. Low Sr rhyolites were formed by partial melting of ancient lithospheric mantle, and the melt subsequently underwent intense fractional crystallization. High Sr rhyolites had an affinity with adakites, which were derived from partial melting of thickened lower crust. The new data obtained by the authors, together with recently published data, led the authors to develop a model of bidirectional subduction and subsequent slab break-off of the lith⁃ osphere of the Bangong-Nujiang Ocean which can explain the two magmatic events in the region from BNSZ to the southern Qiangtang terrane. Research on high Sr rhyolites indicates that the extensive magmatism and continent-continent collision contribut⁃ed significantly to the crustal growth after the closure of Bangong-Nujiang Ocean in Early Cretaceous.

  10. 内蒙古赤峰地区蒙古营子花岗闪长岩LA-ICP-MS锆石U-Pb年龄及成因%LA-ICP-MS zircon U-Pb ages and petrogenesis of granodi-orite in Mengguyingzi, Chifeng, Inner Mongolia

    Institute of Scientific and Technical Information of China (English)

    刘珏; 郗爱华; 葛玉辉; 唐向阳; 徐博文; 王明智; 马艳军


    Located in the south of the Xing'an-Mongolian orogenic belt in northern North China plate, the Mengguyingzi granites are mainly composed of granodiorite. All samples show chemical signatures of high-K calc-alkaline I-type granites and have the fol⁃lowing characteristics:SiO2 is about 56.88%~68.82%, Na2O is about 4.32%~4.54%, K2O is about 2.3%~3.86%, Na2O>K2O, Rittmann indexσ=2.08~2.33, Al2O3 is about 15.1%~16.8%, and A/CNK=0.81~0.92. The granodiorite is enriched in light rare earth (LREE) and relatively depleted in heavy rare earth (HREE) and high field strength elements. The content of Sr is about 782×10-6~1230×10-6, and the average values of Y and Yb are 20.1×10-6 and 1.77×10-6 respectively.δEu=0.81~1.04, and Eu anomaly is not obvious. The granodiorite shows C adakitic rock geochemical properties, implying that its magma might have been derived from partial melting of the thickened lower continental crust. The zircon 206Pb/238U age of granodiorite measured by LA-ICP-MS zircon U-Pb dating is 252.8 ± 2.4Ma, implying that the Mengguyingzi granodiorite were formed in the late Paleozoic-Early Mesozoic. Combined with the tectonic evolution of the Xing'an-Mongolian orogenic belt, the authors hold that the Mengguyingzi granodiorite resulted from post-collision between Siberia plate and North China plate and suggested that the underplating of mantle-derived magma induced crustal growth.%赤峰蒙古营子岩体位于华北板块以北的兴蒙造山带南端,岩性主要为花岗闪长岩。其SiO2含量介于56.88%~68.82%之间,Na2O含量为4.32%~4.54%,K2O含量为2.3%~3.86%,且Na2O>K2O。里特曼指数σ=2.4~3.29,Al2O3含量介于15.1%~16.8%之间,A/CNK=0.81~0.92,属于高钾钙碱性I型花岗岩。富集轻稀土元素(LREE)、亏损重稀土元素(HREE)和高场强元素(HFSE)。Sr含量为782×10-6~1230×10-6,Y和Yb平均值分别为20.1×10-6和1.77×10-6,(La/Yb)N值为19.84~22.03,δEu=0.81~1.04,Eu异常不明显。岩

  11. Lithogeochemistry and Sr-Nd-Pb Isotopic Characteristics of Mujicun Porphyry Cu-Mo Deposit in Taihang Mountains and Their Significances%太行山木吉村斑岩铜(钼)矿床岩石地球化学、S r-Nd-Pb同位素特征及其地质意义

    Institute of Scientific and Technical Information of China (English)

    曲凯; 董国臣; 李胜荣; 申俊峰; 王艳娟; 王霞; 罗薇


    Mujicun porphyry copper-molybdenum deposit, located in the northern section of Taihang Mountains,is an important ore deposit in the Taihang tectonic-magmatic-metallogenic belt.This article is based on the particular field works and systematic analysis of petrology,geochemical data and Sr-Nd-Pb isotopes.The result shows the ore-bearing diorite-porphyry of Mujicun belonging to the high-K calc-alkaline I-type intrusive rock.Geochemical analysis shows that the diorite-porphyry is rich in SiO2,Al2O3 and Sr,a high ratio of Sr/Y, (La/Yb)N ,low in Yb and Y.All the ore-bearing porphyries in the study area have similar distribution of rare earths and trace elements,with right-oblique curve,and unclear postive Eu anomalies.It is characterized by enriched large-ion lithophile elements of Ba,K,U,Sr and depleted high field strength elements such as Nb, Ta,P and Ti with adakite affinity in geochemical characteristic.The diorite porphyry has ISr ratios of 0.705 386 to 0.706 838,εNd(t)values of -16.7 to -14.9.The averages of 208Pb/204Pb,207Pb/204Pb and 206Pb/204Pb ratios are 36.614,15.226 and 16.545,respectively,similar to those lead isotope ratios in ore of Mujicun de-posit.Sr-Nd-Pb isotopes show that the formations of the magma were probably related to origin of partial melting of lower crust with mantle materials contribution.Combining with the geological background of the study area, the authors considered that the Mujicun ore-bearing diorite porphyry possibly resulted from partial melting in lower crust with the mantle mass exchange.%木吉村斑岩铜(钼)矿床位于太行山北段涞源杂岩体的腰部,是太行山构造-岩浆-成矿带的一个重要矿床。在野外调研的基础上,对木吉村斑岩铜(钼)矿床含矿岩体进行了系统的岩石学、地球化学和Sr-Nd-Pb同位素研究。结果表明:木吉村矿床的含矿岩体闪长玢岩为高钾钙碱性I型侵入岩,具有较高的SiO2、Al2 O3、Sr含量

  12. Lithospheric convective removal related post-collisional middle Eocene magmatism along the Izmir-Ankara-Erzincan suture zone (NE Turkey). (United States)

    Göçmengil, Gönenç; Karacık, Zekiye; Genç, Ş. Can


    Obliteration of the Mesozoic Neo-Tethyan Ocean and succeeding collision of the micro plates along the northern part of Turkey lead the development of the İzmir-Ankara-Erzincan suture zone (IAESZ). The suturing and collision stages terminate with the amalgamation of the three different crustal blocks (Pontides, Central Anatolian Crystalline Complex and Anatolide-Tauride Block) in the Paleocene-Early Eocene period. After the collisional stage; a new phase of extension and magmatism concomitantly developed at the both sides and as well as along the IAESZ during the Middle Eocene period. However, the origin, mechanism and driving force of the post-collisional magmatism is still enigmatic. To understand and better constrain the syn-to post collisional evolutionary stages, we have carried out volcano-stratigraphy and geochemistry based study on the middle Eocene magmatic associations along a transect ( 100 km) from Pontides to the Central Anatolian Crystalline Complex (CACC) at the NE part of the Turkey. Middle Eocene magmatic activity in the region has been represented by calc-alkaline, alkaline, shoshonitic volcanic and granitic rocks together with scarce gabbroic intrusions. We particularly focused on middle Eocene volcano-sedimentary successions (MEVSS) to constrain the tectono-magmatic evolution of the abovementioned transect. The volcano-sedimentary succsessions are coevally developed and cover the crustal blocks (Pontides and CACC) and the IAESZ with a region wide unconformity. We have differentiated three lava series (V1-V2-V3) and their sub-groups (V1a-V1b; V2a-V2b) in MEVSS. Generally, all lava series have middle-K to shoshonitic composition with distinct subduction characteristics. V1 series is marked by presence of hydrous phenocrysts such as amphibole+biotite. V1a sub-group constitute the first volcanic product and characterized by the high Mg# (42-69); alkaline basaltic andesite, and hawaiites. V1b sub-group is represented by calc-alkaline, low Mg# (24

  13. Deducing the magma chamber processes of middle Eocene volcanics, Sivas and Tokat regions; NE Turkey: Insights from clinopyroxene chemistry (United States)

    Göçmengil, Gönenç; Karacık, Zekiye; Genç, Ş. Can; Prelevic, Dejan


    Middle Eocene Tokat and Sivas volcanic successions occur within the İzmir-Ankara-Erzincan suture zone. Different models are suggested for the development of the middle Eocene volcanism such as post-collisional, delamination and slab-breakoff models as well as the arc magmatism. In both areas, volcanic units cover all the basement units with a regional disconformity and comprise lavas spanning a compositional range from mainly basalt-basaltic andesite to a lesser amount trachyte. Here, we report mineral chemistry of different basaltic lavas through transect from northern continent (Tokat region, Pontides) to southern continent (Sivas region, Kırşehir block) to deduce the characteristics of the magma chamber processes which are active during the middle Eocene. Basaltic lavas include olivine bearing basalts (Ol-basalt: ± olivine + clinopyroxene + plagioclase); amphibole bearing basaltic andesite (Amp-basaltic andesite: amphibole + clinopyroxene + plagioclase ± biotite) and pyroxene bearing basaltic andesite (Px-basaltic andesite: clinopyroxene + plagioclase). Microlitic, glomeroporphyric and pilotaxitic texture are common. Clinopyroxene phenocrystals (macro ≥ 750 μm and micro ≤300 μm) are common in all three lava series which are investigated by transecting core to rim compositional profiles. They are generally augite and diopside; euhedral to subhedral in shape with oscillatory, normal and reverse zoning patterns. Also, all clinopyroxene phenocrystals are marked by moderately high Mg# (for Ol-basalt: 67-91; avg. 80; Amp-basaltic andesite: 76-83, avg: 80; Px -basaltic andesite 68-95, avg: 81). In Ol-basalt, clinopyroxene phenocrystals show normal zonation (high Mg# cores and low Mg# rims). In Amp-basaltic andesite, clinopyroxenes are generally homogenous in composition with minor variation of Mg# towards the rims. On the contrary, in Px-basaltic andesite, clinopyroxene macro phenocrystals show reverse zonation with the core with low Mg# and the rims with

  14. Carbonate "clumped" isotope signatures in aragonitic scleractinian and calcitic gorgonian deep-sea corals (United States)

    Kimball, Justine; Eagle, Robert; Dunbar, Robert


    Deep-sea corals are a potentially valuable archive of the temperature and ocean chemistry of intermediate and deep waters. Living in near-constant temperature, salinity, and pH and having amongst the slowest calcification rates observed in carbonate-precipitating biological organisms, deep-sea corals can provide valuable constraints on processes driving mineral equilibrium and disequilibrium isotope signatures. Here we report new data to further develop "clumped" isotopes as a paleothermometer in deep-sea corals as well as to investigate mineral-specific, taxon-specific, and growth-rate-related effects. Carbonate clumped isotope thermometry is based on measurements of the abundance of the doubly substituted isotopologue 13C18O16O2 in carbonate minerals, analyzed in CO2 gas liberated on phosphoric acid digestion of carbonates and reported as Δ47 values. We analyzed Δ47 in live-collected aragonitic scleractinian (Enallopsammia sp.) and high-Mg calcitic gorgonian (Isididae and Coralliidae) deep-sea corals and compared results to published data for other aragonitic scleractinian taxa. Measured Δ47 values were compared to in situ temperatures, and the relationship between Δ47 and temperature was determined for each group to investigate taxon-specific effects. We find that aragonitic scleractinian deep-sea corals exhibit higher values than high-Mg calcitic gorgonian corals and the two groups of coral produce statistically different relationships between Δ47-temperature calibrations. These data are significant in the interpretation of all carbonate clumped isotope calibration data as they show that distinct Δ47-temperature calibrations can be observed in different materials recovered from the same environment and analyzed using the same instrumentation, phosphoric acid composition, digestion temperature and technique, CO2 gas purification apparatus, and data handling. There are three possible explanations for the origin of these different calibrations. The offset

  15. Growth performance and root transcriptome remodeling of Arabidopsis in response to Mars-like levels of magnesium sulfate.

    Directory of Open Access Journals (Sweden)

    Anne M Visscher

    Full Text Available BACKGROUND: Martian regolith (unconsolidated surface material is a potential medium for plant growth in bioregenerative life support systems during manned missions on Mars. However, hydrated magnesium sulfate mineral levels in the regolith of Mars can reach as high as 10 wt%, and would be expected to be highly inhibitory to plant growth. METHODOLOGY AND PRINCIPAL FINDINGS: Disabling ion transporters AtMRS2-10 and AtSULTR1;2, which are plasma membrane localized in peripheral root cells, is not an effective way to confer tolerance to magnesium sulfate soils. Arabidopsis mrs2-10 and sel1-10 knockout lines do not mitigate the growth inhibiting impacts of high MgSO(4.7H(2O concentrations observed with wildtype plants. A global approach was used to identify novel genes with potential to enhance tolerance to high MgSO(4.7H(2O (magnesium sulfate stress. The early Arabidopsis root transcriptome response to elevated concentrations of magnesium sulfate was characterized in Col-0, and also between Col-0 and the mutant line cax1-1, which was confirmed to be relatively tolerant of high levels of MgSO(4.7H(2O in soil solution. Differentially expressed genes in Col-0 treated for 45 min. encode enzymes primarily involved in hormone metabolism, transcription factors, calcium-binding proteins, kinases, cell wall related proteins and membrane-based transporters. Over 200 genes encoding transporters were differentially expressed in Col-0 up to 180 min. of exposure, and one of the first down-regulated genes was CAX1. The importance of this early response in wildtype Arabidopsis is exemplified in the fact that only four transcripts were differentially expressed between Col-0 and cax1-1 at 180 min. after initiation of treatment. CONCLUSIONS/SIGNIFICANCE: The results provide a solid basis for the understanding of the metabolic response of plants to elevated magnesium sulfate soils; it is the first transcriptome analysis of plants in this environment. The results foster

  16. Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific (United States)

    Gibson, Kelly Ann; Thunell, Robert C.; Machain-Castillo, Maria Luisa; Fehrenbacher, Jennifer; Spero, Howard J.; Wejnert, Kate; Nava-Fernández, Xinantecatl; Tappa, Eric J.


    To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δ18O and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006-2012. Differences in δ18O between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Niño, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6-8.0) and [3 2-CO] values (∼70-120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios (>9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low

  17. Evidences of microbial mediation in the formation of MDAC in the Gulf of Cadiz (United States)

    Magalhaes, V. H.; Pinheiro, L. M.; Birguel, D.; Peckmann, J.; Niemann, H.; Santos, L.; Vasconcelos, C.; McKenzie, J.; Ivanov, M.


    The study of methane-derived authigenic carbonates (MDAC) in the Gulf of Cadiz allowed the identification and collection of different types of authigenic carbonates: (I) dolomite crusts, dolomite nodules, chimneys or filled burrows and (II) aragonitic slabs or pavements. Both correspond to the cementation of sediments by the precipitation of authigenic carbonates, and the different lithologic types correspond to different geochemical environment of formation. Authigenic carbonates yielded 13C values indicating methane as the major carbon source with ratios as low as -46.9(per mil PDB). Likewise, the crusts and chimneys can be interpreted as a record of extensive methane seepage in this particular area of the Gulf of Cadiz. SEM observations revealed large amounts of structures and textures that clearly indicate microbial activity. In the cement of the dolomite chimneys, which consists of minor aggregates of rhombohedric calcite, high-Mg calcite and dolomite, SEM observations allowed the identification of a large variety of microbial-induced fabrics, such as: (1) microbial filaments; (2) high Mg-calcite and dolomite crystal aggregates calcifying and mimetizing filaments and flattening themselves against dolomite and calcite minerals; (3) rods with brush-like terminations; (4) dumbbell-like and cauliflower structures. The identification of microbial and mucous biofilms is frequent in aragonite pavements, occurring as a coating, draped between the aragonite fibres and needles of the stromatolitic layers. Also, aragonite batons, ball-capped batons and nanograins are observed. Specific 13C-depleted biomarkers indicators of archaea involved in the anaerobic oxidation of methane (AOM) as PMI, squalane, crocetane/phytane have been identified in dolomite chimney samples. The aragonite crusts showed even better preserved biomarkers. PMI is accompanied by unsaturated derivatives with 1 to 3 double bonds. Several bacterial lipid biomarkers, also with 13C-depleted compositions

  18. Geochemistry of the late Holocene rocks from the Tolbachik volcanic field, Kamchatka: Quantitative modelling of subduction-related open magmatic systems (United States)

    Portnyagin, Maxim; Duggen, Svend; Hauff, Folkmar; Mironov, Nikita; Bindeman, Ilya; Thirlwall, Matthew; Hoernle, Kaj


    We present new major and trace element, high-precision Sr-Nd-Pb (double spike), and O-isotope data for the whole range of rocks from the Holocene Tolbachik volcanic field in the Central Kamchatka Depression (CKD). The Tolbachik rocks range from high-Mg basalts to low-Mg basaltic trachyandesites. The rocks considered in this paper represent mostly Late Holocene eruptions (using tephrochronological dating), including historic ones in 1941, 1975-1976 and 2012-2013. Major compositional features of the Tolbachik volcanic rocks include the prolonged predominance of one erupted magma type, close association of middle-K primitive and high-K evolved rocks, large variations in incompatible element abundances and ratios but narrow range in isotopic composition. We quantify the conditions of the Tolbachik magma origin and evolution and revise previously proposed models. We conclude that all Tolbachik rocks are genetically related by crystal fractionation of medium-K primary magmas with only a small range in trace element and isotope composition. The primary Tolbachik magmas contain ~ 14 wt.% of MgO and ~ 4% wt.% of H2O and originated by partial melting (~ 6%) of moderately depleted mantle peridotite with Indian-MORB-type isotopic composition at temperature of ~ 1250 °C and pressure of ~ 2 GPa. The melting of the mantle wedge was triggered by slab-derived hydrous melts formed at ~ 2.8 GPa and ~ 725 °C from a mixture of sediments and MORB- and Meiji-type altered oceanic crust. The primary magmas experienced a complex open-system evolution termed Recharge-Evacuation-Fractional Crystallization (REFC). First the original primary magmas underwent open-system crystal fractionation combined with periodic recharge of the magma chamber with more primitive magma, followed by mixing of both magma types, further fractionation and finally eruption. Evolved high-K basalts, which predominate in the Tolbachik field, and basaltic trachyandesites erupted in 2012-2013 approach steady-state REFC

  19. Garnet-bearing ultramafic rocks from the Dominican Republic: Fossil mantle plume fragments in an ultra high pressure oceanic complex? (United States)

    Gazel, Esteban; Abbott, Richard N.; Draper, Grenville


    Ultra high pressure (UHP) garnet-bearing ultramafic rocks from the Dominican Republic may represent the only known example where such rocks were exhumed at an ocean-ocean convergent plate boundary, and where the protolith crystallized from a UHP magma (> 3.2 GPa, > 1500 °C). This study focuses on the petrology and geochemistry of one of the ultramafic lithologies, the pegmatitic garnet-clinopyroxenite (garnet + clinopyroxene + spinel + corundum + hornblende). Three distinct types of garnet were recognized: Type-1 garnet (low Ca, high Mg) is interpreted as near magmatic (P > 3.2 GPa, > 1500 °C). Type-1‧ garnet (high Ca, low Mg) is interpreted as having formed approximately isochemically from magmatic high-Al clinopyroxene. Type-2 garnet (intermediate Ca, high Mg, and low Fe + Mn) formed together with hornblende as a result of late, low-pressure retrograde hydration. Clinopyroxene is close to diopside-hedenbergite (Mg# ~ 88) and metasomatized by arc-related fluids. Spinel and corundum occur as microinclusions in type-1 and type-1‧ garnets in the only reported natural occurrence of coexisting garnet + spinel + corundum, indicative of very high pressure. Chondrite-normalized REEs (rare earth elements) of the garnets show humped or weakly sinusoidal patterns, typically associated with garnet inclusions in diamond and garnet in kimberlite that crystallized at UHP conditions. These humped to weakly sinusoidal REE patterns developed as the result of interaction with a light REE-enriched metasomatic fluid. Partitioning of REEs between type-1‧ and type-1 garnets is consistent with the former having inherited its REEs from a high-Al clinopyroxene predecessor. The partitioning preserves a record of near-solidus temperatures (~ 1475 °C). Petrology and phase relationships independently suggest near-solidus conditions > 1500 °C (the highest temperature conditions reported in a UHP orogenic setting), providing evidence for an origin in a mantle plume. Therefore, the

  20. Review: the effects of secular variation in seawater Mg/Ca on marine biocalcification

    Directory of Open Access Journals (Sweden)

    J. B. Ries


    Full Text Available Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements throughout Phanerozoic time is believed to have been caused by tectonically-induced variations in seawater molar Mg/Ca (>2="aragonite seas"; <2="calcite seas". Here, I review a series of experiments in which extant calcifying taxa were reared in experimental seawater formulated over the range of mMg/Ca ratios (1.0 to 5.2 that occurred throughout their geologic history.

    Aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibited higher rates of calcification and growth in the experimental seawaters that favored their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification in mineralogically-favorable seawater is consistent with the hypothesis that calcification promotes photosynthesis within autotrophs through the liberation of CO2.

    The Mg/Ca ratio of calcite secreted by the coccolithophores, coralline algae and reef-dwelling animals (crustacea, urchins, calcareous tube worms declined with reductions in seawater Mg/Ca. Calcifying microbial biofilms varied their mineral polymorph with seawater Mg/Ca (mMg/Ca<2=low Mg calc; mMg/Ca>2=arag+high Mg calc, suggesting a nearly abiotic mode of calcification. These results indicate that biomineralogical control can be partially overridden by ambient seawater Mg/Ca and suggests that modern high Mg calcite organisms probably secreted low Mg calcite in calcite seas of the past. Notably, Mg fractionation in autotrophic organisms was more strongly influenced by changes in

  1. Bony fish and their contribution to marine inorganic carbon cycling (United States)

    Salter, Michael; Perry, Chris; Wilson, Rod; Harborne, Alistair


    Conventional understanding of the marine inorganic carbon cycle holds that CaCO3 (mostly as low Mg-calcite and aragonite) precipitates in the upper reaches of the ocean and sinks to a point where it either dissolves or is deposited as sediment. Thus, it plays a key role controlling the distribution of DIC in the oceans and in regulating their capacity to absorb atmospheric CO2. However, several aspects of this cycle remain poorly understood and have long perplexed oceanographers, such as the positive alkalinity anomaly observed in the upper water column of many of the world's oceans, above the aragonite and calcite saturation horizons. This anomaly would be explained by extensive dissolution of a carbonate phase more soluble than low Mg-calcite or aragonite, but major sources for such phases remain elusive. Here we highlight marine bony fish as a potentially important primary source of this 'missing' high-solubility CaCO3. Precipitation of CaCO3 takes place within the intestines of all marine bony fish as part of their normal physiological functioning, and global production models suggest it could account for up to 45 % of total new marine CaCO3 production. Moreover, high Mg-calcite containing >25 % mol% MgCO3 - a more soluble phase than aragonite - is a major component of these precipitates. Thus, fish CaCO3 may at least partially explain the alkalinity anomaly in the upper water column. However, the issue is complicated by the fact that carbonate mineralogy actually varies among fish species, with high Mg-calcite (HMC), low Mg-calcite (LMC), aragonite, and amorphous calcium carbonate (ACC) all being common products. Using data from 22 Caribbean fish species, we have generated a novel production model that resolves phase proportions. We evaluate the preservation/dissolution potential of these phases and consider potential implications for marine inorganic carbon cycling. In addition, we consider the dramatic changes in fish biomass structure that have resulted

  2. The Relationships of Upper Plate Ridge-Trench-Trench and Ridge-Trench-Transform Triple Junction Evolution to Arc Lengthening, Subduction Zone initiation and Ophiolitic Forearc Obduction (United States)

    Casey, J.; Dewey, J. F.


    The principal enigma of large obducted ophiolite slabs is that they clearly must have been generated by some form of organized sea-floor spreading/plate-accretion, such as may be envisioned for the oceanic ridges, yet the volcanics commonly have arc affinity (Miyashiro) with boninites (high-temperature/low-pressure, high Mg and Si andesites), which are suggestive of a forearc origin. PT conditions under which boninites and metamorphic soles form and observations of modern forearc systems lead us to the conclusion that ophiolite formation is associated with overriding plate spreading centers that intersect the trench to form ridge-trench-trench of ridge-trench-tranform triple junctions. The spreading centers extend and lengthen the forearc parallel to the trench and by definition are in supra-subduction zone (SSZ) settings. Many ophiolites likewise have complexly-deformed associated mafic-ultramafic assemblages that suggest fracture zone/transform along their frontal edges, which in turn has led to models involving the nucleation of subduction zones on fracture zones or transpressional transforms. Hitherto, arc-related sea-floor-spreading has been considered to be either pre-arc (fore-arc boninites) or post-arc (classic Karig-style back arc basins that trench-parallel split arcs). Syn-arc boninites and forearc oceanic spreading centers that involve a stable ridge/trench/trench triple or a ridge-trench-transform triple junction, the ridge being between the two upper plates, are consistent with large slab ophiolite formation in an obduction-ready settting. The direction of subduction must be oblique with a different sense in the two subduction zones and the oblique subduction cannot be partitioned into trench orthogonal and parallel strike-slip components. As the ridge spreads, new oceanic lithosphere is created within the forearc, the arc and fore-arc lengthen significantly, and a syn-arc ophiolite forearc complex is generated by this mechanism. The ophiolite ages

  3. Petrogenesis of gold-mineralized magmatic rocks of the Taerbieke area, northwestern Tianshan (western China): Constraints from geochronology, geochemistry and Sr-Nd-Pb-Hf isotopic compositions (United States)

    Tang, Gong-Jian; Wang, Qiang; Wyman, Derek A.; Sun, Min; Zhao, Zhen-Hua; Jiang, Zi-Qi


    Many Late Paleozoic Cu-Au-Mo deposits occur in the Central Asian Orogenic Belt (CAOB). However, their tectonic settings and associated geodynamic processes have been disputed. This study provides age, petrologic and geochemical data for andesites and granitic porphyries of the Taerbieke gold deposit from the Tulasu Basin, in the northwestern Tianshan Orogenic Belt (western China). LA-ICP-MS zircon U-Pb dating indicates that the granitic porphyries have an Early Carboniferous crystallization age (349 ± 2 Ma) that is broadly contemporaneous with the eruption age (347 ± 2 Ma) of the andesites. The andesites have a restricted range of SiO2 (58.94-63.85 wt.%) contents, but relatively high Al2O3 (15.39-16.65 wt.%) and MgO (2.51-6.59 wt.%) contents, coupled with high Mg# (57-69) values. Geochemically, they are comparable to Cenozoic sanukites in the Setouchi Volcanic Belt, SW Japan. Compared with the andesites, the granitic porphyries have relatively high SiO2 (72.68-75.32 wt.%) contents, but lower Al2O3 (12.94-13.84 wt.%) and MgO (0.10-0.33 wt.%) contents, coupled with lower Mg# (9-21) values. The andesites and granitic porphyries are enriched in both large ion lithophile and light rare earth elements, but depleted in high field strength elements, similar to those of typical arc magmatic rocks. They also have similar Nd-Hf-Pb isotope compositions: ɛNd(t) (+0.48 to +4.06 and -0.27 to +2.97) and zircons ɛHf(t) (+3.4 to +8.0 and -1.7 to +8.2) values and high (206Pb/204Pb)i (18.066-18.158 and 17.998-18.055). We suggest that the Taerbieke high-Mg andesitic magmas were generated by the interaction between mantle wedge peridotites and subducted oceanic sediment-derived melts with minor basaltic oceanic crust-derived melts, and that the magmas then fractionated to produce the more felsic members (i.e., the Taerbieke granitic porphyries) during late-stage evolution. Taking into account the Carboniferous magmatic record from the western Tianshan Orogenic Belt, we suggest that

  4. Volcanic structure and composition of Old Shiveluch volcano, Kamchatka (United States)

    Gorbach, Natalia; Portnyagin, Maxim; Tembrel, Igor


    This paper reports results of a new comprehensive geological mapping of the Late Pleistocene Old Shiveluch volcano. The mapping results and geochemical data on major and trace element composition of the volcanic rocks are used to characterize spatial distribution, eruptive sequence and volumetric relationships between different rock types of the volcano. Old Shiveluch volcano had been constructed during two main stages: initial explosive and subsequent effusive ones. Pyroclastic deposits of the initial stage are represented by agglomerate and psephytic tuffs with very few lava flows and form at least 60% of volume of the Old Shiveluch edifice. The deposits of the second stage are dominantly lava flows erupted from four vents: Central, Western, Baidarny and Southern, reconstructed from the field relationships of their lava flows. About 75% of the Old Shiveluch edifice, both pyroclastic deposits and lava, are composed of magnesian andesites (SiO2 = 57.3-63.8 wt.%, Mg# = 0.53-0.57). The most abundant andesitic lavas were coevally erupted from the Central and Western vents in the central part of the edifice. Less voluminous high-Al basaltic andesites (SiO2 = 53.5-55.7 wt.%, Mg# = 0.52-0.56) were produced by the Western, Baidarny and Southern vents situated in the south-western sector. Small volume high-Mg basaltic andesites (SiO2 = 53.9-55.0 wt.%, Mg# = 0.59-0.64) occur in the upper part of the pyroclastic deposits. Andesites of Old and Young Shiveluch Volcanoes have similar compositions, whereas Old Shiveluch basaltic andesites are compositionally distinctive from those of the Young Shiveluch by having lower Mg#, SiO2, Cr and Ni, and higher Al2O3, FeOT, CaO, TiO2, and V contents at given MgO. Geochemical modeling suggests that the compositions of the intermediate Old Shiveluch magmas can be reasonably explained by simple fractional crystallization of olivine, clinopyroxene, plagioclase and magnetite (± hornblende) from water-bearing (~ 3 wt.% H2O) high-Mg# basaltic

  5. The generation of a diverse suite of Late Pleistocene and Holocene basalt through dacite lavas from the northern Cascade arc at Mount Baker, Washington (United States)

    Baggerman, Troy David; Debari, S. M.


    Mt. Baker is a dominantly andesitic stratovolcano in the northern Cascade arc. In this study, we show that the andesites are not all derived from similar sources, and that open-system processes were dominant during their petrogenesis. To this end, we discuss petrographic observations, mineral chemistry, and whole rock major and trace element chemistry for three of Mt. Baker's late Pleistocene to Holocene lava flow units. These include the basalt and basaltic andesite of Sulphur Creek (SC) (51.4-55.8 wt% SiO2, Mg# 57-58), the Mg-rich andesite of Glacier Creek (GC) (58.3-58.7 wt% SiO2, Mg# 63-64), and the andesite and dacite of Boulder Glacier (BG) (60.2-64.2 wt% SiO2, Mg# 50-57). Phenocryst populations in all units display varying degrees of reaction and disequilibrium textures along with complicated zoning patterns indicative of open-system processes. All lavas are medium-K and calc-alkaline, but each unit displays distinctive trace element and REE characteristics that do not correlate with the average SiO2 content of the unit. The mafic lavas of SC have relatively elevated REE abundances with the lowest (La/Yb)N (~4.5). The intermediate GC andesites (Mg- and Ni-rich) have the lowest REE abundances and the highest (La/Yb)N (~6.7) with strongly depleted HREE. The more felsic BG lavas have intermediate REE abundances and (La/Yb)N (~6.4). The high-Mg character of the GC andesites can be explained by addition of 4% of a xenocrystic olivine component. However, their depleted REE patterns are similar to other high-Mg andesites reported from Mt. Baker and require a distinct mantle source. The two dominantly andesitic units (GC and BG) are different enough from each other that they could not have been derived from the same parent basalt. Nor could either of them have been derived from the SC basalt by crystal fractionation processes. Crystal fractionation also cannot explain the compositional diversity within each unit. Compositional diversity within the SC unit (basalt to

  6. La Isla de Gorgona, Colombia: A petrological enigma? (United States)

    Kerr, Andrew C.


    A wide range of intrusive (wehrlite, dunite, gabbro and olivine gabbro) and extrusive (komatiites picrites and basalts) igneous rocks are found on the small pacific island of Gorgona. The island is best known for its ˜90 Ma spinifex-textured komatiites: the only true Phanerozoic komatiites yet discovered. Early work led to suggestions that the rocks of the island formed at a mid-ocean ridge, however more recent research supports an origin as part of a hot mantle plume-derived oceanic plateau. One of the main lines of evidence for this origin stems from the inferred high mantle source temperatures required to form the high-MgO (> 15 wt.%) komatiites and picrites. Another remarkable feature of the island, considering its small size (8 × 2.5 km), is the degree of chemical and radiogenic isotopic heterogeneity shown by the rocks. This heterogeneity requires a mantle source region with at least three isotopically distinctive source regions (two depleted and one enriched). Although these mantle source regions appear to be derived in significant part from recycled oceanic crust and lithosphere, enrichments in 187Os, 186Os and 3He in Gorgona lavas and intrusive rocks, suggest some degree of transfer of material from the outer core to the plume source region at D″. Modelling reveals that the komatiites probably formed by dynamic melting at an average pressure of 3-4 GPa leaving residual harzburgite. Trace element depletion in Gorgona ultramafic rocks appears to be the result of earlier, deeper melting which produced high-MgO trace element-enriched magmas. The discovery of a trace-element enriched picrite on the island has confirmed this model. Gorgona accreted onto the palaeocontinental margin of northwestern South America in the Eocene and palaeomagnetic work reveals that it was formed at ˜26 °S. It has been proposed that Gorgona is a part of the Caribbean-Colombian Oceanic Plateau (CCOP), however, the CCOP accreted in the Late Cretaceous and was derived from a more

  7. Review: geological and experimental evidence for secular variation in seawater Mg/Ca (calcite-aragonite seas) and its effects on marine biological calcification (United States)

    Ries, J. B.


    Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time are believed to have been caused by tectonically induced variations in the Mg/Ca ratio of seawater (molar Mg/Ca>2="aragonite seas", experimental seawaters formulated with seawater Mg/Ca ratios that favor their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification within the bryopsidalean and coccolithophorid algae in mineralogically favorable seawater is consistent with the hypothesis that calcification promotes photosynthesis within some species of these algae through the liberation of CO2. The experiments also revealed that aragonite-secreting bryopsidalean algae and scleractinian corals, and bacterial biofilms that secrete a mixture of aragonite and high Mg calcite, began secreting an increased proportion of their calcium carbonate as the calcite polymorph in the lower-Mg/Ca experimental seawaters. Furthermore, the Mg/Ca ratio of calcite secreted by the coccolithophores, coralline red algae, reef-dwelling animals (crustacea, urchins, calcareous tube worms), bacterial biofilms, scleractinian corals, and bryopsidalean algae declined with reductions in seawater Mg/Ca. Notably, Mg fractionation in autotrophic organisms was more strongly influenced by changes in seawater Mg/Ca than in heterotrophic organisms, a probable consequence of autotrophic organisms inducing a less controlled mode of calcification simply through the removal of CO2 via photosynthesis. These results indicate that biomineralogical control can be partially overridden by ambient seawater Mg/Ca and suggest that modern aragonite

  8. Review: the effects of secular variation in seawater Mg/Ca on marine biocalcification (United States)

    Ries, J. B.


    Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time is believed to have been caused by tectonically-induced variations in seawater molar Mg/Ca (>2="aragonite seas"; experimental seawater formulated over the range of mMg/Ca ratios (1.0 to 5.2) that occurred throughout their geologic history. Aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibited higher rates of calcification and growth in the experimental seawaters that favored their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification in mineralogically-favorable seawater is consistent with the hypothesis that calcification promotes photosynthesis within autotrophs through the liberation of CO2. The Mg/Ca ratio of calcite secreted by the coccolithophores, coralline algae and reef-dwelling animals (crustacea, urchins, calcareous tube worms) declined with reductions in seawater Mg/Ca. Calcifying microbial biofilms varied their mineral polymorph with seawater Mg/Ca (mMg/Ca2=arag+high Mg calc), suggesting a nearly abiotic mode of calcification. These results indicate that biomineralogical control can be partially overridden by ambient seawater Mg/Ca and suggests that modern high Mg calcite organisms probably secreted low Mg calcite in calcite seas of the past. Notably, Mg fractionation in autotrophic organisms was more strongly influenced by changes in seawater Mg/Ca, a probable consequence of them inducing a less controlled mode of calcification simply through the removal of CO2 via photosynthesis. This body of work also has implications for thermal

  9. Mg fractionation in crustose coralline algae: Geochemical, biological, and sedimentological implications of secular variation in the Mg/Ca ratio of seawater (United States)

    Ries, Justin B.


    The Mg/Ca ratio of seawater has varied significantly throughout the Phanerozoic Eon, primarily as a function of the rate of ocean crust production. Specimens of the crustose coralline alga Neogoniolithon sp. were grown in artificial seawaters encompassing the range of Mg/Ca ratios shown to have existed throughout the Phanerozoic. Significantly, the coralline algae's skeletal Mg/Ca ratio varied in lockstep with the Mg/Ca ratio of the artificial seawater. Specimens grown in seawater treatments formulated with identical Mg/Ca ratios but differing absolute concentrations of Mg and Ca exhibited no significant differences in skeletal Mg/Ca ratios, thereby emphasizing the importance of the ambient Mg/Ca ratio, and not the absolute concentration of Mg, in determining the Mg/Ca ratio of coralline algal calcite. Specimens grown in seawater of the lowest molar Mg/Ca ratio ( mMg/Ca = 1.0) actually changed their skeletal mineralogy from high-Mg (skeletal mMg/Ca > 0.04) to low-Mg calcite (skeletal mMg/Ca algae, which exhibit morphologies and modes of calcification comparable to Neogoniolithon sp., would have produced low-Mg calcite from the middle Cambrian to middle Mississippian and during the middle to Late Cretaceous, when oceanic mMg/Ca approached unity. By influencing the original Mg content of carbonate facies in which these algae have been ubiquitous, this condition has significant implications for the geochemistry and diagenesis of algal limestones throughout most of the Phanerozoic. The crustose coralline algae's precipitation of high-Mg calcite from seawater that favors the abiotic precipitation of aragonite indicates that these algae dictate the precipitation of the calcitic polymorph of CaCO 3. However, the algae's nearly abiotic pattern of Mg fractionation in their skeletal calcite suggests that their biomineralogical control is limited to polymorph specification and is generally ineffectual in the regulation of skeletal Mg incorporation. Therefore, the Mg/Ca ratio

  10. Evaluating an impact origin for Mercury's high-magnesium region (United States)

    Frank, Elizabeth A.; Potter, Ross W. K.; Abramov, Oleg; James, Peter B.; Klima, Rachel L.; Mojzsis, Stephen J.; Nittler, Larry R.


    During its four years in orbit around Mercury, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft's X-ray Spectrometer revealed a large geochemical terrane in the northern hemisphere that hosts the highest Mg/Si, S/Si, Ca/Si, and Fe/Si and lowest Al/Si ratios on the planet. Correlations with low topography, thin crust, and a sharp northern topographic boundary led to the proposal that this high-Mg region is the remnant of an ancient, highly degraded impact basin. Here we use a numerical modeling approach to explore the feasibility of this hypothesis and evaluate the results against multiple mission-wide data sets and resulting maps from MESSENGER. We find that an 3000 km diameter impact basin easily exhumes Mg-rich mantle material but that the amount of subsequent modification required to hide basin structure is incompatible with the strength of the geochemical anomaly, which is also present in maps of Gamma Ray and Neutron Spectrometer data. Consequently, the high-Mg region is more likely to be the product of high-temperature volcanism sourced from a chemically heterogeneous mantle than the remains of a large impact event.abstract type="synopsis">Plain Language SummaryDuring its four years in orbit around Mercury, chemical measurements from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft revealed a large region of unusual composition relative to the rest of the planet. Its elevated magnesium abundance, in particular, led to the name of the "high-magnesium region" (HMR). High magnesium abundance in rock can be an indicator of its origin, such as high-temperature volcanism. Although the HMR covers approximately 15% of Mercury's surface, its origin is not obvious. It does roughly correspond to a depression with thin crust, which previously led to the hypothesis that it is an ancient impact crater that was large enough to excavate mantle material, which, in rocky planets, is rich in

  11. Evidence of Meso-Archaean subduction from the Torckler-Tango Layered Complex, Rauer Group, Prydz bay, East Antarctica (United States)

    McCallum, C. A.; Harley, S. L.


    The Archaean Torckler Tango Layered complex (TTLC) of the Rauer Group, East Antarctica, consists of a series of elongate mega-boudins that can be traced over a strike length of 7 km, enclosed within and intruded by c. 2.8 Ga homogeneous tonalitic orthogneisses. Despite later granulite facies metamorphism (860-900°C, 0.7 GPa) original igneous structures and layering features of the TTLC are very well preserved. Graded and cross stratified layering is evident, as are load-cast structures and geopetal structures. Isotopic and LILE signatures indicate that crustal contamination has been negligible and that metamorphic disturbances have been minor. As a result, the whole rock chemistry of the TTLC is considered to reflect its igneous protoliths. This whole rock geochemistry is distinctive, with high MgO (av. 15.8 wt%), high Mg# (av. 79.1) low TiO2 (av.< 0.33 wt%), and high SiO2 (av. 52.5 wt%). The TTLC can be subdivided into two geochemical groupings based upon Al2O3 and Cr abundances, which provide clear evidence for the crystal fractionation and accumulation processes active within the complex. Trace-element and REE element ratios show coherent trends. Based on its systematic major element (Al2O3/TiO2 ~40), trace element ratios Ti/Zr vs. Zr (Ti/Zr ~34-59 at Zr ~15-40 ppm), and negative HSFE anomalies, the TTLC is similar in geochemistry to both modern, neo-Proterozoic and Archaean boninitic rocks. Magmatic zircons define an intrusive age for the TTLC of ca. 3280 ± 22 Ma. HSFE ratios, and whole rock Nd isotope ratios recalculated back to this age, are consistent with a juvenile depleted source for the primary magma. The TTLC is therefore interpreted as the intrusive equivalent of a boninite, produced through the shallow melting of refractory mantle and supportive of the operation of subduction-like processes in the early-mid Archaean.

  12. Enhanced mechanical properties of an Al–Si–Cu–Mg alloy at 300 °C: Effects of Mg and the Q-precipitate phase

    Energy Technology Data Exchange (ETDEWEB)

    Farkoosh, A.R., E-mail:; Pekguleryuz, M., E-mail:


    Strategies to improve the strength of Al–Si alloys at elevated temperatures can follow two routes: (i) improving the age-hardening behavior and/or (ii) producing effective dispersoid strengthening. In this study, the influence of Mg (in the range of 0.3–0.7 wt%) on the precipitation characteristics and mechanical properties of the Al–7Si–0.5Cu–(Mg) alloy was investigated. Thermodynamic calculations were performed via the CALPHAD method which showed that Q-Al{sub 5}Mg{sub 8}Cu{sub 2}Si{sub 6} is the main thermodynamically stable precipitate at 300 °C. The calculations were validated by transmission electron microscopy and differential scanning calorimetry analyses. Increasing the Mg level from 0.3 wt% to the maximum solubility limit of ∼0.5 wt% increased the amount of the Q-Al{sub 5}Mg{sub 8}Cu{sub 2}Si{sub 6} precipitates at 300 °C by ∼60 wt% and significantly improved the tensile strength and creep resistance at the expense of some ductility. Mg in excess of the solubility limit was seen to remain within the microstructure in the form of the large π-Al{sub 8}FeMg{sub 3}Si{sub 6} and β-Mg{sub 2}Si intermetallics after solution treatment at 530 °C. Cracking of the brittle π-Al{sub 8}FeMg{sub 3}Si{sub 6} intermetallics during deformation was accounted for the decreased ductility of the alloys at high Mg levels. It is concluded that the Mg level can be increased to 0.5 wt% in the A–7Si–0.5Cu alloys to improve strength. However, for elevated temperature applications in which both strength and ductility are required (e.g. Diesel engine), modification of the π-Al{sub 8}FeMg{sub 3}Si{sub 6} intermetallics would be required to improve the ductility of the alloys with high Mg contents.

  13. Síntesis geocronológica del magmatismo, metamorfismo y metalogenia de Costa Rica, América Central Geochronological synthesis of magmatism, metamorphism and metallogeny of Costa Rica, Central America

    Directory of Open Access Journals (Sweden)

    Guillermo E. Alvarado


    the Talamanca range (~ 12.4 - 7.8 Ma, Cerros de Escazú (~ 6.0 - 5.9 Ma, and Fila Costeña (~ 18.3 - 16.8 and ~ 14.8 - 11.1 Ma, Tapantí-Montes del Aguacate-Carpintera (~ 4.2 - 2.2 Ma and Guacimal (~ 6.4 - 5.2 Ma. Arc rocks between 29 and 11 Ma are known in the San Carlos plains and in southern Costa Rica. The location and age of the igneous rocks indicated that there was a 20°counterclockwise rotation of the arc (termed as Proto-Volcanic Front between 15 and 8 Ma, with a pole of rotation centered on southern Costa Rica. This rotation is attributed to deformation in the overriding plate (shortening in the south coeval with extension in the NW, accompanied by trench retreat in the south. At ~ 3.45 Ma arc-related volcanism shut off in southern part of the region, but local acid-adakite volcanism persisted in the Talamanca range (4.2 - 0.95 Ma due to the subduction of the Cocos Ridge. The Paleo-Volcanic Front is represented by arc-related rocks (8 - 3.5 Ma along the length of Costa Rica, parallel to but in front of the modern arc. This activity was followed by the Monteverde (2.1 - 1.1 Ma andesitic/basaltic effusive event, which progressively, retreated to the NE. Thus, the Neo-Volcanic Front was established between 2.1 and the present, in which the modern volcanoes grew mainly during the last 0,6 Ma. In general, modern volcanoes represent three volcanic episodes: ancestral cone/shield building at ~ 1,61 - 0,85 Ma (Proto-Cordillera, overlapping in part with Monteverde volcanism; a major constructive event at ~ 0,74 - ~ 0,2 Ma (Paleo-Cordillera, and a relatively small but still active volcanism at 0,25 - 0 Ma (Neo-Cordillera. Submarine volcanism in the Pacific is represented by the Fisher Ridge (30.0 and 19.2 Ma, the Cocos Ridge (14,5 - 0,6 Ma, including the sub-aerial volcanism of Cocos Island (2,2 - 1,5 Ma. The major magmatic, metamorphic and metallogenic events are clearly related to major geotectonic events, including regional unconformities, at Upper Cretaceous

  14. Geochemistry and tectonomagatic setting of Tertiary volcanic rocks of the Kangan area, northeast of Sarbisheh, southern Khorasan

    Directory of Open Access Journals (Sweden)

    Mahshid Malekian Dastjerdi


    , Z., Qiu, H., Chu, Z., Zhao, Z. and Dong, Y., 2008. Triassic Nb-enriched basalts, magnesian andesites, and adakites of the Qiangtang terrane (Central Tibet: evidence for metasomatism by slab-derived melts in the mantle wedge. Contributions to Mineralogy and Petrology, 155(4: 437-490.

  15. Rb-Sr and Nd-Sr isotope geochemistry and petrogenesis of the Misho Mountains mafic dikes (NW Iran

    Directory of Open Access Journals (Sweden)

    Maryam Ahankoub


    the mafic dike. Discussion Geochemistry data indicate that Misho mafic dikes are similar to calc-alkaline basalts of the oceanic island basalts (OIB whereas Nb and Ti negative anomalies of the trace elements patterns are similar to crustal contamination. Negative amount of the εNd(T indicated depleted mantel source (array mantel with some continental crust contamination during AFC processes . Base on the results of analysis, the upper crust is the best candidates for magma contamination of the mafic dikes in Misho. Isotopic data indicated to replace mafic dike 232ma years ago by closing of paleotethys and forming the extension zone (break up in active continental margin. Acknowledgement We thank Professor Yamamoto, head of geochemistry department of the Nagoya University for help .We are grateful to professor Karimpour, Chief Editor of the Journal of Economic Geology, and three anonymous reviewers for their constructive suggestions and comments. Reference Ahankoub, M., 2012. Petrogenesis and geochemistry east Misho granitoides (NW of Iran. Ph.D. Thesis, Tabriz University, Tabriz, Iran, 171 pp. (in Persian with English abstract Eftekharnejad, J., 1981. Tectonic division of Iran with respect to sedimentary basins. Journal of Iran Petroleum Society, 82(3: 19–28. (in Persian with English abstract Martin, H, 1999. Adakitic magmas: modern analogues of Archaean granitoids. Lithos, 46(3: 411–429. Metcalfe, I., 2006. Paleozoic and Mesozoic tectonic evolution and palaeogeography of East Asian crustal fragments: the Korean Peninsula in context. Gondwana Research, 9(1-2: 24–46. Moayyed, M. and Hossainzade, G., 2011. Petrology and petroghraphy of A- type Granitoides of the East-Misho Mountain with theory on its geodynamic importance. Journal of Mineralogy and Crystalography, 3(19: 529–544. (in Persian with English abstract Sun, S.S. and McDonough, W.F., 1989. Chemical and isotopic systematic of ocean basalts: implications for mantle composition and process. In: A

  16. Magmatic-hydrothermal fluid evolution of the Dalli porphyry Cu-Au deposit; using Amphibole and Plagioclas mineral chemistry

    Directory of Open Access Journals (Sweden)

    Houshang Pourkaseb


    Full Text Available Introduction The formation of porphyry copper deposits is attributed to the shallow emplacement, and subsequent cooling of the hydrothermal system of porphyritic intrusive rocks (Titley and Bean, 1981. These deposits have usually been developed along the chain of subduction-related volcanic and calc-alkalin batholiths (Sillitoe, 2010. Nevertheless, it is now confirmed that porphyry copper systems can also form in collisional and post collisional settings (Zarasvandi et al., 2015b. Detailed studies on the geochemical features of ore-hosting porphyry Cu-Mo-Au intrusions indicate that they are generally adakitic, water and sulfur- riched, and oxidized (Wang et al., 2014. For example, high oxygen fugacity of magma has decisive role in transmission of copper and gold to the porphyry systems as revealed in (Wang et al., 2014. In this regard, the present work deals with the mineral chemistry of amphibole and plagioclase in the Dalli porphyry Cu-Au deposit. The data is used to achieve the physical and chemical conditions of magma and its impact on mineralization. Moreover, the results of previous studies on the hydrothermal system of the Dalli deposit such as Raman laser spectroscopy and fluid inclusion studies are included for determination of the evolution from magmatic to hydrothermal conditions. Materials and methods In order to correctly characterize the physical and chemical conditions affecting the trend of mineralization, 20 least altered and fractured samples of diorite and quartz-diorite intrusions were chosen from boreholes. Subsequently, 20 thin-polished sections were prepared in the Shahid Chamran University of Ahvaz. Finally, mineral chemistry of amphibole and plagioclase were determined using electron micro probe analyses (EMPA in the central lab of the Leoben University. Results Amphibole that is one of the the main rock-forming minerals can form in a wide variety of igneous and metamorphic rocks. Accordingly, amphibole chemistry can be

  17. Surface characteristics of nanocrystalline apatites: effect of mg surface enrichment on morphology, surface hydration species, and cationic environments. (United States)

    Bertinetti, Luca; Drouet, Christophe; Combes, Christele; Rey, Christian; Tampieri, Anna; Coluccia, Salvatore; Martra, Gianmario


    The incorporation of foreign ions, such as Mg2+, exhibiting a biological activity for bone regeneration is presently considered as a promising route for increasing the bioactivity of bone-engineering scaffolds. In this work, the morphology, structure, and surface hydration of biomimetic nanocrystalline apatites were investigated before and after surface exchange with such Mg2+ ions, by combining chemical alterations (ion exchange, H2O-D2O exchanges) and physical examinations (Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM)). HRTEM data suggested that the Mg2+/Ca2+ exchange process did not affect the morphology and surface topology of the apatite nanocrystals significantly, while a new phase, likely a hydrated calcium and/or magnesium phosphate, was formed in small amount for high Mg concentrations. Near-infrared (NIR) and medium-infrared (MIR) spectroscopies indicated that the samples enriched with Mg2+ were found to retain more water at their surface than the Mg-free sample, both at the level of H2O coordinated to cations and adsorbed in the form of multilayers. Additionally, the H-bonding network in defective subsurface layers was also noticeably modified, indicating that the Mg2+/Ca2+ exchange involved was not limited to the surface. This work is intended to widen the present knowledge on Mg-enriched calcium phosphate-based bioactive materials intended for bone repair applications.

  18. Magmatic Source Composition and Magmatism of the Volcanic Rocks in the Area of Kuruktag, Southern Xinjiang

    Institute of Scientific and Technical Information of China (English)

    JIANG Changyi; BAI Kaiyin; HI Aizhi; ZHAO Xiaoning; ZHANG Hongbo


    In the Sinian-Cambrian strata in the area of Kuruktag, southern Xingjiang, four layers of volcanic rocks occurred in the Early Sinian Beiyixi Formation, Late Sinian Zhamoketi Formation and Shuiquan Formation, and Early Cambrian Xishanbulake Formation, respectively. Volcanics of the Shuiquan Formation and Xishanbulake Formation are of alkali basalt series, those of the Zhamoketi Formation are of alkali basalt series and tholeiite series, and those of the Beiyixi Formation are obviously characterized by bimodal assemblage and mostly belong to alkali volcanics. Multi-element distribution patterns of the rocks show continental tumescence characters of interplate basalt.Fractional crystallization of plagioclase led to negative Eu-anomalies of some volcanics and the cumulation of olivine resulted in high MgO and low SiO2 content of some volcanic rocks. The SiO2 saturability of volcanic rocks of the Xishanbulake Formation and Shuiquan Formation is lower than that of tholeiite of the Zhamoketi Formation. Correspondingly, the abundance of incompatible elements in the first two formations is higher than those in the last formation, and the differences can be attributed to the different degrees of partial melting. The intense fractionation of REE and the obvious depletion of HREE suggest that these volcanic rocks were derived from garnet Iherzolite of the mantle in the continental lithosphere. The Ba/Nb, La/Nb, Ba/La, Ba/Th and Rb/Nb rations demonstrate that these volcanic rocks were exclusively derived from the enriched mantle, mainly the EMI type mantle.

  19. Chemical–physical characterisation of Early Iron Age glass beads from Central Europe

    Energy Technology Data Exchange (ETDEWEB)

    Agua, F.; Conde, J.F.; Kobylińska, U.; Kobyliński, Z.; García-Heras, M.; Villegas, M.A.


    Archaeological excavation of the Institute of Archaeology and Ethnology (Polish Academy of Sciences, PAN) at several Iron Age sites located in West Poland and South Germany has allowed the recovery of an important set of coloured glass beads mostly decorated (6th–4th centuries BC). The present paper summarises the results obtained through the chemical and microstructural characterisation of such beads. The research was carried out by binocular microscope observations, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry and visible spectrophotometry. The main objective was to attain information on the production technology and conservation state of these beads. The results indicated that all them were produced with soda lime silicate glass, even though two groups can be separated: (i) beads containing high MgO percentages made from plant ashes as an alkaline source, and (ii) beads containing low MgO percentages made from natron as an alkaline source. As regards decorations, opaque white was obtained from tin oxide, turquoise blue from Cu2+-ions, and opaque yellow from lead antimonate. Additionally, results showed microstructural and microcrystalline differences between some glass beads studied here and other glass beads from Mediterranean areas, dated in the same chronological period. This fact pointed out the valuable role given to these beads by Iron Age communities from Central Europe. (Author)

  20. Response of the Miliolid Archaias angulatus to simulated ocean acidification (United States)

    Knorr, Paul O.; Robbins, Lisa L.; Harries, Peter J.; Hallock, Pamela; Wynn, Jonathan


    A common, but not universal, effect of ocean acidification on benthic foraminifera is a reduction in the growth rate. The miliolid Archaias angulatus is a high-Mg (>4 mole% MgCO3), symbiont-bearing, soritid benthic foraminifer that contributes to Caribbean reef carbonate sediments. A laboratory culture study assessed the effects of reduced pH on the growth of A. angulatus. We observed a statistically significant 50% reduction in the growth rate (p < 0.01), calculated from changes in maximum diameter, from 160 μm/28 days in the pH 8.0/pCO2air 480 ppm control group to 80 μm/28 days at a treatment level of pH 7.6/pCO2air 1328 ppm. Additionally, pseudopore area, δ18O values, and Mg/Ca ratio all increased, albeit slightly in the latter two variables. The reduction in growth rate indicates that under a high-CO2 setting, future A. angulatus populations will consist of smaller adults. A model using the results of this study estimates that at pH 7.6 A. angulatus carbonate production in the South Florida reef tract and Florida Bay decreases by 85%, from 0.27 Mt/yr to 0.04 Mt/yr, over an area of 9,000 km2.

  1. Production of Magnesium and Aluminum-Magnesium Alloys from Recycled Secondary Aluminum Scrap Melts (United States)

    Gesing, Adam J.; Das, Subodh K.; Loutfy, Raouf O.


    An experimental proof of concept was demonstrated for a patent-pending and trademark-pending RE12™ process for extracting a desired amount of Mg from recycled scrap secondary Al melts. Mg was extracted by electrorefining, producing a Mg product suitable as a Mg alloying hardener additive to primary-grade Al alloys. This efficient electrorefining process operates at high current efficiency, high Mg recovery and low energy consumption. The Mg electrorefining product can meet all the impurity specifications with subsequent melt treatment for removing alkali contaminants. All technical results obtained in the RE12™ project indicate that the electrorefining process for extraction of Mg from Al melt is technically feasible. A techno-economic analysis indicates high potential profitability for applications in Al foundry alloys as well as beverage—can and automotive—sheet alloys. The combination of technical feasibility and potential market profitability completes a successful proof of concept. This economical, environmentally-friendly and chlorine-free RE12™ process could be disruptive and transformational for the Mg production industry by enabling the recycling of 30,000 tonnes of primary-quality Mg annually.

  2. Optimized assembly and covalent coupling of single-molecule DNA origami nanoarrays. (United States)

    Gopinath, Ashwin; Rothemund, Paul W K


    Artificial DNA nanostructures, such as DNA origami, have great potential as templates for the bottom-up fabrication of both biological and nonbiological nanodevices at a resolution unachievable by conventional top-down approaches. However, because origami are synthesized in solution, origami-templated devices cannot easily be studied or integrated into larger on-chip architectures. Electrostatic self-assembly of origami onto lithographically defined binding sites on Si/SiO2 substrates has been achieved, but conditions for optimal assembly have not been characterized, and the method requires high Mg2+ concentrations at which most devices aggregate. We present a quantitative study of parameters affecting origami placement, reproducibly achieving single-origami binding at 94±4% of sites, with 90% of these origami having an orientation within ±10° of their target orientation. Further, we introduce two techniques for converting electrostatic DNA-surface bonds to covalent bonds, allowing origami arrays to be used under a wide variety of Mg2+-free solution conditions.

  3. Synthesis, Characterization and Cold Workability of Cast Copper-Magnesium-Tin Alloys (United States)

    Bravo Bénard, Agustín Eduardo; Martínez Hernández, David; González Reyes, José Gonzalo; Ortiz Prado, Armando; Schouwenaars Franssens, Rafael


    The use of Mg as an alloying element in copper alloys has largely been overlooked in scientific literature and technological applications. Its supposed tribological compatibility with iron makes it an interesting option to replace Pb in tribological alloys. This work describes the casting process of high-quality thin slabs of Cu-Mg-Sn alloys with different compositions by means of conventional methods. The resulting phases were analyzed using X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray spectroscopy techniques. Typical dendritic α-Cu, eutectic Cu2Mg(Sn) and eutectoid non-equilibrium microstructures were found. Tensile tests and Vickers microhardness show the excellent hardening capability of Mg as compared to other copper alloys in the as-cast condition. For some of the slabs and compositions, cold rolling reductions of over 95 pct have been easily achieved. Other compositions and slabs have failed during the deformation process. Failure analysis after cold rolling reveals that one cause for brittleness is the presence of casting defects such as microshrinkage and inclusions, which can be eliminated. However, for high Mg contents, a high volume fraction of the intermetallic phase provides a contiguous path for crack propagation through the connected interdendritic regions.

  4. Adsorption of pharmaceuticals onto activated carbon fiber cloths - Modeling and extrapolation of adsorption isotherms at very low concentrations. (United States)

    Fallou, Hélène; Cimetière, Nicolas; Giraudet, Sylvain; Wolbert, Dominique; Le Cloirec, Pierre


    Activated carbon fiber cloths (ACFC) have shown promising results when applied to water treatment, especially for removing organic micropollutants such as pharmaceutical compounds. Nevertheless, further investigations are required, especially considering trace concentrations, which are found in current water treatment. Until now, most studies have been carried out at relatively high concentrations (mg L(-1)), since the experimental and analytical methodologies are more difficult and more expensive when dealing with lower concentrations (ng L(-1)). Therefore, the objective of this study was to validate an extrapolation procedure from high to low concentrations, for four compounds (Carbamazepine, Diclofenac, Caffeine and Acetaminophen). For this purpose, the reliability of the usual adsorption isotherm models, when extrapolated from high (mg L(-1)) to low concentrations (ng L(-1)), was assessed as well as the influence of numerous error functions. Some isotherm models (Freundlich, Toth) and error functions (RSS, ARE) show weaknesses to be used as an adsorption isotherms at low concentrations. However, from these results, the pairing of the Langmuir-Freundlich isotherm model with Marquardt's percent standard of deviation was evidenced as the best combination model, enabling the extrapolation of adsorption capacities by orders of magnitude.

  5. Geology and geochemistry of palaeoproterozoic low-grade metabasic volcanic rocks from Salumber area, Aravalli Supergroup, NW India

    Indian Academy of Sciences (India)

    L S Shekhawat; M K Pandit; D W Joshi


    The Palaeoproterozoic Aravalli Supergroup in Salumber region includes a basal unit of metabasic volcanic rocks (Salumber volcanic rocks) overlain by a volcaniclastic/conglomerate one. Although these volcanic rocks have been metamorphosed to green-schist facies, some primary volcanic features are still preserved. This metabasic volcanic sequence can be further differentiated on the basis of textural variations, and the mineral assemblages are: (a) oligoclase + actinolite + chlorite + epidote; and (b) oligoclase + hornblende+ chlorite + biotite + Fe-Ti oxides. The SiO2 content ranges from ∼47.7 to 55.8% and MgO from ∼4.2 to 12.8%. Geochemical characteristics allow their subdivision into high Mg and Fe tholeiites. Inverse relationship of MgO with silica, alkalis and Zr is generally consistent with fractionation mechanism, also suggested by a change in colour of the rocks from dark greenish to light greenish towards the upper parts of the sequence. These metabasic volcanic rocks are enriched in incompatible trace elements and LREE (La = 30 − 40 × chondrite, Lu = 2 − 5 × chondrite), and demonstrate affinity mainly with MORB and within plate settings in geochemical tectonic discrimination schemes. The geochemical characteristics suggest a complex evolutionary history envisaging derivation of the melt from an enriched heterogeneous lithospheric source.

  6. Effect of Magnesium and Osteoblast Cell Presence on Hydroxyapatite Formation on (Ti,Mg)N Thin Film Coatings (United States)

    Onder, Sakip; Calikoglu-Koyuncu, Ayse Ceren; Torun Kose, Gamze; Kazmanli, Kursat; Kok, Fatma Nese; Urgen, Mustafa


    TiN and (Ti,Mg)N thin film coatings were deposited on Ti substrates by an arc-physical vapor deposition technique. The effect of cell presence on hydroxyapatite (HA) formation was investigated using surfaces with four different Mg contents (0, 8.1, 11.31, and 28.49 at.%). Accelerated corrosion above 10 at.% Mg had a negative effect on the performance in terms of both cell proliferation and mineralization. In the absence of cells, Mg-free TiN coatings and low-Mg (8.1 at.%)-doped (Ti,Mg)N surfaces led to an early HA deposition (after 7 days and 14 days, respectively) in cell culture medium (DMEM), but the crystallinity was low. More crystalline HA structures were obtained in the presence of the cells. HA deposits with an ideal Ca/P ratio were obtained at least a week earlier, at day 14, in TiN and low-Mg (8.1 at.%)-doped (Ti,Mg)N compared with that of high-Mg-containing surfaces (>10 at.%). A thicker mineralized matrix was formed on low-Mg (8.1 at.%)-doped (Ti,Mg)N relative to that of the TiN sample. Low-Mg doping (cell proliferation and thicker mineralized matrix formation, so it could be a promising alternative for hard tissue applications.

  7. Wetting and reaction characteristics of crystalline and amorphous SiO2 derived rice-husk ash and SiO2/SiC substrates with Al-Si-Mg alloys (United States)

    Bahrami, A.; Pech-Canul, M. I.; Gutiérrez, C. A.; Soltani, N.


    A study of the wetting behavior of three substrate types (SiC, SiO2-derived RHA and SiC/SiO2-derived RHA) by two Al-Si-Mg alloys using the sessile drop method has been conducted, using amorphous and crystalline SiO2 in the experiment. Mostly, there is a transition from non-wetting to wetting contact angles, being the lowest θ values achieved with the alloy of high Mg content in contact with amorphous SiO2. The observed wetting behavior is attributed to the deposited Mg on the substrates. A strong diffusion of Si from the SiC/Amorphous RHA substrate into the metal drop explains the free Si segregated at the drop/substrate interface and drop surface. Although incorporation of both SiO2-derived RHA structures into the SiC powder compact substrates increases the contact angles in comparison with the SiC substrate alone, the still observed acute contact angles in RHA/SiC substrates make them promising for fabrication of composites with high volume fraction of reinforcement by the pressureless infiltration technique. The observed wetting characteristics, with decrease in surface tension and contact angles is explained by surface related phenomena. Based on contact angle changes, drop dimensions and surface tension values, as well as on the interfacial elemental mapping, and XRD analysis of substrates, some wetting and reaction pathways are proposed and discussed.

  8. Magnesium-Dependent Active-Site Conformational Selection in the Diels-Alderase Ribozyme

    Energy Technology Data Exchange (ETDEWEB)

    Berezniak, Tomasz [University of Heidelberg; Zahran, Mai [ORNL; Imhof, Petra [University of Heidelberg; Jaeschke, Andres [Free University of Berlin; Smith, Jeremy C [ORNL


    The Diels-Alderase ribozyme, an in vitro-evolved ribonucleic acid enzyme, accelerates the formation of carbon-carbon bonds between an anthracene diene and a maleimide dienophile in a [4 + 2] cycloaddition, a reaction with broad application in organic chemistry. Here, the Diels-Alderase ribozyme is examined via molecular dynamics (MD) simulations in both crystalline and aqueous solution environments. The simulations indicate that the catalytic pocket is highly dynamic. At low Mg(2+) ion concentrations, inactive states with the catalytic pocket closed dominate. Stabilization of the enzymatically active, open state of the catalytic pocket requires a high concentration of Mg(2+) ions (e.g., 54 mM), with cations binding to specific phosphate sites on the backbone of the residues bridging the opposite strands of the pocket. The free energy profile for pocket opening at high Mg(2+) cation concentration exhibits a double minimum, with a barrier to opening of approximately 5.5 kJ/mol and the closed state approximately 3 kJ/mol lower than the open state. Selection of the open state on substrate binding leads to the catalytic activity of the ribozyme. The simulation results explain structurally the experimental observation that full catalytic activity depends on the Mg(2+) ion concentration

  9. Abnormal lithium isotope composition from the ancient lithospheric mantle beneath the North China Craton. (United States)

    Tang, Yan-Jie; Zhang, Hong-Fu; Deloule, Etienne; Su, Ben-Xun; Ying, Ji-Feng; Santosh, M; Xiao, Yan


    Lithium elemental and isotopic compositions of olivines in peridotite xenoliths from Hebi in the North China Craton provide direct evidence for the highly variable δ(7)Li in Archean lithospheric mantle. The δ(7)Li in the cores of olivines from the Hebi high-Mg# peridotites (Fo > 91) show extreme variation from -27 to +21, in marked deviation from the δ(7)Li range of fresh MORB (+1.6 to +5.6) although the Li abundances of the olivines are within the range of normal mantle (1-2 ppm). The Li abundances and δ(7)Li characteristics of the Hebi olivines could not have been produced by recent diffusive-driven isotopic fractionation of Li and therefore the δ(7)Li in the cores of these olivines record the isotopic signature of the subcontinental lithospheric mantle. Our data demonstrate that abnormal δ(7)Li may be preserved in the ancient lithospheric mantle as observed in our study from the central North China Craton, which suggest that the subcontinental lithospheric mantle has experienced modification of fluid/melt derived from recycled oceanic crust.

  10. Magnesium and Manganese Silicides For Efficient And Low Cost Thermo-Electric Power Generation

    Energy Technology Data Exchange (ETDEWEB)

    Trivedi, Sudhir B. [Brimrose Technology Corporation; Kutcher, Susan W. [Brimrose Technology Corporation; Rosemeier, Cory A. [Brimrose Technology Corporation; Mayers, David [Brimrose Technology Corporation; Singh, Jogender [Pennsylvania State University


    Thermoelectric Power Generation (TEPG) is the most efficient and commercially deployable power generation technology for harvesting wasted heat from such things as automobile exhausts, industrial furnaces, and incinerators, and converting it into usable electrical power. We investigated the materials magnesium silicide (Mg2Si) and manganese silicide (MnSi) for TEG. MgSi2 and MnSi are environmentally friendly, have constituent elements that are abundant in the earth's crust, non-toxic, lighter and cheaper. In Phase I, we successfully produced Mg2Si and MnSi material with good TE properties. We developed a novel technique to synthesize Mg2Si with good crystalline quality, which is normally very difficult due to high Mg vapor pressure and its corrosive nature. We produced n-type Mg2Si and p-type MnSi nanocomposite pellets using FAST. Measurements of resistivity and voltage under a temperature gradient indicated a Seebeck coefficient of roughly 120 V/K on average per leg, which is quite respectable. Results indicated however, that issues related to bonding resulted in high resistivity contacts. Determining a bonding process and bonding material that can provide ohmic contact from room temperature to the operating temperature is an essential part of successful device fabrication. Work continues in the development of a process for reproducibly obtaining low resistance electrical contacts.

  11. Greenhouse conditions induce mineralogical changes and dolomite accumulation in coralline algae on tropical reefs. (United States)

    Diaz-Pulido, Guillermo; Nash, Merinda C; Anthony, Kenneth R N; Bender, Dorothea; Opdyke, Bradley N; Reyes-Nivia, Catalina; Troitzsch, Ulrike


    Human-induced ocean acidification and warming alter seawater carbonate chemistry reducing the calcification of reef-building crustose coralline algae (CCA), which has implications for reef stability. However, due to the presence of multiple carbonate minerals with different solubilities in seawater, the algal mineralogical responses to changes in carbonate chemistry are poorly understood. Here we demonstrate a 200% increase in dolomite concentration in living CCA under greenhouse conditions of high pCO2 (1,225 μatm) and warming (30 °C). Aragonite, in contrast, increases with lower pCO2 (296 μatm) and low temperature (28 °C). Mineral changes in the surface pigmented skeleton are minor and dolomite and aragonite formation largely occurs in the white crust beneath. Dissolution of high-Mg-calcite and particularly the erosive activities of endolithic algae living inside skeletons play key roles in concentrating dolomite in greenhouse treatments. As oceans acidify and warm in the future, the relative abundance of dolomite in CCA will increase.

  12. Magnesium nutrition of apple trees. III. Comparison of different methods of magnesium fertilization

    Directory of Open Access Journals (Sweden)

    A. Sadowski


    Full Text Available In the period 1969-1973 two experiments were performed in young orchards in Central Poland: a four-year experiment at Julianów, on sandy loamy soil on underlying sand and one-year experiment at Kośmin, on sandy loam soil on clay loam. At Kosmin, in spite of a high Mg content in the subsoil, Mg deficiency symptoms appeared, because of shallow rooting owing to poor aeration. In both experiments, foliar sprays with epsomite were less effective than fertilization to the soil; at Kośmin even eight sprays were less effective than soil dressings. Mg losses from a sandy soil due to leaching were high, particularly where sand was present in the whole profile; under these conditions the least losses of Mg were from split doses of epsomite (Mg3x120. Single doses of epsomite were the most effective in increasing leaf Mg content, reducing Mg deficiency symptoms and promoting growth of trees in the first year after application; in the later years split doses of epsomite and a single initial dose of magnesium lime were more effective. Effects of Mg fertilization on growth and yields of apples were rather slight, when K fertilizer doses were low. No effect of Mg fertilization upon fruit drop and fruit quality was found. Preliminary recommendations for practice are given.

  13. Transient kinetics of Ca2+ transport of sarcoplasmic reticulum. A comparison of cardiac and skeletal muscle. (United States)

    Sumida, M; Wang, T; Mandel, F; Froehlich, J P; Schwartz, A


    Current evidence supports similar functions and mechanisms for cardiac sarcoplasmic reticulum (CSR) as for skeletal sarcoplasmic reticulum (SSR). It is thought that the slower relaxation rate of cardiac muscle compared to fast skeletal muscle reflects the lower ATPase activity and calcium transport of CSR. Possible quantitative differences is phosphorylation, dephosphorylation, and calcium transport of the isolated preparations are studied using a quench-flow apparatus. The results show that both CSR and SSR bind calcium tightly in the absence of ATP, and coupling of E approximately P formation and calcium transport occurs in the transient phase of ATP hydrolysis. The rate of phosphorylation (t-1/2 - 10 ms) of sarcoplasmic reticulum (SR) preloaded with calcium is the same for cardiac and skeletal preparations. However, the rates of dissociation of extra vesicular calcium (10 s-1 versus 15 s-1), phosphorylation of calcium-free SR, and dephosphorylation of E approximately P (8 s-1 versus 12 s-1) are lower for CSR than for SSR. By computer simulation, the apparent rate constants associated with the reduced rates of phosphorylation of calcium-free SR were: 12 s-1 for CSR and 63 s-1 for SSR in the presence of high Mg2+. The difference in the rates may be partly responsible for the lower levels of ATPase and calcium transport activity with characterize cardiac muscle preparations.

  14. The structural characterization and H2 sorption properties of carbon-supported Mg1-xNix nanocrystallites (United States)

    Bogerd, René; Adelhelm, Philipp; Meeldijk, Johannes H.; de Jong, Krijn P.; de Jongh, Petra E.


    Magnesium (hydride) is a promising system for the reversible on-board storage of hydrogen, but suffers from slow sorption kinetics and a high thermodynamic stability of the hydride. We explored a combined approach to tackle these problems: nanosizing and carbon-supporting the magnesium, and doping it with nickel. Samples were prepared by melt infiltration with magnesium of nanoporous carbon onto which 1-12 wt% nickel nanoparticles had been predeposited. For loadings up to 15 wt% MgH2, 10-30 nm crystallites with different compositions were formed inside the porous carbon, each giving a specific H2 desorption signature. Surprisingly, higher Mg loadings resulted in more homogeneously mixed samples, which was due to the facilitated wetting of the carbon with the magnesium due to the presence of nickel. Hydrogen release temperatures close to that of Mg2NiH4 were observed for high MgH2 loadings (50 wt%) and small amounts of Ni (Mg0.95Ni0.05). The favourable H2 desorption properties could mainly be attributed to excellent kinetics due to the efficient mixing of magnesium, nickel and carbon on the nanoscale.

  15. Greenhouse conditions induce mineralogical changes and dolomite accumulation in coralline algae on tropical reefs (United States)

    Diaz-Pulido, Guillermo; Nash, Merinda C.; Anthony, Kenneth R. N.; Bender, Dorothea; Opdyke, Bradley N.; Reyes-Nivia, Catalina; Troitzsch, Ulrike


    Human-induced ocean acidification and warming alter seawater carbonate chemistry reducing the calcification of reef-building crustose coralline algae (CCA), which has implications for reef stability. However, due to the presence of multiple carbonate minerals with different solubilities in seawater, the algal mineralogical responses to changes in carbonate chemistry are poorly understood. Here we demonstrate a 200% increase in dolomite concentration in living CCA under greenhouse conditions of high pCO2 (1,225 μatm) and warming (30 °C). Aragonite, in contrast, increases with lower pCO2 (296 μatm) and low temperature (28 °C). Mineral changes in the surface pigmented skeleton are minor and dolomite and aragonite formation largely occurs in the white crust beneath. Dissolution of high-Mg-calcite and particularly the erosive activities of endolithic algae living inside skeletons play key roles in concentrating dolomite in greenhouse treatments. As oceans acidify and warm in the future, the relative abundance of dolomite in CCA will increase.

  16. Coralline algae (Rhodophyta) in a changing world: integrating ecological, physiological, and geochemical responses to global change. (United States)

    McCoy, Sophie J; Kamenos, Nicholas A


    Coralline algae are globally distributed benthic primary producers that secrete calcium carbonate skeletons. In the context of ocean acidification, they have received much recent attention due to the potential vulnerability of their high-Mg calcite skeletons and their many important ecological roles. Herein, we summarize what is known about coralline algal ecology and physiology, providing context to understand their responses to global climate change. We review the impacts of these changes, including ocean acidification, rising temperatures, and pollution, on coralline algal growth and calcification. We also assess the ongoing use of coralline algae as marine climate proxies via calibration of skeletal morphology and geochemistry to environmental conditions. Finally, we indicate critical gaps in our understanding of coralline algal calcification and physiology and highlight key areas for future research. These include analytical areas that recently have become more accessible, such as resolving phylogenetic relationships at all taxonomic ranks, elucidating the genes regulating algal photosynthesis and calcification, and calibrating skeletal geochemical metrics, as well as research directions that are broadly applicable to global change ecology, such as the importance of community-scale and long-term experiments in stress response.

  17. Microstructure of MgB{sub 2} superconducting wire prepared by internal magnesium diffusion and in-situ powder-in-tube processes – Secondary phase intergrain nanolayers as an oxygen content indicator

    Energy Technology Data Exchange (ETDEWEB)

    Rosová, A., E-mail:; Kováč, P.; Hušek, I.; Brunner, B.; Dobročka, E.


    Highlights: • We compared microstructure of undoped MgB{sub 2} wires made by in-situ PIT and IMD. • The main differences were in MgB{sub 2} density and volume ratio of amorphous MgO. • Thin oriented layers of secondary phases were observed between MgB{sub 2} plate grains. • Only MgO or only Mg oriented layers were in the PIT or IMD samples, resp. • High MgB{sub 2} density and low MgO{sub 2} content caused higher J{sub c} of IMD wire. - Abstract: We analyzed microstructure of two undoped MgB{sub 2} single core wires prepared by two different technologies – in-situ powder-in-tube (PIT) technology and internal magnesium diffusion (IMD) processes. Their microstructure showed mainly different densities of superconducting material, corresponding content of pores and the volume ratio of amorphous MgO phase. We observed a special microstructural feature – thin oriented secondary phase layers on grain boundaries of plate-shaped MgB{sub 2} grains. The significant decrease of oxygen content in IMD wire was reflected in the presence of thin oriented Mg layers while in PIT wire thin oriented MgO layers were observed. The microstructure difference is reflected in increased critical current density J{sub c} of the IMD wire in comparison to the PIT one.

  18. Silicate mineralogy at the surface of Mercury (United States)

    Namur, Olivier; Charlier, Bernard


    NASA's MESSENGER spacecraft has revealed geochemical diversity across Mercury's volcanic crust. Near-infrared to ultraviolet spectra and images have provided evidence for the Fe2+-poor nature of silicate minerals, magnesium sulfide minerals in hollows and a darkening component attributed to graphite, but existing spectral data is insufficient to build a mineralogical map for the planet. Here we investigate the mineralogical variability of silicates in Mercury's crust using crystallization experiments on magmas with compositions and under reducing conditions expected for Mercury. We find a common crystallization sequence consisting of olivine, plagioclase, pyroxenes and tridymite for all magmas tested. Depending on the cooling rate, we suggest that lavas on Mercury are either fully crystallized or made of a glassy matrix with phenocrysts. Combining the experimental results with geochemical mapping, we can identify several mineralogical provinces: the Northern Volcanic Plains and Smooth Plains, dominated by plagioclase, the High-Mg province, strongly dominated by forsterite, and the Intermediate Plains, comprised of forsterite, plagioclase and enstatite. This implies a temporal evolution of the mineralogy from the oldest lavas, dominated by mafic minerals, to the youngest lavas, dominated by plagioclase, consistent with progressive shallowing and decreasing degree of mantle melting over time.

  19. Compositional terranes on Mercury: Information from fast neutrons (United States)

    Lawrence, David J.; Peplowski, Patrick N.; Beck, Andrew W.; Feldman, William C.; Frank, Elizabeth A.; McCoy, Timothy J.; Nittler, Larry R.; Solomon, Sean C.


    We report measurements of the flux of fast neutrons at Mercury from 20ºS to the north pole. On the basis of neutron transport simulations and remotely sensed elemental compositions, cosmic-ray-induced fast neutrons are shown to provide a measure of average atomic mass, , a result consistent with earlier studies of the Moon and Vesta. The dynamic range of fast neutron flux at Mercury is 3%, which is smaller than the fast-neutron dynamic ranges of 30% and 6% at the Moon and Vesta, respectively. Fast-neutron data delineate compositional terranes on Mercury that are complementary to those identified with X-ray, gamma-ray, and slow-neutron data. Fast neutron measurements confirm the presence of a region with high , relative to the mean for the planet, that coincides with the previously identified high-Mg region and reveal the existence of at least two additional compositional terranes: a low- region within the northern smooth plains and a high- region near the equator centered near 90ºE longitude. Comparison of the fast-neutron map with elemental composition maps show that variations predicted from the combined element maps are not consistent with the measured variations in fast-neutron flux. This lack of consistency could be due to incomplete coverage for some elements or uncertainties in the interpretations of compositional and neutron data. Currently available data and analyses do not provide sufficient constraints to resolve these differences.

  20. Response of High Latitude Coralline Algae to pCO2 and Thermal Stress (United States)

    Garlick-Ott, K.; Williams, B.; Chan, P. T. W.; Westfield, I. T.; Rasher, D.; Ries, J. B.; Adey, W.; Halfar, J.


    The impacts of recent and future anthropogenic increases in atmospheric pCO2 causing ocean acidification and temperature on high-latitude oceans, and the marine organisms that inhabit them, are varied and poorly understood. The ecologically important crustose coralline alga Clathromorphum compactum may be particularly vulnerable to ocean acidification due to the relatively high solubility of its high Mg-calcite skeleton . This species of coralline algae is abundant throughout coastal mid-to-high latitude areas of the northern hemisphere, and calcifies annually-banded skeletons with longevities of up to 650 years. Here we used micro-computed tomography (micro-CT) to evaluate the impact of decreasing seawater pH and increasing temperature on skeletal density of algal specimens cultured in a fully crossed pCO2 (280, 400, 700, 2800 µatm) and temperature (6.5, 8.7, 12.4 °C) laboratory experiment. To examine the natural variability in coralline algal skeletal density, additional long-lived wild C. compactum specimens were collected along a latitudinal transect extending from the Gulf of Maine to the Canadian Arctic Archipelago. Density time series generated from the wild specimens spans the past several decades to century, and were used to evaluate other environmental parameters that may influence the skeletal density of coralline algae. This research will evaluate the resiliency of this alga to future environmental change.

  1. Dynamic disease management in Trachymyrmex fungus-growing ants (Attini: Formicidae). (United States)

    Fernández-Marín, Hermógenes; Bruner, Gaspar; Gomez, Ernesto B; Nash, David R; Boomsma, Jacobus J; Wcislo, William T


    Multipartner mutualisms have potentially complex dynamics, with compensatory responses when one partner is lost or relegated to a minor role. Fungus-growing ants (Attini) are mutualistic associates of basidiomycete fungi and antibiotic-producing actinomycete bacteria; the former are attacked by specialized fungi (Escovopsis) and diverse generalist microbes. Ants deploy biochemical defenses from bacteria and metapleural glands (MGs) and express different behaviors to control contaminants. We studied four Trachymyrmex species that differed in relative abundance of actinomycetes to understand interactions among antimicrobial tactics that are contingent on the nature of infection. MG grooming rate and actinomycete abundance were negatively correlated. The two species with high MG grooming rates or abundant actinomycetes made relatively little use of behavioral defenses. Conversely, the two species with relatively modest biochemical defenses relied heavily on behavior. Trade-offs suggest that related species can evolutionarily diverge to rely on different defense mechanisms against the same threat. Neither bacterial symbionts nor MG secretions thus appear to be essential for mounting defenses against the specialized pathogen Escovopsis, but reduced investment in one of these defense modes tends to increase investment in the other.

  2. The 89 Ma Tortugal komatiitic suite, Costa Rica: Implications for a common geological origin of the Caribbean and Eastern Pacific region from a mantle plume (United States)

    Alvarado, Guillermo E.; Denyer, Percy; Sinton, Christopher W.


    Komatiites are reported for the first time in the northern part of the Gulf of Nicoya, Costa Rica. These rocks, dated at 89.7 ± 1.4 Ma (Turonian) by 40Ar/39Ar methods, occur as a large, elongated (14 km long, 1.5 km wide) N60°W striking body in the ophiolitic Nicoya Complex. These lavas have high MgO (26% 29%), Ni, and Cr, have high CaO/Al2O3 (0.98 1.08) and moderate Al2O3/TiO2 (5.55 8.44) ratios, and are depleted in Al2O3 (4% 5.5%), K2O (0.02% 0.37%), and TiO2 (0.59% 0.9%). Although these lavas are cumulates, their geochemical composition indicates an origin from a primary komatiitic magma, with a melting temperature of 1700 °C at a depth of 150 km. Similarities in the petrology and age (88 90 Ma) of Gorgona, Curaìao, and Nicoya-Tortugal mafic and ultramafic volcanic rocks suggest that these rocks had a common origin. These occurrences suggest a single hotspot center over a large area of the Caribbean and Eastern Pacific Mesozoic region due to a major thermal anomaly in the mantle, such as a hot, rising, convective plume.

  3. Phase heterogeneity in carbonate production by marine fish influences their roles in sediment generation and the inorganic carbon cycle. (United States)

    Salter, Michael A; Harborne, Alastair R; Perry, Chris T; Wilson, Rod W


    Marine teleost fish are important carbonate producers in neritic and oceanic settings. However, the fates of the diverse carbonate phases (i.e., mineral and amorphous forms of CaCO3) they produce, and their roles in sediment production and marine inorganic carbon cycling, remain poorly understood. Here we quantify the carbonate phases produced by 22 Bahamian fish species and integrate these data with regional fish biomass data from The Bahamas to generate a novel platform-scale production model that resolves these phases. Overall carbonate phase proportions, ordered by decreasing phase stability, are: ~20% calcite, ~6% aragonite, ~60% high-Mg calcite, and ~14% amorphous carbonate. We predict that these phases undergo differing fates, with at least ~14% (amorphous carbonate) likely dissolving rapidly. Results further indicate that fisheries exploitation in The Bahamas has potentially reduced fish carbonate production by up to 58% in certain habitats, whilst also driving a deviation from natural phase proportions. These findings have evident implications for understanding sedimentary processes in shallow warm-water carbonate provinces. We further speculate that marked phase heterogeneity may be a hitherto unrecognised feature of fish carbonates across a wide range of neritic and oceanic settings, with potentially major implications for understanding their role in global marine inorganic carbon cycling.

  4. The impact of high dietary zinc oxide on the development of the intestinal microbiota in weaned piglets. (United States)

    Starke, Ingo C; Pieper, Robert; Neumann, Konrad; Zentek, Jürgen; Vahjen, Wilfried


    Weaned piglets were fed diets containing 57 (low) or 2425 (high) mg kg(-1) analytical grade ZnO for a period of 5 weeks. Intestinal contents were sampled in weekly intervals and analyzed for bacterial cell numbers and main bacterial metabolites. The most severe effects of high dietary zinc were observed 1 week after weaning in the stomach and small intestine. Pronounced reductions were observed for Enterobacteriaceae and the Escherichia group as well as for Lactobacillus spp. and for three of five studied Lactobacillus species. The impact of high dietary zinc diminished for enterobacteria with increasing age, but was permanent for Lactobacillus species. Bifidobacteria, enterococci, streptococci, Weissella spp. and Leuconostoc spp. as well as the Bacteroides-Prevotella-Porphyromonas group were not influenced by high dietary zinc throughout the trial. High dietary zinc reduced bacterial metabolite concentrations and increased molar acetate ratios at the expense of propionate in the proximal intestine, but differences diminished in older animals. Lower lactate concentrations were observed in the high dietary zinc group throughout the feeding trial. This study has shown that the application of dietary zinc at high concentrations leads to transient and lasting effects during the development of the intestinal microbiota, affecting composition as well as metabolic activity.

  5. Which Type of Planets do We Expect to Observe in the Habitable Zone? (United States)

    Adibekyan, Vardan; Figueira, Pedro; Santos, Nuno C.


    We used a sample of super-Earth-like planets detected by the Doppler spectroscopy and transit techniques to explore the dependence of orbital parameters of the planets on the metallicity of their host stars. We confirm the previous results (although still based on small samples of planets) that super-Earths orbiting around metal-rich stars are not observed to be as distant from their host stars as we observe their metal-poor counterparts to be. The orbits of these super-Earths with metal-rich hosts usually do not reach into the Habitable Zone (HZ), keeping them very hot and inhabitable. We found that most of the known planets in the HZ are orbiting their GK-type hosts which are metal-poor. The metal-poor nature of planets in the HZ suggests a high Mg abundance relative to Si and high Si abundance relative to Fe. These results lead us to speculate that HZ planets might be more frequent in the ancient Galaxy and had compositions different from that of our Earth.

  6. Which type of planets do we expect to observe in the Habitable Zone?

    CERN Document Server

    Adibekyan, Vardan; Santos, Nuno C


    We used a sample of super-Earth-like planets detected by the Doppler spectroscopy and transit techniques to explore the dependence of orbital parameters of the planets on the metallicity of their host stars. We confirm the previous results that super-Earths orbiting around metal-rich stars are not observed to be as distant from their host stars as we observe their metal-poor counterparts to be. The orbits of these super-Earths with metal-rich hosts usually do not reach into the Habitable Zone (HZ), keeping them very hot and inhabitable. We found that most of the known planets in the HZ are orbiting their GK-type hosts which are metal-poor. The metal-poor nature of planets in the HZ suggests a high Mg abundance relative to Si and high Si abundance relative to Fe. These results lead us to speculate that HZ planets might be more frequent in the ancient Galaxy and had compositions different from that of our Earth.

  7. Inhibition of acetylcholinesterase and different ATPases by a novel phosphorothionate (RPR-II) in rat brain. (United States)

    Rahman, M F; Siddiqui, M K; Jamil, K


    A novel phosphorothionate (2-butenoic acid-3-(diethoxy phosphinothioyl)-methyl ester (RPR-II), synthesized at the Indian Institute of Chemical Technology, Hyderabad, targets its effect on rat brain acetylcholinesterase (AChE) and Na(+)-K(+), Mg(2+), and Ca(2+) ATPases, as evident in this investigation. Three subchronic doses 0.014 (low), 0.028 (medium), and 0.042 (high) mg kg(-1) were administered to rats daily for a period of 90 days RPR-II caused statistically significant dose- and time-dependent inhibition in brain AChE and also in Na(+)-K(+), Mg(2+), and Ca(2+) ATPases in both male and female rats after 45 and 90 days of treatment. The low dose was generally insignificant while the medium and high doses were significantly effective. Females were more susceptible than males with regard to brain AChE, Na(+)-K(+), and Mg(2+) ATPases, which indicates sexual dimorphism in the treated rats. Interestingly, after 28 days post-treatment, recovery of these enzymes was observed. The relative sensitivities of these enzymes indicated that brain AChE was more sensitive than any of the ATPases, but among the ATPases Na(+)-K(+) ATPase was more susceptible than Ca(2+) or Mg(2+) ATPases. This compound, besides inhibiting the target of organophosphates, AChE, also inhibited different ATPases, suggesting both synaptic transmission and nerve conduction were affected.

  8. Hematological and clinical chemistry changes induced by subchronic dosing of a novel phosphorothionate (RPR-V) in Wistar male and female rats. (United States)

    Rahman, M F; Siddiqui, M K J


    A novel phosphorothionate [2-butenoic acid-3-(diethoxy phosphinothioyl)-ethyl ester; RPR-V] synthesized at Indian Institute of Chemical Technology (Hyderabad, India) was studied using subchronic doses of 0.033 (low), 0.066 (medium), and 0.099 (high) mg kg(- 1) in male and female rats daily for 90 days. Continuous treatment with RPR-V caused significant (p RPR-V caused significant elevation in serum clinical chemistry parameters calcium, phosphorus, creatinine, and chloride contents, whereas protein and glucose levels were depressed in both male and female treated rats after 45 and 90 days of treatment. These alterations were significant when compared with two-way ANOVA showing that these changes were dose- and time-dependent. The effects of low dose were generally not statistically significant, whereas medium and high doses caused significant effects. The changes in male rats were not significant when compared with female rats showing no sexual dimorphism by this compound. Recovery was observed after 28 days post-treatment (withdrawal study), indicating that the compound entered into the system was eliminated from the body, and the blood parameters were improved. Hematological and clinical chemistry parameters can be detected rapidly and hence can be used for prediction and diagnosis of pesticide toxicity. Alterations in these parameters show toxic stress in the treated animals especially on blood and blood-forming organs.

  9. Histamine Excites Rat Superior Vestibular Nuclear Neurons via Postsynaptic H1 and H2 Receptors in vitro

    Directory of Open Access Journals (Sweden)

    Qian-Xing Zhuang


    Full Text Available The superior vestibular nucleus (SVN, which holds a key position in vestibulo-ocular reflexes and nystagmus, receives direct hypothalamic histaminergic innervations. By using rat brainstem slice preparations and extracellular unitary recordings, we investigated the effect of histamine on SVN neurons and the underlying receptor mechanisms. Bath application of histamine evoked an excitatory response of the SVN neurons, which was not blocked by the low-Ca2+/high-Mg2+ medium, indicating a direct postsynaptic effect of the amine. Selective histamine H1 receptor agonist 2-pyridylethylamine and H2 receptor agonist dimaprit, rather than VUF8430, a selective H4 receptor agonist, mimicked the excitation of histamine on SVN neurons. In addition, selective H1 receptor antagonist mepyramine and H2 receptor antagonist ranitidine, but not JNJ7777120, a selective H4 receptor antagonist, partially blocked the excitatory response of SVN neurons to histamine. Moreover, mepyramine together with ranitidine nearly totally blocked the histamine-induced excitation. Immunostainings further showed that histamine H1 and H2 instead of H4 receptors existed in the SVN. These results demonstrate that histamine excites the SVN neurons via postsynaptic histamine H1 and H2 receptors, and suggest that the central histaminergic innervation from the hypothalamus may actively bias the SVN neuronal activity and subsequently modulate the SVN-mediated vestibular functions and gaze control.

  10. The Role of Garnet Pyroxenite in High-Fe Mantle Melt Generation: High Pressure Melting Experiments (United States)

    Tuff, J.; Takahashi, E.; Gibson, S.


    Evidence for the existence of heterogeneous or 'marble cake' convecting mantle1 is provided recently by rare, high MgO ( ˜ 15 wt.%) primitive magmas with anomalously high abundances of FeO* ( ˜ 13.5 to 16 wt. %2,3; where FeO* = total Fe as FeO). These high-Fe mantle melts show a limited occurrence in the initial stage of magmatism in large igneous provinces (e.g. Deccan, Ethiopia and Paraná-Etendeka) and some have incompatible trace-element and radiogenic-isotopic ratios (Sr, Nd and Pb) that resemble those of ocean-island basalts. This suggests that they are predominantly derived from the convecting mantle2. The ferropicrites are mildly- to sub-alkaline and have low contents of Al2O3 (A297, 447-477 (1980). 2 Gibson et al., Earth and Planetary Science Letters 174, 355-374 (2000). 3 Gibson, Earth and Planetary Science Letters 195, 59-74 (2002).

  11. Mechanism of Calcite Co-Orientation in the Sea Urchin Tooth

    Energy Technology Data Exchange (ETDEWEB)

    Killian, Christopher; Metzler, Rebecca; Gong, Y. U. T.; Olson, Ian; Aizenberg, Joanna; Politi, Yael; Wilt, Fred; Scholl, Andreas; Young, Anthony; Doran, Andrew; Kunz, Martin; Tamura, Nobumichi; Coppersmith, Susan; Gilbert, P. U. P. A.


    Sea urchin teeth are remarkable and complex calcite structures, continuously growing at the forming end and self-sharpening at the mature grinding tip. The calcite (CaCO{sub 3}) crystals of tooth components, plates, fibers, and a high-Mg polycrystalline matrix, have highly co-oriented crystallographic axes. This ability to co-orient calcite in a mineralized structure is shared by all echinoderms. However, the physico-chemical mechanism by which calcite crystals become co-oriented in echinoderms remains enigmatic. Here, we show differences in calcite c-axis orientations in the tooth of the purple sea urchin (Strongylocentrotus purpuratus), using high-resolution X-ray photoelectron emission spectromicroscopy (X-PEEM) and microbeam X-ray diffraction ({mu}XRD). All plates share one crystal orientation, propagated through pillar bridges, while fibers and polycrystalline matrix share another orientation. Furthermore, in the forming end of the tooth, we observe that CaCO{sub 3} is present as amorphous calcium carbonate (ACC). We demonstrate that co-orientation of the nanoparticles in the polycrystalline matrix occurs via solid-state secondary nucleation, propagating out from the previously formed fibers and plates, into the amorphous precursor nanoparticles. Because amorphous precursors were observed in diverse biominerals, solid-state secondary nucleation is likely to be a general mechanism for the co-orientation of biomineral components in organisms from different phyla.

  12. Rapid magmatic processes accompany arc-continent collision: the Western Bismarck arc, Papua New Guinea (United States)

    Cunningham, Heather; Gill, Jim; Turner, Simon; Caulfield, John; Edwards, Louise; Day, Simon


    New U-Th-Ra, major and trace element, and Sr-Nd-Pb isotope data are presented for young lavas from the New Britain and Western Bismarck arcs in Papua New Guinea. New Britain is an oceanic arc, whereas the latter is the site of an arc-continent collision. Building on a recent study of the Manus Basin, contrasts between the two arcs are used to evaluate the processes and timescales of magma generation accompanying arc-continent collision and possible slab detachment. All three suites share many attributes characteristic of arc lavas that can be ascribed to the addition of a regionally uniform subduction component derived from the subducting altered oceanic crust and sediment followed by dynamic melting of the modified mantle. However, the Western Bismarck arc lavas diverge from the Pb isotope mixing array formed by the New Britain and the Manus Basin lavas toward elevated 208Pb/204Pb. We interpret this to reflect a second and subsequent addition of sediment melt at crustal depth during collision. 238U and 226Ra excesses are preserved in all of the lavas and are greatest in the Western Bismarck arc. High-Mg andesites with high Sr/Y ratios in the westernmost arc are attributed to recent shallow mantle flux melting at the slab edge. Data for two historical rhyolites are also presented. Although these rhyolites formed in quite different tectonic settings and display different geochemical and isotopic compositions, both formed from mafic parents within millennia.

  13. The Cerro Bitiche Andesitic Field: petrological diversity and implications for magmatic evolution of mafic volcanic centers from the northern Puna (United States)

    Maro, Guadalupe; Caffe, Pablo J.


    The Cerro Bitiche Andesitic Field (CBAF) is one of the two largest mafic volcanic fields in northern Puna (22-24° S) and is spatially and temporally associated with ignimbrites erupted from some central Andean Altiplano-Puna Volcanic Complex calderas. The CBAF comprises seven scoria cones and widespread high-K calcalkaline lava flows that cover an area of 200 km2. Although all erupted rocks have a relatively narrow chemical range (56-62 % SiO2, 3-6 % MgO), there is a broad diversity of mineral compositions and textures. The least evolved lavas (˜58-61 % SiO2) are high-Mg andesites with scarce (andesites (˜62 wt% SiO2), on the other hand, are porphyritic rocks with plagioclase + orthopyroxene + biotite and ubiquitous phenocryst disequilibrium textures. These magmas were likely stored in crustal reservoirs, where they experienced convection caused by mafic magma underplating, magma mixing, and/or assimilation. Trace element and mineral compositions of CBAF lavas provide evidence for complex evolution of distinct magma batches.


    Directory of Open Access Journals (Sweden)

    I. S. Chuvashova


    Full Text Available A comparative study of major elements, trace elements, and isotopes in high- and moderate-Mg volcanic sequences of 16–14 and 14–13 Ma, respectively, has been performed in the Bereya volcanic center. In the former (small volume sequence, contaminated by crustal material basalts and trachybasalts of K–Na series were followed by uncontaminated basanites and basalts of transitional (K–Na–K compositions and afterwards by picrobasalts and ba­salts of K series. From pressure estimates using equation [Scarrow, Cox, 1995], high-Mg magma originated at the deep range of 115–150 km. In the latter (high-volume sequence, basalts and basaltic andesites of transitional (Na–K–Na compositions and basalts of Na series were overlain by basalts and trachybasalts of K–Na series. First, there was a strong melting of its shallow garnet-free part with coeval weak melting of more deep garnet-bearing portion, then only a deep garnet-bearing portion of the lithospheric mantle melted. It is suggested that the sequential formation of high- and moderate-Mg melts reflected the mid-Miocene thermal impact of the lithosphere by hot material from the Transbaikalian low-velocity domain, which had the potential temperature Tp as high as 1510 °С. This thermal impact triggered the rifting in the lithosphere of the Baikal Rift System.

  15. Making continental crust: The sanukitoid connection

    Institute of Scientific and Technical Information of China (English)

    Yoshiyuki TATSUMI


    The average continental crust possesses intermediate compositions that typify arc magmatism and as a result it is believed to have been created at ancient convergent plate boundaries. One possible mechanism for intermediate continental crust formation is the direct production of andesitic melts in the upper mantle. Sanukitoids, which characterize the Setouchi volcanic belt, SW Japan, include unusually high-Mg andesites (HMA). They were generated by slab melting and subsequent melt-mantle interactions under unusual tectonic settings such as where warm lithosphere subducts into hot upper mantle. Such conditions would have existed in the Archean. Hydrous HMA magmas are likely to have solidified within the crust to form HMA plutons, which were then remelted to produce differentiated sanukitoids. At present, generation and differentiation of HMA magmas may be taking place in the Izu-Bonin-Mariana arc-trench system (IBM), because (1) HMA magmatism characterizes the initial stages of the iBM evolution and (2) the IBM middle crust exhibits Vp identical to that of the bulk continental crust. Vp estimates for plutonic rocks with HMA compositions support this. However tonalitic composition for middle-crust-forming rocks cannot be ruled out, suggesting an alternative possibility that the continental crust has been created by differentiation of mantle-derived basaltic magmas.

  16. The petrological relationship between Kamen volcano and adjacent volcanoes of Klyuchevskaya group (United States)

    Churikova, Tatiana; Gordeychik, Boris; Wörner, Gerhard; Ivanov, Boris; Maximov, Alexander; Lebedev, Igor; Griban, Andrey


    The Klyuchevskaya Group (KG) of volcanoes has the highest magma production rate across the Kamchatka arc and in fact for any arc worldwide. However, modern geochemical studies of Kamen volcano, which is located between Klyuchevskoy, Bezymianny and Ploskie Sopky volcanoes, were not carried out and its relation and petrogenesis in comparison to other KG volcanoes is unknown. Space-time proximity of KG volcanoes and the common zone of seismicity below them may suggest a common source and genetic relationship. However, the lavas of neighboring volcanoes are rather different: high-Mg and high-Al basalts occur at Klyuchevskoy volcano, Hbl-bearing andesites and dаcites dominate at Bezymianny and medium-high-K subalkaline rocks at Ploskie Sopky volcano. Moreover, previously it was shown that distinct fluid signatures were observed in different KG volcanoes. In this report we present geological, petrographical, mineralogical and petrochemical data on the rocks of Kamen volcano in comparison with other KG volcanoes. Three consecutive periods of volcano activity were recognized in geological history of Kamen volcano: stratovolcano formation, development of a dike complex and formation of numerous cinder and cinder-lava monogenetic cones. The rock series of volcano are divided into four groups: olivine-bearing (Ol-2Px and Ol-Cpx), olivine-free (2Px-Pl, Cpx-Pl and abundant Pl), Hb-bearing and subaphyric rocks. While olivine-bearing rocks are observed in all volcanic stages, olivine-free lavas are presented only in the stratovolcano edifice. Lavas of the monogenetic cones are presented by olivine-bearing and subaphyric rocks. Dikes are olivine-bearing and hornblende-bearing rocks. Olivines of the Kamen stratovolcano and dikes vary from Fo60 to Fo83, clinopyroxenes are augites in composition and plagioclases have a bimodal distribution with maximum modes at An50 and An86. Oxides are represented by high-Al spinel, magnetite and titaniferous magnetite. Mineral compositions of the

  17. The role of polybaric crystallization in genesis of andesitic magmas: Phase equilibria simulations of the Bezymianny volcanic subseries (United States)

    Almeev, Renat R.; Ariskin, Alexei A.; Kimura, Jun-Ichi; Barmina, Galina S.


    Using the updated COMAGMAT model, the crystallization sequences of a Bezymianny Volcano basaltic andesite (Kamchatka, Russia) are simulated in a wide range of thermodynamic conditions (P-T-fO2) as a function of H2O concentration. Comparison of the modeled liquid lines of descent with petrochemical trends of the volcanic suite indicates the parental melts contain 1.5-2 wt.% H2O stored under 490-520 MPa pressure in the magma plumbing system beneath Bezymianny Volcano. The initial magma originates as a result of the polybaric evolution of mantle-derived high-Mg basaltic magmas of the adjacent Kliuchevskoi Volcano. The subsequent evolution of derivative hydrous and alumina-rich basaltic andesite magmas may proceed under polybaric conditions with an average decompression of ~ 12 MPa per 1% of crystallization. In the course of polybaric crystallization, compositions of pyroxene-bearing andesites can be numerically reproduced and the modeled liquid compositions follow the natural liquid line of descent. However, hornblende-bearing magmas cannot be produced as a result of continued crystallization from parental basaltic andesite through the stage of pyroxene-bearing andesite formation. They require high water contents and high pressures of crystallization. In this case, liquid composition should deviate from the chemical trend defined by the whole rock compositions.

  18. The Link between Hi - Magnesium Andesite Distribution in Baja California Peninsula and the Undetached Fragments of the Farallon Plate (United States)

    Wang, Y.; Forsyth, D. W.; Savage, B.


    About 12 Ma, the Guadalupe and Magdalena microplates ceased subducting beneath the North American continent, leaving behind plate fragments that became incorporated into the Pacific plate as spreading ceased. Spreading directions changed dramatically on Magdalena spreading centers, suggesting that the Farallon slab detached from the microplate fragments before or during the cessation of spreading. Although the sinking Farallon plate must have detached from those two microplates, it is not known where the detachments occurred and how much of the young slab was left behind still attached to the unsubducted surface microplates. We delineate the undetached Farallon fragments by looking for associated seismic velocity anomalies using teleseismic Rayleigh wave tomography and the stations of the USArray, NARS-Baja and RESBAN arrays. The lateral extent of the remanent plate fragments is indicated by a high (positive) velocity anomaly at 100 km depth (Figure 1). This landward edge of this anomaly coincides with the distribution of post-subduction high-Mg andesites (Bajaites, black region in Figure 1), which are inferred to involve fluid fluxed melting in overlying asthenospheric wedge and melting of the subducted oceanic crust. Shear velocity anomaly at 100 km

  19. Mg-banding in the non-spinose planktic foraminifer Neogloboquadrina dutertrei caused by diurnal light/dark cycle (United States)

    Fehrenbacher, J. S.; Russell, A. D.; Davis, C. V.; Gagnon, A. C.; Spero, H. J.


    The Mg/Ca ratios of planktic foraminifera are commonly used for reconstructing past ocean temperatures. The intrashell Mg/Ca ratios in many species are highly variable, however, and mechanisms for understanding controls on Mg/Ca variability have not been fully explored. Recent laboratory culture experiments demonstrated that the Mg/Ca ratio is driven by a diurnal light/dark cycle in the planktic foraminifer Orbulina universa (Spero et al., 2015). Here we report results from laboratory culture experiments with the non-spinose planktic foraminifer, Neogloboquadrina dutertrei, which confirm that intrashell Mg variability in this species is also caused by a light/dark cycle. We present Laser Ablation-ICP-MS analyses and high-resolution NanoSIMS imaging that show low Mg/Ca ratio calcite forms during the day and high Mg/Ca ratio calcite (Mg bands) forms at night. Our results also clearly demonstrate that N. dutertrei adds a significant amount of calcite, as well as nearly all Mg-bands, after the final chamber forms. Chamber-to-chamber thickness differences are due to differential crust addition, rather than to calcite addition linked to chamber formation. These results have implications for chamber-formation processes in N. dutertrei, and possibly for other non-spinose species. That Mg-variability is driven by the same mechanism in two planktic species with different ecological niches (N. dutertrei and O. universa) suggests that Mg-banding is an intrinsic component of biomineralization in planktic foraminifers.

  20. Link between light-triggered Mg-banding and chamber formation in the planktic foraminifera Neogloboquadrina dutertrei (United States)

    Fehrenbacher, Jennifer S.; Russell, Ann D.; Davis, Catherine V.; Gagnon, Alexander C.; Spero, Howard J.; Cliff, John B.; Zhu, Zihua; Martin, Pamela


    The relationship between seawater temperature and the average Mg/Ca ratios in planktic foraminifera is well established, providing an essential tool for reconstructing past ocean temperatures. However, many species display alternating high and low Mg-bands within their shell walls that cannot be explained by temperature alone. Recent experiments demonstrate that intrashell Mg variability in Orbulina universa, which forms a spherical terminal shell, is paced by the diurnal light/dark cycle. Whether Mg-heterogeneity is also diurnally paced in species with more complex shell morphologies is unknown. Here we show that high