Sample records for refertilized mantle domains

  1. Mantle melting and melt refertilization beneath the Southwest Indian Ridge: Mineral composition of abyssal peridotites

    Chen, Ling; Zhu, Jihao; Chu, Fengyou; Dong, Yan-hui; Liu, Jiqiang; Li, Zhenggang; Zhu, Zhimin; Tang, Limei


    As one of the slowest spreading ridges of the global ocean ridge system, the Southwest Indian Ridge (SWIR) is characterized by discontinued magmatism. The 53°E segment between the Gallieni fracture zone (FZ) (52°20'E) and the Gazelle FZ (53°30'E) is a typical amagmatic segment (crustal thickness directly. We examine the mineral compositions of 17 peridotite samples from the 53°E amagmatic segment. The results show that the peridotites can be divided into two groups. The Group 1 peridotites are characterized by clinopyroxenes having LREE depleted patterns that is typical for the abyssal peridotite, thus are thought to be the residue of the mantle melting. The Group 2 peridotites show the lowest HREE content within the SWIR peridotites but are anomaly enriched in LREE, with flat or U-type REE patterns, thus cannot be the pure residue of mantle melting. Mineral compositions of the Group 2 peridotites are more depleted than that of peridotites sampled near the Bouvet hot spot (Johnson et al., 1990), implying that the depleted mantle beneath the 53°E segment may be the residue of ancient melting event. This hypothesis is supported by the the low Ol/Opx ratios, coarse grain sizes (>1cm) Opx, and Mg-rich mineral compositions akin to harzburgite xenoliths that sample old continental lithospheric mantle (Kelemen et al., 1998). Melt refertilization model shows that Group 2 peridotites were affected by an enriched low-degree partial melt from the garnet stability field. These results indicate that depleted mantle which experiences ancient melting event are more sensitive to melt refertilization, thus may reduce the melt flux, leading to extremely thin crust at 53°E segment. This research was granted by the National Basic Research Programme of China (973 programme) (grant No. 2013CB429705) and the Fundamental Research Funds of Second Institute of Oceanography, State Oceanic Administration (JG1603, SZ1507). References: Johnson K T M, Dick H J B, Shimizu N. Melting in the

  2. Refertilization process in the Patagonian subcontinental lithospheric mantle of Estancia Sol de Mayo (Argentina)

    Melchiorre, Massimiliano; Coltorti, Massimo; Gregoire, Michel; Benoit, Mathieu


    Anhydrous mantle xenoliths equilibrated at 1003-1040 °C from Estancia Sol de Mayo (ESM, Central Patagonia, Argentina) and entrained in post-plateau alkaline lavas belonging to Meseta Lago Buenos Aires have been investigated aiming at reconstructing the depletion and enrichment processes that affected this portion of the Patagonia lithospheric mantle. Xenoliths are characterized by a coarse-grained protogranular texture and are devoid of evident modal metasomatism. They show two texturally different clinopyroxenes: protogranular (cpx1) and texturally related to spinel (cpx2). Three different types of orthopyroxenes are also recognized: large protogranular crystals with exsolution lamellae (opx1); small clean and undeformed grains without exsolution lamellae (opx2) and small grains arranged in a vein (opx3). Major element composition of clinopyroxenes and orthopyroxenes highlights two different trends characterized by i) a high Al2O3 content at almost constant mg# and ii) a slight increase in Al2O3 content with decreasing mg#. Clinopyroxenes are enriched in LREE and are characterized by prominent to slightly negative Nb, Zr and Ti anomalies. No geochemical differences are observed between cpx1 and cpx2, while a discrimination can be observed between opx1 and opx2 (LREE-depleted; prominent to slightly negative Ti and Zr anomalies) and opx3 (prominent positive Zr anomaly). Partial melting modeling using both major and trace elements indicates a melting degree between ~ 5% and ~ 13% (up to ~ 23% according to major element modeling) for lherzolites and between ~ 20% and ~ 30% for harzburgites (down to ~ 5% according to trace element modeling). La/Yb and Al2O3, as well as Sr and Al2O3 negative correlations in clinopyroxenes point to a refertilization event affecting this lithospheric mantle. The agent was most probably a transitional alkaline/subalkaline melt, as indicated by the presence of orthopyroxene in the vein and the similar geochemical features of ESM

  3. Density and P-wave velocity structure beneath the Paraná Magmatic Province: Refertilization of an ancient lithospheric mantle

    Chaves, Carlos; Ussami, Naomi; Ritsema, Jeroen


    We estimate density and P-wave velocity perturbations in the mantle beneath the southeastern South America plate from geoid anomalies and P-wave traveltime residuals to constrain the structure of the lithosphere underneath the Paraná Magmatic Province (PMP) and conterminous geological provinces. Our analysis shows a consistent correlation between density and velocity anomalies. The P-wave speed and density are 1% and 15 kg/m3 lower, respectively, in the upper mantle under the Late Cretaceous to Cenozoic alkaline provinces, except beneath the Goiás Alkaline Province (GAP), where density (+20 kg/m3) and velocity (+0.5%) are relatively high. Underneath the PMP, the density is higher by about 50 kg/m3 in the north and 25 kg/m3 in the south, to a depth of 250 - 300 km. These values correlate with high-velocity perturbations of +0.5% and +0.3%, respectively. Profiles of density perturbation versus depth in the upper mantle are different for the PMP and the adjacent Archean São Francisco (SFC) and Amazonian (AC) cratons. The Paleoproterozoic PMP basement has a high-density root. The density is relatively low in the SFC and AC lithospheres. A reduction of density is a typical characteristic of chemically depleted Archean cratons. A more fertile Proterozoic and Phanerozoic subcontinental lithospheric mantle has a higher density, as deduced from density estimates of mantle xenoliths of different ages and composition. In conjunction with Re-Os isotopic studies of the PMP basalts, chemical and isotopic analyses of peridodite xenoliths from the GAP in the northern PMP, and electromagnetic induction experiments of the PMP lithosphere, our density and P-wave speed models suggest that the densification of the PMP lithosphere and flood basalt generation are related to mantle refertilization. Metasomatic refertilization resulted from the introduction of asthenospheric components from the mantle wedge above Proterozoic subduction zones, which surrounded the Paraná lithosphere

  4. Mantle refertilization by melts of crustal-derived garnet pyroxenite: Evidence from the Ronda peridotite massif, southern Spain

    Marchesi, Claudio; Garrido, Carlos J.; Bosch, Delphine; Bodinier, Jean-Louis; Gervilla, Fernando; Hidas, Károly


    Geochemical studies of primitive basalts have documented the presence of crustal-derived garnet pyroxenite in their mantle sources. The processes whereby melts with the signature of garnet pyroxenite are produced in the mantle are, however, poorly understood and somewhat controversial. Here we investigate a natural example of the interaction between melts of garnet pyroxenite derived from recycled plagioclase-rich crust and surrounding mantle in the Ronda peridotite massif. Melting of garnet pyroxenite at ˜1.5 GPa generated spinel websterite residues with MREE/HREE fractionation and preserved the positive Eu anomaly of their garnet pyroxenite precursor in whole-rock and clinopyroxene. Reaction of melts from garnet pyroxenite with depleted surrounding peridotite generated secondary fertile spinel lherzolite. These secondary lherzolites differ from common spinel lherzolite from Ronda and elsewhere by their lower-Mg# in clinopyroxene, orthopyroxene and olivine, lower-Cr# in spinel and higher whole-rock Al2O3, CaO, Sm/Yb and FeO* at a given SiO2. Remarkably, secondary spinel lherzolite shows the geochemical signature of ghost plagioclase in the form of positive Eu and Sr anomalies in whole-rock and clinopyroxene, reflecting the transfer of a low-pressure crustal imprint from recycled pyroxenite to hybridized peridotite. Garnet pyroxenite melting and melt-peridotite interaction, as shown in the Ronda massif, may explain how the signature of subducted or delaminated crust is transferred to the mantle and how a garnet pyroxenite component is introduced into the source region of basalts. The efficiency of these processes in conveying the geochemical imprint of crustal-derived garnet pyroxenite to extruded lavas depends on the reactivity of pyroxenite melt with peridotite and the mantle permeability, which may be controlled by prior refertilization reactions similar to those documented in the Ronda massif. Highly fertile heterogeneities produced by pyroxenite

  5. Mapping the nature of mantle domains in Western and Central Europe based on clinopyroxene and spinel chemistry: Evidence for mantle modification during an extensional cycle

    Picazo, S.; Müntener, O.; Manatschal, G.; Bauville, A.; Karner, G.; Johnson, C.


    Systematic differences in mineral composition of mantle peridotites are observed in ophiolites and peridotitic bodies from the Alpine Tethys, the Pyrenean domain, the Dinarides and Hellenides, and the Iberia-Newfoundland rifted margins. These differences can be understood in the context of the evolution of rifted margins and allow the identification of 3 major mantle domains: an inherited domain, a refertilized domain and a depleted domain. Most clinopyroxene from the inherited domain equilibrated in the spinel peridotite field and are too enriched in Na2O and Al2O3 to be residues of syn-rift melting. Clinopyroxene from the refertilized domain partially equilibrated with plagioclase and display lower Na2O and Al2O3, and elevated Cr2O3 contents. The refertilized domain is a hybrid zone, which locally preserves remnants from the inherited domain and overlapping chemical compositions. Depleted domains with clinopyroxene similar to abyssal peridotites are rare and Nd-isotopic studies indicate that they represent ancient periods of melting unrelated to the opening of the Jurassic and Cretaceous oceanic basins of the Alpine Tethys and southern North Atlantic. In many studied sections of mantle rocks in exposed ophiolites a systematic spatial distribution of the different domains with respect to the evolution of rifted margins can be identified. This new approach integrates observations from exposed and drilled mantle rocks and proposes that the mantle lithosphere evolved and was modified during an extensional cycle from post-orogenic collapse through several periods of rifting to seafloor spreading. The defined chemical and petrological characteristics of mantle domains based on clinopyroxene and spinel compositions are compiled on present-day and paleogeographic maps of Western and Central Europe. These maps show that the observed distribution of mantle domains are linked to processes related to late post-Variscan extension, rift evolution and refertilization associated

  6. Galapagos-OIB signature in southern Central America: Mantle refertilization by arc-hot spot interaction

    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.

  7. Orthopyroxene refertilization in subduction environment.

    Melchiorre, Massimiliano; Dantas, Celine; Faccini, Barbara; Bonadiman, Costanza; Coltorti, Massimo; Gregoire, Michel


    One of the most fascinating and controversial debate in Earth Science concerns the chemical and mineralogical modifications affecting the mantle during melts/fluids percolation. Particularly in subduction settings it is important to well constrain the role and extent of silica enrichment related to subducted slab dehydratation or melting. This topic is addressed in the present study where a new suite of mantle xenoliths from Estancia Sol de Mayo (ESM, Patagonia) are investigated and compared with other xenolith occurrences nearby. ESM peridotites are mainly represented by spinel-bearing protogranular harzburgites and dunites, with minor lherzolites and one wehrlite. They are avoid of modal metasomatic features, such as spongy cpx, reaction rims around spinel and/or orthopyroxene, glassy patches, as well as of any hydrous minerals. The most interesting petrographic features is one dunitic sample cut by a vein of orthopyroxene (secondary orthopyroxenes, opx2). These are texturally and chemically different from those belonging to the typical protogranular peridotites (primary opx, opx1). Opx1 have mg# (MgO/MgO+FeO, at%) between 88.02 and 92.76 and Al2O3 content varying between 1.37 and 2.97 wt% while opx2 in the vein presents a more restricted range of mg# values at about 90 (89.99-90.88) with a significantly higher Al2O3 content (3.02-3.52 wt%). Similar opx veins were also found in two other Patagonian localities, Cerro Fraile (CF) and Gobernador Gregores (GG), together with orthopyroxenites and wehrlites. A comparison between the two generation of opxs from these localities show two clearly separated Al2O3 enrichment trends, which cannot be explained by a simple partial melting process: one at almost constant mg# with Al2O3 values varying from 1.33 and 4.20 wt% and the other reaching 5.03%wt of Al2O3 but with mg# varying from 86.89 to 67.37 (including the pyroxenites). Textural and chemical features suggest that the latter trend may be accounted for a

  8. Timing of Precambrian melt depletion and Phanerozoic refertilization events in the lithospheric mantle of the Wyoming Craton and adjacent Central Plains Orogen

    Carlson, R.W.; Irving, A.J.; Schulze, D.J.; Hearn, B.C.


    Garnet peridotite xenoliths from the Sloan kimberlite (Colorado) are variably depleted in their major magmaphile (Ca, Al) element compositions with whole rock Re-depletion model ages generally consistent with this depletion occurring in the mid-Proterozoic. Unlike many lithospheric peridotites, the Sloan samples are also depleted in incompatible trace elements, as shown by the composition of separated garnet and clinopyroxene. Most of the Sloan peridotites have intermineral Sm-Nd and Lu-Hf isotope systematics consistent with this depletion occurring in the mid-Proterozoic, though the precise age of this event is poorly defined. Thus, when sampled by the Devonian Sloan kimberlite, the compositional characteristics of the lithospheric mantle in this area primarily reflected the initial melt extraction event that presumably is associated with crust formation in the Proterozoic-a relatively simple history that may also explain the cold geotherm measured for the Sloan xenoliths. The Williams and Homestead kimberlites erupted through the Wyoming Craton in the Eocene, near the end of the Laramide Orogeny, the major tectonomagmatic event responsible for the formation of the Rocky Mountains in the late Cretaceous-early Tertiary. Rhenium-depletion model ages for the Homestead peridotites are mostly Archean, consistent with their origin in the Archean lithospheric mantle of the Wyoming Craton. Both the Williams and Homestead peridotites, however, clearly show the consequences of metasomatism by incompatible-element-rich melts. Intermineral isotope systematics in both the Homestead and Williams peridotites are highly disturbed with the Sr and Nd isotopic compositions of the minerals being dominated by the metasomatic component. Some Homestead samples preserve an incompatible element depleted signature in their radiogenic Hf isotopic compositions. Sm-Nd tie lines for garnet and clinopyroxene separates from most Homestead samples provide Mesozoic or younger "ages" suggesting

  9. Role of the mantle exhumation channel in the formation of ultramafic seafloor

    Muntener, O.; Lavier, L. L.


    Mantle peridotites from ocean-continent transition zones (OCT's) illustrate the distribution of the scale of upper mantle heterogeneity in extensional systems that evolve from rifting to (ultra-) slow seafloor spreading. We summarize research on mantle processes of the conjugate Iberia-Newfoundland rift and from the Alps that show that the basement of OCT's consists of 3 mantle domains. Thermally undisturbed, cold subcontinental mantle formed the ocean floor next to thinned continental crust. This 'subcontinental domain' is separated by ductile shear zones from an infiltrated (e.g. hot) domain dominated by plagioclase peridotite. The footwall of these mantle shear zones display complex refertilization processes and high-temperature deformation. These rocks are highly heterogeneous and are juxtaposed with depleted lherzolites and dunites (extraction domain). Upwelling of partial melts that enter the conductive lithospheric mantle inevitably leads to freezing of the melt and to the formation of a chemical and rheological barrier, which we term mantle exhumation channel. We will discuss an example that displays km-scale refertilization with active deformation (and melt focusing?) on top, and the formation of a domain that represents focused melt extraction at the bottom. We show that an actively deforming refertilization front in Alpine plagioclase peridotites and in the Iberia Newfoundland rift moved ahead of a melting front. Melt lubricated shear zones (or melt bands) focus melt flow. Continuous uplift leads to crystallization and deformation will prevail in the subsolidus state. Final exposure of infiltrated peridotites on the seafloor is accommodated by faults in which hydrous phases crystallize (chlorite, serpentine, talc). We combine petrologic data and numerical models to illustrate that these processes play a key role in the rejuvenation and erosion of the lithospheric mantle and ultimately form ultramafic seafloor in ocean-continent transitions and ultra

  10. Os-isotopic Compositions of Peridotite Xenoliths from the Oceanic Mantle: Implications for the Age of Isotopic Domains in the Oceanic Mantle.

    Jackson, M. G.; Shirey, S. B.; Hauri, E. H.; Kurz, M. D.


    Os-isotopic compositions of abyssal peridotites and peridotite xenoliths from oceanic hotpots that sample the convecting mantle extend to relatively unradiogenic compositions. However, they do not preserve a record of early-formed (Hadean and Archean) depleted mantle domains, either by earlier cycles of ridge-related depletion, continent extraction, or subcontinental lithospheric mantle erosion. The lack of preservation of early-formed (Hadean and Archean) depleted Os-isotopic compositions is consistent with the lack of preservation of Hadean 142Nd/144Nd variability in the modern convecting mantle, but is in stark contrast to the existence of early-formed (early-Hadean), heterogeneous 129Xe/130Xe isotopic anomalies in the modern mantle. Mukhopadhay (Nature, 2012) suggested that the erasure of 142Nd/144Nd, but not 129Xe/130Xe, anomalies from the convecting mantle may be due to the small magnitude of the 142Nd/144Nd anomalies (10% variability observed) because the smaller 142Nd/144Nd anomalies would have been more easily erased than the larger magnitude 129Xe/130Xe anomalies. This model does not work for the Re-Os system because the magnitude of Os-isotopic heterogeneities in the mantle are large, yet early-formed Os-isotopic signatures have been erased. For example, the 187Os/188Os of early-formed depleted mantle at 4.55 Ga was ~0.095, which is >25% lower than the modern mantle. Given that there were substantial amounts of mantle partial melting throughout the Hadean and Archean, it is hard to understand how some refractory residues retaining some vestige of these low, early-formed Os isotopic compositions have not have been preserved in the modern mantle. Therefore, the lack of preservation of early-formed, large magnitude 187Os/188Os excursions in the modern convecting mantle suggests that the preservation of early geochemical heterogeneities was not necessarily a function of the original geochemical anomaly. We explore alternative solutions to the paradox of

  11. Gondwana subduction-modified mantle domain prevents magmatic seafloor generation in the Central Indian Ridge

    Morishita, T.; Nakamura, K.; Senda, R.; Suzuki, K.; Kumagai, H.; Sato, H.; Sato, T.; Shibuya, T.; Minoguchi, K.; Okino, K.


    The creation of oceanic crust at mid-ocean ridges is essential to understanding the genesis of oceanic plate and the evolution of the Earth. Detailed bathymetric measurements coupled with dense sample recovery at mid-ocean ridge revealed a wide range of variations in the ridge and seafloor morphologies, which cannot be simply explained by a spreading rate, but also by ridge geometry, mantle compositions and thermal structure (Dick et al., 2003 Nature; Cannat et al. 2006 Geology). It is now widely accepted that very limited magmatic activity with tectonic stretching generates oceanic core complex and/or smooth seafloor surface in the slow to ultraslow-spreading ridges, where serpentinized peridotite and gabbros are expected to be exposed associated with detachment faults (Cann et al., 1997 Nature; Cannat et al., 2006), although magmatism might be an essential role for the formation of oceanic core complexes (Buck et al., 2005 Nature; Tucholke et al 2008 JGR). A rising question is why magmatic activity is sometimes prevented during the oceanic plate formation. Ancient melting domain, that are too refractory to melt even in adiabatically upwelling to the shallow upper mantle, might cause the amagmatic spreading ridges (Harvey et al., 2006 EPSL, Liu et al.,2008 Nature). Its origin and effect on seafloor generations are, however, not well understood yet. We report an oceanic hill as an example of an ancient subduction-modified mantle domain, probably formed at continental margin of the Gondwanaland~Pangea supercontinent, existing beneath the Central Indian Ridge. This domain is the most likely to have prevented magmatic seafloor generation, resulting in creation of very deep oceanic valley and serpentine diaper (now the studied oceanic hill) at the present Central Indian ridge.

  12. How inheritance, geochemical and geophysical properties of the lithospheric mantle influence rift development and subsequent collision

    Picazo, Suzanne; Chenin, Pauline; Müntener, Othmar; Manatschal, Gianreto; Karner, Garry; Johnson, Christopher


    In magma-poor rifted margins, the rift structures, width of necking zones and overall geometry are controlled by the heterogeneities of geochemical and geophysical properties of the crust and mantle. In this presentation we focus on the mantle heterogeneities and their major implications on the closure of a hyper-extended rifted system. In our study, we review the clinopyroxene and spinel major element composition from the Liguria-Piemonte domain, the Pyrenean domain, the Dinarides and Hellenides ophiolites and the Iberia-Newfoundland rifted margins (Picazo et al, 2016). It would seem that during an extensional cycle i.e., from post-orogenic collapse to polyphase rifting to seafloor spreading, the mineral compositions of mantle peridotites are systematically modified. The initially heterogeneous subcontinental mantle cpx (inherited mantle type 1) equilibrated in the spinel peridotite field and is too enriched in Na2O and Al2O3 to be a residue of syn-rift melting. The heterogeneous inherited subcontinental mantle becomes progressively homogenized due to impregnation by MORB-type melts (refertilized mantle-type 2) during extensional thinning of the lithosphere. At this stage, cpx equilibrate with plagioclase and display lower Na2O and Al2O3 and high Cr2O3 contents. The system might evolve into breakup and oceanization (mantle type 3) i.e., self-sustained steady-state seafloor spreading. The different mantle-types are present in various reconstructed sections of magma-poor margins and display a systematic spatial distribution from mantle type 1 to 3 going oceanwards in Western and Central Europe. We estimated the density of the three identified mantle types using idealized modal peridotite compositions using the algorithm by Hacker et al, (2003). The density of the refertilized plagioclase peridotite is predicted to be lower than that of inherited subcontinental and depleted oceanic mantle. This has some interesting consequences on the reactivation of rifted margins

  13. Recycling of ancient subduction-modified mantle domains in the Purang ophiolite (southwestern Tibet)

    Gong, Xiao-Han; Shi, Ren-Deng; Griffin, W. L.; Huang, Qi-Shuai; Xiong, Qing; Chen, Sheng-Sheng; Zhang, Ming; O'Reilly, Suzanne Y.


    Ophiolites in the Indus-Yarlung Zangbo (IYZ) suture (southern Tibet) have been interpreted as remnants of the Neo-Tethyan lithosphere. However, the discovery of diamonds and super-reducing, ultra-high pressure (SuR-UHP) mineral assemblages (e.g., coesite after stishovite, olivine after wadsleyite, native metals, alloys, and moissanite) in some of these massifs and associated chromitites requires a re-evaluation of their origin and evolution. A new petrological and geochemical study of the Purang ophiolite in the western IYZ suture sheds new lights on these issues. The depleted harzburgites of the Purang massif have low modal contents of clinopyroxene ( 40 ~ 70) and pyroxenes (> 16 in orthopyroxene, and > 20 in clinopyroxene), suggesting high degrees of melt extraction (> 20%). These features are not consistent with formation in a (ultra-) slow-spreading mid-ocean ridge. These peridotites have high modal contents of orthopyroxene; this, and the extremely high Cr# of spinels in these peridotites, suggests modification in a subduction zone. The clinopyroxene-rich harzburgites and lherzolites contain rare spinel-pyroxene symplectites after garnet. Their clinopyroxenes have low MREE-to-HREE ratios ((Sm/Yb)N recycling model for the presence of SuR-UHP phases in the IYZ ophiolites. The infiltration of MORB melts through these ancient depleted peridotites during their final exhumation in a (ultra-) slow-spreading center may have refertilized them to produce the clinopyroxene-rich peridotites.

  14. Polyphase tectono-magmatic and fluid history related to mantle exhumation in an ultra-distal rift domain: example of the fossil Platta domain, SE Switzerland

    Epin, Marie-Eva; Manatschal, Gianreto; Amann, Méderic; Lescanne, Marc


    Despite the fact that many studies have investigated mantle exhumation at magma-poor rifted margins, there are still numerous questions concerning the 3D architecture, magmatic, fluid and thermal evolution of these ultra-distal domains that remain unexplained. Indeed, it has been observed in seismic data from ultra-distal magma-poor rifted margins that top basement is heavily structured and complex, however, the processes controlling the morpho-tectonic and magmatic evolution of these domains remain unknown. The aim of this study is to describe the 3D top basement morphology of an exhumed mantle domain, exposed over 200 km2 in the fossil Platta domain in SE Switzerland, and to define the timing and processes controlling its evolution. The examined Platta nappe corresponds to a remnant of the former ultra-distal Adriatic margin of the Alpine Tethys. The rift-structures are relatively well preserved due to the weak Alpine tectonic and metamorphic overprint during the emplacement in the Alpine nappe stack. Detailed mapping of parts of the Platta nappe enabled us to document the top basement architecture of an exhumed mantle domain and to investigate its link to later, rift/oceanic structures, magmatic additions and fluids. Our observations show a polyphase and/or complex: 1) deformation history associated with mantle exhumation along low-angle exhumation faults overprinted by later high-angle normal faults, 2) top basement morphology capped by magmato-sedimentary rocks, 3) tectono-magmatic evolution that includes gabbros, emplaced at deeper levels and subsequently exhumed and overlain by younger extrusive magmatic additions, and 4) fluid history including serpentinization, calcification, hydrothermal vent, rodingitization and spilitization affecting exhumed mantle and associated magmatic rocks. The overall observations provide important information on the temporal and spatial evolution of the tectonic, magmatic and fluid systems controlling the formation of ultra

  15. Petrological features of suprasubuction mantle: evidence from northern, central and southern Patagonian mantle xenoliths

    Melchiorre, M.; Coltorti, M.; Gregoire, M.; Benoit, M.


    Patagonia has a number of outcrops where xenoliths-bearing lavas can be found. It thus represents a good opportunity to study mantle material in supra-subduction environment both on arc and back-arc position, from as near as 300 km to as far as 600 km from the Chile trench. A wealth of data is nowadays available on these xenoliths, starting from petrographic observations, whole-rock and mineral major and trace element analyses plus few isotopic analyses on whole rock and mineral separates. To this already large dataset the petrological features of another locality (Estancia Sol de Mayo, ESM) were added, allowing a comparison between as much as eight localities coming from northern (Cerro Aznare, Praguaniyeu, Cerro Rio Chubut, Cerro de los Chenques), central (Cerro Clark and Gobernador Gregores) and southern Patagonia (Pali Aike), covering approximately an area of 1000 x 300 km. Most xenoliths are harzburgites, with minor amount of lherzolites, wehrlites and dunites. In the Al2O3 vs mg# [MgO/(MgO+FeO) mol %] diagram clinopyroxene (cpx) compositions highlight three different trends, with orthopyroxene (opx) compositions plotting on two of these. In the first trend Al2O3 content increases at almost constant mg# mol % (trend 1). The second trend comprises only cpx from wehrlites (trend 2) and is situated between the first and the third trend. In the third trend the slight increases of Al2O3 is associated with a remarkable decrease in mg# (trend 3). LREE and LILE abundances in cpx from Tres Lagos and Cerro Rio Chubut are directly correlated to the Al2O3, while they are inversely correlated at Cerro de Los Chenques and Cerro Fraile. In the first case it is likely that a metasomatic process affects the mantle domains beneath those areas, while in the second case a refertilization event caused by a tholeiitic melt is favorite. In other cases, as for Gobernador Gregores, a more complex situation is recorded, with two groups of samples showing both negative and positive

  16. Lithosphere and Asthenosphere Properties beneath Oceans and Continents and their Relationship with Domains of Partial Melt Stability in the Mantle

    Dasgupta, R.


    The depth of the lithosphere-asthenosphere boundary (LAB) and the change in properties across the lithosphere, asthenosphere, and LAB in various tectonic settings are captured in a variety of geophysical data, including seismic velocities and electrical conductivity. A sharp drop in shear wave velocity and increase in electrical conductivity can potentially be caused by the appearance of partial melt at or below the LAB but the chemical and dynamic stability of partial melt across lithosphere and at LAB remain debated. Here I apply the recent models of mantle melting in the presence of water and carbon [1, 2] to evaluate the domains of stability of partial melt both beneath continents and oceans. The model allows prediction of the possible presence, the fraction, and composition of partial melt as a function of depth, bulk C and H2O content, and fO2 [3] in various geologic/tectonic settings. The results show that while a hydrous, carbonated melt is stable only beneath LAB and in the asthenospheric mantle beneath oceans, continental mantle can contain a carbonate-rich melt within the lithosphere. For geotherms corresponding to surface heat flux (SHF) of 40-50 mW m-2, which also match P-T estimates beneath cratons based on thermo-barometry of peridotite xenoliths [4], the solidus of fertile peridotite with trace amount of CO2 and H2O is crossed at depths as shallow as 80-120 km [5]. If elevated geotherms of the Proterozoic and Phanerozoic terrains are applied, carbonatitic melt becomes stable somewhat shallower. These depths are similar to those argued for a mid-lithospheric discontinuity (MLD) where a negative velocity gradient has been detected much shallower than the proposed depth of LAB in many places. With a drop in oxygen fugacity with depth, a freezing of carbonatitic melt may be expected at intermediate depths (~150-200 km). At 200-250 km a hydrous, carbonated silicate melt may reappear owing to the interplay of fO2 and freezing point depression effect of CO

  17. Decreasing µ142Nd Variation in the Archean Convecting Mantle from 4.0 to 2.5 Ga: Heterogeneous Domain Mixing or Crustal Recycling?

    Brandon, A. D.; Debaille, V.


    The 146Sm-142Nd (t1/2=68 Ma) chronometer can be used to examine silicate differentiation in the first 400 Ma of Earth history. Early fractionation between Sm and Nd is recorded in cratonic Archean rocks in their 142Nd/144Nd ratios that that deviate up to ±20 ppm, or μ142Nd - ppm deviation relative to the present-day convecting mantle at 0. These values likely record early extraction of incompatible trace element (ITE) enriched material with -μ142Nd, either as crust or late stage residual melt from a magma ocean, and resulting in a complimentary ITE depleted residual mantle with +μ142Nd. If this early-formed ITE-enriched material was re-incorporated rapidly back into the convecting mantle, both ITE-enriched and ITE-depleted mantle domains would have been established in the Hadean. Alternatively, if it was early-formed crust that remained stable it could have slowly eroded and progressively remixed into the convecting mantle as subducted sediment during the Archean. Each of these scenarios could potentially explain the decrease in the maximum variation in µ142Nd from ±20 at 4.0 Ga to 0 at 2.5 Ga [1,2,3]. In the scenario where these variations reflect mixing of mantle domains, this implies long mantle mixing times of greater than 1 Ga in the Archean in order to preserve the early-formed heterogeneities. This can be achieved in a stagnant lid tectonic regime in the Archean with sporadic and short subduction cycles [2]. This scenario would also indicate that mixing times in the convecting mantle were much slower than the previously proposed 100 Ma in the Hadean and Archean. In the alternative scenario, sediment with -µ142Nd was progressively mixed into the mantle via subduction in the Archean [3]. This scenario doesn't require slow mantle mixing times or a stagnant-lid regime. It requires crustal resident times of up to 750 Ma to maintain a steady supply of ancient sediment recycling over the Archean. Each of these scenarios evoke very contrasting conditions for

  18. Ultra-refractory mantle domains in the Luqu ophiolite (Tibet): Petrology and tectonic setting

    Zhang, Chang; Liu, Chuan-Zhou; Wu, Fu-Yuan; Ji, Wen-Bin; Liu, Tong; Xu, Yang


    Fresh mantle peridotites occur in the Luqu ophiolite, which is located at the central segment of the Yarlung-Tsangpo Suture Zone in the Tibetan Plateau. This study presents major and trace element compositions of clinopyroxene from harzburgites and dunites of the Luqu ophiolite, with the aim to study melt depletion and late-stage melt-rock interaction processes. The studied harzburgites have refractory to ultra-refractory compositions, as indicated by low whole-rock Al2O3 and high MgO contents, as well as high spinel Cr# values. Clinopyroxenes in the Luqu harzburgites are variably depleted in light rare earth elements (LREEs) relative to the middle and heavy rare earth elements (MREEs and HREEs), with Yb contents of 1.4-3.4 times of CI chondrites. Modeling results suggest that the Luqu harzburgites have experienced up to 8% garnet-facies melting followed by 10-18% fractional melting in the stability field of spinel. In both cases melting occurred under anhydrous conditions. This suggests that the Luqu ophiolite originated from a mid-ocean ridge setting rather than a supra-subduction zone environment. Nevertheless, the high degrees of partial melting are inconsistent with the thin oceanic crustal sequence preserved in the Luqu ophiolite, implying that the Luqu peridotites might have experienced melt extraction prior to entering into the spreading centers of the Neo-Tethyan Ocean during the Early Cretaceous. Clinopyroxenes in the dunites are interstitial among olivine grains. They display slightly LREE-enriched patterns and have higher REE contents than those in the harzburgites. They also show markedly positive anomalies in Sr, Zr and Hf. These features suggest that the dunites were generated through reaction between percolating melts and the harzburgites, during which the interstitial clinopyroxenes formed.

  19. Nature and Evolution of the lithospheric mantle beneath the Hoggar swell (Algeria): a record from mantle xenoliths.

    Kourim, Fatna; Bodinier, Jean-Louis; Alard, Olivier; Bendaoud, Abderrahmane; Vauchez, Alain; Dautria, Jean-Marie


    The mantle xenoliths sampled by the Quaternary alkaline volcanics from the Tahalgha district (Central Hoggar) represent the subcontinental lithospheric mantle beneath the boundary between two major structural domains of the Tuareg Shield: the "Polycyclic Central Hoggar" to the East and the "Western Hoggar", or "Pharusian Belt", to the West. Samples were collected from volcanic centres located on both sides of the 4°10, a major lithospheric shear zone separating these two domains. Although showing substantial variations in their deformation microstructures, equilibrium temperatures, and modal and chemical compositions, the studied samples do not display systematic variations of these features across the 4°10. The observed variations rather record small-scale heterogeneities distributed throughout the whole studied area and mostly related to the asthenosphere-lithosphere interaction events associated with the evolution of the Hoggar swell, in the Cenozoic. These features include partial annealing of pre-existing deformation microstructures, post-deformation metasomatic reactions, and trace-element enrichment, coupled with heating from 750-900°C (low-temperature lherzolites) to 900-1150°C (intermediate-T lherzolites and high-T harzburgites and wehrlites). Trace element modelling confirms that the whole range of REE fractionation observed in the Tahalgha xenoliths may be accounted for by reactive porous flow involving a single stage of basaltic melt infiltration into a LREE-depleted protolith. The striking correlations between equilibrium temperatures and trace-element enrichments favor a scenario whereby the high-temperature peridotites record advective heat transport along melt conduits while the intermediate- and low-temperature lherzolites would represent more conductive heating of the host Mechanical Boundary Layer. This indicates that the lithosphere did not reach thermal equilibrium, suggesting that the inferred heating event was transient and rapidly erased

  20. Geodynamic investigation of the processes that control Lu-Hf isotopic differences between different mantle domains and the crust

    Jones, Rosie; van Keken, Peter; Hauri, Erik; Vervoort, Jeff; Ballentine, Chris J.


    The chemical and isotopic composition of both the Earth's mantle and the continental crust are greatly influenced by subduction zone processes, such as the formation of continental crust through arc volcanism and the recycling of surface material into the deep mantle. Here we use a combined geodynamical-geochemical approach to investigate the long term role of subduction on the Lu-Hf isotopic evolution of the mantle and the continental crust. We apply the geodynamic model developed by Brandenburg et al., 2008. This model satisfies the geophysical constraints of oceanic heat flow and average plate velocities, as well as geochemical observations such as 40Ar in the atmosphere, and reproduces the geochemical distributions observed in multiple isotope systems which define the HIMU, MORB and EM1 mantle endmembers. We extend this application to investigate the detail of terrestrial Lu-Hf isotope distribution and evolution, and specifically to investigate the role of sediment recycling in the generation of EM2 mantle compositions. The model has been updated to produce higher resolution results and to include a self-consistent reorganisation of the plates with regions of up-/down-wellings. The model assumes that subduction is initiated at 4.5 Ga and that a transition from 'dry' to 'wet' subduction occurred at 2.5 Ga. The modelling suggests that the epsilon Hf evolution of the upper mantle can be generated through the extraction and recycling of the oceanic crust, and that the formation of continental crust plays a lesser role. Our future intention is to utilise the model presented here to investigate the differences observed in the noble gas compositions (e.g., 40Ar/36Ar, 3He/4He) of MORB and OIB. Brandenburg, J.P., Hauri, E.H., van Keken, P.E., Ballentine, C.J., 2008. Earth and Planetary Science Letters 276, 1-13.

  1. Westward migration of oceanic ridges and related asymmetric upper mantle differentiation

    Chalot-Prat, Françoise; Doglioni, Carlo; Falloon, Trevor


    Combining geophysical, petrological and structural data on oceanic mantle lithosphere, underlying asthenosphere and oceanic basalts, an alternative oceanic plate spreading model is proposed in the framework of the westward migration of oceanic spreading ridges relative to the underlying asthenosphere. This model suggests that evolution of both the composition and internal structure of oceanic plates and underlying upper mantle strongly depends at all scales on plate kinematics. We show that the asymmetric features of lithospheric plates and underlying upper asthenosphere on both sides of oceanic spreading ridges, as shown by geophysical data (seismic velocities, density, thickness, and plate geometry), reflect somewhat different mantle compositions, themselves related to various mantle differentiation processes (incipient to high partial melting degree, percolation/reaction and refertilization) at different depths (down to 300 km) below and laterally to the ridge axis. The fundamental difference between western and eastern plates is linked to the westward ridge migration inducing continuing mantle refertilization of the western plate by percolation-reaction with ascending melts, whereas the eastern plate preserves a barely refertilized harzburgitic residue. Plate thickness on both sides of the ridge is controlled both by cooling of the asthenospheric residue and by the instability of pargasitic amphibole producing a sharp depression in the mantle solidus as it changes from vapour-undersaturated to vapour-saturated conditions, its intersection with the geotherm at 90 km, and incipient melt production right underneath the lithosphere-asthenosphere boundary (LAB). Thus the intersection of the geotherm with the vapour-saturated lherzolite solidus explains the existence of a low-velocity zone (LVZ). As oceanic lithosphere is moving westward relative to asthenospheric mantle, this partially molten upper asthenosphere facilitates the decoupling between lower asthenosphere

  2. Abundances of Ag and Cu in mantle peridotites and the implications for the behavior of chalcophile elements in the mantle

    Wang, Zaicong; Becker, Harry


    Silver abundances in mantle peridotites and the behavior of Ag during high temperature mantle processes have received little attention and, as a consequence, the abundance of Ag in the bulk silicate Earth (BSE) has been poorly constrained. In order to better understand the processes that fractionate Ag and other chalcophile elements in the mantle, abundances of Ag and Cu in mantle peridotites from different geological settings (n = 68) have been obtained by isotope dilution ICP-MS methods. In peridotite tectonites and in a few suites of peridotite xenoliths which display evidence for variable extents of melt depletion and refertilization by silicate melts, Ag and Cu abundances show positive correlations with moderately incompatible elements such as S, Se, Te and Au. The mean Cu/Ag in fertile peridotites (3500 ± 1200, 1s, n = 38) is indistinguishable from the mean Cu/Ag of mid ocean ridge basalts (MORB, 3600 ± 400, 1s, n = 338) and MORB sulfide droplets. The constant mean Cu/Ag ratios indicate similar behavior of Ag and Cu during partial melting of the mantle, refertilization and magmatic fractionation, and thus should be representative of the Earth's upper mantle. The systematic fractionation of Cu, Ag, Au, S, Se and Te in peridotites and basalts is consistent with sulfide melt-silicate melt partitioning with apparent partition coefficients of platinum group elements (PGE) > Au ⩾ Te > Cu ≈ Ag > Se ⩾ S. Because of the effects of secondary processes, the abundances of chalcophile elements, notably S, Se, but also Cu and the PGE in many peridotite xenoliths are variable and lower than in peridotite massifs. Refertilization of peridotite may change abundances of chalcophile and lithophile elements in peridotite massifs, however, this seems to mostly occur in a systematic way. Correlations with lithophile and chalcophile elements and the overlapping mean Cu/Ag ratios of peridotites and ocean ridge basalts are used to constrain abundances of Ag and Cu in the BSE

  3. Evolution of the lithosphere-asthenosphere system in the Carpathian-Pannonian region following the Miocene extension: as viewed in petrology, geochemistry, deformation pattern of mantle xenoliths and geophysical observations

    Kovács, István; Falus, György; Szabó, Csaba; Pintér, Zsanett; Hegedűs, Endre; Mihály, Judith; Németh, Csaba; Liptai, Nóra; Patkó, Levente; Tommasi, Andrea; Barou, Fabrice; Zajacz, Zoltán; Tribus, Martina; Konzett, Jürgen; Stalder, Roland


    Detailed geochemical and deformation analysis of numerous of mantle xenoliths from the Carpathian-Pannonian region revealed that the present lithosphere, which suffered significant thinning in the Miocene, may be divided into two major layers based on the equilibrium temperatures as indicators for the depth of origin. The shallower layer, from the MOHO to ~40 km depth, is characterized mostly by fine grained, equigranular to porphyroclastic xenoliths, generally displays an 'axial [010]' deformation pattern typical for transpressional deformation regime. Mineral constituents from this shallower layer show high Mg#, low H2O content in nominally anhydrous minerals (NAMs) and depleted in basaltic major elements implying that this layer may have undergone considerable depletion. Trace element patterns, however, show enrichment most probably due to subsequent metasomatic enrichment episodes. The deeper layer is below ~40 km and above the present lithosphere-asthenosphere boundary. The xenoliths show mainly coarse grained, protogranular texture with 'A-type' deformation pattern typical for asthenospheric flow. Minerals usually have lower Mg# and richer in basaltic major elements. The NAMs from this layer show higher H2O content than those in the shallow layer. Trace element patterns, on the other hand, do not refer to later refertilization episodes by showing dominantly depleted pattern. There is also a special group of tabular equigranular xenoliths, which may represent a domain separating these shallower and deeper layers of the present day lithosphere. This group shows geochemical and deformation properties resembling more the shallower layer, however, the H2O content of NAMs is the highest among all studied samples. Xenoliths, nevertheless, displaying transitional character among these major groups also occur indicating the complex history of the upper mantle. We suggest that the deeper, more H2O rich and less-depleted layer of the present day lithosphere is a

  4. Peridotite xenoliths from Ethiopia: inferences on mantle processes from Plume to Rift settings

    Beccaluva, Luigi; Bianchini, Gianluca; Ellam, Robert Mark; Natali, Claudio; Santato, Alessandro; Siena, Franca; Stuart, Finlay


    A comprehensive petrological study has been carried out on Ethiopian mantle xenoliths entrained in Neogene-Quaternary alkaline lavas both overlying the Continental Flood Basalt area (Dedessa River - Wollega Region, Injibara - Gojam Region) and from southern Main Ethiopian Rift (MER - Mega, Sidamo Region) in order to investigate the mantle evolution from plume to rift settings. Mantle xenoliths from the plateau area (Injibara, Dedessa River) range in composition from spinel lherzolite to harzburgite and olivine websterite, showing P-T equilibration conditions in the range of 1-2 GPa/950-1050 °C. These xenoliths show flat chondrite-normalized bulk-rock REE patterns, with only few LREE-enriched samples (LaN/YbN up to 5). Clinopyroxene (cpx) REE patterns are generally flat or LREE depleted (LaN/YbN down to 0.6). Sr-Nd isotopes on separated cpx mainly show compositions (87Sr/86Sr 0.5132) approaching the Depleted Mantle end-member, or displaced (87Sr/86Sr 0.7033-0.7034; 143Nd/144Nd 0.5129-0.5128) toward the Enriched Mantle components which also characterize the Ethiopian Oligocene plateau basalts. These characteristics indicate that most xenoliths reflect complex asthenosphere/lithosphere interactions due to plume-related refertilization processes, whose agents may be envisaged as mafic subalkaline melts that infiltrated and reacted with the pristine parageneses ultimately leading to the formation of olivine-websterite domains. On the other hand, mantle xenoliths from southern MER (Mega) consist of spinel lherzolite to harzburgites showing various degree of deformation and recrystallization coupled with an extremely wide incompatible element distribution. Bulk rock Rare Earth Element (REE) patterns show generally flat HREE ranging from 0.1 x chondrite (ch) in harzburgites up to 2 x ch in fertile lherzolites, and are variably enriched in LREE, with LaN/YbN up to 41.5. The constituent clinopyroxenes have flat HREE distribution and LaN/YbN between 0.1 and 55, in general

  5. Domains and enrichment mechanism of the lithospheric mantle in western Yunnan: A comparative study on two types of Cenozoic ultrapotassic rocks

    XIA; Ping; XU; Yigang


    Geochemical comparison of two suites of Cenozoic potassic volcanic rocks in western Yunnan reveals the existence of two mantle domains beneath this region, which correspond to their respective tectonic affinity. The Erhai ultrapotassic rocks (42-24Ma) in western Yangtze Craton are characterized by LILE enrichment, HFSE depletion, low TiO2 content (<1%),high initial 87Sr/86Sr (0.7064-0.7094) and negative εNd (-3.84--4.64). Geochemically similar to K-rich volcanism in subduction setting, they were probably originated from a refractory spinel harzburgitic source metasomatized by subduction-related fluids. In contrast, the Maguan potassic magmas (<16Ma) in the South China Block show an OIB-type trace elemental signature, high TiO2 content (>2%), low initial 87Sr/86Sr (0.7041-0.7060) and positive εNd (5.46-7.03). These features resemble the typical intraplate potassic rocks around the world. These rocks are thus interpreted as melting products of a fertile garnet Iherzolitic source which has been infiltrated by small-volume, asthenosphere-derived silicate melts. The temporal and spatial distribution of these two types of K-rich rocks cannot be explained by any unified tectonic model. It is proposed that the Oligocene magmatism in the Erhai area may have resulted from convective thinning of the thickened lithosphere, whereas the post-Miocene volcanism in the Maguan area was related to the opening of South China Sea.

  6. Peridotite xenoliths from the Polynesian Austral and Samoa hotspots: Implications for the destruction of ancient 187Os and 142Nd isotopic domains and the preservation of Hadean 129Xe in the modern convecting mantle

    Jackson, M. G.; Shirey, S. B.; Hauri, E. H.; Kurz, M. D.; Rizo, H.


    The Re-Os systematics in 13 peridotite xenoliths hosted in young (<0.39 myr) rejuvenated lavas from the Samoan island of Savai'i and 8 peridotite xenoliths from 6 to 10 myr old lavas from the Austral island of Tubuai have been examined to evaluate the history of the oceanic mantle in this region. Modal mineralogy, trace element compositions and 187Os/188Os ratios suggest that these peridotites are not cognate or residual to mantle plumes but rather samples of Pacific oceanic lithosphere created at the ridge. Savai'i and Tubuai islands lie along a flow line in the Pacific plate, and provide two snapshots (separated by over 40 Ma in time) of Pacific mantle that originated in the same region of the East Pacific rise. Tubuai xenoliths exhibit 187Os/188Os from 0.1163 to 0.1304, and Savai'i (Samoa) xenoliths span a smaller range from 0.1173 to 0.1284. The 187Os/188Os ratios measured in Tubuai xenoliths are lower than (and show no overlap with) basalts from Tubuai. The 187Os/188Os of the Savai'i xenoliths overlap the isotopic compositions of lavas from the island of Savai'i, but also extend to lower 187Os/188Os than the lavas. 3He/4He measurements of a subset of the xenoliths range from 2.5 to 6.4 Ra for Tubuai and 10.8 to 12.4 Ra for Savai'i. Like abyssal peridotites and xenoliths from oceanic hotspots that sample the convecting mantle, Os isotopes from the Savai'i and Tubuai xenolith suites are relatively unradiogenic, but do not preserve a record of depleted early-formed (Hadean and Archean) mantle domains expected from earlier cycles of ridge-related depletion, continent extraction, or subcontinental lithospheric mantle erosion. The lack of preservation of early-formed, geochemically-depleted Os-isotopic and 142Nd/144Nd domains in the modern convecting mantle contrasts with the preservation of early-formed (early-Hadean) 129Xe/130Xe isotopic heterogeneities in the convecting mantle. This can be explained if the initial isotopic signatures in Re-Os and Sm-Nd systems

  7. Geochemical heterogeneity in the Arctic mantle at Gakkel Ridge

    D'Errico, M. E.; Warren, J. M.; Godard, M.


    Conductive cooling due to ultraslow spreading has been suggested to limit partial melting of the mantle and crustal production at Gakkel Ridge. In addition, the thick lithosphere induced by cooling should significantly control melt migration and extraction. To explore these effects at ultraslow spreading rates, major and trace element concentrations in pyroxene minerals are presented for 14 dredged Gakkel abyssal peridotites. Samples from the same dredge and among dredges reveal wide compositional variation. Trace element compositions of lherzolites reflect 4-6% non-modal fractional mantle melting. However, these high degrees of melting without a corresponding amount of oceanic crust suggest the occurrence of infertile mantle due to ancient melting event(s). In addition, high degrees of melt depletion at short length-scales (earth elements that can be fit by 6 to ≥13% non-modal melting, but this results in modeled light rare earth element contents that are too low relative to observed concentrations. Instead, harzburgite trace element patterns require open-system melting involving interaction with a percolating melt. Extreme enrichments in highly incompatible elements also suggest the occurrence of late-stage refertilization and melt entrapment. Modeling of several different source melt compositions indicates that the trapped melt was generated from garnet field-equilibrated peridotite. Overall, the compositional variability in Gakkel peridotite samples reflects a heterogeneous mantle resulting from inherited depletion and recent melt percolation and entrapment.

  8. Interaction between protokimberlite melts and mantle lithosphere: Evidence from mantle xenoliths from the Dalnyaya kimberlite pipe, Yakutia (Russia

    I.V. Ashchepkov


    Full Text Available The Dalnyaya kimberlite pipe (Yakutia, Russia contains mantle peridotite xenoliths (mostly lherzolites and harzburgites that show both sheared porphyroclastic (deformed and coarse granular textures, together with ilmenite and clinopyroxene megacrysts. Deformed peridotites contain high-temperature Fe-rich clinopyroxenes, sometimes associated with picroilmenites, which are products of interaction of the lithospheric mantle with protokimberlite related melts. The orthopyroxene-derived geotherm for the lithospheric mantle beneath Dalnyaya is stepped similar to that beneath the Udachnaya pipe. Coarse granular xenoliths fall on a geotherm of 35 mWm−2 whereas deformed varieties yield a 45 mWm−2 geotherm in the 2–7.5 GPa pressure interval. The chemistry of the constituent minerals including garnet, olivine and clinopyroxene shows trends of increasing Fe# (=Fe/(Fe + Mg with decreasing pressure. This may suggest that the interaction with fractionating protokimberlite melts occurred at different levels. Two major mantle lithologies are distinguished by the trace element patterns of their constituent minerals, determined by LA-ICP-MS. Orthopyroxenes, some clinopyroxenes and rare garnets are depleted in Ba, Sr, HFSE and MREE and represent relic lithospheric mantle. Re-fertilized garnet and clinopyroxene are more enriched. The distribution of trace elements between garnet and clinopyroxene shows that the garnets dissolved primary orthopyroxene and clinopyroxene. Later high temperature clinopyroxenes related to the protokimberlite melts partially dissolved these garnets. Olivines show decreases in Ni and increases in Al, Ca and Ti from Mg-rich varieties to the more Fe-rich, deformed and refertilized ones. Minerals showing higher Fe# (0.11–0.15 are found within intergrowths of low-Cr ilmenite-clinopyroxene-garnet related to the crystallization of protokimberlite melts in feeder channels. In P-f(O2 diagrams, garnets and Cr-rich clinopyroxenes

  9. Modelling the interplate domain in thermo-mechanical simulations of subduction: Critical effects of resolution and rheology, and consequences on wet mantle melting

    Arcay, Diane


    The present study aims at better deciphering the different mechanisms involved in the functioning of the subduction interplate. A 2D thermo-mechanical model is used to simulate a subduction channel, made of oceanic crust, free to evolve. Convergence at constant rate is imposed under a 100 km thick upper plate. Pseudo-brittle and non-Newtonian behaviours are modelled. The influence of the subduction channel strength, parameterized by the difference in activation energy between crust and mantle (ΔEa) is investigated to examine in detail the variations in depth of the subduction plane down-dip extent, zcoup . First, simulations show that numerical resolution may be responsible for an artificial and significant shallowing of zcoup if the weak crustal layer is not correctly resolved. Second, if the age of the subducting plate is 100 Myr, subduction occurs for any ΔEa . The stiffer the crust is, that is, the lower ΔEa is, the shallower zcoup is (60 km depth if ΔEa = 20 kJ/mol) and the hotter the fore-arc base is. Conversely, imposing a very weak subduction channel (ΔEa > 135 J/mol) leads there to an extreme mantle wedge cooling and inhibits mantle melting in wet conditions. Partial kinematic coupling at the fore-arc base occurs if ΔEa = 145 kJ/mol. If the incoming plate is 20 Myr old, subduction can occur under the conditions that the crust is either stiff and denser than the mantle, or weak and buoyant. In the latter condition, cold crust plumes rise from the subduction channel and ascend through the upper lithosphere, triggering (1) partial kinematic coupling under the fore-arc, (2) fore-arc lithosphere cooling, and (3) partial or complete hindrance of wet mantle melting. zcoup then ranges from 50 to more than 250 km depth and is time-dependent if crust plumes form. Finally, subduction plane dynamics is intimately linked to the regime of subduction-induced corner flow. Two different intervals of ΔEa are underlined: 80-120 kJ/mol to reproduce the range of slab

  10. 186Os-187Os and highly siderophile element abundance systematics of the mantle revealed by abyssal peridotites and Os-rich alloys

    Day, James M. D.; Walker, Richard J.; Warren, Jessica M.


    Abyssal peridotites are oceanic mantle fragments that were recently processed through ridges and represent residues of both modern and ancient melting. To constrain the nature and timing of melt depletion processes, and the composition of the mantle, we report high-precision Os isotope data for abyssal peridotites from three ocean basins, as well as for Os-rich alloys, primarily from Mesozoic ophiolites. These data are complemented by whole-rock highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, Re), trace- and major-element abundances for the abyssal peridotites, which are from the Southwest Indian (SWIR), Central Indian (CIR), Mid-Atlantic (MAR) and Gakkel Ridges. The results reveal a limited role for melt refertilization or secondary alteration processes in modifying abyssal peridotite HSE compositions. The abyssal peridotites examined have experienced variable melt depletion (2% to >16%), which occurred >0.5 Ga ago for some samples. Abyssal peridotites typically exhibit low Pd/Ir and, combined with high-degrees of estimated total melt extraction, imply that they were relatively refractory residues prior to incorporation into their present ridge setting. Recent partial melting processes and mid-ocean ridge basalt (MORB) generation therefore played a limited role in the chemical evolution of their precursor mantle domains. The results confirm that many abyssal peridotites are not simple residues of recent MORB source melting, having a more complex and long-lived depletion history. Peridotites from the Gakkel Ridge, SWIR, CIR and MAR indicate that the depleted MORB mantle has 186Os/188Os of 0.1198356 ± 21 (2SD). The Phanerozoic Os-rich alloys yield an average 186Os/188Os within uncertainty of abyssal peridotites (0.1198361 ± 20). Melt depletion trends defined between Os isotopes and melt extraction indices (e.g., Al2O3) allow an estimate of the primitive mantle (PM) composition, using only abyssal peridotites. This yields 187Os/188Os (0.1292 ± 25), and 186Os

  11. Late Devonian and Triassic basalts from the southern continental margin of the East European Platform, tracers of a single heterogeneous lithospheric mantle source

    Chalot-Prat, Françoise; Tikhomirov, Petr; Saintot, Aline


    In Late Devonian and Early-to-Late Triassic times, the southern continental margin of the Eastern European Platform was the site of a basaltic volcanism in the Donbas and Fore-Caucasus areas respectively. Both volcanic piles rest unconformably upon Paleoproterozoic and Late Paleozoic units respectively, and emplaced during continental rifting periods some 600 km away from expected locations of active oceanic subduction zones. This paper reports a comparative geochemical study of the basaltic rocks, and views them as the best tracers of the involved mantle below the Eastern European Platform. The Late Devonian alkaline basic rocks differ from the calc-alkaline Triassic basic rocks by their higher alkali-silica ratio, their higher TiO2, K2O, P2O5 and FeO contents, their higher trace element contents, a higher degree of fractionation between the most and the least incompatible elements and the absence of Ta-Nb negative anomalies. These general features, clearly distinct from those of partial melting and fractional crystallization, are due to mantle source effects. With similar Nd and Sr isotopic signatures indicating mantle-crust mixing, both suites would originate from the melting of a same but heterogeneous continental mantle lithosphere (refertilized depleted mantle). Accordingly the Nd model ages, the youngest major event associated with mantle metasomatism occurred during Early Neoproterozoic times (˜650Ma).

  12. Late Devonian and Triassic basalts from the southern continental margin of the East European Platform, tracers of a single heterogeneous lithospheric mantle source

    Françoise Chalot-Prat; Petr Tikhomirov; Aline Saintot


    In Late Devonian and Early-to-Late Triassic times, the southern continental margin of the Eastern European Platform was the site of a basaltic volcanism in the Donbas and Fore-Caucasus areas respectively. Both volcanic piles rest unconformably upon Paleoproterozoic and Late Paleozoic units respectively, and emplaced during continental rifting periods some 600 km away from expected locations of active oceanic subduction zones. This paper reports a comparative geochemical study of the basaltic rocks, and views them as the best tracers of the involved mantle below the Eastern European Platform. The Late Devonian alkaline basic rocks differ from the calc-alkaline Triassic basic rocks by their higher alkali-silica ratio, their higher TiO2, K2O, P2O5 and FeO contents, their higher trace element contents, a higher degree of fractionation between the most and the least incompatible elements and the absence of Ta-Nb negative anomalies. These general features, clearly distinct from those of partial melting and fractional crystallization, are due to mantle source effects. With similar Nd and Sr isotopic signatures indicating mantle-crust mixing, both suites would originate from the melting of a same but heterogeneous continental mantle lithosphere (refertilized depleted mantle). Accordingly the Nd model ages, the youngest major event associated with mantle metasomatism occurred during Early Neoproterozoic times (∼650Ma).

  13. The link between Hawaiian mantle plume composition, magmatic flux, and deep mantle geodynamics

    Harrison, Lauren N.; Weis, Dominique; Garcia, Michael O.


    Oceanic island basalts sample mantle reservoirs that are isotopically and compositionally heterogeneous. The Hawaiian-Emperor chain represents ∼85 Myr of volcanism supplied by a deep mantle plume. Two geographically and geochemically delineated trends, Kea and Loa, are well documented within the Hawaiian Islands. Enriched Loa compositions originate from subduction recycled or primordial material stored in deep mantle reservoirs such as the large low shear velocity province (LLSVP) below Hawai'i. Loa compositions have not been observed along the Emperor Seamounts (>50 Ma), whereas lavas on the Hawaiian Islands (chain and the Hawaiian Islands record the geochemical evolution of the Hawaiian mantle plume over a time period when many geophysical parameters (volcanic propagation rate, magmatic flux, mantle potential temperature) increased significantly. Along the NWHR, the Loa geochemical component appears ephemerally, which we link to the sampling of different lower mantle compositional domains by the Hawaiian mantle plume. The plume initially sampled only the deep Pacific mantle (Kea component) from outside the LLSVP during the formation of the Emperor Seamounts. Southward migration and anchoring of the plume on the LLSVP led to entrainment of increasing amounts of LLSVP material (Loa component) along the NWHR as documented by an increase in 208Pb*/206Pb* with decreasing age. The correlation between 208Pb*/206Pb* and magmatic flux suggests source composition affects the magmatic flux, and explains why the Hawaiian mantle plume has dramatically strengthened through time.

  14. Persistence of fertile and hydrous lithospheric mantle beneath the northwestern Ethiopian plateau: Evidence from modal, trace element and Sr-Nd-Hf isotopic compositions of amphibole-bearing mantle xenoliths

    Alemayehu, Melesse; Zhang, Hong-Fu; Aulbach, Sonja


    We present new trace element compositions of amphiboles, Sr-Nd-Hf isotope compositions of clinopyroxenes and mineral modes for spinel peridotite xenoliths that were entrained in a Miocene alkali basalt (Gundeweyn, northwestern Ethiopian plateau), in order to understand the geochemical evolution and variation occurring within the continental lithospheric mantle (CLM) in close proximity to the East African Rift system, and its dynamic implications. With the exception of a single amphibole-bearing sample that is depleted in LREE (La/YbN = 0.45 × Cl), amphiboles in lherzolites and in one harzburgite show variable degrees of LREE enrichment (La/YbN = 2.5-12.1 × Cl) with flat HREE (Dy/YbN = 1.5-2.1 × Cl). Lherzolitic clinoyroxenes have 87Sr/86Sr (0.70227 to 0.70357), 143Nd/144Nd (0.51285 to 0.51346), and 176Hf/177Hf (0.28297 to 0.28360) ranging between depleted lithosphere and enriched mantle. LREE-enriched clinopyroxenes generally have more enriched isotope compositions than depleted ones. While lherzolites with isotope compositions similar to those of the Afar plume result from the most recent metasomatic overprint, isotope compositions more depleted than present-day MORB can be explained by an older melt extraction and/or isotopic rehomogenisation event, possibly related to the Pan-African orogeny. Several generations of amphibole are recognized in accord with this multi-stage evolution. Texturally unequilibrated amphibole occurring within the peridotite matrix and in melt pockets attest to continued hydration and refertilization of the lithospheric mantle subsequent to Oligocene flood basalt magmatism, during which an earlier-emplaced inventory of amphibole was likely largely consumed. However, a single harzburgite contains amphibole with the highest Mg# and lowest TiO2 content, which is interpreted as sampling a volumetrically subordinate mantle region beneath the Ethiopian plateau that was not tapped during flood basalt magmatism. Strikingly, both trace

  15. Zoned mantle convection.

    Albarède, Francis; Van Der Hilst, Rob D


    We review the present state of our understanding of mantle convection with respect to geochemical and geophysical evidence and we suggest a model for mantle convection and its evolution over the Earth's history that can reconcile this evidence. Whole-mantle convection, even with material segregated within the D" region just above the core-mantle boundary, is incompatible with the budget of argon and helium and with the inventory of heat sources required by the thermal evolution of the Earth. We show that the deep-mantle composition in lithophilic incompatible elements is inconsistent with the storage of old plates of ordinary oceanic lithosphere, i.e. with the concept of a plate graveyard. Isotopic inventories indicate that the deep-mantle composition is not correctly accounted for by continental debris, primitive material or subducted slabs containing normal oceanic crust. Seismological observations have begun to hint at compositional heterogeneity in the bottom 1000 km or so of the mantle, but there is no compelling evidence in support of an interface between deep and shallow mantle at mid-depth. We suggest that in a system of thermochemical convection, lithospheric plates subduct to a depth that depends - in a complicated fashion - on their composition and thermal structure. The thermal structure of the sinking plates is primarily determined by the direction and rate of convergence, the age of the lithosphere at the trench, the sinking rate and the variation of these parameters over time (i.e. plate-tectonic history) and is not the same for all subduction systems. The sinking rate in the mantle is determined by a combination of thermal (negative) and compositional buoyancy and as regards the latter we consider in particular the effect of the loading of plates with basaltic plateaux produced by plume heads. Barren oceanic plates are relatively buoyant and may be recycled preferentially in the shallow mantle. Oceanic plateau-laden plates have a more pronounced

  16. Where is mantle's carbon?

    Oganov, A. R.; Ono, S.; Ma, Y.


    Due to the strongly reducing conditions (the presence of metallic iron was suggested both by experiments [1] and theory [2]), diamond was believed to be the main host of carbon through most of the lower mantle [3]. We showed [4] that cementite Fe3C is another good candidate to be the main host of "reduced" carbon in the mantle, reinforcing an earlier hypothesis [5]. The fate of "oxidised" carbon (in subducted slabs) is of particular importance - if carbonates decompose producing fluid CO2, this would have important implications for the chemistry and rheology of the mantle. Knowledge of crystal structures and phase diagrams of carbonates is crucial here. The high-pressure structures of CaCO3 were predicted [6] and subsequently verified by experiments. For MgCO3, Isshiki et al. [7] found a new phase above 110 GPa, and several attempts were made to solve it [8,9]. Here [4], using an evolutionary algorithm for crystal structure prediction [10], we show that there are two post-magnesite phases at mantle-relevant pressure range, one stable at 82-138 GPa, and the other from 138 GPa to ~160 GPa. Both are based on threefold rings of CO4-tetrahedra and are more favourable than all previously proposed structures. We show that through most of the P-T conditions of the mantle, MgCO3 is the major host of oxidized carbon in the Earth. We predict the possibility of CO2 release at the very bottom of the mantle (in SiO2-rich basaltic part of subducted slabs), which could enhance partial melting of rocks and be related to the geodynamical differences between the Earth and Venus. 1.Frost D.J., Liebske C., Langenhorst F., McCammon C.A., Tronnes R.G., Rubie D.C. (2004). Experimental evidence for the existence of iron-rich metal in the Earth's lower mantle. Nature 428, 409-412. 2.Zhang F., Oganov A.R. (2006). Valence and spin states of iron impurities in mantle-forming silicates. Earth Planet. Sci. Lett. 249, 436-443. 3.Luth R.W. (1999). Carbon and carbonates in the mantle. In: Mantle

  17. The ruthenium isotopic composition of the oceanic mantle

    Bermingham, K. R.; Walker, R. J.


    The approximately chondritic relative, and comparatively high absolute mantle abundances of the highly siderophile elements (HSE), suggest that their concentrations in the bulk silicate Earth were primarily established during a final ∼0.5 to 1% of ;late accretion; to the mantle, following the cessation of core segregation. Consequently, the isotopic composition of the HSE Ru in the mantle reflects an amalgamation of the isotopic compositions of late accretionary contributions to the silicate portion of the Earth. Among cosmochemical materials, Ru is characterized by considerable mass-independent isotopic variability, making it a powerful genetic tracer of Earth's late accretionary building blocks. To define the Ru isotopic composition of the oceanic mantle, the largest portion of the accessible mantle, we report Ru isotopic data for materials from one Archean and seven Phanerozoic oceanic mantle domains. A sample from a continental lithospheric mantle domain is also examined. All samples have identical Ru isotopic compositions, within analytical uncertainties, indicating that Ru isotopes are well mixed in the oceanic mantle, defining a μ100Ru value of 1.2 ± 7.2 (2SD). The only known meteorites with the same Ru isotopic composition are enstatite chondrites and, when corrected for the effects of cosmic ray exposure, members of the Main Group and sLL subgroup of the IAB iron meteorite complex which have a collective CRE corrected μ100Ru value of 0.9 ± 3.0. This suggests that materials from the region(s) of the solar nebula sampled by these meteorites likely contributed the dominant portion of late accreted materials to Earth's mantle.

  18. Modeling mantle convection in the spherical annulus

    Hernlund, John W.; Tackley, Paul J.


    Most methods for modeling mantle convection in a two-dimensional (2D) circular annular domain suffer from innate shortcomings in their ability to capture several characteristics of the spherical shell geometry of planetary mantles. While methods such as rescaling the inner and outer radius to reduce anomalous effects in a 2D polar cylindrical coordinate system have been introduced and widely implemented, such fixes may have other drawbacks that adversely affect the outcome of some kinds of mantle convection studies. Here we propose a new approach that we term the "spherical annulus," which is a 2D slice that bisects the spherical shell and is quantitatively formulated at the equator of a spherical polar coordinate system after neglecting terms in the governing equations related to variations in latitude. Spherical scaling is retained in this approximation since the Jacobian function remains proportional to the square of the radius. We present example calculations to show that the behavior of convection in the spherical annulus compares favorably against calculations performed in other 2D annular domains when measured relative to those in a fully three-dimensional (3D) spherical shell.

  19. Moho vs crust-mantle boundary: Evolution of an idea

    O'Reilly, Suzanne Y.; Griffin, W. L.


    The concept that the Mohorovicic Discontinuity (Moho) does not necessarily coincide with the base of the continental crust as defined by rock-type compositions was introduced in the early 1980s. This had an important impact on understanding the nature of the crust-mantle boundary using information from seismology and from deep-seated samples brought to the surface as xenoliths in magmas, or as tectonic terranes. The use of empirically-constrained P-T estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment. The xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere, and revealed that the crust-mantle boundary in off-craton regions commonly is transitional over a depth range of about 5-20 km. Early seismic-reflection data showed common layering near the Moho, correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust-mantle boundary. Developments in seismology, petrophysics and experimental petrology have refined interpretation of lithospheric domains. The expansion of in situ geochronology (especially zircon U-Pb ages and Hf-isotopes; Os isotopes of mantle sulfides) has defined tectonic events that affected whole crust-mantle sections, and revealed that the crust-mantle boundary can change in depth through time. However, the nature of the crust-mantle boundary in cratonic regions remains enigmatic, mainly due to lack of key xenoliths or exposed sections. The observation that the Moho may lie significantly deeper than the crust-mantle boundary has important implications for modeling the volume of the crust. Mapping the crust using seismic techniques alone, without consideration of the petrological problems, may lead to an overestimation of crustal thickness by 15-30%. This will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust-formation processes

  20. Genesis of Ultra-High Pressure Garnet Pyroxenite in Orogenic Peridotites and its bearing on the Isotopic Chemical Heterogeneity in the Mantle Source of Oceanic Basalts

    Varas Reus, María Isabel; Garrido, Carlos J.; Marchesi, Claudio; Bosch, Delphine; Hidas, Károly


    ., Davies, G. R. & Nixon, P. H. (1993). Geochemical constraints on the petrogenesis of diamond facies pyroxenites from the Beni Bousera peridotite massif, North Morocco. Journal of Petrology 34, 125-172. [2] Blichert-Toft, J., Albarède, F. & Kornprobst, J. (1999). Lu-Hf Isotope systematics of garnet pyroxenites from Beni Bousera, Morocco: implications for basalt origin. Science 283, 1303-1306. [3] Garrido, C. J. & Bodinier, J. L. (1999). Diversity of mafic rocks in the Ronda peridotite: Evidence for pervasive melt-rock reaction during heating of subcontinental lithosphere by upwelling asthenosphere. Journal of Petrology 40, 729-754. [4] Marchesi, C., Garrido, C.J., Bosch, D., Bodinier, J.-L., Gervilla, F., Hidas, K., 2013. Mantle refertilization by melts of crustal-derived garnet pyroxenite: Evidence from the Ronda peridotite massif, southern Spain. Earth and Planetary Science Letters 362, 66-75. doi: 10.1016/j.epsl.2012.11.047. [5] Marchesi, C., Dale, C.W., Garrido, C.J., Pearson, D.G., Bosch, D., Bodinier, J.-L., Gervilla, F., Hidas, K., 2014. Fractionation of highly siderophile elements in refertilized mantle: Implications for the Os isotope composition of basalts. Earth and Planetary Science Letters 400, 33-44. doi: 10.1016/j.epsl.2014.05.025 [6] Montanini, A. & Tribuzio, R. (2015). Evolution of recycled crust within the mantle: Constraints from the garnet pyroxenites of the External Ligurian ophiolites (northern Apennines, Italy). Geology 43, 911-914. [7] Allègre, C. J. & Turcotte, D. L. (1986). Implications of a two-component marble-cake mantle. Nature 323, 123-127.

  1. Mantle hydrocarbons: abiotic or biotic?

    Sugisaki, R; Mimura, K


    Analyses of 227 rocks from fifty localities throughout the world showed that mantle derived rocks such as tectonized peridotites in ophiolite sequences (tectonites) arid peridotite xenoliths in alkali basalts contain heavier hydrocarbons (n-alkanes), whereas igneous rocks produced by magmas such as gabbro arid granite lack them. The occurrence of hydrocarbons indicates that they were not derived either from laboratory contamination or from held contamination; these compounds found in the mantle-derived rocks are called here "mantle hydrocarbons." The existence of hydrocarbons correlates with petrogenesis. For example, peridotite cumulates produced by magmatic differentiation lack hydrocarbons whereas peridotite xenoliths derived from the mantle contain them. Gas chromatographic-mass spectrometric records of the mantle hydrocarbons resemble those of aliphatics in meteorites and in petroleum. Features of the hydrocarbons are that (a) the mantle hydrocarbons reside mainly along grain boundaries and in fluid inclusions of minerals; (b) heavier isoprenoids such as pristane and phytane are present; and (c) delta 13C of the mantle hydrocarbons is uniform (about -27%). Possible origins for the mantle hydrocarbons are as follows. (1) They were in organically synthesized by Fischer-Tropsch type reaction in the mantle. (2) They were delivered by meteorites and comets to the early Earth. (3) They were recycled by subduction. The mantle hydrocarbons in the cases of (1) and (2) are abiogenic and those in (3) are mainly biogenic. It appears that hydrocarbons may survive high pressures and temperatures in the mantle, but they are decomposed into lighter hydrocarbon gases such as CH4 at lower pressures when magmas intrude into the crust; consequently, peridotite cumulates do not contain heavier hydrocarbons but possess hydrocarbon gases up to C4H10.

  2. Mantle flow influence on the evolution of subduction systems.

    Chertova, Maria; Spakman, Wim; Steinberger, Bernhard


    Evolution of the subducting slab has been widely investigated in the past two decades be means of numerical and laboratory modeling, including analysis of the factors controlling its behavior. However, until present, relatively little attention has been paid to the influence of the mantle flow. While for large subduction zones, due to the high slab buoyancy force, this effect might be small, mantle flow might be a primary factor controlling the evolution of a regional subduction zone. Here we investigate the impact of prescribed mantle flow on the evolution of both generic and real-Earth subduction models by means of 3D thermo-mechanical numerical modeling. The generic setup consists of a laterally symmetric subduction model using a 3000×2000×1000 km modeling domain with a lateral slab width varying from 500 to 1500 km. Non-linear rheology is implemented including diffusion, dislocation creep and a viscosity-limiter. To satisfy mass conservation, while implementing mantle inflow on some side boundaries, we keep other sides open (Chertova et al. 2012). To test the mantle flow influence on the dynamics of real-Earth subduction zone we adopt the numerical model from Chertova et al. (2014) for the evolution of the western Mediterranean subduction since 35 Ma. First, this model was tested with the arbitrary mantle flow prescribed on one of the four side boundaries or for the combination of two boundaries. In the last set of experiments, for side boundary conditions we use time-dependent estimates of actual mantle flow in the region based on Steinberger (2015) given for every 1 My. We demonstrate that for the western-Mediterranean subduction, the surrounding mantle flow is of second-order compared to slab buoyancy in controlling the dynamics of the subducting slab. Introducing mantle flow on the side boundaries might, however, improve the fit between the modeled and real slab imaged by tomography, although this may also trade-off with varying rheological parameters of

  3. Predicting lower mantle heterogeneity from 4-D Earth models

    Flament, Nicolas; Williams, Simon; Müller, Dietmar; Gurnis, Michael; Bower, Dan J.


    The Earth's lower mantle is characterized by two large-low-shear velocity provinces (LLSVPs), approximately ˜15000 km in diameter and 500-1000 km high, located under Africa and the Pacific Ocean. The spatial stability and chemical nature of these LLSVPs are debated. Here, we compare the lower mantle structure predicted by forward global mantle flow models constrained by tectonic reconstructions (Bower et al., 2015) to an analysis of five global tomography models. In the dynamic models, spanning 230 million years, slabs subducting deep into the mantle deform an initially uniform basal layer containing 2% of the volume of the mantle. Basal density, convective vigour (Rayleigh number Ra), mantle viscosity, absolute plate motions, and relative plate motions are varied in a series of model cases. We use cluster analysis to classify a set of equally-spaced points (average separation ˜0.45°) on the Earth's surface into two groups of points with similar variations in present-day temperature between 1000-2800 km depth, for each model case. Below ˜2400 km depth, this procedure reveals a high-temperature cluster in which mantle temperature is significantly larger than ambient and a low-temperature cluster in which mantle temperature is lower than ambient. The spatial extent of the high-temperature cluster is in first-order agreement with the outlines of the African and Pacific LLSVPs revealed by a similar cluster analysis of five tomography models (Lekic et al., 2012). Model success is quantified by computing the accuracy and sensitivity of the predicted temperature clusters in predicting the low-velocity cluster obtained from tomography (Lekic et al., 2012). In these cases, the accuracy varies between 0.61-0.80, where a value of 0.5 represents the random case, and the sensitivity ranges between 0.18-0.83. The largest accuracies and sensitivities are obtained for models with Ra ≈ 5 x 107, no asthenosphere (or an asthenosphere restricted to the oceanic domain), and a

  4. Iron geochemistry of the mantle

    Humayun, M.; Campbell, T. J.; Brandon, A. D.; Davis, F. A.; Hirschmann, M. M.


    The Fe/Mg ratio is an important constraint on the compositionally controlled density of the mantle. However, this ratio cannot be inferred from erupted lavas from OIB or MORB sources, but must be determined directly from mantle peridotites. Recently, the Fe/Mn ratio of erupted lavas has been used as an indicator of potential Fe variability in the mantle driven by core-mantle interaction, recycled oceanic crust, or even variations in the temperature of mantle melting. The classic compilation of McDonough & Sun (1995) provided the currently accepted Fe/Mn ratio of the upper mantle, 60±10. The uncertainty on this ratio allows for 15-30% variability in mantle iron abundances, which is equivalent to a density variation larger than observed by seismic tomography in the mantle. To better understand the relationship between mantle peridotites and erupted lavas, and to search for real variability in the Fe/Mn ratio of mantle peridotites, we report precise new ICP-MS measurements of the transition element geochemistry of suites of mantle xenoliths that have known Fe/Mg ratios. For 12 Kilbourne Hole xenoliths, we observe a clear correlation between Fe/Mn and MgO (or Fe/Mg) over an Fe/Mn range of 59-72. Extrapolation of this trend to a Primitive Mantle (PM) MgO content of 37.8 yields an Fe/Mn of 59±1 for the PM. Our new analyses of KLB-1 powder and fused glass beads yield an Fe/Mn of 61.4 for both samples, which plots on the Kilbourne Hole Fe/Mn vs. MgO trend. A set of ten xenoliths from San Carlos yield a wide range of Fe/Mn (56-65) not correlated with MgO content. The San Carlos xenoliths may have experienced a metasomatic effect that imprinted variable Fe/Mn. A clinopyroxene-rich lithology from San Carlos yields an Fe/Mn of 38, which plots on an extension of the Kilbourne Hole Fe/Mn vs. MgO trend. These new results, and those from other xenolith localities being measured in our lab, provide new constraints on the compositional variability of the Earth's upper mantle. Mc

  5. Compositional Evolution of the Mantle

    Bennett, V. C.


    The mantle is the Earth's largest chemical reservoir comprising 82% of its total volume and 65% of its mass. The mantle constitutes almost all of the silicate Earth, extending from the base of the crust (which comprises only 0.6% of the silicate mass) to the top of the metallic core at 2,900 km depth. The chemical compositions of direct mantle samples such as abyssal peridotites (Chapter 2.04) and peridotite xenoliths (Chapter 2.05), and of indirect probes of the mantle such as basalts from mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs) (Chapter 2.03), and some types of primitive granites, tell us about the compositional state of the modern mantle, with ever increasingly detailed information providing strong evidence for chemical complexity and heterogeneity at all scales (Chapter 2.03). This chemical heterogeneity must reflect the complex physical interplay of a number of distinct long-lived geochemical reservoirs that are identified primarily by their radiogenic isotopic compositions.Many of the chapters in this volume provide detailed images of the current chemical and physical state of the Earth's mantle, whereas other contributions examine the starting composition for the Earth (Chapter 2.01). This chapter attempts to link these two areas by tracking the composition of the mantle through time. The first part of this chapter is a summary of the empirical evidence for secular change in the chemical composition of the mantle from the formation of the Earth at 4.56 Ga throughto the present day. The emphasis is on results from the long-lived radiogenic isotopic systems, in particular 147Sm-143Nd, 176Lu-176Hf, 87Rb-87Sr, and 187Re-187Os systems as these isotopic data provide some of the best constraints on the composition of the mantle in the first half of Earth history, and the timing and extent of chemical differentiation that has affected the mantle over geologic time. Selected trace element data and the "short-lived" 146Sm-142Nd isotopic systems

  6. Redox conditions for mantle plumes

    Heister, L. E.; Lesher, C. E.


    The vanadium to scandium ratio (V/Sc) for basalts from mid-ocean ridge (MOR) and arc environments has been proposed as a proxy for fO2 conditions during partial melting (e.g. [1] and [2]). Contrary to barometric measurements of the fO2 of primitive lavas, the V/Sc ratio of the upper mantle at mid-ocean ridges and arcs is similar, leading previous authors to propose that the upper mantle has uniform redox potential and is well-buffered. We have attempted to broaden the applicability of the V/Sc parameter to plume-influenced localities (both oceanic and continental), where mantle heterogeneities associated with recycled sediments, mafic crust, and metasomatized mantle, whether of shallow or deep origin, exist. We find that primitive basalts from the North Atlantic Igneous Province (NAIP), Hawaii (both the Loa and Kea trends), Deccan, Columbia River, and Siberian Traps show a range of V/Sc ratios that are generally higher (average ~9) than those for MOR (average ~ 6.7) or arc (average ~7) lavas. Based on forward polybaric decompression modeling, we attribute these differences to polybaric melting and melt segregation within the garnet stability field rather than the presence of a more oxidized mantle in plume-influenced settings. Like MORB, the V/Sc ratios for plume-influenced basalts can be accounted for by an oxidation state approximately one log unit below the Ni-NiO buffer (NNO-1). Our analysis suggests that source heterogeneities have little, if any, resolvable influence on mantle redox conditions, although they have significant influence on the trace element and isotopic composition of mantle-derived melts. We suggest that variations in the redox of erupted lavas is largely a function of shallow lithospheric processes rather than intrinsic to the mantle source, regardless of tectonic setting. [1] Li and Lee (2004) EPSL, [2] Lee et al. (2005) J. of Petrology

  7. Mantle xenoliths from Marosticano area (Northern Italy): a comparison with Veneto Volcanic Province lithospheric mantle

    Brombin, Valentina; Bonadiman, Costanza; Coltorti, Massimo


    The Tertiary Magmatic Province of Veneto, known as Veneto Volcanic Province (VVP), in the North-East of Italy, represents the most important volcanic distric of Adria Plate. It is composed by five volcanic bodies: Val d'Adige, Marosticano, Mts. Lessini, Berici Hills and Euganean Hills. Most of the volcanic products are relatively undifferentiated lavas and range in composition from nephelinites to tholeiites. Often VVP nephelinites and basanites carry mantle xenoliths (mainly harzburgites and lherzolite). This study reports petrological comparison between Marosticano xenoliths (new outcrop) and xenoliths from the Lessinean and Val d'Adige areas already studied by many Authors (Siena & Coltorti 1989; Beccaluva et al., 2001, Gasperini et al., 2006). Mineral major elements analyses show that the Marosticano lherzolites and harzburgites reflect "more restitic" composition than the mantle domain beneath the other VVP districts (Lessini Mts. and Val d'Adige). In fact, olivine and pyroxene of Marosticano xenoliths have the highest mg# values of the entire district (Marosticano→90-93; literature→86-92). At comparable mg# (45-85 wt%) Marosticano spinels tend to be higher in Cr2O3 (23-44 wt%) contents with respect to the other VVP sp (7-25 wt%). It is worth noting that, Ni contents of Marosticano olivines in both harzburgites and lherzolites are higher (2650-3620 ppm) than those of the Lessinean xenoliths (1500- 3450 ppm), and similar to that of Val d'Adige lherzolites (3000-3500 ppm), approaching the contents of Archean cratonic mantle (Kelemen, 1998). In turn, Lessinean olivines properly fall in the Ni-mg# Phanerozoic field. At fixed pressure of 15 kbar, the equilibration temperature of Marosticano xenoliths are similar (Brey & Köhler: 920-1120°C) to those of Lessini (O'Neill & Wall: 990-1110°C; Beccaluva et al., 2007), but higher than those of Val d'Adige (Wells: 909-956°C; Gasperini et al., 2006). Finally, Marosticano mantle fragment show similar relatively high

  8. Mantle Volatiles - Distribution and Consequences

    Luth, R. W.


    Volatiles in the mantle have, for many years, been the subject of intensive study from a number of perspectives. They are of interest because of their potential effects on melting relationships, on transport of major and trace elements, and on the rheological and other physical properties of the mantle. By convention, "volatiles" in this context are constituents that are liquid or gaseous at normal Earth surface conditions. This review will look at the behavior of C-O-H-S-halogen volatiles, beginning with H2O and C-O volatiles.There have been tremendous strides made recently towards understanding how volatiles in general and water in particular is transported and stored in the mantle. This progress is based on research on a number of fronts: studies of mantle-derived samples have provided insight into the nature and occurrence of hydrous phases such as amphibole, mica, and chlorite, and have provided constraints on the capacity of nominally anhydrous minerals (NAMs) such as olivine, pyroxenes, and garnet to contain "water" by a variety of substitution mechanisms. Experimental studies on mantle-derived magmas have provided constraints on volatile contents in their source regions. Other studies have constrained the pressure, temperature, and composition conditions over which hydrous phases are stable in the mantle.Fundamental questions remain about the geochemical cycling of volatiles in the mantle, and between the mantle and the surface. Much attention has focused on the capability of hydrous phases such as amphibole, mica, serpentine, chlorite, and a family of "dense hydrous magnesian silicates" (DHMSs) to act as carriers of water in subducting slabs back into the mantle. It has been clear since the work of Ito et al. (1983) that there is a discrepancy between the amount of volatiles subducted into the mantle and those returned to the surface by arc magmatism. A recent overview of volatile cycling in subduction systems by Bebout (1996) suggests that 5-15% of the H2

  9. Towards a Global Upper Mantle Attenuation Model

    Karaoglu, Haydar; Romanowicz, Barbara


    Global anelastic tomography is crucial for addressing the nature of heterogeneity in the Earth's interior. The intrinsic attenuation manifests itself through dispersion and amplitude decay. These are contaminated by elastic effects such as (de)focusing and scattering. Therefore, mapping anelasticity accurately requires separation of elastic effects from the anelastic ones. To achieve this, a possible approach is to try and first predict elastic effects through the computation of seismic waveforms in a high resolution 3D elastic model, which can now be achieved accurately using numerical wavefield computations. Building upon the recent construction of such a whole mantle elastic and radially anisotropic shear velocity model (SEMUCB_WM1, French and Romanowicz, 2014), which will be used as starting model, our goal is to develop a higher resolution 3D attenuation model of the upper mantle based on full waveform inversion. As in the development of SEMUCB_WM1, forward modeling will be performed using the spectral element method, while the inverse problem will be treated approximately, using normal mode asymptotics. Both fundamental and overtone time domain long period waveforms (T>60s) will be used from a dataset of over 200 events observed at several hundred stations globally. Here we present preliminary results of synthetic tests, exploring different iterative inversion strategies.

  10. Petrology of suprasubductive mantle xenoliths from Estancia Sol De Mayo (Central Patagonia, Argentina)

    Melchiorre, M.; Coltorti, M.; Gregoire, M.; Benoit, M.


    A new suite of mantle xenoliths from Estancia Sol de Mayo (Patagonia) has been investigated. They were entrained in alkaline lavas from the south western sector of Meseta Lago Buenos Aires. Trace element abundances of these lavas are well comparable with those of the main and post-plateau lavas from the Triple Junction Province and resemble those of OIB. Xenoliths are spinel-bearing harzburgites and dunites, with minor lherzolites and one wehrlite. They are characterized by a coarse grained protogranular texture and devoid of modal metasomatic features and hydrated minerals. They show two texturally different clinopyroxenes. One is protogranular (cpx1), while the second surrounds, and is genetically related to, spinel (cpx2). Three different types of orthopyroxenes are also recognized: the first one is represented by large protogranular crystals with exsolution lamellae (opx1), the second one by small clean and undeformed grains without exsolution lamellae (opx2) and the last one occurs as small grains filling veins (opx3). Major element compositions of both clinopyroxenes and orthopyroxenes highlight two different trends. The first one is characterized by high Al2O3 (high-Al trend) content at almost constant mg# [MgO/(MgO+FeO) mol %], while the second shows a slight increase in Al2O3 (low-Al trend) content with decreasing mg#. Trace element contents of cpx are enriched in LREE and characterized by prominent to slightly negative Nb, Zr and Ti anomalies. No differences are observed between cpx1 and cpx2. The three groups of orthopyroxenes are variably depleted in LREE, with opx1 and opx2 always showing prominent to slightly negative Ti and Zr anomalies, while opx3 is characterized by a prominent positive Zr anomaly. Al2O3 in cpx is inversely correlated with LREE and LILE suggesting that a refertilization event occur within the upper mantle beneath Estancia Sol de Mayo. The most likely melt which can account for this event has a tholeiitic affinity, as supported by i

  11. Compositional layering within the large low shear-wave velocity provinces (LLSVPs) in the lower mantle

    Ballmer, Maxim; Lekic, Vedran; Schumacher, Lina; Ito, Garrett; Thomas, Christine


    Seismic tomography reveals two antipodal LLSVPs in the Earth's mantle, each extending from the core-mantle boundary (CMB) up to ~1000 km depth. The LLSVPs are thought to host primordial mantle materials that bear witness of early-Earth processes, and/or subducted basalt that has accumulated in the mantle over billions of years. A compositional distinction between the LLSVPs and the ambient mantle is supported by anti-correlation of bulk-sound and shear-wave velocity (Vs) anomalies as well as abrupt lateral gradients in Vs along LLSVP margins. Both of these observations, however, are mainly restricted to the LLSVP bottom domains (2300~2900 km depth), or hereinafter referred to as "deep distinct domains" (DDD). Seismic sensitivity calculations suggest that DDDs are more likely to be composed of primordial mantle material than of basaltic material. On the other hand, the seismic signature of LLSVP shallow domains (1000~2300 km depth) is consistent with a basaltic composition, though a purely thermal origin cannot be ruled out. Here, we explore the dynamical, seismological, and geochemical implications of the hypothesis that the LLSVPs are compositionally layered with a primordial bottom domain (or DDD) and a basaltic shallow domain. We test this hypothesis using 2D thermochemical mantle-convection models. Depending on the density difference between primordial and basaltic materials, the materials either mix or remain separate as they join to form thermochemical piles in the deep mantle. Separation of both materials within these piles provides an explanation for LLSVP seismic properties, including substantial internal vertical gradients in Vs observed at 400-700 km height above the CMB, as well as out-of-plane reflections on LLSVP sides over a range of depths. Predicted geometry of thermochemical piles is compared to LLSVP and DDD shapes as constrained by seismic cluster analysis. Geodynamic models predict short-lived "secondary" plumelets to rise from LLSVP roofs and

  12. Rogue mantle helium and neon.

    Albarède, Francis


    The canonical model of helium isotope geochemistry describes the lower mantle as undegassed, but this view conflicts with evidence of recycled material in the source of ocean island basalts. Because mantle helium is efficiently extracted by magmatic activity, it cannot remain in fertile mantle rocks for long periods of time. Here, I suggest that helium with high 3He/4He ratios, as well as neon rich in the solar component, diffused early in Earth's history from low-melting-point primordial material into residual refractory "reservoir" rocks, such as dunites. The difference in 3He/4He ratios of ocean-island and mid-ocean ridge basalts and the preservation of solar neon are ascribed to the reservoir rocks being stretched and tapped to different extents during melting.

  13. Complex metasomatism of lithospheric mantle by asthenosphere-derived melts: Evidence from peridotite xenoliths in Weichang at the northern margin of the North China Craton

    Zou, Dongya; Zhang, Hongfu; Hu, Zhaochu; Santosh, M.


    The petrology, in situ analyses of major and trace elements as well as Sr isotopic compositions of spinel-facies lherzolite and harzburgite xenoliths from Weichang within the northern margin of the North China Craton (NCC) are reported for the first time in this study to evaluate the nature and evolution of the lithospheric mantle. These peridotite xenoliths display porphyroclastic texture and can be subdivided into two groups. Group I peridotites have slightly higher forsterite contents (Fo) (90.6-91.2) and 87Sr/86Sr ratios (0.7025-0.7043) in the cores than those in the rims (89.8-90.8; 0.7025-0.7038) of olivines and clinopyroxenes, respectively. The clinopyroxenes in these rocks exhibit uniform LREE-depleted patterns. These geochemical features suggest that the Group I peridotites were weakly metasomatized by recent asthenospheric melts. In contrast, Group II peridotites show sieve-texture and clear compositional zoning in minerals. The olivines and clinopyroxenes from these rocks have higher Fo (86.9-91.3) and 87Sr/86Sr ratios (0.7035-0.7049) in the cores than those in the rims (76.9-90.6; 0.7021-0.7046). The clinopyroxenes show three types of REE patterns: LREE-enriched, convex-upward and spoon-shaped. The LREE-enriched clinopyroxenes have the highest (La/Yb)N and lowest Ti/Eu and those with spoon-shaped REE patterns show an increase in LREE, Ba, Th and U contents from the cores to the rims. These features indicate that the Group II peridotites witnessed a high degree of refertilization by recent asthenosphere-derived silicate and carbonatite melts or their mixture. Compared with the data of the Mesozoic NCC lithospheric mantle, the heterogeneous and low 87Sr/86Sr ratios (0.7025-0.7049) in the LREE-depleted clinopyroxenes reveal that the ancient lithospheric mantle could have been modified by asthenospheric melts before the recent metasomatism event. We conclude that the lithospheric mantle beneath Weichang underwent multiple modifications through asthenosphere

  14. Mantle hydrous-fluid interaction with Archaean granite.

    Słaby, E.; Martin, H.; Hamada, M.; Śmigielski, M.; Domonik, A.; Götze, J.; Hoefs, J.; Hałas, S.; Simon, K.; Devidal, J.-L.; Moyen, J.-F.; Jayananda, M.


    Water content/species in alkali feldspars from late Archaean Closepet igneous bodies as well as growth and re-growth textures, trace element and oxygen isotope composition have been studied (Słaby et al., 2011). Both processes growth and re-growth are deterministic, however they differ showing increasing persistency in element behaviour during interaction with fluids. The re-growth process fertilized domains and didn't change their oxygen-isotope signature. Water speciation showed persistent behaviour during heating at least up to 600oC. Carbonate crystals with mantle isotope signature are associated with the recrystallized feldspar domains. Fluid-affected domains in apatite provide evidence of halide exchange. The data testify that the observed recrystallization was a high-temperature reaction with fertilized, halide-rich H2O-CO2 mantle-derived fluids of high water activity. A wet mantle being able to generate hydrous plumes, which appear to be hotter during the Archean in comparison to the present time is supposed by Shimizu et al. (2001). Usually hot fluids, which can be strongly carbonic, precede asthenospheric mantle upwelling. They are supposed to be parental to most recognized compositions, which can be derived by their immiscible separation into saline aqueous-silicic and carbonatitic members (Klein-BenDavid et al., 2007). The aqueous fractions are halogen-rich with a significant proportion of CO2. Both admixed fractions are supposed to be fertile. The Closepet granite emplaced in a major shear zone that delimitates two different terrains. Generally such shear zones, at many places, are supposed to be rooted deep into the mantle. The drain, that favoured and controlled magma ascent and emplacement, seemed to remain efficient after granite crystallization. In the southern part of the Closepet batholiths an evidence of intensive interaction of a lower crust fluid (of high CO2 activity) is provided by the extensive charnockitization of amphibolite facies (St

  15. Petrological evidence for secular cooling in mantle plumes.

    Herzberg, Claude; Gazel, Esteban


    Geological mapping and geochronological studies have shown much lower eruption rates for ocean island basalts (OIBs) in comparison with those of lavas from large igneous provinces (LIPs) such as oceanic plateaux and continental flood provinces. However, a quantitative petrological comparison has never been made between mantle source temperature and the extent of melting for OIB and LIP sources. Here we show that the MgO and FeO contents of Galapagos-related lavas and their primary magmas have decreased since the Cretaceous period. From petrological modelling, we infer that these changes reflect a cooling of the Galapagos mantle plume from a potential temperature of 1,560-1,620 degrees C in the Cretaceous to 1,500 degrees C at present. Iceland also exhibits secular cooling, in agreement with previous studies. Our work provides quantitative petrological evidence that, in general, mantle plumes for LIPs with Palaeocene-Permian ages were hotter and melted more extensively than plumes of more modern ocean islands. We interpret this to reflect episodic flow from lower-mantle domains that are lithologically and geochemically heterogeneous.

  16. Domains and domain loss

    Haberland, Hartmut


    The domain concept, originally suggested by Schmidt-Rohr in the 1930’s (as credited in Fishman’s writings in the 1970s), was an attempt to sort out different areas of language use in multilingual societies, which are relevant for language choice. In Fishman’s version, domains were considered...... not described in terms of domains, and recent research e.g. about the multilingual communities in the Danish-German border area seems to confirm this....

  17. Mantle superplumes induce geomagnetic superchrons

    Peter eOlson


    Full Text Available We use polarity reversal systematics from numerical dynamos to quantify the hypothesis that the modulation of geomagnetic reversal frequency, including geomagnetic superchrons, results from changes in core heat flux related to growth and collapse of lower mantle superplumes. We parameterize the reversal frequency sensitivity from numerical dynamos in terms of average core heat flux normalized by the difference between the present-day core heat flux and the core heat flux at geomagnetic superchron onset. A low-order polynomial fit to the 0-300 Ma Geomagnetic Polarity Time Scale (GPTS reveals that a decrease in core heat flux relative to present-day of approximately 30% can account for the Cretaceous Normal Polarity and Kiaman Reverse Polarity Superchrons, whereas the hyper-reversing periods in the Jurassic require a core heat flux equal to or higher than present-day. Possible links between GPTS transitions, large igneous provinces (LIPs, and the two lower mantle superplumes are explored. Lower mantle superplume growth and collapse induce GPTS transitions by increasing and decreasing core heat flux, respectively. Age clusters of major LIPs postdate transitions from hyper-reversing to superchron geodynamo states by 30-60 Myr, suggesting that superchron onset may be contemporaneous with LIP-forming instabilities produced during collapses of lower mantle superplumes.

  18. Mantle flow and dynamic topography associated with slab window opening: Insights from laboratory models

    Guillaume, Benjamin; Moroni, Monica; Funiciello, Francesca; Martinod, Joseph; Faccenna, Claudio


    We present dynamically self-consistent mantle-scale laboratory models that have been conducted to improve our understanding of the influence of slab window opening on subduction dynamics, mantle flow and associated dynamic topography over geological time scales. The adopted setup consists of a two-layer linearly viscous system simulating the subduction of a fixed plate of silicone (lithosphere) under negative buoyancy in a viscous layer of glucose syrup (mantle). Our experimental setting is also characterized by a constant-width rectangular window located at the center of a laterally confined slab, modeling the case of the interaction of a trench-parallel spreading ridge with a wide subduction zone. We found that the opening of a slab window does not produce consistent changes of the geometry and the kinematics of the slab. On the contrary, slab-induced mantle circulation, quantified both in the vertical and horizontal sections using the Feature Tracking image analysis technique, is strongly modified. In particular, rollback subduction and the opening of the slab window generate a complex mantle circulation pattern characterized by the presence of poloidal and toroidal components, with the importance of each evolving according to kinematic stages. Mantle coming from the oceanic domain floods through the slab window, indenting the supra-slab mantle zone and producing its deformation without any mixing between mantle portions. The opening of the slab window and the upwelling of sub-slab mantle produce a regional-scale non-isostatic topographic uplift of the overriding plate that would correspond to values ranging between ca. 1 and 5 km in nature. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compared them to the tectonics and volcanism of the Patagonian subduction zone. We found that the anomalous backarc volcanism that has been developing since the middle Miocene could result from the lateral flow of sub

  19. Dipping fossil fabrics of continental mantle lithosphere as tectonic heritage of oceanic paleosubductions

    Babuska, Vladislav; Plomerova, Jaroslava; Vecsey, Ludek; Munzarova, Helena


    Subduction and orogenesis require a strong mantle layer (Burov, Tectonophys. 2010) and our findings confirm the leading role of the mantle lithosphere. We have examined seismic anisotropy of Archean, Proterozoic and Phanerozoic provinces of Europe by means of shear-wave splitting and P-wave travel-time deviations of teleseismic waves observed at dense arrays of seismic stations (e.g., Vecsey et al., Tectonophys. 2007). Lateral variations of seismic-velocity anisotropy delimit domains of the mantle lithosphere, each of them having its own consistent fabric. The domains, modeled in 3D by olivine aggregates with dipping lineation a, or foliation (a,c), represent microplates or their fragments that preserved their pre-assembly fossil fabrics. Evaluating seismic anisotropy in 3D, as well as mapping boundaries of the domains helps to decipher processes of the lithosphere formation. Systematically dipping mantle fabrics and other seismological findings seem to support a model of continental lithosphere built from systems of paleosubductions of plates of ancient oceanic lithosphere (Babuska and Plomerova, AGU Geoph. Monograph 1989), or from stacking of the plates (Helmstaedt and Schulze, Geol. Soc. Spec. Publ. 1989). Seismic anisotropy in the oceanic mantle lithosphere, explained mainly by the olivine A- or D-type fabric (Karato et al., Annu. Rev. Earth Planet. Sci. 2008), was discovered a half century ago (Hess, Nature 1964). Field observations and laboratory experiments indicate the oceanic olivine fabric might be preserved in the subducting lithosphere to a depth of at least 200-300 km. We thus interpret the dipping anisotropic fabrics in domains of the European mantle lithosphere as systems of "frozen" paleosubductions (Babuska and Plomerova, PEPI 2006) and the lithosphere base as a boundary between the fossil anisotropy in the lithospheric mantle and an underlying seismic anisotropy related to present-day flow in the asthenosphere (Plomerova and Babuska, Lithos 2010).

  20. Fossilized Dipping Fabrics in Continental Mantle Lithosphere as Possible Remnants of Stacked Oceanic Paleosubductions

    Babuska, V.; Plomerova, J.; Vecsey, L.; Munzarova, H.


    We have examined seismic anisotropy within the mantle lithosphere of Archean, Proterozoic and Phanerozoic provinces of Europe by means of shear-wave splitting and P-wave travel-time deviations of teleseismic waves observed at dense arrays of seismic stations (e.g., Vecsey et al., Tectonophys. 2007). Lateral variations of seismic-wave anisotropy delimit domains of the mantle lithosphere, each of them having a consistent fabric. The domains, modeled in 3D by olivine aggregates with dipping lineation a, or foliation (a,c), represent microplates or their fragments that preserved their pre-assembly fossil fabrics in the mantle lithosphere. Evaluating seismic anisotropy in 3D, as well as mapping boundaries of the domains helps to decipher processes of the lithosphere formation. Systematically dipping mantle fabrics and other seismological findings seem to support a model of continental lithosphere built from systems of paleosubductions of plates of ancient oceanic lithosphere (Babuska and Plomerova, AGU Geoph. Monograph 1989), or by stacking of the plates (Helmstaedt and Schulze, Geol. Soc. Spec. Publ. 1989). Seismic anisotropy in the oceanic mantle lithosphere, explained mainly by the olivine A- or D-type fabric (Karato et al., Annu. Rev. Earth Planet. Sci. 2008), was discovered a half century ago (Hess, Nature 1964). Field observations and laboratory experiments indicate the oceanic olivine fabric might be preserved in the subducting lithosphere to a depth of at least 200-300 km. We thus interpret the dipping anisotropic fabrics in domains of the European mantle lithosphere as systems of "frozen" paleosubductions (Babuska and Plomerova, PEPI 2006), and the lithosphere base as a boundary between a fossil anisotropy in the lithospheric mantle and an underlying seismic anisotropy related to present-day flow in the asthenosphere (Plomerova and Babuska, Lithos 2010).

  1. Numerical Modeling of Deep Mantle Flow: Thermochemical Convection and Entrainment

    Mulyukova, Elvira; Steinberger, Bernhard; Dabrowski, Marcin; Sobolev, Stephan


    ) upwelling of the ambient material in the vicinity of the dense material (mechanism of selective withdrawal (Lister, 1989)), and (iii) cold downwellings sliding along the bottom boundary, and forcing the dense material upwards. The objective of this study is to compare the efficiency of entrainment by each of these mechanisms, and its dependence on the density and viscosity anomaly of the dense material with respect to the ambient mantle. To perform this study, we have developed a two-dimensional FEM code to model thermal convection in a hollow cylinder domain with presence of chemical heterogeneities, and using a realistic viscosity profile. We present the results of the simulations that demonstrate the entrainment mechanisms described above. In addition, we perfom numerical experiments in a Cartesian box domain, where the bottom right boundary of the box is deformed to resemble the geometry of an LLSVP edge. In some of the experiments, the bottom left part of the boundary is moving towards the right boundary, simulating a slab sliding along the core-mantle boundary towards an LLSVP. These experiments allow a detailed study of the process of entrainment, and its role in the thermochemical evolution of the Earth.

  2. Experimental study of diamond resorption during mantle metasomatism

    Fedorchuk, Yana; Schmidt, Max W.; Liebske, Christian


    Many of kimberlite-derived diamonds are partially dissolved to various degree but show similar resorption style. This resorption style has been observed in experiments with aqueous fluid at the conditions corresponding to kimberlite emplacement (1-2 GPa). At the same time, each diamond population has more than ten percent of diamond crystals with several drastically different resorption styles, which have not been observed in experiments, and may represent partial dissolution of diamonds during metasomatism in different mantle domains. Metasomatic processes modify the composition of subcratonic mantle, may trigger the formation of kimberlite magma, and result in the growth and partial dissolution of diamonds. Composition of metasomatic agents as constrained from studies of the reaction rims on mantle minerals (garnet, clinopyroxene) and experimental studies vary between carbonatitic melt, aqueous silicate melt, and CHO fluid. However, complex chemical pattern of mantle minerals and estimates of redox regime in subcratonic mantle allow different interpretations. Here we explore diamond dissolution morphology as an indicator of the composition of mantle metasomatic agents. Towards this end we examine diamond dissolution morphologies developed in experiments at the conditions of mantle metasomatism in different reacting media and compare them to the mantle-derived dissolution features of natural diamonds. The experiments were conducted in multi-anvil (Walker-Type) apparatus at 6 GPa and 1200-1500oC. Dissolution morphology of natural octahedral diamond crystals (0.5 mg) was examined in various compositions in synthetic system MgO-CaO- SiO2-CO2-H2O. The runs had the following phases present: solid crystals with fluid (various ratio of H2O-CO2-SiO2, and in the air), carbonate melt, carbonate-silicate melt, and carbonate melt with CHO fluid. Experiments produced three different styles of diamond resorption. In the presence of a fluid phase with variable proportions of H2O

  3. Initial Feasibility Study to Drill and Core the Ocean Mantle

    Nicolas Pilisi


    Full Text Available An initial feasibility study (Pilisi and Whitney, 2011 of drilling through the Mohorovičić discontinuity (Moho into the oceanic mantle specifically focused on future requirements for planning, drilling and coring a hole 500 m into the oceanic mantle from three candidate locations in the Pacific Ocean (Cocos Plate, Baja California, and offshore Hawaii. The study points out some of the critical issues that need to be resolved before embarking upon such a challengingproject. It was conducted on the basis of data provided by the Integrated Ocean Drilling Program–Management International (IODP-MI, the Center for Deep Earth Exploration (CDEX operating the drilling vessel Chikyu within IODP, public domain information, and past experience that Blade Energy Partners (hereafter mentioned as “Blade”; has had with frontier projects in the offshore deepwater oil and gas and geothermal industries.

  4. Petrology of a Neoproterozoic Alaskan-type complex from the Eastern Desert of Egypt: Implications for mantle heterogeneity

    Khedr, Mohamed Zaki; Arai, Shoji


    This paper details petrological and geochemical studies of an ultramafic-mafic intrusion in the Southern Eastern Desert of Egypt. The Dahanib complex shows a concentric zonation, from dunites at the core, through chromitites, clinopyroxene-rich dunites, wehrlites, harzburgites, gabbronorites and layered gabbros, to hornblende gabbros/diorites at the rim, similar to other Alaskan-type complexes. These lithologies typically feature cumulate textures and layering. Their pyroxenes (Mg#s, 0.54-0.94) evidence Fe, Mn and Na enrichment, but Al, Cr, Mg and Ti are depleted with differentiation. Their chromian spinels have a wide range of Cr# (0.31-0.61), along with high Ti and Fe, as a result of their origin through crystal accumulation and reaction with interstitial liquids. The clinopyroxenes (Cpxs) in peridotites and gabbroic rocks, which are high in REE concentration (2-100 times chondrite), are depleted in LREE relative to HREE and are similar to Cpx crystallized from asthenospheric melts. The mineral inclusions in spinel, the chemistry of Cpx in peridotites (rich in Al, Cr, Na, Ti and ΣREE = 13.7), and the melts in equilibrium with Cpx suggest that the Neoproterozoic lithosphere were partially refertilized by trace asthenospheric melts. The early magmas were possibly enriched by Mg, Cr, Ni, Ti, V and Sr, while the evolved types were rich in Fe, Mn, Na, Li, Zr, Co and REE via crystal accumulation and the interaction with interstitial liquids. The Neoproterozoic sub-arc mantle in Egypt is chemically heterogeneous and generally low in Nb, Ta, Zr and K, due to the low solubility of HFSE in slab-derived fluids and no other external addition of these elements. The large variations in lithology and chemistry, as well as the occurrence of scattered chromitite clots in the Dahanib peridotites, are related to a continuous supply of primitive magmas and/or the reaction between interstitial liquids and early cumulus crystals during multistage fractional crystallization. The

  5. How stratified is mantle convection?

    Puster, Peter; Jordan, Thomas H.


    We quantify the flow stratification in the Earth's mid-mantle (600-1500 km) in terms of a stratification index for the vertical mass flux, Sƒ (z) = 1 - ƒ(z) / ƒref (z), in which the reference value ƒref(z) approximates the local flux at depth z expected for unstratified convection (Sƒ=0). Although this flux stratification index cannot be directly constrained by observations, we show from a series of two-dimensional convection simulations that its value can be related to a thermal stratification index ST(Z) defined in terms of the radial correlation length of the temperature-perturbation field δT(z, Ω). ST is a good proxy for Sƒ at low stratifications (SƒUniformitarian Principle. The bound obtained here from global tomography is consistent with local seismological evidence for slab flux into the lower mantle; however, the total material flux has to be significantly greater (by a factor of 2-3) than that due to slabs alone. A stratification index, Sƒ≲0.2, is sufficient to exclude many stratified convection models still under active consideration, including most forms of chemical layering between the upper and lower mantle, as well as the more extreme versions of avalanching convection governed by a strong endothermic phase change.

  6. Mid-mantle heterogeneities and iron spin transition in the lower mantle: Implications for mid-mantle slab stagnation

    Shahnas, M. H.; Yuen, D. A.; Pysklywec, R. N.


    Recent high pressure experimental results reveal that the elastic and transport properties of mantle materials are impacted by the electronic spin transition in iron under lower mantle pressure and temperature conditions. The electronic transition in ferropericlase (Fp), the second major constituent mineral of the lower mantle material, is associated with a smooth increase in density starting from the mid-mantle depth to the core-mantle boundary (CMB). The transition also yields softening in the elastic moduli and an increase in the thermal expansivity over the transition zone in the lower mantle. Although there is not yet robust experimental evidence for spin-transition induced density change in the perovskite (Pv) phase (the major constituent mineral in the lower mantle), the spin transition in the octahedral (B) site in Al-free perovskite causes a bulk modulus hardening (increase in the bulk modulus) in the mineral. We have incorporated these physical processes into high resolution 3D-spherical control volume models for mantle convection. A series of numerical experiments explore how the electronic spin transition in iron modifies the mantle flow, and in particular the fate of sinking cold slabs. Such mid-mantle stagnations are prevalent globally in seismic tomographic inversions, but previous explanations for their existence are not satisfactory. Employing density anomalies from the iron spin transition in ferropericlase and density anomaly models for perovskite, we study the influence of the spin transition in the minerals of the lower mantle on mantle flow. Our model results reveal that while the spin transition-induced property variations in ferropericlase enhance mixing in the lower depths of the mantle, the density anomaly arising from the hardening in the bulk modulus of Al-free perovskite can be effective in slowing the descent of slabs and may cause stagnation at mid-mantle levels. A viscosity hill in the lower mantle may further enhance the stagnation

  7. Mantle wedge serpentinization effects on slab dips

    Eh Tan


    Full Text Available The mechanical coupling between a subducting slab and the overlying mantle wedge is an important factor in controlling the subduction dip angle and the flow in mantel wedge. This paper investigates the role of the amount of mantle serpentinization on the subduction zone evolution. With numerical thermos-mechanical models with elasto-visco-plastic rheology, we vary the thickness and depth extent of mantle serpentinization in the mantle wedge to control the degree of coupling between the slab and mantle wedge. A thin serpentinized mantle layer is required for stable subduction. For models with stable subduction, we find that the slab dip is affected by the down-dip extent and the mantle serpentinization thickness. A critical down-dip extent exists in mantle serpentinization, determined by the thickness of the overriding lithosphere. If the down-dip extent does not exceed the critical depth, the slab is partially coupled to the overriding lithosphere and has a constant dip angle regardless of the mantle serpentinization thickness. However, if the down-dip extent exceeds the critical depth, the slab and the base of the overriding lithosphere would be separated and decoupled by a thick layer of serpentinized peridotite. This allows further slab bending and results in steeper slab dip. Increasing mantle serpentinization thickness will also result in larger slab dip. We also find that with weak mantle wedge, there is no material flowing from the asthenosphere into the serpentinized mantle wedge. All of these results indicate that serpentinization is an important ingredient when studying the subduction dynamics in the mantle wedge.

  8. Age and evolution of the lithospheric mantle beneath the Khanka Massif: Geochemical and Re-Os isotopic evidence from Sviyagino mantle xenoliths

    Guo, Peng; Xu, Wen-Liang; Wang, Chun-Guang; Wang, Feng; Ge, Wen-Chun; Sorokin, A. A.; Wang, Zhi-Wei


    New geochemical and Re-Os isotopic data of mantle xenoliths entrained in Cenozoic Sviyagino alkali basalts from the Russian Far East provide insights into the age and evolution of the sub-continental lithospheric mantle (SCLM) beneath the Khanka Massif, within the Central Asian Orogenic Belt (CAOB). These mantle xenoliths are predominantly spinel lherzolites with minor spinel harzburgite. The lherzolites contain high whole-rock concentrations of Al2O3 and CaO, with low forsterite content in olivine (Fo = 89.5-90.3%) and low Cr# in spinel (0.09-0.11). By contrast, the harzburgite is more refractory, containing lower whole rock Al2O3 and CaO contents, with higher Fo (91.3%) and spinel Cr# (0.28). Their whole rock and mineral compositions suggest that the lherzolites experienced low-degree (1-4%) batch melting and negligible metasomatism, whereas the harzburgite underwent a higher degree (10%) of fractional melting, and experienced minor post-melting silicate metasomatism. Two-pyroxene rare earth element (REE)-based thermometry (TREE) yields predominant equilibrium temperatures of 884-1043 °C, similar to values obtained from two-pyroxene major element-based thermometry (TBKN = 942-1054 °C). Two lherzolite samples yield high TREE relative to TBKN (TREE - TBKN ≥ 71 °C), suggesting that they cooled rapidly as a result of the upwelling of hot asthenospheric mantle material that underplated a cold ancient lithosphere. The harzburgite with a low Re/Os value has an 187Os/188Os ratio of 0.11458, yielding an Os model age (TMA) relative to the primitive upper mantle (PUM) of 2.09 Ga, and a Re depletion ages (TRD) of 1.91 Ga; both of which record ancient melt depletion during the Paleoproterozoic ( 2.0 Ga). The 187Os/188Os values of lherzolites (0.12411-0.12924) correlate well with bulk Al2O3 concentrations and record the physical mixing of ancient mantle domains and PUM-like ambient mantle material within the asthenosphere. This indicates that the SCLM beneath the Khanka

  9. Geochemical and mantle-like isotopic (Nd, Sr) composition of the Baklan Granite from the Muratdağı Region (Banaz, Uşak), western Turkey: Implications for input of juvenile magmas in the source domains of western Anatolia Eocene Miocene granites

    Aydoğan, M. Selman; Çoban, Hakan; Bozcu, Mustafa; Akıncı, Ömer


    The (late syn)- post-collisional magmatic activities of western and northwestern Anatolia are characterized by intrusion of a great number of granitoids. Amongst them, Baklan Granite, located in the southern part of the Muratdağı Region from the Menderes Massif (Banaz, Uşak), has peculiar chemical and isotopic characteristics. The Baklan rocks are made up by K-feldspar, plagioclase, quartz, biotite and hornblende, with accessory apatite, titanite and magnetite, and include mafic microgranular enclaves (MME). Chemically, the Baklan intrusion is of sub-alkaline character, belongs to the high-K, calc-alkaline series and displays features of I-type affinity. It is typically metaluminous to mildly peraluminous, and classified predominantly as granodiorite in composition. The spider and REE patterns show that the rocks are fractionated and have small negative Eu anomalies (Eu/Eu ∗ = 0.62-0.86), with the depletion of Nb, Ti, P and, to a lesser extent, Ba and Sr. The pluton was dated by the K-Ar method on the whole-rock, yielded ages between 17.8 ± 0.7 and 19.4 ± 0.9 Ma (Early Miocene). The intrusion possesses primitive low initial 87Sr/ 86Sr ratios (0.70331-0.70452) and negative ɛNd(t) values (-5.0 to -5.6). The chemical contrast between evolved Baklan rocks (SiO 2, 62-71 wt.%; Cr, 7-27 ppm; Ni, 5-11 ppm; Mg#, 45-51) and more primitive clinopyroxene-bearing monzonitic enclaves (SiO 2, 54-59 wt.%; Cr, 20-310 ppm; Ni, 10-70 ppm; Mg#, 50-61) signifies that there is no co-genetic link between host granite and enclaves. The chemical and isotopic characteristics of the Baklan intrusion argue for an important role of a juvenile component, such as underplated mantle-derived basalt, in the generation of the granitoids. Crustal contamination has not contributed significantly to their origin. However, with respect to those of the Baklan intrusion, the generation of the (late syn)- post-collisional intrusions with higher Nd(t) values from the western Anatolia require a much

  10. Radioactivity released from burning gas lantern mantles.

    Luetzelschwab, J W; Googins, S W


    Gas lantern mantles contain thorium to produce incandescence when lantern fuel is burned on the mantle. Although only thorium is initially present on the mantle, the thorium daughters build up, some over a period of weeks and some over a period of years, and significant quantities of these daughters are present when the mantle is used. Some of these daughters are released when the lantern fuel is burned on the mantle. The amounts of radioactivity released during burning is studied by measuring the gamma radiation emitted by the daughters. Results of this study show that some of the radium (224Ra and 228Ra) and more than half the 212Pb and 212Bi is released during the first hour of a burn. The actual amounts release depend on the age of the mantle.

  11. Evolution of the mantle beneath the eastern North China Craton during the Cenozoic: Linking geochemical and geophysical observations

    Li, Hong-Yan; Xu, Yi-Gang; Ryan, Jeffrey G.; Whattam, Scott A.


    Recent discoveries related to the geochemistry of Cenozoic basalts and the geophysics of the deep mantle beneath eastern Eurasia make it possible to place constraints on the relationship between the seismic tomography of subcontinental mantle domains and their geochemical heterogeneities. Basalts with ocean island basalt-like trace elements erupted during (56-23 Ma) and after (≤23 Ma) rifting of the eastern North China Craton (NCC) show evidence for the mixing of an isotopically depleted source and an EMI (Enriched mantle type I) pyroxenitic mantle. NCC rifting-stage basalts exhibit anomalously low MgO and Fe2O3T and high SiO2 and Al2O3, as well as low Dy/Yb and Y/Yb and high ɛHf at a given ɛNd, as compared to the postrifting basalts. Temporal compositional variations and their association with basin subsidence indicate that heterogeneity in the eastern NCC asthenospheric mantle is the primary driver for intraplate magmatism in this region. The specific magmatic sources shifted in terms of depth, related to lithospheric thinning and thickening in the eastern NCC. The NCC EMI mantle domain most likely developed due to ancient events, is persistent through time, and is not related to dehydration of the stagnant Pacific slab in the mantle transition zone. Based on the chemical signatures of postrifting basalts, contributions from the Pacific slab are likely to be carbonatite rich. Mantle metasomatism by carbonatite melts from the Pacific slab and the interaction of these melts at shallower depths with EMI pyroxenitic mantle domains to trigger melting are contributors to the observed low P wave velocity zone beneath eastern Eurasia.

  12. Thermal Stratification in Vertical Mantle Tanks

    Knudsen, Søren; Furbo, Simon


    It is well known that it is important to have a high degree of thermal stratification in the hot water storage tank to achieve a high thermal performance of SDHW systems. This study is concentrated on thermal stratification in vertical mantle tanks. Experiments based on typical operation conditions...... are carried out to investigate how the thermal stratification is affected by different placements of the mantle inlet. The heat transfer between the solar collector fluid in the mantle and the domestic water in the inner tank is analysed by CFD-simulations. Furthermore, the flow pattern in the vertical mantle...... tank is investigated....

  13. Diamond growth in mantle fluids

    Bureau, Hélène; Frost, Daniel J.; Bolfan-Casanova, Nathalie; Leroy, Clémence; Esteve, Imène; Cordier, Patrick


    In the upper mantle, diamonds can potentially grow from various forms of media (solid, gas, fluid) with a range of compositions (e.g. graphite, C-O-H fluids, silicate or carbonate melts). Inclusions trapped in diamonds are one of the few diagnostic tools that can constrain diamond growth conditions in the Earth's mantle. In this study, inclusion-bearing diamonds have been synthesized to understand the growth conditions of natural diamonds in the upper mantle. Diamonds containing syngenetic inclusions were synthesized in multi-anvil presses employing starting mixtures of carbonates, and silicate compositions in the presence of pure water and saline fluids (H2O-NaCl). Experiments were performed at conditions compatible with the Earth's geotherm (7 GPa, 1300-1400 °C). Results show that within the timescale of the experiments (6 to 30 h) diamond growth occurs if water and carbonates are present in the fluid phase. Water promotes faster diamond growth (up to 14 mm/year at 1400 °C, 7 GPa, 10 g/l NaCl), which is favorable to the inclusion trapping process. At 7 GPa, temperature and fluid composition are the main factors controlling diamond growth. In these experiments, diamonds grew in the presence of two fluids: an aqueous fluid and a hydrous silicate melt. The carbon source for diamond growth must be carbonate (CO32) dissolved in the melt or carbon dioxide species in the aqueous fluid (CO2aq). The presence of NaCl affects the growth kinetics but is not a prerequisite for inclusion-bearing diamond formation. The presence of small discrete or isolated volumes of water-rich fluids is necessary to grow inclusion-bearing peridotitic, eclogitic, fibrous, cloudy and coated diamonds, and may also be involved in the growth of ultradeep, ultrahigh-pressure metamorphic diamonds.

  14. Isotopic characterisation of the sub-continental lithospheric mantle beneath Zealandia, a rifted fragment of Gondwana

    Waight, Tod Earle; Scott, James M.; van der Meer, Quinten Har Adriaan


    and that contained a HIMU component. The volcanics have tapped two adjacent but chemically contrasting upper mantle domains: a fertile eastern domain and an extremely depleted western domain. Both domains underlie Mesozoic metasedimentary crust. Radiogenic isotope compositions of the clinopyroxene have 87Sr/86Sr......The greater New Zealand region, known as Zealandia, represents an amalgamation of crustal fragments accreted to the paleo-Pacific Gondwana margin and which underwent significant thinning during the subsequent split from Australia and Antarctica in the mid-Cretaceous following opening of the Tasman...

  15. Mantle plumes and continental tectonics.

    Hill, R I; Campbell, I H; Davies, G F; Griffiths, R W


    Mantle plumes and plate tectonics, the result of two distinct modes of convection within the Earth, operate largely independently. Although plumes are secondary in terms of heat transport, they have probably played an important role in continental geology. A new plume starts with a large spherical head that can cause uplift and flood basalt volcanism, and may be responsible for regional-scale metamorphism or crustal melting and varying amounts of crustal extension. Plume heads are followed by narrow tails that give rise to the familiar hot-spot tracks. The cumulative effect of processes associated with tail volcanism may also significantly affect continental crust.

  16. Upper mantle convection beneath northwest China and its adjacent region driven by density anomaly

    XU Ping; FU Rong-shan; HUANG Jian-ping; ZHAXian-jie; DAI Zhi-yang


    We assume that the density anomalies, which are transformed from seismic tomography data, are corresponding to temperature distribution in a convective mantle. We take density anomalies as the driving force for mantle convec tion and solve the basic equation with given boundary conditions in a wave-number domain by using the FFT arithmetic. Using the physical model of upper mantle convection and the seismic tomography data supplied by XU et al, we calculated upper mantle convection beneath northwestern China and adjacent region. The flow patterns in the upper mantle show that there are upward and divergent flows in the basin regions, such as Tarim, Qaidam,Junggar and Kazakhstan, where the lithosphere is thin. There are downward and convergent flows in the mountain regions,such as Tianshan, Kunlun and Qilian, where the lithosphere is thick. In addition, because of the divergent flow under the Tarim Basin the upper mantle material in this region is driven southward to the north part of Tibetan Plateau and northward to Tianshan Mountain. Maybe, it is one of the reasons for the recent uplift of the Tianshan Mountain.

  17. Seismic evidence for flow in the hydrated mantle wedge of the Ryukyu subduction zone

    Nagaya, Takayoshi; Walker, Andrew M.; Wookey, James; Wallis, Simon R.; Ishii, Kazuhiko; Kendall, J.-Michael


    It is widely accepted that water-rich serpentinite domains are commonly present in the mantle above shallow subducting slabs and play key roles in controlling the geochemical cycling and physical properties of subduction zones. Thermal and petrological models show the dominant serpentine mineral is antigorite. However, there is no good consensus on the amount, distribution and alignment of this mineral. Seismic velocities are commonly used to identify antigorite-rich domains, but antigorite is highly-anisotropic and depending on the seismic ray path, its properties can be very difficult to distinguish from non-hydrated olivine-rich mantle. Here, we utilize this anisotropy and show how an analysis of seismic anisotropy that incorporates measured ray path geometries in the Ryukyu arc can constrain the distribution, orientation and amount of antigorite. We find more than 54% of the wedge must consist of antigorite and the alignment must change from vertically aligned to parallel to the slab. This orientation change suggests convective flow in the hydrated forearc mantle. Shear wave splitting analysis in other subduction zones indicates large-scale serpentinization and forearc mantle convection are likely to be more widespread than generally recognized. The view that the forearc mantle of cold subduction zones is dry needs to be reassessed.

  18. Mantle contamination and the Izu-Bonin-Mariana (IBM) 'high-tide mark': evidence for mantle extrusion caused by Tethyan closure

    Flower, M. F. J.; Russo, R. M.; Tamaki, K.; Hoang, N.


    Western Pacific basins are characterized by three remarkable attributes: (1) complex kinematic histories linked to global-scale plate interactions; (2) DUPAL-like contaminated mantle; and (3) rapid post-Mesozoic rollback of the confining arc-trench systems. The coincidence of slab steepening, extreme arc curvature, and vigorous basin opening associated with the Mariana convergent margin suggests that rollback continues in response to an east-directed mantle 'wind'. Against a backdrop of conflicting kinematic and genetic interpretations we explore the notion that eastward asthenospheric flow driven by diachronous Tethyan closure caused stretching of eastern Eurasia and concomitant opening of western Pacific basins. Marking the eastern boundary of the latter, the Izu-Bonin-Mariana forearc may be regarded as a litho-tectonic 'high-tide mark' comprising igneous and metamorphic products from successive episodes (since ca. 45 Ma.) of arc sundering and backarc basin opening. The forearc also forms an isotopic boundary separating contaminated western Pacific mantle from the N-MORB Pacific Ocean reservoir. While the isotopic composition of western Pacific mantle resembles that feeding Indian Ocean hotspot and spreading systems, its spatial-temporal variation and the presence of subduction barriers to the south appear to preclude northward flow of Indian Ocean mantle and require an endogenous origin for sub-Eurasian contaminated mantle. It is concluded that the extrusion of Tethyan asthenosphere, contaminated by sub-Asian cratonic lithosphere, was a major cause of western Pacific arc rollback and basin opening. The model is consistent with paleomagnetic and geologic evidence supporting independent kinematic histories for constituent parts of the Philippine Sea and Sunda plates although interpretation of these is speculative. Compounded by effects of the Australia-Indonesia collision, late-Tethyan mantle extrusion appears to have produced the largest DUPAL domain in the

  19. A case for mantle plumes

    Geoffrey F. Davies


    The existence of at least several plumes in the Earth's mantle can be inferred with few assumptions from well-established observations. As well, thermal mantle plumes can be predicted from well-established and quantified fluid dynamics and a plausible assumption about the Earth's early thermal state. Some additional important observations, especially of flood basalts and rift-related magmatism, have been shown to be plausibly consistent with the physical theory. Recent claims to have detected plumes using seismic tomography may comprise the most direct evidence for plumes, but plume tails are likely to be difficult to resolve definitively and the claims need to be well tested. Although significant questions remain about its viability, the plume hypothesis thus seems to be well worth continued investigation. Nevertheless there are many non-plate-related magmatic phenomena whose association with plumes is unclear or unlikely. Compositional buoyancy has recently been shown potentially to substantially complicate the dynamics of plumes, and this may lead to explanations for a wider range of phenomena, including "headless" hotspot tracks, than purely thermal plumes.

  20. Numerical modeling of mantle plume diffusion

    Krupsky, D.; Ismail-Zadeh, A.


    To clarify the influence of the heat diffusion on the mantle plume evolution, we develop a two-dimensional numerical model of the plume diffusion and relevant efficient numerical algorithm and code to compute the model. The numerical approach is based on the finite-difference method and modified splitting algorithm. We consider both von Neumann and Direchlet conditions at the model boundaries. The thermal diffusivity depends on pressure in the model. Our results show that the plume is disappearing from the bottom up - the plume tail at first and its head later - because of the mantle plume geometry (a thin tail and wide head) and higher heat conductivity in the lower mantle. We study also an effect of a lateral mantle flow associated with the plate motion on the distortion of the diffusing mantle plume. A number of mantle plumes recently identified by seismic tomography seem to disappear in the mid-mantle. We explain this disappearance as the effect of heat diffusion on the evolution of mantle plume.

  1. Deep Mantle Seismic Modeling and Imaging

    Lay, Thorne; Garnero, Edward J.


    Detailed seismic modeling and imaging of Earth's deep interior is providing key information about lower-mantle structures and processes, including heat flow across the core-mantle boundary, the configuration of mantle upwellings and downwellings, phase equilibria and transport properties of deep mantle materials, and mechanisms of core-mantle coupling. Multichannel seismic wave analysis methods that provide the highest-resolution deep mantle structural information include network waveform modeling and stacking, array processing, and 3D migrations of P- and S-wave seismograms. These methods detect and identify weak signals from structures that cannot be resolved by global seismic tomography. Some methods are adapted from oil exploration seismology, but all are constrained by the source and receiver distributions, long travel paths, and strong attenuation experienced by seismic waves that penetrate to the deep mantle. Large- and small-scale structures, with velocity variations ranging from a fraction of a percent to tens of percent, have been detected and are guiding geophysicists to new perspectives of thermochemical mantle convection and evolution.

  2. Heat transfer correlations in mantle tanks

    Furbo, Simon; Knudsen, Søren


    Small solar domestic hot water systems are best designed as low flow systems based on vertical mantle tanks. Theoretical investigations of the heat transfer in differently designed vertical mantle tanks during different operation conditions have been carried out. The investigations are based...... of the inner hot water tank and the domestic water in all levels of the tank. The heat transfer analysis showed that the heat transfer near the mantle inlet port between the solar collector fluid in the mantle and the walls surrounding the mantle is in the mixed convection regime, and as the distance from...... the inlet increases, natural convection starts to dominate. The heat transfer between the wall of the inner hot water tank and the domestic water is governed by natural convection. The results of the CFD-calculations are used to determine improved heat transfer correlations based on dimensionless analysis...

  3. Viscosity jump in Earth's mid-mantle.

    Rudolph, Maxwell L; Lekić, Vedran; Lithgow-Bertelloni, Carolina


    The viscosity structure of Earth's deep mantle affects the thermal evolution of Earth, the ascent of mantle plumes, settling of subducted oceanic lithosphere, and the mixing of compositional heterogeneities in the mantle. Based on a reanalysis of the long-wavelength nonhydrostatic geoid, we infer viscous layering of the mantle using a method that allows us to avoid a priori assumptions about its variation with depth. We detect an increase in viscosity at 800- to 1200-kilometers depth, far greater than the depth of the mineral phase transformations that define the mantle transition zone. The viscosity increase is coincident in depth with regions where seismic tomography has imaged slab stagnation, plume deflection, and changes in large-scale structure and offers a simple explanation of these phenomena.

  4. Domain analysis

    Hjørland, Birger


    The domain-analytic approach to knowledge organization (KO) (and to the broader field of library and information science, LIS) is outlined. The article reviews the discussions and proposals on the definition of domains, and provides an example of a domain-analytic study in the field of art studie....... Varieties of domain analysis as well as criticism and controversies are presented and discussed....

  5. Sinking of spherical slablets through a non-Newtonian mantle

    Crameri, Fabio; Stegman, Dave; Petersen, Robert; Tackley, Paul


    The dominant driving force for plate tectonics is slab pull, in which sinking slabs pull the trailing plate. Forward plate velocities are typically similar in magnitude (7 cm/yr) as estimates for sinking velocities of slabs through the upper mantle. However, these estimates are based on data for slabs that are coherent into the transition zone as well as models that considered the upper mantle to be entirely Newtonian. Dislocation creep in the upper mantle can strongly influence mantle flow, and is likely activated for flow around vertically sinking slabs in the uppermost mantle. Thus, it is possible that in some scenarios, a non-Newtonian mantle will have an influence on plate motions but it is unclear to what degree. To address this question, we investigate how the non-Newtonian rheology modifies the sinking velocities of slablets (spherical, negatively buoyant and highly viscous blobs). The model set-up is similar to a Stokes sphere sinking, but is in 2-D cartesian with temperature-and stress-dependent rheology. For these numerical models, we use the Stag-YY code (e.g., Tackley 2008) and apply a pseudo-free surface using the 'sticky-air' approach (Matsumoto and Tomoda 1983; Schmeling et al, 2008, Crameri et al., 2012). The sinking blob is both highly viscous and compositionally dense, but is the same temperature as the background fluid which eliminates thermal diffusion and associated variations in thermal buoyancy. The model domain is 2x1 or 4x1 and allows enough distance to the sidewalls so that sinking velocities are not influenced by the boundary conditions. We compare our results with those previously obtained for salt diapirs rising through a power-law rheology mantle/crust (Weinberg, 1993; Weinberg and Podladchikov, 1994), which provided both numerical and analytic results. Previous results indicate a speed-up of an order of magnitude is possible. Finally, we then extend the models and analysis to mantle convection systems that include for single

  6. Upper and mid mantle fabric developing during subduction-induced mantle flow

    Faccenda, Manuele


    Subduction zones are convergent margins where the rigid lithosphere sinks into the Earth's mantle inducing complex 3D flow patterns. Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. We computed the seismic anisotropy of the upper and mid mantle due to strain-induced LPO in 3D mechanical models of dynamic subduction by using, respectively, D-Rex and Underworld. Subsequently, FSTRACK was used to compute seismogram synthetics and SKS splitting patterns. Strong anisotropy develops in the upper mantle, while weak or null seismic anisotropy is formed in the upper transition zone/lower mantle and lower transition zone, respectively. The distribution of the fabric in the mantle depends on the distribution and amount of the deformation, and not on the rate at which the slab subducts. The SKS splitting patterns are controlled by the anisotropy in the upper mantle because SKS waves are more sensitive to the anisotropy in the shallowest layers. Horizontally propagating shear waves in the mid mantle originating from local earthquakes are characterized by significant splitting that is mostly due to the fabric in the uppermost lower mantle. We discuss the implications of our results for real subduction settings like Tonga, where a discrete amount of observations have been collected in the past 10 years on the anisotropy in the upper and mid mantle.

  7. Mantle wedge dynamics from seismic anisotropy (Invited)

    Long, M. D.; Wirth, E. A.


    The mantle wedge above subducting slabs plays a critical role in many of the physical processes associated with subduction, including water transport into the upper mantle and the generation and transport of melts. Our understanding of mantle wedge dynamics is incomplete; in particular, the mantle flow field above subducting slabs remains poorly understood. Because seismic anisotropy is a consequence of deformation, observations of anisotropy (such as shear wave splitting and P-to-SH converted waves) can constrain the geometry of the wedge flow field. Additionally, because the presence of water (either in nominally anhydrous minerals or as hydrous phases) can have a large effect on anisotropic structure, a detailed understanding of mantle wedge anisotropy can help to constrain processes related to water cycling in subduction systems. We present a global, synoptic view of anisotropy observations in subduction zone mantle wedges, compiled from a large number of individual studies, with the goal of understanding the first-order controls on wedge anisotropy and flow patterns. This compilation allows us to explicitly test the predictions made by many different conceptual models for wedge anisotropy, as well as to explore the relationships between observed anisotropy parameters and other parameters that describe subduction. We find that no simple model can explain all of the trends observed in the global data set. Mantle wedge flow is likely controlled by a combination of downdip motion of the slab, trench migration, ambient mantle flow, small-scale convection, proximity to slab edges, and slab morphology, with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology. There is also a likely contribution from B-type olivine and/or serpentinite fabric in many subduction zones, governed by the local thermal structure and volatile distribution.

  8. Primary magmas and mantle temperatures through time

    Ganne, Jérôme; Feng, Xiaojun


    Chemical composition of mafic magmas is a critical indicator of physicochemical conditions, such as pressure, temperature, and fluid availability, accompanying melt production in the mantle and its evolution in the continental or oceanic lithosphere. Recovering this information has fundamental implications in constraining the thermal state of the mantle and the physics of mantle convection throughout the Earth's history. Here a statistical approach is applied to a geochemical database of about 22,000 samples from the mafic magma record. Potential temperatures (Tps) of the mantle derived from this database, assuming melting by adiabatic decompression and a Ti-dependent (Fe2O3/TiO2 = 0.5) or constant redox condition (Fe2+/∑Fe = 0.9 or 0.8) in the magmatic source, are thought to be representative of different thermal "horizons" (or thermal heterogeneities) in the ambient mantle, ranging in depth from a shallow sublithospheric mantle (Tp minima) to a lower thermal boundary layer (Tp maxima). The difference of temperature (ΔTp) observed between Tp maxima and minima did not change significantly with time (˜170°C). Conversely, a progressive but limited cooling of ˜150°C is proposed since ˜2.5 Gyr for the Earth's ambient mantle, which falls in the lower limit proposed by Herzberg et al. [2010] (˜150-250°C hotter than today). Cooling of the ambient mantle after 2.5 Ga is preceded by a high-temperature plateau evolution and a transition from dominant plumes to a plate tectonics geodynamic regime, suggesting that subductions stabilized temperatures in the Archaean mantle that was in warming mode at that time.abstract type="synopsis">Plain Language SummaryThe Earth's upper mantle constitutes a major interface between inner and outer envelops of the planet. We explore at high resolution its thermal state evolution (potential temperature of the ambient mantle, Tp) in depth and time using a multi-dimensional database of mafic lavas chemistry (>22,000 samples formed in

  9. Contrasting origins of the upper mantle revealed by hafnium and lead isotopes from the Southeast Indian Ridge.

    Hanan, Barry B; Blichert-Toft, Janne; Pyle, Douglas G; Christie, David M


    The origin of the isotopic signature of Indian mid-ocean ridge basalts has remained enigmatic, because the geochemical composition of these basalts is consistent either with pollution from recycled, ancient altered oceanic crust and sediments, or with ancient continental crust or lithosphere. The radiogenic isotopic signature may therefore be the result of contamination of the upper mantle by plumes containing recycled altered ancient oceanic crust and sediments, detachment and dispersal of continental material into the shallow mantle during rifting and breakup of Gondwana, or contamination of the upper mantle by ancient subduction processes. The identification of a process operating on a scale large enough to affect major portions of the Indian mid-ocean ridge basalt source region has been a long-standing problem. Here we present hafnium and lead isotope data from across the Indian-Pacific mantle boundary at the Australian-Antarctic discordance region of the Southeast Indian Ridge, which demonstrate that the Pacific and Indian upper mantle basalt source domains were each affected by different mechanisms. We infer that the Indian upper-mantle isotope signature in this region is affected mainly by lower continental crust entrained during Gondwana rifting, whereas the isotope signature of the Pacific upper mantle is influenced predominantly by ocean floor subduction-related processes.

  10. Retrospective Analysis and Thoughts on the Work of Refertility in the Worst-Hit Area of Wenchuan Earthquake in Sichuan Province%四川汶川地震极重灾区再生育工作回顾性分析与思考

    刘琼; 宋涛; 胡春


    Objective To analyze the pregnancy and spontaneous abortion of the refertility women in the worst hit area of Wenchuan earthquake in Sichuan province, and explore the influence of the earthquake disaster, age and other factors on the pregnancy and the result of pregnancy. Methods From May 2008 to March 2010,the whole service work of refertility in the 5 · 12 worst hit area of Wenchuan earthquake in Sichuan province were summed up, and 860 women who had the willing of refertility were included in the study. They were divided into age<35 years old group (n = 323) ,35 39 years old group(n = 270) , and ≥40 years old group(n = 267) according to their age. Analyzed their pregnancy, results of pregnancy and other influencing factors by retrospective method. The study protocol was approved by the Ethical Review Board of Investigation in Human Being of Birth Control Service Station of Mianzhu. Results Among these 860 women, 704 cases had successful pregnancy. The pregnant rate was 81. 86% (704/860). Meanwhile, the spontaneous abortion rate was 19. 32%(136/704) ,and the older they were, the higher spontaneous abortion rate was. The pregnant rates of the refertility women in ≥ 40 years old group was obviously lower than those of <35 years old group and 35 39 years old group(P<0. 05). Conclusion The spontaneous abortion rates of the refertility women in the earthquake disaster area are obviously higher than those of normal pregnancy women [19. 32% vs. (10% 15%)] because of the comprehensive factors. So immediately and effective comprehensive measures of prevention and intervention were necessary to improve the pregnancy rate and decline the spontaneous abortion rate.%目的 分析四川汶川地震极重灾区再生育妇女妊娠及流产情况,探讨地震灾害、年龄及其他因素对再生育妇女妊娠及妊娠结局的影响.方法 选取2008年5月至2010年3月来自汶川地震极重灾区的860例有再生育意愿的妇女为研究

  11. LAB as Boundary Between Fossil and Present-day Mantle Seismic Anisotropy

    Plomerova, J.; Babuska, V.


    Besides the importance of the crust-mantle boundary discovered by Mohorovicic hundred years ago, the significance of the first-order active upper mantle boundary between the lithosphere and asthenospere has been increasing during several last decades, after a general acceptance of the Earth’s plate-tectonic concept. Topology of the lithosphere-asthenosphere boundary (LAB) and structure of the continental lithosphere record the geodynamic development of outer parts of the Earth. Knowledge of the Moho relief and of crustal velocities is crucial for the LAB and lithosphere modelling, as the upper mantle studies require applying proper crustal corrections. We present a uniform updated model of the European lithosphere-asthenosphere boundary recalculated from data collected during our regional studies of seismic anisotropy and other tomographic experiments, and show results of mapping of large-scale domains of mantle lithosphere characterized by uniform fossil fabrics. Thanks to a long memory of the fabric of the deep continental lithosphere, we define the LAB as a boundary between a fossil anisotropy in the mantle lithosphere and an underlying seismic anisotropy related to present-day flow in the asthenosphere. Analysis of static terms of teleseismic P-wave travel time deviations shows the LAB topology is more distinct beneath the Phanerozoic part of Europe compared with its Precambrian part. The LAB deepens down to ~220 km beneath the two Alpine roots, the South Carpathians and eastward of the Trans-European Suture Zone. Decomposition of the relative residuals into the static and directional-dependent terms of P residuals, shear-wave splitting analysis and joint inversion of the anisotropic parameters, reveal the mantle lithosphere consists of domains with consistent olivine fabrics, which can be modelled by peridotite aggregates with plunging foliation or lineation. Changes of the fossil fabric allow us to map the domain boundaries within the mantle lithosphere. We

  12. Characteristics of Vertical Mantle Heat Exchangers for Solar Water Heaters

    Shah, Louise Jivan; Morrison, G.L.; Behnia, M.


    exchangers was also developed for detailed evaluation of the heat flux distribution over the mantle surface. Both the experimental and simulation results indicate that distribution of the flow around the mantle gap is governed by buoyancy driven recirculation in the mantle. The operation of the mantle...

  13. Trace-element geochemistry of mantle olivine and application to mantle petrogenesis and geothermobarometry

    De Hoog, Cees-Jan; Gall, Louise; Cornell, David H.


    Trace-element compositions of olivine from 75 mantle rocks of diverse origin, including xenoliths from kimberlites, basaltic lavas and orogenic peridotites, were determined by laser ablation ICP-MS to study systematic variations between mantle lithologies, partitioning mechanisms in olivine and their potential for geothermobarometry and unravelling mantle processes. Samples were selected to cover a wide range of forsterite contents (89.1-93.4), equilibration temperatures and pressures (750-14...

  14. Thermoconvective waves in the earth's mantle

    Birger, B. I.


    The thermoconvective instability of the Earth's mantle is analysed. The mantle is modelled as an infinite horizontal layer with a free upper surface, heated from below. The creep in the mantle is supposed to be transient when strains are small. This transient creep is described by Lomnitz's law modified by Jeffreys (1958a). It is shown that disturbances, in the form of thermoconvective waves with a period of 10 8 - 10 9y and wavelength of the order 10 3 km, can propagate through the mantle without attenuation. These waves induce oscillations of the Earth's surface. The pattern of flows differs greatly from that suggested by plate tectonics. An attempt is made to give a new explanation for the linear magnetic anomalies over oceanic ridges.

  15. Can mantle convection be self-regulated?

    Korenaga, Jun


    The notion of self-regulating mantle convection, in which heat loss from the surface is constantly adjusted to follow internal radiogenic heat production, has been popular for the past six decades since Urey first advocated the idea. Thanks to its intuitive appeal, this notion has pervaded the solid earth sciences in various forms, but approach to a self-regulating state critically depends on the relation between the thermal adjustment rate and mantle temperature. I show that, if the effect of mantle melting on viscosity is taken into account, the adjustment rate cannot be sufficiently high to achieve self-regulation, regardless of the style of mantle convection. The evolution of terrestrial planets is thus likely to be far from thermal equilibrium and be sensitive to the peculiarities of their formation histories. Chance factors in planetary formation are suggested to become more important for the evolution of planets that are more massive than Earth.

  16. How mantle slabs drive plate tectonics.

    Conrad, Clinton P; Lithgow-Bertelloni, Carolina


    The gravitational pull of subducted slabs is thought to drive the motions of Earth's tectonic plates, but the coupling between slabs and plates is not well established. If a slab is mechanically attached to a subducting plate, it can exert a direct pull on the plate. Alternatively, a detached slab may drive a plate by exciting flow in the mantle that exerts a shear traction on the base of the plate. From the geologic history of subduction, we estimated the relative importance of "pull" versus "suction" for the present-day plates. Observed plate motions are best predicted if slabs in the upper mantle are attached to plates and generate slab pull forces that account for about half of the total driving force on plates. Slabs in the lower mantle are supported by viscous mantle forces and drive plates through slab suction.


    Shah, Louise Jivan; Morrison, G.L.; Behnia, Masud


    Characteristics of vertical mantle heat exchanger tanks for SDHW systems have been investigated experimentally and theoretically using particle image velocimetry (PIV) and CFD modelling. A glass model of a mantle heat exchanger tank was constructed so that the flow distribution in the mantle could...... be studied using the PIV test facility. Two transient three-dimensional CFD-models of the glass model mantle tank were developed using the CFD-programmes CFX and FLUENT.The experimental results illustrate that the mantle flow structure in the mantle is complicated and the distribution of flow in the mantle...

  18. Comparisons between radioactive and non-radioactive gas lantern mantles.

    Furuta, E; Yoshizawa, Y; Aburai, T


    Gas lantern mantles containing radioactive thorium have been used for more than 100 years. Although thorium was once believed to be indispensable for giving a bright light, non-radioactive mantles are now available. From the radioactivities of the daughter nuclides, we estimated the levels of radioactivity of 232Th and 228Th in 11 mantles. The mantles contained various levels of radioactivity from background levels to 1410 +/- 140 Bq. Our finding that radioactive and non-radioactive mantles are equally bright suggests that there is no advantage in using radioactive mantles. A remaining problem is that gas lantern mantles are sold without any information about radioactivity.

  19. Influence of the Ringwoodite-Perovskite transition on mantle convection in spherical geometry as a function of Clapeyron slope and Rayleigh number

    M. Wolstencroft


    Full Text Available We investigate the influence on mantle convection of the negative Clapeyron slope ringwoodite to perovskite and ferro-periclase mantle phase transition, which is correlated with the seismic discontinuity at 660 km depth. In particular, we focus on understanding the influence of the magnitude of the Clapeyron slope (as measured by the Phase Buoyancy parameter, P and the vigour of convection (as measured by the Rayleigh number, Ra on mantle convection. We have undertaken 76 simulations of isoviscous mantle convection in spherical geometry, varying Ra and P. Three domains of behaviour were found: layered convection for high Ra and more negative P, whole mantle convection for low Ra and less negative P, and transitional behaviour in an intervening domain. The boundary between the layered and transitional domain was fit by a curve P = α Raβ where α = −1.05, and β = −0.1, and the fit for the boundary between the transitional and whole mantle convection domain was α = −4.8, and β = −0.25. These two curves converge at Ra ≈ 2.5 × 104 (well below Earth mantle vigour and P ≈ −0.38. Extrapolating to high Ra, which is likely earlier in Earth history, this work suggests a large transitional domain. It is therefore likely that convection in the Archean would have been influenced by this phase change, with Earth being at least in the transitional domain, if not the layered domain.

  20. Subduction and volatile recycling in Earth's mantle

    King, S. D.; Ita, J. J.; Staudigel, H.


    The subduction of water and other volatiles into the mantle from oceanic sediments and altered oceanic crust is the major source of volatile recycling in the mantle. Until now, the geotherms that have been used to estimate the amount of volatiles that are recycled at subduction zones have been produced using the hypothesis that the slab is rigid and undergoes no internal deformation. On the other hand, most fluid dynamical mantle flow calculations assume that the slab has no greater strength than the surrounding mantle. Both of these views are inconsistent with laboratory work on the deformation of mantle minerals at high pressures. We consider the effects of the strength of the slab using two-dimensional calculations of a slab-like thermal downwelling with an endothermic phase change. Because the rheology and composition of subducting slabs are uncertain, we consider a range of Clapeyron slopes which bound current laboratory estimates of the spinel to perovskite plus magnesiowustite phase transition and simple temperature-dependent rheologies based on an Arrhenius law diffusion mechanism. In uniform viscosity convection models, subducted material piles up above the phase change until the pile becomes gravitationally unstable and sinks into the lower mantle (the avalanche). Strong slabs moderate the 'catastrophic' effects of the instabilities seen in many constant-viscosity convection calculations; however, even in the strongest slabs we consider, there is some retardation of the slab descent due to the presence of the phase change.

  1. Archimedean Proof of the Physical Impossibility of Earth Mantle Convection

    Herndon, J Marvin


    Eight decades ago, Arthur Holmes introducted the idea of mantle convection as a mechanism for continental drift. Five decades ago, continental drift was modified to become plate tectonics theory, which included mantle convection as an absolutely critical component. Using the submarine design and operation concept of "neutral buoyancy", which follows from Archimedes' discoveries, the concept of mantle convection is proven to be incorrect, concomitantly refuting plate tectonics, refuting all mantle convection models, and refuting all models that depend upon mantle convection.

  2. Teaching machines to find mantle composition

    Atkins, Suzanne; Tackley, Paul; Trampert, Jeannot; Valentine, Andrew


    The composition of the mantle affects many geodynamical processes by altering factors such as the density, the location of phase changes, and melting temperature. The inferences we make about mantle composition also determine how we interpret the changes in velocity, reflections, attenuation and scattering seen by seismologists. However, the bulk composition of the mantle is very poorly constrained. Inferences are made from meteorite samples, rock samples from the Earth and inferences made from geophysical data. All of these approaches require significant assumptions and the inferences made are subject to large uncertainties. Here we present a new method for inferring mantle composition, based on pattern recognition machine learning, which uses large scale in situ observations of the mantle to make fully probabilistic inferences of composition for convection simulations. Our method has an advantage over other petrological approaches because we use large scale geophysical observations. This means that we average over much greater length scales and do not need to rely on extrapolating from localised samples of the mantle or planetary disk. Another major advantage of our method is that it is fully probabilistic. This allows us to include all of the uncertainties inherent in the inference process, giving us far more information about the reliability of the result than other methods. Finally our method includes the impact of composition on mantle convection. This allows us to make much more precise inferences from geophysical data than other geophysical approaches, which attempt to invert one observation with no consideration of the relationship between convection and composition. We use a sampling based inversion method, using hundreds of convection simulations run using StagYY with self consistent mineral physics properties calculated using the PerpleX package. The observations from these simulations are used to train a neural network to make a probabilistic inference

  3. Shear wave splitting and subcontinental mantle deformation

    Silver, Paul G.; Chan, W. Winston


    We have made measurements of shear wave splitting in the phases SKS and SKKS at 21 broadband stations in North America, South America, Europe, Asia, and Africa. Measurements are made using a retrieval scheme that yields the azimuth of the fast polarization direction ϕ and delay time δt of the split shear wave plus uncertainties. Detectable anisotropy was found at most stations, suggesting that it is a general feature of the subcontinental mantle. Delay times range from 0.65 s to 1.70 s and average about 1 s. Somewhat surprisingly, the largest delay time is found in the 2.7 b.y.-old Western Superior Province of the Canadian Shield. The splitting observations are interpreted in terms of the strain-induced lattice preferred orientation of mantle minerals, especially olivine. We consider three hypotheses concerning the origin of the continental anisotropy: (1) strain associated with absolute plate motion, as in the oceanic upper mantle, (2) crustal stress, and (3) the past and present internal deformation of the subcontinental upper mantle by tectonic episodes. It is found that the last hypothesis is the most successful, namely that the most recent significant episode of internal deformation appears to be the best predictor of ϕ. For stable continental regions, this is interpreted as "fossil" anisotropy, whereas for presently active regions, such as Alaska, the anisotropy reflects present-day tectonic activity. In the stable portion of North America there is a good correlation between delay time and lithospheric thickness; this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant. The acceptance of this hypothesis has several implications for subcontinental mantle deformation. First, it argues for coherent deformation of the continental lithosphere (crust and mantle) during orogenies. This implies that the anisotropic portion of the lithosphere was present since the

  4. Multiscale seismic tomography and mantle dynamics

    Zhao, Dapeng


    Multiscale (local, regional and global) tomographic studies are made to determine the 3-D structure of the Earth, particularly for imaging mantle plumes and subducting slabs. Plume-like slow anomalies are clearly visible under the major hotspot regions in most parts of the mantle, in particular, under Hawaii, Iceland, Kerguelen, South Pacific and Africa (Zhao, 2001, 2004, 2009). The slow anomalies under South Pacific and Africa have lateral extensions of over 1000 km and exist in the entire mantle, representing two superplumes. The Pacific superplume has a larger spatial extent and stronger slow anomalies than that of the Africa superplume. The Hawaiian plume is not part of the Pacific superplume but an independent whole-mantle plume (Zhao, 2004, 2009). The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, suggesting that plumes are not fixed in the mantle but can be deflected by the mantle flow. As a consequence, hotspots are not really fixed but can wander on the Earth's surface, as evidenced by the recent paleomagnetic and numeric modeling studies. Wider and more prominent slow anomalies are visible at the core-mantle boundary (CMB) than most of the lower mantle, and there is a good correlation between the distribution of slow anomalies at the CMB and that of hotspots on the surface, suggesting that most of the strong mantle plumes under the hotspots originate from the CMB. However, there are some small-scaled, weak plumes originating from the transition zone or mid mantle depths (Zhao et al., 2006; Zhao, 2009; Lei et al., 2009; Gupta et al., 2009). Clear images of subducting slabs and magma chambers in the upper-mantle wedge beneath active arc volcanoes are obtained, indicating that geodynamic systems associated with arc magmatism and back-arc spreading are related to deep processes, such as convective circulation in the mantle wedge and dehydration reactions of the subducting slab (Zhao et al., 2002, 2007

  5. Slab mantle dehydrates beneath Kamchatka—Yet recycles water into the deep mantle

    Konrad-Schmolke, Matthias; Halama, Ralf; Manea, Vlad C.


    The subduction of hydrated slab mantle is the most important and yet weakly constrained factor in the quantification of the Earth's deep geologic water cycle. The most critical unknowns are the initial hydration state and the dehydration behavior of the subducted oceanic mantle. Here we present a combined thermomechanical, thermodynamic, and geochemical model of the Kamchatka subduction zone that indicates significant dehydration of subducted slab mantle beneath Kamchatka. Evidence for the subduction of hydrated oceanic mantle comes from across-arc trends of boron concentrations and isotopic compositions in arc volcanic rocks. Our thermodynamic-geochemical models successfully predict the complex geochemical patterns and the spatial distribution of arc volcanoes in Kamchatka assuming the subduction of hydrated oceanic mantle. Our results show that water content and dehydration behavior of the slab mantle beneath Kamchatka can be directly linked to compositional features in arc volcanic rocks. Depending on hydration depth of the slab mantle, our models yield water recycling rates between 1.1 × 103 and 7.4 × 103 Tg/Ma/km corresponding to values between 0.75 × 106 and 5.2 × 106 Tg/Ma for the entire Kamchatkan subduction zone. These values are up to one order of magnitude lower than previous estimates for Kamchatka, but clearly show that subducted hydrated slab mantle significantly contributes to the water budget in the Kamchatkan subduction zone.

  6. Mantle strength of the San Andreas fault system and the role of mantle-crust feedbacks

    Chatzaras, V.; Tikoff, B.; Newman, J.; Withers, A.C.; Drury, M.R.


    In lithospheric-scale strike-slip fault zones, upper crustal strength is well constrained from borehole observations and fault rock deformation experiments, but mantle strength is less well known. Using peridotite xenoliths, we show that the upper mantle below the San Andreas fault system (Californi

  7. a View of the Marble-Cake Mantle from the Southeast Indian Ridge

    Hanan, B. B.; Graham, D. W.; Hemond, C.; Blichert-Toft, J.; Albarede, F.


    Along the Southeast Indian Ridge, variations in axial depth, crustal thickness, hydrothermal venting [1], basaltic major elements and U-series disequilibria [2] all indicate a west-to-east decrease in magma supply and mantle temperature from the Amsterdam-St. Paul hotspot to the Australian-Antarctic Discordance. Paired Hf-Pb isotopes in closely spaced glasses (5-10 km) from 81-100°E define two populations revealing compositional streaks in the upper mantle [3]. The number density of the streaks follows a Poisson distribution with a characteristic thickness of ~20 km. K/Ti and Na8 do not correlate with Pb or Hf isotopes, and both isotopic domains encompass N- and E-MORB types indicating the variations represent mantle source heterogeneities. 3He/4He varies from 7.5 - 10.2 RA, more than half the range in global MORB away from hotspot influence [4]. No systematic relationship exists between 3He/4He and Pb or Hf isotopes. A general negative correlation between K/Ti and Fe8 for the SEIR resembles that for MORBs globally, with higher K/Ti associated with lower 3He/4He. Collectively the observations suggest the presence of lithologically heterogeneous mantle. Lower 3He/4He derives from a source containing a few percent pyroxenite or ecologite, while 3He/4He > 9 RA arises from peridotite. Mantle convection has folded together distinct composite reservoirs of heterogeneous mantle, and stretched them into streaks that remain discernible units. The mantle 'unit' giving rise to each MORB sample represents a 'mixture of mixtures' with a multi-stage mixing history. Spectral analysis of the length scales of Hf, Pb and He isotopic variability allows a visual representation of this upper mantle 'texture'. The dominant length scales reflect large (1000, 500 km) and regional scale (100-150 km) structures in mantle flow, and sampling of heterogeneities during partial melting (20-30 km). 1-Baker et al., doi:10.1002/2014GC005344; 2-Russo et al., doi:10.1016/j.epsl.2008.11.016; 3-Hanan

  8. Geochemical evolution of lithospheric mantle underlying Intrasudetic Fault (SW Poland).

    Ćwiek, Mateusz; Matusiak-Małek, Magdalena; Puziewicz, Jacek; Ntaflos, Theodoros


    The Pilchowice basanite (SW Poland) forms volcanic plug located exactly on Intrasudetic Fault, which is one of the major tectonic lines in northern part of the Bohemian Massif. It originated during the formation of Variscan Orogen and marks the contact between two different crustal domains. The basanite is rhönite-bearing (Ladenberger et al., 2005. Min.Pol-Spec. Pap.) and contains small (JoP), which is in an opposition to modal content of clinopyroxene (0-4.1 vol.%). This suggests, that clinopyroxene is a "stealth" metasomatic phase (O'Reillly and Griffin, 2013, Springer). As trace element composition of clinopyroxene shows features typical for reaction with alkaline silicate melt (negative inflection at the most incompatible trace elements) and carbonatite (Ti, Zr, Hf anomalies), we suggest that majority of xenoliths were metasomatized by the an agent being a carbonatite-silicate melt or by CO2-bearing alkaline silicate melt. Xenolith where clinopyroxene shows constant enrichment in LREE may represent a part of mantle affected by pure carbonatitic metasomatism. Xenoliths with the lowest Fo content in olivine are probably cumulates of mafic silicate melt. Intergranular aggregates originated during reaction between primary phases and infiltrating, possibly mafic melt. The "glassy patch" might be a product of complete breakdown of amphibole in upper mantle conditions (Shaw, 2009, Lithos). However, presence of rhönite in host basanite suggests that some amphibole might have been broken also in lower pressures. Chemical composition of peridotites from Pilchowice resembles that recorded by group A mantle xenoliths from Krzeniów (Matusiak-Małek et al., 2014, JoP). In Pilchowice we have described the first xenolith affected by purely carbonatitic metasomatism. We also suggest that hydrous phases might have been present in upper mantle beneath this Pilchowice, which is believed to be nominally anhydrous (Puziewicz et al., 2015, IJES, DOI 10.1007/s00531

  9. Melting and Crystallization at Core Mantle Boundary

    Fiquet, G.; Pradhan, G. K.; Siebert, J.; Auzende, A. L.; Morard, G.; Antonangeli, D.; Garbarino, G.


    Early crystallization of magma oceans may generate original compositional heterogeneities in the mantle. Dense basal melts may also be trapped in the lowermost mantle and explain mantle regions with ultralow seismic velocities (ULVZs) near the core-mantle boundary [1]. To test this hypothesis, we first constructed the solidus curve of a natural peridotite between 36 and 140 gigapascals using laser-heated diamond anvil cells. In our experiments, melting at core-mantle boundary pressures occurs around 4100 ± 150 K, which is a value that can match estimated mantle geotherms. Similar results were found for a chondritic mantle [2] whereas much lower pyrolitic melting temperatures were recently proposed from textural and chemical characterizations of quenched samples [3]. We also investigated the melting properties of natural mid ocean ridge basalt (MORB) up to core-mantle boundary (CMB) pressures. At CMB pressure (135 GPa), we obtain a MORB solidus temperature of 3950 ±150 K. If our solidus temperatures are in good agreement with recent results proposed for a similar composition [4], the textural and chemical characterizations of our recovered samples made by analytical transmission electron microscope indicate that CaSiO3 perovskite (CaPv) is the liquidus phase in the entire pressure range up to CMB. The partial melt composition is enriched in FeO, which suggests that such partial melts could be gravitationnally stable at the core mantle boundary. Our observations are tested against calculations made using a self-consistent thermodynamic database for the MgO-FeO-SiO2 system from 20 GPa to 140 GPa [5]. These observations and calculations provide a first step towards a consistent thermodynamic modelling of the crystallization sequence of the magma ocean, which shows that the existence of a dense iron rich and fusible layer above the CMB at the end of the crystallization is plausible [5], which is in contradiction with the conclusions drawn in [4]. [1] Williams

  10. The He isotope composition of the earliest picrites erupted by the Ethiopia plume, implications for mantle plume source

    Stuart, Finlay; Rogers, Nick; Davies, Marc


    The earliest basalts erupted by mantle plumes are Mg-rich, and typically derived from mantle with higher potential temperature than those derived from the convecting upper mantle at mid-ocean ridges and ocean islands. The chemistry and isotopic composition of picrites from CFB provide constraints on the composition of deep Earth and thus the origin and differentiation history. We report new He-Sr-Nd-Pb isotopic composition of the picrites from the Ethiopian flood basalt province from the Dilb (Chinese Road) section. They are characterized by high Fe and Ti contents for MgO = 10-22 wt. % implying that the parent magma was derived from a high temperature low melt fraction, most probably from the Afar plume head. The picrite 3He/4He does not exceed 21 Ra, and there is a negative correlation with MgO, the highest 3He/4He corresponding to MgO = 15.4 wt. %. Age-corrected 87Sr/86Sr (0.70392-0.70408) and 143Nd/144Nd (0.512912-0.512987) display little variation and are distinct from MORB and OIB. Age-corrected Pb isotopes display a significant range (e.g. 206Pb/204Pb = 18.70-19.04) and plot above the NHRL. These values contrast with estimates of the modern Afar mantle plume which has lower 3He/4He and Sr, Nd and Pb isotope ratios that are more comparable with typical OIB. These results imply either interaction between melts derived from the Afar mantle plume and a lithospheric component, or that the original Afar mantle plume had a rather unique radiogenic isotope composition. Regardless of the details of the origins of this unusual signal, our observations place a minimum 3He/4He value of 21 Ra for the Afar mantle plume, significantly greater than the present day value of 16 Ra, implying a significant reduction over 30 Myr. In addition the Afar source was less degassed than convecting mantle but more degassed than mantle sampled by the proto-Iceland plume (3He/4He ~50 Ra). This suggests that the largest mantle plumes are not sourced in a single deep mantle domain with a

  11. Ferrous iron partitioning in the lower mantle

    Muir, Joshua M. R.; Brodholt, John P.


    We used density functional theory (DFT) to examine the partitioning of ferrous iron between periclase and bridgmanite under lower mantle conditions. To study the effects of the three major variables - pressure, temperature and concentration - these have been varied from 0 to 150 GPa, from 1000 to 4000 K and from 0 to 100% total iron content. We find that increasing temperature increases KD, increasing iron concentration decreases KD, while pressure can both increase and decrease KD. We find that KD decreases slowly from about 0.32 to 0.06 with depth under lower mantle conditions. We also find that KD increases sharply to 0.15 in the very lowermost mantle due to the strong temperature increases near the CMB. Spin transitions have a large effect on the activity of ferropericlase which causes KD to vary with pressure in a peak-like fashion. Despite the apparently large changes in KD through the mantle, this actually results in relatively small changes in total iron content in the two phases, with XFefp ranging from about 0.20 to 0.35, before decreasing again to about 0.28 at the CMB, and XFebd has a pretty constant value of about 0.04-0.07 throughout the lower mantle. For the very high Fe concentrations suggested for ULVZs, Fe partitions very strongly into ferropericlase.

  12. Topology in isotopic multispace and origin of mantle chemical heterogeneities

    Allegre, C.J.; Hamelin, B.; Provost, A.; Dupre, B.


    In this paper we present a simple technique for multidimensional treatment of isotopic data, which allows a global and rigorous correlation between the various radiogenic tracers. This technique is based on the determination of eigenvectors of the data matrix, allowing a geometric description of the inertia ellipsoid corresponding to the cluster of experimental data points. The relationships between the various sets of samples can be analyzed using the projections on the main elongation planes. When processing the Pb-Sr-Nd data for the oceanic mantle (OIB+MORB) with this technique we find that at least four different end-members are needed to define the 'mantle array' which thus cannot be a plane surface. Samples from island arcs (IAB) show the contribution of a component clearly out of the oceanic domain and very similar to terrigenous sediments. Continental tholeiites (CFB) also show some sort of contamination (but distinct from that of IAB) by the continental crust. They also show a domain overlapping with that of the oceanic islands corresponding to the compositions of the 'Dupal anomaly'. Multispace analysis also permits a rigorous comparison of relationships between the various isotopic tracers. In particular, we demonstrate that a U-Pb fractionation independent from the correlated Sr-Nd, Th-U and Th-Sr ones does exist. Consequently, a three-dimensional analysis performed only with lead isotopes yields by itself the main information that can be inferred from the five Pb-Sr-Nd dimensions. Helium also yields independent information decoupled with respect to the other tracers, adding one fifth end-member (Loihi, Hawaii islands) to the OIB+MORB array.

  13. Seawater storage and element transfer associated with mantle serpentinization in magma-poor rifted margins: A quantitative approach

    Pinto, Victor Hugo G.; Manatschal, Gianreto; Karpoff, Anne Marie; Ulrich, Marc; Viana, Adriano R.


    Continental breakup in magma-poor rifted margins can develop, in some instances, after the formation of a wide exhumed domain that can be several hundreds of km wide. As exhumation of the continental mantle occurs serpentinization, due to seawater circulation, can extend as far down as 5-6 km, as observed in refraction seismic data. The impact caused by the process of serpentinization within the evolving ocean may have the potential to change: (i) seawater chemistry; (ii) sustain the evolution of primitive life; (iii) control depositional environments; and (iv) form weak zones preferentially used during the formation, reactivation and subduction of distal rifted margins. Based on geological observations, and geophysical and geochemical data from present-day and fossil zones of exhumed continental mantle, we present a first-order quantification showing that approximately 0.380 km3 of water per km2 can be stored in the mantle. Using simple methods, it can be shown that serpentinization may account for a significant loss of Si, Mg, Fe, Mn, Ca, Ni and Cr during serpentinization of mantle rocks. In particular during latest stages of rifting, when basins are often restricted and seaways are not yet connected, exhumation and the serpentinization of large areas of continental mantle may result in a major transfer of elements between the main Earth reservoirs, such as the mantle and seawater.

  14. Towards the Next Generation Upper-Mantle 3D Anelastic Tomography

    Karaoglu, H.; Romanowicz, B. A.


    In order to distinguish the thermal and compositional heterogeneities in the mantle, it is crucial to resolve the lateral variations not only in seismic velocities but also in intrinsic attenuation. Indeed, the high sensitivity of intrinsic attenuation to temperature and water content, governed by a form of Arrhenius equation, contrasts with the quasi-linear dependence of velocities on both temperature and major element composition. The major challenge in imaging attenuation lies in separating its effects on seismic waves from the elastic ones. The latter originate from the wave propagation in media with strong lateral elastic gradients causing (de)focusing and scattering. We have previously developed a 3D upper-mantle shear attenuation model based on time domain waveform inversion of long period (T > 60s) fundamental and overtone surface wave data (Gung & Romanowicz, 2004). However, at that time, resolution was limited to very long wavelength structure, because elastic models were still rather smooth, and the effects of focusing could only be estimated approximately, using asymptotic normal mode perturbation theory.With recent progress in constraining global mantle shear velocity from waveform tomography based on the Spectral Element Method (e.g. SEMUCB_WM1, French & Romanowicz, 2014), we are now in a position to develop an improved global 3D model of shear attenuation in the upper mantle. In doing so, we use a similar time domain waveform inversion approach, but (1) start with a higher resolution elastic model with better constraints on lateral elastic gradients and (2) jointly invert, in an iterative fashion, for shear attenuation and elastic parameters. Here, we present the results of synthetic tests that confirm our inversion strategy, as well as preliminary results towards the construction of the next generation upper-mantle anelastic model.

  15. Redox-induced lower mantle density contrast and effect on mantle structure and primitive oxygen

    Gu, Tingting; Li, Mingming; McCammon, Catherine; Lee, Kanani K. M.


    The mantle comprises nearly three-quarters of Earth's volume and through convection connects the deep interior with the lithosphere and atmosphere. The composition of the mantle determines volcanic emissions, which are intimately linked to evolution of the primitive atmosphere. Fundamental questions remain on how and when the proto-Earth mantle became oxidized, and whether redox state is homogeneous or developed large-scale structures. Here we present experiments in which we subjected two synthetic samples of nearly identical composition that are representative of the lower mantle (enstatite chondrite), but synthesized under different oxygen fugacities, to pressures and temperatures up to 90 GPa and 2,400 K. In addition to the mineral bridgmanite, compression of the more reduced material also produced Al2O3 as a separate phase, and the resulting assemblage is about 1 to 1.5% denser than in experiments with the more oxidized material. Our geodynamic simulations suggest that such a density difference can cause a rapid ascent and accumulation of oxidized material in the upper mantle, with descent of the denser reduced material to the core-mantle boundary. We suggest that the resulting heterogeneous redox conditions in Earth's interior can contribute to the large low-shear velocity provinces in the lower mantle and the evolution of atmospheric oxygen.

  16. Influence of the Ringwoodite-Perovskite transition on mantle convection in spherical geometry as a function of Clapeyron slope and Rayleigh number

    M. Wolstencroft


    Full Text Available We investigate the influence on mantle convection of the negative Clapeyron slope ringwoodite to perovskite and ferro-periclase mantle phase transition, which is correlated with the seismic discontinuity at 660 km depth. In particular, we focus on understanding the influence of the magnitude of the Clapeyron slope (as measured by the Phase Buoyancy parameter, P and the vigour of convection (as measured by the Rayleigh number, Ra on mantle convection. We have undertaken 76 simulations of isoviscous mantle convection in spherical geometry varying Ra and P. Three domains of behaviour were found: layered convection for high Ra and more negative P, whole mantle convection for low Ra and less negative P and transitional behaviour in an intervening domain. The boundary between the layered and transitional domain was fit by a curve P = αRaβ where α = −1.05, and β = −0.1, and the fit for the boundary between the transitional and whole mantle convection domain was α = −4.8, and β = −0.25. These two curves converge at Ra≈2.5×104 and P≈−0.38. Extrapolating to high Ra, which is likely earlier in Earth history, this work suggests a large transitional domain. It is therefore likely that convection in the Archean would have been influenced by this phase change, with Earth being at least in the transitional domain, if not the layered domain.

  17. Mantle flow in subduction systems: The mantle wedge flow field and implications for wedge processes

    Long, Maureen D.; Wirth, Erin A.


    The mantle wedge above subducting slabs is associated with many important processes, including the transport of melt and volatiles. Our understanding of mantle wedge dynamics is incomplete, as the mantle flow field above subducting slabs remains poorly understood. Because seismic anisotropy is a consequence of deformation, measurements of shear wave splitting can constrain the geometry of mantle flow. In order to identify processes that make first-order contributions to the pattern of wedge flow, we have compiled a data set of local S splitting measurements from mantle wedges worldwide. There is a large amount of variability in splitting parameters, with average delay times ranging from ~0.1 to 0.3 s up to ~1.0-1.5 s and large variations in fast directions. We tested for relationships between splitting parameters and a variety of parameters related to subduction processes. We also explicitly tested the predictions made by 10 different models that have been proposed to explain splitting patterns in the mantle wedge. We find that no simple model can explain all of the trends observed in the global data set. Mantle wedge flow is likely controlled by a combination of downdip motion of the slab, trench migration, ambient mantle flow, small-scale convection, proximity to slab edges, and slab morphology, with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology. There is also a likely contribution from B-type olivine and/or serpentinite fabric in many subduction zones, governed by the local thermal structure and volatile distribution.

  18. Melting of subducted basalt at the core-mantle boundary.

    Andrault, Denis; Pesce, Giacomo; Bouhifd, Mohamed Ali; Bolfan-Casanova, Nathalie; Hénot, Jean-Marc; Mezouar, Mohamed


    The geological materials in Earth's lowermost mantle control the characteristics and interpretation of seismic ultra-low velocity zones at the base of the core-mantle boundary. Partial melting of the bulk lower mantle is often advocated as the cause, but this does not explain the nonubiquitous character of these regional seismic features. We explored the melting properties of mid-oceanic ridge basalt (MORB), which can reach the lowermost mantle after subduction of oceanic crust. At a pressure representative of the core-mantle boundary (135 gigapascals), the onset of melting occurs at ~3800 kelvin, which is ~350 kelvin below the mantle solidus. The SiO2-rich liquid generated either remains trapped in the MORB material or solidifies after reacting with the surrounding MgO-rich mantle, remixing subducted MORB with the lowermost mantle.

  19. Mixing properties of thermal convection in the earth's mantle

    Schmalzl, J.T.


    The structure of mantle convection will greatly influence the generation and the survival of compositional heterogeneities. Conversely, geochemical observations can be used to obtain information about heterogeneities in the mantle and then, with certain model assumptions, information about the patte


    Shah, Louise Jivan; Furbo, Simon


    A model, describing the heat transfer coefficients in the mantle of a mantle tank has been developed. The model is validated by means of measurements with varying operational conditions for different designed mantle tanks. The model has been implemented in an existing detailed mathematical...... programme that simulates the thermal behaviour of low flow SDHW systems. The yearly thermal performance of low flow SDHW systems with different designed mantle tanks has been calculated. The influence of the mantle tank design on the thermal performance is investigated by means of the calculations...... with the programme and by means of tests of three SDHW systems with different designed mantle tanks. Based on the investigations design rules for mantle tanks are proposed. The model, describing the heat transfer coefficients in the mantle is approximate. In addition, the measurements have revealed...

  1. The Earth's heterogeneous mantle a geophysical, geodynamical, and geochemical perspective

    Khan, Amir


    This book highlights and discusses recent developments that have contributed to an improved understanding of observed mantle heterogeneities and their relation to the thermo-chemical state of Earth's mantle, which ultimately holds the key to unlocking the secrets of the evolution of our planet. This series of topical reviews and original contributions address 4 themes. Theme 1 covers topics in geophysics, including global and regional seismic tomography, electrical conductivity and seismic imaging of mantle discontinuities and heterogeneities in the upper mantle, transition zone and lower mantle. Theme 2 addresses geochemical views of the mantle including lithospheric evolution from analysis of mantle xenoliths, composition of the deep Earth and the effect of water on subduction-zone processes. Theme 3 discusses geodynamical perspectives on the global thermo-chemical structure of the deep mantle. Theme 4 covers application of mineral physics data and phase equilibrium computations to infer the regional-scale ...

  2. The coupled 182W-142Nd record of early terrestrial mantle differentiation

    Puchtel, Igor S.; Blichert-Toft, Janne; Touboul, Mathieu; Horan, Mary F.; Walker, Richard J.


    New Sm-Nd, Lu-Hf, Hf-W, and Re-Os isotope data, in combination with highly siderophile element (HSE, including Re, Os, Ir, Ru, Pt, and Pd) and W abundances, are reported for the 3.55 Ga Schapenburg komatiites, South Africa. The Schapenburg komatiites define a Re-Os isochron with an age of 3550 ± 87 Ma and initial γ187Os = +3.7 ± 0.2 (2SD). The absolute HSE abundances in the mantle source of the Schapenburg komatiite system are estimated to be only 29 ± 5% of those in the present-day bulk silicate Earth (BSE). The komatiites were derived from mantle enriched in the decay products of the long-lived 147Sm and 176Lu nuclides (initial ɛ143Nd = +2.4 ± 0.1, ɛ176Hf = +5.7 ± 0.3, 2SD). By contrast, the komatiites are depleted, relative to the modern mantle, in 142Nd and 182W (μ182W = -8.4 ± 4.5, μ142Nd = -4.9 ± 2.8, 2SD). These results constitute the first observation in terrestrial rocks of coupled depletions in 142Nd and 182W. Such isotopic depletions require derivation of the komatiites from a mantle domain that formed within the first ˜30 Ma of Solar System history and was initially geochemically enriched in highly incompatible trace elements as a result of crystal-liquid fractionation in an early magma ocean. This mantle domain further must have experienced subsequent melt depletion, after 182Hf had gone extinct, to account for the observed initial excesses in 143Nd and 176Hf. The survival of early-formed 182W and 142Nd anomalies in the mantle until at least 3.55 Ga indicates that the products of early planetary differentiation survived both later planetary accretion and convective mantle mixing during the Hadean. This work moreover renders unlikely that variable late accretion, by itself, can account for all of the observed W isotope variations in Archean rocks.

  3. Role of the transition zone and 660 km discontinuity in mantle dynamics

    Ringwood, A. E.


    of differentiated oceanic lithosphere, with discrete lithological domains of former oceanic crust, former harzburgite and former lherzolite. However, in the upper mantle, these lithologies have been homogenized via convective mixing and partial melting to form a uniform pyrolite composition. Seismic velocity gradients in the heterogeneous mixture of lithologies of the transition zone are higher than they would be in homogeneous pyrolite, because of the survival of clinopyroxene to a depth of about 500 km. This may contribute towards high seismic velocity gradients observed in the transition zone. The behavior during partial melting of heterogeneous lithologies from the transition zone is also quite different from the partial melting of homogeneous pyrolite. The transition zone provides the principal source region for alkaline intraplate basalts world-wide (including ocean island basalts) whereas the homogeneous pyrolite source region of the upper mantle yields mid-ocean ridge basalt magmas.

  4. Steady-state creep in the mantle



    Full Text Available SUMMARY - The creep equations for steady-state flow of olivine at high
    pressure and temperature are compared in an attempt to elucidate the rheological
    behaviour of the mantle. Results are presented in terms of applied deformation
    maps and curves of effective viscosity v depth.
    In the upper mantle, the transition stress between dislocation and diffusion
    creep is between 10 to 102 bar (as orders of magnitude for grain sizes from
    0.01 to 1 cm. The asthenosphere under continents is deeper, and has higher
    viscosity, than under oceans. Predominance of one creep mechanism above the
    others depends on grain size, strain rate, and volume fraction of melt; the
    rheological response can be different for different geodynamic processes.
    In the lower mantle, on the other hand, dislocation creep is predominant
    at all realistic grain sizes and strain rates. If the effective viscosity has to be only
    slightly higher than in the upper mantle, as some interpretations of glacioisostatic
    rebound suggest, then the activation volume cannot be larger than
    11 cm3 mole^1.

  5. Volcanism, Earth Degassing and Replenished Lithosphere Mantle

    Bailey, D. K.


    Volcanism that pierces plate interiors is characteristically rich in alkalis and volatiles, and its cause and persistence are essentially expressions of the Earth's outgassing. The general balance of mobile elements (such as H, C, F and Cl) rules out recycling of sea floor, hydrosphere, sediments or atmosphere: furthermore, it is not in accord with accepted planet degassing budgets. The typical eruptive mode of volatile-rich magmatism means that the observed regional chemical variations, and even differences between adjacent volcanoes, must largely reflect source heterogeneity. In a broader context, this magmatism is also at odds with a concept of continental crust underlain by strongly depleted (refractory) mantle. Repetition of activity along crustal zones of weakness shows that the lithosphere mantle (a) is structurally complex and (b) still holds continuing (or continual) rich reserves of mobile elements. Unbroken lithosphere muffles the evolutionary escape of volatiles from the deep mantle: any lesion that appears then offers easy escape channels, whereby volatiles are drained from a large mantle region and funnelled through the plate. Horizontal movement of thick continental lithosphere releases volatiles from deep sources, imparting some of the special chemical characteristics of the stable continental magmatism. Present evidence requires consideration of the continental lithosphere as a site of primordial heterogeneity that has been accentuated rather than diminished by geological processes.

  6. Explosion of Ultrahigh Pressure Minerals in Mantle

    BAI Wenji; YANG Jingsui; FANG Qingsong; YAN Binggang; ZHANG Zhongming


    @@ The microexplosion stucture of ultrahigh pressure minerals was found for the first time in podform chromitites within the mantle peridotite facies of Luobusa ophiolite along the Yarlung Zangbo suture zone.The explosion stuctures of high-energy silicate inclusions are commonly seen in thin sections (see figure).

  7. Geodynamo Modeling of Core-Mantle Interactions

    Kuang, Wei-Jia; Chao, Benjamin F.; Smith, David E. (Technical Monitor)


    Angular momentum exchange between the Earth's mantle and core influences the Earth's rotation on time scales of decades and longer, in particular in the length of day (LOD) which have been measured with progressively increasing accuracy for the last two centuries. There are four possible coupling mechanisms for transferring the axial angular momentum across the core-mantle boundary (CMB): viscous, magnetic, topography, and gravitational torques. Here we use our scalable, modularized, fully dynamic geodynamo model for the core to assess the importance of these torques. This numerical model, as an extension of the Kuang-Bloxham model that has successfully simulated the generation of the Earth's magnetic field, is used to obtain numerical results in various physical conditions in terms of specific parameterization consistent with the dynamical processes in the fluid outer core. The results show that depending on the electrical conductivity of the lower mantle and the amplitude of the boundary topography at CMB, both magnetic and topographic couplings can contribute significantly to the angular momentum exchange. This implies that the core-mantle interactions are far more complex than has been assumed and that there is unlikely a single dominant coupling mechanism for the observed decadal LOD variation.

  8. Elasticity of ferropericlase at lower mantle conditions

    Wu, Z.; Justo, J. F.; Wentzcovitch, R. M.


    Clarification of the effect of the iron spin change on properties of Fp is important to address the relative abundance of Fp in the lower mantle. However, recent reports to this question show completely different conclusions. The calculated density of a pyrolite aggregate with spin crossover-related change in iron partitioning up to 45 GPa compared well with the density in PREM [1]. On the other hand, Murakami et al's analysis of VS in aggregates with variable amounts of Fp concluded the opposite - the lower mantle is more perovskitic than pyrolitic [2]. We investigated thermoelasticity of Fp with first principles DFT+U calculations. The calculated thermoelasticity are in good consitence with the available experimental data on samples with various iron concentrations. The results can well explain discrepancy on softening of the shear modulus of Fp among different experiments[3,4]. We predict velocities of Fp at lower mantle conditions and suggest that pyrolite is a reasonable compositional model for the lower mantle. Our results show the importance of constraining the elastic properties of minerals without extrapolations for analyses of the thermochemical state of this region[5]. [1] Irifune et al., Science 327, 193 (2010). [2] Murakami et al., Nature 485, 90 (2012). [3] Crowhurst et al., Science 319, 451 (2008). [4] Marquardt et al., Science 324, 224 (2009). [5]Wu et al., Phys. Rev. Lett. 110. 228501 (2013)

  9. The lithospheric mantle below southern West Greenland

    Sand, Karina Krarup; Waight, Tod Earle; Pearson, D. Graham


    Geothermobarometry of primarily garnet lherzolitic xenoliths from several localities in southern West Greenland is applied to address the diamond potential, pressure and temperature distribution and the stratigraphy of the subcontinental lithospheric mantle ~600 Ma ago. The samples are from kimbe...... into the reworked Archean North of the Naqssugtoqidian deformation front....

  10. Plate tectonics: Delayed response to mantle pull

    Nedimović, Mladen R.


    At mid-ocean ridges, the directions in which plates spread and the underlying mantle flows were thought to broadly align. A synthesis of results from ridges that spread at a variety of rates reveals that instead there may be a systematic skew.

  11. Chondritic Xenon in the Earth's mantle: new constrains on a mantle plume below central Europe

    Caracausi, Antonio; Avice, Guillaume; Bernard, Peter; Furi, Evelin; Marty, Bernard


    Due to their inertness, their low abundances, and the presence of several different radiochronometers in their isotope systematics, the noble gases are excellent tracers of mantle dynamics, heterogeneity and differentiation with respect to the atmosphere. Xenon deserves particular attention because its isotope systematic can be related to specific processes during terrestrial accretion (e.g., Marty, 1989; Mukhopadhyay, 2012). The origin of heavy noble gases in the Earth's mantle is still debated, and might not be solar (Holland et al., 2009). Mantle-derived CO2-rich gases are particularly powerful resources for investigating mantle-derived noble gases as large quantities of these elements are available and permit high precision isotope analysis. Here, we report high precision xenon isotopic measurements in gases from a CO2 well in the Eifel volcanic region (Germany), where volcanic activity occurred between 700 ka and 11 ka years ago. Our Xe isotope data (normalized to 130Xe) show deviations at all masses compared to the Xe isotope composition of the modern atmosphere. The improved analytical precision of the present study, and the nature of the sample, constrains the primordial Xe end-member as being "chondritic", and not solar, in the Eifel mantle source. This is consistent with an asteroidal origin for the volatile elements in Earth's mantle and it implies that volatiles in the atmosphere and in the mantle originated from distinct cosmochemical sources. Despite a significant fraction of recycled atmospheric xenon in the mantle, primordial Xe signatures still survive in the mantle. This is also a demonstration of a primordial component in a plume reservoir. Our data also show that the reservoir below the Eifel region contains heavy-radiogenic/fissiogenic xenon isotopes, whose ratios are typical of plume-derived reservoirs. The fissiogenic Pu-Xe contribution is 2.26±0.28 %, the UXe contribution is negligible, the remainder being atmospheric plus primordial. Our

  12. Shear wave speeds at the base of the mantle

    Castle, John C.; Hilst, R.D. van der; Creager, K.C.; Winchester, John P.


    We inverted 4864 ScS-S and 1671 S(diff)-SKS residual travel times for shear wave speed anomalies at the base of the Earth's mantle. We applied ellipticity corrections, accounted for mantle structure outside of the basal layer using mantle tomography models, and employed finite size sensitivity kerne

  13. Global correlation of lower mantle structure and past subduction

    Domeier, M.; Doubrovine, Pavel V.; Torsvik, Trond H.; Spakman, W.|info:eu-repo/dai/nl/074103164; Bull, A.L.


    Advances in global seismic tomography have increasingly motivated identification of subducted lithosphere in Earth's deep mantle, creating novel opportunities to link plate tectonics and mantle evolution. Chief among those is the quest for a robust subduction reference frame, wherein the mantle asse

  14. Shear wave speeds at the base of the mantle

    Castle, John C.; Hilst, R.D. van der; Creager, K.C.; Winchester, John P.


    We inverted 4864 ScS-S and 1671 S(diff)-SKS residual travel times for shear wave speed anomalies at the base of the Earth's mantle. We applied ellipticity corrections, accounted for mantle structure outside of the basal layer using mantle tomography models, and employed finite size sensitivity

  15. European Lithospheric Mantle; geochemical, petrological and geophysical processes

    Ntaflos, Th.; Puziewicz, J.; Downes, H.; Matusiak-Małek, M.


    The second European Mantle Workshop occurred at the end of August 2015, in Wroclaw, Poland, attended by leading scientists in the study the lithospheric mantle from around the world. It built upon the results of the first European Mantle Workshop (held in 2007, in Ferrara, Italy) published in the Geological Society of London Special Publication 293 (Coltorti & Gregoire, 2008).

  16. Mantle Temperature, Mantle Composition, Mantle Heterogeneity, and the Composition of the Upper Mantle: The View from a Global Synthesis of MORB

    Langmuir, C. H.; Gale, A.; Dalton, C. A.


    A new comprehensive review of global MORB can address outstanding issues such mantle temperature vs. mantle composition in controlling MORB compositions, the mean composition of ocean ridge basalts, the K/U ratio of the MORB reservoir, and the implications for silicate Earth mass balance of the composition of the upper mantle. We created a global catalogue of ridge segments to assign every sample to a segment. We carried out interlaboratory corrections for major elements, and examined data from each segment to ensure appropriate fractionation correction. We included large unpublished data sets from the Langmuir and Schilling laboratories, assembling the most comprehensive data set for MORB. Data averaged by segment permit calculation of averages that include weighting by segment length and spreading rate. The segment-based approach, comprehensive data set, individualized fractionation correction and interlaboratory corrections distinguish these results from earlier efforts. We also carried out bootstrapping statistical tests for meaningful errors on average compositions. The mean composition of the ocean crust is best determined by a segment length and spreading rate weighted arithmetic mean. As with other recent efforts, notably Su (2002) and also Arevalo and McDonough (2009), the mean composition is substantially more enriched than previous MORB estimates. Average MORB implies a MORB mantle Sm/Nd and Nd isotopic composition similar to the 'non-chondritic primitive mantle' composition based on 142Nd. Then continental crust/MORB mantle mass balance is not possible using a non-chondritic (depleted) bulk silicate earth composition, unless there is a large unsampled depleted reservoir. In contrast to Arevalo and McDonough, who suggested a K/U ratio for MORB of 19,000, we find K/U of 12,340±810, in line with earlier estimates. The discrepancy can be understood from contrasts in methodology, as we determine average K/ average U, while they determine average K/U. To

  17. Mantle Convection Models Constrained by Seismic Tomography

    Durbin, C. J.; Shahnas, M.; Peltier, W. R.; Woodhouse, J. H.


    Although available three dimensional models of the lateral heterogeneity of the mantle, based upon the latest advances in seismic tomographic imaging (e.g. Ritsema et al., 2004, JGR) have provided profound insights into aspects of the mantle general circulation that drives continental drift, the compatibility of the tomography with explicit models of mantle mixing has remained illusive. For example, it remains a significant issue as to whether hydrodynamic models of the mixing process alone are able to reconcile the observed detailed pattern of surface plate velocities or whether explicit account must be taken of elastic fracture processes to account for the observed equipartition of kinetic energy between the poloidal and toroidal components of the surface velocity pattern (e.g. Forte and Peltier, 1987, JGR). It is also an issue as to the significance of the role of mantle chemical heterogeneity in determining the buoyancy distribution that drives mantle flow, especially given the expected importance of the spin transition of iron that onsets in the mid-lower mantle, at least in the ferropericlase component of the mineralogy. In this paper we focus upon the application of data assimilation techniques to the development of a model of mantle mixing that is consistent with a modern three dimensional tomography based model of seismic body wave heterogeneity. Beginning with the simplest possible scenario, that chemical heterogeneity is irrelevant to first order, we employ a three dimensional version of the recently published control volume based convection model of Shahnas and Peltier (2010, JGR) as the basis for the assimilation of a three dimensional density field inferred from our preferred tomography model (Ritsema et al., 2004, JGR). The convection model fully incorporates the dynamical influence of the Olivine-Spinel and Spinel-Perovskite+Magnesiowustite solid-solid phase transformations that bracket the mantle transition zone as well as the recently discovered

  18. Compositions of Upper Mantle Fluids Beneath Eastern China:Implications for Mantle Evolution

    ZHANG Mingjie; WANG Xianbin; LIU Gang; ZHANG Tongwei; BO Wenrui


    The composition of gases trapped in olivine, orthopyroxene and clinopyroxene in lherzolite xenoliths collected from different locations in eastern China has been measured by the vacuum stepped-heating mass spectrometry.These xenoliths are hosted in alkali basalts and considered as residues of partial melting of the upper mantle, and may contain evidence of mantle evolution. The results show that various kinds of fluid inclusions in lherzolite xenoliths have been released at distinct times, which could be related to different stages of mantle evolution. In general, primitive fluids of the upper mantle (PFUM) beneath eastern China are dominated by H2, CO2 and CO, and are characterized by high contents of H2 and reduced gases. The compositions of PFUM are highly variable and related to tectonic settings. CO, CO2 and H2 are the main components of the PFUM beneath cratons; the PFUM in the mantle enriched in potassic metasomatism in the northern part of northeastern China has a high content of H2, while CO2 and SO2 are the dominant components of the PFUM in the Su-Lu-Wan (Jiangsu-Shandong-Anhui) region, where recycled crustal fluids were mixed with deeper mantle components. There are several fluids with distinct compositions beneath eastern China, such as primitive fluids of upper mantle (CO, CO2 and H2), partial melting fluids (CO2 and CO) and metasomatic fluids mixed with recycled crustal fluids (CO2, N2, 8O2 and CH4) etc. Fluids of the upper mantle beneath the North China craton are different from that of the South China craton in total gases and chemical compositions: the contents of the reduced gases of the PFUM in the NCC are higher than those in the SCC.

  19. Finding the patterns in mantle convection

    Atkins, Suzanne; Rozel, Antoine; Valentine, Andrew; Tackley, Paul; Trampert, Jeannot


    Inverting mantle flow for past configurations is one of the great outstanding problems in geodynamics. We demonstrate a new method for probabilistic inversion of present-day Earth observations for mantle properties and history. Convection is a non-linear and chaotic, thwarting most standard inversion methods. Because of its chaotic and unpredictable nature, small errors in initial conditions, parameter selection, and computational precision can all significantly change the results produced by mantle convection simulations. However, some patterns and statistics of convection contain the signature of the parameters used in the simulations over long time-scales. Geodynamical studies often vary these parameters to investigate their effects on the patterns produced. We show that with a large enough set of simulations, we can investigate the relationship between input parameters and convection patterns in a more rigorous way. Probabilistic inversion is the only way to approach highly non-linear problems. We use neural networks to represent the probability density function linking convection simulation input parameters and the patterns they produce. This allows us to find input parameters, whilst taking into account all of the uncertainties that are inherent in the inversion of any Earth system: how well do we understand the physics of the process; what do we already know about the input parameters; and how certain are our observations? We show that the mantle structures produced by 4.5 Gyr of convection simulations contain enough information on yield stress, viscosity coefficients, mantle heating rate, and the initial state of primordial material that we can infer them directly without requiring any other information, such as plate velocity.

  20. Nitrogen speciation in mantle and crustal fluids

    Li, Yuan; Keppler, Hans


    Seventy-nine experiments have been carried out at 600-1400 °C, 2-35 kbar, and oxygen fugacities ranging from the Fe-FeO to the Re-ReO2 buffer to investigate the nitrogen speciation in mantle and crustal N-H-O fluids. Laser Raman analyses of fluid inclusions trapped in situ in quartz and olivine crystals show that N2 and/or NH3 are the only detectable nitrogen species in the fluids at the conditions of the present study. The results further show that in the fluids of the oxidized shallow upper mantle, nitrogen is mostly present as N2, while in the deep reduced upper mantle, NH3 is the dominant nitrogen species. Nitrogen speciation in subduction zone fluids is also calculated from the experimental data to constrain the efficiency of nitrogen recycling. The data show that a hot, oxidized slab is an efficient barrier for deep nitrogen subduction, while a cold, reduced slab would favor recycling nitrogen into the deep mantle. The nitrogen species in magmatic fluids of mid-ocean ridge basalt and arc magmas are predominantly N2, but a significant fraction of nitrogen can be NH3 at certain conditions. The nitrogen species in fluids released from the solidifying magma ocean and the reduced young mantle may have been mostly NH3. The release of such fluids may have created a reduced atmosphere on the every early Earth, with an elevated concentration of NH3. This may not only resolve the faint young Sun paradox but may also have created favorable conditions for the formation of biomolecules through Miller-Urey type reactions.

  1. Nickel isotopic composition of the mantle

    Gall, Louise; Williams, Helen M.; Halliday, Alex N.; Kerr, Andrew C.


    This paper presents a detailed high-precision study of Ni isotope variations in mantle peridotites and their minerals, komatiites as well as chondritic and iron meteorites. Ultramafic rocks display a relatively large range in δ60 Ni (permil deviation in 60 Ni /58 Ni relative to the NIST SRM 986 Ni isotope standard) for this environment, from 0.15 ± 0.07‰ to 0.36 ± 0.08‰, with olivine-rich rocks such as dunite and olivine cumulates showing lighter isotope compositions than komatiite, lherzolite and pyroxenite samples. The data for the mineral separates shed light on the origin of these variations. Olivine and orthopyroxene display light δ60 Ni whereas clinopyroxene and garnet are isotopically heavy. This indicates that peridotite whole-rock δ60 Ni may be controlled by variations in modal mineralogy, with the prediction that mantle melts will display variable δ60 Ni values due to variations in residual mantle and cumulate mineralogy. Based on fertile peridotite xenoliths and Phanerozoic komatiite samples it is concluded that the upper mantle has a relatively homogeneous Ni isotope composition, with the best estimate of δ60Nimantle being 0.23 ± 0.06‰ (2 s.d.). Given that >99% of the Ni in the silicate Earth is located in the mantle, this also defines the Ni isotope composition of the Bulk Silicate Earth (BSE). This value is nearly identical to the results obtained for a suite of chondrites and iron meteorites (mean δ60 Ni 0.26 ± 0.12‰ and 0.29 ± 0.10‰, respectively) showing that the BSE is chondritic with respect to its Ni isotope composition, with little to no Ni mass-dependent isotope fractionation resulting from core formation.

  2. Water in the Cratonic Mantle Lithosphere

    Peslier, A. H.


    The fact that Archean and Proterozoic cratons are underlain by the thickest (>200 km) lithosphere on Earth has always puzzled scientists because the dynamic convection of the surrounding asthenosphere would be expected to delaminate and erode these mantle lithospheric "keels" over time. Although density and temperature of the cratonic lithosphere certainly play a role in its strength and longevity, the role of water has only been recently addressed with data on actual mantle samples. Water in mantle lithologies (primarily peridotites and pyroxenites) is mainly stored in nominally anhydrous minerals (olivine, pyroxene, garnet) where it is incorporated as hydrogen bonded to structural oxygen in lattice defects. The property of hydrolytic weakening of olivine [4] has generated the hypothesis that olivine, the main mineral of the upper mantle, may be dehydrated in cratonic mantle lithospheres, contributing to its strength. This presentation will review the distribution of water concentrations in four cratonic lithospheres. The distribution of water contents in olivine from peridotite xenoliths found in kimberlites is different in each craton (Figure 1). The range of water contents of olivine, pyroxene and garnet at each xenolith location appears linked to local metasomatic events, some of which occurred later then the Archean and Proterozoic when these peridotites initially formed via melting. Although the low olivine water contents ( 6 GPa at the base of the Kaapvaal cratonic lithosphere may contribute to its strength, and prevent its delamination, the wide range of those from Siberian xenoliths is not compatible with providing a high enough viscosity contrast with the asthenophere. The water content in olivine inclusions from Siberian diamonds, on the other hand, have systematically low water contents (water contents. The olivine inclusions, however, may have been protected from metasomatism by their host diamond and record the overall low olivine water content of

  3. Cosmochemical Estimates of Mantle Composition

    Palme, H.; O'Neill, H. St. C.


    In 1794 the German physicist Chladni published a small book in which he suggested the extraterrestrial origin of meteorites. The response was skepticism and disbelief. Only after additional witnessed falls of meteorites did scientists begin to consider Chladni's hypothesis seriously. The first chemical analyses of meteorites were published by the English chemist Howard in 1802, and shortly afterwards by Klaproth, a professor of chemistry in Berlin. These early investigations led to the important conclusion that meteorites contained the same elements that were known from analyses of terrestrial rocks. By the year 1850, 18 elements had been identified in meteorites: carbon, oxygen, sodium, magnesium, aluminum, silicon, phosphorous, sulfur, potassium, calcium, titanium, chromium, manganese, iron, cobalt, nickel, copper, and tin (Burke, 1986). A popular hypothesis, which arose after the discovery of the first asteroid Ceres on January 1, 1801 by Piazzi, held that meteorites came from a single disrupted planet between Mars and Jupiter. In 1847 the French geologist Boisse (1810-1896) proposed an elaborate model that attempted to account for all known types of meteorites from a single planet. He envisioned a planet with layers in sequence of decreasing densities from the center to the surface. The core of the planet consisted of metallic iron surrounded by a mixed iron-olivine zone. The region overlying the core contained material similar to stony meteorites with ferromagnesian silicates and disseminated grains of metal gradually extending into shallower layers with aluminous silicates and less iron. The uppermost layer consisted of metal-free stony meteorites, i.e., eucrites or meteoritic basalts. About 20 years later, Daubrée (1814-1896) carried out experiments by melting and cooling meteorites. On the basis of his results, he came to similar conclusions as Boisse, namely that meteorites come from a single, differentiated planet with a metal core, a silicate mantle

  4. Importance of Mantle Viscosity in Interseismic Deformation

    Wang, K.; He, J.; Hu, Y.


    The role of mantle viscosity in subduction earthquake cycles was postulated when the plate tectonics theory had just gained wide acceptance. The process was described using Elsasser's 1-D model for diffusion of stress from the subduction boundary to the plate interior. Main features of interseismic surface deformation predicted by this elegantly simple model were later verified by GPS observations following giant subduction earthquakes. However, and intriguingly, the vast majority of interseismic deformation models developed in the era of space geodesy assume an elastic Earth, incorrectly regarding interseismic deformation as a subdued mirror image of coseismic deformation. The reason is four-fold. (1) The 1-D model and subsequent 2-D viscoelastic models failed to recognize the role of rupture length in the strike direction and could not self-consistently explain deformation following medium and small earthquakes. (2) Based on global mantle viscosity models derived from glacial isostatic adjustment studies, the viscoelastic mantle should indeed behave elastically in earthquake cycles of a few hundred years. (3) The effect of viscous mantle deformation can often be equivalently described by deep fault creep in a purely elastic Earth. (4) The use of an elastic model provides convenience in inverting geodetic data to determine fault locking and creep. Here we use 3D finite element models to show that the main characteristics of surface deformation following subduction earthquakes of all sizes can be explained with a viscoelastic Earth in which the mantle wedge is less viscous than global upper-mantle average of 1020 - 1021 Pa s by one to two orders of magnitude. Following giant earthquakes, such as 1700 Cascadia, 1960 Chile, 1964 Alaska, 2004 Sumatra, and 2011 Japan, upper-plate land deformation undergoes phases of wholesale seaward motion, opposing motion of coastal and inland areas, and wholesale landward motion. The "speed" of the evolution scales inversely with

  5. Role of viscoelasticity in mantle convection models

    Patocka, Vojtech; Cadek, Ondrej; Tackley, Paul


    constitutive equations in a way more suitable for global studies, which is different from the method refered to earlier. The computational domain is expected to be composed of two parts: One in which elastic effects are important and where material does not move significantly within one elastic time step and one where elastic effects are not important, where material is allowed to move across many cells within one elastic time step. Local accumulation of stress in viscoelastic simulations is observed, suggesting elasticity could e.g. trigger plasticity in realistic cases. References Moresi L., Dufour F., Mühlhaus H.-B., 2003: A Lagrangian integration point finite element method for large deformation modeling of viscoelastic geomaterials, Journal of Computational Physics, 184 (2003), 476 - 497 Tackley P., 2008: Modelling compressible mantle convection with large viscosity contrasts in a three-dimensional spherical shell using the yin-yang grid, Physics of the Earth and Planetary Interiors, 171 (2008), 7-18

  6. Geophysical and geochemical constraints on geoneutrino fluxes from Earth's mantle

    Šrámek, Ondřej; Kite, Edwin S; Lekić, Vedran; Dye, Steve; Zhong, Shijie


    Knowledge of the amount and distribution of radiogenic heating in the mantle is crucial for understanding the dynamics of the Earth, including its thermal evolution, the style and planform of mantle convection, and the energetics of the core. Although the flux of heat from the surface of the planet is robustly estimated, the contributions of radiogenic heating and secular cooling remain poorly defined. Constraining the amount of heat-producing elements in the Earth will provide clues to understanding nebula condensation and planetary formation processes in early Solar System. Mantle radioactivity supplies power for mantle convection and plate tectonics, but estimates of mantle radiogenic heat production vary by a factor of up to 30. Recent experimental results demonstrate the potential for direct assessment of mantle radioactivity through observations of geoneutrinos, which are emitted by naturally occurring radionuclides. Predictions of the geoneutrino signal from the mantle exist for several established est...

  7. Role of mantle flow in Nubia-Somalia plate divergence

    Stamps, D. S.; Iaffaldano, G.; Calais, E.


    Present-day continental extension along the East African Rift System (EARS) has often been attributed to diverging sublithospheric mantle flow associated with the African Superplume. This implies a degree of viscous coupling between mantle and lithosphere that remains poorly constrained. Recent advances in estimating present-day opening rates along the EARS from geodesy offer an opportunity to address this issue with geodynamic modeling of the mantle-lithosphere system. Here we use numerical models of the global mantle-plates coupled system to test the role of present-day mantle flow in Nubia-Somalia plate divergence across the EARS. The scenario yielding the best fit to geodetic observations is one where torques associated with gradients of gravitational potential energy stored in the African highlands are resisted by weak continental faults and mantle basal drag. These results suggest that shear tractions from diverging mantle flow play a minor role in present-day Nubia-Somalia divergence.

  8. Mantle convection, tectonics and the evolution of the Tethyan subduction zone

    Jolivet, Laurent; Sternai, Pietro; Menant, Armel; Faccenna, Claudio; Becker, Thorsten; Burov, Evguenii


    Mantle convection drives plate tectonics and the size, number and thermotectonic age of plates codetermines the convection pattern. However, the degree of coupling of surface deformation and mantle flow is unclear. Most numerical models of lithospheric deformation are designed such that strain is a consequence of kinematic boundary conditions, and rarely account for basal stresses due to mantle flow. On the other hand, convection models often treat the lithosphere as a single-layer stagnant lid with vertically undeformable surface. There is thus a gap between convection models and lithospheric-scale geodynamic models. The transmission of stresses from the flowing mantle to the crust is a complex process. The presence of a ductile lower crust inhibits the upward transmission of stresses but a highly extended crust in a hot environment such as a backarc domain, with no lithospheric mantle and a ductile lower crust in direct contact with asthenosphere, will be more prone to follow the mantle flow than a thick and stratified lithosphere. We review geological observations and present reconstructions of the Aegean and Middle East and discuss the possible role played by basal drag in governing lithospheric deformation. In Mediterranean backarc regions, lithosphere-mantle coupling is effective on geological time scale as shown by the consistency of SKS fast orientations in the mantle with stretching directions in the crust. The long-term geological history of the Tethyan convergent zone suggests that asthenospheric flow has been an important player. The case of Himalaya and Tibet strongly supports a major contribution of a northward asthenospheric push, with no persistent slab that could drive India after collision, large thrust planes being then decoupling zones between deep convection and surface tectonics. The African plate repeatedly fragmented during its northward migration with the separation of Apulia and Arabia. Indeed, extension has been active on the northern

  9. Volatile-rich Melts in the Earth's Upper Mantle (AGU Kuno Medal)

    Dasgupta, Rajdeep


    The onset of silicate magma generation in the Earth's upper mantle influences the thermal evolution of the planet, fluxes of key volatiles to the exosphere, and geochemical and geophysical properties of the mantle. Although carbonatitic fluid with variable water content could be stable ≤250 km beneath mid oceanic ridges [1-3], owing to the small fraction (oxygen fugacity of the mantle in the garnet peridotite field [2, 3], we suggest that on a global scale, carbonated silicate melt generation at ~250-180 km deep redox solidus, with destabilization of metal and majorite in the upwelling mantle, explains oceanic low-velocity zone and electrical conductivity structure of the mantle. In locally oxidized domains (i.e., higher than average Fe3+/Fetotal), deeper carbonated silicate melt may contribute to the X-discontinuity. Furthermore, the new experimental results along with the electrical conductivity of molten carbonated peridotite [8] and that of the oceanic upper mantle [6] suggest that if CO2-rich melt is the only possible agent to explain the high electrical conductivity of the asthenospheric mantle then the mantle at depth is CO2-rich but H2O-poor; higher H2O content in the mantle enhances melting, lowers the CO2 content and likely the conductivity of such melts. Finally, carbonated silicate melts restrict the stability of carbonatite in the Earth's deep oceanic upper mantle and the inventory of carbon, water, and other highly incompatible elements at ridges becomes controlled by flux of the former [7]. Although the stability of carbonatitic melt may be eliminated beneath oceanic ridges at all depths, beneath continents stability of carbonatitic melt is expected. Archean cratonic mantle (geotherms corresponding to surface heat flux of 40-50 mW m-2) crosses the carbonated peridotite solidus, at a depth of ~100-220 km [9]; thus considering the oxygen fugacity profile for cratons [3], carbonatitic melt is expected to be stable at 100-180 km depths, at a narrow

  10. Analysis on the results of 976 patients assisted re-fertility in the earthquake-devastated area of Wenchuan County%976例汶川地震极重灾区再生育妇女助孕结果分析

    刘琼; 宋涛; 胥泽坤


    Objective:To analyze the results including pregnancy and abortion rate of assisted re-fertility in the earthquake-devastated area of Wenchuan County in Sichuan Province,and explore the influence of the earthquake,age and other related factors on the pregnancy outcome.Methods:From May 2008 to May 2012,976 women who wished re-fertility were included in this study and divided into three groups by their age:<35 years old(n=340),35-39 years old (n=295) and ≥40 years old(n=341).Their pregnancy outcome and other influencing factor were analyzed retrospectively.Results:Among these 976 women,800 patients successfully got pregnancy.The pregnant rate was 81.97 % (800/976),and the abortion rate was 20.25% (162/800).The lower pregnant rate and the higher abortion rate were associated with elder age.Seven patients were terminated the pregnancy due to the fetus suffered congenital malformation.This effective intervention avoids the birth of the fetus with congenital malformation.Conclusions:The spontaneous abortion rate (20.25%) of the re-fertility women in the earthquake area is obviously higher than normal (10%-15%).Because of the comprehensive factors,the lower pregnant rate and the higher abortion rate were associated with elder age.The immediate and effective comprehensive measures of prevention and intervention were necessary to improve the pregnancy rate,decline the abortion rate and prevent the birth of the fetus with congenital malformation.%目的 总结汶川地震灾区4年来再生育服务工作和助孕结果,对妇女的妊娠、流产及其他相关因素进行分析,探讨地震灾害、年龄及其他因素对再生育妇女妊娠及妊娠结局的影响. 方法 选取2008年5月至2012年5月,有再生育意愿妇女976例为研究对象,将其按年龄分为<35岁组(n=340)、35~39岁组(n=295)和≥40岁组(n=341).采取回顾性分析法对其妊娠、妊娠结局及其他影响因素进行分析. 结果 976例再生育妇女中,800

  11. Eight good reasons why the uppermost mantle could be magnetic

    Ferré, Eric C.; Friedman, Sarah A.; Martín-Hernández, Fatíma; Feinberg, Joshua M.; Till, Jessica L.; Ionov, Dmitri A.; Conder, James A.


    Wasilewski et al. (1979) concluded that no magnetic remanence existed in the uppermost mantle and that even if present, such sources would be at temperatures too high to contribute to long wavelength magnetic anomalies (LWMA). However, new collections of unaltered mantle xenoliths indicate that the uppermost mantle could contain ferromagnetic minerals. 1. The analysis of some LWMA over cratons and forearcs suggest magnetic sources in the uppermost mantle. 2. The most common ferromagnetic phase in the uppermost mantle is stoichiometric magnetite. Assuming a 30 km-thick crust, and crustal and mantle geotherms of 15 °C/km and 5 °C/km, respectively, the 600 °C Curie temperature implies a 30 km-thick layer of mantle. 3. The uppermost mantle is cooler than 600 °C in Archean and Proterozoic shields (> 350 °C), subduction zones (> 300 °C) and old oceanic basins (> 250 °C). 4. Recently investigated sets of unaltered mantle xenoliths contain pure magnetite inclusions in olivine and pyroxene formed in equilibrium with the host silicate. 5. The ascent of mantle xenoliths occurs in less than a day. Diffusion rates in olivine suggest that the growth of magnetite possible within this time frame cannot account for the size and distribution of magnetite particles in our samples. 6. Demagnetization of natural remanent magnetization (NRM) of unaltered mantle xenoliths unambiguously indicates only a single component acquired upon cooling at the Earth's surface. This is most easily explained as a thermoremanent magnetization acquired by pre-existing ferromagnetic minerals as xenoliths cool rapidly at the Earth's surface from magmatic temperatures, acquired during ascent. 7. Modern experimental data suggest that the wüstite-magnetite oxygen buffer and the fayalite-magnetite-quartz oxygen buffer extend several tens of km within the uppermost mantle. 8. The magnetic properties of mantle xenoliths vary consistently across tectonic settings. In conclusion, the model of a uniformly

  12. The Central Sudetes Rheic Ocean Ophiolites: Quantifying the spatial and temporal extent of the Indian Ocean-Dupal mantle signature

    band, Ade R.; Barry, Tiffany; Murphy, Brendan; Saunders, Andrew


    The Indian Ocean-Dupal (Dupal herein) mantle signature is documented to be an integral component in the formation of the Carboniferous Palaeo-Tethys ophiolites. Spatially associated with the Palaeo-Tethys Ocean, the Rheic Ocean separated Laurussia and Gondwana after its conception during the latest Cambrian until closure during the Devonian-Carboniferous Variscan-Alleghanian orogeny. The age and location of Rheic Ocean ophiolites preserved within the Variscide belt offers an insight into the spatial and temporal extent, and also the origin of the Dupal mantle signature. The Central Sudetes Ophiolites consist of the low metamorphic grade, partially dismembered Nowa Ruda, Braszowice and Ślęża mafic/ultramafic bodies of Lower Silesia, Poland. Geochemical analysis of extrusive and hypabyssal lithologies indicate that despite the majority of samples exhibiting characteristics compatible with formation within a SSZ setting (Th and LILE enrichment, Ta and Nb depletion), a significant MORB suite is also present. MORB offer an opportunity to isotopically fingerprint the underlying mantle source region, thus offering an insight into the chemistry of the southern hemisphere mantle at c. 420-400 Ma. Utilising the robust Hf-Nd systematics this study has succeeded in documenting the mantle domain from which the eastern Rheic Ocean was sourced whilst simultaneously constraining the timing and nature of a previous melt extraction event.

  13. Mantle plumes: Why the current skepticism?

    Gillian R. Foulger


    The present reappraisal of the mantle plume hypothesis is perhaps the most exciting current debate in Earth science. Nevertheless, the fundamental reasons for why it has arisen are often not well understood. They are that 1) many observations do not agree with the predictions of the original model, 2) it is possible that convection of the sort required to generate thermal plumes in the Earth's mantle does not occur, 3) so many variants of the original model have been invoked to accommodate conflicting data that the plume hypthesis is in practice no longer testable, and 4) alternative models are viable, though these have been largely neglected by researchers. Regardless of the final outcome, the present vigorous debate is to be welcomed since it is likely to stimulate new discoveries in a way that unquestioning acceptance of the conventional plume model will not.

  14. A Consensus on Mantle Potential Temperatures? (Invited)

    Putirka, K. D.


    Recent publications may indicate a mounting consensus regarding mantle temperatures - an agreement that can be crucial for improving our understanding of mantle dynamics. To compare temperatures at various localities, McKenzie & Bickle (1988) proposed the concept of a mantle potential temperature (Tp) as a reference; Tp is the temperature the mantle would have at the surface, if it ascended along an adiabat without undergoing melting. Perhaps the most precise method to estimate Tp involves estimating the conditions of partial melting, and then correcting for the heat of fusion. The several sources of error include estimation of: a parental liquid, an equilibrium mantle olivine, the degree of partial melting (F), and the depth at which the parental melt is generated. There is also model error inherent to any thermometer. And when correcting for the heat of fusion we assume that we are correcting up to the convective adiabat, but if the parental melt was generated within the conductive lithosphere, Tp will be low. In any case, if we accept that the highest Tp estimates at Hawaii are of most interest (since magmas generated away from a plume centerline will not reflect the full heat content of a high T source), then in spite of these sources of error, recent estimates, published over a span of 10 months by three independent research groups, indicate considerable convergence. At Hawaii maximum Tp values are: 1600 deg. C by Herzberg & Asimow (2008), ca. 1630 deg. C by Lee et al. (2009; their Fig. 2B), and using two slightly different equation sets, 1687 deg. C by Putirka (2008; Geology) and 1660 deg. C by Putirka (2008; RiMG volume 69), yielding an average of 1644±38oC. Similarly, there is convergence for mean Tp at MORs (accepting that MORs are not isothermal; Klein and Langmuir, 1987): Herzberg & Asimow (2008) and Lee et al. (2009) estimate that Tp is ca. 1350 deg. C, and Putirka (2008; Geology) estimates a Tp of 1396 deg. C; these estimates average to 1365±26o

  15. Lunar maria - result of mantle plume activity?

    Sharkov, E.

    It is generally accepted that lunar maria are the result of catastrophic impact events. However, comparative studying of the Earth's and the Moon's tectonomagmatic evolution could evidence about another way of these specific structures origin. Such studies showed that the both planetary bodies evolved on the close scenario: their geological development began after solidification of global magmatic oceans which led to appearance of their primordial crusts: granitic on the Earth and anorthositic - on the Moon. The further evolution of the both bodies occurred in two stages. For their first stages, lasted ˜2.5 mlrd. years on the Earth and ˜1.5 mlrd. years on the Moon, were typical melts, generated in depleted mantle (Bogatikov et al., 2000). However, at the boundary 2.2-2.0 Ga ago on the Earth and 3.9-3.8 Ga on the Moon another type of magmas appeared: geochemical enriched Fe-Ti picrites and basalts, characteristic for the terrestrial Phanerozoic plume-related situations, and basaltic mare magmatism with high-Ti varieties on the Moon. It suggests that evolution of the Earth's magmatism was linked with ascending of mantle plumes (superplumes) of two generation: (1) generated in the mantle, depleted during solidification of magmatic ocean and Archean magmatic activity, and (2) generated at the core-mantle boundary (CMB). The latter were enriched in the mantle fluid components (Fe, Ti, alkalies, etc); this lighter material could ascend to shallower depths, leading to change of tectonic processes, in particular, to appearance of plate tectonics as the major type of tectonomagmatic activity till now (Bogatikov et al., 2000). By analogy to the Earth, magmatism of the Moon was also linked with ascending of mantle plumes: (1) generated in the depleted mantle (magnesian suite) and (2) generated at the lunar CMB with liquid at that time metallic core (mare basalt and picrites with high-Ti varieties). Like on the Earth, these plumes were lighter than the older plumes, and

  16. Constitution and structure of earth's mantle

    Zunino, Andrea; Khan, Amir; Cupillard, Paul


    This chapter describes a quantitative approach that integrates data and results from mineral physics, petrological analyses, and geophysical inverse calculations to map geophysical data directly for mantle composition and thermal state. Seismic tomography has proved an important tool to image...... the inaccessible parts of the Earth. Computation of physical properties using thermodynamic models is described and discussed, and an application of the joint inverse methodology is illustrated in a case study where mantle composition and thermal state beneath continental Australia is determined directly from...... seismic data. There is a growing consensus that the cause of the imaged wavespeed anomalies not only relates to variations in temperature, but also bears a strong compositional component. However, separation of thermal and chemical effects from seismic wave speeds alone is difficult and is further...

  17. An overview of the Mesozoic-Cenozoic magmatism and tectonics in Eastern Paraguay and central Andes (Western Gondwana): Implications for the composition of mantle sources

    Omarini, Ricardo H.; Gasparon, Massimo; De Min, Angelo; Comin-Chiaramonti, Piero


    The amalgamation of the Western Gondwana (including the Greater Gondwana supercraton) occurred at 600 Ma during the Brazilian - Pan African orogeny. A plate junction related to this event is marked by the Transbrazilian lineament which separates the South American continent into two sectors: the Eastern Paraguay-Brazilian and Central Andean domains. An overview of the geodynamic data from these two sectors indicates that the two domains were subjected to distinct evolutions from the Proterozoic to the present. The Andean domain is characterized by long-lived subduction processes linked to the convergence and consequent collision of microplates since the Middle Proterozoic (western Amazonian Craton) with a peak at about 600-580 Ma. The Paraguay-Brazilian domain remained relatively stable but was affected by extension episodes that reactivated ancient (Early and Middle Proterozoic) suture zones. These different geodynamic evolutions seem to reflect broadly distinct mantle compositions. In the subduction zones of the Andean domain the mantle was deeply modified by metasomatic processes following the subduction of oceanic plates. Consequently, the Andean type magma sources show a clear HIMU imprint inherited from the MORB, whereas the Paraguay-Brazilian sector shows a prevalent EMI and subordinate EMII character. The petrological data mainly from Mesozoic and Cenozoic magmatic events in the two sectors are reviewed to investigate the current mantle plume and mantle dome models for the uprising of the asthenospheric (or sub-lithospheric) material.

  18. Sulfide Composition and Melt Stability Field in the Earth's Upper Mantle

    Zhang, Z.; Hirschmann, M. M.


    estimates, and consequently likely refractory. Together with future work on metal/sulfur ratio of sulfide, we will define the sulfide composition-depth profile and its corresponding melt stability field in different mantle redox/geotherm domains.

  19. Hydrogen storage in Earth's mantle and core

    Prewitt, Charles T.


    Two different approaches to explaining how hydrogen might be stored in the mantle are illustrated by a number of papers published over the past 25-30 years, but there has been little attempt to provide objective comparisons of the two. One approach invokes the presence in the mantle of dense hydrous magnesium silicates (DHMS) stable at elevated pressures and temperatures. The other involves nominally anhydrous minerals (NAM) that contain hydrogen as a minor constituent on the ppm level. Experimental studies on DHMS indicate these phases may be stable to pressures and temperatures as high at 16 GPa and 1200 C. This temperature is lower than that indicated by a mantle geotherm at 16 GPa, but may be reasonable for a subducting slab. It is possible that other DHMS could be stable to even higher pressures, but little is known about maximum temperature limits. For NAM, small amounts of hydrogen (up to several hundred ppm) have been detected in olivine, orthopyroxene, clinopyroxene, and garnet recovered from xenoliths in kimberlites, eclogites, and alkali basalts; it has been demonstrated that synthetic wadsleyite and perovskite can accommodate significant amounts of hydrogen. A number of problems are associated with each possibility. For NAM originating in the mantle, one would like to assume that the hydrogen measured in samples recovered on Earth's surface was incorporated when the phase-crystallized at high temperatures and pressures, but it could have been introduced during transport to the surface. Major problems for the DHMS proponents are that none of these phases have been found as minerals and little is yet known about their stabilities in systems containing other cations such as Fe, Al, and Ca.

  20. Thermal Conductivity Measurement of Synthesized Mantle Minerals

    Asimow, P. D.; Luo, S.; Mosenfelder, J. L.; Liu, W.; Staneff, G. D.; Ahrens, T. J.; Chen, G.


    Direct thermal conductivity (k) measurement of mantle minerals is crucial to constrain the thermal profile of the Earth as well as geodynamic studies of the mantle (e.g., to determine the Rayleigh number). We have embarked on systematic multi-anvil syntheses of dense polycrystalline specimens of mantle phases of adequate size and zero porosity for precise thermal conductivity measurements by the 3ω method (\\textit{Cahill and Pohl, Phys. Rev. B, 1987}) under elevated temperatures (T). Coesite and stishovite (see \\textit{Luo et al., GRL, 2002}) as well as majorite and wadsleyite have been synthesized; ringwoodite and perovskite are scheduled. Preliminary thermal conductivity measurements at ambient pressure on coesite (120 - 300 K, 9.53 Wm-1K-1 at 300 K) are consistent with prior room temperature data (\\textit{Yukutake & Shimada, PEPI, 1978}), while our stishovite data at 300 K appear to be low (1.96 Wm-1K-1). Efforts are being made to extend the measurement to higher temperatures (e.g., above Debye temperature Θ D), thus allowing determination of k(T) relationship (say, k~ T-n); success will depend on the decomposition kinetics of these metastable phases. The pressure dependence of k of these synthesized samples can also be measured (\\textit{e.g., Osako et al., HPMPS-6, 2002; Xu et al., EOS, 2001}). Recent thermal conductivity measurement on LiF and Al2O_3 from shock wave loading (\\textit{Holland & Ahrens, 1998}) is consistent with the modeling on MgO and Al2O_3 (\\textit{Manga & Jeanloz, JGR, 1997}) with classical theories. Thus, k values at modest pressures and T (say, above Θ D) would allow extrapolation of k to appropriate mantle conditions.

  1. The role of thermodynamics in mantle convection: is mantle-layering intermittent?

    Stixrude, L. P.; Cagney, N.; Lithgow-Bertelloni, C. R.


    We examine the thermal evolution of the Earth using a 1D model in which mixing length theory is used to characterise the role of thermal convection. Unlike previous work, our model accounts for the complex role of thermodynamics and phase changes through the use of HeFESTo (Stixrude & Lithgow-Bertelloni, Geophys. J. Int. 184, 2011), a comprehensive thermodynamic model that enables self-consistent computation of phase equilibria, physical properties (e.g. density, thermal expansivity etc.) and mantle isentropes. Our model also accounts for the freezing of the inner core, radiogenic heating and Arrhenius rheology, and is validated by comparing our results to observations, including the present-day size of the inner core and the heat flux at the surface.If phase changes and the various thermodynamic effects on mantle properties are neglected, the results are weakly dependent on the initial conditions, as has been observed in several previous studies. However, when these effects are accounted for, the initial temperature profile has a strong influence on the thermal evolution of the mantle, because small changes in the temperature and phase-assemblage can lead to large changes in the local physical properties and the adiabatic gradient.The inclusion of thermodynamic effects leads to some new and interesting insights. We demonstrate that the Clapeyron slope and the thermal gradient at the transition zone both vary significantly with time; this causes the mantle to switch between a layered state, in which convection across the transition zone is weak or negligible, and an un-layered state, in which there is no resistance to mass transfer between the upper and lower mantles.Various plume models describe plumes either rising directly from the CMB to the lithosphere, or stalling at the transition zone before spawning new plumes in the upper mantle. The observance of switching behaviour indicates that both models may be applicable depending on the state of the mantle: plumes

  2. Echocardiographic Assessment of Mantle Radiation Mitral Stenosis.

    Bastiaenen, Rachel; Sneddon, James; Sharma, Rajan


    The long-term sequelae of mantle radiotherapy include lung disease and cardiac disorders. Dyspnea on exertion is a common complaint and can be due to one or more pathologies. We describe a case of mantle radiotherapy-induced mitral stenosis, characterized by aorto-mitral continuity calcification and absent commissural fusion which precludes balloon valvotomy. The latency period is long, and this patient presented 42 years after radiotherapy. Importantly, as previously described with radiation-induced valve disease, significant mitral stenosis developed 10 years after surgery for significant aortic stenosis. Two-dimensional and three-dimensional transthoracic and transesophageal echocardiography should be considered during assessment of symptomatic survivors of Hodgkin's disease where the index of suspicion for valvular stenosis increases over time. Given the natural history of mantle radiation valvular disease, a lower threshold for surgical intervention in radiation-induced mitral stenosis may need to be considered if cardiac surgery is planned for other reasons in order to avoid repeated sternotomy in patients with prior irradiation.

  3. Mantle updrafts and mechanisms of oceanic volcanism

    Anderson, Don L.; Natland, James H.


    Convection in an isolated planet is characterized by narrow downwellings and broad updrafts-consequences of Archimedes' principle, the cooling required by the second law of thermodynamics, and the effect of compression on material properties. A mature cooling planet with a conductive low-viscosity core develops a thick insulating surface boundary layer with a thermal maximum, a subadiabatic interior, and a cooling highly conductive but thin boundary layer above the core. Parts of the surface layer sink into the interior, displacing older, colder material, which is entrained by spreading ridges. Magma characteristics of intraplate volcanoes are derived from within the upper boundary layer. Upper mantle features revealed by seismic tomography and that are apparently related to surface volcanoes are intrinsically broad and are not due to unresolved narrow jets. Their morphology, aspect ratio, inferred ascent rate, and temperature show that they are passively responding to downward fluxes, as appropriate for a cooling planet that is losing more heat through its surface than is being provided from its core or from radioactive heating. Response to doward flux is the inverse of the heat-pipe/mantle-plume mode of planetary cooling. Shear-driven melt extraction from the surface boundary layer explains volcanic provinces such as Yellowstone, Hawaii, and Samoa. Passive upwellings from deeper in the upper mantle feed ridges and near-ridge hotspots, and others interact with the sheared and metasomatized surface layer. Normal plate tectonic processes are responsible both for plate boundary and intraplate swells and volcanism.

  4. Density profile of pyrolitic lower mantle

    Sinmyo, R.; Hirose, K.; Ohishi, Y.


    Density profile of pyrolite at lower mantle high-pressure (P) and -temperature (T) conditions was investigated by using laser-heated diamond-anvil cell up to 117 GPa and 2800 K. The density was determined from chemical composition and unit-cell volume of each constituent mineral (MgSiO3-rich perovskite, ferropericlase and CaSiO3-rich perovskite). The chemical compositions of coexisting phases were analyzed by transmission electron microscope, and their volumes were obtained by in-situ X-ray diffraction measurements. To avoid extensive chemical segregation during laser-heating, sample was coated by gold that worked as a laser absorber (Sinmyo and Hirose 2010 PEPI). Results of chemical analyses show that Mg-Fe (total Fe) partitioning coefficient between MgSiO3-rich perovskite and ferropericlase [K* = (Fe*/Mg)Pv/(Fe*/Mg)Fp] is about 0.6, slightly higher than the value previously reported in the pyrolitic bulk composition (Murakami et al. 2005 GRL). The lower K* value in the previous study may be attributed to the chemical heterogeneity in the sample induced by strong temperature gradient during laser heating. The calculated density profile of pyrolite is indeed in good agreement with the PREM model within experimental errors, in contrast with the mismatch reported by the previous study (Ricolleau et al. 2009 GRL). Our results support the lower mantle has pyrolitic bulk composition, and thus it is not necessary to suppose the chemically stratification in the lower mantle.

  5. Trusted Domain

    Hjorth, Theis Solberg; Torbensen, Rune


    that enables secure end-to-end communication with home automation devices, and it supports device revocations as well as a structure of intersecting sets of nodes for scalability. Devices in the Trusted Domain are registered in a list that is distributed using a robust epidemic protocol optimized...

  6. Domain crossing

    Schraefel, M. C.; Rouncefield, Mark; Kellogg, Wendy


    In CSCW, how much do we need to know about another domain/culture before we observe, intersect and intervene with designs. What optimally would that other culture need to know about us? Is this a “how long is a piece of string” question, or an inquiry where we can consider a variety of contexts a...

  7. The effect of water to mantle rheology and convection

    Brändli, Stefan


    Water has a significant influence to mantle rheology and therefore also to the convection of the mantle and the plate tectonics. The viscosity of the mantle can be decreased by up to two orders of magnitude when water is present. Another effect of the water is the change in the solidus of the mantle and therefore the melting regime. These two effects of water in the mantle have a significant influence on mantle convection and plate tectonics. The influx of water to the mantle is driven by plate tectonics as wet oceanic lithosphere is subducted into the mantle, then water is brought back to the lithosphere and the surface by MOR-, arc- and hotspot volcanism. Studies show that the amount of water in the mantle is about three times bigger than the water in the oceans. To model this water cycle multiple additions to our simulation code StagYY are necessary. A water diffusion to complement the water transport due to advection, and water dependent viscosity law are implemented. This additions to StagYY will be followed by implementations of a pressure-temperature law for maximum water content, additional transport mechanisms for water, water dependent solidus functions and the implementation of recent values for plate velocities and water capacities in subducting slabs. This will allow us to research the influence of water to the mantle convection and rheology over the past 200Ma.

  8. Pattern recognition constrains mantle properties, past and present

    Atkins, S.; Rozel, A. B.; Valentine, A. P.; Tackley, P.; Trampert, J.


    Understanding and modelling mantle convection requires knowledge of many mantle properties, such as viscosity, chemical structure and thermal proerties such as radiogenic heating rate. However, many of these parameters are only poorly constrained. We demonstrate a new method for inverting present day Earth observations for mantle properties. We use neural networks to represent the posterior probability density functions of many different mantle properties given the present structure of the mantle. We construct these probability density functions by sampling a wide range of possible mantle properties and running forward simulations, using the convection code StagYY. Our approach is particularly powerful because of its flexibility. Our samples are selected in the prior space, rather than being targeted towards a particular observation, as would normally be the case for probabilistic inversion. This means that the same suite of simulations can be used for inversions using a wide range of geophysical observations without the need to resample. Our method is probabilistic and non-linear and is therefore compatible with non-linear convection, avoiding some of the limitations associated with other methods for inverting mantle flow. This allows us to consider the entire history of the mantle. We also need relatively few samples for our inversion, making our approach computationally tractable when considering long periods of mantle history. Using the present thermal and density structure of the mantle, we can constrain rheological and compositional parameters such as viscosity and yield stress. We can also use the present day mantle structure to make inferences about the initial conditions for convection 4.5 Gyr ago. We can constrain initial mantle conditions including the initial concentration of heat producing elements in the mantle and the initial thickness of primordial material at the CMB. Currently we use density and temperature structure for our inversions, but we can

  9. Mineralogy and composition of the oceanic mantle

    Putirka, Keith; Ryerson, F.J.; Perfit, Michael; Ridley, W. Ian


    The mineralogy of the oceanic basalt source region is examined by testing whether a peridotite mineralogy can yield observed whole-rock and olivine compositions from (1) the Hawaiian Islands, our type example of a mantle plume, and (2) the Siqueiros Transform, which provides primitive samples of normal mid-ocean ridge basalt. New olivine compositional data from phase 2 of the Hawaii Scientific Drilling Project (HSDP2) show that higher Ni-in-olivine at the Hawaiian Islands is due to higher temperatures (T) of melt generation and processing (by c. 300°C) related to the Hawaiian mantle plume. DNi is low at high T, so parental Hawaiian basalts are enriched in NiO. When Hawaiian (picritic) parental magmas are transported to shallow depths, olivine precipitation occurs at lower temperatures, where DNi is high, leading to high Ni-in-olivine. Similarly, variations in Mn and Fe/Mn ratios in olivines are explained by contrasts in the temperatures of magma processing. Using the most mafic rocks to delimit Siqueiros and Hawaiian Co and Ni contents in parental magmas and mantle source compositions also shows that both suites can be derived from natural peridotites, but are inconsistent with partial melting of natural pyroxenites. Whole-rock compositions at Hawaii and Siqueiros are also matched by partial melting experiments conducted on peridotite bulk compositions. Hawaiian whole-rocks have elevated FeO contents compared with Siqueiros, which can be explained if Hawaiian parental magmas are generated from peridotite at 4-5 GPa, in contrast to pressures of slightly greater than 1 GPa for melt generation at Siqueiros; these pressures are consistent with olivine thermometry, as described in an earlier paper. SiO2-enriched Koolau compositions are reproduced if high-Fe Hawaiian parental magmas re-equilibrate at 1-1·5 GPa. Peridotite partial melts from experimental studies also reproduce the CaO and Al2O3 contents of Hawaiian (and Siqueiros) whole-rocks. Hawaiian magmas have TiO2

  10. Anisotropic Structure of the Upper Mantle, Imaged with Surface and S Waveform Tomography

    Schaeffer, A. J.; Lebedev, S.


    The rapid recent expansion of global and regional seismic networks has paved the way for a new generation of tomographic models, with significantly improved resolution at global and regional scales. We present a new global model of shear velocity and azimuthal anisotropy in the upper mantle, down to the base of the transition zone. The model is constrained by an unprecedentedly large waveform dataset collected from over 2000 stations of GSN and affiliates, USArray, VEBSN, CNSN, PASSCAL experiments, and other networks with data available from IRIS, ORFEUS, and GFZ data centers. Applying the accurate and efficient automated multimode inversion of surface- and S-wave forms to this massive dataset, we generated linear constraints on elastic structure within approximate sensitivity volumes between individual source-receiver pairs, with respect to a 3D reference model. The full waveform inversions resulted in more than one million successful fits (one million seismograms), with structural information extracted from both the fundamental and higher modes. The linear equations were then simultaneously solved for a high-resolution, 3D model of shear velocity and azimuthal anisotropy in the upper mantle. In continental domains, clearly identifiable boundaries between different tectonic features such as basins and relic mountain ranges are readily observable, as well as the signature of deep cratonic roots versus juvenile accretionary margins. Both active and fossil subduction zones are marked by slab signatures deep in the upper mantle and extending through the transition zone. In oceanic regions, largest mid-ocean-ridge anomalies indicative of melting terminate at depths of 100-120 km, with evidence for vertical flow in the upper mantle observed through a combination of VSV, VSH, and azimuthal anisotropy. Spatio-temporal evolution (cooling and thickening) of lithosphere away from the spreading ridges matches the signature expected from geodynamic and thermal modeling. The

  11. The Upper Mantle Flow Field around South-Africa as Reflected by Isotopic Provinciality

    Meyzen, C.; Blichert-Toft, J.; Ludden, J.; Humler, E.; Mevel, C.; Albarede, F.


    Isotopic studies of MORB have established the existence of broad isotopic provinces within the underlying asthenosphere, such as in the Indian Ocean (DUPAL). How these features relate to mantle circulation is, however, still unknown. The steepness of the transition between such isotopic provinces will define the geometry of the velocity field in the upper mantle. In this respect, the transition between the Indian and South Atlantic provinces, two domains that are isotopically contrasted, should be readily identifiable over this long ridge segment. Here, we present Hf isotope data for 60 samples dredged along the SWIR between 35° and 69°E. The new Hf isotope data show that the Indian asthenosphere does not spill directly into the South Atlantic upper mantle: the general decreasing southward gradient observed for ^{176}Hf/^{177}Hf down the mid- Atlantic Ridge, and also for Sr isotopes and model Th/U ratios (derived from Pb isotopes), is overprinted by material with radiogenic Sr, unradiogenic Hf and high Th/U. The Indian domain grades into the South Atlantic around Bouvet, while the South Atlantic collides with the Atlantic province around Tristan. We interpret these features to represent fronts between three adjacent isotopic provinces similar to what has been suggested for the Australian-Antarctic Discordance. The common DUPAL signature of MORB and OIB from the Indian province and the geochemistry of Gulf of Aden MORB and the Afar plume suggest that the source of this distinctive mantle component is deep and lies to the north of the province. This is also what the three-dimensional flow field computed by Behn et al. (2004) from shear-wave splitting shows with a major lower mantle upwelling radiating at the base of the asthenosphere under the Afar plume. Lower mantle gushing out from this source flows southward unimpeded along the Indian ridges, whereas it only reaches the South Atlantic ridge after first having been deflected under the deep roots of the South

  12. Electrical conductivity of mantle peridotite at the uppermost lower mantle condition

    Yoshino, T; Katsura, T; Yamazaki, D; Ito, E, E-mail: [Institute for Study of the Earth' s Interior, Okayama University, 827 Yamada, Misasa, Tottori 682-1093 (Japan)


    Electrical conductivity of mantle peridotite was measured at 25 GPa and temperature up to 1800 K in a Kawai-type multi-anvil apparatus. The starting material was gel with a composition of fertile spinel lherzolite (KLB1). After the conductivity measurement, mineral phases of run products are composed of magnesium silicate perovskite, ferro-periclase and Ca perovskite. The conductivity value of the peridotite is distinctly higher than those of post-spinel and magnesian silicate perovskite with a composition of (Mg{sub 0.9},Fe{sub 0.1})SiO{sub 3}, but lower than that of ferro-periclase. Both absolute values and change in activation enthalpy for the conductivity of the mantle peridotite are similar to those for the silicate perovskite. A presence of aluminous perovskite with substantial amount of ferric iron in crystal structure would enhance bulk conductivity of the lower mantle.

  13. Numerical modeling of mantle wedge processes and exhumation of UHP mantle in subduction zones

    Gorczyk, W.; Gerya, T. V.; Guillot, S.; Connolly, J. A.; Yuen, D.


    The upwelling of subduction generated partially molten rocks is potentially a mechanism for the exhumation of UHP rocks through the mantle wedge. We investigated this processes using a 2-D coupled petrological- thermomechanical model that incorporates slab dehydration and water transport as well as partial melting of mantle and crustal rocks. This approach allows us to study the dynamics of mantle wedge processes including evolution of partially molten plumes and their interaction with surrounding dry mantle. To study the internal structure of the plumes we used ultra-high resolution numerical simulations with 10 billion active markers to detail the internal structure of natural plumes originating from the slab. The plumes consist of partially molten hydrated peridotite, dry solid mantle and subducted oceanic crust, which may comprise up to 12 volume % of the plume. As the plumes grow and mature these materials mix chaotically resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges. The recent discovery of garnet bearing peridotites in the subduction zone of the Great Antilles in Hispaniola has raised questions about the process that leads to their exhumation. To evaluate whether upwelling plumes are a plausible exhumation mechanism we investigated the dynamics of subduction of slow spreading ridges. The results show that subduction of strongly serpentinized oceanic plate causes strong dehydration of the slab and leads to a rheological weakening of the interface between subducting and overriding plate. This weakening triggers trench retreat and massive asthenospheric upwelling into the gap between the

  14. Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern

    Paul; SILVER; Lucy; FLESCH


    By using the polarization analysis of teleseismic SKS waveform data recorded at 116 seismic stations which respectively involved in China National Digital Seismograph Network, and Yunnan, Sichuan, Gansu and Qinghai regional digital networks, and portable broadband seismic networks deployed in Sichuan, Yunnan and Tibet, we obtained the SKS fast-wave direction and the delay time between fast and slow waves of each station by use of the stacking analysis method, and finally acquired the fine image of upper mantle anisotropy in the eastern Tibetan Plateau and its adjacent regions. We analyzed the crust-mantle coupling deformation on the basis of combining the GPS observation results and the upper mantle anisotropy distribution in the study area. The Yunnan region out of the plateau has dif-ferent features of crust-mantle deformation from the inside plateau. There exists a lateral transitional zone of crust-mantle coupling in the eastern edge of the Tibetan Plateau, which is located in the region between 26° and 27°N in the west of Sichuan and Yunnan. To the south of transitional zone, the fast-wave direction is gradually turned from S60°―70°E in southwestern Yunnan to near EW in south-eastern Yunnan. To the north of transitional zone in northwestern Yunnan and the south of western Sichuan, the fast-wave direction is nearly NS. From crust to upper mantle, the geophysical parameters (e.g. the crustal thickness, the Bouguer gravity anomaly, and tectonic stress direction) show the feature of lateral variation in the transitional zone, although the fault trend on the ground surface is inconsis-tent with the fast-wave direction. This transitional zone is close by the eastern Himalayan syntaxis, and it may play an important role in the plate boundary dynamics.

  15. Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern

    WANG ChunYong; CHANG LiJun; L(U) ZhiYong; QIN JiaZheng; SU Wei; Paul SILVER; Lucy FLESCH


    By using the polarization analysis of teleseismic SKS waveform data recorded at 116 seismic stations which respectively involved in China National Digital Seismograph Network, and Yunnan, Sichuan,Gansu and Qinghai regional digital networks, and portable broadband seismic networks deployed in Sichuan, Yunnan and Tibet, we obtained the SKS fast-wave direction and the delay time between fast and slow waves of each station by use of the stacking analysis method, and finally acquired the fine image of upper mantle anisotropy in the eastern Tibetan Plateau and its adjacent regions. We analyzed the crust-mantle coupling deformation on the basis of combining the GPS observation results and the upper mantle anisotropy distribution in the study area. The Yunnan region out of the plateau has different features of crust-mantle deformation from the inside plateau. There exists a lateral transitional zone of crust-mantle coupling in the eastern edge of the Tibetan Plateau, which is located in the region between 26° and 27°N in the west of Sichuan and Yunnan. To the south of transitional zone, the fast-wave direction is gradually turned from S60°-70°E in southwestern Yunnan to near EW in southeastern Yunnan. To the north of transitional zone in northwestern Yunnan and the south of western Sichuan, the fast-wave direction is nearly NS. From crust to upper mantle, the geophysical parameters(e.g. the crustal thickness, the Bouguer gravity anomaly, and tectonic stress direction) show the feature of lateral variation in the transitional zone, although the fault trend on the ground surface is inconsistent with the fast-wave direction. This transitional zone is close by the eastern Himalayan syntaxis, and it may play an important role in the plate boundary dynamics.

  16. Dihedral angle of carbonatite melts in mantle residue near the upper mantle and transition zone

    Ghosh, S. K.; Rohrbach, A.; Schmidt, M. W.


    Carbonate melts are thought to be ideal metasomatic agents in the deep upper mantle (Green & Wallace, 1988) and these melts are low in viscosities (10-1-10-3 Pa·s) compared to primitive basalt (101-102 Pa·s), furthermore the ability to form an interconnected grain-edge melt network at low melt fractions (3 GPa (Dasgupta et al. 2006, Ghosh et al., 2009), dissolve a number of geochemically incompatible elements much better than silicate melts (Blundy and Dalton, 2000). Previous studies of carbonate melt dihedral angles in olivine-dominated matrices yielded 25-30oat 1-3 GPa, relatively independent of melt composition (Watson et al., 1990) and temperature (Hunter and McKenzie, 1989). Dihedral angles of carbonate melts in contact with deep mantle silicate phases (e.g. garnet, wadsleyite, and ringwoodite) which constitute more than 70 % of the deep upper mantle and transition zone have not been studied yet. We have performed multi-anvil experiments on carbonate-bearing peridotites with 5.0 wt% CO2 from 13.5 to 20 GPa 1550 oC to investigate the dihedral angle of magnesio-carbonatite melts in equilibrium with garnet, olivine (and its high-pressure polymorphs), and clinoenstatite. The dihedral angle of carbonate melts in the deep upper mantle and transition zone is ~30° for majorite garnet and olivine (and its polymorphs) dominated matrices. It does not change with increasing pressure in the range 13.5-20 GPa. Our results suggest that very low melt fractions of carbonatite melt forming in the deep upper mantle and transition zone are interconnected at melt fractions less than 0.01. Consistent with geophysical observations, this could possibly explain low velocity regions in the deep mantle and transition zone.

  17. Determining resolvability of mantle plumes with synthetic seismic modeling

    Maguire, R.; Van Keken, P. E.; Ritsema, J.; Fichtner, A.; Goes, S. D. B.


    Hotspot volcanism in locations such as Hawaii and Iceland is commonly thought to be associated with plumes rising from the deep mantle. In theory these dynamic upwellings should be visible in seismic data due to their reduced seismic velocity and their effect on mantle transition zone thickness. Numerous studies have attempted to image plumes [1,2,3], but their deep mantle origin remains unclear. In addition, a debate continues as to whether lower mantle plumes are visible in the form of body wave travel time delays, or whether such delays will be erased due to wavefront healing. Here we combine geodynamic modeling of mantle plumes with synthetic seismic waveform modeling in order to quantitatively determine under what conditions mantle plumes should be seismically visible. We model compressible plumes with phase changes at 410 km and 670 km, and a viscosity reduction in the upper mantle. These plumes thin from greater than 600 km in diameter in the lower mantle, to 200 - 400 km in the upper mantle. Plume excess potential temperature is 375 K, which maps to seismic velocity reductions of 4 - 12 % in the upper mantle, and 2 - 4 % in the lower mantle. Previous work that was limited to an axisymmetric spherical geometry suggested that these plumes would not be visible in the lower mantle [4]. Here we extend this approach to full 3D spherical wave propagation modeling. Initial results using a simplified cylindrical plume conduit suggest that mantle plumes with a diameter of 1000 km or greater will retain a deep mantle seismic signature. References[1] Wolfe, Cecily J., et al. "Seismic structure of the Iceland mantle plume." Nature 385.6613 (1997): 245-247. [2] Montelli, Raffaella, et al. "Finite-frequency tomography reveals a variety of plumes in the mantle." Science 303.5656 (2004): 338-343. [3] Schmandt, Brandon, et al. "Hot mantle upwelling across the 660 beneath Yellowstone." Earth and Planetary Science Letters 331 (2012): 224-236. [4] Hwang, Yong Keun, et al

  18. Life Cycle of Mantle Plumes: A perspective from the Galapagos Plume (Invited)

    Gazel, E.; Herzberg, C. T.


    plume model of the CLIP. The exact form of the secular cooling curve depends on whether the Gorgona komatiites were produced by the Galapagos or another plume. Iceland also exhibits secular cooling, in agreement with previous studies. In general, mantle plumes for LIPS with Paleocene-Permian ages were hotter and melted more extensively than plumes of more modern oceanic islands. This is interpreted to reflect episodic flow from lower mantle domains that are lithologically and geochemically heterogeneous. The majority of lavas from the present-day Galapagos plume formed in a column where melting ended at pressures less than 2 GPa, and this pressure is highly variable. Melting ended at much lower pressures for lavas from the Cocos and Carnegie Ridges, consistent with the channeling of the Galapagos plume to locations of thinner lithosphere. Low pressures of final melting are also inferred for older CLIP lavas, which suggest that the plume head impacted a mid-ocean ridge system.

  19. Can the mantle control the core?: Energetics and dynamics

    Nakagawa, T.


    The sustainability of magnetic field generation is discussed from a coupled model of numerical mantle convection simulation and core energetics theory. The pattern of geomagnetic field could be also controlled as a consequence of mantle convection [e.g. Amit and Choblet, 2009]. Our previous studies have suggested that the best-fit scenario for explaining both sustainability of magnetic field generation caused by dynamo actions and the size of inner core would be strongly controlled by the heat transfer of mantle convection with strongly compositional heterogeneities [Nakagawa and Tackley, 2004; Nakagawa and Tackley, 2010]. Here we investigate effects of initial mantle temperature and radioactive heat source in a convecting mantle with extremely high initial temperature at the core-mantle boundary that has been suggested from the hypothesis of early Earth [Labrosse et al., 2007] for checking how the mantle can control the thermal evolution of the core. Main consequence is that the amount of heat production rate and initial mantle temperature are not very sensitive to the thermal evolution of Earth's core but the convective vigor seems to be sensitive to the results. For the mantle side, the Urey ratio is not very good constraint for understanding thermal evolution of the whole Earth. In addition, we also show an example of numerical dynamo simulations with both a stably stratified layer and lateral variation of heat flux across the core-mantle boundary (CMB), which expands a paper by Nakagawa [2011], evaluated from numerical mantle convection simulations for checking how the mantle can control the dynamics of the core, which checks dead or alive for the magnetic field generated by dynamo actions with strongly lateral variation of CMB heat flux.

  20. Archimedean Proof of the Physical Impossibility of Earth Mantle Convection

    Herndon, J. Marvin


    Eight decades ago, Arthur Holmes introducted the idea of mantle convection as a mechanism for continental drift. Five decades ago, continental drift was modified to become plate tectonics theory, which included mantle convection as an absolutely critical component. Using the submarine design and operation concept of "neutral buoyancy", which follows from Archimedes' discoveries, the concept of mantle convection is proven to be incorrect, concomitantly refuting plate tectonics, refuting all ma...

  1. Scales of Heterogeneities in the Continental Crust and Upper Mantle

    M. Tittgemeyer; F. Wenzel; Trond Ryberg; Fuchs, K


    A seismological characterization of crust and upper mantle can refer to large-scale averages of seismic velocities or to fluctuations of elastic parameters. Large is understood here relative to the wavelength used to probe the earth. In this paper we try to characterize crust and upper mantle by the fluctuations in media properties rather than by their average velocities. As such it becomes evident that different scales of heterogeneities prevail in different layers of crust mantle. Although ...

  2. Water concentrations in mantle peridotite minerals

    Warren, J. M.; Hauri, E. H.


    The concentration and distribution of volatiles in the mantle is important for constraining many key properties, including melting systematics at ridges and subduction zones. We present measurements of water concentrations in nominally anhydrous minerals from abyssal, orogenic and xenolith peridotites. Analyses of fresh and altered samples from a variety of locations are used to assess the extent to which mineral water concentrations reflect primary mantle compositions, versus diffusive loss and/or hydration due to secondary processes. Water concentrations were measured in olivine (Ol), orthopyroxene (Opx) and clinopyroxene (Cpx) by ion microprobe, using mineral specific standards and monitoring background concentrations by analysis of synthetic forsterite. Analytical reproducibility, based on 11 repeat analyses of an Ol grain, is 10%, while background H2O levels varied from 7-19 ppm. Samples include xenoliths from Pali Aike, Samoa and Spitsbergen, along with unusually fresh oceanic peridotites from the Gakkel Ridge and the Tonga Trench. In addition, samples were analyzed from the Southwest Indian Ridge (SWIR) and the Josephine Peridotite, both of which have moderate degrees of alteration. In olivine, water concentrations are Pali Aike xenoliths, which have water concentrations of 16-33 ppm. On average, peridotite Opx have 187 ppm and Cpx have 474 ppm. Pyroxenite veins from the Southwest Indian Ridge have systematically lower concentrations, with an average of 12 ppm in Opx and 55 ppm in Cpx. Water partition coefficients for Opx/Ol have an average value of 28 and Cpx/Ol of 57, significantly higher than previous estimates (e.g., Hirth and Kohlstedt, 1996). Excluding the pyroxenites, the average Cpx/Opx partition coefficient is 2, in agreement with published estimates. This suggests that Cpx and Opx preserve mantle water concentrations, whereas Ol has undergone hydrogen loss. Mineral rims have water concentrations that are within error of core concentrations. The

  3. The composition of mantle plumes and the deep Earth

    Hastie, Alan R.; Fitton, J. Godfrey; Kerr, Andrew C.; McDonald, Iain; Schwindrofska, Antje; Hoernle, Kaj


    Determining the composition and geochemical diversity of Earth's deep mantle and subsequent ascending mantle plumes is vital so that we can better understand how the Earth's primitive mantle reservoirs initially formed and how they have evolved over the last 4.6 billion years. Further data on the composition of mantle plumes, which generate voluminous eruptions on the planet's surface, are also essential to fully understand the evolution of the Earth's hydrosphere and atmosphere with links to surface environmental changes that may have led to mass extinction events. Here we present new major and trace element and Sr-Nd-Pb-Hf isotope data on basalts from Curacao, part of the Caribbean large igneous province. From these and literature data, we calculate combined major and trace element compositions for the mantle plumes that generated the Caribbean and Ontong Java large igneous provinces and use mass balance to determine the composition of the Earth's lower mantle. Incompatible element and isotope results indicate that mantle plumes have broadly distinctive depleted and enriched compositions that, in addition to the numerous mantle reservoirs already proposed in the literature, represent large planetary-scale geochemical heterogeneity in the Earth's deep mantle that are similar to non-chondritic Bulk Silicate Earth compositions.

  4. Mantle Structure Beneath Central South America

    Vandecar, J. C.; Silver, P. G.; James, D. E.; Assumpcao, M.; Schimmel, M.; Zandt, G.


    Making use of 60 digital broadband seismic stations that have operated across central South America in recent years, we have undertaken an inversion for the upper- and uppermost lower-mantle P- and S-wave velocity structures beneath the region. We have combined data from four portable PASSCAL-type experiments as well as the 3 GTSN permanent stations (LPAZ, BDFB and CPUP) and 1 Geoscope station (SPB) located in the region. The portable data were deployed at various times between 1992 and 1999 and include: 28 sites from the Brazilian Lithosphere Seismic Project (BLSP: Carnegie Institution of Washington and Universidade de Sao Paulo), 16 sites from the Broadband ANdean JOint experiment (BANJO: Carnegie Institution of Washington and University of Arizona), 8 sites from the Seismic Exploration of the Deep Altiplano project (SEDA: Lawrence Livermore National Laboratory) and 4 sites from the University of Brasilia. The P- and S-wave relative delay times are independently obtained via a multi-channel cross correlation of band-passed waveforms for each teleseismic event. These data are then inverted using an iterative, robust, non-linear scheme which parameterizes the 3-D velocity variations as splines under tension constrained at over 120,000 nodes across South America between latitudes of 15 and 30 degrees South. Amongst other features, we robustly image the high-velocity subducting Nazca plate penetrating into the lower mantle and the high-velocity root of the ~3.2 Gyr old Sao Francisco Craton extending to depths of 200-300 km. We will discuss the consistency between our tomographic models and predictions of dynamic mantle models based on plate tectonic reconstructions of subduction.

  5. How Depleted is the MORB mantle?

    Hofmann, A. W.; Hart, S. R.


    Knowledge of the degree of mantle depletion of highly incompatible elements is critically important for assessing Earth's internal heat production and Urey number. Current views of the degree of MORB source depletion are dominated by Salters and Stracke (2004), and Workman and Hart (2005). The first is based on an assessment of average MORB compositions, whereas the second considers trace element data of oceanic peridotites. Both require an independent determination of one absolute concentration, Lu (Salters & Stracke), or Nd (Workman & Hart). Both use parent-daughter ratios Lu/Hf, Sm/Nd, and Rb/Sr calculated from MORB isotopes combined with continental-crust extraction models, as well as "canonical" trace element ratios, to boot-strap the full range of trace element abundances. We show that the single most important factor in determining the ultimate degree of incompatible element depletion in the MORB source lies in the assumptions about the timing of continent extraction, exemplified by continuous extraction versus simple two-stage models. Continued crust extraction generates additional, recent mantle depletion, without affecting the isotopic composition of the residual mantle significantly. Previous emphasis on chemical compositions of MORB and/or peridotites has tended to obscure this. We will explore the effect of different continent extraction models on the degree of U, Th, and K depletion in the MORB source. Given the uncertainties of the two most popular models, the uncertainties of U and Th in DMM are at least ±50%, and this impacts the constraints on the terrestrial Urey ratio. Salters, F.J.M. and Stracke, A., 2004, Geochem. Geophys. Geosyst. 5, Q05004. Workman, R.K. and Hart, S.R., 2005, EPSL 231, 53-72.

  6. Trans-Pacific whole mantle structure

    Liu, Lijun; Tan, Ying; Sun, Daoyuan; Chen, Min; Helmberger, Don


    Recent reports on modeling USArray data reveal mostly vertical microplates with little resemblance to preliminary reference Earth model (PREM). Such complexity at plate boundaries makes it difficult to form reliable images of ocean basins using global paths. Here, we report on modeling stacked seismograms obtained from the first broadband array (TriNet) situated on the edge of the Pacific Plate, southern California, with no major subduction zone blocking its view. Extended records, including multi-S and ScS waves up to four bounces from 18 Tonga-Fiji deep events (140 to 620 km) are analyzed to check the validity of existing models and derive the whole mantle shear velocity structure along this corridor. Synthetics generated from 3-D tomographic models do not fit the upper mantle triplication data or the mantle reverberations associated with the ScS multiples as well as the 1-D model PAC06. We construct a hybrid model (HPAC), which remains one dimensional down to 800 km (PAC06). The lower portion of HPAC is essentially the tomography model S20RTS with velocity variation inflated by a factor of 2 for the lowermost 600 km. Thus, the mid-Pacific large low shear velocity province (LLSVP) has a lower shear velocity of about 2% relative to PREM and extends into the midmantle, similar to that beneath South Africa. Moreover, rapid changes in the differential (ScS-S) and (ScS2-S) times as a function of distance suggest ultra low velocity zones near the eastern edge and under the LLSVP, again similar to that found beneath Africa.

  7. Is there seismic attenuation in the mantle?

    Ricard, Y.; Durand, S.; Montagner, J.-P.; Chambat, F.


    The small scale heterogeneity of the mantle is mostly due to the mixing of petrological heterogeneities by a smooth but chaotic convection and should consist in a laminated structure (marble cake) with a power spectrum S(k) varying as 1/k, where k is the wavenumber of the anomalies. This distribution of heterogeneities during convective stirring with negligible diffusion, called Batchelor regime is documented by fluid dynamic experiments and corresponds to what can be inferred from geochemistry and seismic tomography. This laminated structure imposes density, seismic velocity and potentially, anisotropic heterogeneities with similar 1/k spectra. A seismic wave of wavenumber k0 crossing such a medium is partly reflected by the heterogeneities and we show that the scattered energy is proportional to k0S(2k0). The reduction of energy for the propagating wave appears therefore equivalent to a quality factor 1/Q∝k0S(2k0). With the specific 1/k spectrum of the mantle, the resulting apparent attenuation should therefore be frequency independent. We show that the total contribution of 6-9% RMS density, velocity and anisotropy would explain the observed S and P attenuation of the mantle. Although these values are large, they are not unreasonable and we discuss how they depend on the range of frequencies over which the attenuation is explained. If such a level of heterogeneity were present, most of the attenuation of the Earth would be due to small scale scattering by laminations, not by intrinsic dissipation. Intrinsic dissipation must certainly exist but might correspond to a larger, yet unobserved Q. This provocative result would explain the very weak frequency dependence of the attenuation, and the fact that bulk attenuation seems negligible, two observations that have been difficult to explain for 50 years.

  8. Sizes of mantle heteogeneities and seismic attenuation

    Ricard, Y. R.; durand, S.; Chambat, F.; Montagner, J.


    The small scale heterogeneity of the mantle, being mostly due to the mixing of petrological heterogeneities by a smooth but chaotic convection should consist in a laminated structure (marble cake) with a power spectrum S(k) varying as 1/k, where k is the wavenumber of the anomalies. This distribution of heterogeneities during convective stirring with negligible diffusion, called Batchelor regime is documented by fluid dynamic experiments and corresponds to what can be inferred from geochemistry and seismic tomography. This laminated structure imposes density, seismic velocity and potentially, anisotropic heterogeneities with similar 1/k spectrums. We show that a seismic wave of wavenumber k_0 crossing such medium is partly reflected by the heterogeneities and the scattered energy has an energy found proportional to k_0 S(2k_0). The reduction of energy for the propagating wave appears therefore equivalent to a quality factor 1/Q proportional to k_0 S(2k_0). With the specific 1/k spectrum of the mantle, the resulting apparent attenuation should therefore be frequency independent. We show that the total contribution of 6-9% RMS density, velocity and anisotropy would explain the observed S and P attenuation of the mantle. Although these values are large there are not unreasonable and we discuss how they are likely overestimated. In this case, most of the attenuation of the Earth would be due to small scale scattering by laminations not by intrinsic dissipation. Intrinsic dissipation must certainly exists but might correspond to a larger, yet unobserved Q. This provocative result would explain the observed very weak frequency dependence of the attenuation, and the fact that bulk attenuation seems negligeable, two observations that have been difficult to explain for 50 years.

  9. Pyroxenes as tracers of mantle water variations

    Warren, Jessica M.; Hauri, Erik H.


    The concentration and distribution of volatiles in the Earth's mantle influence properties such as melting temperature, conductivity, and viscosity. To constrain upper mantle water content, concentrations of H2O, P, and F were measured in olivine, orthopyroxene, and clinopyroxene in mantle peridotites by secondary ion mass spectrometry. Analyzed peridotites are xenoliths (Pali Aike, Spitsbergen, Samoa), orogenic peridotites (Josephine Peridotite), and abyssal peridotites (Gakkel Ridge, Southwest Indian Ridge, Tonga Trench). The comparison of fresh and altered peridotites demonstrates that low to moderate levels of alteration do not affect H2O concentrations, in agreement with mineral diffusion data. Olivines have diffusively lost water during emplacement, as demonstrated by disequilibrium between olivine and coexisting pyroxenes. In contrast, clinopyroxene and orthopyroxene preserve their high-temperature water contents, and their partitioning agrees with published experiments and other xenoliths. Hence, olivine water concentrations can be determined from pyroxene concentrations using mineral-mineral partition coefficients. Clinopyroxenes have 60-670 ppm H2O, while orthopyroxenes have 10-300 ppm, which gives calculated olivine concentrations of 8-34 ppm. The highest olivine water concentration translates to an effective viscosity of 6 × 1019 Pa s at 1250°C and ~15 km depth, compared to a dry effective viscosity of 2.5 × 1021 Pa s. Bulk rock water concentrations, calculated using mineral modes, are 20-220 ppm and correlate with peridotite indices of melt depletion. However, trace element melt modeling indicates that peridotites have too much water relative to their rare earth element concentrations, which may be explained by late-stage melt addition, during which only hydrogen diffuses fast enough for reequilibration.

  10. Primary mantle cell lymphoma of the trachea.

    Guddati, Achuta K; Marak, Creticus P


    Primary mantle cell lymphoma (MCL) is a controversial entity. It is difficult to diagnose MCL in a single organ without lymph node involvement. However, with the advent of PET-CT scans and large panels of immunohistochemistry markers, there have been increasing reports of primary MCL detected in various organs of which the GI tract is the most common. In this case report, we describe the diagnosis and clinical course of a patient who presented with "B symptoms" and respiratory distress. On further investigation, he was found to have a mass in his trachea, which was diagnosed as primary MCL.

  11. Cratonic lithospheric mantle: Is anything subducted?

    William L. Griffin; Suzanne Y. O'ReiUy


    @@ If the subcontinental lithospheric mantle (SCLM) formed through the repeated underthrusting of oceanic slabs, peridotitic SCLM should resemble oceanic peridotites, and mafic rocks (eclogites, s.l.) should be distributed throughout the SCLM. However, cratonic peridotites (both exposed massifs and xenoliths) differ markedly from oceanic and ophiolitic peridotites in their Fe-Cr-Al relationships and abundances of trace elements (Li and B) diagnostic of subduction. "Typical"cratonic peridotites have experienced extensive metaso matism; modelling of their refractory protoliths indicates high-degree melting at high P, perhaps a uniquely Archean process.

  12. Geochemical Characterization of Endmember Mantle Components


    in Figs. 7 & 8). Production of the EM component by deep mantle fractionations involving high-pressure phases such as Ca or Mg perovskite likewise... Hafnium isotopes in basalts from the southern Mid-Atlantic Ridge from 40°S to 55°S: Discovery and Shona plume-ridge interactions and the role of recycled...171 (1999) 49-61. Bowring, S. A. and T. Housh, The Earth’s Early Evolution, Science 269 (1995) 1535-1540. Chauvel, C. and J. Blichert-Toft, A hafnium

  13. Singular spectrum analysis and its applications in mapping mantle seismic structure

    Dokht, Ramin M. H.; Gu, Yu Jeffrey; Sacchi, Mauricio D.


    Seismic discontinuities are fundamental to the understanding of mantle composition and dynamics. Their depths and impedance contrasts are generally determined using secondary phases such as SS precursors and P-to-S converted waves. However, analysing and interpreting these weak signals often suffer from incomplete data coverage, high noise levels and interfering seismic arrivals, especially near tectonically complex regions such as subduction zones. To overcome these pitfalls, we adopt a singular spectrum analysis (SSA) method to remove random noise, reconstruct missing traces and enhance the robustness of SS precursors and P-to-S conversions from mantle seismic discontinuities. Our method takes advantage of the predictability of time series in the frequency-space domain and performs rank reduction using a singular value decomposition of the trajectory matrix. We apply SSA to synthetic record sections as well as the observations of (1) SS precursors beneath the northwestern Pacific subduction zones, and (2) P-to-S converted waves from southwestern Canada. In comparison with raw or interpolated data, the SSA enhanced seismic sections exhibit greater resolution due to the suppression of random noise (which reduces signal amplitude during standard averaging procedures) through rank reduction. SSA also enables an effective separation of the SS precursors from the postcursors of S-wave core diffractions. This method will greatly benefit future analyses of weak crustal and mantle seismic phases, especially when data coverages are less than ideal.

  14. Multiple subduction imprints in the mantle below Italy detected in a single lava flow

    Nikogosian, Igor; Ersoy, Özlem; Whitehouse, Martin; Mason, Paul R. D.; de Hoog, Jan C. M.; Wortel, Rinus; van Bergen, Manfred J.


    Post-collisional magmatism reflects the regional subduction history prior to collision but the link between the two is complex and often poorly understood. The collision of continents along a convergent plate boundary commonly marks the onset of a variety of transitional geodynamic processes. Typical responses include delamination of subducting lithosphere, crustal thickening in the overriding plate, slab detachment and asthenospheric upwelling, or the complete termination of convergence. A prominent example is the Western-Central Mediterranean, where the ongoing slow convergence of Africa and Europe (Eurasia) has been accommodated by a variety of spreading and subduction systems that dispersed remnants of subducted lithosphere into the mantle, creating a compositionally wide spectrum of magmatism. Using lead isotope compositions of a set of melt inclusions in magmatic olivine crystals we detect exceptional heterogeneity in the mantle domain below Central Italy, which we attribute to the presence of continental material, introduced initially by Alpine and subsequently by Apennine subduction. We show that superimposed subduction imprints of a mantle source can be tapped during a melting episode millions of years later, and are recorded in a single lava flow.

  15. Subduction initiation, recycling of Alboran lower crust, and intracrustal emplacement of subcontinental lithospheric mantle in the Westernmost Mediterranean

    Varas-Reus, María Isabel; Garrido, Carlos J.; Bosch, Delphine; Marchesi, Claudio; Hidas, Károly; Booth-Rea, Guillermo; Acosta-Vigil, Antonio


    Unraveling the tectonic settings and processes involved in the annihilation of subcontinental mantle lithosphere is of paramount importance for our understanding of the endurance of continents through Earth history. Unlike ophiolites -- their oceanic mantle lithosphere counterparts -- the mechanisms of emplacement of the subcontinental mantle lithosphere in orogens is still poorly known. The emplacement of subcontinental lithospheric mantle peridotites is often attributed to extension in rifted passive margins or continental backarc basins, accretionary processes in subduction zones, or some combination of these processes. One of the most prominent features of the westernmost Mediterranean Alpine orogenic arcs is the presence of the largest outcrops worldwide of diamond facies, subcontinental mantle peridotite massifs; unveiling the mechanisms of emplacement of these massifs may provide important clues on processes involved in the destruction of continents. The western Mediterranean underwent a complex Alpine evolution of subduction initiation, slab fragmentation, and rollback within a context of slow convergence of Africa and Europe In the westernmost Mediterranean, the alpine orogeny ends in the Gibraltar tight arc, which is bounded by the Betic, Rif and Tell belts that surround the Alboran and Algero-Balearic basins. The internal units of these belts are mostly constituted of an allochthonous lithospheric domain that collided and overthrusted Mesozoic and Tertiary sedimentary rocks of the Mesozoic-Paleogene, South Iberian and Maghrebian rifted continental paleomargins. Subcontinental lithospheric peridotite massifs are intercalated between polymetamorphic internal units of the Betic (Ronda, Ojen and Carratraca massifs), Rif (Beni Bousera), and Tell belts. In the Betic chain, the internal zones of the allochthonous Alboran domain include, from bottom to top, polymetamorphic rock of the Alpujarride and Malaguide complexes. The Ronda peridotite massif -- the

  16. Intraplate volcanism and mantle dynamics in East Asia: Big mantle wedge (BMW) model (Invited)

    Zhao, D.


    In the East Asia continent there are many Cenozoic volcanoes, but only a few are still active now, such as the Changbai, Wudalianchi, and Tengchong volcanoes which have erupted several times in the past 1000 years. Although many studies have been made by using various approaches, the origin of the intraplate volcanoes in East Asia is still not very clear. Recently we used regional and global seismic tomography to determine high-resolution 3-D mantle structure under Western Pacific to East Asia (Zhao, 2004; Huang and Zhao, 2006; Zhao et al., 2009). Our results show prominent low-velocity anomalies from the surface down to 410 km depth beneath the intraplate volcanoes and a broad high-velocity anomaly in the mantle transition zone under East Asia. Focal-mechanism solutions of deep earthquakes indicate that the subducting Pacific slab under the Japan Sea and the East Asia margin is subject to compressive stress regime. These results suggest that the Pacific slab meets strong resistance at the 660-km discontinuity and so it becomes stagnant in the mantle transition zone under East Asia. The Philippine Sea slab has also subducted down to the mantle transition zone under western Japan and the Ryukyu back-arc region. The western edge of the stagnant slab is generally parallel with the Japan trench and the Ryukyu trench and roughly coincides with a prominent surface topography and gravity boundary in East China, which is located approximately 1800 km west of the trenches. The upper mantle under East Asia has formed a big mantle wedge (BMW) above the stagnant slab. The BMW exhibits low seismic-velocity and high electrical-conductivity, which is hot and wet because of the deep dehydration reactions of the stagnant slab and the convective circulation process in the BMW. These processes lead to the upwelling of hot and wet asthenospheric materials and thinning and fracturing of the continental lithosphere, leading to the formation of the active intraplate volcanoes in East

  17. Evidence of enriched mantle in the Archaean beneath eastern Indian Singhbhum Craton: constraints from geochemistry and Sr-Nd isotopic studies of mafic-ultramafic rocks from Bangriposi, Orissa, India

    Mouli Chakraborti, Tushar; Ray, Arijit; Deb, Gautam Kumar; Chakrabarti, Ramananda; Banerjee, Anupam


    Mafic-ultramafic rocks around Bangriposi (22° 9' N; 86° 32' E) are found to have been emplaced within polydeformed metasedimentary rocks of Singhbhum Group, belonging to the North Singhbhum Mobile Belt (NSMB) assemblage. Recent studies have assessed Mesoarchaean ( 3.09 Ga) age of these rocks and categorized the ultramafic unit as ultrahigh-pressure obducted bodies. The rocks are exposed mainly in two separate locations- Layered gabbroic rocks are found in an area SE of Bangriposi, and a well foliated, N-S trending Cr-spinel bearing wehrlite body is found S of Bangriposi. The gabbroic body (dubbed as "Kuliana Gabbro") is modally layered, contains plagioclase, clinopyroxene and orthopyroxene, and shows petrographic evidence of adcumulus growth and textural coarsening mechanisms. Cr-spinel bearing wehrlite rocks are highly serpentinized, containing serpentinized olivine, clinopyroxene, phlogopite, Cr-spinel, magnetite, and displays textural evidence of tectonic deformation. Geochemically, the Kuliana gabbro shows effects of fractional crystallization, and has relatively unfractionated REE patterns. The ultramafic rocks have high LOI contents (8- 9.3 wt%), with low Mg# (0.72- 0.77), and LREE enriched REE patterns. Parental melt calculations of the Kuliana Gabbro rocks have yielded an enriched-MORB like liquid, a product of low degree partial melting (8- 30%) in garnet facies. Cr-spinel bearing wehrlite rocks on the other hand exhibit ample evidences of modal and cryptic metasomatism in the mantle depth. Presence of phlogopite, diopside as reaction rims around serpentinized olivine, lack of primary orthopyroxene and presence of apatite are considered effects of modal metasomatism. Elevated LREE contents define cryptic metasomatism, which is also conspicuously visible in LREE enriched patterns of clinopyroxene separates from wehrlite. The metasomatism in the mantle may be due to multiple events involving separate melts or a single event of re-fertilization by

  18. Pre-subduction metasomatic enrichment of the oceanic lithosphere induced by plate flexure

    Pilet, S.; Abe, N.; Rochat, L.; Kaczmarek, M.-A.; Hirano, N.; Machida, S.; Buchs, D. M.; Baumgartner, P. O.; Müntener, O.


    Oceanic lithospheric mantle is generally interpreted as depleted mantle residue after mid-ocean ridge basalt extraction. Several models have suggested that metasomatic processes can refertilize portions of the lithospheric mantle before subduction. Here, we report mantle xenocrysts and xenoliths in petit-spot lavas that provide direct evidence that the lower oceanic lithosphere is affected by metasomatic processes. We find a chemical similarity between clinopyroxene observed in petit-spot mantle xenoliths and clinopyroxene from melt-metasomatized garnet or spinel peridotites, which are sampled by kimberlites and intracontinental basalts respectively. We suggest that extensional stresses in oceanic lithosphere, such as plate bending in front of subduction zones, allow low-degree melts from the seismic low-velocity zone to percolate, interact and weaken the oceanic lithospheric mantle. Thus, metasomatism is not limited to mantle upwelling zones such as mid-ocean ridges or mantle plumes, but could be initiated by tectonic processes. Since plate flexure is a global mechanism in subduction zones, a significant portion of oceanic lithospheric mantle is likely to be metasomatized. Recycling of metasomatic domains into the convecting mantle is fundamental to understanding the generation of small-scale mantle isotopic and volatile heterogeneities sampled by oceanic island and mid-ocean ridge basalts.

  19. Extensional crustal tectonics and crust-mantle coupling, a view from the geological record

    Jolivet, Laurent; Menant, Armel; Clerc, Camille; Sternai, Pietro; Ringenbach, Jean-Claude; Bellahsen, Nicolas; Leroy, Sylvie; Faccenna, Claudio; Gorini, Christian


    In passive margins or back-arc regions, extensional deformation is often asymmetric, i.e. normal faults or extensional ductile shear zones dip in the same direction over large distances. We examine a number of geological examples in convergent or divergent contexts suggesting that this asymmetry results from a coupling between asthenospheric flow and crustal deformation. This is the case of the Mediterranean back-arc basins, such as the Aegean Sea, the northern Tyrrhenian Sea, the Alboran domain or the Gulf of Lion passive margin. Similar types of observation can be made on some of the Atlantic volcanic passive margins and the Afar region, which were all formed above a mantle plume. We discuss these contexts and search for the main controlling parameters for this asymmetric distributed deformation that imply a simple shear component at the scale of the lithosphere. The different geodynamic settings and tectonic histories of these different examples provide natural case-studies of the different controlling parameters, including a pre-existing heterogeneity of the crust and lithosphere (tectonic heritage) and the possible contribution of the underlying asthenospheric flow through basal drag or basal push. We show that mantle flow can induce deformation in the overlying crust in case of high heat flow and thin lithosphere. In back-arc regions, the cause of asymmetry resides in the relative motion between the asthenosphere below the overriding plate and the crust. When convergence and slab retreat work concurrently the asthenosphere flows faster than the crust toward the trench and the sense of shear is toward the upper plate. When slab retreat is the only cause of subduction, the sense of shear is opposite. In both cases, mantle flow is mostly the consequence of slab retreat and convergence. Mantle flow can however result also from larger-scale convection, controlling rifting dynamics prior to the formation of oceanic crust. In volcanic passive margins, in most cases

  20. Thermal and compositional structure of the upper mantle

    Gilbert, Hersh Joseph

    Constraints for models of the convective, thermal, and mineralogical structure within the mantle depend heavily on seismic observations of the deep, and otherwise inaccessible, Earth. Studies presented within this dissertation focus primarily on the upper mantle discontinuities that bound the transition zone between the upper and lower mantle at the nominal depths of 410 and 660 km. These discontinuities are attributed to phase transitions of the mantle mineral olivine to denser configurations. Additionally, they may demark compositional layers within the mantle. This region figures prominently in the convective style of the planet. I address the questions of whether the 660-km discontinuity in some way inhibits flow from crossing between the upper and lower mantle and, more specifically, if it coincides with a compositional barrier in the mantle. Thermal variations associated with warm-rising and cool-sinking material in the mantle produce observable variations in the depths of the discontinuities. If rising or sinking materials cross the entire extent of the mantle, then the transition zone should respond to its associated thermal perturbations in a correlated manner. If instead, convection were divided between the upper and lower mantle, then thermal perturbations in the transition zone need not be spatially correlated. Observations presented in this dissertation display regions in which both the 410- and 660-km discontinuities possess greater than 20 km of peak-to-peak topography that is not correlated between the two. Studying the upper mantle below the western United States, I find no correlation between the upper mantle and the surface tectonics of the region. The topography on both discontinuities in this region is nearly as pronounced as that found where the cold subducting Tonga slab interacts with the upper mantle, suggesting the presence of a similar thermal anomaly. Additionally, amplitudes of the velocity jumps associated with the discontinuities

  1. Application of Core Dynamics Modeling to Core-Mantle Interactions

    Kuang, Weijia


    Observations have demonstrated that length of day (LOD) variation on decadal time scales results from exchange of axial angular momentum between the solid mantle and the core. There are in general four core-mantle interaction mechanisms that couple the core and the mantle. Of which, three have been suggested likely the dominant coupling mechanism for the decadal core-mantle angular momentum exchange, namely, gravitational core-mantle coupling arising from density anomalies in the mantle and in the core (including the inner core), the electromagnetic coupling arising from Lorentz force in the electrically conducting lower mantle (e.g. D-layer), and the topographic coupling arising from non-hydrostatic pressure acting on the core-mantle boundary (CMB) topography. In the past decades, most effort has been on estimating the coupling torques from surface geomagnetic observations (kinematic approach), which has provided insights on the core dynamical processes. In the meantime, it also creates questions and concerns on approximations in the studies that may invalidate the corresponding conclusions. The most serious problem is perhaps the approximations that are inconsistent with dynamical processes in the core, such as inconsistencies between the core surface flow beneath the CMB and the CMB topography, and that between the D-layer electric conductivity and the approximations on toroidal field at the CMB. These inconsistencies can only be addressed with numerical core dynamics modeling. In the past few years, we applied our MoSST (Modular, Scalable, Self-consistent and Three-dimensional) core dynamics model to study core-mantle interactions together with geodynamo simulation, aiming at assessing the effect of the dynamical inconsistencies in the kinematic studies on core-mantle coupling torques. We focus on topographic and electromagnetic core-mantle couplings and find that, for the topographic coupling, the consistency between the core flow and the CMB topography is

  2. High-resolution 3D seismic model of the crustal and uppermost mantle structure in Poland

    Grad, Marek; Polkowski, Marcin; Ostaficzuk, Stanisław R.


    In the area of Poland a contact between the Precambrian and Phanerozoic Europe and the Carpathians has a complicated structure and a complex P-wave velocity of the sedimentary cover, crystalline crust, Moho depth and the uppermost mantle. The geometry of the uppermost several kilometers of sediments is relatively well recognized from over 100,000 boreholes. The vertical seismic profiling (VSP) from 1188 boreholes provided detailed velocity data for regional tectonic units and for stratigraphic successions from Permian to the Tertiary and Quaternary deposits. These data, however, do not provide information about the velocity and basement depth in the central part of the Trans-European suture zone (TESZ) and in the Carpathians. So, the data set is supplemented by 2D velocity models from 32 deep seismic sounding refraction profiles which also provide information about the crust and uppermost mantle. Together with the results of other methods: vertical seismic profiling, magnetotelluric, allow for the creation of a detailed, high-resolution 3D model for the entire Earth's crust and the uppermost mantle down to a depth of 60 km. The thinnest sedimentary cover in the Mazury-Belarus anteclise is only 0.3 to 1 km thick, which increases to 7 to 8 km along the East European Craton (EEC) margin, and 9 to 12 km in the TESZ. The Variscan domain is characterized by a 1-4 km thick sedimentary cover, while the Carpathians are characterized by very thick sedimentary layers, up to about 20 km. The crystalline crust is differentiated and has a layered structure. The crust beneath the West European Platform (WEP; Variscan domain) is characterized by P-wave velocities of 5.8-6.6 km/s. The upper and middle crusts beneath the EEC are characterized by velocities of 6.1-6.6 km/s, and are underlain by a high velocity lower crust with a velocity of about 7 km/s. A general decrease in velocity is observed from the older to the younger tectonic domains. The TESZ is associated with a steep dip

  3. Geochemistry on mantle-derived volatiles in natural gases from eastern China oil/gas provinces (I )——Helium, argon and hydrocarbons in mantle volatiles

    徐永昌; 沈平; 陶明信; 刘文汇


    Researches on helium, argon, carbon dioxide and methane are very significant in studies of mantle substance characteristics and mantle evolution. A < -shaped pattern of the isotope composition distribution of helium and argon sourced from the mantle and the crust, abundance distribution, isotopic composition and reservoir formation of carbon dioxide, and mantle-sourced methane are discussed.

  4. Iron isotope tracing of mantle heterogeneity within the source regions of oceanic basalts

    Williams, Helen M.; Bizimis, Michael


    Mineralogical variations in the Earth's mantle and the relative proportions of peridotitic versus enriched and potentially crustally-derived pyroxenitic domains within the mantle have important implications for mantle dynamics, magma generation, and the recycling of surface material back into the mantle. Here we present iron (Fe) stable isotope data (δ57Fe, deviation in 57Fe/54Fe from the IRMM-014 standard in parts per thousand) for peridotite and garnet-pyroxenite xenoliths from Oahu, Hawaii and explore Fe isotopes as tracer of both peridotitic and pyroxenitic components in the source regions of oceanic basalts. The pyroxenites have δ57Fe values that are heavy (0.10 to 0.27‰) relative to values for mid-ocean ridge and ocean island basalts (MORB; OIB; δFe57∼0.16‰) and the primitive mantle (PM; δFe57∼0.04‰). Pyroxenite δ57Fe values are positively correlated with bulk pyroxenite titanium and heavy rare earth element (REE) abundances, which can be interpreted in terms of stable isotope fractionation during magmatic differentiation and pyroxene cumulate formation. In contrast, the peridotites have light δ57Fe values (-0.34 to 0.14‰) that correlate negatively with degree of melt depletion and radiogenic hafnium isotopes, with the most depleted samples possessing the most radiogenic Hf isotope compositions and lightest δ57Fe values. While these correlations are broadly consistent with a scenario of Fe isotope fractionation during partial melting, where isotopically heavy Fe is extracted into the melt phase, leaving behind low-δ57Fe peridotite residues, the extent of isotopic variation is far greater than predicted by partial melting models. One possibility is derivation of the samples from a heterogeneous source containing both light-δ57Fe (relative to PM) and heavy-δ57Fe components. While pyroxenite is a viable explanation for the heavy-δ57Fe component, the origin of the depleted light-δ57Fe component is more difficult to explain, as melting

  5. Water pumping in mantle shear zones

    Précigout, Jacques; Prigent, Cécile; Palasse, Laurie; Pochon, Anthony


    Water plays an important role in geological processes. Providing constraints on what may influence the distribution of aqueous fluids is thus crucial to understanding how water impacts Earth's geodynamics. Here we demonstrate that ductile flow exerts a dynamic control on water-rich fluid circulation in mantle shear zones. Based on amphibole distribution and using dislocation slip-systems as a proxy for syn-tectonic water content in olivine, we highlight fluid accumulation around fine-grained layers dominated by grain-size-sensitive creep. This fluid aggregation correlates with dislocation creep-accommodated strain that localizes in water-rich layers. We also give evidence of cracking induced by fluid pressure where the highest amount of water is expected. These results emphasize long-term fluid pumping attributed to creep cavitation and associated phase nucleation during grain size reduction. Considering the ubiquitous process of grain size reduction during strain localization, our findings shed light on multiple fluid reservoirs in the crust and mantle.

  6. The latest geodynamics in Asia: Synthesis of data on volcanic evolution, lithosphere motion, and mantle velocities in the Baikal-Mongolian region

    Sergei Rasskazov


    Full Text Available From a synthesis of data on volcanic evolution, movement of the lithosphere, and mantle velocities in the Baikal-Mongolian region, we propose a comprehensive model for deep dynamics of Asia that assumes an important role of the Gobi, Baikal, and North Transbaikal transition-layer melting anomalies. This layer was distorted by lower-mantle fluxes at the beginning of the latest geodynamic stage (i.e. in the early late Cretaceous due to avalanches of slab material that were stagnated beneath the closed fragments of the Solonker, Ural-Mongolian paleoceans and Mongol-Okhotsk Gulf of Paleo-Pacific. At the latest geodynamic stage, Asia was involved in east–southeast movement, and the Pacific plate moved in the opposite direction with subduction under Asia. The weakened upper mantle region of the Gobi melting anomaly provided a counterflow connected with rollback in the Japan Sea area. These dynamics resulted in the formation of the Honshu-Korea flexure of the Pacific slab. A similar weakened upper mantle region of the North Transbaikal melting anomaly was associated with the formation of the Hokkaido-Amur flexure of the Pacific slab, formed due to progressive pull-down of the slab material into the transition layer in the direction of the Pacific plate and Asia convergence. The early–middle Miocene structural reorganization of the mantle processes in Asia resulted in the development of upper mantle low-velocity domains associated with the development of rifts and orogens. We propose that extension at the Baikal Rift was caused by deviator flowing mantle material, initiated under the moving lithosphere in the Baikal melting anomaly. Contraction at the Hangay orogen was created by facilitation of the tectonic stress transfer from the Indo-Asian interaction zone due to the low-viscosity mantle in the Gobi melting anomaly.

  7. The maximum water storage capacities in nominally anhydrous minerals in the mantle transition zone and lower mantle

    Inoue, T.; Yurimoto, H.


    Water is the most important volatile component in the Earth, and affects the physicochemical properties of mantle minerals, e.g. density, elastic property, electrical conductivity, thermal conductivity, rheological property, melting temperature, melt composition, element partitioning, etc. So many high pressure experiments have been conducted so far to determine the effect of water on mantle minerals. To clarify the maximum water storage capacity in nominally anhydrous mantle minerals in the mantle transition zone and lower mantle is an important issue to discuss the possibility of the existence of water reservoir in the Earth mantle. So we have been clarifying the maximum water storage capacity in mantle minerals using MA-8 type (KAWAI-type) high pressure apparatus and SIMS (secondary ion mass spectroscopy). Upper mantle mineral, olivine can contain ~0.9 wt% H2O in the condition just above 410 km discontinuity in maximum (e.g. Chen et al., 2002; Smyth et al., 2006). On the other hand, mantle transition zone mineral, wadsleyite and ringwoodite can contain significant amount (about 2-3 wt.%) of H2O (e.g. Inoue et al., 1995, 1998, 2010; Kawamoto et al., 1996; Ohtani et al., 2000). But the lower mantle mineral, perovskite can not contain significant amount of H2O, less than ~0.1 wt% (e.g. Murakami et al., 2002; Inoue et al., 2010). In addition, garnet and stishovite also can not contain significant amount of H2O (e.g. Katayama et al., 2003; Mookherjee and Karato, 2010; Litasov et al., 2007). On the other hand, the water storage capacities of mantle minerals are supposed to be significantly coupled with Al by a substitution with Mg2+, Si4+ or Mg2+ + Si4+, because Al3+ is the trivalent cation, and H+ is the monovalent cation. To clarify the degree of the substitution, the water contents and the chemical compositions of Al-bearing minerals in the mantle transition zone and the lower mantle were also determined in the Al-bearing systems with H2O. We will introduce the

  8. Strong, Multi-Scale Heterogeneity in Earth's Lowermost Mantle.

    Tkalčić, Hrvoje; Young, Mallory; Muir, Jack B; Davies, D Rhodri; Mattesini, Maurizio


    The core mantle boundary (CMB) separates Earth's liquid iron outer core from the solid but slowly convecting mantle. The detailed structure and dynamics of the mantle within ~300 km of this interface remain enigmatic: it is a complex region, which exhibits thermal, compositional and phase-related heterogeneity, isolated pockets of partial melt and strong variations in seismic velocity and anisotropy. Nonetheless, characterising the structure of this region is crucial to a better understanding of the mantle's thermo-chemical evolution and the nature of core-mantle interactions. In this study, we examine the heterogeneity spectrum from a recent P-wave tomographic model, which is based upon trans-dimensional and hierarchical Bayesian imaging. Our tomographic technique avoids explicit model parameterization, smoothing and damping. Spectral analyses reveal a multi-scale wavelength content and a power of heterogeneity that is three times larger than previous estimates. Inter alia, the resulting heterogeneity spectrum gives a more complete picture of the lowermost mantle and provides a bridge between the long-wavelength features obtained in global S-wave models and the short-scale dimensions of seismic scatterers. The evidence that we present for strong, multi-scale lowermost mantle heterogeneity has important implications for the nature of lower mantle dynamics and prescribes complex boundary conditions for Earth's geodynamo.

  9. Solar combi system based on a mantle tank

    Yazdanshenas, Eshagh; Furbo, Simon


    . The thermal performance of the solar combisystem is compared to the thermal performance of a solar domestic hot water system based on a mantle tank. In the experimental study, tank temperatures and the heat transfer coefficient for the top mantle for a discharge test is determined. The investigations showed...

  10. Tectonic evolution and mantle structure of the Caribbean

    van Benthem, S.; Govers, R.; Spakman, W.; Wortel, R.


    We investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic P wave velocity structure under the Caribbean region. In the upper mantle, positive seismic anomalies are imaged under the Lesser Antilles and Puerto Ric

  11. Waves in the core and mechanical core-mantle interactions

    Jault, D.; Finlay, Chris


    the motions in the direction parallel to the Earth'srotation axis. This property accounts for the signicance of the core-mantle topography.In addition, the stiening of the uid in the direction parallel to the rotation axis gives riseto a magnetic diusion layer attached to the core-mantle boundary, which would...

  12. Abundant carbon in the mantle beneath Hawai`i

    Anderson, Kyle R.; Poland, Michael


    Estimates of carbon concentrations in Earth’s mantle vary over more than an order of magnitude, hindering our ability to understand mantle structure and mineralogy, partial melting, and the carbon cycle. CO2 concentrations in mantle-derived magmas supplying hotspot ocean island volcanoes yield our most direct constraints on mantle carbon, but are extensively modified by degassing during ascent. Here we show that undegassed magmatic and mantle carbon concentrations may be estimated in a Bayesian framework using diverse geologic information at an ocean island volcano. Our CO2 concentration estimates do not rely upon complex degassing models, geochemical tracer elements, assumed magma supply rates, or rare undegassed rock samples. Rather, we couple volcanic CO2 emission rates with probabilistic magma supply rates, which are obtained indirectly from magma storage and eruption rates. We estimate that the CO2content of mantle-derived magma supplying Hawai‘i’s active volcanoes is 0.97−0.19+0.25 wt%—roughly 40% higher than previously believed—and is supplied from a mantle source region with a carbon concentration of 263−62+81 ppm. Our results suggest that mantle plumes and ocean island basalts are carbon-rich. Our data also shed light on helium isotope abundances, CO2/Nb ratios, and may imply higher CO2 emission rates from ocean island volcanoes.

  13. Hf isotope evidence for a hidden mantle reservoir

    Bizzarro, Martin; Simonetti, A.; Stevenson, R.K.


    High-precision Hf isotopic analyses and U-Pb ages of carbonatites and kimberlites from Greenland and eastern North America, including Earth's oldest known carbonatite (3 Ga), indicate derivation from an enriched mantle source. This previously unidentified mantle reservoir-marked by an unradiogeni...

  14. Seismic velocity anisotropy and heterogeneity beneath the Mantle Electromagnetic and Tomography Experiment (MELT) region of the East Pacific Rise from analysis of P and S body waves

    Hammond, W.C.; Toomey, D.R.


    We use teleseismic P and S delay times and shear wave splitting measurements to constrain isotropic and anisotropic heterogeneity in the mantle beneath the southern East Pacific Rise (SEPR). The data comprise 462 P and S delay times and 18 shear wave splitting observations recorded during the Mantle Electromagnetic and Tomography (MELT) Experiment. We estimate the mantle melt content (F) and temperature (T) variation from the isotropic velocity variation. Our results indicate that the maximum variation in F beneath our array is between zero and ???1.2%, and maximum variation in T is between zero and ???100 K. We favor an explanation having partial contributions from both T and F. We approximate the seismic anisotropy of the upper mantle with hexagonal symmetry, consistent with the assumption of two dimensionality of mantle flow. Our new tomographic technique uses a nonlinear inversion of P and slow S polarization delay times to simultaneously solve for coupled VP and VS heterogeneity throughout the model and for the magnitude of anisotropy within discrete domains. The domain dimensions and the dip of the anisotropy are fixed for each inversion but are varied in a grid search, obtaining the misfit of the models to the body wave delay data and to split times of vertically propagating S waves. The data misfit and the isotropic heterogeneity are sensitive to domain dimensions and dip of anisotropy. In a region centered beneath the SEPR the best average dip of the hexagonal symmetry axis is horizontal or dipping shallowly (<30??) west. Given the resolution of our data, a subaxial region characterized by vertically aligned symmetry axes may exist but is limited to be <80 km deep. We infer that the mantle flow beneath the SEPR is consistent with shallow asthenospheric return flow from the direction of the South Pacific superswell.

  15. Cascaded Evolution of Mantle Plumes and Metallogenesis of Core- and Mantle-derived Elements

    NIU Shuyin; HOU Quanlin; HOU Zengqian; SUN Aiqun; WANG Baode; LI Hongyang; XU Chuanshi


    Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation andevolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion,lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals. migrated upwards;whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had atendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in theEarth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressureand viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly bycascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth wereinterdependent and constituted the motive force of the mantle-core movement. The cascaded evolution of mantle plumesopens the passageways for the migration of deep-seated ore-forming material, and thus elements such as gold and silverconcentrated in the core and on the core-mantle boundary migrate as the gaseous state together with the hot material flowof mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas-liquid state to the near-surface level and finally are concentrated in favorable structural expansion zones, forming mineraldeposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other manyelements. Take for example the NE-plunging crown of the Fuping mantle-branch structure, the paper analyzes ductile-brittle shear zone-type gold fields (Weijiayu) at the core of the magmatic-metamorphic complex, principal detachment-type gold fields (Shangmingyu) and hanging-wall cover fissure-vein-type lead-zinc polymetallic ore fields

  16. Global correlation of lower mantle structure and past subduction

    Domeier, Mathew; Doubrovine, Pavel V.; Torsvik, Trond H.; Spakman, Wim; Bull, Abigail L.


    Advances in global seismic tomography have increasingly motivated identification of subducted lithosphere in Earth's deep mantle, creating novel opportunities to link plate tectonics and mantle evolution. Chief among those is the quest for a robust subduction reference frame, wherein the mantle assemblage of subducted lithosphere is used to reconstruct past surface tectonics in an absolute framework anchored in the deep Earth. However, the associations heretofore drawn between lower mantle structure and past subduction have been qualitative and conflicting, so the very assumption of a correlation has yet to be quantitatively corroborated. Here we show that a significant, time-depth progressive correlation can be drawn between reconstructed subduction zones of the last 130 Myr and positive S wave velocity anomalies at 600-2300 km depth, but that further correlation between greater times and depths is not presently demonstrable. This correlation suggests that lower mantle slab sinking rates average between 1.1 and 1.9 cm yr-1.

  17. Mantle circulation and the lateral migration of subducted slabs

    Garfunkel, Z.; Anderson, C. A.; Schubert, G.


    The geometry of transverse migration of subducted lithospheric slabs is examined, and the way in which this influences the flow in the mantle is studied. The migration of subducted slabs generally appears to be retrograde (at rates of 10-25 mm/yr), so that the descent of material is actually steeper than the slab dip. Retrograde slab migration is probably caused by the tendence of negatively buoyant slabs to sink in the surrounding mantle. The properties of the flow driven by such retrograde slab migration are explored in simple two-dimensional models. The results are used as a guide to infer the contribution of retrograde slab motion to the more complex mantle flow and to examine some consequences of the additional component of mantle flow. It is shown that slab migration is an important factor that causes mantle flow to be geometrically complex and time dependent.

  18. Molybdenum isotope fractionation in the mantle

    Liang, Yu-Hsuan; Halliday, Alex N.; Siebert, Chris; Fitton, J. Godfrey; Burton, Kevin W.; Wang, Kuo-Lung; Harvey, Jason


    We report double-spike molybdenum (Mo) isotope data for forty-two mafic and fifteen ultramafic rocks from diverse locations and compare these with results for five chondrites. The δ98/95Mo values (normalized to NIST SRM 3134) range from -0.59 ± 0.04 to +0.10 ± 0.08‰. The compositions of one carbonaceous (CI) and four ordinary chondrites are relatively uniform (-0.14 ± 0.01‰, 95% ci (confidence interval)) in excellent agreement with previous data. These values are just resolvable from the mean of 10 mid-ocean ridge basalts (MORBs) (0.00 ± 0.02‰, 95% ci). The compositions of 13 mantle-derived ultramafic xenoliths from Kilbourne Hole, Tariat and Vitim are more diverse (-0.39 to -0.07‰) with a mean of -0.22 ± 0.06‰ (95% ci). On this basis, the isotopic composition of the bulk silicate Earth (BSE or Primitive Mantle) is within error identical to chondrites. The mean Mo concentration of the ultramafic xenoliths (0.19 ± 0.07 ppm, 95% ci) is similar in magnitude to that of MORB (0.48 ± 0.13 ppm, 95% ci), providing evidence, either for a more compatible behaviour than previously thought or for selective Mo enrichment of the subcontinental lithospheric mantle. Intraplate and ocean island basalts (OIBs) display significant isotopic variability within a single locality from MORB-like to strongly negative (-0.59 ± 0.04‰). The most extreme values measured are for nephelinites from the Cameroon Line and Trinidade, which also have anomalously high Ce/Pb and low Mo/Ce relative to normal oceanic basalts. δ98/95Mo correlates negatively with Ce/Pb and U/Pb, and positively with Mo/Ce, explicable if a phase such as an oxide or a sulphide liquid selectively retains isotopically heavy Mo in the mantle and fractionates its isotopic composition in low degree partial melts. If residual phases retain Mo during partial melting, it is possible that the [Mo] for the BSE may be misrepresented by values estimated from basalts. This would be consistent with the high Mo

  19. Petrology of periodotites as a tool of insight into mantle processes: a review. Jobu mantle kanrangan no gansekigaku (ikani mantle process wo yomitoruka)

    Arai, S. (Kanazawa University, Ishikawa (Japan). Faculty of Science)


    Petrological studies of the upper mantle materials are reviewed mainly in terms of recent topics. Along with on increase in depletion degree (degree of slipped-out magma) of resistate which remains after magma slipped out from the upper mantle materials, a series from lherzolite to Harzburgites is obtained and as an example, the Horoman peridotite complex which intrudes into the Hidaka metamorphic belt (Hokkaido) is shown. In this connection, a theory is introduced where the bedded structure of this peridotite complex was formed by a series of processes accompanied by the cracks generated in the mantle peridotite. Then, the following topics are explained: strongly incompatible trace elements can be enriched in resistate with high depletion degree (REE paradox); and the recent research trend on issues which relates to the interaction between the magma and mantle, such as the formation of dunites, the origin of picrite basalt, and the origin of chromitite are described. 40 refs., 13 figs.

  20. Mantle differentiation and chemical cycling in the Archean (Invited)

    Lee, C.


    Differentiation of Earth’s silicate mantle is largely controlled by solid-state convection. Today, upwelling mantle leads to decompression melting. Melts, being of low density, rise to form the continental and oceanic crusts. Because many trace elements, such as heat-producing U, Th and K, as well as the noble gases, preferentially partition into melts, melt extraction concentrates these elements into the crust or atmosphere. However, one by-product of whole-mantle convection is that melting during the Earth’s first billion years was likely deep and hot. Such high pressure melts may have been dense, allowing them to stall, crystallize and later founder back into the lower mantle. These sunken lithologies would have ‘primordial’ chemical signatures despite a non-primordial origin. As the Earth cools, the proportion of upwards melt segregation relative to downwards melt segregation increases, removing volatiles and other incompatible elements to the surface. Recycling of these elements back into the Earth’s interior occurs by subduction, but because of chemical weathering, hydrothermal alteration and photosynthetic reactions occurring in the Earth’s exosphere, these recycled materials may re-enter the mantle already chemically transformed. In particular, photosynthetic production of oxygen and, especially, the progressive oxygenation of the Earth’s atmosphere require removal of reduced carbon from the Earth’s surface. If such removal occurred by subduction, the mantle would have become progressively reduced. During the Archean and early Proterozoic, much of this material may have contributed to making cratonic mantle, and if so, cratonic mantle may have been assembled by reduced building blocks, perhaps explaining the origin of diamonds with organic carbon isotopic signatures. The origin of peridotitic diamonds in cratonic mantle could then be explained if the underlying convecting mantle was in fact more oxidizing such that carbonatitic liquids

  1. Iron-carbonate interaction at Earth's core-mantle boundary

    Dorfman, S. M.; Badro, J.; Nabiei, F.; Prakapenka, V.; Gillet, P.


    Carbon storage and flux in the deep Earth are moderated by oxygen fugacity and interactions with iron-bearing phases. The amount of carbon stored in Earth's mantle versus the core depends on carbon-iron chemistry at the core-mantle boundary. Oxidized carbonates subducted from Earth's surface to the lowermost mantle may encounter reduced Fe0 metal from disproportionation of Fe2+ in lower mantle silicates or mixing with the core. To understand the fate of carbonates in the lowermost mantle, we have performed experiments on sandwiches of single-crystal (Ca0.6Mg0.4)CO3 dolomite and Fe foil in the laser-heated diamond anvil cell at lower mantle conditions of 49-110 GPa and 1800-2500 K. Syntheses were conducted with in situ synchrotron X-ray diffraction to identify phase assemblages. After quench to ambient conditions, samples were sectioned with a focused Ga+ ion beam for composition analysis with transmission electron microscopy. At the centers of the heated spots, iron melted and reacted completely with the carbonate to form magnesiowüstite, iron carbide, diamond, magnesium-rich carbonate and calcium carbonate. In samples heated at 49 and 64 GPa, the two carbonates exhibit a eutectoid texture. In the sample heated at 110 GPa, the carbonates form rounded ~150-nm-diameter grains with a higher modal proportion of interspersed diamonds. The presence of reduced iron in the deep lower mantle and core-mantle boundary region will promote the formation of diamonds in carbonate-bearing subducted slabs. The complete reaction of metallic iron to oxides and carbides in the presence of mantle carbonate supports the formation of these phases at the Earth's core-mantle boundary and in ultra-low velocity zones.

  2. Effects of Contrasting Nazca Slab Subduction Angles on Mantle Flow: Results From Three-Dimensional Numerical Models

    Wild, S. C.; Georgen, J. E.


    In the southern Andes, the downgoing Nazca plate has adjacent zones with slab dip angles of 10° and 30°. To better understand the nature of mantle flow and plate deformation across the transition region between the juxtaposed angles, we calculate a steady-state, three-dimensional finite element numerical model. The overall three-dimensional model domain contains a rigid overlying plate, two subducting slabs (with dips of 10° and 30°), and a mantle wedge with a geometry that changes in the trench-parallel direction. The model space is generated by using two-dimensional solutions as boundary conditions for the trench-perpendicular "endcaps" of the numerical domain. Models solve the conservation equations of mass, momentum, and energy, neglecting heat production and thermal buoyancy and assuming isoviscous mantle flow. The sensitivity of the model to overriding plate thickness, coupling between the downgoing and overriding plates in the wedge corner region, and convergence velocity is also investigated. Temperature solutions from the three-dimensional models are used in calculations to delineate the brittle and ductile zones of the model domain. Models predict a significant amount of trench-parallel flow, as a result of the juxtaposition of the two slab angles. Also, the uppermost portion of the model space shows a continuous brittle section for trench-perpendicular distances of up to ~240 km, implying that the formation of a slab tear is relatively unlikely for the conditions and parameters simulated in this investigation. Future work will focus on different treatments of mantle viscosity and examining the sensitivity of the three-dimensional model to the selection of slab dip angle.

  3. Whole-mantle convection with tectonic plates preserves long-term global patterns of upper mantle geochemistry.

    Barry, T L; Davies, J H; Wolstencroft, M; Millar, I L; Zhao, Z; Jian, P; Safonova, I; Price, M


    The evolution of the planetary interior during plate tectonics is controlled by slow convection within the mantle. Global-scale geochemical differences across the upper mantle are known, but how they are preserved during convection has not been adequately explained. We demonstrate that the geographic patterns of chemical variations around the Earth's mantle endure as a direct result of whole-mantle convection within largely isolated cells defined by subducting plates. New 3D spherical numerical models embedded with the latest geological paleo-tectonic reconstructions and ground-truthed with new Hf-Nd isotope data, suggest that uppermost mantle at one location (e.g. under Indian Ocean) circulates down to the core-mantle boundary (CMB), but returns within ≥100 Myrs via large-scale convection to its approximate starting location. Modelled tracers pool at the CMB but do not disperse ubiquitously around it. Similarly, mantle beneath the Pacific does not spread to surrounding regions of the planet. The models fit global patterns of isotope data and may explain features such as the DUPAL anomaly and long-standing differences between Indian and Pacific Ocean crust. Indeed, the geochemical data suggests this mode of convection could have influenced the evolution of mantle composition since 550 Ma and potentially since the onset of plate tectonics.

  4. Can Lower Mantle Slab-like Seismic Anomalies be Explained by Thermal Coupling Between the Upper and Lower Mantles?

    Cízková, H. (Hana); Cadek, O.; Berg, A.P. van den; Vlaar, N.J.


    Below subduction zones, high resolution seismic tomographic models resolve fast anomalies that often extend into the deep lower mantle. These anomalies are generally interpreted as slabs penetrating through the 660-km seismic discontinuity, evidence in support of whole-mantle convection. However, th

  5. .Gov Domains API

    General Services Administration — This dataset offers the list of all .gov domains, including state, local, and tribal .gov domains. It does not include .mil domains, or other federal domains outside...

  6. The North American upper mantle: density, composition, and evolution

    Mooney, Walter D.; Kaban, Mikhail K.


    The upper mantle of North America has been well studied using various seismic methods. Here we investigate the density structure of the North American (NA) upper mantle based on the integrative use of the gravity field and seismic data. The basis of our study is the removal of the gravitational effect of the crust to determine the mantle gravity anomalies. The effect of the crust is removed in three steps by subtracting the gravitational contributions of (1) topography and bathymetry, (2) low-density sedimentary accumulations, and (3) the three-dimensional density structure of the crystalline crust as determined by seismic observations. Information regarding sedimentary accumulations, including thickness and density, are taken from published maps and summaries of borehole measurements of densities; the seismic structure of the crust is based on a recent compilation, with layer densities estimated from P-wave velocities. The resultant mantle gravity anomaly map shows a pronounced negative anomaly (−50 to −400 mGal) beneath western North America and the adjacent oceanic region and positive anomalies (+50 to +350 mGal) east of the NA Cordillera. This pattern reflects the well-known division of North America into the stable eastern region and the tectonically active western region. The close correlation of large-scale features of the mantle anomaly map with those of the topographic map indicates that a significant amount of the topographic uplift in western NA is due to buoyancy in the hot upper mantle, a conclusion supported by previous investigations. To separate the contributions of mantle temperature anomalies from mantle compositional anomalies, we apply an additional correction to the mantle anomaly map for the thermal structure of the uppermost mantle. The thermal model is based on the conversion of seismic shear-wave velocities to temperature and is consistent with mantle temperatures that are independently estimated from heat flow and heat production data

  7. Molecular pathogenesis of mantle cell lymphoma

    Jares, Pedro; Colomer, Dolors; Campo, Elias


    Mantle cell lymphoma is a B cell malignancy in which constitutive dysregulation of cyclin D1 and the cell cycle, disruption of DNA damage response pathways, and activation of cell survival mechanisms contribute to oncogenesis. A small number of tumors lack cyclin D1 overexpression, suggesting that its dysregulation is always not required for tumor initiation. Some cases have hypermutated IGHV and stable karyotypes, a predominant nonnodal disease, and an indolent clinical evolution, which suggests that they may correspond to distinct subtypes of the disease. In this review, we discuss the molecular pathways that contribute to pathogenesis, and how improved understanding of these molecular mechanisms offers new perspectives for the treatment of patients. PMID:23023712

  8. MicroRNAs in mantle cell lymphoma

    Husby, Simon; Geisler, Christian; Grønbæk, Kirsten


    Mantle cell lymphoma (MCL) is a rare and aggressive subtype of non-Hodgkin lymphoma. New treatment modalities, including intensive induction regimens with immunochemotherapy and autologous stem cell transplant, have improved survival. However, many patients still relapse, and there is a need...... for novel therapeutic strategies. Recent progress has been made in the understanding of the role of microRNAs (miRNAs) in MCL. Comparisons of tumor samples from patients with MCL with their normal counterparts (naive B-cells) have identified differentially expressed miRNAs with roles in cellular growth...... and survival pathways, as demonstrated in various biological model systems. In addition, MCL clinico-pathological and prognostic subtypes can be identified using individual miRNAs or miRNA classifiers. miRNA based therapies have now shown efficacy in animal models, and many efforts are currently being made...

  9. P-V-T equations of state of lower mantle minerals: Constraints on mantle composition models

    Fei, Y.; Zhang, L.; Frank, M.; Corgne, A.; Wheeler, K.; Meng, Y.


    Ferropericlase (Mg,Fe)O is likely a stable phase coexisting with silicate perovskite in the Earth's lower mantle. Determination of a reliable P-V-T equation-of-state of this phase is therefore crucial for developing compositional and mineralogical models of the Earth's interior. In this study, we report new compression data on ferropericlase up to 136 GPa, covering the entire pressure range of the lower mantle. The experiments were performed at the HPCAT 16-ID-B beamline (Advanced Photon Source), using monochromatic X-radiation and a CCD area detector. We used (Mg0.6Fe0.4)O as the starting material. The powdered sample was sandwiched between NaCl and a mixture of NaCl-Au in an externally heated high-temperature diamond anvil cell. The sample was annealed at each pressure increment by laser heating. High-quality diffraction data were collected up to 136 GPa. The same starting material was also studied up to 27 GPa and 2173 K in a multi-anvil apparatus by X-ray diffraction. A reliable P-V-T equation of state for (Mg0.6Fe0.4)O was developed by combining the two data sets. The new results, together with our recent P-V-T data for Al-bearing perovskite up to 105 GPa and 1000 K, provide solid density measurements for the two most important lower mantle minerals under simultaneous high pressure and temperature conditions. The new data are used to model the density profile of the lower mantle and provide tight constraints on its chemical composition.

  10. Crust-Mantle Structures and Gold Enrichment Mechanism of Mantle Fluid System

    邓军; 孙忠实; 王庆飞; 韦延光


    Gold enrichment mechanism of ore-forming fluid is the essence of gold metallization.This paper summarizes the distinguishing symbols of mantle fluid and effect of crust-mantlestructure on fluid movement. Fluid moving processes include osmosis, surge, gas-liquid alterna-tion and mutation of fluid speed. During fluid movement, gold will be enriched gradually. Final-ly, a layered circulatory system is illustrated in this paper.

  11. The mantle transition zone and the upper mantle in Central-Eastern Greenland

    Anja Kraft, Helene; Thybo, Hans; Vinnik, Lev


    We present a receiver function (RF) study of the mantle transition zone (MTZ) and upper mantle in central-eastern Greenland. Our results are based on data from 18 temporary broad-band seismometers and 5 additional stations from the GLISN and GLATIS networks. The stations were operating in the region between Scoresby Sund and Summit (~ 70 ° N) with half of them installed on ice, the other half on bedrock. For our analysis we calculated low frequency PRF and SRF, which use the difference in travel times between converted and not converted phases at discontinuities. We see clear signals from P410s and P660s in most of our PRF and from S410p in the SRF. Their delay times suggest a surprisingly thin MTZ for most parts of the study area with up to 25 km of thinning compared to standard Earth models. The only exception is a small region in the centre of the study area, which shows times close to standard. It is mainly the delay time for P410s, that varies, while P660s is stable throughout our study area. This indicates, that the thinning of the MTZ is mainly due to topography on the 410-discontinuity. We furthermore observe an M-shaped signal for P410s at stations in the western part around Summit. A similar, complicated signal has been observed previously in different settings and is interpreted as a thin low velocity layer between 410 km and 520 km. In addition we jointly inverted the PRF and SRF for upper mantle velocities. These results show velocities slower than IASP91 for the entire study area. Both the low velocities in the upper mantle and the thinning of the MTZ are in contrary to simple models of old continental shields and might indicate a fairly recent heating event.

  12. Formation and modification of chromitites in the mantle

    Arai, Shoji; Miura, Makoto


    Podiform chromitites have long supplied us with unrivaled information on various mantle processes, including the peridotite-magma reaction, deep-seated magmatic evolution, and mantle dynamics. The recent discovery of ultrahigh-pressure (UHP) chromitites not only sheds light on a different aspect of podiform chromitites, but also changes our understanding of the whole picture of podiform chromitite genesis. In addition, new evidence was recently presented for hydrothermal modification/formation chromite/chromitite in the mantle, which is a classical but innovative issue. In this context, we present here an urgently needed comprehensive review of podiform chromitites in the upper mantle. Wall-rock control on podiform chromitite genesis demonstrates that the peridotite-magma reaction at the upper mantle condition is an indispensable process. We may need a large system in the mantle, far larger than the size of outcrops or mining areas, to fulfill the Cr budget requirement for podiform chromitite genesis. The peridotite-magma reaction over a large area may form a melt enriched with Na and other incompatible elements, which mixes with a less evolved magma supplied from the depth to create chromite-oversaturated magma. The incompatible-element-rich magma trapped by the chromite mainly precipitates pargasite and aspidolite (Na analogue of phlogopite), which are stable under upper mantle conditions. Moderately depleted harzburgites, which contain chromite with a moderate Cr# (0.4-0.6) and a small amount of clinopyroxene, are the best reactants for the chromitite-forming reaction, and are the best hosts for podiform chromitites. Arc-type chromitites are dominant in ophiolites, but some are of the mid-ocean ridge type; chromitites may be common beneath the ocean floor, although it has not yet been explored for chromitite. The low-pressure (upper mantle) igneous chromitites were conveyed through mantle convection or subduction down to the mantle transition zone to form

  13. Primitive magmas at five Cascade volcanic fields: Melts from hot, heterogeneous sub-arc mantle

    Bacon, C.R.; Bruggman, P.E.; Christiansen, R.L.; Clynne, M.A.; Donnelly-Nolan, J. M.; Hildreth, W.


    ; and OIB-source-like domains. Lavas with arc and intraplate (OIB) geochemical signatures were erupted close to HAOT, and many lavas are blends of two or more magma types. Pre-eruptive H2O contents of HAOT, coupled with phase-equilibrium studies, suggest that these magmas were relatively dry and last equilibrated in the mantle wedge at temperatures of ???1300??C and depths of ???40 km, virtually at the base of the crust. Arc basalt and basaltic andesite represent greater extents of melting than HAOT, presumably in the same general thermal regime but at somewhat lower mantle separation temperatures, of domains of sub-arc mantle that have been enriched by a hydrous subduction component derived from the young, relatively hot Juan de Fuca plate. The primitive magmas originated by partial melting in response to adiabatic upwelling within the mantle wedge. Tectonic extension in this part of the Cascade arc, one characterized by slow oblique convergence, contributes to mantle upwelling and facilitates eruption of primitive magmas.

  14. Thermal evolution of Earth's mantle and core: Influence of reference viscosity and concentration of radioactive elements in the mantle

    Nakagawa, T.; Tackley, P. J.


    In a series of studies on the thermal evolution of Earth’s mantle and core [Nakagawa and Tackley, 2004; 2005; 2010], we have assumed a reference viscosity (at T=1600 K and P=0) of 1022 Pa.s and a concentration of radioactive elements based on the surface heat flux of the Earth’s mantle (6x10-12 W/kg). In addition, the initial mantle temperature in these studies was also based on the mantle adiabat estimated from present potential temperature (1600 K). Problems with these models are that (1) the average mantle temperature increases in the initial phase of the calculation and (2) the final (present-day) surface heat flux is a factor of two lower than expected from observational constraints (46 TW [Jaupart et al., 2007]), which means the Urey ratio is higher than the expected value (~0.3) [Jaupert et al., 2007; Korenaga, 2007]. Here we present results of a coupled model of thermo-chemical mantle convection in a 2-D spherical annulus and parameterized core heat balance, in which we vary (i) the reference viscosity down to 1020 Pa.s, giving a "surface" Rayleigh number of 109, (ii) the concentration of radioactive heat-producing elements in the mantle are tried (either a theoretical estimate [Schubert et al., 2001; 25 TW], geochemical estimate [McDonough and Sun, 1995; 20 TW] and modified geochemical estimate [Lyubetskaya and Korenaga, 2006; 16 TW]) and (iii) the initial mantle adiabat (up to 2500 K at the surface). Preliminary results indicate a preference for an initial mantle adiabat of more than 2500 K and the modified geochemical estimate of radioactive element concentration, in order to understand the current thermal state of Earth’s mantle when the reference viscosity is 1022 Pa s. Results with lower reference viscosity will be presented.

  15. The Effect of Lower Mantle Metallization on Magnetic Field Generation in Rocky Exoplanets

    Vilim, Ryan; Elkins-Tanton, Linda


    Recent theoretical and experimental evidence indicates that many of the materials that are thought to exist in the mantles of terrestrial exoplanets will metallize and become good conductors of electricity at mantle pressures. This allows for strong electromagnetic coupling of the core and the mantle in these planets. We use a numerical dynamo model to study the effect of a metallized lower mantle on the dynamos of terrestrial exoplanets using several inner core sizes and mantle conductivities. We find that the addition of an electrically conducting mantle results in stronger core-mantle boundary fields because of the increase in magnetic field stretching. We also find that a metallized mantle destabilizes the dynamo resulting in less dipolar, less axisymmetric poloidal magnetic fields at the core-mantle boundary. The conducting mantle efficiently screens these fields to produce weaker surface fields. We conclude that a conducting mantle will make the detection of extrasolar terrestrial magnetic fields more d...

  16. Highly CO2-supersaturated melts in the Pannonian lithospheric mantle - A transient carbon reservoir?

    Créon, Laura; Rouchon, Virgile; Youssef, Souhail; Rosenberg, Elisabeth; Delpech, Guillaume; Szabó, Csaba; Remusat, Laurent; Mostefaoui, Smail; Asimow, Paul D.; Antoshechkina, Paula M.; Ghiorso, Mark S.; Boller, Elodie; Guyot, François


    Subduction of carbonated crust is widely believed to generate a flux of carbon into the base of the continental lithospheric mantle, which in turn is the likely source of widespread volcanic and non-volcanic CO2 degassing in active tectonic intracontinental settings such as rifts, continental margin arcs and back-arc domains. However, the magnitude of the carbon flux through the lithosphere and the budget of stored carbon held within the lithospheric reservoir are both poorly known. We provide new constraints on the CO2 budget of the lithospheric mantle below the Pannonian Basin (Central Europe) through the study of a suite of xenoliths from the Bakony-Balaton Highland Volcanic Field. Trails of secondary fluid inclusions, silicate melt inclusions, networks of melt veins, and melt pockets with large and abundant vesicles provide numerous lines of evidence that mantle metasomatism affected the lithosphere beneath this region. We obtain a quantitative estimate of the CO2 budget of the mantle below the Pannonian Basin using a combination of innovative analytical and modeling approaches: (1) synchrotron X-ray microtomography, (2) NanoSIMS, Raman spectroscopy and microthermometry, and (3) thermodynamic models (Rhyolite-MELTS). The three-dimensional volumes reconstructed from synchrotron X-ray microtomography allow us to quantify the proportions of all petrographic phases in the samples and to visualize their textural relationships. The concentration of CO2 in glass veins and pockets ranges from 0.27 to 0.96 wt.%, higher than in typical arc magmas (0-0.25 wt.% CO2), whereas the H2O concentration ranges from 0.54 to 4.25 wt.%, on the low end for estimated primitive arc magmas (1.9-6.3 wt.% H2O). Trapping pressures for vesicles were determined by comparing CO2 concentrations in glass to CO2 saturation as a function of pressure in silicate melts, suggesting pressures between 0.69 to 1.78 GPa. These values are generally higher than trapping pressures for fluid inclusions

  17. Tracing recycled volatiles in a heterogeneous mantle with boron isotopes

    Walowski, Kristina; Kirstein, Linda; de Hoog, Cees-Jan; Elliot, Tim; Savov, Ivan; Devey, Colin


    Recycling of oceanic lithosphere drives the chemical evolution of the Earth's mantle supplying both solids and volatiles to the Earth's interior. Yet, how subducted material influences mantle composition remains unclear. A perfect tracer for slab recycling should be only fractionated at the Earth's surface, have a strong influence on mantle compositions but be resistant to perturbations en route back to the surface. Current understanding suggests that boron concentrations linked to B isotope determinations fulfil all these requirements and should be an excellent tracer of heterogeneity in the deep mantle. Here, we present the trace element, volatile and the B isotope composition of basaltic glasses and melt inclusions in olivine from distinct end-member ocean island basalts (OIB) to track the fate of recycled lithosphere and ultimately document how recycling contributes to mantle heterogeneity. The chosen samples represent the different end member OIB compositions and include: EMI (Pitcairn), EMII (MacDonald), HIMU (St. Helena), and FOZO (Cape Verde & Reunion). The data is derived from both submarine and subaerial deposits, with B isotope determination of both basaltic glass and melt inclusions from each locality. Preliminary results suggest OIB have B isotopic compositions that overlap the MORB array (-7.5‰±0.7; Marschall et al., 2015) but extend to both lighter and heavier values. These results suggest that B isotopes will be useful for resolving mantle source heterogeneity at different ocean islands and contribute to our understanding of the volatile budget of the deep mantle.

  18. Propagating buoyant mantle upwelling on the Reykjanes Ridge

    Martinez, Fernando; Hey, Richard


    Crustal features of the Reykjanes Ridge have been attributed to mantle plume flow radiating outward from the Iceland hotspot. This model requires very rapid mantle upwelling and a "rheological boundary" at the solidus to deflect plume material laterally and prevent extreme melting above the plume stem. Here we propose an alternative explanation in which shallow buoyant mantle upwelling instabilities propagate along axis to form the crustal features of the ridge and flanks. As only the locus of buoyant upwelling propagates this mechanism removes the need for rapid mantle plume flow. Based on new geophysical mapping we show that a persistent sub-axial low viscosity channel supporting buoyant mantle upwelling can explain the current oblique geometry of the ridge as a reestablishment of its original configuration following an abrupt change in opening direction. This mechanism further explains the replacement of ridge-orthogonal crustal segmentation with V-shaped crustal ridges and troughs. Our findings indicate that crustal features of the Reykjanes Ridge and flanks are formed by shallow buoyant mantle instabilities, fundamentally like at other slow spreading ridges, and need not reflect deep mantle plume flow.

  19. Limited latitudinal mantle plume motion for the Louisville hotspot

    Koppers, Anthony A. P.; Yamazaki, Toshitsugu; Geldmacher, Jörg; Gee, Jeffrey S.; Pressling, Nicola; Koppers, Anthony A. P.; Yamazaki, Toshitsugu; Geldmacher, Jörg; Gee, Jeffrey S.; Pressling, Nicola; Hoshi, Hiroyuki; Anderson, L.; Beier, C.; Buchs, D. M.; Chen, L.-H.; Cohen, B. E.; Deschamps, F.; Dorais, M. J.; Ebuna, D.; Ehmann, S.; Fitton, J. G.; Fulton, P. M.; Ganbat, E.; Hamelin, C.; Hanyu, T.; Kalnins, L.; Kell, J.; Machida, S.; Mahoney, J. J.; Moriya, K.; Nichols, A. R. L.; Rausch, S.; Sano, S.-I.; Sylvan, J. B.; Williams, R.


    Hotspots that form above upwelling plumes of hot material from the deep mantle typically leave narrow trails of volcanic seamounts as a tectonic plate moves over their location. These seamount trails are excellent recorders of Earth's deep processes and allow us to untangle ancient mantle plume motions. During ascent it is likely that mantle plumes are pushed away from their vertical upwelling trajectories by mantle convection forces. It has been proposed that a large-scale lateral displacement, termed the mantle wind, existed in the Pacific between about 80 and 50 million years ago, and shifted the Hawaiian mantle plume southwards by about 15° of latitude. Here we use 40Ar/39Ar age dating and palaeomagnetic inclination data from four seamounts associated with the Louisville hotspot in the South Pacific Ocean to show that this hotspot has been relatively stable in terms of its location. Specifically, the Louisville hotspot--the southern hemisphere counterpart of Hawai'i--has remained within 3-5° of its present-day latitude of about 51°S between 70 and 50 million years ago. Although we cannot exclude a more significant southward motion before that time, we suggest that the Louisville and Hawaiian hotspots are moving independently, and not as part of a large-scale mantle wind in the Pacific.


    Miyagoshi, Takehiro [Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi, Kanazawa-ku, Yokohama 236-0001 (Japan); Tachinami, Chihiro [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551 (Japan); Kameyama, Masanori [Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577 (Japan); Ogawa, Masaki, E-mail:, E-mail:, E-mail:, E-mail: [Department of Earth Sciences and Astronomy, University of Tokyo at Komaba, 3-8-1 Komaba, Meguro, Tokyo 153-8902 (Japan)


    Numerical models are presented to clarify how adiabatic compression affects thermal convection in the mantle of super-Earths ten times the Earth's mass. The viscosity strongly depends on temperature, and the Rayleigh number is much higher than that of the Earth's mantle. The strong effect of adiabatic compression reduces the activity of mantle convection; hot plumes ascending from the bottom of the mantle lose their thermal buoyancy in the middle of the mantle owing to adiabatic decompression, and do not reach the surface. A thick lithosphere, as thick as 0.1 times the depth of the mantle, develops along the surface boundary, and the efficiency of convective heat transport measured by the Nusselt number is reduced by a factor of about four compared with the Nusselt number for thermal convection of incompressible fluid. The strong effect of adiabatic decompression is likely to inhibit hot spot volcanism on the surface and is also likely to affect the thermal history of the mantle, and hence, the generation of magnetic field in super-Earths.

  1. Water Distribution in the Continental and Oceanic Upper Mantle

    Peslier, Anne H.


    Nominally anhydrous minerals such as olivine, pyroxene and garnet can accommodate tens to hundreds of ppm H2O in the form of hydrogen bonded to structural oxygen in lattice defects. Although in seemingly small amounts, this water can significantly alter chemical and physical properties of the minerals and rocks. Water in particular can modify their rheological properties and its distribution in the mantle derives from melting and metasomatic processes and lithology repartition (pyroxenite vs peridotite). These effects will be examined here using Fourier transform infrared spectrometry (FTIR) water analyses on minerals from mantle xenoliths from cratons, plume-influenced cratons and oceanic settings. In particular, our results on xenoliths from three different cratons will be compared. Each craton has a different water distribution and only the mantle root of Kaapvaal has evidence for dry olivine at its base. This challenges the link between olivine water content and survival of Archean cratonic mantle, and questions whether xenoliths are representative of the whole cratonic mantle. We will also present our latest data on Hawaii and Tanzanian craton xenoliths which both suggest the intriguing result that mantle lithosphere is not enriched in water when it interacts with melts from deep mantle upwellings (plumes).

  2. Conflicting Geophysical and Geochemical Indicators of Mantle Temperature Beneath Tibet

    Klemperer, S. L.


    In Tibet a small number of earthquakes occurs at 75-100 km depth, spanning the Moho, reaching >350 km and >550 km north of the Himalayan front in south-eastern Tibet and western Tibet respectively. 'Earthquake thermometry' implies these deep earthquakes occur in anhydrous lower lithosphere, either anorthitic or ultramafic, at 0.1RA (~1% mantle fluid) are conventionally taken to imply an unequivocal mantle component. Time-averaged upward flow rates calculated from measured 3He/4He ratios (R) and [4He] range from ~1-15 cm/a, implying transport times of 0.5-7 Ma through a 70-km thick crust. Discussion of 3He in Tibet in the western literature has been dominated by a single paper (Hoke et al., EPSL, 2000) that reported modest mantle helium (0.110% mantle fluids are reported 120 km and 150 km south of the northern limit of deep earthquakes in southeastern and western Tibet respectively. These hot springs apparently sampled mantle with T>800°C south of the locations where earthquake thermometry implies Moho temperatures India, Nepal and Pakistan, even though the 800°C isotherm is substantially shallower there than beneath southern Tibet? More plausibly the mantle helium is derived from an Asian mantle wedge above the region of deep earthquakes, in which case underthrusting Indian lithosphere is not intact, but breaks into an upper layer forming the lower crust of the Tibetan Plateau, and a lower seismogenic layer that is subducted more deeply into the mantle. Based on the geothermal springs, an Asian mantle wedge extended south of the Indus Tsangpo suture in SE Tibet and to the Karakoram fault in W Tibet until the latest Miocene, or even more recently.

  3. Seismic anisotropy: tracing plate dynamics in the mantle.

    Park, Jeffrey; Levin, Vadim


    Elastic anisotropy is present where the speed of a seismic wave depends on its direction. In Earth's mantle, elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation. Earthquakes generate two seismic wave types: compressional (P) and shear (S) waves, whose coupling in anisotropic rocks leads to scattering, birefringence, and waves with hybrid polarizations. This varied behavior is helping geophysicists explore rock textures within Earth's mantle and crust, map present-day upper-mantle convection, and study the formation of lithospheric plates and the accretion of continents in Earth history.

  4. Mantle structure and tectonic history of SE Asia

    Hall, Robert; Spakman, Wim


    Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia and including Malaysia, parts of the Philippines, New Guinea and northern Australia. We begin with an explanation of seismic tomography and causes of velocity anomalies in the mantle, and discuss assessment of model quality for tomographic models created from P-wave travel times. We then introduce the global P-wave velocity anomaly model UU-P07 and the tectonic model used in this paper and give an overview of previous interpretations of mantle structure. The slab-related velocity anomalies we identify in the upper and lower mantle based on the UU-P07 model are interpreted in terms of the tectonic model and illustrated with figures and movies. Finally, we discuss where tomographic and tectonic models for SE Asia converge or diverge, and identify the most important conclusions concerning the history of the region. The tomographic images of the mantle record subduction beneath the SE Asian region to depths of approximately 1600 km. In the upper mantle anomalies mainly record subduction during the last 10 to 25 Ma, depending on the region considered. We interpret a vertical slab tear crossing the entire upper mantle north of west Sumatra where there is a strong lateral kink in slab morphology, slab holes between c.200-400 km below East Java and Sumbawa, and offer a new three-slab explanation for subduction in the North Sulawesi region. There is a different structure in the lower mantle compared to the upper mantle and the deep structure changes from west to east. What was imaged in earlier models as a broad and deep anomaly below SE Asia has a clear internal structure and we argue that many features can be identified as older subduction zones. We identify remnants of slabs

  5. Mercury's Plasma Mantle – a survey of MESSENGER observations

    Jasinski, Jamie Matthew; Slavin, James A.; Raines, Jim; DiBraccio, Gina


    The plasma mantle is a region of solar wind plasma entry into the nightside high-latitude magnetosphere. We present a survey of plasma mantles identified in particle and magnetic field measurements from four years of MESSENGER spacecraft observations of Mercury's magnetosphere. The two common observational signatures of this region are ion energy latitude dispersions as well as diamagnetic depressions. From these observations we estimate the contribution of plasma from the solar wind via the mantle and infer magnitude and variability in the cross-magnetospheric electric fields present at Mercury's dynamic magnetosphere.

  6. Volatile cycling and the thermal evolution of planetary mantle

    Sandu, Constantin

    The thermal histories of terrestrial planets are investigated using two parameterized mantle convection models for either Earth like planets and planets with no active plate tectonics. Using parameterized models of mantle convection, we performed computer simulations of planetary cooling and volatile cycling. The models estimate the amount of volatile in mantle reservoir, and calculate the outgassing and regassing rates. A linear model of volatile concentration-dependent is assumed for the activation energy of the solid-state creep in the mantle. The kinematic viscosity of the mantle is thus dynamically affected by the activation energy through a variable concentration in volatile. Mantle temperature and heat flux is calculated using a model derived from classic thermal boundary layer theory of a single layered mantle with temperature dependent viscosity. The rate of volatile exchanged between mantle and surface is calculated by balancing the amount of volatiles degassed in the atmosphere by volcanic and spreading related processes and the amount of volatiles recycled back in the mantle by the subduction process. In the cases that lack plate tectonics, the degassing efficiency is dramatically reduced and the regassing process is absent. The degassing effect is dependent on average spreading rate of tectonic plates and on the amount of volatile in the melt extract in the transition zone between mantle and upper boundary laver. The regassing effect is dependent on the subduction rate and on the amount of volatile present on a hydrated layer on top of the subducting slab. The degassing and regassing parameters are all related to the intensity of the convection in the mantle and to the surface temperature of the planet, and they are regulated by the amount of volatiles in reservoir. Comparative study with the previous models display significant differences and improve the versatility of the model. The optimum efficiency factors found are in the range of 0.01--0.06 for

  7. Accumulation of 'anti-continent' at the base of the mantle and its recycling in mantle plumes

    Tatsumi, Yoshiyuki; Suzuki, Toshihiro; Ozawa, Haruka; Hirose, Kei; Hanyu, Takeshi; Ohishi, Yasuo


    The continental crust is a unique reservoir of light elements in the solid Earth; it possesses an intermediate composition and is believed to have been created principally along volcanic arcs, which are major sites of terrestrial andesitic magmatism. Mantle-derived arc magmas are, however, generally mafic or basaltic. A simple mechanism to overcome this apparent dilemma and generate andesitic melts in such a setting is through the partial remelting of an initial mafic arc crust by heat supplied from underplating basaltic magmas. An antithesis to the formation of continental crust in this way should be the production of refractory melting residue, here referred to as 'anti-continent'. This anti-continent is likely to detach from arc crust as a result of a density inversion and descend into the upper mantle. High-pressure experiments demonstrate that sinking anti-continent is, in contrast to the subducting oceanic crust, always denser than the surrounding mantle, suggesting that it penetrates through the upper-lower mantle boundary, without stagnation, and accumulates at the base of the mantle to form a 200-400 km thick mass known as the D″ layer. Geochemical modeling provides further evidence that this accumulating anti-continent contributes to a deep-seated hotspot source. Therefore, through complementary processes, Earth creates buoyant continents and dense anti-continents at the top and the base of the mantle, respectively, and has recycled portions of anti-continent in mantle plumes.

  8. Global-scale water circulation in the Earth's mantle: Implications for the mantle water budget in the early Earth

    Nakagawa, Takashi; Spiegelman, Marc W.


    We investigate the influence of the mantle water content in the early Earth on that in the present mantle using numerical convection simulations that include three processes for redistribution of water: dehydration, partitioning of water into partially molten mantle, and regassing assuming an infinite water reservoir at the surface. These models suggest that the water content of the present mantle is insensitive to that of the early Earth. The initial water stored during planetary formation is regulated up to 1.2 OMs (OM = Ocean Mass; 1.4 ×1021 kg), which is reasonable for early Earth. However, the mantle water content is sensitive to the rheological dependence on the water content and can range from 1.2 to 3 OMs at the present day. To explain the evolution of mantle water content, we computed water fluxes due to subducting plates (regassing), degassing and dehydration. For weakly water dependent viscosity, the net water flux is almost balanced with those three fluxes but, for strongly water dependent viscosity, the regassing dominates the water cycle system because the surface plate activity is more vigorous. The increased convection is due to enhanced lubrication of the plates caused by a weak hydrous crust for strongly water dependent viscosity. The degassing history is insensitive to the initial water content of the early Earth as well as rheological strength. The degassing flux from Earth's surface is calculated to be approximately O (1013) kg /yr, consistent with a coupled model of climate evolution and mantle thermal evolution.

  9. Upper mantle anisotropy beneath Peru from SKS splitting: Constraints on flat slab dynamics and interaction with the Nazca Ridge

    Eakin, Caroline M.; Long, Maureen D.; Wagner, Lara S.; Beck, Susan L.; Tavera, Hernando


    The Peruvian flat slab is by far the largest region of flat subduction in the world today, but aspects of its structure and dynamics remain poorly understood. In particular, questions remain over whether the relatively narrow Nazca Ridge subducting beneath southern Peru provides dynamic support for the flat slab or it is just a passive feature. We investigate the dynamics and interaction of the Nazca Ridge and the flat slab system by studying upper mantle seismic anisotropy across southern Peru. We analyze shear wave splitting of SKS, sSKS, and PKS phases at 49 stations distributed across the area, primarily from the PerU Lithosphere and Slab Experiment (PULSE). We observe distinct spatial variations in anisotropic structure along strike, most notably a sharp transition from coherent splitting in the north to pervasive null (non-split) arrivals in the south, with the transition coinciding with the northern limit of the Nazca Ridge. For both anisotropic domains there is evidence for complex and multi-layered anisotropy. To the north of the ridge our *KS splitting measurements likely reflect trench-normal mantle flow beneath the flat slab. This signal is then modified by shallower anisotropic layers, most likely in the supra-slab mantle, but also potentially from within the slab. To the south the sub-slab mantle is similarly anisotropic, with a trench-oblique fast direction, but widespread nulls appear to reflect dramatic heterogeneity in anisotropic structure above the flat slab. Overall the regional anisotropic structure, and thus the pattern of deformation, appears to be closely tied to the location of the Nazca Ridge, which further suggests that the ridge plays a key role in the mantle dynamics of the Peruvian flat slab system.

  10. Isotopic (Pb, Sr, Nd, C, O) evidence for plume-related sampling of an ancient, depleted mantle reservoir

    Chen, Wei; Simonetti, Antonio


    The exact mantle source for carbonatite melts remains highly controversial. Despite their predominant occurrence within continental (lithospheric) domains, the radiogenic isotope data from young (oceanic island basalts (OIBs). This feature suggests an intimate petrogenetic relationship with asthenospheric mantle. New Pb, Sr, C, and O isotopic data are reported here for constituent minerals from the Oka carbonatite complex, which is associated with the Cretaceous Monteregian Igneous Province (MIP), northeastern North America. The Pb isotope data define linear arrays in Pb-Pb isotope diagrams, with the corresponding Sr isotope ratios being highly variable (0.70314-0.70343); both these features are consistent with open system behavior involving at least three distinct mantle reservoirs. Compared to the isotope composition of known mantle sources for OIBs and carbonatite occurrences worldwide, the least radiogenic 207Pb/204Pb (14.96 ± 0.07) and 208Pb/204Pb (37.29 ± 0.15) isotopic compositions relative to their corresponding 206Pb/204Pb ratios (18.86 ± 0.08) reported here are distinct, and indicate the involvement of an ancient depleted mantle (ADM) source. The extremely unradiogenic Pb isotope compositions necessitate U/Pb fractionation early in Earth's history (prior to 4.0 Ga ago) and growth via a multi-stage Pb evolution model. The combined stable (C and O) and radiogenic isotopic compositions effectively rule out crustal/lithosphere contamination during the petrogenetic history of the Oka complex. Instead, the isotopic variations reported here most likely result from the mixing of discrete, small volume partial melts derived from a heterogeneous plume source characterized by a mixed HIMU-EM1-ADM signature.

  11. Tracking the Martian Mantle Signature in Olivine-Hosted Melt Inclusions of Basaltic Shergottites Yamato 980459 and Tissint

    Peters, T. J.; Simon, J. I.; Jones, J. H.; Usui, T.; Moriwaki, R.; Economos, R.; Schmitt, A.; McKeegan, K.


    The Martian shergottite meteorites are basaltic to lherzolitic igneous rocks that represent a period of relatively young mantle melting and volcanism, approximately 600-150 Ma (e.g. [1,2]). Their isotopic and elemental composition has provided important constraints on the accretion, evolution, structure and bulk composition of Mars. Measurements of the radiogenic isotope and trace element concentrations of the shergottite meteorite suite have identified two end-members; (1) incompatible trace element enriched, with radiogenic Sr and negative epsilon Nd-143, and (2) incompatible traceelement depleted, with non-radiogenic Sr and positive epsilon 143-Nd(e.g. [3-5]). The depleted component represents the shergottite martian mantle. The identity of the enriched component is subject to debate, and has been proposed to be either assimilated ancient martian crust [3] or from enriched domains in the martian mantle that may represent a late-stage magma ocean crystallization residue [4,5]. Olivine-phyric shergottites typically have the highest Mg# of the shergottite group and represent near-primitive melts having experienced minimal fractional crystallization or crystal accumulation [6]. Olivine-hosted melt inclusions (MI) in these shergottites represent the most chemically primitive components available to understand the nature of their source(s), melting processes in the martian mantle, and origin of enriched components. We present trace element compositions of olivine hosted melt inclusions in two depleted olivinephyric shergottites, Yamato 980459 (Y98) and Tissint (Fig. 1), and the mesostasis glass of Y98, using Secondary Ionization Mass Spectrometry (SIMS). We discuss our data in the context of understanding the nature and origin of the depleted martian mantle and the emergence of the enriched component.

  12. Large Scale, High Resolution, Mantle Dynamics Modeling

    Geenen, T.; Berg, A. V.; Spakman, W.


    To model the geodynamic evolution of plate convergence, subduction and collision and to allow for a connection to various types of observational data, geophysical, geodetical and geological, we developed a 4D (space-time) numerical mantle convection code. The model is based on a spherical 3D Eulerian fem model, with quadratic elements, on top of which we constructed a 3D Lagrangian particle in cell(PIC) method. We use the PIC method to transport material properties and to incorporate a viscoelastic rheology. Since capturing small scale processes associated with localization phenomena require a high resolution, we spend a considerable effort on implementing solvers suitable to solve for models with over 100 million degrees of freedom. We implemented Additive Schwartz type ILU based methods in combination with a Krylov solver, GMRES. However we found that for problems with over 500 thousend degrees of freedom the convergence of the solver degraded severely. This observation is known from the literature [Saad, 2003] and results from the local character of the ILU preconditioner resulting in a poor approximation of the inverse of A for large A. The size of A for which ILU is no longer usable depends on the condition of A and on the amount of fill in allowed for the ILU preconditioner. We found that for our problems with over 5×105 degrees of freedom convergence became to slow to solve the system within an acceptable amount of walltime, one minute, even when allowing for considerable amount of fill in. We also implemented MUMPS and found good scaling results for problems up to 107 degrees of freedom for up to 32 CPU¡¯s. For problems with over 100 million degrees of freedom we implemented Algebraic Multigrid type methods (AMG) from the ML library [Sala, 2006]. Since multigrid methods are most effective for single parameter problems, we rebuild our model to use the SIMPLE method in the Stokes solver [Patankar, 1980]. We present scaling results from these solvers for 3D

  13. P-V-T Equation of State of (Al,Fe)-bearing Mantle Perovskite and its Implications for Mantle Models

    Fei, Y.; Ricolleau, A.; Litasov, K.; Prakapenka, V.


    We have made significant progress on accurate measurements of P-V-T equations-of-state of mantle minerals that are of fundamental importance for developing compositional and mineralogical models of the Earth's mantle. In this study, we report new compression data on (Al,Fe)-bearing mantle perovskite up to simultaneous pressure and temperature of 113 GPa and 2120 K. The mantle perovskite was synthesized in the multi-anvil apparatus at 27 GPa and 2073 K, with chemical compositions expected in a peridotitic mantle. It contains 5.86 wt% FeO and 3.84 wt% Al2O3. The pre-synthesized perovsite mixed with Au powder was compressed in neon pressure medium in a symmetric diamond anvil cell. The sample was heated with a double-sided laser-heating system at the GSECARS 13-ID-D beamline (Advanced Photon Source). We performed 8 heating cycles in the pressure range of 30-113 GPa and temperatures up to 2560 K. In-situ synchrotron X-ray diffraction data were collected within a uniformly heated area, using a MAR-CCD area detector. The diffraction pattern contains peaks of orthorhombic perovskite, internal standard Au, and pressure medium Ne. The triplet (020, 112, and 200 diffraction peaks) of the orthorhombic perovskite is well resolve. The present dataset covers the entire P-T range of the lower mantle and requires no extrapolation to compare the mantle density profile derived from seismic observations. In light of the new P-V-T data on the (Al,Fe)-bearing mantle perovskite combined with our recent density data and spin transition of ferropericlase, we finally discuss the compositional and mineralogical models of the lower mantle.

  14. European upper mantle tomography: adaptively parameterized models

    Schäfer, J.; Boschi, L.


    We have devised a new algorithm for upper-mantle surface-wave tomography based on adaptive parameterization: i.e. the size of each parameterization pixel depends on the local density of seismic data coverage. The advantage in using this kind of parameterization is that a high resolution can be achieved in regions with dense data coverage while a lower (and cheaper) resolution is kept in regions with low coverage. This way, parameterization is everywhere optimal, both in terms of its computational cost, and of model resolution. This is especially important for data sets with inhomogenous data coverage, as it is usually the case for global seismic databases. The data set we use has an especially good coverage around Switzerland and over central Europe. We focus on periods from 35s to 150s. The final goal of the project is to determine a new model of seismic velocities for the upper mantle underlying Europe and the Mediterranean Basin, of resolution higher than what is currently found in the literature. Our inversions involve regularization via norm and roughness minimization, and this in turn requires that discrete norm and roughness operators associated with our adaptive grid be precisely defined. The discretization of the roughness damping operator in the case of adaptive parameterizations is not as trivial as it is for the uniform ones; important complications arise from the significant lateral variations in the size of pixels. We chose to first define the roughness operator in a spherical harmonic framework, and subsequently translate it to discrete pixels via a linear transformation. Since the smallest pixels we allow in our parameterization have a size of 0.625 °, the spherical-harmonic roughness operator has to be defined up to harmonic degree 899, corresponding to 810.000 harmonic coefficients. This results in considerable computational costs: we conduct the harmonic-pixel transformations on a small Beowulf cluster. We validate our implementation of adaptive

  15. Density structure of the cratonic mantle in southern Africa

    Artemieva, Irina; Vinnik, Lev P.


    . An unusually high topography may be caused by a low density (high depletion) of the cratonic lithospheric mantle and/or by the dynamic support of the mantle with origin below the depth of isostatic compensation (assumed here to be at the lithosphere base). We use free-board constraints to examine the relative...... contributions of the both factors to surface topography in the cratons of southern Africa. Our analysis takes advantage of the SASE seismic experiment which provided high resolution regional models of the crustal thickness.We calculate the model of density structure of the lithospheric mantle in southern Africa...... and show that it has an overall agreement with xenolith-based data for lithospheric terranes of different ages. Density of lithospheric mantle has significant short-wavelength variations in all tectonic blocks of southern Africa and has typical SPT values of ca. 3.37-3.41g/cm3 in the Cape Fold and Namaqua...

  16. Inference of mantle viscosity for depth resolutions of GIA observations

    Nakada, Masao; Okuno, Jun'ichi


    Inference of the mantle viscosity from observations for glacial isostatic adjustment (GIA) process has usually been conducted through the analyses based on the simple three-layer viscosity model characterized by lithospheric thickness, upper- and lower-mantle viscosities. Here, we examine the viscosity structures for the simple three-layer viscosity model and also for the two-layer lower-mantle viscosity model defined by viscosities of η670,D (670-D km depth) and ηD,2891 (D-2891 km depth) with D-values of 1191, 1691 and 2191 km. The upper-mantle rheological parameters for the two-layer lower-mantle viscosity model are the same as those for the simple three-layer one. For the simple three-layer viscosity model, rate of change of degree-two zonal harmonics of geopotential due to GIA process (GIA-induced J˙2) of -(6.0-6.5) × 10-11 yr-1 provides two permissible viscosity solutions for the lower mantle, (7-20) × 1021 and (5-9) × 1022 Pa s, and the analyses with observational constraints of the J˙2 and Last Glacial Maximum (LGM) sea levels at Barbados and Bonaparte Gulf indicate (5-9) × 1022 Pa s for the lower mantle. However, the analyses for the J˙2 based on the two-layer lower-mantle viscosity model only require a viscosity layer higher than (5-10) × 1021 Pa s for a depth above the core-mantle boundary (CMB), in which the value of (5-10) × 1021 Pa s corresponds to the solution of (7-20) × 1021 Pa s for the simple three-layer one. Moreover, the analyses with the J˙2 and LGM sea level constraints for the two-layer lower-mantle viscosity model indicate two viscosity solutions: η670,1191 > 3 × 1021 and η1191,2891 ˜ (5-10) × 1022 Pa s, and η670,1691 > 1022 and η1691,2891 ˜ (5-10) × 1022 Pa s. The inferred upper-mantle viscosity for such solutions is (1-4) × 1020 Pa s similar to the estimate for the simple three-layer viscosity model. That is, these analyses require a high viscosity layer of (5-10) × 1022 Pa s at least in the deep mantle, and suggest

  17. Coupling surface and mantle dynamics: A novel experimental approach

    Kiraly, Agnes; Faccenna, Claudio; Funiciello, Francesca; Sembroni, Andrea


    Recent modeling shows that surface processes, such as erosion and deposition, may drive the deformation of the Earth's surface, interfering with deeper crustal and mantle signals. To investigate the coupling between the surface and deep process, we designed a three-dimensional laboratory apparatus, to analyze the role of erosion and sedimentation, triggered by deep mantle instability. The setup is constituted and scaled down to natural gravity field using a thin viscous sheet model, with mantle and lithosphere simulated by Newtonian viscous glucose syrup and silicon putty, respectively. The surface process is simulated assuming a simple erosion law producing the downhill flow of a thin viscous material away from high topography. The deep mantle upwelling is triggered by the rise of a buoyant sphere. The results of these models along with the parametric analysis show how surface processes influence uplift velocity and topography signals.

  18. Mantle structure beneath the western edge of the Colorado Plateau

    Sine, C.R.; Wilson, D.; Gao, W.; Grand, S.P.; Aster, R.; Ni, J.; Baldridge, W.S.


    Teleseismic traveltime data are inverted for mantle Vp and Vs variations beneath a 1400 km long line of broadband seismometers extending from eastern New Mexico to western Utah. The model spans 600 km beneath the moho with resolution of ???50 km. Inversions show a sharp, large-magnitude velocity contrast across the Colorado Plateau-Great Basin transition extending ???200 km below the crust. Also imaged is a fast anomaly 300 to 600 km beneath the NW portion of the array. Very slow velocities beneath the Great Basin imply partial melting and/or anomalously wet mantle. We propose that the sharp contrast in mantle velocities across the western edge of the Plateau corresponds to differential lithospheric modification, during and following Farallon subduction, across a boundary defining the western extent of unmodified Proterozoic mantle lithosphere. The deep fast anomaly corresponds to thickened Farallon plate or detached continental lithosphere at transition zone depths. Copyright 2008 by the American Geophysical Union.

  19. Thermochemical structure of the Earth's mantle and continental crust

    Guerri, Mattia

    A detailed knowledge of the Earth's thermal structure and chemical composition is fundamental in order to understand the processes driving the planet ormation and evolution. The inaccessibility of most of the Earth's interior makes the determination of its thermo-chemical conditions a challenging...... in determining crustal seismic discontinuities. In the second chapter, I deal about the possibility to disentangle the dynamic and isostatic contribution in shaping the Earth's surface topography. Dynamic topography is directly linked to mantle convection driven by mantle thermo-chemical anomalies, and can...... argue therefore that our understandings of the lithosphere density structure, needed to determine the isostatic topography, and of the mantle density and viscosity, required to compute the dynamic topography, are still too limited to allow a robust determination of mantle convection effects on the Earth...

  20. Generation and control of thoron emanated from lantern mantles

    Sorimachi, Atsuyuki; Sahoo, Sarata Kumar; Tokonami, Shinji


    This paper describes the performance of a thoron (R220n) flowthrough source made of a commercially available lantern mantle. This R220n source is easy to construct and operate and has a negligible radon (R222n) gas generated when the air was passed through the source. We studied the R220n concentration generated from the lantern mantles in terms of the variability in concentration associated with both the total weight of the lantern mantles used in the source and the air flow rate used in the experimental chamber. We found that the concentration of R220n generated in air ranged from 0.9 to 150 kBq m-3 and exponentially depended on the absolute humidity. The R220n concentration increased linearly with increasing total weight of the lantern mantles, but variations in the rate of air flow passed through the source had no influence on the observed R220n concentration.

  1. On the deep-mantle origin of the Deccan Traps

    Glišović, Petar; Forte, Alessandro M.


    The Deccan Traps in west-central India constitute one of Earth’s largest continental flood basalt provinces, whose eruption played a role in the Cretaceous-Paleogene extinction event. The unknown mantle structure under the Indian Ocean at the start of the Cenozoic presents a challenge for connecting the event to a deep mantle origin. We used a back-and-forth iterative method for time-reversed convection modeling, which incorporates tomography-based, present-day mantle heterogeneity to reconstruct mantle structure at the start of the Cenozoic. We show a very low-density, deep-seated upwelling that ascends beneath the Réunion hot spot at the time of the Deccan eruptions. We found a second active upwelling below the Comores hot spot that likely contributed to the region of partial melt feeding the massive eruption.

  2. Lithology and temperature: How key mantle variables control rift volcanism

    Shorttle, O.; Hoggard, M.; Matthews, S.; Maclennan, J.


    Continental rifting is often associated with extensive magmatic activity, emplacing millions of cubic kilometres of basalt and triggering environmental change. The lasting geological record of this volcanic catastrophism are the large igneous provinces found at the margins of many continents and abrupt extinctions in the fossil record, most strikingly that found at the Permo-Triassic boundary. Rather than being considered purely a passive plate tectonic phenomenon, these episodes are frequently explained by the involvement of mantle plumes, upwellings of mantle rock made buoyant by their high temperatures. However, there has been debate over the relative role of the mantle's temperature and composition in generating the large volumes of magma involved in rift and intra-plate volcanism, and even when the mantle is inferred to be hot, this has been variously attributed to mantle plumes or continental insulation effects. To help resolve these uncertainties we have combined geochemical, geophysical and modelling results in a two stage approach: Firstly, we have investigated how mantle composition and temperature contribute to melting beneath Iceland, the present day manifestation of the mantle plume implicated in the 54Ma break up of the North Atlantic. By considering both the igneous crustal production on Iceland and the chemistry of its basalts we have been able to place stringent constraints on the viable temperature and lithology of the Icelandic mantle. Although a >100°C excess temperature is required to generate Iceland's thick igneous crust, geochemistry also indicates that pyroxenite comprises 10% of its source. Therefore, the dynamics of rifting on Iceland are modulated both by thermal and compositional mantle anomalies. Secondly, we have performed a global assessment of the mantle's post break-up thermal history to determine the amplitude and longevity of continental insulation in driving excess volcanism. Using seismically constrained igneous crustal

  3. Role of the subduction filter in mantle recycling

    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

  4. The origin of volatiles in the Earth's mantle

    Hier-Majumder, Saswata; Hirschmann, Marc M.


    The Earth's deep interior contains significant reservoirs of volatiles such as H, C, and N. Due to the incompatible nature of these volatile species, it has been difficult to reconcile their storage in the residual mantle immediately following crystallization of the terrestrial magma ocean (MO). As the magma ocean freezes, it is commonly assumed that very small amounts of melt are retained in the residual mantle, limiting the trapped volatile concentration in the primordial mantle. In this article, we show that inefficient melt drainage out of the freezing front can retain large amounts of volatiles hosted in the trapped melt in the residual mantle while creating a thick early atmosphere. Using a two-phase flow model, we demonstrate that compaction within the moving freezing front is inefficient over time scales characteristic of magma ocean solidification. We employ a scaling relation between the trapped melt fraction, the rate of compaction, and the rate of freezing in our magma ocean evolution model. For cosmochemically plausible fractions of volatiles delivered during the later stages of accretion, our calculations suggest that up to 77% of total H2O and 12% of CO2 could have been trapped in the mantle during magma ocean crystallization. The assumption of a constant trapped melt fraction underestimates the mass of volatiles in the residual mantle by more than an order of magnitude.Plain Language SummaryThe Earth's deep interior contains substantial amounts of volatile elements like C, H, and N. How these elements got sequestered in the Earth's interior has long been a topic of debate. It is generally assumed that most of these elements escaped the interior of the Earth during the first few hundred thousand years to create a primitive atmosphere, leaving the mantle reservoir nearly empty. In this work, we show that the key to this paradox involves the very early stages of crystallization of the mantle from a global magma ocean. Using numerical models, we show

  5. Water content in the Martian mantle: A Nakhla perspective

    Weis, Franz A.; Bellucci, Jeremy J.; Skogby, Henrik; Stalder, Roland; Nemchin, Alexander A.; Whitehouse, Martin J.


    Water contents of the Martian mantle have previously been investigated using Martian meteorites, with several comprehensive studies estimating the water content in the parental melts and mantle source regions of the shergottites and Chassigny. However, no detailed studies have been performed on the Nakhla meteorite. One possible way to determine the water content of a crystallizing melt is to use the water content in nominally anhydrous minerals (NAMs) such as clinopyroxene and olivine. During or after eruption on the surface of a planetary body and during residence in a degassing magma, these minerals may dehydrate. By reversing this process experimentally, original (pre-dehydration) water concentrations can be quantified. In this study, hydrothermal rehydration experiments were performed at 2 kbar and 700 °C on potentially dehydrated Nakhla clinopyroxene crystals. Rehydrated clinopyroxene crystals exhibit water contents of 130 ± 26 (2σ) ppm and are thus similar to values observed in similar phenocrysts from terrestrial basalts. Utilizing clinopyroxene/melt partition coefficients, both the water content of the Nakhla parent melt and mantle source region were estimated. Despite previous assumptions of a relatively dry melt, the basaltic magma crystallizing Nakhla may have had up to 1.42 ± 0.28 (2σ) wt.% H2O. Based on an assumed low degree of partial melting, this estimate can be used to calculate a minimum estimate of the water content for Nakhla's mantle source region of 72 ± 16 ppm. Combining this value with values determined for other SNC mantle sources, by alternative methods, gives an average mantle value of 102 ± 9 (2σ) ppm H2O for the Martian upper mantle throughout geologic time. This value is lower than the bulk water content of Earth's upper mantle (∼250 ppm H2O) but similar to Earth's MORB source (54-330 ppm, average ∼130 ppm H2O).

  6. Execution of mantle field with multileaf collimator: A simple approach

    Prabhakar Ramachandran


    Full Text Available Background: Until very recently mantle field radiotherapy remained the gold standard for the treatment of favorable early-stage Hodgkin′s lymphoma. The classic mantle includes all the major lymph nodes above the diaphragm and extends from the inferior portion of the mandible to the level of the insertion of the diaphragm. Aims: To describe a simple technique that has been devised to treat the mantle field with the help of multileaf collimator and using computed tomography (CT-based treatment planning. Materials and Methods: CT scan was performed with the patient in the supine position and the datasets were transferred to the Eclipse™ treatment planning system. Elekta Precise™ linear accelerator equipped with 40 pairs of multileaf collimator (MLC was used for the execution of the mantle field. The MLC′s shapes were designed to take the shape of the conventional customized blocks used for treatment of mantle field. The anterior mantle field was divided into three separate MLC segments with the collimator kept at 0°. The first MLC segment was shaped to cover the neck, clavicular regions, and mediastinum. The second and the third MLC segments covered the right and left axilla, respectively. The posterior fields were opposed to the anterior subfields in a similar fashion. The dose was prescribed at the midplane, using reference points. Results and Conclusion: The technique described in this study is very simple, easy to implement, and avoids unnecessary delay in the execution of the mantle field. The mantle field can be easily shaped with the multileaf collimators, without any collimator rotation.

  7. Initial Feasibility Study to Drill and Core the Ocean Mantle


    An initial feasibility study (Pilisi and Whitney, 2011) of drilling through the Mohorovičić discontinuity (Moho) into the oceanic mantle specifically focused on future requirements for planning, drilling and coring a hole 500 m into the oceanic mantle from three candidate locations in the Pacific Ocean (Cocos Plate, Baja California, and offshore Hawaii). The study points out some of the critical issues that need to be resolved before embarking upon such a challengingproject. It was conducted ...

  8. Origin of geochemical mantle components: Role of subduction filter

    Kimura, Jun-Ichi; Gill, James B.; Skora, Susanne; van Keken, Peter E.; Kawabata, Hiroshi


    We quantitatively explore element redistribution at subduction zones using numerical mass balance models to evaluate the roles of the subduction zone filter in the Earth's geochemical cycle. Our models of slab residues after arc magma genesis differ from previous ones by being internally consistent with geodynamic models of modern arcs that successfully explain arc magma genesis and include element fluxes from the dehydration/melting of each underlying slab component. We assume that the mantle potential temperature (Tp) was 1400-1650°C at 3.5-1.7 Ga and gradually decreased to 1300-1350°C today. Hot subduction zones with Tp ˜1650°C have a thermal structure like modern SW Japan where high-Mg andesite is formed which is chemically like continental crust. After 2.5-1.7 Gyr of storage in the mantle, the residual igneous oceanic crust from hot subduction zones can evolve isotopically to the HIMU mantle component, the residual base of the mantle wedge to EMI, the residual sediment becomes an essential part of EMII, and the residual top of the mantle wedge can become the subcontinental lithosphere component. The Common or Focal Zone component is a stable mixture of the first three residues occasionally mixed with early depleted mantle. Slab residues that recycled earlier (˜2.5 Ga) form the DUPAL anomaly in the southern hemisphere, whereas residues of more recent recycling (˜1.7 Ga) underlie the northern hemisphere. These ages correspond to major continental crust forming events. The east-west heterogeneity of the depleted upper mantle involves subcontinental mantle except in the Pacific.

  9. Alpine Lithosphere and Upper Mantle Passive Seismic Monitoring

    Brückl, Ewald; Hausmann, Helmut; Behm, Michael; Lippitsch, Regina; Mitterbauer, Ulrike; Institute of Geodesy and Geophysics Vienna University of Technology (Hrsg.)


    The project ALPASS is a passive seismic monitoring project aiming to reveal upper mantle, lower lithosphere, and asthenosphere beneath the wider Eastern Alpine region, including the Bohemian Massive, the Carpathians, the Pannonian Basin, and the Dinarides. A 3D seismic model which will provide crustal corrections to the seismic travel times has been generated in this area down to the Moho and the uppermost mantle from data of former projects CELEBRATION 2000 and ALP 2002. ALPASS will yield in...

  10. Properties of the Plasma Mantle in the Earth's Magnetotail

    Shodhan-Shah, Sheela


    The plasma mantle is the site where the solar wind enters the Earth's magnetosphere. As yet, the mantle in the magnetotail (downstream part of the magnetosphere) has remained an enigma, for this region is remote and inaccessible. However, new results from the GEOTAIL spacecraft have yielded data on the mantle, making its study possible. The research reported in this dissertation uses the measurements made by the GEOTAIL spacecraft when it was beyond 100 Re (1 Re = Earth radius) in the magnetotail to determine the global geometrical and dynamical properties of the mantle. The model and the data together provide a cross-sectional picture of the mantle, as well as its extent into the tail and along the circumference of the tail. The model assesses the mass and momentum flux flowing through the mantle and merging with the plasma sheet (a relatively dense region that separates the oppositely directed fields of the tail lobes). In this way, the thesis examines the importance of the mantle as a source that replenishes and moves the plasma sheet. Moreover, it addresses the relative importance of the global dynamical modes of the tail. The analysis finds that the tail's 'breathing' mode, of shape change, occurs on a timescale of tens of minutes while a windsock-type motion, responding to changes in the solar wind direction, occurs on a scale of hours. The mantle extends about 140o around the circumference of the tail rather than 90o as previously thought and is about 20 ± 9 Re thick. It is capable of feeding the plasma sheet with sufficient particles to make up for those lost and can drag it away with a force that compares with the Earthward force on it. The rate at which the energy flows through the tail at 100 Re is about 10% of that in the solar wind and is a factor of 10 higher than the energy dissipated.

  11. Lower mantle heterogeneity, dynamic topography and the geoid

    Hager, B. H.; Clayton, R. W.; Richards, M. A.; Comer, R. P.; Dziewonski, A. M.


    Density contrasts in the lower mantle, recently imaged using seismic tomography, drive convective flow which results in kilometers of dynamically maintained topography at the core-mantle boundary and at the earth's surface. The total gravity field due to interior density constrasts and boundary topography predicts the largest wavelength components of the geoid remarkably well. Neglecting dynamic surface deformation leads to geoid anomalies of opposite sign than are observed.

  12. Mercurian impact ejecta: Meterorites and mantle

    Gladman, B


    We have examined the fate of impact ejecta liberated from the surface of Mercury due to impacts by comets or asteroids, in order to study (1) meteorite transfer to Earth, and (2) re-accumulation of an expelled mantle in giant-impact scenarios seeking to explain Mercury's large core. In the context of meteorite transfer, we note that Mercury's impact ejecta leave the planet's surface much faster (on average) than other planet's in the Solar System because it is the only planet where impact speeds routinely range from 5-20 times the planet's escape speed. Thus, a large fraction of mercurian ejecta may reach heliocentric orbit with speeds sufficiently high for Earth-crossing orbits to exist immediately after impact, resulting in larger fractions of the ejecta reaching Earth as meteorites. We calculate the delivery rate to Earth on a time scale of 30 Myr and show that several percent of the high-speed ejecta reach Earth (a factor of -3 less than typical launches from Mars); this is one to two orders of magnitude ...

  13. Deuterium enrichment of the interstellar grain mantle

    Das, Ankan; Chakrabarti, Sandip K


    We carry out Monte-Carlo simulation to study deuterium enrichment of interstellar grain mantles under various physical conditions. Based on the physical properties, various types of clouds are considered. We find that in diffuse cloud regions, very strong radiation fields persists and hardly a few layers of surface species are formed. In translucent cloud regions with a moderate radiation field, significant number of layers would be produced and surface coverage is mainly dominated by photo-dissociation products such as, C,CH_3,CH_2D,OH and OD. In the intermediate dense cloud regions (having number density of total hydrogen nuclei in all forms ~ 2 x 10^4 cm^-3), water and methanol along with their deuterated derivatives are efficiently formed. For much higher density regions (~ 10^6 cm^-3), water and methanol productions are suppressed but surface coverage of CO,CO_2,O_2,O_3 are dramatically increased. We find a very high degree of fractionation of water and methanol. Observational results support a high frac...

  14. Deep mantle forces and the uplift of the Colorado Plateau

    Moucha, R; Forte, A M; Rowley, D B; Mitrovica, J X; Simmons, N A; Grand, S P


    Since the advent of plate tectonics, it has been speculated that the northern extension of the East Pacific Rise, specifically its mantle source, has been over-ridden by the North American Plate in the last 30 Myrs. Consequently, it has also been postulated that the opening of the Gulf of California, the extension in the Basin and Range province, and the uplift of the Colorado Plateau are the resulting continental expressions of the over-ridden mantle source of the East Pacific Rise. However, only qualitative models based solely on surface observations and heuristic, simplified conceptions of mantle convection have been used in support or against this hypothesis. We introduce a quantitative model of mantle convection that reconstructs the detailed motion of a warm mantle upwelling over the last 30 Myrs and its relative advance towards the interior of the southwestern USA. The onset and evolution of the crustal uplift in the central Basin and Range province and the Colorado Plateau is determined by tracking the topographic swell due to this mantle upwelling through time. We show that (1) the extension and magmatism in the central Basin and Range province between 25 and 10 Ma coincides with the reconstructed past position of this focused upwelling, and (2) the southwestern portion of the Colorado Plateau experienced significant uplift between 10 Ma and 5 Ma that progressed towards the northeastern portion of the plateau. These uplift estimates are consistent with a young, ca. 6 Ma, Grand Canyon model and the recent commencement of mafic magmatism.

  15. Oceanic crust recycling and the formation of lower mantle heterogeneity

    van Keken, Peter E.; Ritsema, Jeroen; Haugland, Sam; Goes, Saskia; Kaneshima, Satoshi


    The Earth's lower mantle is heterogeneous at multiple scales as demonstrated for example by the degree-2 distribution of LLSVPs seen in global tomography and widespread distribution of small scale heterogeneity as seen in seismic scattering. The origin of this heterogeneity is generally attributed to leftovers from Earth's formation, the recycling of oceanic crust, or a combination thereof. Here we will explore the consequences of long-term oceanic crust extraction and recycling by plate tectonics. We use geodynamical models of mantle convection that simulate plates in an energetically consistent manner. The recycling of oceanic crust over the age of the Earth produces persistent lower mantle heterogeneity while the upper mantle tends to be significantly more homogeneous. We quantitatively compare the predicted heterogeneity to that of the present day Earth by tomographic filtering of the geodynamical models and comparison with S40RTS. We also predict the scattering characteristics from S-P conversions and compare these to global scattering observations. The geophysical comparison shows that lower mantle heterogeneity is likely dominated by long-term oceanic crust recycling. The models also demonstrate reasonable agreement with the geochemically observed spread between HIMU-EM1-DMM in ocean island basalts as well as the long-term gradual depletion of the upper mantle as observed in Lu-Hf systematics.

  16. [Biochemistry and functional characterization of squid mantle meat (Dosidicus gigas)].

    Abugoch, L; Guarda, A; María Pérez, L; Isabel Donghi, M


    A study for the characterization of frozen giant squid mantle (meat) protein stored at -25 degrees C for 8 month was started. In the present research, the following functional properties were investigate: emulsifying, water holding and gel forming capacities. Optimal conditions for the separation and differentiation of miofibrillar and sarcoplasmatic proteins were also studied. It was found that the unfrozen giant squid mantle meat es capable of emulifying 2.817,4 g of oil/g of protein and holding capacity was 3.64 g of water/g of protein. Related to the gel forming capacity, it was not obtain, probably due to excessive storage of the meat. With regard to miofibrilar protein obtention of the squid mantle meat, it was found that two low ionic strength washings (I = 0.05), the sarcoplasmic proteins were practically eliminated from the protein matrix. The differentiation of miofibrilar and sarcoplasmatic proteins was obtained by PAGE-SDS of the squid mantle meat extracted at two different ionic strength (I = 0.05 and I = 0.5). This work demonstrates that the giant squid mantle protein has a high emulsifying and water holding capacity, and it can be used, as a raw material, for the improvement of sausage products. About the gelling products, more studies will be necessary with fresh squid mantle meat to conclude about this functional property.

  17. Mantle Xenoliths of Cerro Mercedes, Costa Rica, Central America

    Lindsay, F. N.; Carr, M. J.; Herzberg, C. T.; Feigenson, M. D.


    Mantle peridotite occurs as xenoliths in lavas and bombs at Cerro Mercedes, a Plio-Quaternary potassic alkaline basalt volcano approximately 70 km behind the volcanic front of northern Costa Rica (Tournon and Alvarado, 1997). Mineral exploration led to the first discovery of abundant mantle xenoliths in Central America (Vargas and Alfaro, 1992). The compositions of 71 xenoliths recovered in January 2003 include dunite, harzburgite, lherzolite and olivine websterite. Twenty xenoliths have a diameter of at least 3 cm. The nodules are abundant in basalt outcrops and the rare bombs. In spite of substantial soil development in a rain forest environment, both xenoliths and host lava remain well preserved. Olivine, pyroxenes and spinel are common, plagioclase is present and garnet appears to be absent. There is no obvious shearing or deformation and several pyroxenes are as much as 1 cm in diameter. The mineralogy suggests a relatively shallow upper mantle source, within either the lithosphere or possibly the uppermost asthenosphere. Cerro Mercedes, at latitude 10° 58' N and longitude 82° 21' W, lies along the Rio San Juan, which is locally the border between Nicaragua and Costa Rica, Central America. This location approximately coincides with a boundary between dominantly depleted mantle to the northwest and OIB or Galapagos-like mantle to the southeast. We will use mineralogical data to better define the likely depths and oxidation states of representative nodules and isotopic data to define the type of mantle source.

  18. Seismic scatterers in the mid-lower mantle

    Kaneshima, Satoshi


    Recent seismological studies have revealed that rocks with significantly different elastic properties are juxtaposed in the mid-lower mantle and often scatter seismic waves efficiently enough to be detected by seismic array analyses. Seismic networks all over the world with various aperture and geometry have been utilized for detecting scattered waves. A large number of objects that act as scatterers in the mid-lower mantle have been mapped out by analyzing several different types of scattered waves, mostly of short period: S-to-P scattering, P-to-P scattering prior to PP waves, P-to-P scattering prior to P‧P‧, P-to-P scattering in P coda waves, and P-to-P scattering prior to PKP. The scatterers have a lesser size that is smaller than the wavelengths (∼10 km), and probably extend several tens of kilometers at least. The mid-mantle scatterers are most likely to represent basaltic rocks that subducted into the lower mantle. Revealing the elastic properties relative to the surrounding rocks and the geometry of the individual scatterers, as well as the global distribution of the scatterers, should shed new light on the style of mantle convection. Relevant observations of mid-lower mantle scatterers are reviewed, and the directions of future progress are suggested.

  19. Generation of mantle heterogeneity via reaction between MORB-pyroxenite derived partial melts and peridotite

    Mallik, A.; Dasgupta, R.


    Characterization of mineralogy and lithology of mantle heterogeneities is important as they affect melting processes and physical properties of the mantle in turn influencing mantle dynamics. Direct evidence of such heterogeneities are found as lithospheric xenoliths and in tectonically exposed mantle sections. However, possible major element compositions of heterogeneities that can be produced in the convective mantle remain unclear. Reaction between silica-rich melt from subducted oceanic crust and peridotite has been deemed responsible for generation of secondary pyroxenite and olivine-free mantle beneath Hawaii [1]. However, no studies till date have systematically characterized the evolution of mineralogy and lithology owing to such a melt-rock reaction. We performed reaction experiments between two MORB-pyroxenite derived basaltic andesites and a volatile-free lherzolite using piston-cylinder apparatus and Pt/Gr capsules, at 2.5-3 GPa, 1375°C and 1440°C. The fraction of melt was varied from ~8 to 50%. Melt was introduced either in a layered geometry or mixed homogeneously with peridotite to simulate channelized and porous flow, respectively. Layered experiments produced a zone of (± garnet-) websterite separating a pool of reacted melt from four-phase lherzolite. They show that olivine-exhaustion is possible only locally along melt channels and the peridotite domains away from melt bands remain effectively unaltered in terms of modal mineralogy although slight diffusive enrichment in TiO2, Al2O3 and FeO is observed. In the mixed experiments, olivine mode diminishes at the expense of orthopyroxene producing a continuous spectrum from lherzolite to olivine websterite and finally websterite with increasing melt-rock ratio. With increasing orthopyroxene modal enrichment, orthopyroxene composition displays increase in TiO2 (~0.2 to ~0.9 wt%), Al2O3 (~4.5 to ~6.7 wt%), FeO (~6 to ~8 wt%), Na2O (~0.2 to 0.8 wt%) and decrease in Cr2O3 (~0.35 to 0.15 wt%) compared

  20. Reconstructing the Cenozoic evolution of the mantle: Implications for mantle plume dynamics under the Pacific and Indian plates

    Glišović, Petar; Forte, Alessandro M.


    The lack of knowledge of the initial thermal state of the mantle in the geological past is an outstanding problem in mantle convection. The resolution of this problem also requires the modelling of 3-D mantle evolution that yields maximum consistency with a wide suite of geophysical constraints. Quantifying the robustness of the reconstructed thermal evolution is another major concern. To solve and estimate the robustness of the time-reversed (inverse) problem of mantle convection, we analyse two different numerical techniques: the quasi-reversible (QRV) and the backward advection (BAD) methods. Our investigation extends over the 65 Myr interval encompassing the Cenozoic era using a pseudo-spectral solution for compressible-flow thermal convection in 3-D spherical geometry. We find that the two dominant issues for solving the inverse problem of mantle convection are the choice of horizontally-averaged temperature (i.e., geotherm) and mechanical surface boundary conditions. We find, in particular, that the inclusion of thermal boundary layers that yield Earth-like heat flux at the top and bottom of the mantle has a critical impact on the reconstruction of mantle evolution. We have developed a new regularisation scheme for the QRV method using a time-dependent regularisation function. This revised implementation of the QRV method delivers time-dependent reconstructions of mantle heterogeneity that reveal: (1) the stability of Pacific and African ‘large low shear velocity provinces’ (LLSVP) over the last 65 Myr; (2) strong upward deflections of the CMB topography at 65 Ma beneath: the North Atlantic, the south-central Pacific, the East Pacific Rise (EPR) and the eastern Antarctica; (3) an anchored deep-mantle plume ascending directly under the EPR (Easter and Pitcairn hotspots) throughout the Cenozoic era; and (4) the appearance of the transient Reunion plume head beneath the western edge of the Deccan Plateau at 65 Ma. Our reconstructions of Cenozoic mantle

  1. The LIP-OIB transitional phase in the Galapagos mantle plume

    Trela, J.; Gazel, E.; Vidito, C. A.; Class, C.; Jicha, B. R.; Bizimis, M.; Herzberg, C. T.; Alvarado-Induni, G.


    Although significant work has been done on LIPS and OIB, no complete record of the evolution of a mantle plume is available at this point. Galapagos-related lavas provide a complete record of the evolution of a mantle plume since the plume's initial stages in the Cretaceous. Our petrological models (PRIMELT2) suggest that the Galapagos plume head that formed the Caribbean Large Igneous Province (CLIP) at ~95 Ma melted at hotter temperatures than the ocean island basalt (OIB) equivalents of the modern archipelago. While this work suggests a significant decrease in mantle potential temperatures (Tp) over time, the exact mechanism responsible for secular cooling of the Galapagos plume remains unclear. One viable explanation is that plumes entraining recycled oceanic crust (pyroxenite) will be cooler than purely peridotite plumes, due to the effect of dense pyroxenite on the plume's buoyancy. High-precision electron microprobe analyses on olivine cores from the ~70 Ma Galapagos-related Quepos terrane in Costa Rica indicate a mixed peridotite-pyroxenite source lithology, not evident during the LIP stage. The appearance of this pyroxenitic component correlates with the first record of an EMII isotopic signature (Northern Galapagos Domain), and significant high-field strength enrichments in the Galapagos plume related lavas. This dense pyroxenite component may explain the marked decrease in Tp observed at ~70 Ma due to its effect on the plume's buoyancy. Otherwise, the pyroxenite component may have been diluted during voluminous basalt production of the CLIP by high peridotite melt fractions. Future research will incorporate further petrological modeling, olivine chemistry, and radiogenic isotope work of accreted Galapagos terranes in Central America to test whether or not a decrease in Tp correlates with increasing pyroxenite content in source melts.

  2. Melting curve of the deep mantle applied to properties of early magma ocean and actual core-mantle boundary

    Andrault, Denis; Lo Nigro, Giacomo; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed A.; Garbarino, Gaston; Mezouar, Mohamed


    Our planet experienced partial melting early in its history as a consequence of energy release due to accretion. Partial mantle melting could still happen today in the lowermost mantle. Occurrence of melting is primordial for the chemical segregation between the different Earth's reservoirs and for the dynamics of the whole planet. Melting of iron-alloys is relatively easy to achieve, but the silicated mantle happens to be more refractory. We investigated experimentally melting properties of two starting material, forsterite and chondritic-mantle, at pressures ranging from 25 to 140 GPa, using laser-heated diamond anvil cell coupled with synchrotron radiation. We show that partial melting in the lowermost mantle, as suggested by seismology on the basis of the ultra-low velocity zones (ULVZ), requires temperatures above 4200 K at the core-mantle boundary. At low pressures, our curve plots significantly lower than previous reports. Compared to recent estimates of mantle geotherm, while this temperature remains possible if the Earth's core is very hot, it is more likely that ULVZs correspond to high concentration of incompatible elements driven down to the D"-layer by subducting slabs or extracted out from the outer core. When our chondritic melting curve is coupled with recent isentropic temperature profiles for a magma ocean, we obtain a correlation between magma ocean depth and the potential temperature (Tp) at its surface; an ocean depth of 1000 km (equivalent to ~40 GPa) corresponds to Tp=2000 K, which happens to be significantly hotter than the estimated surface temperature of a sustained magma ocean. It emphasizes the importance of a lid at the magma ocean surface at an epoch as early as that of core-mantle segregation.

  3. Trace element mass balance in hydrous adiabatic mantle melting: The Hydrous Adiabatic Mantle Melting Simulator version 1 (HAMMS1)

    Kimura, Jun-Ichi; Kawabata, Hiroshi


    numerical mass balance calculation model for the adiabatic melting of a dry to hydrous peridotite has been programmed in order to simulate the trace element compositions of basalts from mid-ocean ridges, back-arc basins, ocean islands, and large igneous provinces. The Excel spreadsheet-based calculator, Hydrous Adiabatic Mantle Melting Simulator version 1 (HAMMS1) uses (1) a thermodynamic model of fractional adiabatic melting of mantle peridotite, with (2) the parameterized experimental melting relationships of primitive to depleted mantle sources in terms of pressure, temperature, water content, and degree of partial melting. The trace element composition of the model basalt is calculated from the accumulated incremental melts within the adiabatic melting regime, with consideration for source depletion. The mineralogic mode in the primitive to depleted source mantle in adiabat is calculated using parameterized experimental results. Partition coefficients of the trace elements of mantle minerals are parameterized to melt temperature mostly from a lattice strain model and are tested using the latest compilations of experimental results. The parameters that control the composition of trace elements in the model are as follows: (1) mantle potential temperature, (2) water content in the source mantle, (3) depth of termination of adiabatic melting, and (4) source mantle depletion. HAMMS1 enables us to obtain the above controlling parameters using Monte Carlo fitting calculations and by comparing the calculated basalt compositions to primary basalt compositions. Additionally, HAMMS1 compares melting parameters with a major element model, which uses petrogenetic grids formulated from experimental results, thus providing better constraints on the source conditions.

  4. High-pressure phase of brucite stable at Earth's mantle transition zone and lower mantle conditions

    Hermann, Andreas; Mookherjee, Mainak


    We investigate the high-pressure phase diagram of the hydrous mineral brucite, Mg(OH)2, using structure search algorithms and ab initio simulations. We predict a high-pressure phase stable at pressure and temperature conditions found in cold subducting slabs in Earth’s mantle transition zone and lower mantle. This prediction implies that brucite can play a much more important role in water transport and storage in Earth’s interior than hitherto thought. The predicted high-pressure phase, stable in calculations between 20 and 35 GPa and up to 800 K, features MgO6 octahedral units arranged in the anatase–TiO2 structure. Our findings suggest that brucite will transform from a layered to a compact 3D network structure before eventual decomposition into periclase and ice. We show that the high-pressure phase has unique spectroscopic fingerprints that should allow for straightforward detection in experiments. The phase also has distinct elastic properties that might make its direct detection in the deep Earth possible with geophysical methods.

  5. Magnesium stable isotope composition of Earth's upper mantle

    Handler, Monica R.; Baker, Joel A.; Schiller, Martin; Bennett, Vickie C.; Yaxley, Gregory M.


    The mantle is Earth's largest reservoir of Mg containing > 99% of Earth's Mg inventory. However, no consensus exists on the stable Mg isotope composition of the Earth's mantle or how variable it is and, in particular, whether the mantle has the same stable Mg isotope composition as chondrite meteorites. We have determined the Mg isotope composition of olivine from 22 mantle peridotites from eastern Australia, west Antarctica, Jordan, Yemen and southwest Greenland by pseudo-high-resolution MC-ICP-MS on Mg purified to > 99%. The samples include fertile lherzolites, depleted harzburgites and dunites, cryptically metasomatised ('dry') peridotites and modally metasomatised apatite ± amphibole-bearing harzburgites and wehrlites. Olivine from these samples of early Archaean through to Permian lithospheric mantle have δ25Mg DSM-3 = - 0.22 to - 0.08‰. These data indicate the bulk upper mantle as represented by peridotite olivine is homogeneous within current analytical uncertainties (external reproducibility ≤ ± 0.07‰ [2 sd]). We find no systematic δ25Mg variations with location, lithospheric age, peridotite fertility, or degree or nature of mantle metasomatism. Although pyroxene may have slightly heavier δ25Mg than coexisting olivine, any fractionation between mantle pyroxene and olivine is also within current analytical uncertainties with a mean Δ25Mg pyr-ol = +0.06 ± 0.10‰ (2 sd; n = 5). Our average mantle olivine δ25Mg DSM-3 = - 0.14 ± 0.07‰ and δ26Mg DSM-3 = - 0.27 ± 0.14‰ (2 sd) are indistinguishable from the average of data previously reported for terrestrial basalts, confirming that basalts have stable Mg isotope compositions representative of the mantle. Olivine from five pallasite meteorites have δ25Mg DSM-3 = - 0.16 to - 0.11‰ that are identical to terrestrial olivine and indistinguishable from the average δ25Mg previously reported for chondrites. These data provide no evidence for measurable heterogeneity in the stable Mg isotope

  6. Oceanic provenance of lithospheric mantle beneath Lower Silesia (SW Poland) and the two kinds of its "Fe-metasomatism"

    Puziewicz, Jacek; Matusiak-Małek, Magdalena; Ntaflos, Theodoros; Kukuła, Anna; Ćwiek, Mateusz


    Our recent studies (Puziewicz et al. 2015, IJES 104:1913-1924, and references therein) show that the subcontinental lithospheric mantle (SCLM) beneath Lower Silesia (SW Poland) and neighbouring part of Upper Lusatia (SE Germany) is dominated by harzburgites. Part of them contain small amounts of clinopyroxene which, despite its primary textural appearance, is a late addition to the protoliths which are residues after extensive (up to 30 %) partial melting. This clinopyroxene was added to the harzburgites in Cenozoic times by alkaline basaltic melts migrating upwards from their asthenospheric sources during rifting in the Variscan foreland of the Alpine-Carpathian chain. The pre-rifting history of the SCLM beneath the region is thus recorded in the olivine and orthopyroxene. The forsterite content in olivine divides the Lower Silesian harzburgites into two groups: A (olivine Fo 90.5 - 92.0), and B (olivine Fo 84.0 - 90.0; for data see Puziewicz et al. 2015, op. cit.). The Al content in orthopyroxene is low and similar in both A and part of B harzburgites, called B1 in the following. The orthopyroxene occurring in the B1 harzburgites contains typically 0.05 - 0.10 atoms of Al per formula unit (corresponding to 0.5 - 2.5 wt. % Al2O3), although slightly lower (down to 0.02 a pfu) and slightly higher (up to 0.13 a pfu) Al contents occur in subordinate number of samples. The Al content in the B1 orthopyroxene is not correlated with forsterite content in coexisting olivine. The B2 harzburgites occur only in one site (Księginki). They contain orthopyroxene which Al content exhibits negative correlation with forsterite content in coexisting olivine. The most Al -rich orthopyroxene (0.24 atoms of Al pfu, corresponding to ca. 5.7 wt % Al2O3) coexists with olivine Fo 86.5 in Księginki. The low contents of Al in orthopyroxene is specific for the Lower Silesian/Upper Lusatian domain of European lithospheric mantle. The Al-poor mantle domain below Lower Silesia and upper

  7. Subduction History and the Evolution of Earth's Lower Mantle

    Bull, Abigail; Shephard, Grace; Torsvik, Trond


    Understanding the complex structure, dynamics and evolution of the deep mantle is a fundamental goal in solid Earth geophysics. Close to the core-mantle boundary, seismic images reveal a mantle characterised by (1) higher than average shear wave speeds beneath Asia and encircling the Pacific, consistent with sub ducting lithosphere beneath regions of ancient subduction, and (2) large regions of anomalously low seismic wavespeeds beneath Africa and the Central Pacific. The anomalously slow areas are often referred to as Large Low Shear Velocity Provinces (LLSVPs) due to the reduced velocity of seismic waves passing through them. The origin, composition and long-term evolution of the LLSVPs remain enigmatic. Geochemical inferences of multiple chemical reservoirs at depth, strong seismic contrasts, increased density, and an anticorrelation of shear wave velocity to bulk sound velocity in the anomalous regions imply that heterogeneities in both temperature and composition may be required to explain the seismic observations. Consequently, heterogeneous mantle models place the anomalies into the context of thermochemical piles, characterised by an anomalous component whose intrinsic density is a few percent higher relative to that of the surrounding mantle. Several hypotheses have arisen to explain the LLSVPs in the context of large-scale mantle convection. One end member scenario suggests that the LLSVPs are relatively mobile features over short timescales and thus are strongly affected by supercontinent cycles and Earth's plate motion history. In this scenario, the African LLSVP formed as a result of return flow in the mantle due to circum-Pangean subduction (~240 Ma), contrasting a much older Pacific LLSVP, which may be linked to the Rodinia supercontinent and is implied to have remained largely unchanged since Rodinian breakup (~750-700 Ma). This propounds that Earth's plate motion history plays a controlling role in LLSVP development, suggesting that the location

  8. Seismology in Ryukyu arc, Japan reveals the distribution and orientation of serpentine minerals suggesting convection and low viscosity of forearc mantle

    Nagaya, T.; Walker, A.; Wookey, J. M.; Kendall, M.; Wallis, S.


    invisible antigorite bearing domains, allows an estimate of the volume percent of serpentinite in the forearc mantle to be made and indicates the pattern of large scale induced flow in this domain.

  9. Mantle cell lymphoma in cyclin D1 transgenic mice with Bim-deficient B cells.

    Katz, Samuel G; Labelle, James L; Meng, Hailong; Valeriano, Regina P; Fisher, Jill K; Sun, Heather; Rodig, Scott J; Kleinstein, Steven H; Walensky, Loren D


    Mantle cell lymphoma (MCL) is a highly aggressive B-cell lymphoma resistant to conventional chemotherapy. Although defined by the characteristic t(11;14) translocation, MCL has not been recapitulated in transgenic mouse models of cyclin D1 overexpression alone. Indeed, several genetic aberrations have been identified in MCL that may contribute to its pathogenesis and chemoresistance. Of particular interest is the frequent biallelic deletion of the proapoptotic BCL-2 family protein BIM. BIM exerts its pro-death function via its α-helical BH3 death domain that has the dual capacity to inhibit antiapoptotic proteins such as BCL-2 and MCL-1 and directly trigger proapoptotic proteins such as the mitochondrial executioner protein BAX. To evaluate a functional role for Bim deletion in the pathogenesis of MCL, we generated cyclin D1-transgenic mice harboring Bim-deficient B cells. In response to immunization, Eμ(CycD1)CD19(CRE)Bim(fl/fl) mice manifested selective expansion of their splenic mantle zone compartment. Three distinct immune stimulation regimens induced lymphomas with histopathologic and molecular features of human MCL in a subset of mice. Thus, deletion of Bim in B cells, in the context of cyclin D1 overexpression, disrupts a critical control point in lymphoid maturation and predisposes to the development of MCL. This genetic proof of concept for MCL pathogenesis suggests an opportunity to reactivate the death pathway by pharmacologic mimicry of proapoptotic BIM.

  10. Comparing the nature of the western and eastern Azores mantle

    Genske, Felix S.; Beier, Christoph; Stracke, Andreas; Turner, Simon P.; Pearson, Norman J.; Hauff, Folkmar; Schaefer, Bruce F.; Haase, Karsten M.


    The Azores islands in the central North-Atlantic originate from a regional melting anomaly, probably created by melting hot, unusually hydrous and geochemically enriched mantle. Here, we present Hf, Pb and Os isotopic data in geochemically well-characterised primitive lavas from the islands Flores and Corvo that are located west of the Mid-Atlantic Ridge (MAR), as well as submarine samples from a subsided island west of Flores and from Deep Sea Drilling Project (DSDP) holes drilled in the western part of the Azores platform and beyond. These are compared to existing data from the Azores islands east of the MAR. The geodynamic origin of the two islands west of the ridge axis and furthest from the inferred plume centre in the central part of the plateau is enigmatic. The new data constrain the source compositions of the Flores and Corvo lavas and show that the western and eastern Azores mantle is isotopically similar, with the exception of an enriched component found exclusively on eastern São Miguel. Trace element ratios involving high field strength elements (HFSE) are distinctly different in the western islands (e.g. twofold higher Nb/Zr) compared to any of the islands east of the MAR. A similar signature is observed in MAR basalts to the south of the Azores platform and inferred to originate from (auto-) metasomatic enrichment of the sub-ridge mantle (Gale et al., 2011, 2013). In a similar fashion, low degree melts from an enriched source component may metasomatise the ambient plume mantle underneath the western Azores islands. Melting such a modified plume mantle can explain the chemical differences between lavas from the western and eastern Azores islands without the need for additional plume components. Recent re-enrichment and intra melting column modification of the upwelling mantle can cause local to regional scale geochemical differences in mantle-derived melts.

  11. Sulfur in Earth's Mantle and Its Behavior During Core Formation

    Chabot, Nancy L.; Righter,Kevin


    The density of Earth's outer core requires that about 5-10% of the outer core be composed of elements lighter than Fe-Ni; proposed choices for the "light element" component of Earth's core include H, C, O, Si, S, and combinations of these elements [e.g. 1]. Though samples of Earth's core are not available, mantle samples contain elemental signatures left behind from the formation of Earth's core. The abundances of siderophile (metal-loving) elements in Earth's mantle have been used to gain insight into the early accretion and differentiation history of Earth, the process by which the core and mantle formed, and the composition of the core [e.g. 2-4]. Similarly, the abundance of potential light elements in Earth's mantle could also provide constraints on Earth's evolution and core composition. The S abundance in Earth's mantle is 250 ( 50) ppm [5]. It has been suggested that 250 ppm S is too high to be due to equilibrium core formation in a high pressure, high temperature magma ocean on early Earth and that the addition of S to the mantle from the subsequent accretion of a late veneer is consequently required [6]. However, this earlier work of Li and Agee [6] did not parameterize the metalsilicate partitioning behavior of S as a function of thermodynamic variables, limiting the different pressure and temperature conditions during core formation that could be explored. Here, the question of explaining the mantle abundance of S is revisited, through parameterizing existing metal-silicate partitioning data for S and applying the parameterization to core formation in Earth.

  12. Ensemble data assimilation for the reconstruction of mantle circulation

    Bocher, Marie; Coltice, Nicolas; Fournier, Alexandre; Tackley, Paul


    The surface tectonics of the Earth is the result of mantle dynamics. This link between internal and surface dynamics can be used to reconstruct the evolution of mantle circulation. This is classically done by imposing plate tectonics reconstructions as boundary conditions on numerical models of mantle convection. However, this technique does not account for uncertainties in plate tectonics reconstructions and does not allow any dynamical feedback of mantle dynamics on surface tectonics to develop. Mantle convection models are now able to produce surface tectonics comparable to that of the Earth to first order. We capitalize on these convection models to propose a more consistent integration of plate tectonics reconstructions into mantle convection models. For this purpose, we use the ensemble Kalman filter. This method has been developed and successfully applied to meteorology, oceanography and even more recently outer core dynamics. It consists in integrating sequentially a time series of data into a numerical model, starting from an ensemble of possible initial states. The initial ensemble of states is designed to represent an approximation of the probability density function (pdf) of the a priori state of the system. Whenever new observations are available, each member of the ensemble states is corrected considering both the approximated pdf of the state, and the pdf of the new data. Between two observation times, each ensemble member evolution is computed independently, using the convection model. This technique provides at each time an approximation of the pdf of the state of the system, in the form of a finite ensemble of states. We perform synthetic experiments to assess the efficiency of this method for the reconstruction of mantle circulation.

  13. Iron carbonates in the Earth's lower mantle: reality or imagination?

    Cerantola, V.; McCammon, C. A.; Merlini, M.; Bykova, E.; Kupenko, I.; Ismailova, L.; Chumakov, A. I.; Kantor, I.; Dubrovinsky, L. S.; Prescher, C.


    Carbonates play a fundamental role in the recycling of carbon inside our planet due to their presence in oceanic slabs that sink through the Earth's interior. Through this process, iron carbonates are potential stable carbon-bearing minerals in the deep mantle in part due to spin crossover of ferrous iron. Our goal is to identify which minerals may be the dominant carriers of carbon into the deep mantle at the relevant conditions of fO2, P and T. All experiments were performed using synthetic FeCO3 and MgFeCO3 single crystals in laser heated diamond anvil cells up to 100 GPa and 3000 K in order to simulate the conditions prevailing in the Earth's lower mantle. Transformation and decomposition products of the original carbonates were characterized at different synchrotron facilities by means of single-crystal XRD, synchrotron Mössbauer source spectroscopy and XANES techniques. At deep lower mantle conditions, we observed the transformation of FeCO3 to two new HP-carbonate structures, monoclinic Fe22+Fe23+C4O13 and trigonal Fe43+(CO4)3, both characterized by the presence of CO4 tetrahedra with different degrees of polymerization. At shallower depths in the lower mantle where temperatures are lower following the geotherm, Fe-carbonates decompose to different Fe-oxides instead of new HP-carbonates. However, at slab temperatures several hundred degrees lower than the surrounding mantle, carbonates could be stabilized until reaching conditions that trigger their transformation to HP-structures. We postulate that Fe-rich carbonates could exist in regions down to the core-mantle boundary in the proximity of subducting slabs, i.e., a "cold" environment with relatively high fO2.

  14. Analysis of the flow structure and heat transfer in a vertical mantle heat exchanger

    Knudsen, Søren; Morrison, GL; Behnia, M


    initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level. (C......The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image...... Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heat exchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both...

  15. Discrepant NOXA (PMAIP1) transcript and NOXA protein levels: a potential Achilles' heel in mantle cell lymphoma


    Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm with transient response to conventional chemotherapy. We here investigated the role of the Bcl-2 homology domain 3-only protein NOXA for life–death decision in MCL. Surprisingly, NOXA (PMAIP1) mRNA and NOXA protein levels were extremely discrepant in MCL cells: NOXA mRNA was found to be highly expressed whereas NOXA protein levels were low. Chronic active B-cell receptor signaling and to a minor degree cyclin D1 overexpression cont...

  16. Contamination of the Convecting Mantle in Eastern Tethyan 'Subduction Factories'

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


    As subduction gives way to collision at the end of a Wilson Cycle the associated magmatic activity becomes increasingly enriched in potassium and other large-ion lithophile elements. This is usually attributed to the addition of continental crust-derived material to the convecting mantle wedge. Corresponding depletions in high-field strength elements (Ti and Nb) are more commonly explained in terms of accessory phase buffering or protracted reaction of melts with mantle wallrock. It is increasingly apparent that mantle wedge magmatic sources range from 'fertile' (lherzolitic) to 'refractory' (harzburgitic) although the extent to which this corresponds to the LILE and HFSE variation is unclear. Mantle wedge mass balances clearly hold clues to enrichment-depletion histories of the convecting asthenosphere with respect to both the overriding and subducting plates. With a view to better understanding these effects we have used the MELTS algorithm to calculate hypothetical partial melt compositions as a function of source fertility and H2O content, in the pressure range, 0-1.0 GPa as a basis comparison for natural partial melts. Primitive magmas characterizing the Mariana (western Pacific) and Sunda-Banda (Indonesia) arcs, and the northeastern syntaxis of the India-Asia collision suture (Yunnan) appear to resemble calculated equilibrium melts of refractory (basalt-depleted) peridotite, variably enriched in lithophile and light rare earth elements. These comparisons lead to three observations. 1) HFSE and Fe abundances in primitive MORB, calcalkaline, and boninite magmas, and their respective high-potassium variants are consistent with those implied by phase equilibria associated with partial melting and fractionation, suggesting accessory phases, wall-rock reaction, and slab contamination are probably not important as causes of HFSE depletions. 2) Magmatic sources at convergent and colliding margins are typically refractory (basalt-depleted) compared to those yielding

  17. Anatomy of mantle plumes: hot heads and cold stems

    Davaille, A. B.; Kumagai, I.; Vatteville, J.; Touitou, F.; Brandeis, G.


    Recent petrological studies show evidences for secular cooling in mantle plumes: the source temperature of oceanic plateaus could be 100°C hotter than the source temperature of volcanic island chains (Herzberg and Gazel, Nature, 2009). In terms of mantle plumes, it would mean that the temperature of the plume head is hotter than that of the plume stem. This is at odd with a model where a plume head would entrain so much ambient mantle on its journey towards the Earth's surface that it would end up being considerably colder than its narrow stem. So we revisited the problem using laboratory experiments and new visualization techniques to measure in situ simultaneously the temperature, velocity and composition fields. At time t=0, a hot instability is created by heating a patch of a given radius at constant power or constant temperature. The fluids are mixtures of sugar syrups , with a strongly temperature-dependent viscosity, and salt. Rayleigh numbers were varied from 104 to 108, viscosity ratios between 1.8 and 4000, and buoyancy ratios between 0 and 2. After a stage where heat transport is by conduction only, the hot fluid gathers in a sphere and begins to rise, followed by a stem anchored on the hot patch. In all cases, temperatures in the head start with higher values than in the subsequent stem. This is also the case for the thermal instabilities rising from a infinite plate heated uniformly. However, the head also cools faster than the stem as they rise, so that they will eventually have the same temperature if the mantle is deep enough. Moreover, all the material sampled by partial melting in the plume head or stem would be coming from the heated area around the deep source, and very little entrainment from the ambient mantle is predicted. The difference in temperature between head and stem strongly depends on the mantle depth, the viscosity ratio and the buoyancy ratio. Our scaling laws predict that Earth's mantle plumes can indeed have hot heads and colder

  18. Isotopic constraints of mantle derived carbonatitic melts from Calatrava, Spain

    Humphreys, E. R.; Bailey, K.; Hawkesworth, C. J.; Wall, F.; Avanzinelli, R.


    Carbonatite volcanism is typically associated both spatially and temporally with alkaline, ultramafic volcanism (Woolley & Church, 2005). Recent discoveries in Calatrava, Spain illustrate the activity of carbonatite in the source melts of leucitite volcanism. Melilitite pyroclastic lapilli tuffs also show a clear association with volcanic carbonate. Carbonatitic activity has been shown to initiate at depths greater than 100km (Humphreys et al., 2010) despite a maximum estimate of lithospheric thickness of 80km. The presence of aragonite and abundant mantle xenoliths in many deposits are clear indication of the rapid emplacement rates of such magmas. Carbonatitic activity in the source of the leucitite melts is indicated by carbonate inclusions within olivine xenocrysts and the presence of occasional carbonatite lenses. The composition of lead and strontium isotope ratios in the bulk rock, and spatially resolved analysis of carbonate from the groundmass and from inclusions demonstrates a genetic affinity between the inclusions and the related bulk rock composition. Lead and strontium isotopic analysis suggest that such melts do not represent the composition of convecting asthenospheric mantle. 87Sr/86Sr (0.7055-0.7068) values are higher than those of MORB and most OIB. Lead isotope ratios show a trend displaced to higher 207Pb/204Pb relative to MORB and OIB. Carbonate inclusions have less radiogenic lead values than the more radiogenic bulk rocks. Our data indicate that carbonatitic activity in the mantle is intrinsic in the generation of the leucitite lava. However, petrographic and isotopic evidence suggest a complex melt history. Olivine xenocrysts are not in equilibrium with the host leucitite, despite inclusions within olivine showing an isotopic affinity to the bulk rock. We suggest that in this example, alkaline magmatism was induced by the presence of CO2 in the mantle source. Isotopic evidence shows that the mantle producing such melts was not

  19. Mapping small-scale mantle heterogeneities using seismic arrays

    Bentham, H. L.; Rost, S.


    In recent years array seismology has been used extensively to detect and locate the small scale (~10 km) structure of the Earth. In the mantle, small scale structure likely represents chemical heterogeneity and is essential in our understanding of mechanical mixing processes within mantle convection. As subducted crust is chemically distinct from the background mantle, imaging the remains of the crust provides a tracer for convectional flow. Evidence for heterogeneities has been found in the lower mantle in previous seismology studies but the arrivals associated with such heterogeneities are difficult to detect in the seismic data as they are typically low amplitude and are often masked by a multitude of larger amplitude arrivals. In this study we find global and regional seismic heterogeneities in the mantle by processing teleseismic earthquake data through array seismology methods. We find global patterns of heterogeneity using a stacking approach. To locate regional heterogeneities, we target the "quiet" window prior to the PP arrival for earthquakes with epicentral distances of 90-110°. Within this time window, we enhance the weak coherent energy that arrives off great circle path by calculating the observed directivity (slowness and backazimuth) and using a semblance weighted beampower measure. We use the directivity and travel times of suitable precursors to back-trace the energy to the origin of P-to-P reflections, using a 1D raytracer. Most of the P-to-P reflections that we observe have reflection origins in the upper/mid mantle. Beneath the western Pacific subduction zones, such reflections show a good correlation with subduction zone contours that are derived from subduction zone seismicity, and correlate well with tomography gradients of 0.01-0.5% per degree, interpreted as the edge of the slab. Deep mantle reflections (>600 km) are also observed to depths of ~1900 km. The locations of these heterogeneities are combined with previous seismological

  20. Protein domain prediction

    Ingolfsson, Helgi; Yona, Golan


    Domains are considered to be the building blocks of protein structures. A protein can contain a single domain or multiple domains, each one typically associated with a specific function. The combination of domains determines the function of the protein, its subcellular localization and the interacti

  1. Mantle conductivity obtained by 3-D inversion of magnetic satellite data

    Kuvshinov, A.; Olsen, Nils

    for blockwise constant conductivities on a given 3-D spatial mesh. The predicted induced space-time satellite signal is obtained numerically using a frequency-domain modeling based on the integral equation (IE) approach, and using a space-time structure of external (inducing) field as found from globally......We present an approach to determine the three-dimensional (3-D) conductivity distribution of the Earth’s upper mantle from magnetic satellite data. The approach is based on a minimization of the misfit between the measured and modeled (predicted) magnetic field using a quasi-Newton method, solving...... and perform the most consuming-time part of the IE forward simulations (the calculation of electric and magnetic tensor Green’s functions) only once. Approximate calculation of the data sensitivities also gives essential speed up of the inversion. We validate our inversion scheme using synthetic induction...

  2. Nd-isotopes in selected mantle-derived rocks and minerals and their implications for mantle evolution

    Basu, A.R.; Tatsumoto, M.


    The Sm-Nd systematics in a variety of mantle-derived samples including kimberlites, alnoite, carbonatite, pyroxene and amphibole inclusions in alkali basalts and xenolithic eclogites, granulites and a pyroxene megacryst in kimberlites are reported. The additional data on kimberlites strengthen our earlier conclusion that kimberlites are derived from a relatively undifferentiated chondritic mantle source. This conclusion is based on the observation that the e{open}Nd values of most of the kimberlites are near zero. In contrast with the kimberlites, their garnet lherzolite inclusions show both time-averaged Nd enrichment and depletion with respect to Sm. Separated clinopyroxenes in eclogite xenoliths from the Roberts Victor kimberlite pipe show both positive and negative e{open}Nd values suggesting different genetic history. A whole rock lower crustal scapolite granulite xenolith from the Matsoku kimberlite pipe shows a negative e{open}Nd value of -4.2, possibly representative of the base of the crust in Lesotho. It appears that all inclusions, mafic and ultramafic, in kimberlites are unrelated to their kimberlite host. The above data and additional Sm-Nd data on xenoliths in alkali basalts, alpine peridotite and alnoite-carbonatites are used to construct a model for the upper 200 km of the earth's mantle - both oceanic and continental. The essential feature of this model is the increasing degree of fertility of the mantle with depth. The kimberlite's source at depths below 200 km in the subcontinental mantle is the most primitive in this model, and this primitive layer is also extended to the suboceanic mantle. However, it is clear from the Nd-isotopic data in the xenoliths of the continental kimberlites that above 200 km the continental mantle is distinctly different from their suboceanic counterpart. ?? 1980 Springer-Verlag.

  3. The mantle transition zone beneath the Afar Depression and adjacent regions: implications for mantle plumes and hydration

    Reed, C. A.; Gao, S. S.; Liu, K. H.; Yu, Y.


    The Afar Depression and its adjacent areas are underlain by an upper mantle marked by some of the world's largest negative velocity anomalies, which are frequently attributed to the thermal influences of a lower-mantle plume. In spite of numerous studies, however, the existence of a plume beneath the area remains enigmatic, partially due to inadequate quantities of broad-band seismic data and the limited vertical resolution at the mantle transition zone (MTZ) depth of the techniques employed by previous investigations. In this study, we use an unprecedented quantity (over 14 500) of P-to-S receiver functions (RFs) recorded by 139 stations from 12 networks to image the 410 and 660 km discontinuities and map the spatial variation of the thickness of the MTZ. Non-linear stacking of the RFs under a 1-D velocity model shows robust P-to-S conversions from both discontinuities, and their apparent depths indicate the presence of an upper-mantle low-velocity zone beneath the entire study area. The Afar Depression and the northern Main Ethiopian Rift are characterized by an apparent 40-60 km depression of both MTZ discontinuities and a normal MTZ thickness. The simplest and most probable interpretation of these observations is that the apparent depressions are solely caused by velocity perturbations in the upper mantle and not by deeper processes causing temperature or hydration anomalies within the MTZ. Thickening of the MTZ on the order of 15 km beneath the southern Arabian Plate, southern Red Sea and western Gulf of Aden, which comprise the southward extension of the Afro-Arabian Dome, could reflect long-term hydration of the MTZ. A 20 km thinning of the MTZ beneath the western Ethiopian Plateau is observed and interpreted as evidence for a possible mantle plume stem originating from the lower mantle.

  4. Tomography of core-mantle boundary and lowermost mantle coupled by geodynamics: joint models of shear and compressional velocity

    Gaia Soldati


    Full Text Available We conduct joint tomographic inversions of P and S travel time observations to obtain models of delta v_P  and delta v_S in the entire mantle. We adopt a recently published method which takes into account the geodynamic coupling between mantle heterogeneity and core-mantle boundary (CMB topography by viscous flow, where sensitivity of the seismic travel times to the CMB is accounted for implicitly in the inversion (i.e. the CMB topography is not explicitly inverted for. The seismic maps of the Earth's mantle and CMB topography that we derive can explain the inverted seismic data while being physically consistent with each other. The approach involved scaling P-wave velocity (more sensitive to the CMB to density anomalies, in the assumption that mantle heterogeneity has a purely thermal origin, so that velocity and density heterogeneity are proportional to one another. On the other hand, it has sometimes been suggested that S-wave velocity might be more directly sensitive to temperature, while P heterogeneity is more strongly influenced by chemical composition. In the present study, we use only S-, and not P-velocity, to estimate density heterogeneity through linear scaling, and hence the sensitivity of core-reflected P phases to mantle structure. Regardless of whether density is more closely related to P- or S-velocity, we think it is worthwhile to explore both scaling approaches in our efforts to explain seismic data. The similarity of the results presented in this study to those obtained by scaling P-velocity to density suggests that compositional anomaly has a limited impact on viscous flow in the deep mantle.

  5. Blending geological observations and convection models to reconstruct mantle dynamics

    Coltice, Nicolas; Bocher, Marie; Fournier, Alexandre; Tackley, Paul


    Knowledge of the state of the Earth mantle and its temporal evolution is fundamental to a variety of disciplines in Earth Sciences, from the internal dynamics to its many expressions in the geological record (postglacial rebound, sea level change, ore deposit, tectonics or geomagnetic reversals). Mantle convection theory is the centerpiece to unravel the present and past state of the mantle. For the past 40 years considerable efforts have been made to improve the quality of numerical models of mantle convection. However, they are still sparsely used to estimate the convective history of the solid Earth, in comparison to ocean or atmospheric models for weather and climate prediction. The main shortcoming is their inability to successfully produce Earth-like seafloor spreading and continental drift self-consistently. Recent convection models have begun to successfully predict these processes. Such breakthrough opens the opportunity to retrieve the recent dynamics of the Earth's mantle by blending convection models together with advanced geological datasets. A proof of concept will be presented, consisting in a synthetic test based on a sequential data assimilation methodology.

  6. Mantle decarbonation and Archean high-Mg magmas

    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.

  7. Laboratory-based electrical conductivity at Martian mantle conditions

    Verhoeven, Olivier; Vacher, Pierre


    Information on temperature and composition of planetary mantles can be obtained from electrical conductivity profiles derived from induced magnetic field analysis. This requires a modeling of the conductivity for each mineral phase at conditions relevant to planetary interiors. Interpretation of iron-rich Martian mantle conductivity profile therefore requires a careful modeling of the conductivity of iron-bearing minerals. In this paper, we show that conduction mechanism called small polaron is the dominant conduction mechanism at temperature, water and iron content conditions relevant to Mars mantle. We then review the different measurements performed on mineral phases with various iron content. We show that, for all measurements of mineral conductivity reported so far, the effect of iron content on the activation energy governing the exponential decrease in the Arrhenius law can be modeled as the cubic square root of the iron content. We recast all laboratory results on a common generalized Arrhenius law for iron-bearing minerals, anchored on Earth's mantle values. We then use this modeling to compute a new synthetic profile of Martian mantle electrical conductivity. This new profile matches perfectly, in the depth range [100,1000] km, the electrical conductivity profile recently derived from the study of Mars Global Surveyor magnetic field measurements.

  8. Seismic anisotropy of upper mantle in Sichuan and adjacent regions

    CHANG LiJun; WANG ChunYong; DING ZhiFeng


    Based on the polarization analysis of teleseismic SKS waveform data recorded at 94 broadband seismic stations in Sichuan and adjacent regions, the SKS fast-wave direction and the delay time between the fast and slow shear waves were determined at each station using the grid searching method of minimum transverse energy and the stacking analysis method, and the image of upper mantle anisotropy was acquired. The fast-wave polarization directions are mainly NW-SE in the study area,NWW-SEE to its northeast and NS to its west. The delay time falls into the interval [0.47 s, 1.68 s]. The spatial variation of the fast-wave directions is similar to the variation of GPS velocity directions. The anisotropic image indicates that the regional tectonic stress field has resulted in deformation and flow of upper mantle material, and made the alignment of upper mantle peridotite lattice parallel to the direction of material deformation. The crust-upper mantle deformation in Sichuan and adjacent regions accords with the mode of vertically coherent deformation. In the eastern Tibetan Plateau, the crustal material was extruded to east or southeast clue to SE traction force of the upper mantle material. The extrusion might be obstructed by a rigid block under the Sichuan Basin and the crust has been deformed. After a long-term accumulation of tectonic strain energy, the accumulative energy suddenly released in Yingxiu town of the Longmenshan region, and Wenchuan Ms8.0 earthquake occurred.

  9. On the consistency of seismically imaged lower mantle slabs.

    Shephard, G E; Matthews, K J; Hosseini, K; Domeier, M


    The geoscience community is increasingly utilizing seismic tomography to interpret mantle heterogeneity and its links to past tectonic and geodynamic processes. To assess the robustness and distribution of positive seismic anomalies, inferred as subducted slabs, we create a set of vote maps for the lower mantle with 14 global P-wave or S-wave tomography models. Based on a depth-dependent threshold metric, an average of 20% of any given tomography model depth is identified as a potential slab. However, upon combining the 14 models, the most consistent positive wavespeed features are identified by an increasing vote count. An overall peak in the most robust anomalies is found between 1000-1400 km depth, followed by a decline to a minimum around 2000 km. While this trend could reflect reduced tomographic resolution in the middle mantle, we show that it may alternatively relate to real changes in the time-dependent subduction flux and/or a mid-lower mantle viscosity increase. An apparent secondary peak in agreement below 2500 km depth may reflect the degree-two lower mantle slow seismic structures. Vote maps illustrate the potential shortcomings of using a limited number or type of tomography models and slab threshold criteria.

  10. The 5 GPa mantle solidus revisited

    Lesher, C. E.; Pickering-Witter, J.; Baxter, G.; Walter, M. J.


    We critically examine the recent claim that interlaboratory discrepancies in the solidus temperatures of nominally dry, fertile mantle peridotite between 4 and 6 GPa are related to encapsulating material (Re- foil capsules [1] versus graphite-lined Pt capsules [2]). Herzberg et al. [1] argue that reaction between silicate and graphite produces CO2, which causes a substantial freezing point depression of the peridotite solidus (>50\\deg~C at 5 GPa). We report results of a direct experimental comparison of peridotite melting in Re-foil and graphite-lined Pt capsules. We locate both capsules, containing fertile peridotite KR4003 [2], into the central portion of a stepped graphite heater, where thermal gradients are modest and well-characterized. Our experiments are performed in a MA6/8 multianvil, using octahedra of Ceramacast 584 cast with fins to fit 10-mm truncated edge length carbide anvils and calibrated by [3]. We insert axial W-Re (D-type) thermocouples into both ends of the furnace; butting thermocouple leads against the metal capsules to complete the circuit. This arrangement closely matches the thermocouple configurations used in the studies of [1] and [2]. Thermocouple voltage, power consumption, and load are recorded continuously during the experiment. Temperature is controlled by the thermocouple connected through the Pt capsule. We find that the voltage from the second thermocouple drifts significantly above 1650\\deg~C, and gives false temperatures after only 10 minutes at the set point temperature. We also find that the phase assemblages in both capsules of a given experiment are identical down to conditions with trace amounts of quenched melt. At 1670\\deg~C, based on the control thermocouple, KR4003 was partially melted to ~35% and has a residual mineralogy of olivine, orthopyroxene, and garnet. This run temperature is 15\\deg~C below the 5 GPa solidus of [1]. Extrapolation of melt fraction versus temperature data gives a solidus temperature for KR

  11. Membrane binding domains

    Hurley, James H.


    Eukaryotic signaling and trafficking proteins are rich in modular domains that bind cell membranes. These binding events are tightly regulated in space and time. The structural, biochemical, and biophysical mechanisms for targeting have been worked out for many families of membrane binding domains. This review takes a comparative view of seven major classes of membrane binding domains, the C1, C2, PH, FYVE, PX, ENTH, and BAR domains. These domains use a combination of specific headgroup inter...

  12. Early mantle heterogeneities in the Réunion hotspot source inferred from highly siderophile elements in cumulate xenoliths

    Peters, Bradley J.; Day, James M. D.; Taylor, Lawrence A.


    remarkably homogeneous Os, Pb, and noble-gas isotopic signatures of Réunion, which plot near the convergence point of isotopic data for many hotspots, such a conclusion provides evidence for an early differentiated and subsequently isolated mantle domain that may be partially sampled by some ocean island basalts.

  13. Tomographic imaging of the Nazca slab and surrounding mantle in the mantle transition zone beneath the Central Andes

    Scire, A. C.; Biryol, C. B.; Zandt, G.; Beck, S. L.; Wagner, L. S.; Long, M. D.; Minaya, E.; Tavera, H.


    The central Andes in South America is an ideal location to investigate the interaction between a subducting slab and the surrounding mantle to the base of the mantle transition zone (MTZ). We used finite-frequency teleseismic P-wave tomography to image velocity anomalies in the mantle from 100 - 700 km between 10° and 28°S in the central Andes by combining data from twelve separate networks deployed in the region between 1994 and 2013. P- and PKIKP- (diffracted PKP) arrivals were picked in multiple frequency bands for earthquakes at distances between 30° and 90° and between 155° to 180° from the array, respectively. The tomographic algorithm used calculates approximate finite frequency kernels for each ray, providing additional sampling for each model layer to potentially increase the resolution of our images. The trench-parallel, fast anomaly which appears to correspond with the subducting Nazca slab is the most prominent anomaly in our tomograms. Variations in the width of the slab anomaly in the deeper parts of the model show evidence for deformation of the slab between 300 and 660 km. Our results show localized thickening of the Nazca slab in the MTZ north of 14°S, between 16° and 18°S, and south of 25°S, in agreement with the idea that the Nazca slab stagnates at least temporarily in the transition zone before resuming subduction into the lower mantle. Our images of the deeply subducted Nazca slab also show evidence of varying degrees of thinning in the mantle transition zone, particularly at 20° and 24°S, possibly indicating that the stress state changes along strike as the slab deforms in the MTZ before resuming subduction into the lower mantle. We also image along-strike variations in the sub-slab mantle in the MTZ including a strong low velocity anomaly between 22° and 28°S which is similar to those seen in other subduction zones, and is interpreted as either a local thermal anomaly or a region of hydrated material in the MTZ. A similar

  14. Upper mantle viscosity and lithospheric thickness under Iceland determined from a microphysical modelling approach of mantle rheology

    Barnhoorn, A.; van der Wal, W.; Drury, M. R.


    The Vatnajökull glacier, located in the south-east of Iceland is the largest ice cap of Iceland having a mean radius of ~50 km covering an area of ˜8100 km2. The Vatnajökull glacier is situated directly on top of the spreading axis in the eastern volcanic zone (EVZ) of the Icelandic mid-ocean ridge and near the inferred center of the Icelandic hotspot. Due to the vicinity of the glacier to the active tectonic area, the response of the solid earth to melting of the ice cap is strongly controlled by the properties of the hot newly formed upper mantle underneath the mid-ocean ridge. The relatively high temperatures in the mantle during rifting result in relatively low upper mantle viscosities and fast relaxation times in comparison with tectonically inactive glaciated areas such as in. In this study, estimates for lithospheric thickness and upper mantle viscosity under Iceland are produced by a microphysical modelling approach using the theoretical temperature distribution under mid-ocean ridges combined with olivine diffusion and dislocation creep flow laws. Large lateral variations in upper mantle viscosity and especially lithospheric thickness are expected for Iceland perpendicular to the ridge axis due to the large changes in temperatures away from the ridge axis. The lithospheric thickness (27-40 km) and upper mantle viscosity (2 × 1018-1019 Pa s) outcomes for the recent glaciation are consistent with previous reports of viscosity and lithospheric thickness from glacial isostatic adjustment studies. A combination of a 40 km thick elastic lithosphere and an average upper mantle viscosity of 5 × 1018 Pa s would suggest that the upper mantle under Iceland is most likely dry. Also, the results indicate that the presence of a plume under Iceland cannot explain the recent low viscosity values reported for Iceland. Using a larger extent and larger thickness of the Icelandic icecap during the Weichselian glaciation event (˜10,000 BP) this study predicts that during

  15. Upper mantle geotherm for eastern China and its geological implications

    徐义刚; 林传勇; 史兰斌; J-C.C.Mercier; J.V.Ross


    The equilibrium temperature and pressure of both spinel and garnet peridotite xenolithsfrom eastern China have been estimated by using different geothermobarometers that are currentlyconsidered to be reliable.Based on these data,the upper mantle geotherm for eastern China has beenconstructed.The obtained geotherm is higher than that for old craton regions,but is similar to that for southeasternAustralia.The most prominent feature of the geotherm is that there is a slight gradient at about 60 kmdepth,and the inflection of the geotherm just passes through the transition line between spinel and garnetfacies.It is likely that the inflection represents the botmdary between the lithosphere and asthenosphere.Thestructures of the upper mantle beneath eastern China have also been discussed by combining the results ofpetrologic,rheological and dynamical studies of the upper mantle.

  16. Mantle Degassing and Diamond Genesis:A Carbon Isotope Perspective



    The effect of Co2 and CH4 degassing from the mantle on the carbon isotopic composition of diamond has been quantitatively modeled in terms of the principles of Rayleigh distillation.Assuming the δ13 C value of -5‰ for the mantle,the outgassing of CO2 can result in the large negative δ13 C values of diamond,whereas the outgassing of CH4 can drive the δ13C values of diamond in the positive direction.The theoretical expectations can be used to explain the full range of δ13 C values from-34.4‰5 to+5‰ observed for natural diamonds.It is possible that diamond formation was triggered by the degassing of Co2 and/or CH4 from the mantle and the associated fractional crystallization of carbonate-bearing melt.

  17. An olivine-free mantle source of Hawaiian shield basalts.

    Sobolev, Alexander V; Hofmann, Albrecht W; Sobolev, Stephan V; Nikogosian, Igor K


    More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations.

  18. Large gem diamonds from metallic liquid in Earth's deep mantle.

    Smith, Evan M; Shirey, Steven B; Nestola, Fabrizio; Bullock, Emma S; Wang, Jianhua; Richardson, Stephen H; Wang, Wuyi


    The redox state of Earth's convecting mantle, masked by the lithospheric plates and basaltic magmatism of plate tectonics, is a key unknown in the evolutionary history of our planet. Here we report that large, exceptional gem diamonds like the Cullinan, Constellation, and Koh-i-Noor carry direct evidence of crystallization from a redox-sensitive metallic liquid phase in the deep mantle. These sublithospheric diamonds contain inclusions of solidified iron-nickel-carbon-sulfur melt, accompanied by a thin fluid layer of methane ± hydrogen, and sometimes majoritic garnet or former calcium silicate perovskite. The metal-dominated mineral assemblages and reduced volatiles in large gem diamonds indicate formation under metal-saturated conditions. We verify previous predictions that Earth has highly reducing deep mantle regions capable of precipitating a metallic iron phase that contains dissolved carbon and hydrogen.

  19. Estimating Upper Mantle Hydration from In Situ Electrical Conductivity

    Behrens, J.; Constable, S.; Heinson, G.; Everett, M.; Weiss, C.; Key, K.


    The electrical conductivity of 35-40 Ma Pacific plate has been measured in situ; one robust result is the presence of bulk anisotropy in the lithospheric upper mantle. We interpret this anisotropy to be a result of hydrothermal circulation into the upper mantle along spreading-ridge-parallel normal faults: the associated zones of serpentinized peridotite provide the pathways of enhanced electrical conductivity required by the data. Our modeling bounds the range of possible anisotropic ratios, which are then used to estimate the amount of water required to serpentinize the requisite amounts of peridotite. These data sets, however, do not indicate anisotropy in the bulk conductivity of the crust, nor in the asthenospheric mantle. This second point is significant, as recent measurements of sub-continental asthenospheric conductivity have been interpreted to indicate anisotropy aligned with present plate motion, with the diffusion of hydrogen through olivine advanced as an explanation.

  20. Mantle olivine xenocrysts entrained in Mesozoic basalts from the North China craton:Implication for replacement process of lithospheric mantle

    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.

  1. The Structure of the Mantle Lithosphere in Central Europe from S-Receiver Functions

    Kind, Rainer; Handy, Mark; Yuan, Xiaohui; Meier, Thomas


    Data from about 650 permanent and temporary seismic broadband stations accessed from the open EIDA Archive yielded about 49.000 S-receiver functions. Selection criteria were a signal-to-noise ratio of at least two of the S signal on the SV component, low noise on the P component before the S arrival time and a relatively good approximation of the delta im- pulse on the SV component after deconvolution. All traces were checked visually. The time domain traces were migrated to depth domain by back projection along the ray path. Smooth images of major discontinuities in the upper mantle were obtained by applying an eight-seconds low-pass filter. Observations of the Moho and the discontinuity at 410 km depth serve as a check of the quality of the analysis. We observe two widespread negative (i.e., downward reduction in velocity) discontinuities. The shallower one in about the 50 km to 150 km depth interval occurs everywhere in the study area and is interpreted as the lithosphere-asthenosphere boundary (LAB) in Phanerozoic Europe. According to similar observations in the north American craton, it is interpreted as mid-lithospheric discontinuity (MLD) in the east European craton (EEC). The second negative discontinuity seen beneath the EEC, the Trans-European Suture Zone, the Bohemian Massive, and parts of the Pannonian Basin lies at a depth interval of about 150 km to 300 km. It is interpreted as cratonic LAB reaching well the S and E of the Torn- quist-Teisseyre Zone, which is considered the boundary of the EEC at the shallower levels. The deeper cratonic LAB has anomalous topography: Below the Pannonian Basin it shal- lows to c. 150 km but deepens to c. 300 km below the Bohemian Massif. There is a jump in the cratonic LAB along the northern edge of the Bohemian Massif, where the LAB sud- denly changes depth from 200 km in the north to 300 km in the south. We tentatively inter- pret these observations as a result of overthrusting the EEC mantle lithosphere during the

  2. Solid pole tide in global GPS and superconducting gravimeter observations: Signal retrieval and inference for mantle anelasticity

    Ding, Hao; Chao, Benjamin F.


    The mantle anelasticity plays an important role in Earth's interior dynamics. Here we seek to determine the lower-mantle anelasticity through the solution of the complex Love numbers at the Chandler wobble period. The Love numbers h21, l21, δ21 and k21 are obtained in the frequency domain by dividing off the observed polar motion, or more specifically the pole tide potential, from the observed GPS 3-D displacement field and SG gravity variation. The latter signals are obtained through the array processing method of OSE (optimal sequence estimation) that results in greatly enhanced signals to be extracted from global array data. The resultant Love number estimates h21 = 0.6248 (± 5 e - 4) - 0.013 (± 5 e - 3) i, l21 = 0.0904 (± 8 e - 4) - 0.0008 (± 2 e - 3) i, δ21 = 1.156 (± 2 e - 3) - 0.003 (± 1 e - 3) i and k21 = 0.3125 (± 2 e - 3) - 0.0069 (± 3 e - 3) i are thus well-constrained in comparison to past estimates that vary considerably. They further lead to estimates of the corresponding mantle anelastic parameters fr and fi, which in turn determines, under the single-absorption band assumption, the dispersion exponent of α = 0.21 ± 0.02 with respect to the reference frequency of 5 mHz. We believe our estimate is robust and hence can better constrain the mantle anelasticity and attenuation models of the Earth interior.

  3. Mantle fluids in the Karakoram fault: Helium isotope evidence

    Klemperer, Simon L.; Kennedy, B. Mack; Sastry, Siva R.; Makovsky, Yizhaq; Harinarayana, T.; Leech, Mary L.


    The Karakoram fault (KKF) is the 1000 km-long strike-slip fault separating the western Himalaya from the Tibetan Plateau. From geologic and geodetic data, the KKF is argued either to be a lithospheric-scale fault with hundreds of km of offset at several cm/a, or to be almost inactive with cumulative offset of only a few tens of kilometers and to be just the upper-crustal localization of distributed deformation at depth. Here we show 3He/4He ratios in geothermal springs along a 500-km segment of the KKF are 3-100 times the normal ratio in continental crust, providing unequivocal evidence that a component of these hydrologic systems is derived from tectonically active mantle. Mantle enrichment is absent along the Indus-Yarlung suture zone (ISZ) just 35 km southwest of the KKF, suggesting that the mantle fluids flow only within the KKF. Within the last few Ma, the KKF must have accessed tectonically active Tibetan mantle northeast of the "mantle suture" which we therefore locate vertically beneath the KKF, very close to the surface trace of the ISZ. Hence, in southwestern Tibet, Indian crust may not now be underthrusting substantially north of the ISZ, even though Miocene underthrusting may have placed Indian crust north of the ISZ in the lower half of the Tibetan Plateau crust. This is in significant contrast to central and eastern Tibet where underthrust Indian material not only forms the lower half of the Tibetan crust but is also currently underthrusting for ∼200 km north of the ISZ. Our new constraint on KKF penetration to the mantle allows an improved description of the continuously evolving Karakoram fault, as a tectonically significant yet perhaps geologically ephemeral lithospheric structure.

  4. West Antarctic Mantle Plume Hypothesis and Basal Water Generation

    Ivins, Erik; Seroussi, Helene; Wiens, Doug; Bondzio, Johannes


    The hypothesis of a deep mantle plume that manifests Pliocene and Quaternary volcanism and present-day seismicity in West Antarctica has been speculated for more than 30 years. Recent seismic images support the plume hypothesis as the cause of Marie Byrd Land (MBL) volcanism and geophysical structure [ Lloyd et al., 2015; Ramirez et al., 2016]. Mantle plumes can more that double the geothermal heat flux, qGHF, above nominal continental values at their axial peak position and raise qGHF in the surrounding plume head to 60 mW/m2 or higher. Unfortunately, there is a dearth of in-situ basal ice sheet data that sample the heat flux. Consequently, we examine a realistic distribution of heat flux associated with a late-Cenozoic mantle plume in West Antarctica and explore its impact on thermal and melt conditions near the ice sheet base. The solid Earth model assumes a parameterized deep mantle plume and head. The 3-D ice flow model includes an enthalpy framework and full-Stokes stress balance. Both the putative plume location and extent are uncertain. Therefore, we perform broadly scoped experiments to characterize plume related basal conditions. The experiments show that mantle plumes have an important local impact on the ice sheet, with basal melting rates reaching several centimeters per year directly above the hotspot. The downstream active lake system of Whillans Ice Stream suggests a rift-related source of anomalous mantle heat. However, the lack of lake and stream activity in MBL suggests a relatively weak plume: one that delivers less flux by 35% below the heat flux to the crustal surface at the site of the Yellowstone hotspot [e.g., DeNosaquo et al., 2009], with peak value no higher than about 145 mW/m2.

  5. Mantle flow and dynamic topography associated with slab window opening

    Guillaume, Benjamin; Moroni, Monica; Funiciello, Francesca; Martinod, Joseph; Faccenna, Claudio


    A slab window is defined as an 'hole' in the subducting lithosphere. In the classical view, slab windows develop where a spreading ridge intersects a subduction zone. The main consequences of this phenomenon are the modifications of the physical, chemical and thermal conditions in the backarc mantle that in turn affect the tectonic and magmatic evolution of the overriding plate. In this work, we perform dynamically self-consistent mantle-scale laboratory models, to evaluate how the opening of a window in the subducting panel influences the geometry and the kinematics of the slab, the mantle circulation pattern and, finally, the overriding plate dynamic topography. The adopted setup consists in a two-layer linearly viscous system simulating the roll-back of a fixed subducting plate (simulated using silicone putty) into the upper mantle (simulated using glucose syrup). Our experimental setting is also characterized by a constant-width rectangular window located at the center of a laterally confined slab, modeling the case of the interaction of a trench-parallel spreading ridge with a wide subduction zone. We find that the geometry and the kinematics of the slab are only minorly affected by the opening of a slab window. On the contrary, slab induced mantle circulation, quantified using Feature Tracking image analysis technique, is strongly modified and produces a peculiar non-isostatic topographic signal on the overriding plate. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compare them to the Patagonian subduction zone finding that anomalous backarc volcanism that developed since middle Miocene could result from the lateral flowage of subslab mantle, and that part of the Patagonian uplift could be dynamically supported.

  6. Vertical velocity of mantle flow of East Asia and adjacent areas

    CHENG Xianqiong; ZHU Jieshou; CAI Xuelin


    Based on the high-resolution body wave tomo- graphic image and relevant geophysical data, we calculated the form and the vertical and tangential velocities of mantle flow. We obtained the pattern of mantle convection for East Asia and the West Pacific. Some important results and under- standings are gained from the images of the vertical velocity of mantle flow for East Asia and the West Pacific. There is an upwelling plume beneath East Asia and West Pacific, which is the earth's deep origin for the huge rift valley there. We have especially outlined the tectonic features of the South China Sea, which is of the "工" type in the upper mantle shield type in the middle and divergent in the lower; the Siberian clod downwelling dives from the surface to near Core and mantle bounary (CMB), which is convergent in the upper mantle and divergent in the lower mantle; the Tethyan subduction region, centered in the Qinghai-Tibet plateau, is visible from 300 to 2 000 km, which is also convergent in the upper mantle and divergent in the lower mantle. The three regions of mantle convection beneath East Asia and the West Pacific are in accordance with the West Pacific, Ancient Asia and the Tethyan structure regions. The mantle upwelling orig- inates from the core-mantle boundary and mostly occurs in the middle mantle and the lower part of the upper mantle. The velocities of the vertical mantle flow are about 1-4 cm per year and the tangential velocities are 1-10 cm per year. The mantle flow has an effect on controlling the movement of plates and the distributions of ocean ridges, subduction zones and collision zones. The mantle upwelling regions are clearly related with the locations ofhotspots on the earth's surface.

  7. Seismic Constraints on the Mantle Viscosity Structure beneath Antarctica

    Wiens, Douglas; Heeszel, David; Aster, Richard; Nyblade, Andrew; Wilson, Terry


    Lateral variations in upper mantle viscosity structure can have first order effects on glacial isostatic adjustment. These variations are expected to be particularly large for the Antarctic continent because of the stark geological contrast between ancient cratonic and recent tectonically active terrains in East and West Antarctica, respectively. A large misfit between observed and predicted GPS rates for West Antarctica probably results in part from the use of a laterally uniform viscosity structure. Although not linked by a simple relationship, mantle seismic velocities can provide important constraints on mantle viscosity structure, as they are both largely controlled by temperature and water content. Recent higher resolution seismic models for the Antarctic mantle, derived from data acquired by new seismic stations deployed in the AGAP/GAMSEIS and ANET/POLENET projects, offer the opportunity to use the seismic velocity structure to place new constraints on the viscosity of the Antarctic upper mantle. We use an Antarctic shear wave velocity model derived from array analysis of Rayleigh wave phase velocities [Heeszel et al, in prep] and examine a variety of methodologies for relating seismic, thermal and rheological parameters to compute a suite of viscosity models for the Antarctic mantle. A wide variety of viscosity structures can be derived using various assumptions, but they share several robust common elements. There is a viscosity contrast of at least two orders of magnitude between East and West Antarctica at depths of 80-250 km, reflecting the boundary between cold cratonic lithosphere in East Antarctica and warm upper mantle in West Antarctica. The region beneath the Ellsworth-Whitmore Mtns and extending to the Pensacola Mtns. shows intermediate viscosity between the extremes of East and West Antarctica. There are also significant variations between different parts of West Antarctica, with the lowest viscosity occurring beneath the Marie Byrd Land (MBL

  8. A New Carbonate Chemistry in the Earth's Lower Mantle

    Boulard, E.; Gloter, A.; Corgne, A.; Antonangeli, D.; Auzende, A.; Perrillat, J.; Guyot, F. J.; Fiquet, G.


    The global geochemical carbon cycle involves exchange between the Earth’s mantle and the surface. Carbon (C) is recycled into the mantle via subduction and released to the atmosphere via volcanic outgassing. Carbonates are the main C-bearing minerals that are transported deep in the Earth’s mantle via subduction of the oceanic lithosphere [1]. The way C is recycled and its contribution to the lower mantle reservoir is however largely unknown [ e.g 2, 3]. In this respect, it is important to assess if carbonates can be preserved in the deep mantle, or if decarbonatation, melting or reduction play a role in the deep carbon cycle. To clarify the fate of carbonates in the deep mantle, we carried out high-pressure and high-temperature experiments up to 105 GPa and 2850 K. Natural Fe-Mg carbonates or oxide mixtures of (Mg,Fe)O + CO2 were loaded into laser heated diamond anvil cells. In situ characterizations were done by X-ray Diffraction (XRD) using synchrotron radiation at the high-pressure beamline ID27 of the European Synchrotron Radiation Facility. A focused ion beam technique was then used to prepare the recovered samples for electron energy loss spectroscopy in a dedicated scanning transmission electron microscope (EELS-STEM) and scanning transmission X-ray microscopy (STXM). In situ XRD clearly shows the transformation of the initial carbonate phase into a new Mg-Fe high pressure carbonate phase at lower mantle conditions. We also provide direct evidence for recombination of CO2 with (Mg,Fe)O to form this new carbonate structure. In addition, subsequent EELS-STEM and STXM spectroscopies carried out on recovered samples yields C K-edge and stoechiometry characteristic to this new carbonate structure. This new high pressure phase concentrates a large amount of Fe(III), as a result of redox reactions within the siderite-rich carbonate. The oxidation of iron is balanced by partial reduction of carbon into CO groups and/or diamond. These reactions may provide an

  9. Evidence for Little Shallow Entrainment in Starting Mantle Plumes

    Lohmann, F. C.; Phipps Morgan, J.; Hort, M.


    Basalts from intraplate or hotspot ocean islands show distinct geochemical signatures. Their diversity in composition is generally believed to result from the upwelling plume entraining shallow mantle material during ascent, while potentially also entraining other deep regions of the mantle. Here we present results from analogue laboratory experiments and numerical modelling that there is evidence for little shallow entrainment into ascending mantle plumes, i.e. most of the plume signature is inherited from the source. We conducted laboratory experiments using glucose syrup contaminated with glass beads to visualize fluid flow and origin. The plume is initiated by heating from below or by injecting hot, uncontaminated syrup. Particle movement is captured by a CCD camera. In our numerical experiments we solve the Stokes equations for a viscous fluid at infinite Prandtl number with passive tracer particles being used to track fluid flow and entrainment rates, simulating laboratory as well as mantle conditions. In both analogue experiments and numerical models we observe the classical plume structure being embedded in a `sheath' of material from the plume source region that retains little of the original temperature anomaly of the plume source. Yet, this sheath ascends in the `slipstream' of the plume at speeds close to the ascent speed of the plume head, and effectively prevents the entrainment of surrounding material into the plume head or plume tail. We find that the source region is most effectively sampled by an ascending plume and that compositional variations in the source region are preserved during plume ascent. The plume center and plume sheath combined are composed of up to 85% source material. However, there is also evidence of significant entrainment of up to 30% of surrounding material into the outer layers of the plume sheath. Entrainment rates are found to be influenced by mantle composition and structure, with the radial viscosity profile of the

  10. Primary cutaneous blastoid mantle cell lymphoma-case report.

    Estrozi, Bruna; Sanches, José A; Varela, Paulo C S; Bacchi, Carlos E


    Mantle cell lymphoma (MCL) commonly involves extranodal sites, usually as a manifestation of disseminated disease. In rare cases, MCLs may arise as a primary tumor in the skin. Blastoid mantle cell lymphoma (BV-MCL) is a rare variant and has a more aggressive clinical course. The phenotype of BV-MCL is characterized as CD20+, CD5+, cyclin D1+, CD23-, and CD10-. Interphase fluorescence in situ hybridization shows a characteristic t(11;14) fusion pattern. We report a case of a BV-MCL arising in skin as primary cutaneous MCL with the characteristic immunophenotype and translocation.

  11. Seismic determination of elastic anisotropy and mantle flow.

    Park, J; Yu, Y


    When deformed, many rocks develop anisotropic elastic properties. On many seismic records, a long-period (100 to 250 seconds), "quasi-Love" wave with elliptical polarization arrives slightly after the Love wave but before the Rayleigh wave. Mantle anisotropy is sufficient to explain these observations qualitatively as long as the "fast" axis of symmetry is approximately horizontal. Quasi-Love observations for several propagation paths near Pacific Ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the Pacific plate.

  12. Helium isotopic systematics of oceanic islands and mantle heterogeneity

    Kurz, M.D.; Jenkins, W.J. (Woods Hole Oceanographic Institution, MA (USA)); Hart, S.R. (Massachusetts Inst. of Tech., Cambridge (USA). Dept. of Earth and Planetary Sciences)


    The results of helium isotopic analyses in basaltic phenocrysts from the islands of Gough and Tristan da Cunha are reported which seem to indicate that the mantle beneath these islands are not primitive or undepleted relative to mid-ocean ridge basalt (MORB). New analyses from Loihi Seamount are also reported which do indicate a more primitive source. When these data are combined with values for MORBs previously obtained and plotted with respect to /sup 87/Sr//sup 86/Sr, the observed trends offer insight into the different source regions for oceanic island basalts and the nature of mantle heterogeneity.

  13. Water contents in pyroxenes of intraplate lithospheric mantle

    Bonadiman, C.; Hao, Y.-T.; Coltorti, M.; Dallai, L.; Faccini, B.; Hu, H.; Qunke, X.


    Water contents of clinopyroxene and orthopyroxene in mantle peridotites from various xenolith occurrences in intraplate settings (both oceanic and continental) were determined by Fourier Transform Infrared Spectroscopy (FTIR). The localities are as follow: Sal Island (Cape Verde Archipelago); Baker Rocks and Greene Point (Northern Victoria Land, Antarctica); Panshishan and Lianshan (Subei Basin, Eastern China). They represent well-known localities where detailed petrographical and geochemical studies have already been carried out or areas which are currently under investigation. The water incorporated in these pyroxenes is low (cpx, 37-399ppm; opx: 9-166ppm)(or very low as in Greene Point, Antarctica; cpx, 5-16ppm; opx: 9-16ppm) and, among each population, no clear correlation with melting parameters (MgO contents) in single mineral is evident. Results are compared with the available literature data on water contents in mantle pyroxene which includes peridotites from on-craton (hosted by kimberlitic-type magmas) and off-craton (hosted by alkaline basic magmas), as well as subarc mantle settings. The "relatively dry" (cpx: 140-528 ppm; opx: 38-280 ppm) sub-arc mantle xenoliths (Peslier et al., 2002) are shown to be wetter than the intraplate (off-craton) xenoliths. Cratonic mantle pyroxenes are only represented by a few determinations on garnet peridotites and eclogite from Kaapvaal and Colorado Plateau. They record the highest water contents (cpx: 342-1012 ppm; opx: 180-491 ppm) so far measured in mantle pyroxenes from various tectonic settings. Despite the limited data set, the indication that the cratonic mantle is strongly hydrated is compelling. Rehydration for the Colorado Plateau craton may be due to the Farallon plate subduction (Li et al., 2008), while for Kaapvaal Craton it might be related to young (<100Ma) metasomatic enrichments (Griffin et al., 2003a; Kobussen et al., 2008). If this is the case then the Archean mantle water content needs to be

  14. A mantle plume below the Eifel volcanic fields, Germany

    Ritter, Joachim R. R.; Jordan, Michael; Christensen, Ulrich R.; Achauer, Ulrich


    We present seismic images of the upper mantle below the Quaternary Eifel volcanic fields, Germany, determined by teleseismic travel time tomography. The data were measured at a dedicated network of more than 200 stations. Our results show a columnar low P-velocity anomaly in the upper mantle with a lateral contrast of up to 2%. The 100 km wide structure extends to at least 400 km depth and is equivalent to about 150–200 K excess temperature. This clear evidence for a plume below a region of c...

  15. Domains via Graphs

    ZHANG Guoqiang; CHEN Yixiang


    This paper provides a concrete and simple introduction to two pillars of domain theory: (1) solving recursive domain equations, and (2) universal and saturated domains. Our exposition combines Larsen and Winskel's idea on solving domain equations using information systems with Girard's idea of stable domain theory in the form of coherence spaces, or graphs.Detailed constructions are given for universal and even homogeneous objects in two categories of graphs: one representing binary complete, prime algebraic domains with complete primes covering the bottom; the other representing ω-algebraic, prime algebraic lattices. The backand-forth argument in model theory helps to enlighten the constructions.

  16. The initiation, temporal evolution and dynamics of deep mantle heterogeneities

    Bull-Aller, Abigail; Torsvik, Trond; Domeier, Mathew; Doubrovine, Pavel


    Understanding the first-order dynamical structure and temporal evolution of Earth's mantle is a fundamental goal in solid-earth geophysics. Recent tomographic observations reveal a lower mantle characterised by higher-than-average shear-wave speeds beneath Asia and encircling the Pacific, consistent with cold slabs of descending lithosphere beneath regions of ancient subduction, and lower-than-average shear-wave speeds in broad regional areas beneath Africa and the Central Pacific (LLSVPs). The LLSVPs, although not as easily understood from a dynamical perspective, are inferred to be broad upwelling centres between Mesozoic and Cenozoic subduction zones. Heterogeneous mantle models place these anomalies into the context of thermochemical piles, characterised by an anomalously dense component, with their location and geometry being controlled by the movement of subducting slabs. The origin and temporal evolution of the LLSVPs remain enigmatic. Recent numerical studies propose that the LLSVP beneath Africa formed as a result of return flow in the mantle due to circum-Pacific subduction beneath the Pangean supercontinent. This suggests that prior to the formation of Pangea, the lower mantle was dominated by a degree-1 convection pattern, with a major upwelling centred close to the present-day Pacific LLSVP and subduction concentrated in the antipodal hemisphere. The African LLSVP would thus have developed within the time frame of the Pangean supercontinent (i.e., 300Ma-180Ma), in contrast to a much older Pacific LLSVP. It is further proposed that a cyclic alternation between a degree-1 pattern and a degree-2 pattern of mantle convection may accompany the supercontinent cycle and characterise the temporal convective evolution of Earth's mantle. In contrast, a more long-term persistence for both the African and Pacific LLSVPs, and thus for the planform of mantle convection within the Earth as a whole, is suggested by recent palaeomagnetic studies, which show that over

  17. Deep mantle heat flow and thermal evolution of the Earth's core based on thermo-chemical mantle convection

    Nakagawa, T.; Tackley, P.; Buffett, B.


    A coupled core-mantle evolution model that combines the global heat balance in the core with a fully-dynamical thermo-chemical mantle convection [Nakagawa and Tackley, 2004 published in EPSL] is used to investigate the deep mantle heat flow that is required to sustain the magnetic field generated by the geodynamo process. Effects of a radioactive heat source due to potassium in the core are also included in the global heat balance in the Earth??s core. Two important parameters are checked in this study; (1) density variation between depleted hartzbergite and basaltic material (0 to 3 percent) and (2) concentration of radioactive potassium in the core alloy (0ppm to 400ppm). The parameter set that most closely satisfies the criteria of size of the inner core (1220km at present time) is around 2 percent of density difference in a convecting mantle and 200ppm of radioactive heat source in the core. The concentration of potassium in the core is consistent with the geochemical approach [Murthy et al., 2003] but smaller than other successful thermal evolution models [Labrosse, 2003; Nimmo et al., 2004]. Heat flow through the core-mantle boundary and the contribution of radioactive heat sources in the core are consistent with theoretical estimates [e.g. Buffett, 2002] and geochemical constraints [Gessmann and Wood, 2002]. The power available to the geodynamo, based on the predicted heat flow through the core-mantle boundary, is approximately four times greater than the value predicted by numerical models of the geodynamo [Christensen and Kutzner, 2004] but closer to theoretical estimates [e.g. Buffett, 2002].

  18. Layering of the lithospheric mantle beneath the Siberian Craton: Modeling using thermobarometry of mantle xenolith and xenocrysts

    Ashchepkov, I. V.; Vladykin, N. N.; Ntaflos, T.; Kostrovitsky, S. I.; Prokopiev, S. A.; Downes, H.; Smelov, A. P.; Agashev, A. M.; Logvinova, A. M.; Kuligin, S. S.; Tychkov, N. S.; Salikhov, R. F.; Stegnitsky, Yu. B.; Alymova, N. V.; Vavilov, M. A.; Minin, V. A.; Babushkina, S. A.; Ovchinnikov, Yu. I.; Karpenko, M. A.; Tolstov, A. V.; Shmarov, G. P.


    Single-grain thermobarometric studies of xenocrysts were used to compile local SCLM transects through the major regions of kimberlite magmatism in Siberia and longer transects through the subcontinental mantle lithosphere (SCLM) beneath the Siberian craton. The mantle structure was obtained using P-Fe#, Ca in garnets, oxygen fugacity values fO2 and calculated temperatures T°C. The most detail transect obtained for the Daldyn field on the Udachnaya-Zarnitsa reveals layering showing an inclination of > 35° to Udachnaya. Mantle layering beneath the Alakit field determined from the Krasnopresnenskaya-Sytykanskaya transect shows a moderate inclination from N to S. The inflection near Yubileinaya-Aykhal is also supported by the extreme depletion in peridotites with low-Fe sub-Ca garnets. Beneath the Malo-Botuobinsky field the sharply layered mantle section starts from 5.5 GPa and reveals step-like P-Fe#Ol trends for garnets and ilmenites. The deeper part of SCLM in this field was originally highly depleted but has been regenerated by percolation of protokimberlites and hybrid melts especially beneath Internationalnaya pipe. The three global transects reveal flat layering in granite-greenstone terranes and fluctuations in the granulite-orthogneiss Daldyn collision terranes. The mantle layering beneath the Daldyn - Alakite region may have been created by marginal accretion. Most of southern fields including the Malo-Botuobinsky field reveal flat layering. The primary subduction layering is smoothed beneath the Alakit field. Lower Jurassic kimberlites from the Kharamai-Anabar kimberlite fields reveal a small decrease of the thickness of the SCLM and heating of its base. The Jurassic Kuoyka field shows an uneven base of the SCLM inclined from west to east. SCLM sequences sampled at this time started mainly from depths of 130 km, but some pipes still showed mantle roots to 250 km. The garnet series demonstrates an inclined straight line pyroxenite P-Fe# trend due to

  19. Rhenium - osmium heterogeneity of enriched mantle basalts explained by composition and behaviour of mantle-derived sulfides

    Harvey, J.; Dale, C. W.; Gannoun, A.; Burton, K. W.


    Analyses of enriched mantle (EM) -basalts, using lithophile element-based isotope systems have long provided evidence for discrete, but variable mantle reservoirs [1]. Upon partial melting, the isotopic fingerprint of each reservoir is imparted upon the partial melt produced. However, recent work involving the Re-Os isotope systematics of EM-basalts [2] suggests that it may not be so simple to delimit these previously well defined mantle reservoirs; the “mantle zoo” [3] may contain more reservoirs than previously envisaged. However, a simple model, with varying contributions from two populations of compositionally distinct mantle sulfides can readily account for the observed heterogeneities in Re-Os isotope systematics of such basalts without additional mantle reservoirs. Rhenium-osmium elemental and isotopic analyses of individual sulfide grains separated from spinel lherzolites from Kilbourne Hole, NM, USA demonstrate that two discrete populations of mantle sulfide exist in terms of both Re-Os systematics and textural relationship with co-existing silicates. One population, with a rounded morphology, is preserved in silicate grains and typically possesses high [Os], low [Re] with unradiogenic, typically sub-chondritic, 187Os/188Os attributable to long term isolation in a low-Re environment. By contrast, irregular-shaped sulfides, preserved along silicate grain boundaries, possess low [Os], higher [Re] and a wider range of, but generally supra-chondritic, 187Os/188Os ([Os] typically ≤ 1-2 ppm, 187Os/188Os ≤ 0.3729; this study). This population is thought to represent metasomatic sulfide (e.g. [4,5]). Uncontaminated silicate phases contain negligible Os (mobilized and incorporated into the melt, adding their radiogenic 187Os/188Os signature. Only when sulfides armored within silicates are exposed to the melt through continued partial melting will enclosed sulfides add their high [Os] and unradiogenic 187Os/188Os to the aggregate melt. Platinum-group element

  20. Traces of the crustal units and the upper mantle structure in the southwestern part of the East European Craton

    I. Janutyte


    Full Text Available The presented study is a part of the passive seismic experiment PASSEQ 2006–2008 which took place around the Trans-European Suture Zone (TESZ from May 2006 to June 2008. The dataset of 4195 manually picked arrivals of teleseismic P waves of 101 earthquakes (EQs recorded in the PASSEQ seismic stations deployed to the east of the TESZ was inverted using the non-linear teleseismic tomography algorithm TELINV. Two 3-D crustal models were used to estimate the crustal travel time (TT corrections. As a result, we obtained a model of P wave velocity variations in the upper mantle beneath the TESZ and the EEC. In the study area beneath the craton we observed 5 to 6.5% higher and beneath the TESZ about 4% lower seismic velocities compared to the IASP91 velocity model. We found the seismic lithosphere-asthenosphere boundary (LAB beneath the TESZ at a depth of about 180 km, while we observed no seismic LAB beneath the EEC. The inversion results obtained with the real and the synthetic datasets indicated a ramp shape of the LAB in the northern TESZ where we observed values of seismic velocities close to those of the craton down to about 150 km. The lithosphere thickness in the EEC increases going from the TESZ to the NE from about 180 km beneath Poland to 300 km or more beneath Lithuania. Moreover, in western Lithuania we possibly found an upper mantle dome. In our results the crustal units are not well resolved. There are no clear indications of the features in the upper mantle which could be related with the crustal units in the study area. On the other hand, at a depth of 120–150 km we possibly found a trace of a boundary of proposed palaeosubduction zone between the East Lithuanian Domain (EL and the West Lithuanian Granulite Domain (WLG. Also, in our results we may have identified two anorogenic granitoid plutons.

  1. Domains of laminin

    Engvall, E; Wewer, U M


    Extracellular matrix molecules are often very large and made up of several independent domains, frequently with autonomous activities. Laminin is no exception. A number of globular and rod-like domains can be identified in laminin and its isoforms by sequence analysis as well as by electron...... microscopy. Here we present the structure-function relations in laminins by examination of their individual domains. This approach to viewing laminin is based on recent results from several laboratories. First, some mutations in laminin genes that cause disease have affected single laminin domains, and some...... laminin isoforms lack particular domains. These mutants and isoforms are informative with regard to the activities of the mutated and missing domains. These mutants and isoforms are informative with regard to the activities of the mutated and missing domains. Second, laminin-like domains have now been...

  2. The Elephants' Graveyard: Constraints from Mantle Plumes on the Fate of Subducted Slabs and Implications for the Style of Mantle Convection

    Lassiter, J. C.


    The style of mantle convection (e.g., layered- vs. whole-mantle convection) is one of the most hotly contested questions in the Geological Sciences. Geochemical arguments for and against mantle layering have largely focused on mass-balance evidence for the existence of "hidden" geochemical reservoirs. However, the size and location of such reservoirs are largely unconstrained, and most geochemical arguments for mantle layering are consistent with a depleted mantle comprising most of the mantle mass and a comparatively small volume of enriched, hidden material either within D" or within seismically anomalous "piles" beneath southern Africa and the South Pacific. The mass flux associated with subduction of oceanic lithosphere is large and plate subduction is an efficient driver of convective mixing in the mantle. Therefore, the depth to which oceanic lithosphere descends into the mantle is effectively the depth of the upper mantle in any layered mantle model. Numerous geochemical studies provide convincing evidence that many mantle plumes contain material which at one point resided close to the Earth's surface (e.g., recycled oceanic crust ± sediments, possibly subduction-modified mantle wedge material). Fluid dynamic models further reveal that only the central cores of mantle plumes are involved in melt generation. The presence of recycled material in the sources of many ocean island basalts therefore cannot be explained by entrainment of this material during plume ascent, but requires that recycled material resides within or immediately above the thermo-chemical boundary layer(s) that generates mantle plumes. More recent Os- isotope studies of mantle xenoliths from OIB settings reveal the presence not only of recycled crust in mantle plumes, but also ancient melt-depleted harzburgite interpreted to represent ancient recycled oceanic lithosphere [1]. Thus, there is increasing evidence that subducted slabs accumulate in the boundary layer(s) that provide the source

  3. Evolution of the Oxidation State of the Earth's Mantle

    Danielson, L. R.; Righter, K.; Keller, L.; Christoffersen, E.; Rahman, Z.


    The oxidation state of the Earth's mantle during formation remains an unresolved question, whether it was constant throughout planetary accretion, transitioned from reduced to oxidized, or from oxidized to reduced. We investigate the stability of Fe3(+) at depth, in order to constrain processes (water, late accretion, dissociation of FeO) which may reduce or oxidize the Earth's mantle. In our previous experiments on shergottite compositions, variable fO2, T, and P less than 4 GPa, Fe3(+)/sigma Fe decreased slightly with increasing P, similar to terrestrial basalt. For oxidizing experiments less than 7GPa, Fe3(+)/sigma Fe decreased as well, but it's unclear from previous modelling whether the deeper mantle could retain significant Fe3(+). Our current experiments expand our pressure range deeper into the Earth's mantle and focus on compositions and conditions relevant to the early Earth. Preliminary multi-anvil experiments with Knippa basalt as the starting composition were conducted at 5-7 GPa and 1800 C, using a molybdenum capsule to set the fO2 near IW, by buffering with Mo-MoO3. TEM and EELS analyses revealed the run products quenched to polycrystalline phases, with the major phase pyroxene containing approximately equal to Fe3(+)/2(+). Experiments are underway to produce glassy samples that can be measured by EELS and XANES, and are conducted at higher pressures.

  4. Olivine crystals align during diffusion creep of Earth's upper mantle.

    Miyazaki, Tomonori; Sueyoshi, Kenta; Hiraga, Takehiko


    The crystallographic preferred orientation (CPO) of olivine produced during dislocation creep is considered to be the primary cause of elastic anisotropy in Earth's upper mantle and is often used to determine the direction of mantle flow. A fundamental question remains, however, as to whether the alignment of olivine crystals is uniquely produced by dislocation creep. Here we report the development of CPO in iron-free olivine (that is, forsterite) during diffusion creep; the intensity and pattern of CPO depend on temperature and the presence of melt, which control the appearance of crystallographic planes on grain boundaries. Grain boundary sliding on these crystallography-controlled boundaries accommodated by diffusion contributes to grain rotation, resulting in a CPO. We show that strong radial anisotropy is anticipated at temperatures corresponding to depths where melting initiates to depths where strongly anisotropic and low seismic velocities are detected. Conversely, weak anisotropy is anticipated at temperatures corresponding to depths where almost isotropic mantle is found. We propose diffusion creep to be the primary means of mantle flow.

  5. Experimental Constraints on the Chemical Differentiation of Mercurys Mantle

    Boujibar, A.; Righter, K.; Pando, K.; Danielson, L.


    Mercury is known as being the most reduced terrestrial planet with the highest core/mantle ratio. Results from MESSENGER spacecraft have shown that its surface is FeO-poor (2-4 wt%) and S-rich (up to 6-7 wt%), which confirms the reducing nature of its silicate mantle. In addition several features suggest important melting stages of the Mercurian mantle: widespread volcanic deposits on its surface, a high crustal thickness (approximately 10% of the planet's volume) and chemical compositions of its surface suggesting several stages of differentiation and remelting processes. Therefore it is likely that igneous processes like magma ocean crystallization and continuous melting have induced chemical and mineralogical heterogeneities in the Mercurian mantle. The extent and nature of compositional variations produced by partial melting remains poorly constrained for the particular compositions of Mercury (very reducing conditions, low FeO-contents and high sulfur-contents). Melting experiments with bulk Mercury-analogue compositions are scarce and with poorly con-trolled starting compositions. Therefore additional experimental data are needed to better understand the differentiation processes that lead to the observed chemical compositions of Mercury's surface.

  6. Dehydrogenation of goethite in Earth’s deep lower mantle

    Hu, Qingyang; Kim, Duck Young; Liu, Jin; Meng, Yue; Yang, Liuxiang; Zhang, Dongzhou; Mao, Wendy L.; Mao, Ho-kwang


    The cycling of hydrogen influences the structure, composition, and stratification of Earth’s interior. Our recent discovery of pyrite-structured iron peroxide (designated as the P phase) and the formation of the P phase from dehydrogenation of goethite FeO2H implies the separation of the oxygen and hydrogen cycles in the deep lower mantle beneath 1,800 km. Here we further characterize the residual hydrogen, x, in the P-phase FeO2Hx. Using a combination of theoretical simulations and high-pressure–temperature experiments, we calibrated the x dependence of molar volume of the P phase. Within the current range of experimental conditions, we observed a compositional range of P phase of 0.39 < x < 0.81, corresponding to 19–61% dehydrogenation. Increasing temperature and heating time will help release hydrogen and lower x, suggesting that dehydrogenation could be approaching completion at the high-temperature conditions of the lower mantle over extended geological time. Our observations indicate a fundamental change in the mode of hydrogen release from dehydration in the upper mantle to dehydrogenation in the deep lower mantle, thus differentiating the deep hydrogen and hydrous cycles.

  7. Origin of azimuthal seismic anisotropy in oceanic plates and mantle

    Becker, Thorsten W.; Conrad, Clinton P.; Schaeffer, Andrew J.; Lebedev, Sergei


    Seismic anisotropy is ubiquitous in the Earth's mantle but strongest in its thermo-mechanical boundary layers. Azimuthal anisotropy in the oceanic lithosphere and asthenosphere can be imaged by surface waves and should be particularly straightforward to relate to well-understood plate kinematics and large-scale mantle flow. However, previous studies have come to mixed conclusions as to the depth extent of the applicability of paleo-spreading and mantle flow models of anisotropy, and no simple, globally valid, relationships exist. Here, we show that lattice preferred orientation (LPO) inferred from mantle flow computations produces a plausible global background model for asthenospheric anisotropy underneath oceanic lithosphere. The same is not true for absolute plate motion (APM) models. A ˜200 km thick layer where the flow model LPO matches observations from tomography lies just below the ˜1200 °C isotherm of a half-space cooling model, indicating strong temperature-dependence of the processes that control the development of azimuthal anisotropy. We infer that the depth extent of shear, and hence the thickness of a relatively strong oceanic lithosphere, can be mapped this way. These findings for the background model, and ocean-basin specific deviations from the half-space cooling pattern, are found in all of the three recent and independent tomographic models considered. Further exploration of deviations from the background model may be useful for general studies of oceanic plate formation and dynamics as well as regional-scale tectonic analyses.

  8. Using pattern recognition to infer parameters governing mantle convection

    Atkins, Suzanne; Valentine, Andrew P.; Tackley, Paul J.; Trampert, Jeannot


    The results of mantle convection simulations are fully determined by the input parameters and boundary conditions used. These input parameters can be for initialisation, such as initial mantle temperature, or can be constant values, such as viscosity exponents. However, knowledge of Earth-like values for many input parameters are very poorly constrained, introducing large uncertainties into the simulation of mantle flow. Convection is highly non-linear, therefore linearised inversion methods cannot be used to recover past configurations over more than very short periods of time, which makes finding both initial and constant simulation input parameters very difficult. In this paper, we demonstrate a new method for making inferences about simulation input parameters from observations of the mantle temperature field after billions of years of convection. The method is fully probabilistic. We use prior sampling to construct probability density functions for convection simulation input parameters, which are represented using neural networks. Assuming smoothness, we need relatively few samples to make inferences, making this approach much more computationally tractable than other probabilistic inversion methods. As a proof of concept, we show that our method can invert the amplitude spectra of temperature fields from 2D convection simulations, to constrain yield stress, surface reference viscosity and the initial thickness of primordial material at the CMB, for our synthetic test cases. The best constrained parameter is yield stress. The reference viscosity and initial thickness of primordial material can also be inferred reasonably well after several billion years of convection.

  9. Investigations of Eurasian Seismic Sources and Upper Mantle Structure


    in classical Earth models include the free surface, the Mohorovicic (M) discontinuity, the core-mantle boundary (CMB), and the inner core-outer core...rather to the superposition of first- and higher-order reverberations generated at the Mohorovicic (M) discontinuity. Figure 3.1 depicts the effect of

  10. Electrical Conductivity of the Lower-Mantle Ferropericlase

    Lin, J F; Weir, S T; Jackson, D D; Evans, W J; Vohra, Y K; Qiu, W; Yoo, C S


    Electrical conductivity of the lower-mantle ferropericlase-(Mg{sub 0.75},Fe{sub 0.25})O has been studied using designer diamond anvils to pressures over one megabar and temperatures up to 500 K. The electrical conductivity of (Mg{sub 0.75},Fe{sub 0.25})O gradually rises by an order of magnitude up to 50 GPa but decreases by a factor of approximately three between 50 to 70 GPa. This decrease in the electrical conductivity is attributed to the electronic high-spin to low-spin transition of iron in ferropericlase. That is, the electronic spin transition of iron results in a decrease in the mobility and/or density of the charge transfer carriers in the low-spin ferropericlase. The activation energy of the low-spin ferropericlase is 0.27 eV at 101 GPa, similar to that of the high-spin ferropericlase at relatively low temperatures. Our results indicate that low-spin ferropericlase exhibits lower electrical conductivity than high-spin ferropericlase, which needs to be considered in future geomagnetic models for the lower mantle. The extrapolated electrical conductivity of the low-spin ferropericlase, together with that of silicate perovskite, at the lower mantle pressure-temperature conditions is consistent with the model electrical conductivity profile of the lower mantle.

  11. Seismic structure of the mantle ; from subduction zone to craton

    Kennett, B.L.N.; Hilst, R.D. van der


    Seismological techniques have provided much of the currently available information on the internal structure of the Earth, and in particular on the mantle. Early studies revealed the need for an increase in seismic velocity with depth in the Earth, and by 1915 Gutenberg was able to make a good estim

  12. Upper mantle viscosity and lithospheric thickness under Iceland

    Barnhoorn, A.; Wal, W. van der; Drury, M.R.


    Deglaciation during the Holocene on Iceland caused uplift due to glacial isostatic adjustment. Relatively low estimates for the upper mantle viscosity and lithospheric thickness result in rapid uplift responses to the deglaciation cycles on Iceland. The relatively high temperatures of the upper mant

  13. Trench migration, net rotation and slab mantle coupling

    Funiciello, F.; Faccenna, C.; Heuret, A.; Lallemand, S.; Di Giuseppe, E.; Becker, T. W.


    Laboratory models have been conducted to improve our understanding of the role that the resistance of the slab to bending and its coupling to the ambient mantle play in subduction dynamics over geological time scales. Our models are set up with a viscous plate of silicone (lithosphere) subducting under negative buoyancy in a viscous layer of glucose syrup (mantle). For our study, the lithosphere/upper mantle viscosity contrast has been systematically varied, from ~ 10 to ~ 10 5 in order to explore the parameter space between weak and strong slab dynamics. We found that subduction is characterized by a retreating mode for viscosity ratios > 10 4, by the coexistence of a retreating mode and an advancing mode for viscosity ratios between ~ 10 4 and ~ 10 2, and quasi-stationary, Rayleigh-Taylor like behaviour for ratios < 10 2. By combining our experimental results and kinematic data from current subduction zones in four reference frames which differ in the amount of net rotation, we infer that a lithosphere/upper mantle viscosity contrast of 150-500 is necessary to obtain realistic trench/subducting plate velocity ratios as well as the variability of subduction styles observed in nature.

  14. Treatment of older patients with mantle-cell lymphoma

    Kluin-Nelemans, H C; Hoster, E; Hermine, O;


    The long-term prognosis for older patients with mantle-cell lymphoma is poor. Chemoimmunotherapy results in low rates of complete remission, and most patients have a relapse. We investigated whether a fludarabine-containing induction regimen improved the complete-remission rate and whether mainte...

  15. Pitfalls in modeling mantle convection with internal heat production

    Korenaga, Jun


    The mantle of the Earth, and probably of other terrestrial planets as well, is heated from below and within. The heating mode of mantle convection is thus mixed heating, and it is also time dependent because the amount of heat-producing isotopes in the mantle is steadily decreasing by radioactive decay and because the basal heat flux originating in the cooling of the core can vary with time. This mode of transient mixed heating presents its own challenges to the study of mantle convection, but such difficulties are not always appreciated in the recent literature. The purpose of this tutorial is to clarify the issue of heating mode by explaining relevant concepts in a coherent manner, including the internal heating ratio, the Urey ratio, secular cooling, and the connection between the thermal budget of the Earth and the geochemical models of the Earth. The importance of such basic concepts will be explained with some illustrative examples in the context of the thermal evolution of the Earth, and a summary of common pitfalls will be provided, with a possible strategy for how to avoid them.

  16. Mantle geoneutrinos in KamLAND and Borexino

    Fiorentini, G; Lisi, E; Mantovani, F; Rotunno, A M


    The KamLAND and Borexino experiments have observed, each at ~4 sigma level, signals of electron antineutrinos produced in the decay chains of thorium and uranium in the Earth's crust and mantle (Th and U geoneutrinos). Various pieces of geochemical and geophysical information allow an estimation of the crustal geoneutrino flux components with relatively small uncertainties. The mantle component may then be inferred by subtracting the estimated crustal flux from the measured total flux. To this purpose, we analyze in detail the experimental Th and U geoneutrino event rates in KamLAND and Borexino, including neutrino oscillation effects. We estimate the crustal flux at the two detector sites, using state-of-the-art information about the Th and U distribution on global and local scales. We find that crust-subtracted signals show hints of a residual mantle component, emerging at ~2.4 sigma level by combining the KamLAND and Borexino data. The inferred mantle flux slightly favors scenarios with relatively high Th ...

  17. Mantle structure and tectonic history of SE Asia

    Hall, Robert; Spakman, Wim|info:eu-repo/dai/nl/074103164


    Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia

  18. Modeling the effect of water on mantle rheology

    Bounama, CH.; Franck, S.


    To study the thermal history of the Earth we use a parameterized model of mantle convection. This model includes a mathematical description of de- and regassing processes of water from the Earth's mantle. The rates of this processes are considered to be directly proportional to the seafloor spreading rate. The kinematic viscosity of the mantle depends on the temperature/pressure as well as on the volatile content. Dissolved volatiles such as water weaken the minerals by reducing their activation energy for solid state creep. Karato and Toriumi showed a power law dependence between creep rate and water fugacity derived from experimental results. Therefore, we use such flow parameters of diffusion creep in olivine under wet and dry conditions to calculate the mantle viscosity as a function of the water content. Because the creep rate is proportional to the concentration of water-related point deflects we assume that the water fugacity is proportional to the water weight fraction. An equation for the steady-state strain rate under wet conditions is established. To assess the unknown constant K in this equation, we use flow law parameters given by Karato and Wu as well as the results of McGovern and Schubert.

  19. Mantle cell lymphoma in the orbital and adnexal region

    Rasmussen, Peter Kristian; Sjö, L D; Prause, J U


    AIMS: To characterise clinicopathological features of mantle cell lymphoma (MCL) in the orbital and adnexal region. METHODS: Data on lymphoid lesions were retrieved searching the Danish Ocular Lymphoma Database 1980-2005. Specimens were collected from Danish pathological departments and re-evalua...

  20. Laboratory-Scale Simulation of Spiral Plumes in the Mantle

    Sharifulin, A N


    On the basis of laboratory simulation a mechanism is established for the formation of the upper mantle convection spiral plumes from a hot point in the presence of a roll-type large-scale convective flow. The observed plume has horizontal sections near the upper limit, which may lead to the formation of chains of volcanic islands.

  1. Zinc isotope fractionation during mantle melting and constraints on the Zn isotope composition of Earth's upper mantle

    Wang, Ze-Zhou; Liu, Sheng-Ao; Liu, Jingao; Huang, Jian; Xiao, Yan; Chu, Zhu-Yin; Zhao, Xin-Miao; Tang, Limei


    The zinc (Zn) stable isotope system has great potential for tracing planetary formation and differentiation processes due to its chalcophile, lithophile and moderately volatile character. As an initial approach, the terrestrial mantle, and by inference, the bulk silicate Earth (BSE), have previously been suggested to have an average δ66Zn value of ∼+0.28‰ (relative to JMC 3-0749L) primarily based on oceanic basalts. Nevertheless, data for mantle peridotites are relatively scarce and it remains unclear whether Zn isotopes are fractionated during mantle melting. To address this issue, we report high-precision (±0.04‰; 2SD) Zn isotope data for well-characterized peridotites (n = 47) from cratonic and orogenic settings, as well as their mineral separates. Basalts including mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) were also measured to avoid inter-laboratory bias. The MORB analyzed have homogeneous δ66Zn values of +0.28 ± 0.03‰ (here and throughout the text, errors are given as 2SD), similar to those of OIB obtained in this study and in the literature (+0.31 ± 0.09‰). Excluding the metasomatized peridotites that exhibit a wide δ66Zn range of -0.44‰ to +0.42‰, the non-metasomatized peridotites have relatively uniform δ66Zn value of +0.18 ± 0.06‰, which is lighter than both MORB and OIB. This difference suggests a small but detectable Zn isotope fractionation (∼0.1‰) during mantle partial melting. The magnitude of inter-mineral fractionation between olivine and pyroxene is, on average, close to zero, but spinels are always isotopically heavier than coexisting olivines (Δ66ZnSpl-Ol = +0.12 ± 0.07‰) due to the stiffer Zn-O bonds in spinel than silicate minerals (Ol, Opx and Cpx). Zinc concentrations in spinels are 11-88 times higher than those in silicate minerals, and our modelling suggests that spinel consumption during mantle melting plays a key role in generating high Zn concentrations and heavy Zn isotopic

  2. Improved design of mantle tanks for small low flow SDHW systems

    Furbo, Simon; Knudsen, Søren


    Side-by-side tests of two small low flow SDHW systems based on mantle tanks have been carried out under the same test conditions in a laboratory test facility. The systems are identical with exception of the mantle tanks. One of the mantle tanks has the mantle inlet port located at the top...... of the mantle and the other mantle tank has the mantle inlet port moved 0.175 m down from the top of the mantle. The thermal performance is almost the same for the two systems in the measuring period of 252 days. The solar fractions were 0.66 and 0.68 for the two systems. The tests showed also that the system...... with the low mantle inlet perform better than the system with the high mantle inlet in periods with low solar fractions, that is in less sunny periods. Further, calculations with a simulation model for low flow SDHW systems based on mantle tanks showed that mantle tanks currently marketed can be greatly...

  3. Mapping mantle flow during retreating subduction: Laboratory models analyzed by feature tracking

    Funiciello, F.; Moroni, M.; Piromallo, C.; Faccenna, C.; Cenedese, A.; Bui, H. A.


    Three-dimensional dynamically consistent laboratory models are carried out to model the large-scale mantle circulation induced by subduction of a laterally migrating slab. A laboratory analogue of a slab-upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. The circulation pattern is continuously monitored and quantitatively estimated using a feature tracking image analysis technique. The effects of plate width and mantle viscosity/density on mantle circulation are systematically considered. The experiments show that rollback subduction generates a complex three-dimensional time-dependent mantle circulation pattern characterized by the presence of two distinct components: the poloidal and the toroidal circulation. The poloidal component is the answer to the viscous coupling between the slab motion and the mantle, while the toroidal one is produced by lateral slab migration. Spatial and temporal features of mantle circulation are carefully analyzed. These models show that (1) poloidal and toroidal mantle circulation are both active since the beginning of the subduction process, (2) mantle circulation is intermittent, (3) plate width affects the velocity and the dimension of subduction induced mantle circulation area, and (4) mantle flow in subduction zones cannot be correctly described by models assuming a two-dimensional steady state process. We show that the intermittent toroidal component of mantle circulation, missed in those models, plays a crucial role in modifying the geometry and the efficiency of the poloidal component.

  4. Dynamics of Pre-3 Ga Crust-Mantle Evolution

    Patchett, P. J.; Chase, C. G.; Vervoort, J. D.


    During 3.0 to 2.7 Ga, the Earth's crust underwent a non-uniformitarian change from a pre-3.0 Ga environment where long-term preservation of cratons was rare and difficult, to post-2.7 Ga conditions where cratons were established and new continental crust generation took place largely at craton margins. Many models view the Earth's surface during pre-3 Ga time as broadly equivalent to the post 2.7 Ga regime. Any such uniformitarian or gradual evolution cannot explain the conundrum that only a tiny amount of pre-3 Ga crust is preserved today coupled with the fact that very little pre-3 Ga crust was incorporated into the large amount of new craton that came into existence during 3.0-2.7 Ga. If large volumes of pre-3 Ga continental crust existed, it disappeared either just prior to 3 Ga, or during 3.0-2.7 Ga. To explain sudden appearance of surviving but dominantly juvenile continental crust in a model where continents were large prior to 3 Ga, it would be necessary either that pre-3 Ga continent was recycled into the mantle at sites systematically different from those where new 3.0-2.7 Ga crust was made, or that widespread continent destruction preceded the 3.0-2.7 Ga crustal genesis. From expected mantle overturn in response to the heat budget, it is likely that most pre-3 Ga crust was both more mafic and shorter-lived than after 3 Ga. Although Nd and Hf ratios for pre-3 Ga rocks are uncertain due to polymetamorphism, it appears that depleted upper mantle was widespread by 2.7 Ga, even pre-3 Ga. Depletion may have been largely achieved by formation, subduction and storage of mafic crust for periods of 200-500 m.y. The rapid change to large surviving continents during 3.0-2.7 Ga was due to declining mantle overturn, and particularly to development of the ability to maintain subduction in one zone of the earth's surface for the time needed to allow evolution to felsic igneous rock compositions. In as much as storage of subducted slabs is probably occurring today, and

  5. Morphology of seismically slow lower-mantle structures

    Cottaar, Sanne; Lekic, Vedran


    Large low shear velocity provinces (LLSVPs), whose origin and dynamic implication remain enigmatic, dominate the lowermost mantle. For decades, seismologists have created increasingly detailed pictures of the LLSVPs through tomographic models constructed with different modeling methodologies, data sets, parametrizations and regularizations. Here, we extend the cluster analysis methodology of Lekic et al., to classify seismic mantle structure in five recent global shear wave speed (VS) tomographic models into three groups. By restricting the analysis to moving depth windows of the radial profiles of VS, we assess the vertical extent of features. We also show that three clusters are better than two (or four) when representing the entire lower mantle, as the boundaries of the three clusters more closely follow regions of high lateral VS gradients. Qualitatively, we relate the anomalously slow cluster to the LLSVPs, the anomalously fast cluster to slab material entering the lower mantle and the neutral cluster to `background' lower mantle material. We obtain compatible results by repeating the analysis on recent global P-wave speed (VP) models, although we find less agreement across VP models. We systematically show that the clustering results, even in detail, agree remarkably well with a wide range of local waveform studies. This suggests that the two LLSVPs consist of multiple internal anomalies with a wide variety of morphologies, including shallowly to steeply sloping, and even overhanging, boundaries. Additionally, there are indications of previously unrecognized meso-scale features, which, like the Perm anomaly, are separated from the two main LLSVPs beneath the Pacific and Africa. The observed wide variety of structure size and morphology offers a challenge to recreate in geodynamic models; potentially, the variety can result from various degrees of mixing of several compositionally distinct components. Finally, we obtain new, much larger estimates of the volume

  6. Mantle Sulfur Cycle: A Case for Non-Steady State ?

    Cartigny, Pierre; Labidi, Jabrane


    Data published over the last 5 years show that the early inference that mantle is isotopically homogeneous is no more valid. Instead, new generation data on lavas range over a significant 34S/32S variability of up to 5‰ with δ 34S values often correlated to Sr- and Nd-isotope compositions. This new set of data also reveals the Earth's mantle to have a sub-chondritic 34S/32S ratio, by about ˜ 1‰. We will present at the conference our published and unpublished data on samples characterizing the different mantle components (i.e. EM1, EM2, HIMU and LOMU). All illustrate 34S-enrichments compared to MORB with Δ 33S and Δ 36S values indistinguishable from CDT or chondrites at the 0.03‰ level. These data are consistent with the recycling of subducted components carrying sulfur with Δ 33S and Δ 36S-values close to zero. Archean rocks commonly display Δ 33S and Δ 36S values deviating from zero by 1 to 10 ‰. The lack of variations for Δ 33S and Δ 36S values in present day lava argue against the sampling of any subducted protolith of Archean age in their mantle source. Instead, our data are consistent with the occurrence of Proterozoic subducted sulfur in the source of the EM1, EM2, LOMU and HIMU endmember at the St-Helena island. This is in agreement with the age of those components early derived through the use of the Pb isotope systematic. Currently, the negative δ 34S-values of the depleted mantle seem to be associated with mostly positive values of enriched components. This would be inconsistent with the concept a steady state of sulfur. Assuming that the overall observations of recycled sulfur are not biased, the origin of such a non-steady state remains unclear. It could be related to the relatively compatible behavior of sulfur during partial melting, as the residue of present-day melting can be shown to always contain significant amounts of sulfide (50{%} of what is observed in a fertile source). This typical behavior likely prevents an efficient

  7. Bases of the Mantle-Carbonatite Conception of Diamond Genesis

    Litvin, Yuriy; Spivak, Anna; Kuzyura, Anastasia


    In the mantle-carbonatite conception of diamond genesis, the results of physic-chemical experiments are coordinated with the data of analytic mineralogy of primary inclusions in natural diamonds. Generalization of the solutions of principal genetic problems constitutes the bases of the conception. The solutions are following: (1) it is grounded that diamond-parental melts of the upper mantle have peridotite/eclogite - carbonatite - carbon compositions, of the transition zone - (wadsleite↔ringwoodite) - majorite - stishovite - carbonatite - carbon compositions, and of the lower mantle - periclase/wustite - bridgmanite - Ca-perovskite -stishovite - carbonatite - carbon compositions; (2) a construction of generalized diagrams for the diamond-parental media, which reveal changeable compositions of the growth melts of diamonds and associated phases, their genetic relations to the mantle substance, and classification connections of the primary inclusions in natural diamonds; (3) experimental equilibrium phase diagrams of syngenesis of diamonds and primary inclusions, which characterize the nucleation and growth conditions of diamonds and a capture of paragenetic and xenogenetic minerals by the growing diamonds; (4) a determination of the phase diagrams of diamonds and inclusions syngenesis under the regime of fractional crystallization, which discover the regularities of ultrabasic-basic evolution and paragenesis transitions in the diamond-forming systems of the upper and lower mantle. The evidence of the physic-chemically united mode of diamond genesis at the mantle depths with different mineralogy is obtained. References. Litvin Yu.A. (2007). High-pressure mineralogy of diamond genesis. In: Advances in High-Pressure Mineralogy (edited by Eiji Ohtani), Geological Society of America Special paper 421, 83-103. Litvin Yu.A. (2012). Experimental study of physic-chemical conditions of natural diamond formation on an example of the eclogite

  8. Europium and strontium anomalies in the MORB source mantle

    Tang, Ming; McDonough, William F.; Ash, Richard D.


    Lower crustal recycling depletes the continental crust of Eu and Sr and returns Eu and Sr enriched materials into the mantle (e.g., Tang et al., 2015, Geology). To test the hypothesis that the MORB source mantle balances the Eu and Sr deficits in the continental crust, we carried out high precision Eu/Eu∗ and Sr/Sr∗ measurement for 72 MORB glasses with MgO >8.5% from the Pacific, Indian, and Atlantic mid-ocean ridges. MORB glasses with MgO ⩾ 9 wt.% have a mean Eu/Eu∗ of 1.025 ± 0.025 (2 σm, n = 46) and Sr/Sr∗ of 1.242 ± 0.093 (2 σm, n = 41) and these ratios are positively correlated. These samples show both positive and negative Eu and Sr anomalies, with no correlations between Eu/Eu∗ vs. MgO or Sr/Sr∗ vs. MgO, suggesting that the anomalies are not produced by plagioclase fractionation at MgO >9 wt.% and, thus, other processes must be responsible for generating the anomalies. We term these MORB samples primitive MORBs, as they record the melt Eu/Eu∗ and Sr/Sr∗ before plagioclase fractionation. Consequently, the mean oceanic crust, including cumulates, has a bulk Eu/Eu∗ of ∼1 and 20% Sr excess. Considering that divalent Sr and Eu(II) diffuse faster than trivalent Pr, Nd, Sm, and Gd, we evaluated this kinetic effect on Sm-Eu-Gd and Pr-Sr-Nd fractionations during spinel peridotite partial melting in the MORB source mantle. Our modeling shows that the correlated Eu and Sr anomalies seen in primitive MORBs may result from disequilibrium mantle melting. Melt fractions produced during early- and late-stage melting may carry positive and negative Eu and Sr anomalies, respectively, that overlap with the ranges documented in primitive MORBs. Because the net effect of disequilibrium melting is to produce partial melts with bulk positive Eu and Sr anomalies, the MORB source mantle must have Eu/Eu∗ continental crustal materials, which have positive Eu and Sr anomalies, are partially mixed into the upper mantle (i.e., MORB source region), a

  9. Subduction-zone cycling of nitrogen in serpentinized mantle rocks

    Halama, R.; Bebout, G. E.; John, T.; Scambelluri, M.


    Nitrogen (N) has shown great potential as a geochemical tracer of volatiles recycling, in part because of large differences in the N isotope composition of the various Earth reservoirs. The subduction flux of N in serpentinized oceanic mantle could be as important as N input flux in oceanic crust and even sediment because, although its N concentrations are lower, its volume is potentially far greater than that of the crust/sediment. However, recycling of oceanic mantle rocks is still poorly constrained for the N cycle, and N isotope data for subduction-related ultramafic rocks are scarce [1]. The primary goal of this study is to characterize the subduction flux of N in subducting altered oceanic mantle by documenting concentrations and isotopic compositions of N in mantle rocks that reflect different stages of the metamorphic subduction zone cycle. The results are crucial to assess the composition of N recycled into the mantle, to determine the extent to which N can be retained in subducted mantle rocks to depths approaching those beneath arcs, and to balance N subduction-zone inputs with outputs in arc volcanic gases. Moreover, information has been gained regarding the redistribution and isotope fractionation of N via ultramafic dehydration and metamorphic fluid-rock interaction. The samples analyzed in this study are ultramafic rocks from shallow oceanic environments to increasing P-T conditions up to depths of ~70 km. Three distinct metamorphic grades, reflecting seafloor fluid uptake, water release due to brucite breakdown and the final antigorite breakdown, were investigated: 1. Pre-subduction serpentinized mantle peridotite from non-subducted ophiolite sequences from the Northern Apennines, Italy (Monte Nero). 2. Eclogite-facies antigorite serpentinites from the Ligurian Alps, Italy (Erro Tobbio). 3. Eclogite-facies chlorite harzburgites derived from dehydration of serpentinites from the Betic Cordillera, Spain (Cerro de Almirez). The pre

  10. Superweak asthenosphere in light of upper mantle seismic anisotropy

    Becker, Thorsten W.


    Earth's upper mantle includes a ˜200 km thick asthenosphere underneath the plates where viscosity and seismic velocities are reduced compared to the background. This zone of weakness matters for plate dynamics and may be required for the generation of plate tectonics itself. However, recent seismological and electromagnetic studies indicate strong heterogeneity in thinner layers underneath the plates which, if related to more extreme, global viscosity reductions, may require a revision of our understanding of mantle convection. Here, I use dynamically consistent mantle flow modeling and the constraints provided by azimuthal seismic anisotropy as well as plate motions to explore the effect of a range of global and local viscosity reductions. The fit between mantle flow model predictions and observations of seismic anisotropy is highly sensitive to radial and lateral viscosity variations. I show that moderate suboceanic viscosity reductions, to ˜0.01-0.1 times the upper mantle viscosity, are preferred by the fit to anisotropy and global plate motions, depending on layer thickness. Lower viscosities degrade the fit to azimuthal anisotropy. Localized patches of viscosity reduction, or layers of subducted asthenosphere, however, have only limited additional effects on anisotropy or plate velocities. This indicates that it is unlikely that regional observations of subplate anomalies are both continuous and indicative of dramatic viscosity reduction. Locally, such weak patches may exist and would be detectable by regional anisotropy analysis, for example. However, large-scale plate dynamics are most likely governed by broad continent-ocean asthenospheric viscosity contrasts rather than a thin, possibly high melt fraction layer.

  11. Seismic anisotropy of upper mantle in eastern China


    Based on the polarization analysis of teleseismic SKS waveform data recorded at 65 seismic stations which respectively involved in the permanent and temporary broadband seismograph networks deployed in eastern China, the SKS fast-wave direction and the delay time between the fast and slow shear waves at each station were determined by use of SC method and the stacking analysis method, and then the image of upper mantle anisotropy in eastern China was acquired. In the study region, from south to north, the fast-wave polarization directions are basically EW in South China, gradually clockwise rotate to NWW-SEE in North China, then to NW-SE in Northeast China. The delay time falls into the interval [0.41 s, 1.52 s]. Anisotropic characteristics in eastern China indicate that the upper mantle anisotropy is possibly caused by both the collision between the Indian and Eurasian Plates and the subduction from the Pacific and Philippine Sea Plates to the Eurasian Plate. The collision between two plates made the crust of western China thickening and uplifting and the material eastwards extruding, and then caused the upper mantle flow eastwards and southeastwards. The subduction of Pacific Plate and Philippine Sea Plate has resulted in the lithosphere and the asthenosphere deformation in eastern China, and made the alignment of upper mantle peridotite lattice parallel to the deformation direction. The fast-wave polarization direction is consistent with the direction of lithosphere extension and the GPS velocity direction, implying that the crust-upper mantle deformation is possibly a vertically coherent deformation.

  12. Seismic anisotropy of upper mantle in eastern China

    CHANG LiJun; WANG ChunYong; Ding ZhiFeng


    Based on the polarization analysis of teleseismic SKS waveform data recorded at 65 seismic stations which respectively involved in the permanent and temporary broadband seismograph networks de-ployed in eastern China,the SKS fast-wave direction and the delay time between the fast and slow shear waves at each station were determined by use of SC method and the stacking analysis method,and then the image of upper mantle anisotropy in eastern China was acquired.In the study region,from south to north,the fast-wave polarization directions are basically EW in South China,gradually clock-wise rotate to NWW-SEE in North China,then to NW-SE in Northeast China.The delay time falls into the Interval [0.41 s,1.52 s].Anisotropic characteristics in eastern China indicate that the upper mantle anisotropy is possibly caused by both the collision between the Indian and Eurasian Plates and the subduction from the Pacific and Philippine Sea Plates to the Eurasian Plate.The collision between two plates made the crust of western China thickening and uplifting and the material eastwards extruding,and then caused the upper mantle flow eastwards and southeastwards.The subduction of Pacific Plate and Philippine Sea Plate has resulted in the lithosphere and the asthenosphere deformation in eastern China,and made the alignment of upper mantle peridotite lattice parallel to the deformation direction.The fast-wave polarization direction is consistent with the direction of lithosphere extension and the GPS velocity direction,implying that the crust-upper mantle deformation is possibly a vertically co-herent deformation.

  13. Upper-Mantle Flow Driven Dynamic Topography in Eastern Anatolia

    Sengul Uluocak, Ebru; Pysklywec, Russell; Eken, Tuna; Hakan Gogus, Oguz


    Eastern Anatolia is characterized by 2 km plateau uplift -in the last 10 Myrs-, high surface heat flow distribution, shallow Curie-point depth, anomalous gravity field. Seismological observations indicate relatively high Pn and Sn attenuation and significant low seismic velocity anomalies in the region. Moreover, the surface geology is associated predominantly with volcanic rocks in which melt production through mantle upwelling (following lithospheric delamination) has been suggested. It has been long known that the topographic loading in the region cannot be supported by crustal thickness (~45 km) based on the principle of Airy isostasy. Recent global geodynamic studies carried out for evaluating the post-collisional processes imply that there is an explicit dynamic uplift in Eastern Anatolia and its adjacent regions. In this study we investigate the instantaneous dynamic topography driven by 3-D upper-mantle flow in Eastern Anatolia. For this purpose we conducted numerous thermo-mechanical models using a 2-D Arbitrary Lagrangian Eulerian (ALE) finite element method. The available P-wave tomography data extracted along 10 profiles were used to obtain depth-dependent density anomalies in the region. We present resulting dynamic topography maps and estimated 3D mantle flow velocity vectors along these 2-D cross sections for each profile. The residual topography based on crustal thickness and observed topography was calculated and compared with other independent datasets concerning geological deformation and dynamic topography predictions. The results indicate an upper mantle driven dynamic uplift correlated with the under-compensated characteristic in Eastern Anatolia. We discuss our results combined with 3D mantle flow by considering seismic anisotropy studies in the region. Initial results indicate that high dynamic uplift and the localized low Pn velocities in concurrence with Pn anisotropy structures show nearly spatial coherence in Eastern Anatolia.

  14. Zn isotopic heterogeneity in the mantle: A melting control?

    Doucet, Luc S.; Mattielli, Nadine; Ionov, Dmitri A.; Debouge, Wendy; Golovin, Alexander V.


    We present new Zn elemental and isotope data on seventeen fertile and refractory mantle peridotite xenoliths. Eleven fertile peridotites are garnet and spinel lherzolites from Vitim and Tariat (Siberia and Mongolia) and represent some of the most pristine fertile peridotites available. Six refractory peridotites are spinel harzburgites from the Udachnaya kimberlite (Siberian craton) that are nearly pristine residues of high-degree polybaric melting at high pressure (7-4 GPa). Geochemical data suggest that Zn isotopic compositions in the peridotites have not been affected by post-melting processes such as metasomatism, contamination by the host-magmas or alteration. The fertile peridotites have uniform Zn concentrations (59 ± 2 ppm) and Zn isotopic compositions with δ66Zn (relative to JMC-Lyon-03-0749l) = +0.30 ± 0.03‰ consistent with the Bulk Silicate Earth estimates of δ66Zn = +0.28 ± 0.05‰ (Chen et al., 2013). The refractory peridotites have Zn concentrations ranging from 30 to 48 ppm and δ66Zn from + 0.10 ± 0.01 ‰ to + 0.18 ± 0.01 ‰ with an average of + 0.14 ± 0.03 ‰. Our data suggest that the lithospheric mantle has a heterogeneous Zn isotopic composition. Modeling of Zn isotope partitioning during partial melting of fertile mantle suggests that high degrees of melt extraction (>30%) may significantly fractionate Zn isotopes (up to 0.16‰) and that during mantle melting, Zn concentrations and isotopic compositions are mainly controlled by the stability of clinopyroxene and garnet within the melting residue. Because the stability of clinopyroxene and garnet is mainly pressure dependent we suggest that both the depth and the degrees of melt extraction may control Zn isotope fractionation during mantle melting.

  15. Numerical modelling of volatiles in the deep mantle

    Eichheimer, Philipp; Thielmann, Marcel; Golabek, Gregor J.


    The transport and storage of water in the mantle significantly affects several material properties of mantle rocks and thus water plays a key role in a variety of geodynamical processes (tectonics, magmatism etc.). The processes driving transport and circulation of H2O in subduction zones remain a debated topic. Geological and seismological observations suggest different inflow mechanisms of water e.g. slab bending, thermal cracking and serpentinization (Faccenda et al., 2009; Korenaga, 2017), followed by dehydration of the slab. On Earth both shallow and steep subduction can be observed (Li et al., 2011). However most previous models (van Keken et al., 2008; Wilson et al., 2014) did not take different dip angles and subduction velocities of slabs into account. To which extent these parameters and processes influence the inflow of water still remains unclear. We present 2D numerical models simulating the influence of the various water inflow mechanisms on the mantle with changing dip angle and subduction velocity of the slab over time. The results are used to make predictions regarding the rheological behavior of the mantle wedge, dehydration regimes and volcanism at the surface. References: van Keken, P. E., et al. A community benchmark for subduction zone modeling. Phys. Earth Planet. Int. 171, 187-197 (2008). Faccenda, M., T.V. Gerya, and L. Burlini. Deep slab hydration induced by bending-related variations in tectonic pressure. Nat. Geosci. 2, 790-793 (2009). Korenaga, J. On the extent of mantle hydration caused by plate bending. Earth Planet. Sci. Lett. 457, 1-9 (2017). Wilson, C. R., et al. Fluid flow in subduction zones: The role of solid rheology and compaction pressure. Earth Planet. Sci. Lett. 401, 261-274 (2014). Li, Z. H., Z. Q. Xu, and T. V. Gerya. Flat versus steep subduction: Contrasting modes for the formation and exhumation of high- to ultrahigh-pressure rocks in continental collision zones. Earth Planet. Sci. Lett. 301, 65-77 (2011).

  16. BurnMan: A lower mantle mineral physics toolkit

    Cottaar, Sanne


    We present BurnMan, an open-source mineral physics toolbox to determine elastic properties for specified compositions in the lower mantle by solving an Equation of State (EoS). The toolbox, written in Python, can be used to evaluate seismic velocities of new mineral physics data or geodynamic models, and as the forward model in inversions for mantle composition. The user can define the composition from a list of minerals provided for the lower mantle or easily include their own. BurnMan provides choices in methodology, both for the EoS and for the multiphase averaging scheme. The results can be visually or quantitatively compared to observed seismic models. Example user scripts show how to go through these steps. This paper includes several examples realized with BurnMan: First, we benchmark the computations to check for correctness. Second, we exemplify two pitfalls in EoS modeling: using a different EoS than the one used to derive the mineral physical parameters or using an incorrect averaging scheme. Both pitfalls have led to incorrect conclusions on lower mantle composition and temperature in the literature. We further illustrate that fitting elastic velocities separately or jointly leads to different Mg/Si ratios for the lower mantle. However, we find that, within mineral physical uncertainties, a pyrolitic composition can match PREM very well. Finally, we find that uncertainties on specific input parameters result in a considerable amount of variation in both magnitude and gradient of the seismic velocities. © 2014. American Geophysical Union. All Rights Reserved.

  17. Numerical Modeling of Deep Mantle Convection: Advection and Diffusion Schemes for Marker Methods

    Mulyukova, Elvira; Dabrowski, Marcin; Steinberger, Bernhard


    Thermal and chemical evolution of Earth's deep mantle can be studied by modeling vigorous convection in a chemically heterogeneous fluid. Numerical modeling of such a system poses several computational challenges. Dominance of heat advection over the diffusive heat transport, and a negligible amount of chemical diffusion results in sharp gradients of thermal and chemical fields. The exponential dependence of the viscosity of mantle materials on temperature also leads to high gradients of the velocity field. The accuracy of many numerical advection schemes degrades quickly with increasing gradient of the solution, while the computational effort, in terms of the scheme complexity and required resolution, grows. Additional numerical challenges arise due to a large range of length-scales characteristic of a thermochemical convection system with highly variable viscosity. To examplify, the thickness of the stem of a rising thermal plume may be a few percent of the mantle thickness. An even thinner filament of an anomalous material that is entrained by that plume may consitute less than a tenth of a percent of the mantle thickness. We have developed a two-dimensional FEM code to model thermochemical convection in a hollow cylinder domain, with a depth- and temperature-dependent viscosity representative of the mantle (Steinberger and Calderwood, 2006). We use marker-in-cell method for advection of chemical and thermal fields. The main advantage of perfoming advection using markers is absence of numerical diffusion during the advection step, as opposed to the more diffusive field-methods. However, in the common implementation of the marker-methods, the solution of the momentum and energy equations takes place on a computational grid, and nodes do not generally coincide with the positions of the markers. Transferring velocity-, temperature-, and chemistry- information between nodes and markers introduces errors inherent to inter- and extrapolation. In the numerical scheme

  18. Mantle convection and plate tectonics: toward an integrated physical and chemical theory



    Plate tectonics and convection of the solid, rocky mantle are responsible for transporting heat out of Earth. However, the physics of plate tectonics is poorly understood; other planets do not exhibit it. Recent seismic evidence for convection and mixing throughout the mantle seems at odds with the chemical composition of erupted magmas requiring the presence of several chemically distinct reservoirs within the mantle. There has been rapid progress on these two problems, with the emergence of the first self-consistent models of plate tectonics and mantle convection, along with new geochemical models that may be consistent with seismic and dynamical constraints on mantle structure.

  19. Asteroids and meteorites - Origin of stony-iron meteorites at mantle-core boundaries

    Greenberg, R.; Chapman, C. R.


    Stony-iron meteorites formed at the core/mantle interfaces of small asteroidal parents. The mesosiderites formed when the thick crust of a largely molten parent body (100-200 km in diameter) foundered and sank through the mantle to the core. Pallasites formed in smaller parent bodies (50-100 km) in which olivine crystals from the partially molten mantle sank to the core/mantle interface and rafted there. Subsequent collisions stripped away the rocky mantles of both kinds of parent bodies, exposing the stony-iron surfaces of their cores to direct impacts, which continue to knock off meteorite fragments.

  20. Pre-plate tectonics and structure of the Archean mantle lithosphere imaged by seismic anisotropy - inferences from the LAPNET array in northern Fennoscandia

    Plomerova, Jaroslava; Vecsey, Ludek; Babuska, Vladislav; Lapnet Working Group


    Various studies of seismic anisotropy clearly demonstrate the Archean mantle lithosphere consists of domains with different fabrics reflecting fossil anisotropic structures. We detect anisotropic signal both in the P-wave travel-time deviations and shear-wave splitting recorded by the LAPNET array (2007-2009) in the Archean craton of Fennoscandia (Plomerova et al., 2011). The anisotropic parameters change across the array and stations with similar characteristics form groups. The geographical variations of seismic-wave anisotropy delimit individual sharply bounded domains of the mantle lithosphere, each of them having a consistent fabric. The domains can be modelled in 3D by peridotite aggregates with dipping lineation a, or foliation (a,c). Also radial anisotropy of the Archean lithosphere derived from surface waves indicates inclined structure of all the cratonic regions of the continents, though with less detailed lateral resolution in comparison with body-wave anisotropy. These findings allow us to interpret the domains as micro-plate fragments retaining fossil fabrics in the mantle lithosphere, reflecting thus an olivine LPO created before the micro-plates assembled. Successive subductions of oceanic lithosphere is a mechanism which can work in modern-style plate tectonics as we know it now, being considered as widespread since 2.7 Ga. Though the modern plate tectonics is the most distinct tectonic style acting up to now, we have to consider a mechanism creating oriented structures (fabrics) in a pre-plate-tectonic style. The early lithosphere formed in dynamic conditions far from simple cooling which would result in sub-horizontal layered structure of the lithosphere. Earlier tectonic modes in a hotter and more dynamic Earth might be similar in some respects to those of the modern-plate tectonics. Basaltic "rockbergs" on convecting magma ocean in the Hadean Earth are supposed to turn to either proto-plate tectonics with platelets and supercratonal, or, to

  1. Lithosphere structure and upper mantle characteristics below the Bay of Bengal

    Rao, G. Srinivasa; Radhakrishna, M.; Sreejith, K. M.; Krishna, K. S.; Bull, J. M.


    The oceanic lithosphere in the Bay of Bengal (BOB) formed 80-120 Ma following the breakup of eastern Gondwanaland. Since its formation, it has been affected by the emplacement of two long N-S trending linear aseismic ridges (85°E and Ninetyeast) and by the loading of ca. 20-km of sediments of the Bengal Fan. Here, we present the results of a combined spatial and spectral domain analysis of residual geoid, bathymetry and gravity data constrained by seismic reflection and refraction data. Self-consistent geoid and gravity modelling defined by temperature-dependent mantle densities along a N-S transect in the BOB region revealed that the depth to the lithosphere-asthenosphere boundary (LAB) deepens steeply from 77 km in the south to 127 km in north, with the greater thickness being anomalously thick compared to the lithosphere of similar-age beneath the Pacific Ocean. The Geoid-Topography Ratio (GTR) analysis of the 85°E and Ninetyeast ridges indicate that they are compensated at shallow depths. Effective elastic thickness (Te) estimates obtained through admittance/ coherence analysis as well as the flexural modelling along these ridges led to the conclusions: (i) 85°E Ridge was emplaced in off-ridge environment (Te = 10-15 km); (ii) the higher Te values of ˜25 km over the Afanasy Nikitin Seamount (ANS) reflect the secondary emplacement of the seamount peaks in off-ridge environment, (iii) that the emplacement of the Ninetyeast Ridge north of 2°N occurred in an off-ridge environment as indicated by higher Te values (25-30 km). Furthermore, the admittance analysis of geoid and bathymetry revealed that the admittance signatures at wavelengths >800 km are compensated by processes related to upper mantle convection.

  2. Concentrates and mantle xenocrysts from the Lao river Guinea and reconstructions of the mantle structure

    Afanasiev, Valentin; Ashchepkov, Igor; Nikolenko, Eeugeny


    The discovery of the kimberlite dykes in Quinea in the basin of the Lao river means finding of the new diamondiferous kimberlite field in the West Africa. It is locating 100 km SW from Bubudu and contains large dykes and placers in Lao river. The kimberlite concentrate and diamondiferous placers are containing pyropes, chromites, Ilmenites and Cr diosides and low Cr- pyroxenes. Two river placers in Lao and Bobeko and newly discovered dyke slightly differ in compositions of minerals. mainly in representatives of the minerals though their compositional trends are in general similar. The concentrates from and Druzhba pipe (Bunudu) contains mainly ilmenite and more are pyropes. Garnets from all localities are close and belong mainly to the lherzolite field to 10 wt%Cr2O3. But the dyke contains essential amount of harzburgitic garnets starting from 2 %wt Cr2O3 and they became prevailing from 6 wt %Cr2O3. There are also megacrystic low - Cr pyropes in dyke concentrate. Dyke is rich in peridotites and coarse grained garnet pyroxenite xenoliths which are ranging from the low Cr -to Cr -diopside type Chromites from Dyke are Ti - low but are often Al rich. While chromites from Bobeko and especially Lao placers define the Cr- rich trend from 60 to 40 wt%Cr2O3 and demonstrate the deviation to ulvospinel trends with increasing of Al2O3 . Cr - Diopsides clinopyroxenites trace the Fe- Ti-Na-Al enrichment trend. Ilmenites from three localities - define close trends splitting to the two intervals 60-40 wt% TiO2 and 33-27 TiO2 which are enriched in Cr2O3 to 5wt% reflecting the crystallization of megacrystalline association at the lithosphere base and Ilm metasomatic vein stockwark near the Moho in pre-eruption feeding system. The Dyke ilmenites are Mg rich and mainly are captured from the deep part of the mantle section. Babeko and Druzhba localities are similar variations of ilmenite trends. Some ilmenites from Lao and Druzhba are Mn - rich and are less in Cr possibly reflecting

  3. Effect of core--mantle and tidal torques on Mercury's spin axis orientation

    Peale, Stanton J; Hauck,, Steven A; Solomon, Sean C


    The rotational evolution of Mercury's mantle and its core under conservative and dissipative torques is important for understanding the planet's spin state. Dissipation results from tides and viscous, magnetic and topographic core--mantle interactions. The dissipative core--mantle torques take the system to an equilibrium state wherein both spins are fixed in the frame precessing with the orbit, and in which the mantle and core are differentially rotating. This equilibrium exhibits a mantle spin axis that is offset from the Cassini state by larger amounts for weaker core--mantle coupling for all three dissipative core--mantle coupling mechanisms, and the spin axis of the core is separated farther from that of the mantle, leading to larger differential rotation. The relatively strong core--mantle coupling necessary to bring the mantle spin axis to its observed position close to the Cassini state is not obtained by any of the three dissipative core--mantle coupling mechanisms. For a hydrostatic ellipsoidal core...

  4. Deep Mantle Cycling of Oceanic Crust: Evidence from Diamonds and Their Mineral Inclusions

    Walter, M. J.; Kohn, S. C.; Araujo, D.; Bulanova, G. P.; Smith, C. B.; Gaillou, E.; Wang, J.; Steele, A.; Shirey, S. B.


    A primary consequence of plate tectonics is that basaltic oceanic crust subducts with lithospheric slabs into the mantle. Seismological studies extend this process to the lower mantle, and geochemical observations indicate return of oceanic crust to the upper mantle in plumes. There has been no direct petrologic evidence, however, of the return of subducted oceanic crustal components from the lower mantle. We analyzed superdeep diamonds from Juina-5 kimberlite, Brazil, which host inclusions with compositions comprising the entire phase assemblage expected to crystallize from basalt under lower-mantle conditions. The inclusion mineralogies require exhumation from the lower to upper mantle. Because the diamond hosts have carbon isotope signatures consistent with surface-derived carbon, we conclude that the deep carbon cycle extends into the lower mantle.

  5. Linking mantle upwelling with the lithosphere descent [corrected] and the Japan Sea evolution: a hypothesis.

    Ismail-Zadeh, Alik; Honda, Satoru; Tsepelev, Igor


    Recent seismic tomography studies image a low velocity zone (interpreted as a high temperature anomaly) in the mantle beneath the subducting Pacific plate near the Japanese islands at the depth of about 400 km. This thermal feature is rather peculiar in terms of the conventional view of mantle convection and subduction zones. Here we present a dynamic restoration of the thermal state of the mantle beneath this region assimilating geophysical, geodetic, and geological data up to 40 million years. We hypothesise that the hot mantle upwelling beneath the Pacific plate partly penetrated through the subducting plate into the mantle wedge and generated two smaller hot upwellings, which contributed to the rapid subsidence in the basins of the Japan Sea and to back-arc spreading. Another part of the hot mantle migrated upward beneath the Pacific lithosphere, and the presently observed hot anomaly is a remnant part of this mantle upwelling.

  6. Core cooling by subsolidus mantle convection. [thermal evolution model of earth

    Schubert, G.; Cassen, P.; Young, R. E.


    Although vigorous mantle convection early in the thermal history of the earth is shown to be capable of removing several times the latent heat content of the core, a thermal evolution model of the earth in which the core does not solidify can be constructed. The large amount of energy removed from the model earth's core by mantle convection is supplied by the internal energy of the core which is assumed to cool from an initial high temperature given by the silicate melting temperature at the core-mantle boundary. For the smaller terrestrial planets, the iron and silicate melting temperatures at the core-mantle boundaries are more comparable than for the earth; the models incorporate temperature-dependent mantle viscosity and radiogenic heat sources in the mantle. The earth models are constrained by the present surface heat flux and mantle viscosity and internal heat sources produce only about 55% of the earth model's present surface heat flow.

  7. Tomography images of the Alpine roots and surrounding upper mantle

    Plomerova, Jaroslava; Babuska, Vladislav


    Teleseismic body-wave tomography represents powerful tool to study regional velocity structure of the upper mantle and to image velocity anomalies, such as subducted lithosphere plates in collisional zones. In this contribution, we recapitulate 3D models of the upper mantle beneath the Alps, which developed at a collision zone of the Eurasian and African plates. Seismic tomography studies indicate a leading role of the rigid mantle lithosphere that functioned as a major stress guide during the plate collisions. Interactions of the European lithosphere with several micro-plates in the south resulted in an arcuate shape of this mountain range on the surface and in a complicated geometry of the Alpine subductions in the mantle. Early models with one bended lithosphere root have been replaced with more advanced models showing two separate lithosphere roots beneath the Western and Eastern Alps (Babuska et al., Tectonophysics 1990; Lippitsch et al., JGR 2003). The standard isotropic velocity tomography, based on pre-AlpArray data (the currently performed passive seismic experiment in the Alps and surroundings) images the south-eastward dipping curved slab of the Eurasian lithosphere in the Western Alps. On the contrary, beneath the Eastern Alps the results indicate a very steep northward dipping root that resulted from the collision of the European plate with the Adriatic microplate. Dando et al. (2011) interpret high-velocity heterogeneities at the bottom of their regional tomographic model as a graveyard of old subducted lithospheres. High density of stations, large amount of rays and dense ray-coverage of the volume studied are not the only essential pre-requisites for reliable tomography results. A compromise between the amount of pre-processed data and the high-quality of the tomography input (travel-time residuals) is of the high importance as well. For the first time, the existence of two separate roots beneath the Alps has been revealed from carefully pre

  8. Effects of grain size evolution on mantle dynamics

    Schulz, Falko; Tosi, Nicola; Plesa, Ana-Catalina; Breuer, Doris


    The rheology of planetary mantle materials is strongly dependent on temperature, pressure, strain-rate, and grain size. In particular, the rheology of olivine, the most abundant mineral of the Earth's upper mantle, has been extensively studied in the laboratory (e.g., Karato and Wu, 1993; Hirth and Kohlstedt, 2003). Two main mechanisms control olivine's deformation: dislocation and diffusion creep. While the former implies a power-law dependence of the viscosity on the strain-rate that leads to a non-Newtonian behaviour, the latter is sensitively dependent on the grain size. The dynamics of planetary interiors is locally controlled by the deformation mechanism that delivers the lowest viscosity. Models of the dynamics and evolution of planetary mantles should thus be capable to self-consistently distinguish which of the two mechanisms dominates at given conditions of temperature, pressure, strain-rate and grain size. As the grain size can affect the viscosity associated with diffusion creep by several orders of magnitude, it can strongly influence the dominant deformation mechanism. The vast majority of numerical, global-scale models of mantle convection, however, are based on the use of a linear diffusion-creep rheology with constant grain-size. Nevertheless, in recent studies, a new equation has been proposed to properly model the time-dependent evolution of the grain size (Austin and Evens, 2007; Rozel et al., 2010). We implemented this equation in our mantle convection code Gaia (Hüttig et al., 2013). In the framework of simple models of stagnant lid convection, we compared simulations based on the fully time-dependent equation of grain-size evolution with simulations based on its steady-state version. In addition, we tested a number of different parameters in order to identify those that affects the grain size to the first order and, in turn, control the conditions at which mantle deformation is dominated by diffusion or dislocation creep. References Austin

  9. Mantle xenoliths from Central Vietnam: evidence for at least Meso-Proterozoic formation of the lithospheric mantle

    Proßegger, Peter; Ntaflos, Theodoros; Ackerman, Lukáš; Hauzenberger, Christoph; Tran, Tuan Anh


    Intraplate Cenozoic basalts that are widely dispersed along the continental margin of East Asia belong to the Western Pacific "diffuse" igneous province. They consist mainly of alkali basalts, basanites,rarely nephelinites, which are mantle xenolith-bearing, potassic rocks and quartz tholeiites. The volcanism in this area has been attributed to the continental extension caused by the collision of India with Asia and by the subduction of the Pacific Ocean below Asia. We studied a suite of 24 mantle xenoliths from La Bang Lake, Dak Doa district and Bien Ho, Pleiku city in the Gia Province, Central Vietnam. They are predominantly spinel lherzolites (19) but spinel harburgites (3) and two garnet pyroxenites are present as well. The sizes of the xenoliths range from 5 to 40 cm in diameter with medium to coarse-grained protogranular textures. Whole rock major and trace element analyses display a wide range of compositions. The MgO concentration varies from 36.0 to 45.8 wt% whereas Al2O3 and CaO range from 0.63 to 4.36 wt% and from 0.52 to 4.21 wt% (with one sample having CaO of 6.63 wt%) respectively. Both CaO and Al2O3 positively correlate with MgO most likely indicating that the sampled rocks were derived from a common mantle source experienced variable degrees of partial melting. Mineral analyses show that the rock forming minerals are chemically homogeneous. The Fo contents of olivine vary between 89.2 and 91.2 and the Mg# of orthopyroxene and clinopyroxene range from 89 to 92 and 89 to 94 respectively. The range of Cr# for spinel is 0.06-0.26. Model calculations in both whole rock and clinopyroxenes show that lithospheric mantle underneath Central Vietnam experienced melt extractions that vary between 2-7, 12-15 and 20-30%. The majority of the primitive mantle-normalized whole rock and clinopyroxene REE patterns are parallel to each other indicating that clinopyroxene is the main repository of the trace elements. Clinopyroxenes are divided into two groups: group A

  10. Long-term cycling of mantle Pb: A trace element study of the major mantle mineral phases in abyssal peridotites

    D'Errico, M. E.; Warren, J. M.; Godard, M.; Ildefonse, B.


    Peridotites from ultraslow-spreading ridges preserve signatures of the depleted mantle, while also reflecting the fine scale compositional variability present in the mantle. Traditional analyses of these depleted rocks have focused on clinopyroxene, the main trace element host in spinel peridotites. However, key isotopic systems, such as lead and osmium, are hosted in other phases at low but significant concentration levels. The amount of lead contained within mantle mineral phases is of critical importance to understanding the long-term evolution of the Earth, because the radiogenic isotopes of lead are sensitive to past material cycling and melt-rock interaction. Sulfides have long been suggested as the main host for lead (Pb) in the mantle, but recent studies have demonstrated that Pb is not exclusively hosted in this trace phase. Therefore, the Pb contents of the major peridotite mineral phases (olivine, orthopyroxene, and clinopyroxene) need to be reassessed. Lead concentration data is available for orogenic and xenolith peridotite samples, which are typically more enriched than abyssal peridotites, but these do not provide direct information on the oceanic upper mantle. Direct measurement of Pb in abyssal peridotites has so far been limited because of its extremely low concentration (often plasma mass spectrometry (LA-ICP-MS). The LA-ICP-MS technique achieves high spatial resolution combined with detection of low elemental abundances. External precision varied from 6% to 17%, with a precision of 6% for Pb, based on 14 repeat analyses of BIR-1G standard basalt glass. Laser spot size varied from 102-163 microns, which produced a detection limit of 0.42-0.81 ppb for Pb. This study focused on abyssal peridotites from the ultra-slow spreading Gakkel and Southwest Indian Ridges (SWIR), with samples coming from segments with full spreading rates fresh samples from Gakkel. A total of five Gakkel and six SWIR peridotites were analyzed by LA-ICP-MS, with a subset of

  11. Translation domains in multiferroics

    Meier, D; Leo, N; Jungk, T.; Soergel, E.; Becker, P.; Bohaty, L.; Fiebig, M.


    Translation domains differing in the phase but not in the orientation of the corresponding order parameter are resolved in two types of multiferroics. Hexagonal (h-) YMnO$_3$ is a split-order-parameter multiferroic in which commensurate ferroelectric translation domains are resolved by piezoresponse force microscopy whereas MnWO$_4$ is a joint-order-parameter multiferroic in which incommensurate magnetic translation domains are observed by optical second harmonic generation. The pronounced ma...

  12. Frustratingly Easy Domain Adaptation

    Daumé, Hal


    We describe an approach to domain adaptation that is appropriate exactly in the case when one has enough ``target'' data to do slightly better than just using only ``source'' data. Our approach is incredibly simple, easy to implement as a preprocessing step (10 lines of Perl!) and outperforms state-of-the-art approaches on a range of datasets. Moreover, it is trivially extended to a multi-domain adaptation problem, where one has data from a variety of different domains.

  13. Staggered domain wall fermions

    Hoelbling, Christian


    We construct domain wall fermions with a staggered kernel and investigate their spectral and chiral properties numerically in the Schwinger model. In some relevant cases we see an improvement of chirality by more than an order of magnitude as compared to usual domain wall fermions. Moreover, we present first results for four-dimensional quantum chromodynamics, where we also observe significant reductions of chiral symmetry violations for staggered domain wall fermions.

  14. Mantle discontinuities beneath Izu-Bonin and the implications

    臧绍先; 周元泽; 蒋志勇


    The SdP, pdP and sdP phases are picked up with the Nth root slant stack method from the digital waveform data recorded by the networks and arrays in USA, Germany and Switzerland for the earthquakes occurring beneath Izu-Bonin and Japan Sea. The mantle discontinuities and the effects of subducting slab on the 660 km and 410 km discontinuities are studied. It is found that there are mantle discontinuities existing at the depths of 170, 220, 300, 410, 660, 850 and 1150 km. Beneath Izu-Bonin, the 410 km discontinuity is elevated, while the 660 km discontinuity is depressed; for both discontinuities, there are regionalized differences. Beneath Japan Sea, however, there is no depth variation of the 410 km discontinuity, and the 660 km discontinuity is depressed without obvious effect of the subducting slab.

  15. Lasting mantle scars lead to perennial plate tectonics.

    Heron, Philip J; Pysklywec, Russell N; Stephenson, Randell


    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a 'perennial' phenomenon.

  16. Geoelectromagnetic investigation of the earth’s crust and mantle

    Rokityansky, Igor I


    Electrical conductivity is a parameter which characterizes composition and physical state of the Earth's interior. Studies of the state equations of solids at high temperature and pressure indicate that there is a close relation be­ tween the electrical conductivity of rocks and temperature. Therefore, measurements of deep conductivity can provide knowledge of the present state and temperature of the Earth's crust and upper mantle matter. Infor­ mation about the temperature of the Earth's interior in the remote past is derived from heat flow data. Experimental investigation of water-containing rocks has revealed a pronounced increase of electrical conductivity in the temperature range D from 500 to 700 DC which may be attributed to the beginning of fractional melting. Hence, anomalies of electrical conductivity may be helpful in identitying zones of melting and dehydration. The studies of these zones are perspective in the scientific research of the mobile areas of the Earth's crust and upper mantle where t...

  17. Magnification of mantle resonance as a cause of tectonics

    Omerbashich, M


    Variance spectral analysis of superconducting gravimeter (SG) decadal data (noise inclusive) suggests conceptually that the Earth tectonogenesis could in part be based on magnification of the mantle mechanical resonance, in addition to previously hypothesized causes. Aanalogously to the atmospheric tidal forcing of global high frequency free oscillation, I propose that the Moon synodically recurring pull could likewise drive the long-periodic (12 to 120 minutes) oscillation of the Earth. To demonstrate this, I show that the daily magnitudes of mass (gravity) oscillation, as a relative measure of the Earth kinetic energy, get synodically periodic while correlating up to 0.97 with seismic energies on the day of shallow and 3 days before deep earthquakes. The forced oscillator equations for the mantle usual viscosity and the Earth springtide and grave mode periods successfully model an identical 3 days phase. Finally, whereas reports on gravest earthquakes (of around M9.5) put the maximum coseismic displacement ...

  18. Crustal Heat Production and Mantle Heat Flow in Southeast China

    胡圣标; 汪集旸


    The correlation between seismic velocity (vp) and radiogenic heat production (A) en-ables the distribution of crustal heat production to be evaluated,from which the mantle heat flow for 21seismic velocity-depth profiles located along the two continental geotraverses in Southeast China can bededuced.Several approaches have been proposed to special problems connected with the conversion ofseismic velocities into heat production in orogenic areas.The results show that the crustal heat flow inSoutheast China is quite inhomogeneous,varying between 17.8 and 46 mW·m-2,which can be attribut-ed to the complicated crustal structure related to overthrusting and overlapping in the upper crust.The re-markable regional variation in the mantle heat flow,ranging from 23.2 to 41.6 mW·m-2,correspondsto the large-scale tectonothermal evolution of the orogenic belts.

  19. Lasting mantle scars lead to perennial plate tectonics

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell


    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a `perennial' phenomenon.

  20. Consequences of an unstable chemical stratification on mantle dynamics

    Plesa, Ana-Catalina; Tosi, Nicola; Breuer, Doris


    Early in the history of terrestrial planets, the fractional crystallization of primordial magma oceans may have led to the formation of large scale chemical heterogeneities. These may have been preserved over the entire planetary evolution as suggested for Mars by the isotopic analysis of the so-called SNC meteorites. The fractional crystallization of a magma ocean leads to a chemical stratification characterized by a progressive enrichment in heavy elements from the core-mantle boundary to the surface. This results in an unstable configuration that causes the overturn of the mantle and the subsequent formation of a stable chemical layering. Assuming scaling parameters appropriate for Mars, we first performed simulations of 2D thermo-chemical convection in Cartesian geometry with the numerical code YACC [1]. We investigated systems heated either solely from below or from within by varying systematically the buoyancy ratio B, which measures the relative importance of chemical to thermal buoyancy, and the mantle rheology, by considering systems with constant, strongly temperature-dependent and plastic viscosity. We ran a large set of simulations spanning a wide parameter space in order to understand the basic physics governing the magma ocean cumulate overturn and its consequence on mantle dynamics. Moreover, we derived scaling laws that relate the time over which chemical heterogeneities can be preserved (mixing time) and the critical yield stress (maximal yield stress that allows the lithosphere to undergo brittle failure) to the buoyancy ratio. We have found that the mixing time increases exponentially with B, while the critical yield stress shows a linear dependence. We investigated then Mars' early thermo-chemical evolution using the code GAIA in a 2D cylindrical geometry [2] and assuming a detailed magma ocean crystallization sequence as obtained from geochemical modeling [3]. We used an initial composition profile adapted from [3], accounted for an exothermic

  1. Melting of MORB at core-mantle boundary

    Pradhan, Gopal K.; Fiquet, Guillaume; Siebert, Julien; Auzende, Anne-Line; Morard, Guillaume; Antonangeli, Daniele; Garbarino, Gaston


    We investigated the melting properties of natural mid-ocean ridge basalt (MORB) up to core-mantle boundary (CMB) pressures using laser-heated diamond anvil cell. Textural and chemical characterizations of quenched samples were performed by analytical transmission electron microscopy. We used in situ X-ray diffraction primarily for phase identification whereas our melting criterion based on laser power versus temperature plateau combined with textural analysis of recovered solidus and subsolidus samples is accurate and unambiguous. At CMB pressure (135 GPa), the MORB solidus temperature is 3970 (± 150) K. Quenched melt textures observed in recovered samples indicate that CaSiO3 perovskite (CaPv) is the liquidus phase in the entire pressure range up to CMB. The partial melt composition derived from the central melt pool is enriched in FeO, which suggests that such melt pockets may be gravitationally stable at the core mantle boundary.

  2. Pragmatic circuits frequency domain

    Eccles, William


    Pragmatic Circuits: Frequency Domain goes through the Laplace transform to get from the time domain to topics that include the s-plane, Bode diagrams, and the sinusoidal steady state. This second of three volumes ends with a-c power, which, although it is just a special case of the sinusoidal steady state, is an important topic with unique techniques and terminology. Pragmatic Circuits: Frequency Domain is focused on the frequency domain. In other words, time will no longer be the independent variable in our analysis. The two other volumes in the Pragmatic Circuits series include titles on DC

  3. Nazca plate subduction, mantle flow and Cordilleras formation

    Capitanio, Fabio A.


    The Nazca-South America convergence represents a unique natural laboratory to probe our understanding of subduction, mantle flow and stress coupling at Andean-type margins. Here, it is shown that the most fundamental balance of forces associated with the downgoing slab, the upper plates and the mantle can account for the Nazca plate motions, although it does not adequately explain the variations of the Cordilleran tectonics found along the ~6000 km wide margin. Using three-dimensional numerical models it is shown that trench-parallel gradients in both the driving and resisting forces are an essential component of the force balance, and necessary to reproduce the macroscopic features observed. When along-trench buoyancy variations similar to the Nazca plate's are included, the slab dips and upper plate deformations observed in the Nazca slab, in the Cordilleras and South American continent interiors can be reproduced. The models show that gradients in the resisting shear force along the trench can be as relevant, as they modulate the trench retreat to form the concave Bolivian Orocline. Pressure gradients in the mantle follow the Nazca buoyancy gradients, and effectively rearrange the flow introducing a trench-parallel component, similar to what suggested by seismic anisotropy in this area. Although they introduce only secondary variations to the primary subduction and mantle flow dynamics, the regional features of the Nazca and South American plates exert a primary control at the margin-local scale. This suggests that far-field forces, e.g. from spreading Atlantic or large-scale convection, should play a minor role in the formation of the Cordilleras.

  4. Lasting mantle scars lead to perennial plate tectonics

    Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell


    Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their p...

  5. Mantle plumes in the vicinity of subduction zones

    Mériaux, C. A.; Mériaux, A.-S.; Schellart, W. P.; Duarte, J. C.; Duarte, S. S.; Chen, Z.


    We present three-dimensional deep-mantle laboratory models of a compositional plume within the vicinity of a buoyancy-driven subducting plate with a fixed trailing edge. We modelled front plumes (in the mantle wedge), rear plumes (beneath the subducting plate) and side plumes with slab/plume systems of buoyancy flux ratio spanning a range from 2 to 100 that overlaps the ratios in nature of 0.2-100. This study shows that 1) rising side and front plumes can be dragged over thousands of kilometres into the mantle wedge, 2) flattening of rear plumes in the trench-normal direction can be initiated 700 km away from the trench, and a plume material layer of lesser density and viscosity can ultimately almost entirely underlay a retreating slab after slab/plume impact, 3) while side and rear plumes are not tilted until they reach ∼600 km depth, front plumes can be tilted at increasing depths as their plume buoyancy is lessened, and rise at a slower rate when subjected to a slab-induced downwelling, 4) rear plumes whose buoyancy flux is close to that of a slab, can retard subduction until the slab is 600 km long, and 5) slab-plume interaction can lead to a diversity of spatial plume material distributions into the mantle wedge. We discuss natural slab/plume systems of the Cascadia/Bowie-Cobb, and Nazca/San Felix-Juan Fernandez systems on the basis of our experiments and each geodynamic context and assess the influence of slab downwelling at depths for the starting plumes of Java, Coral Sea and East Solomon. Overall, this study shows how slab/plume interactions can result in a variety of geological, geophysical and geochemical signatures.

  6. New interpretation of the deep mantle structure beneath eastern China

    Ma, Pengfei; Liu, Shaofeng; Lin, Chengfa; Yao, Xiang


    Recent study of high resolution seismic tomography presents a large mass of high velocity abnormality beneath eastern China near the phase change depth, expanding more than 1600km-wide in East-west cross-section across the North China plate. This structure high is generally believed to be the subducted slab of Pacific plate beneath the Eurasia continent, while its origin and dynamic effect on the Cenozoic tectonic evolution of eastern China remain to be controversial. We developed a subduction-driven geodynamic mantle convection model that honors a set of global plate reconstruction data since 230Ma to help understand the formation and evolution of mantle structure beneath eastern China. The assimilation of plate kinematics, continuous evolving plate margin, asymmetric subduction zone, and paleo seafloor age data enables the spatial and temporal consistency between the geologic data and the mantle convection model, and guarantees the conservation of the buoyancy flux across the lithosphere and subducted slabs. Our model achieved a first order approximation between predictions and the observed data. Interestingly, the model suggests that the slab material stagnated above discontinuity didn't form until 15Ma, much later than previous expected, and the fast abnormality in the mid-mantle further west in the tomographic image is interpreted to be the remnants of the Mesozoic Izanagi subduction. Moreover, detailed analysis suggests that the accelerated subduction of Philippine Sea plate beneath Eurasia plate along the Ryukyu Trench and Nankai Trough since 15Ma may largely contribute to extending feature above 670km discontinuity. The long distance expansion of the slab material in the East-west direction may be an illusion caused by the approximate spatial perpendicularity between the cross-section and the subduction direction of the Philippine Sea plate. Our model emphasizes the necessity of the re-examination on the geophysical observation and its tectonic and

  7. Geochronological Constraints on the Exhumation and Emplacement of Subcontinental Lithospheric Mantle Peridotites in the Westernmost Mediterranean

    Garrido, Carlos J.; Hidas, Károly; Marchesi, Claudio; Varas-Reus, María Isabel; Booth-Rea, Guillermo


    Exhumation of subcontinental mantle peridotite in the Western Mediterranean has been attributed to different tectonic processes including pure extension, transpression, or alternating contractive and extensional processes related with continental subduction followed by extension, before final their contractive intracrustal emplacement. Any model trying to explain the exhumation and emplacement of subcontinental lithospheric mantle peridotites in the westernmost Mediterranean should take into account the available geochronological constraints, as well as the petrological and geochemical processes that lead to internal tectono-magmatic zoning so characteristic of the Betic and Rif orogenic peridotites. Different studies have suggested a Hercynian, Cenozoic-Mesozoic or an Alpine age for the late tectono-magmatic evolution and intra-crustal emplacement of Betic-Rif peridotites. The pervasive presence of Mesozoic U-Pb zircon ages in Ronda UHP and HP garnet pyroxenites does not support a Hercynian age for the intracrustal emplacement of the peridotite. A hyper-extended margin setting for is in good agreement with the Jurassic extensional event that pervasively affected ALKAPECA terrains (i.e. the Alboran, Kabylides, Peloritani, and Calabria domains) in the western Mediterranean due to the opening of the Piemonte-Ligurian Ocean. However, a Jurassic age and a passive margin tectonic setting do not account, among other observations, for the late Miocene thermochronological ages recorded in zircons rims (U-Pb) and garnets (Lu-Hf) in garnet pyroxenites from the Betic-Rif peridotites, the pervasive Miocene resetting of U-Pb zircon and monazite ages in the overlying Jubrique crustal section, the supra-subduction radiogenic signature of late pyroxenite intrusive dikes in the Ronda peridotite, and the arc tholeiitic affinity of late mantle-derived, gabbroic dykes intruding in the Ronda and Ojen plagioclase lherzolites. These data are more consistent with a supra

  8. Visualizing domain wall and reverse domain superconductivity.

    Iavarone, M; Moore, S A; Fedor, J; Ciocys, S T; Karapetrov, G; Pearson, J; Novosad, V; Bader, S D


    In magnetically coupled, planar ferromagnet-superconductor (F/S) hybrid structures, magnetic domain walls can be used to spatially confine the superconductivity. In contrast to a superconductor in a uniform applied magnetic field, the nucleation of the superconducting order parameter in F/S structures is governed by the inhomogeneous magnetic field distribution. The interplay between the superconductivity localized at the domain walls and far from the walls leads to effects such as re-entrant superconductivity and reverse domain superconductivity with the critical temperature depending upon the location. Here we use scanning tunnelling spectroscopy to directly image the nucleation of superconductivity at the domain wall in F/S structures realized with Co-Pd multilayers and Pb thin films. Our results demonstrate that such F/S structures are attractive model systems that offer the possibility to control the strength and the location of the superconducting nucleus by applying an external magnetic field, potentially useful to guide vortices for computing application.

  9. Mantle electrical conductivity profile of Niger delta region

    Daniel N Obiora; Francisca N Okeke; K Yumoto; Stan O Agha


    The mantle electrical conductivity-depth profile of the Niger delta region in Nigeria has been determined using solar quiet day ionospheric current (Sq).The magnetometer data obtained in 2010 from geomagnetic stations installed in Lagos by magnetic dataset (MAGDAS) in 2008 and data from magnetometers installed in some parts of Niger delta by Center for Basic Space Science, University of Nigeria, Nsukka, were employed in this study. Gauss spherical harmonic analysis (SHA) method was used to separate the internal and external field contributions to Sq current system. The result depicted that the conductivity profile rose steadily from about 0.032 S/m at a depth of 89 km to 0.041 S/m at 100 km and 0.09 S/m at 221 km. This high conductivity region agreed with the global seismic low velocity region, the asthenosphere. The conductivity profile continued increasing downward until it got to 0.157 S/m at a depth of about 373 km (close to the base of upper mantle), 0.201 S/m at 784 km and reached 0.243 S/m at a depth of 1179 km at the lower mantle.

  10. Was core formation violent enough to homogenize the early mantle?

    Cooperman, S. A.; Kaula, W. M.


    The dynamics of iron, its thermal state and its phase in the accreting Earth probably played a major role in the Earth's early thermal evolution. Plausible impact thermal histories make it possible that pure iron was molten in the accreting Earth after it was about 10% grown. Hence, iron eutectic alloys (FeS, FeO) certainly were. Additionally, the initial temperature of the core is an important constraint on the secular cooling of the early Earth and on the strength of the early geodynamo. Whether iron is solid or molten would influence geochemical equilibria in the upper and lower mantle; the mode of core formation, by spherical or near-spherical blobs, stalk-like instabilities, or something more catastrophic would influence the partitioning of siderophiles between silicate and iron phases. Early descent of iron (during accretion) favors partitioning according to low-pressure phase equilibria, whereas late descent favors higher pressure. The later core formation occurs, the greater the heat pulse, due to the strong dependence of gravitational potential energy on planetary radius. The heat may homogenize the mantle if core formation is global; otherwise, heterogeneity of iron differentiation may leave some of the pre-archean mantle unaffected. The larger the chunks of proto-core (and hence smaller surface/volume ratios) the greater the heterogeneity.

  11. Experimental evidence supports mantle partial melting in the asthenosphere

    Chantel, Julien; Manthilake, Geeth; Andrault, Denis; Novella, Davide; Yu, Tony; Wang, Yanbin


    The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts. It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions. The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals. The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics. We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the LVZ. Our measurements provide direct compressional (VP) and shear (VS) wave velocities and constrain attenuation as a function of melt fraction. Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~0.2%. In contrast, the presence of volatile elements appears necessary to explaining the extremely high VP/VS values observed in some local areas. The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere. PMID:27386548

  12. Growth and mixing dynamics of mantle wedge plumes

    Gorczyk, Weronika; Gerya, Taras V.; Connolly, James A. D.; Yuen, David A.


    Recent work suggests that hydrated partially molten thermal-chemical plumes that originate from subducted slab as a consequence of Rayleigh-Taylor instability are responsible for the heterogeneous composition of the mantle wedge. We use a two-dimensional ultrahigh-resolution numerical simulation involving 10 × 109 active markers to anticipate the detailed evolution of the internal structure of natural plumes beneath volcanic arcs in intraoceanic subduction settings. The plumes consist of partially molten hydrated peridotite, dry solid mantle, and subducted oceanic crust, which may compose as much as 12% of the plume. As plumes grow and mature these materials mix chaotically, resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for the strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges.

  13. Diffusion and infrared properties of molecules in ice mantles

    Schmitt, Bernard; Grim, Ruud; Greenberg, J. Mayo


    Within dense molecular clouds the formation of frozen icy mantles on interstellar dust grains is thought to be the result of various growth conditions. The molecules, which make up the ice mantles are probably completely mixed. To study the physical properties of such ice mixtures the experiments were performed on the evaporation processes and on the spectroscopic properties of CO, CO2, and CH4 in water rich ices. The decrease in concentration of volatile molecules in ice samples deposited at 10 K and subsequently heated is found to occur essentially in two steps. The first one, corresponding to an evaporation of part of the volatile molecules, starts at about 25 K for CO, 32 K for CH4, and 70 K for CO2. During the crystallization of H2O ice at temperatures greater than 120 K a second evaporation occurs leading to the complete disappearance of the volatile molecules in the solid phase. The main astrophysical implications of the diffusion and spectroscopic behaviors are presented. The possible effects of a heating source on the fraction of volatile molecules, such as CO trapped in grain mantles, are discussed.

  14. H2-rich interstellar grain mantles: An equilibrium description

    Dissly, Richard W.; Allen, Mark; Anicich, Vincent G.


    Experiments simulating the codeposition of molecular hydrogen and water ice on interstellar grains demonstrate that amorphous water ice at 12 K can incorporate a substantial amount of H2, up to a mole ratio of H2/H2O = 0.53. We find that the physical behavior of approximately 80% of the hydrogen can be explained satisfactorily in terms of an equilibrium population, thermodynamically governed by a wide distribution of binding site energies. Such a description predicts that gas phase accretion could lead to mole fractions of H2 in interstellar grain mantles of nearly 0.3; for the probable conditions of WL5 in the rho Ophiuchi cloud, an H2 mole fraction of between 0.05 and 0.3 is predicted, in possible agreement with the observed abundance reported by Sandford, Allamandola, & Geballe. Accretion of gas phase H2 onto grain mantles, rather than photochemical production of H2 within the ice, could be a general explanation for frozen H2 in interstellar ices. We speculate on the implications of such a composition for grain mantle chemistry and physics.

  15. The geobiological nitrogen cycle: From microbes to the mantle.

    Zerkle, A L; Mikhail, S


    Nitrogen forms an integral part of the main building blocks of life, including DNA, RNA, and proteins. N2 is the dominant gas in Earth's atmosphere, and nitrogen is stored in all of Earth's geological reservoirs, including the crust, the mantle, and the core. As such, nitrogen geochemistry is fundamental to the evolution of planet Earth and the life it supports. Despite the importance of nitrogen in the Earth system, large gaps remain in our knowledge of how the surface and deep nitrogen cycles have evolved over geologic time. Here, we discuss the current understanding (or lack thereof) for how the unique interaction of biological innovation, geodynamics, and mantle petrology has acted to regulate Earth's nitrogen cycle over geologic timescales. In particular, we explore how temporal variations in the external (biosphere and atmosphere) and internal (crust and mantle) nitrogen cycles could have regulated atmospheric pN2 . We consider three potential scenarios for the evolution of the geobiological nitrogen cycle over Earth's history: two in which atmospheric pN2 has changed unidirectionally (increased or decreased) over geologic time and one in which pN2 could have taken a dramatic deflection following the Great Oxidation Event. It is impossible to discriminate between these scenarios with the currently available models and datasets. However, we are optimistic that this problem can be solved, following a sustained, open-minded, and multidisciplinary effort between surface and deep Earth communities. © 2017 The Authors Geobiology Published by John Wiley & Sons Ltd.

  16. Experimental evidence supports mantle partial melting in the asthenosphere.

    Chantel, Julien; Manthilake, Geeth; Andrault, Denis; Novella, Davide; Yu, Tony; Wang, Yanbin


    The low-velocity zone (LVZ) is a persistent seismic feature in a broad range of geological contexts. It coincides in depth with the asthenosphere, a mantle region of lowered viscosity that may be essential to enabling plate motions. The LVZ has been proposed to originate from either partial melting or a change in the rheological properties of solid mantle minerals. The two scenarios imply drastically distinct physical and geochemical states, leading to fundamentally different conclusions on the dynamics of plate tectonics. We report in situ ultrasonic velocity measurements on a series of partially molten samples, composed of mixtures of olivine plus 0.1 to 4.0 volume % of basalt, under conditions relevant to the LVZ. Our measurements provide direct compressional (V P) and shear (V S) wave velocities and constrain attenuation as a function of melt fraction. Mantle partial melting appears to be a viable origin for the LVZ, for melt fractions as low as ~0.2%. In contrast, the presence of volatile elements appears necessary to explaining the extremely high V P/V S values observed in some local areas. The presence of melt in LVZ could play a major role in the dynamics of plate tectonics, favoring the decoupling of the plate relative to the asthenosphere.

  17. Electronic spin state of iron in lower mantle perovskite.

    Li, Jie; Struzhkin, Viktor V; Mao, Ho-Kwang; Shu, Jinfu; Hemley, Russell J; Fei, Yingwei; Mysen, Bjorn; Dera, Przemek; Prakapenka, Vitali; Shen, Guoyin


    The electronic spin state of iron in lower mantle perovskite is one of the fundamental parameters that governs the physics and chemistry of the most voluminous and massive shell in the Earth. We present experimental evidence for spin-pairing transition in aluminum-bearing silicate perovskite (Mg,Fe)(Si,Al)O(3) under the lower mantle pressures. Our results demonstrate that as pressure increases, iron in perovskite transforms gradually from the initial high-spin state toward the final low-spin state. At 100 GPa, both aluminum-free and aluminum-bearing samples exhibit a mixed spin state. The residual magnetic moment in the aluminum-bearing perovskite is significantly higher than that in its aluminum-free counterpart. The observed spin evolution with pressure can be explained by the presence of multiple iron species and the occurrence of partial spin-paring transitions in the perovskite. Pressure-induced spin-pairing transitions in the perovskite would have important bearing on the magnetic, thermoelastic, and transport properties of the lower mantle, and on the distribution of iron in the Earth's interior.

  18. Noble gases recycled into the mantle through cold subduction zones

    Smye, Andrew J.; Jackson, Colin R. M.; Konrad-Schmolke, Matthias; Hesse, Marc A.; Parman, Steve W.; Shuster, David L.; Ballentine, Chris J.


    Subduction of hydrous and carbonated oceanic lithosphere replenishes the mantle volatile inventory. Substantial uncertainties exist on the magnitudes of the recycled volatile fluxes and it is unclear whether Earth surface reservoirs are undergoing net-loss or net-gain of H2O and CO2. Here, we use noble gases as tracers for deep volatile cycling. Specifically, we construct and apply a kinetic model to estimate the effect of subduction zone metamorphism on the elemental composition of noble gases in amphibole - a common constituent of altered oceanic crust. We show that progressive dehydration of the slab leads to the extraction of noble gases, linking noble gas recycling to H2O. Noble gases are strongly fractionated within hot subduction zones, whereas minimal fractionation occurs along colder subduction geotherms. In the context of our modelling, this implies that the mantle heavy noble gas inventory is dominated by the injection of noble gases through cold subduction zones. For cold subduction zones, we estimate a present-day bulk recycling efficiency, past the depth of amphibole breakdown, of 5-35% and 60-80% for 36Ar and H2O bound within oceanic crust, respectively. Given that hotter subduction dominates over geologic history, this result highlights the importance of cooler subduction zones in regassing the mantle and in affecting the modern volatile budget of Earth's interior.

  19. The Mantle Transition Zone in Central-Eastern Greenland

    Kraft, H. A.; Thybo, H.; Vinnik, L. P.


    We present results of a Receiver Function (RF) study of the mantle transition zone (TZ) in Central-Eastern Greenland. The base of this study is data from 19 broad-band seismometers, which were temporarily installed from 2009 to 2012 in the region between Scoresbysund and Summit (~ 70º N) plus 5 permanent stations from the GLISN network. One half of these stations were installed on the ice, the other half on bedrock.Our analysis is based on low frequency PRF, which use the difference in travel times between converted and not converted phasesat discontinuities. Most of our RFs show clear signals for P410s and P660s. Their delay times suggest a surprisingly thin mantle transition zone for most parts of the study area in comparison to standard Earth models, and much thinner than below other continental shield and platform areas. This could indicate a fairly recent heating of the TZ. Another observation is an M-shaped signal around the 410 km - discontinuity at some of the stations mainly in the western part around Summit. This observation is contrary to the expected simple negative signal. It may indicate a thin low velocity layer between 410 km and 520 km, as it has previously been observed in several settings based on converted waves and also explosion data. Most of our stations show positive travel time anomalies for the upper mantle, which again is contrary to simple models of old continental shields.

  20. Melting experiments on peridotite to lowermost mantle conditions

    Tateno, Shigehiko; Hirose, Kei; Ohishi, Yasuo


    Melting experiments on a pyrolitic mantle material were performed in a pressure range from 34 to 179 GPa based on laser-heated diamond-anvil cell (DAC) techniques. The textural and chemical characterizations of quenched samples were made by using field-emission-type electron microprobe (FE-EPMA). Melts formed by 46 to 77 wt.% partial melting in this study were ultrabasic in composition and became more depleted in SiO2 and more enriched in FeO with increasing pressure. Melting textures indicate that the liquidus phase changed from ferropericlase to MgSiO3-rich perovskite at least above 34 GPa and further to post-perovskite. The first phase to melt (disappear) changed from CaSiO3 perovskite to (Mg,Fe)O ferropericlase between 68 and 82 GPa. The stability of ferropericlase above solidus temperature shrinks with increasing pressure (melting last below 34 GPa and first 82 GPa), resulting in higher (MgO + FeO)/SiO2 ratio in partial melt at higher pressure. Additionally, the Fe-Mg distribution coefficients (KD) between perovskite/post-perovskite and melt decreased considerably with increasing pressure, leading to strong Fe-enrichment in partial melts. It supports dense partial melts in a deep lower mantle, which migrate downward to the core mantle boundary (CMB).

  1. Isotope geochemistry of boron in mantle rocks, tektites and meteorites

    Chaussidon, M. [Centre National de la Recherche Scientifique (CNRS), 54 - Nancy (France). Centre de Recherches Petrographiques et Geochimiques


    Recent ion microprobe studies of fresh oceanic basalt glasses and chondrules from primitive meteorites give an overview of the distribution of boron isotopes in the mantle and in extra-terrestrial rocks. After removal of secondary boron isotope variations due to interactions between mantle melts and the oceanic crust, the primitive mantle is found to have a constant {delta}{sup 11}B value of -10 {+-} 2 per mill, similar to that of the bulk continental crust. In contrast, large isotopic variations between -50 and +40 per mill are present at the micron scale in meteoritic chondrules which are among the most primitive objects of the solar system. These isotopic variations imply that a significant part of the boron of the solar system was synthesized in the presolar cloud, likely by spallation reactions between lo-energy cosmic rays and nebular hydrogen. These heterogeneities were partly preserved in chondrules which formed early in the evolution of the solar system but are not observed for the silicate Earth implying an efficient mixing just before or during the accretion of the Earth. (authors). 74 refs., 5 figs., 2 tabs.

  2. Effect of NaCl on texture modification of cuttlefish mantle (Sepia brevimana

    Chakree Tongraung


    Full Text Available The mechanical properties of cleaned cuttlefish mantle (Sepia brevimana before and after spinning in cold salt solution were characterized by tensile and shear test. The objective was to relate the physical changes of the cuttlefish mantle to the composition and microstructure changes mediated by spinning in 5 % (w/v NaCl solution at 0-(-50C for 10 min. Textural difference between outer and inner surface of the cleaned mantle was revealed by the tensile force applied to transverse direction of the longitudinal axis of the mantle. Shear test was found suitable to highlight textural modification due to the spinning. It was found that the operation increased the mantle total weight and caused mantle curvature and hardening. These changes were concomitant with an increase of the mantle moisture and salt content at specific layers in the mantle. Microstructure of the mantle obtained by scanning electron microscopy (SEM showed both expanded and packed fibers depending on their position. The results suggested that modification of the mantle texture due to spinning in the cold NaCl solution was a complex process coupled with changes in chemical composition and microstructure.

  3. Platinum-group elements for the mantle peridotites in the Dazhuka ophiolite, Tibet, China


    The total PGE amounts of mantle peridotites in the Dazhuka ophiolite, Tibet, are 28.37-50.67 ng/g, slightly higher than those of mantle peridotites in the primitive mantle, and typical ophiolites in the world, and the Alps-type mantle peridotites. The PGE distribution patterns in the Dazhuka mantle peridotites are also different from those of the mantle peridotites of partial melting relict origin. The Dazhuka mantle peridotites have relatively high total PGE amounts and are enriched in Pt, Pd, and Ru. Their PGE distribution patterns belong to the positively inclined- or swallow-type patterns. The PGE distribution patterns in the mantle peridotites of partial melting relict origin belong to the negative-slope patterns or flat patterns. This reflects the unique features of the upper mantle in this region. Relative enrichment in Pt and Pd, as well as in the incompatible ele-ments Cu, Au, Cs, Rb, Ba, Th, U and LREE, indicates that the partial melting-derived relict mantle peridotites in the Dazhuka ophiolite had experienced intensive permeating and mixing processes of the melt and fluid both containing abundant incompatible elements.

  4. Tracing Mantle Plumes: Quantifying their Morphology and Behavior from Seismic Tomography

    O'Farrell, K. A.; Eakin, C. M.; Jones, T. D.; Garcia, E.; Robson, A.; Mittal, T.; Lithgow-Bertelloni, C. R.; Jackson, M. G.; Lekic, V.; Rudolph, M. L.


    Hotspot volcanism provides a direct link between the deep mantle and the surface, but the location, depth and source of the mantle plumes that feed hotspots are highly controversial. In order to address this issue it is important to understand the journey along which plumes have travelled through the mantle. The general behavior of plumes in the mantle also has the potential to tell us about the vigor of mantle convection, net rotation of the mantle, the role of thermal versus chemical anomalies, and important bulk physical properties of the mantle such as the viscosity profile. To address these questions we developed an algorithm to trace plume-like features in shear-wave (Vs) seismic tomographic models based on picking local minima in velocity and searching for continuous features with depth. We apply this method to several of the latest tomographic models and can recover 30 or more continuous plume conduits that are >750 km long. Around half of these can be associated with a known hotspot at the surface. We study the morphology of these plume chains and find that the largest lateral deflections occur near the base of the lower mantle and in the upper mantle. We analyze the preferred orientation of the plume deflections and their gradient to infer large scale mantle flow patterns and the depth of viscosity contrasts in the mantle respectively. We also retrieve Vs profiles for our traced plumes and compare with velocity profiles predicted for different mantle adiabat temperatures. We use this to constrain the thermal anomaly associated with these plumes. This thermal anomaly is then converted to a density anomaly and an upwelling velocity is derived. We compare this to buoyancy fluxes calculated at the surface and use this in conjunction with our measured plume tilts/deflections to estimate the strength of the "mantle wind".

  5. Oceanic mantle alteration in the trench-outer rise region of the Japan trench

    Fujie, G.; Takahashi, T.; Kodaira, S.; Obana, K.; Yamada, T.


    Dehydration processes and the expulsion of the water from the subducting oceanic plate affect various subduction-zone processes, including arc volcanism and generation of earthquakes and tremor. Since the amount of chemically bound water in the oceanic plate is highest in serpentinized mantle, it is important to reveal the degree of oceanic mantle serpentinization prior to subduction.In 2009 and 2013, to reveal the structural evolution of the incoming oceanic plate prior to subduction, we conducted wide-angle seismic structural surveys in the trench-outer rise region of the Japan trench. We found P-wave velocity (Vp) within the oceanic crust and mantle gradually decreases toward the trench axis, especially beneath the well-developed horst and grabens. Generally, reduction of Vp suggests two possibilities; one is a fracturing (dry mechanism) and the other is fracturing and water penetration (wet mechanism). The Vp/Vs ratio is a key to distinguish these two possibilities. Using P-to-S converted phases, we successfully modeled Vs within the oceanic crust by the travel-time inversion, and we found the Vp/Vs ratio within the oceanic crust gradually increases toward the trench, suggesting the water infiltration into the oceanic crust. However, it is not straightforward to determine Vs within the oceanic mantle because signal-to-noise ratio of S-wave mantle refraction was too poor to pick arrival times. Therefore, we calculated S-wave mantle refractions by assuming wide variety of Vp/Vs ratio within the oceanic mantle and compared with the observed horizontal data. Although S-wave mantle refraction was observed at only limited number of OBSs, we found that Vp/Vs ratio within the oceanic mantle did not change even in the area where mantle Vp become lower. This implies that the mantle Vp reduction in our seismic profile is mainly governed by the "dry mechanism" or mantle hydration might be confined in only topmost mantle.

  6. The enterprise engineering domain

    De Vries, M


    Full Text Available representation of the EE domain within the emerging EE discipline. We used a questionnaire to gather the views of EE and enterprise architecture (EA) researchers and practitioners on the EE domain. The main contributions of this article include: (1...

  7. Domain wall filters

    Bär, O; Neuberger, H; Witzel, O; Baer, Oliver; Narayanan, Rajamani; Neuberger, Herbert; Witzel, Oliver


    We propose using the extra dimension separating the domain walls carrying lattice quarks of opposite handedness to gradually filter out the ultraviolet fluctuations of the gauge fields that are felt by the fermionic excitations living in the bulk. This generalization of the homogeneous domain wall construction has some theoretical features that seem nontrivial.

  8. Domain Walls on Singularities

    Halyo, Edi


    We describe domain walls that live on $A_2$ and $A_3$ singularities. The walls are BPS if the singularity is resolved and non--BPS if it is deformed and fibered. We show that these domain walls may interpolate between vacua that support monopoles and/or vortices.

  9. Domains of Learning.

    Gagne, Robert M.

    In planning educational research, recognition needs to be made of five domains of learning: (1) motor skills, (2) verbal information, (3) intellectual skills, (4) cognitive strategies, and (5) attitudes. In being cognizant of these domains, the researcher is able to distinguish the parts of a content area which are subject to different…

  10. A Domain Analysis Bibliography


    Bauhaus , a prototype CASE workstation for D-SAPS development. [ARAN88A] Guillermo F. Arango. Domain Engineering for Software Reuse. PhD thesis...34 VITA90B: Domain Analysis within the ISEC Rapid Center 48 CMU/SEI-90-SR-3 Appendix III Alphabetical by Organization/Project BAUHAUS * ALLE87A

  11. Illuminating the electrical conductivity of the lowermost mantle from below

    Jault, Dominique


    The magnetic field that originates in the earth's core is transformed across the electrically conducting mantle before being observed, at the earth's surface or above. Assuming that the conductivity depends only on radius, it has been customary to treat the mantle as a linear time-invariant filter for the core magnetic field, with properties (as a function of the frequency ω) specified by the transfer function Γ(ω). An high-frequency approximation to Γ(ω), which is derived from a three terms WKBJ expansion with ω-1/2 as small parameter, is found here to reproduce adequately, for low harmonic degrees and/or thin conducting layers, the exact solution, which is evaluated numerically. It is contrasted with the low-frequency estimation of Γ, which consists in a perturbation procedure and in writing Γ(ω) as a series in powers of ω (ω → 0). The low-frequency theory is applied to the magnetic variations produced by the geostrophic core flows with about 6 yr period as the phase of these flows is independently determined from their effect on the length of the day. Apart from that, the low-frequency approximation overestimates the screening by the mantle of high-frequency signals, especially the low harmonic degree ones. In practice, the attenuating factor defined from the O(ω2) term in the expansion of Γ as ω → 0 cannot be retrieved from analyses of geomagnetic time-series. Application of the mantle filter theory hinges on our knowledge about the time spectrum of the magnetic field at the core surface. The low-frequency theory had been previously applied to observatory series on the assumption that geomagnetic jerks occurring in the core are rare and isolated events. Rather than following up these earlier studies, I note that the spectral density function for the second time derivative of the main magnetic field coefficients is approximately independent of ω in a frequency range for which the mantle has undoubtedly negligible influence. In the absence of

  12. Phase transition in aluminous silica in the lowermost mantle

    Tronnes, R. G.; Andrault, D.; Konopkova, Z.; Morgenroth, W.; Liermann, H.


    Lower mantle basaltic lithologies contain 35-40% Mg-perovskite, 20-30% Ca-perovskite, 15-25% Al-rich phases (NAL and Ca-ferrite phases) and 15-20% silica-dominated phases. The Fe-rich Mg-perovskite makes basaltic material denser than peridotite throughout the lower mantle below 720 km depth, with important implications for mantle dynamics. Partial separation of subducted basaltic crust from depleted lithosphere might occur within the strongly heterogeneous D" zone. Further details on phase transitions and equation of states for the various minerals, however, are needed for more complete insights. The silica-dominated phases have considerable solubility of alumina [1]. We investigated silica with 4 and 6 wt% alumina to 120 GPa, using LH-DAC at the Extreme Conditions Beamline (P02.2) at PETRA-III, DESY. Powdered glass mixed with 10-15 wt% Pt-powder was compressed and heated in NaCl pressure media in Re-gaskets. The transition from the CaCl2-structured phase to seifertite (alpha-PbO2-structure) occurs at about 116 GPa at 2500 K. This is intermediate between the transition pressures of about 122 GPa and 100-113 GPa reported for similar temperatures for pure SiO2 [2] and a basalt composition [1], respectively. The CaCl2-structured silica phase crystallized along with seifertite, consistent with a binary phase loop trending towards lower pressure with increasing Al-content. The presence of an Al-rich Ca-ferrite phase (near the MgAl2O4-NaAlSiO4-join) in basaltic material indicates that the Al-solubility limits for the silica-dominated phases in basaltic compositions may be similar to those in the binary system SiO2-AlO1.5. Based on the X-ray pattern refinement, our samples show no significant volume change across the transition. Even so, the transition could be associated with a significant density change if the Al substitution mechanisms are different in CaCl2-structured phase and seifertite. The most likely situation is that Al-substitution occurs via O-vacancies in the

  13. Nature of the mantle roots beneath the North American craton: mantle xenolith evidence from Somerset Island kimberlites

    Schmidberger, S. S.; Francis, D.


    The recently discovered Nikos kimberlite on Somerset Island, in the Canadian Arctic, hosts an unusually well preserved suite of mantle xenoliths dominated by garnet-peridotite (lherzolite, harzburgite, dunite) showing coarse and porphyroclastic textures, with minor garnet-pyroxenite. The whole rock and mineral data for 54 Nikos xenoliths indicate a highly refractory underlying mantle with high olivine forsterite contents (ave. Fo=92.3) and moderate to high olivine abundances (ave. 80 wt.%). These characteristics are similar to those reported for peridotites from the Archean Kaapvaal and Siberian cratons (ave. olivine Fo=92.5), but are clearly distinct from the trend defined by oceanic peridotites and mantle xenoliths in alkaline basalts and kimberlites from post-Archean continental terranes (ave. olivine Fo=91.0). The Nikos xenoliths yield pressures and temperatures of last equilibration between 20 and 55 kb and 650 and 1300°C, and a number of the peridotite nodules appear to have equilibrated in the diamond stability field. The pressure and temperature data define a conductive paleogeotherm corresponding to a surface heat flow of 44 mW/m 2. Paleogeotherms based on xenolith data from the central Slave province of the Canadian craton require a lower surface heat flow (˜40 mW/m 2) indicating a cooler geothermal regime than that beneath the Canadian Arctic. A large number of kimberlite-hosted peridotites from the Kaapvaal craton in South Africa and parts of the Siberian craton are characterized by high orthopyroxene contents (ave. Kaapvaal 32 wt.%, Siberia 20 wt.%). The calculated modal mineral assemblages for the Nikos peridotites show moderate to low contents of orthopyroxene (ave. 12 wt.%), indicating that the orthopyroxene-rich mineralogy characteristic of the Kaapvaal and Siberian cratons is not a feature of the cratonic upper mantle beneath Somerset Island.

  14. Analysis of the antibody repertoire of patients with mantle cell lymphoma directed against mantle cell lymphoma-associated antigens

    Zwick, Carsten; Preuss, Klaus-Dieter; Kubuschok, Boris; Held, Gerhard; Ahlgrimm, Manfred; Bittenbring, Joerg; Schubert, Joerg; Neumann, Frank; Pfreundschuh, Michael


    Abstract Treatment results of mantle cell lymphomas (MCL) are not satisfactory and novel therapeutic approaches are warranted. Because ?shared? tumor antigens like the group of cancer testis antigens are only rarely expressed in MCL, we applied serological analysis of antigens using recombinant expression cloning (SEREX) to a complementary DNA library derived from five cases of MCL using the sera of eight patients with MCL in order to define MCL-associated antigens that are immunog...

  15. Subduction—Modified Subcontinental Mantle in South China:Trace Element and Isotope Evidence in Basalts from Hainan Island

    张明; 解广轰; 等


    Cenozoic lavas from Hainan Island,South China,comprise quartz tholeiite,olivine tholeiite,alkali basalt,and basanite and form a continuous,tholeiite-dominated,compositional spectrum.Highly incompatible elements and their relationships with isotopes in these lavas are shown to be useful in evaluating mantle-source composition,whereas modeling suggests that ratios of elements with bulk partition coefficients significantly larger than those of Nb and Ta may be sensitive to partial melting.Th/Ta and La/Nb ratios of alkali basalts are lower than those of tholeiites,and they are all lower than those of the primitive mantle,These ratios correlate positively with 207Pb/204Pb and 87Sr/86Sr ratios.Such relationships can be explained by mixing of depleted and enriched source components.A depleted component is indicated by alkali basalt compositions and is similar to some depleted OIB (PREMA).The enriched component,similar to sediment compositions,is indicated by tholeiites with high LILE/HFSE,207Pb/204Pb,and 87Sr/86Sr ratios.In general,basalts from Hainan and the South China Basin(SCB)share common geochemical characters.e.g.high Rb/Sr,Th/Ta,207Pb/206Pb,and low Ba/Th ratios.Such a geochemical trend is comparable to that of EMII-type OIB and best explained as the result of subduction.Occurrence of these characteristics in both continental Hainan basalts and SCB seamout basalts indicates the presence of a South China geochemical domain that exists in the mantle region below the lithosphere.

  16. Thrusting between exhumed mantle blocks at the Gorringe Bank (SW Iberian margin): Evidence from combined seismic and gravity modeling

    Sallarès, V.; Martinez-Loriente, S.; Prada, M.; Gailler, A.; Gutscher, M.-A.; Bartolome, R.; Gracia, E.


    The Gorringe Bank is a massive seamount located offshore the SW Iberian margin that displays one of the largest gravity anomalies on Earth's oceans. To determine its deep seismic structure, a wide-angle seismic transect with OBS/H crossing it from the Tagus to Horseshoe Abyssal plains, was acquired in 2008. The corresponding velocity model, obtained by joint refraction and reflection travel-time inversion, displays a variably-thick sedimentary layer on top of a basement showing a strong vertical velocity gradient and no evidence for a crust-mantle boundary, not only in the Gorringe Bank but also in the adjacent segments of the deep oceanic basins. The seismic structure closely resembles that of exhumed mantle sections described along the Western Iberian margin and largely differs from that of either oceanic or extended continental crust. A velocity-derived density model assuming that the basement is made of serpentinized peridotite matches well the observed gravity anomaly, showing a basement with a variable degree of serpentinization, decreasing from ~90 % at the seafloor to ~20 % at 10 km deep. Our preferred interpretation is that the Gorringe Bank was initially the central segment of an exhumed mantle band that included also the present-day Eastern Tagus and Western Horseshoe basins. This band, which constitutes the southernmost and oldest section of the Western Iberia oceanic domain, was probably exhumed in the Earliest Cretaceous, during the onset of the North Atlantic opening. During the WNW-ESE Neogene compression, the westernmost Horseshoe basin was thrust on top of the easternmost Tagus basin, uplifting the Gorringe Bank.

  17. Lead and neodymium isotopic results from metabasalts of the Haveri Formation, southern Finland: evidence for Palaeoproterozoic enriched mantle

    Vaasjoki, M.


    Full Text Available Tholeiitic metabasalts and coexisting sulphides have been analysed for their Pb and Nd isotopic compositions from the Proterozoic Haveri Formation, which forms the basal unit of the Tampere Schist Belt in southern Finland. Ten whole rock samples analysed for Pb isotopes form a sublinear array which yields rather uncertain age estimates in the 1900-2000 Ma range and lies on the 207Pb/204Pb vs. 206Pb/204Pb diagram well below the average global lead evolution curve. The initial lead isotopic composition inferred from the whole rock data and measured on chalcopyrite is the least radiogenic obtained from the Svecofennian domain, and precludes involvement of old upper crustal material in basalt genesis. This together with the geochemical composition and initial eNd (1900 of +0.5±0.6 suggest that the Haveri mafic metavolcanic rocks were not derived from convective MORB-type mantle. The source was rather a mantle, which had been enriched in LREE for a considerable time period. Some chalcopyrite trace leads plot close to the whole rock array while others lie above it. This is interpreted as indicating two distinct mineralisation processes. The primary and major process involved lead which was cogenetic with the basalts, while the second mineralising fluid introduced radiogenic (high 207Pb upper crustal lead scavenged from the adjacent sedimentary rocks. The least radiogenic leads at Haveri and in the Outokumpu ophiolite complex some 300 km NE are similar and the two occurrences can be coeval. The preservation of original mantle material at Haveri may be interpreted as suggesting that continental crust had formed in the Tampere area 1900-2000 Ma ago.

  18. Ca. 2.7 Ga ferropicritic magmatism: A record of Fe-rich heterogeneities during Neoarchean global mantle melting

    Milidragovic, Dejan; Francis, Don


    Although terrestrial picritic magmas with FeOTOT ⩾13 wt.% are rare in the geological record, they were relatively common ca. 2.7 Ga during the Neoarchean episode of enhanced global growth of continental crust. Recent evidence that ferropicritic underplating played an important role in the ca. 2.74-2.70 Ga reworking of the Ungava craton provides the impetus for a comparison of ca. 2.7 Ga ferropicrite occurrences in the global Neoarchean magmatic record. In addition to the Fe-rich plutons of the Ungava craton, volumetrically minor ferropicritic flows, pyroclastic deposits, and intrusive rocks form parts of the Neoarchean greenstone belt stratigraphy of the Abitibi, Wawa, Wabigoon and Vermillion domains of the southern and western Superior Province. Neoarchean ferropicritic rocks also occur on five other Archean cratons: West Churchill, Slave, Yilgarn, Kaapvaal, and Karelia; suggesting that ca. 2.7 Ga Fe-rich magmatism was globally widespread. Neoarchean ferropicrites form two distinct groups in terms of their trace element geochemistry. Alkaline ferropicrites have fractionated REE profiles and show no systematic HFSE anomalies, broadly resembling the trace element character of modern-day ocean island basalt (OIB) magmas. Magmas parental to ca. 2.7 Ga alkaline ferropicrites also had high Nb/YPM (>2), low Al2O3/TiO2 (SNC) and howardite-eucrite-diogenite (HED) differentiated meteorites suggests, however, that the Fe-rich mantle may originate from the infall of Fe-rich chondritic meteorites. The occurrence of ca. 2.7 Ga Fe-rich rocks on at least six cratons that are commonly coeval with the more ubiquitous komatiites and Mg-tholeiites is consistent with the existence of heterogeneous Fe-rich "plums" throughout the Neoarchean mantle. The paucity of ferropicrites in the post-2.7 Ga geological record suggests that majority of these Fe-rich plums have been melted out during the global Neoarchean melting of the mantle.

  19. Lithospheric Mantle heterogeneities beneath northern Santa Cruz province, Argentina

    Mundl, Andrea; Ntaflos, Theodoros; Bjerg, Ernesto


    Mantle xenoliths from Don Camilo, an area located on the North margin of the Deseado Masiff in Patagonia, comprise spinel bearing lherzolites, harburgites and dunites, wehrlites, clinopyroxenites and gabbros. The most common rock type in our collection is spinel-lherzolite followed by dunites. Harzurgites, wehrlites and gabbros are less widespread. Spinel-lherzolites and harzburgites have protogranular textures whereas dunites have equigranular to equigranular tabular textures. There are two kinds of dunites: mantle dunites and cumulate dunites. The olivine mg# in the mantle dunites vary within a narrow range, from 90.5 to 91.5 and the NiO content from 0.39 to 0.42 wt%, whereas in the cumulate dunites the mg# ranges from 87 to 90.5 and the NiO content from 0.22 to 0.40 wt%. Both types of dunites contain fine grained interstitial diopside. Hydrous phases, besides one sample that contains amphibole, were so far not found. The spinel peridotites have whole rock REE abundances depleted in LREE [(La/Yb)N=0.34-0.85)] and the dunitesare LREE enriched [(La/Yb)N=3.49]. LA-ICP-MS analyses of cpx show that a number of the studied spinel peridotite xenoliths experienced cryptic metasomatism. Three groups of xenoliths have been recognized according to REE and other incompatible trace element patterns in cpx: group I has depleted LREE abundances, group II is highly enriched in LREE (La=20-30 x C1) and group 3 has moderate LREE enrichments. The core of some clinopyroxenes in group II has depleted LREE similar to those in group I, apparently representing relictic cores not affected by metasomatism. In addition the metasomatized clinopyroxenes are significantly enriched in Sr, Th and U. Evidently, the metasomatic agent was a H2O-rich fluid (high LREE, Sr, Th and U). Clinopyroxene Sr and Nd isotopic ratios vary largely from 0.702671 to 0.705788 and from 0.51229 to 0.513251 respectively. Mantle and cumulate dunites have experienced modal metasomatism. In both types of dunites the

  20. Constraints from Water on Mantle Melting and Slab Fluid Composition

    Plank, T.; Wade, J.


    Water drives mantle melting and fluid migration in subduction zones, but most models for these phenomena have been developed without constraints from water measurements in arc magmas. For example, the Central American volcanic arc (CAVA) records systematic variations in La/Yb, Ba/La and d18O, and these proxies have been used to predict the extent of mantle melting during decompression [1] and water-addition [2]. Here we use water concentrations in olivine-hosted melt inclusions from arc tephra, along with estimates derived from a clinopyroxene hygrometer [3], to test different models for mantle melting and slab fluid composition along the CAVA (from Nicaragua to Costa Rica). We use Ti as a proxy for mantle melt fraction (F) and invert H2O concentrations in CAVA magmas to obtain those in the mantle source (H2Oo), as in [4]. The relationship between F and H2Oo is nominally linear for Costa Rica mantle, with wet melting productivity dF/dH2O = 30 (wt%/wt%), higher than that used in [2], but consistent with experimentally-determined and MELTS-calculated productivity at 50 degrees above the dry solidus. This predicts mantle temperature beneath Costa Rica of at least 1350°C, and allows for a small (1-2% F) decompression-melting contribution, relative to the wet melting contribution (8-20% F). The percent of wet melting correlates locally with Ba/La, but not regionally, and so the use of Ba/La as a wet melting proxy [1] should be limited to single volcanoes or clusters. The water content of the CAVA melting region varies from 2500-9000 ppm H2O but does not decrease monotonically from Nicaragua to Costa Rica as does Ba/La. The relationship between H2Oo and Ba/La is thus complex, and requires a large along-strike decrease in Ba/La and H2O/La in the slab fluids towards the southeast. Such variation appears to be driven largely by La concentration, reflecting more dilute fluids (higher H2O/La) beneath Nicaragua and more solute-rich fluids (e.g., sediment melts with high La/ H

  1. Origin of the Luobusa diamond-bearing peridotites from the sub-arc mantle

    Liu, Chuanzhou; Zhang, Chang; Wu, Fuyuang; Chung, Sunlin


    Ophiolites are the remnants of ancient oceanic lithosphere that were emplaced onto continental margins. Ophiolites along the E-W trending Yarlung-Tsangpo Suture (YTS), which separates the Indian plate from the Eurasian plate, have been regarded as relics of the Neo-Tethys Ocean. The Luobusa ophiolite outcrops at the eastern YTS and mainly consists of harzburgites and dunites that have been intruded by gabbroic/diabase dykes at ca 130 Ma (Zhang et al., 2015). Basaltic lavas are rarely outcropped, and volumetrically minor (ocean ridge and subsequently reacted with boninitic magmas in subduction zone, which gave rise to podifiorm chromitites (Zhou et al., 1996). However, such a shallow depth origin fails to explain the occurrence of diamond and other ultra-high pressure (UHP) minerals in both peridotites and chromitites (Yang et al., 2007, 2014). A mantle plume origin has been proposed for the Luobusa ophiolite to explain the UHP minerals. However, this model is not reconciled with the occurrence of low-pressure crustal minerals in both chromitites and peridotites (Robinson et al., 2015). Here we report whole-rock Re-Os isotope data, which suggest that most Luobusa peridotites have subjected to ancient melting events older than 1.9 billion years. High contents of heavy rare earth elements in clinopyroxenes support the occurrence of ancient melting in garnet stability field. Hf-Nd isotopes of clinopyroxenes, which yield young model ages as 110 Ma, with one showing the lowest ɛNd(T) value of -3, do not preserve the signatures of ancient melting but record metasomatism by subduction-related agents. Consequently, we argue that protoliths of the Luobusa peridotites originated from ancient domains in the transition zone and, together with diamond-bearing chromitites, were accreted through a plume activity (Yang et al., 2014) up to the lithospheric mantle beneath the Lhasa terrane, where they have been metasomatized by Neo-Tethyan subduction processes. This sub

  2. Long Wavelenth Subsidence of Western Europe during Late Eocene-Oligocene (38-23 Ma): Mantle Dynamic Effect?

    Guillocheau, Francois; Robin, Cécile; Bessin, Paul


    Western Europe (France, southern Britain, southern Belgium, western Germany) is subsiding during Late Eocene to Oligocene (38-23 Ma) as suggested by the growth of numerous small sedimentary basins mainly filled by lacustrine deposits with some brackish to marine deposits. This large-scale subsidence is coeval with the early stage of the so-called Oligocene rifts (in fact Late Bartonian to Rupelian): Lower Rhinegraben, Bresse, Limagnes. The subsiding domain extends from Cornwall to the Rhine Graben including the Armorican Massif, the southern Paris Basin, the northern Aquitaine Basin, the French Central Massif, the Ardennes-Eifel… This subsidence occurred at a period of global sea level fall and then an eustatic component cannot explain (1) the accommodation space creation and (2) the marine floding with a paroxysm during Early Oligocene times (Armorican Massif, ?Ardennes, French Massif central). This marine flooding also indicate that the relief of the Hercynian basement was less elevated and smoother than today. Some of those small "basins" were interpreted as little rifts, but new mapping (e.g. Puy-en-Velay or Forez Plain in the French Massif central) or new geophysical data (e.g. Rennes Basin in the Armorican massif) suggest that no faults control those basins or that they result from post-depositional collapses. This long wavelength subsidence is at the scale of the mantle dynamic. Possible mantle mechanisms and the relationships with the "Oligocene" rifts and the North Sea inversion will be discussed.

  3. Density heterogeneity of the North American upper mantle from satellite gravity and a regional crustal model

    Herceg, Matija; Artemieva, Irina; Thybo, Hans


    and by introducing variations into the crustal structure which corresponds to the uncertainty of its resolution by highquality and low-quality seismic models. We examine the propagation of these uncertainties into determinations of lithospheric mantle density. Given a relatively small range of expected density......We present a regional model for the density structure of the North American upper mantle. The residual mantle gravity anomalies are based on gravity data derived from the GOCE geopotential models with crustal correction to the gravity field being calculated from a regional crustal model. We analyze...... how uncertainties and errors in the crustal model propagate from crustal densities to mantle residual gravity anomalies and the density model of the upper mantle. Uncertainties in the residual upper (lithospheric) mantle gravity anomalies result from several sources: (i) uncertainties in the velocity-density...

  4. A Study on the Ore-forming Effect of Mantle-derived Fluid

    Meng Qingqiang; Wu Jianfeng; Zhang Liuping


    Based on summarizing of the effect of mantle-derived fluid on the formation of ores, especially on gold ore,and with the latest investigations, such as the formation of ore from the action of shallow-deep fluid, the transportation effect of the thermal energy by mantle-derived fluid, this paper mainly aims at the effect of mantle-derived fluid on the generation of hydrocarbons. With the proof from geochemistry and fluid inclusion, it was suggested that the mantle-derived fluid not only supplied source materials for hydrocarbons, but also supplied essential energy and matter necessary for the generation of hydrocarbons. The mantle-derived fluid had a good effect, but at the same time it had an adverse effect under specific conditions, on the formation of reservoirs. This paper also discusses the future direction and significance of studying mantle-derived fluid.

  5. Radiative conductivity and abundance of post-perovskite in the lowermost mantle

    Lobanov, Sergey S; Lin, Jung-Fu; Goncharov, Alexander F


    Thermal conductivity of the lowermost mantle governs the heat flow out of the core energizing planetary-scale geological processes. Yet, there are no direct experimental measurements of thermal conductivity at relevant pressure-temperature conditions of Earth's core-mantle boundary. Here we determine the radiative conductivity of post-perovskite at near core-mantle boundary conditions by optical absorption measurements in a laser-heated diamond anvil cell. Our results show that the radiative conductivity of Mg0.9Fe0.1SiO3 post-perovskite (< 1.2 W/m/K) is ~ 40% smaller than bridgmanite at the base of the mantle. By combining this result with the present-day core-mantle heat flow and available estimations on the lattice thermal conductivity we conclude that post-perovskite is as abundant as bridgmanite in the lowermost mantle which has profound implications for the dynamics of the deep Earth.

  6. Role of plate-driven mantle flow in distribution of the global heat flow

    叶正仁; 安镇文


    Heat flow in the Earth, from its hot interior to its relatively cool exterior, is the primary energy flow responsible for the dynamic nature of our planet. The motion of the plates excites a forced convective motion in the mantle, and this plate-driven mantle flow will strongly modulate the temperature field in the mantle because of the relatively high Peeler number of the mantle dynamic system. Here the role of the plate-driven mantle flow in the observed global heat flow is examined. The result reveals that the main feature of the distribution of the observed heat flow at the surface of the Earth matches well with the prediction and nearly one half of the average heat flow can be attributed to the thermal effect of the plate-driven mantle flow.

  7. Compositional Variation of Terrestrial Mantle Apatites and Implications for the Halogen and Water Budgets of the Terrestrial Mantle

    Roden, M.; Patino Douce, A. E.; Chaumba, J. B.; Fleisher, C.; Yogodzinski, G. M.


    Apatite in ultramafic xenoliths from various tectonic enviroments including arc (Kamchatka), plume (Hawaii), and intraplate (Lunar Crater, Nunivak, Colorado Plateau) were analyzed by electron microprobe with the aim of characterizing the Cl and F contents, and from these measured compositions to infer the nature of fluids/melts that the apatites equilibrated with. The impetus for the study derived from the generalization of O'Reilly and Griffin (1) that mantle-derived metasomatic apatites tend to be Cl-rich and mantle-derived igneous apatites tend to be F-rich. Our work largely corroborates their generalization with Cl- and/or H2O-rich compositions characterizing the apatites from Nunivak and Kamchatka while apatites from igneous or Group II xenoliths tend to be Cl-poor and be either nearly pure fluorapatite or a mix of hydroxylapatite and fluorapatite. We attribute the Cl-rich nature of the Kamchatka apatites to formation from Cl-rich fluids generated from subducted lithosphere; however the Nunivak occurrence is far removed from subducted lithosphere and may reflect a deep seated source for Cl as also indicated by brine inclusions in diamonds, Cl-rich apatites in carbonate-bearing xenoliths and a Cl-rich signature in some plumes such as Iceland, Azores and Samoa. One curious aspect of mantle-derived apatite compositions is that xenoliths with evidence of carbonatitic metasomatism commonly have Cl-rich apatites while apatites from carbonatites are invariably Cl-poor - perhaps reflecting loss of Cl in fluids evolved from the carbonatitic magma. Apatites from Group II xenoliths at Hawaii are solid solutions between fluorapatite and hydroxylapatite and show no evidence for deep-seated Cl at Hawaii. Samples of the terrestrial mantle are almost uniformly characterized by mineral assemblages with a single Ca-rich phosphate phase but the mantles of Mars, Vesta and the Moon have two Ca-rich phosphates, apatite and volatile-poor merrillite - apatite compositions existing

  8. Implementation and application of adaptive mesh refinement for thermochemical mantle convection studies

    Leng, Wei; Zhong, Shijie


    Numerical modeling of mantle convection is challenging. Owing to the multiscale nature of mantle dynamics, high resolution is often required in localized regions, with coarser resolution being sufficient elsewhere. When investigating thermochemical mantle convection, high resolution is required to resolve sharp and often discontinuous boundaries between distinct chemical components. In this paper, we present a 2-D finite element code with adaptive mesh refinement techniques for si...

  9. An assessment of upper mantle heterogeneity based on abyssal peridotite isotopic compositions

    Warren, J. M.; Shimizu, N.; Sakaguchi, C.; Dick, H. J. B.; Nakamura, E.


    Abyssal peridotites, the depleted solid residues of ocean ridge melting, are the most direct samples available to assess upper oceanic mantle composition. We present detailed isotope and trace element analyses of pyroxene mineral separates from Southwest Indian Ridge abyssal peridotites and pyroxenites in order to constrain the size and length scale of mantle heterogeneity. Our results demonstrate that the mantle can be highly heterogeneous to account adequately for the complexities of ancient and recent melting processes.

  10. Melting the hydrous, subarc mantle: the origin of primitive andesites

    Mitchell, Alexandra L.; Grove, Timothy L.


    This experimental study is the first comprehensive investigation of the melting behavior of an olivine + orthopyroxene ± spinel—bearing fertile mantle (FM) composition as a function of variable pressure and water content. The fertile composition was enriched with a metasomatic slab component of ≤0.5 % alkalis and investigated from 1135 to 1470 °C at 1.0-2.0 GPa. A depleted lherzolite with 0.4 % alkali addition was also studied from 1225 to 1240 °C at 1.2 GPa. Melts of both compositions were water-undersaturated: fertile lherzolite melts contained 0-6.4 wt% H2O, and depleted lherzolite melts contained ~2.5 wt% H2O. H2O contents of experimental glasses are measured using electron microprobe, secondary ion mass spectrometry, and synchrotron-source reflection Fourier transform infrared spectroscopy, a novel technique for analyzing H2O in petrologic experiments. Using this new dataset in conjunction with results from previous hydrous experimental studies, a thermobarometer and a hygrometer-thermometer are presented to determine the conditions under which primitive lavas were last in equilibration with the mantle. These predictive models are functions of H2O content and pressure, respectively. A predictive melting model is also presented that calculates melt compositions in equilibrium with an olivine + orthopyroxene ± spinel residual assemblage (harzburgite). This model quantitatively predicts the following influences of H2O on mantle lherzolite melting: (1) As melting pressure increases, melt compositions become more olivine-normative, (2) as melting extent increases, melt compositions become depleted in the normative plagioclase component, and (3) as melt H2O content increases, melts become more quartz-normative. Natural high-Mg# [molar Mg/(Mg + Fe2+)], high-MgO basaltic andesite and andesite lavas—or primitive andesites (PAs)—contain high SiO2 contents at mantle-equilibrated Mg#s. Their compositional characteristics cannot be readily explained by melting

  11. Dynamic topography as constraints on stress and viscosity in the mantle and lithosphere

    Zhong, S.


    Mantle convection generates stress in the mantle and lithosphere. The lithosphere stress is responsible for localized deformation including seismic deformation at plate boundaries, and localized stress highs in lithosphere are also suggested to cause dynamically self-consistent generation of plate tectonics and continental lithosphere instability, as the stress exceeds a threshold or yield stress. Modeling load-induced deformation at oceanic islands (e.g., Hawaii) constrains lithospheric stress at 100-200 MPa in the plate interiors, leading to a lower limit on lithospheric yield stress (Zhong and Watts, 2013). However, convection-induced lithospheric stress is poorly understood, ranging from 500 MPa to tens of MPa as reported in mantle convection studies. The magnitude and distribution of lithospheric and mantle stress depend critically on buoyancy and viscosity, particularly the latter. Unfortunately, lithospheric and mantle viscosity is also poorly constrained. For example, the inferred lower mantle viscosity from post-glacial rebound and geoid modeling studies ranges from 1023 Pas to 1022 Pas (e.g., Mitrovica and Forte, 2004; Simons and Hager, 1996; Paulson et al., 2007). In addition to the stress, the lower mantle viscosity may also affect the time evolution of mantle structure including sinking rate of slabs and formation of the degree-2 mantle seismic structure. Therefore, it is important to develop independent constraints on mantle viscosity and convection-induced stress. In this study, I demonstrate that dynamic topography can be used to place first-order constraints on both lithospheric stress and mantle viscosity. For a given superadiabatic temperature difference across the mantle (e.g., 2500 K), a larger mantle viscosity (or a smaller Rayleigh number) leads to a larger lithospheric stress and a larger dynamic topography. To be consistent with the inferred dynamic topography, the lower mantle viscosity is constrained to be significantly smaller than 1023

  12. A perovskitic lower mantle inferred from high-pressure, high-temperature sound velocity data.

    Murakami, Motohiko; Ohishi, Yasuo; Hirao, Naohisa; Hirose, Kei


    The determination of the chemical composition of Earth's lower mantle is a long-standing challenge in earth science. Accurate knowledge of sound velocities in the lower-mantle minerals under relevant high-pressure, high-temperature conditions is essential in constraining the mineralogy and chemical composition using seismological observations, but previous acoustic measurements were limited to a range of low pressures and temperatures. Here we determine the shear-wave velocities for silicate perovskite and ferropericlase under the pressure and temperature conditions of the deep lower mantle using Brillouin scattering spectroscopy. The mineralogical model that provides the best fit to a global seismic velocity profile indicates that perovskite constitutes more than 93 per cent by volume of the lower mantle, which is a much higher proportion than that predicted by the conventional peridotitic mantle model. It suggests that the lower mantle is enriched in silicon relative to the upper mantle, which is consistent with the chondritic Earth model. Such chemical stratification implies layered-mantle convection with limited mass transport between the upper and the lower mantle.

  13. Preservation of Primordial Mantle in the Aftermath of a Giant Impact

    Lock, S. J.; Stewart, S. T.; Mukhopadhyay, S.


    Terrestrial planets experience a number of giant impacts in the final stages of accretion. These highly energetic events force planets into hot, partially vaporized, and occasionally rapidly-rotating states. However, recent measurements of Xe and W isotopes in mantle plume-derived basalts imply that the terrestrial mantle was not homogenized during this violent stage of Earth's accretion. Understanding the physical structure of post-impact states is key for interpreting these primitive mantle signatures. Post-impact states are highly thermally stratified: the lowermost mantle has lower entropy than the rest of the mantle. Usually, the lowermost mantle is near the solidus or partially molten. The high-entropy portion of the mantle is super-liquidus, smoothly grading to a silicate vapor atmosphere. Here, we consider the competing processes acting on these distinct layers as the mantle establishes a single thermal gradient. If the whole mantle chemically mixed during cooling, then any pre-impact chemical signature would be erased. Previous work has neglected the critical time period between the highly vaporized post-impact state and a fully-condensed silicate body, i.e., a separated magma ocean and atmosphere. The post-impact structure cools rapidly by radiation from the photosphere, causing contraction of the body and redistribution of mass and angular momentum. One consequence of contraction is that the pressure in the mantle increases significantly (on the order of several to 10s GPa at the core mantle boundary) over 10s-1000s years. The increased pressure causes part of the mantle to solidify. Significantly, the timescale for pressure-induced freezing is shorter than the timescale for thermal equilibration between the low and high entropy mantle layers and the timescale for melt percolation (both >100s yrs). Therefore, pressure-induced freezing in the aftermath of a giant impact may be an important factor in preserving primordial Xe and W signatures in the lower

  14. Toward a coherent model for the melting behavior of the deep Earth's mantle

    Andrault, D.; Bolfan-Casanova, N.; Bouhifd, M. A.; Boujibar, A.; Garbarino, G.; Manthilake, G.; Mezouar, M.; Monteux, J.; Parisiades, P.; Pesce, G.


    Knowledge of melting properties is critical to predict the nature and the fate of melts produced in the deep mantle. Early in the Earth's history, melting properties controlled the magma ocean crystallization, which potentially induced chemical segregation in distinct reservoirs. Today, partial melting most probably occurs in the lowermost mantle as well as at mid upper-mantle depths, which control important aspects of mantle dynamics, including some types of volcanism. Unfortunately, despite major experimental and theoretical efforts, major controversies remain about several aspects of mantle melting. For example, the liquidus of the mantle was reported (for peridotitic or chondritic-type composition) with a temperature difference of ∼1000 K at high mantle depths. Also, the Fe partitioning coefficient (DFeBg/melt) between bridgmanite (Bg, the major lower mantle mineral) and a melt was reported between ∼0.1 and ∼0.5, for a mantle depth of ∼2000 km. Until now, these uncertainties had prevented the construction of a coherent picture of the melting behavior of the deep mantle. In this article, we perform a critical review of previous works and develop a coherent, semi-quantitative, model. We first address the melting curve of Bg with the help of original experimental measurements, which yields a constraint on the volume change upon melting (ΔVm). Secondly, we apply a basic thermodynamical approach to discuss the melting behavior of mineralogical assemblages made of fractions of Bg, CaSiO3-perovskite and (Mg,Fe)O-ferropericlase. Our analysis yields quantitative constraints on the SiO2-content in the pseudo-eutectic melt and the degree of partial melting (F) as a function of pressure, temperature and mantle composition; For examples, we find that F could be more than 40% at the solidus temperature, except if the presence of volatile elements induces incipient melting. We then discuss the melt buoyancy in a partial molten lower mantle as a function of pressure

  15. Domain-Specific Multimodeling

    Hessellund, Anders

    Enterprise systems are complex artifacts. They are hard to build, manage, understand, and evolve. Existing software development paradigms fail to properly address challenges such as system size, domain complexity, and software evolution when development is scaled to enterprise systems. We propose...... domain-specific multimodeling as a development paradigm to tackle these challenges in a language-oriented manner. The different concerns of a system are conceptually separated and made explicit as independent domain-specific languages. This approach increases productivity and quality by raising...... the overall level of abstraction. It does, however, also introduce a new problem of coordinating multiple different languages in a single system. We call this problem the coordination problem. In this thesis, we present the coordination method for domain-specific multimodeling that explicitly targets...

  16. Conserved Domain Database (CDD)

    U.S. Department of Health & Human Services — CDD is a protein annotation resource that consists of a collection of well-annotated multiple sequence alignment models for ancient domains and full-length proteins.

  17. Towards implementing plate tectonics in 3D mantle convection simulations

    Bollada, Peter; Davies, Huw


    One of the great challenges in numerical mantle convection simulations is to achieve models that naturally develop plate tectonic like behaviour at the surface. In this work we are looking to achieve such models by investigating the set of models where a single consistent rheology is used for the whole model. We have started by investigating a viscoelastic rheology, related to the Oldroyd-B model from the field of polymers. The goal will be to have the parameter that controls the relaxation between elastic and viscous behaviour to depend upon temperature, pressure and strain-rate. With an appropriate choice of this dependence we have, on the near surface, high viscous/elastic regions interfaced with lower, pure viscous, regions of high strain-rate; while it also becomes more viscous at depth in the interior. In this way we hope to obtain plate like behaviour at the surface which naturally progresses to viscous convective behaviour in the interior. We have started to implement this model in the established mantle 3D finite element spherical mantle convection code TERRA (Baumgardner, 1984). Some parts of the model have been implemented as a force (to be combined with the gravitational body force) on the right hand side. The work has required us to develop and code in TERRA: (i) methods to overcome the continuity problem of the stress field stemming from the fact that the velocity field is represented by linear finite elements; (ii) new operators to handle stress and its gradients; (iii) methods to analyse plate-like behaviour at the surface (iv) the necessary functional dependence of viscosity and elastic relaxation time on temperature, strain-rate and pressure We will present the background to the work, its implementation and results.

  18. Heterogeneity of Water Concentrations in the Mantle Lithosphere Beneath Hawaii

    Bizimis, M.; Peslier, A. H.; Clague, D.


    The amount and distribution of water in the oceanic mantle lithosphere has implications on its strength and of the role of volatiles during plume/lithosphere interaction. The latter plays a role in the Earth's deep water cycle as water-rich plume lavas could re-enrich an oceanic lithosphere depleted in water at the ridge, and when this heterogeneous lithosphere gets recycled back into the deep mantle. The main host of water in mantle lithologies are nominally anhydrous minerals like olivine, pyroxene and garnet, where hydrogen (H) is incorporated in mineral defects by bonding to structural oxygen. Here, we report water concentrations by Fourier transform infrared spectrometry (FTIR) on olivine, clino- and orthopyroxenes (Cpx & Opx) from spinel peridotites from the Pali vent and garnet pyroxenite xenoliths from Aliamanu vent, both part of the rejuvenated volcanism at Oahu (Hawaii). Pyroxenes from the Aliamanu pyroxenites have high water concentrations, similar to the adjacent Salt Lake Crater (SLC) pyroxenites (Cpx 400-500 ppm H2O, Opx 200 ppm H2O). This confirms that pyroxenite cumulates form water-rich lithologies within the oceanic lithosphere. In contrast, the Pali peridotites have much lower water concentrations than the SLC ones (10% modal Cpx and low spinel Cr# (0.09-0.10). The contrast between the two peridotite suites is also evident in their trace elements and radiogenic isotopes. The Pali Cpx are depleted in light REE, consistent with minimal metasomatism. Those of SLC have enriched light REE patterns and Nd and Hf isotopes consistent with metasomatism by alkaline melts. These observations are consistent with heterogeneous water distribution in the oceanic lithosphere that may be related to metasomatism, as well as relatively dry peridotites cross-cut by narrow (?) water-rich melt reaction zones.

  19. Lattice thermal conductivity of minerals in the deep mantle condition

    Dekura, H.; Tsuchiya, T.; Tsuchiya, J.


    Thermal transport property of materials under pressure and temperature is of importance for understanding the dynamics of the solid Earth and the thermal history. Both experimental and theoretical determinations of the thermal conductivity, however, still remain technically challenging particularly at the deep mantle condition. Recent progress in ab initio computational method based on the density-functional theory is now makes it possible to examine the transport phenomena including the lattice thermal conduction. The intrinsic bulk thermal conduction of insulator is caused by lattice anharmonicity owing to phonon-phonon interaction. The key parameter to predict lattice thermal conductivity is thus the anharmonic coupling constant. Earlier theoretical works calculated the lattice thermal conductivity of MgO with ab initio molecular dynamics simulation or finite difference lattice dynamics simulation (Nico de Koker, Phys. Rev. Lett. 103, 125902, 2009; X. Tang and J. Dong, Proc. Natl. Acad. Sci. U.S.A. 107, 4539, 2010). However, in these approaches, the simulation cell size could often be insufficient for accurate description of the long wavelength phonon scattering. This leads to a lack of the decay channels for the phonons. As an alternative approach, the anharmonic coupling strength between phonon modes can be evaluated within the density-functional perturbation theory. In this approach, the higher-order force tensors are calculated through a number of phonon decay channels obtained within the perturbative scheme taking care only of the primitive cell. We have been developing a technique for calculation of the phonon linewidth necessary to obtain the phonon lifetime. Then the lattice thermal conductivity is evaluated combining with additional harmonic-level of propeties. In this presentation, we show the behavior of lattice thermal conductivity in lower mantle minerals, and discuss the effects of pressure and temperature on their conductivities up to the deep

  20. Tracking Silica in the Earth's Subduction Zone and Upper Mantle

    Chen, T.; Wang, X.; Zou, Y.; Gwanmesia, G. D.; Liebermann, R. C.; Li, B.


    The X-discontinuity (~300 km) in the upper mantle has been revealed under some continental or oceanic region by a number of seismic studies, at which depth the P and S wave velocities increase by about 2%. One possible cause for this discontinuity is the coesite-stishovite phase transition. In this study, we conducted ultrasonic interferometry measurements on polycrystalline coesite and stishovite up to 12.6 GPa at ambient temperature and 14GPa 1073K, respectively. While the P wave velocities of coesite continuously increase with pressure, the S wave velocities exhibit a monotonic decrease to the peak pressure of the current experiment followed by a reversible recovery upon release of pressure. As a result, within the pressure range of 8-12 GPa (corresponding to ~250-350 km depths), the velocity contrasts between coesite and stishovite reach as high as ~38% for P wave and 48%-50% for S wave together with impedance contrasts of 71-69% and ~78% for P and S waves, respectively, the highest among all known phase transitions in mantle minerals. With such extreme contrasts, the coesite-stishovite phase transition in the MORB composition with 4-10wt% of SiO2 is sufficient to generate velocity and impedance contrasts comparable to those reported for the X-discontinuity. The current data, together with the seismic X-discontinuity, may provide a geophysical approach to track the ancient subducted oceanic slabs, and place constraints on the amount of silica in the upper mantle.