Geochemistry and magmatic history of eclogites and ultramafic rocks from the Chinese continental scientific drill hole: Subduction and ultrahigh-pressure metamorphism of lower crustal cumulates     

Yongsheng Liu  Keqing Zong  Peter B. Kelemen  Shan Gao 《Chemical Geology》2008,247(1-2):133-153

Three distinct groups of eclogites (low-Mg–Ti eclogites, high-Ti eclogites and Mg-rich eclogites) and ultramafic rocks from the depth interval of 100–680 m of the Chinese Continental Scientific Drill Hole were studied. The low Mg#s (= 100^?molar Mg/(Mg + Fe)) (81–84%) and low Ni (1150–1220 ppm) and high Fe₂O₃^total (13–15 wt.%) contents of ultramafic rocks suggest a cumulate origin. Mg-rich eclogites show middle and heavy REE enrichments, which could not be produced by metamorphic growth of garnet. Instead, if the rocks formed from a light REE enriched magma, there may be an igneous precursor for some garnets in their protolith. Alternatively, perhaps they formed from a light REE depleted magma without garnet. The high-Ti eclogites are characterized by unusually high Fe₂O₃^total contents (up to 24.5 wt.%) and decoupling of high TiO₂ from low Nb and Ta contents. These features cannot be produced by concentration of rutile during UHP metamorphism (even for samples with TiO₂ > 4 wt.%) of high-Ti basalts, but could be attributed to crystal fractionation of titanomagnetite (for those with TiO₂ < ～ 4 wt.%) or titanomagnetite + ilmenite (for those with TiO₂ > ～ 4 wt.%). Thus, we suggest that protoliths of the high-Ti eclogites were titanomagnetite/ilmenite-rich gabbroic cumulates. As a whole, the low-Mg–Ti eclogites are geochemically complementary to the high-Ti eclogites, Mg-rich eclogites and ultramafic rocks, and could be metamorphic products of gabbroic/dioritic cumulates formed by high degree crystal fractionation. All these observations suggest that parental materials of the ultramafic rock-eclogite assemblage could represent a complete sequence of fractional crystallization of tholeiitic or picritic magmas at intermediate to high pressure, which were later carried to ultrahigh-pressure conditions during a continental collision event.  相似文献   

Magmatic and metamorphic evolution of the oceanic crust in the western flank of the MAR crest zone at 15°44′N: Investigation of cores from sites 1275B and 1275D,JOIDES resolution Leg 209     

S. A. Silantyev  Yu. A. Kostitsyn  D. V. Cherkashin  H. J. B. Dick  P. B. Kelemen  N. N. Kononkova  E. M. Kornienko 《Petrology》2008,16(4):353-375

This paper reports the results of an investigation of a representative collection of samples recovered by deep-sea drilling from the oceanic basement 10 miles west of the rift valley axis in the crest zone of the Mid-Atlantic Ridge at 15°44′N (sites 1275B and 1275D). The drilling operations were carried out during Leg 209 of the drilling vessel JOIDES Resolution within the framework of the Ocean Drilling Program (ODP). The oceanic crust was penetrated to a depth of 108.7 m at Site 1275B and 209 m at Site 1275D. We reconstructed the following sequence of magmatic and metamorphic events resulting in the formation of a typical oceanic core complex of slow-spreading ridges: (1) formation of a strongly fractionated (enriched in iron and titanium) tholeiitic magmatic melt parental to the gabbroids under investigation in a large magma chamber located in a shallow mantle and operating for a long time under steady-state conditions; (2) transfer of the parental magmatic melt of the gabbroids to the base of the oceanic crust, its interaction with the host mantle peridotites, and formation of troctolites and plagioclase peridotites; (3) intrusion of enriched trondhjemite melts as veins and dikes in the early formed plutonic complex, contact recrystallization of the gabbro, and development in the peridotite-gabbro complex of enriched geochemical signatures owing to the influence of the trondhjemite injections; (4) emplacement of dolerite dikes (transformed to diabases); (5) metamorphism of upper epidoteamphibolite facies with the participation of marine fluids; and (6) rapid exhumation of the plutonic complex to the seafloor accompanied by greenschist-facies metamorphism. The distribution patterns of Sr and Nd isotopes and strongly incompatible elements in the rocks suggest contributions from two melt sources to the magmatic evolution of the MAR crest at 15°44′N: a depleted reservoir responsible for the formation of the gabbros and diabases and an enriched reservoir from which the trondhjemites (granophyres) were derived.  相似文献   

Observations of Li isotopic variations in the Trinity Ophiolite: Evidence for isotopic fractionation by diffusion during mantle melting     

Craig C. Lundstrom  Marc Chaussidon  Peter Kelemen 《Geochimica et cosmochimica acta》2005,69(3):735-751

The Trinity peridotite (northern CA) contains numerous lithologic sequences consisting of dunite to harzburgite to spinel lherzolite to plagioclase lherzolite. Previous workers have documented geochemical gradients in these sequences consistent with melt-rock reaction processes occurring around dunites, interpreted to reflect conduits for melt ascent. We have undertaken a study of Li isotope compositions of clinopyroxene and some olivine within these sequences using ion probe techniques to test the hypothesis that the geochemical gradients are related to diffusive fluxing of alkali elements into or away from the melt conduit.Results show large variations in ⁷Li/⁶Li occurring in a consistent pattern across three transects from dunite to plagioclase lherzolite within the Trinity peridotite. Specifically, measurements of average δ⁷Li for single thin sections along the traverse reveal a low in δ⁷Li in the harzburgite adjacent to the dunite returning to higher values farther from the dunite with a typical offset of ∼10 per mil in the low δ⁷Li trough. This pattern is consistent with a process whereby Li isotopes are fractionated during diffusion through a melt either from the dunite conduit to the surrounding peridotite, or from the surrounding peridotite into the dunite conduit. The patterns in ⁷Li/⁶Li occur over a length scale similar to the decrease in REE concentration in these same samples. Explaining both the trace element and Li isotopic gradients requires a combined process of alkali diffusion and melt extraction.We develop a numerical model and examine several scenarios of the combined diffusion-extraction process. Using experimentally constrained values for the change in Li diffusion coefficient with isotope mass, large changes in δ⁷Li as a function of distance can be created in year to decade timescales. The addition of the melt extraction term allows larger Li concentration gradients to be developed and thus produces larger isotopic fractionations than diffusion only models. The extraction aspect of the model can also account for the observed decrease in rare earth element concentrations across the transects.  相似文献   

South East Europe electricity roadmap – modelling energy transition in the electricity sectors     

László Szabó  Ágnes Kelemen  András Mezősi  Zsuzsanna Pató  Enikő Kácsor  Gustav Resch 《Climate Policy》2019,19(4):495-510

One of the most important challenges for the South East Europe region will be replacing more than 30% of its presently installed fossil fuel generation capacity by the end of 2030, and more than 95% by 2050 if its age structure is considered. This requires a strong policy framework to incentivise new investments in a region currently lacking investors, but also presents an opportunity to shape the electricity sector over the long term according to the broader energy transition strategy of the EU and the Energy Community. The aim of this paper is to assess what type of long-term pathways exist for electricity sector development in the region if they follow the energy transition process of the EU. In this model-based scenario assessment, long term electricity sector futures are explored using a set of interlinked electricity models evaluating the level of renewable energy investment required in the region to reach a deep decarbonization target, assuming emission reduction above 94% by 2050 compared to 1990 in line with the long term market integration and climate policy goals of the EU. It also explores what are the most important system wide impacts of the high deployment of renewable energy concerning generation adequacy and security of supply.

Key policy insights

• Energy policies in the South East Europe (SEE) region, both at the national and regional level, should focus on enabling renewable energy integration, as this will be a key component of the future energy mix.

• EU and Energy Community policies should be incorporated into national energy planning to ensure that SEE countries embark on the energy transition process at an early stage.

• Stranded costs should be carefully considered in decision-making on new fossil-fuel generation and gas network investment in order to avoid lock-in to carbon intensive technologies.

• If consistent decarbonization policy prevails, with a significant and persistent CO2 price signal, the role of natural gas remains transitory in the region.

• The SEE region offers relatively cheap decarbonization options: the power sector can reduce GHG emissions above 94% by 2050 in the modelled scenarios.

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Near-solidus melts of MORB + 4 wt% H<Subscript>2</Subscript>O at 0.8–2.8 GPa applied to issues of subduction magmatism and continent formation     

T.?W.?SissonEmail authorView author&#;s OrcID profile  P.?B.?Kelemen 《Contributions to Mineralogy and Petrology》2018,173(9):70

Experiments on MORB?+?4 wt% H₂O at 0.8–2.8 GPa and 700–950 °C (Liu in High pressure phase equilibria involving the amphibolite–eclogite transformation. PhD dissertation, Stanford University, Stanford, California, 1997; Liu et al. in Earth Planet Sci Lett 143:161–171, 1996) were reexamined for their major and trace element melt compositions and melting relations. Degree of melting diminishes at greater pressures, with corresponding evolution of melt from andesitic at the lowest pressures and hottest temperatures to high-silica rhyolitic at the greatest pressure and coolest temperature. Quartz contributes greatly to the production of near-solidus melts of basaltic eclogite, with the result that melt productivity falls markedly following quartz exhaustion. This limits the extent of melting attainable in the basaltic eclogite portions of sub-arc subducting plates to no more than ~?2?×?the modal wt% quartz in the mafic eclogite protolith. Synthesized residual mineral assemblages lack an epidote-series mineral at temperatures?>?750 °C, and as a result, melts from the rutile eclogite and rutile-amphibole eclogite facies have elevated concentrations of light rare earth elements, U, Th, have elevated Ba, K, and Sr, high Sr/Y, and are strongly depleted in Nb, Y, and the heavy rare earth elements. Models of eclogite partial melt reacting with peridotite of the mantle wedge reproduce major and trace element characteristics of parental arc magmas so long as the proportions of infiltrating melt to peridotite are relatively high, consistent with channelized ascent. Melt mass is estimated to increase roughly three- to ten-fold, consistent with H₂O concentrations of 3–7 wt% in the magmas produced by reaction. Partial melts of subducting basaltic eclogite are predicted to have positive Sr concentration anomalies, relative to Ce and Nd, that persist through melt-peridotite reactions. Primitive arc magmas commonly have positive Sr anomalies, whereas such anomalies are smaller in estimates of the bulk continental crust. Overall, Sr anomalies diminish passing from primitive to more evolved arc volcanic rocks, consistent with extensive mineral-melt differentiation (crystallization, partial remelting) involving plagioclase. On the order of 50 wt% differentiation would be necessary to eliminate Sr positive anomalies, based on geochemical variations in the Cascade and western Aleutian magmatic arcs. Loss to the mantle of cumulates and restites with high Sr anomalies, in abundances broadly equal to the mass of the preserved crust, would be required to form the continents via processes similar to present-day subduction magmatism.  相似文献   

Mantle thermal structure and active upwelling during continental breakup in the North Atlantic   总被引：4，自引：0，他引：4  

W.Steven Holbrook  H.C. Larsen  J. Korenaga  T. Dahl-Jensen  I.D. Reid  P.B. Kelemen  J.R. Hopper  G.M. Kent  D. Lizarralde  S. Bernstein  R.S. Detrick 《Earth and Planetary Science Letters》2001,190(3-4):251-266

Seismic reflection and refraction data acquired on four transects spanning the Southeast Greenland rifted margin and Greenland–Iceland Ridge (GIR) provide new constraints on mantle thermal structure and melting processes during continental breakup in the North Atlantic. Maximum igneous crustal thickness varies along the margin from >30 km in the near-hotspot zone (<500 km from the hotspot track) to 18 km in the distal zone (500–1100 km). Magmatic productivity on summed conjugate margins of the North Atlantic decreases through time from 1800±300 to 600±50 km³/km/Ma in the near-hotspot zone and from 700±200 to 300±50 km³/km/Ma in the distal zone. Comparison of our data with the British/Faeroe margins shows that both symmetric and asymmetric conjugate volcanic rifted margins exist. Joint consideration of crustal thickness and mean crustal seismic velocity suggests that along-margin changes in magmatism are principally controlled by variations in active upwelling rather than mantle temperature. The thermal anomaly (ΔT) at breakup was modest (100–125°C), varied little along the margin, and transient. Data along the GIR indicate that the potential temperature anomaly (125±50°C) and upwelling ratio (4 times passive) of the Iceland hotspot have remained roughly constant since 56 Ma. Our results are consistent with a plume–impact model, in which (1) a plume of radius 300 km and ΔT of 125°C impacted the margin around 61 Ma and delivered warm material to distal portions of the margin; (2) at breakup (56 Ma), the lower half of the plume head continued to feed actively upwelling mantle into the proximal portion of the margin; and (3) by 45 Ma, both the remaining plume head and the distal warm layer were exhausted, with excess magmatism thereafter largely confined to a narrow (<200 km radius) zone immediately above the Iceland plume stem. Alternatively, the warm upper mantle layer that fed excess magmatism in the distal portion of the margin may have been a pre-existing thermal anomaly unrelated to the plume.  相似文献   

Ultra-depleted, shallow cratonic mantle beneath West Greenland: dunitic xenoliths from Ubekendt Ejland   总被引：1，自引：0，他引：1  

Stefan Bernstein  Karen Hanghøj  Peter B. Kelemen  C. Kent Brooks 《Contributions to Mineralogy and Petrology》2006,152(3):335-347

Dunitic xenoliths from late Palaeogene, alkaline basalt flows on Ubekendt Ejland, West Greenland contain olivine with 100 × Mg/(Mg + Fe), or Mg#, between 92.0 and 93.7. Orthopyroxene has very low Al₂O₃ and CaO contents (0.024–1.639 and 0.062–0.275 wt%, respectively). Spinel has 100 × Cr/(Cr + Al), or Cr#, between 46.98 and 95.67. Clinopyroxene is absent. The osmium isotopic composition of olivine and spinel mineral separates shows a considerable span of ¹⁸⁷Os/¹⁸⁸Os values. The most unradiogenic ¹⁸⁷Os/¹⁸⁸Os value of 0.1046 corresponds to a Re-depletion age of ca. 3.3 Gy, while the most radiogenic value of 0.1336 is higher than present-day chondrite. The Os isotopic composition of the xenoliths is consistent with their origin as restites from a melt extraction event in the Archaean, followed by one or more subsequent metasomatic event(s). The high Cr# in spinel and low modal pyroxene of the Ubekendt Ejland xenoliths are similar to values of some highly depleted mantle peridotites from arc settings. However, highly depleted, arc-related peridotites have higher Cr# in spinel for a given proportion of modal olivine, compared to cratonic xenolith suites from Greenland, which instead form coherent trends with abyssal peridotites, dredged from modern mid-ocean ridges. This suggests that depleted cratonic harzburgites and dunites from shallow lithospheric mantle represent the residue from dry melting in the Archaean.  相似文献   

Testing polymineral post-IR IRSL and quartz SAR-OSL protocols on Middle to Late Pleistocene loess at Batajnica,Serbia     

Anca Avram  Daniela Constantin  Daniel Veres  Szabolcs Kelemen  Igor Obreht  Ulrich Hambach  Slobodan B. Marković  Alida Timar-Gabor 《Boreas: An International Journal of Quaternary Research》2020,49(3):615-633

The loess–palaeosol sequence of Batajnica (Vojvodina region, Serbia) is considered as one of the most complete and thickest terrestrial palaeoclimate archives for the Middle and Late Pleistocene. In order to achieve a numerical chronology for this profile, four sets of ages were obtained on 18 individual samples. Equivalent doses were determined using the SAR protocol on fine (4–11 μm) and coarse (63–90 μm) quartz fractions, as well as on polymineral fine grains by using two elevated temperature infrared stimulation methods, pIRIR₂₉₀ and pIRIR₂₂₅. We show that the upper age limit of coarse quartz OSL and polymineral pIRIR₂₉₀ and pIRIR₂₂₅ techniques is restricted to the Last Glacial/Interglacial cycle due to the field saturation of the natural signals. Luminescence ages on coarse quartz, pIRIR₂₂₅ and pIRIR₂₉₀ polymineral fine grains are in general agreement. Fine quartz ages are systematically lower than the coarse quartz and pIRIR ages, the degree of underestimation increasing with age. Comparison between natural and laboratory dose response curves indicate the age range over which each protocol provides reliable ages. For fine and coarse quartz, the natural and laboratory dose response curves overlap up to ~150 and ~250 Gy, respectively, suggesting that the SAR protocol provides reliable ages up to c. 50 ka on fine quartz and c. 100 ka on coarse quartz. Using the pIRIR₂₂₅ and pIRIR₂₉₀ protocols, equivalent doses up to ~400 Gy can be determined, beyond which in the case of the former the natural dose response curve slightly overestimates the laboratory dose response curve. Our results suggest that the choice of the mineral and luminescence technique to be used for dating loess sediments should take into consideration the reported limited reliability.  相似文献   

Potential for offsetting diamond mine carbon emissions through mineral carbonation of processed kimberlite: an assessment of De Beers mine sites in South Africa and Canada     

Mervine  Evelyn M.  Wilson  Sasha  Power  Ian M.  Dipple  Gregory M.  Turvey  Connor C.  Hamilton  Jessica L.  Vanderzee  Sterling  Raudsepp  Mati  Southam  Colette  Matter  Juerg M.  Kelemen  Peter B.  Stiefenhofer  Johann  Miya  Zandile  Southam  Gordon 《Mineralogy and Petrology》2018,112(2):755-765

De Beers kimberlite mine operations in South Africa (Venetia and Voorspoed) and Canada (Gahcho Kué, Victor, and Snap Lake) have the potential to sequester carbon dioxide (CO₂) through weathering of kimberlite mine tailings, which can store carbon in secondary carbonate minerals (mineral carbonation). Carbonation of ca. 4.7 to 24.0 wt% (average = 13.8 wt%) of annual processed kimberlite production could offset 100% of each mine site’s carbon dioxide equivalent (CO₂e) emissions. Minerals of particular interest for reactivity with atmospheric or waste CO₂ from energy production include serpentine minerals, olivine (forsterite), brucite, and smectite. The most abundant minerals, such as serpentine polymorphs, provide the bulk of the carbonation potential. However, the detection of minor amounts of highly reactive brucite in tailings from Victor, as well as the likely presence of brucite at Venetia, Gahcho Kué, and Snap Lake, is also important for the mineral carbonation potential of the mine sites.

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Characterization of solid bitumens originating from thermal chemical alteration and thermochemical sulfate reduction   总被引：1，自引：0，他引：1  

Simon R. Kelemen  Peter J. Kwiatek  Mobae Afeworki  William A. Lamberti  Hans G. Machel  Trudy Bolin 《Geochimica et cosmochimica acta》2010,74(18):5305-4687

Solid bitumen can arise from several reservoir processes acting on migrated petroleum. Insoluble solid organic residues can form by oxidative processes associated with thermochemical sulfate reduction (TSR) as well as by thermal chemical alteration (TCA) of petroleum. TCA may follow non-thermal processes, such as biodegradation and asphaltene precipitation, that produce viscous fluids enriched in polar compounds that are then altered into solid bitumens. It is difficult to distinguish solid bitumen formed by TCA from TSR since both processes occur under relatively high temperatures. The focus of the present work is to characterize solid bitumen samples associated with TSR- or TCA-processes using a combination of solid-state X-ray Photoelectron Spectroscopy (XPS), Sulfur X-ray Absorption Near Edge Structure Spectroscopy (S-XANES), and ¹³C NMR. Naturally occurring solid bitumens from three locations, Nisku Formation, Brazeau River area (TSR-related); La Barge Field, Madison Formation (TSR-related); and, the Alaskan North Slope, Brooks Range (TCA-related), are compared to solid bitumens generated in laboratory simulations of TSR and TCA.The chemical nature of solid bitumens with respect to organic nitrogen and sulfur can be understood in terms of (1) the nature of hydrocarbon precursor molecules, (2) the mode of sulfur incorporation, and (3) their concentration during thermal stress. TSR-solid bitumen is highly aromatic, sulfur-rich, and nitrogen-poor. These heteroatom distributions are attributed to the ability of TSR to incorporate copious amounts of inorganic sulfur (S/C atomic ratio >0.035) into aromatic structures and to initial low levels of nitrogen in the unaltered petroleum. In contrast, TCA-solid bitumen is derived from polar materials that are initially rich in sulfur and nitrogen. Aromaticity and nitrogen increase as thermal stress cleaves aliphatic moieties and condensation reactions take place. TCA-bitumens from the Brooks Range have <75% aromatic carbon. TCA-bitumens exposed to greater thermal stress can have a higher aromaticity, like that observed in TSR-bitumens. Organic sulfur in TCA-organic solids remains relatively constant with increasing maturation (S/C atomic ratio <0.035) due to offsetting preservation and H₂S elimination reactions. Although S-XANES and ¹³C NMR provide information needed to understand changes in structure and reactivity that occur in the formation of petroleum solids, in some cases XPS analysis is sufficient to determine whether a solid bitumen is formed by TCA or TSR.  相似文献