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Metamorphic consequences of secular changes in oceanic crust composition and implications for uniformitarianism in the geological record

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Geoscience Frontiers 2018年第4期9卷 1009-1019页

作者： Richard M.Palin Brendan Dyck Department of Geology and Geological Engineering Colorado School of Mines Department of Earth Sciences Simon Fraser University

Cooling of the Earth＇s mantle since the Meso-Archean is predicted by thermal and petrological models to have induced a secular change in the composition of primary mantle-derived magmas-and thus bulk oceanic crust; in particular, suggesting a decrease in maficity over time. This hypothesis underpins several recent studies that have addressed key geological questions concerning evolving plate tectonic styles, the rates and timing of continental crust formation, comparative planetology, and the emergence of complex life on Earth. Major, minor, and trace element geochemical analyses of（meta）mafic rocks preserved in the geological record allows exploration of this theory, although no consensus currently exists about the magnitude of this change and what compositions-if anything-constitute representative examples of Paleo-, Meso-, or Neo-Archean primitive oceanic crust. In this work, we review the current state of understanding of this issue, and use phase equilibria to examine the different mineral assemblages and rock types that would form during metamorphism of basalt of varying maficity in subduction zone environments. The presence（or absence） of such metamorphic products in the geological record is often used as evidence for（or against） the operation of modern-day subductiondriven plate tectonics on Earth at particular time periods; however, the control that secular changes in composition have on the stability of mineral assemblages diagnostic of subduction-zone metamorphism weakens such uniformitarianistic approaches. Geodynamic interpretations of the Archean metamorphic rock record must therefore employ a different set of petrological criteria for determining tectonothermal histories than those applied to Proterozoic or Phanerozoic equivalents.

关键词： Archean Mantle cooling oceanic crust Basalt Metamorphism Uniformitarianism

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Underplating generated A- and I-type granitoids of the East Junggar from the lower and the upper oceanic crust with mixing of mafic magma:Insights from integrated zircon U-Pb ages,petrography,geochemistry and Nd-Sr-Hf isotopes

Underplating generated A- and I-type granitoids of the East ...

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中国科学院地质与地球物理研究所2013年度（第13届）学术年会

作者： Wei Liu Xiu-Jin Liu Li-Juan Liu Key Laboratory of Mineral Resources Institute of Geology and GeophysicsChinese Academy of Sciences Graduate University of Chinese Academy of Sciences

Whole rock major and trace element,Nd-Sr and zircon Hf isotopic compositions and secondary-ion mass spectrometry zircon U-Pb ages of eleven granitoid intrusions and dioritic rocks from the East Junggar(NW China) were analyzed in this study,The East Junggar granitoids were emplaced during terminal Early to Late Carboniferous (325-301 Ma)following volcanic eruption of the Batamayi Formation,Zircons from the East Junggar granitoids yielded 210 concordant Pb/U ages which are all younger than 334 Ma and exhibitε(t)values distinctly higher than Devonian arc volcanic-rocks,Seismic P-wave velocities of deep crust of the East Junggar proper resemble those of oceanic crust(OC),These characteristics suggest absence of volcanic rock and volcano-sedimentary rock of Devonian and Early Carboniferous from the source *** East Junggar granitoids showε(t)and initial Sr/Sr values substantially overlapping those of the Armantai ophiolite in the area, The Early Paleozoic OC with seamount-like composition as the Zhaheba-Armantai ophiolites remained in the lower crust and formed main source rock of the East Junggar granitoids,Based on petrography and geochemistry, the East Junggar granitoids are classified into peralkaline A-type in the northern subarea,I-type(I and I subgroups) mainly in the north and A-type in the south of the southern *** perthitic or argillated core and oligoclasic rim with an argillated boundary of feldspar phenocrysts and inclusion of perthites or its overgrowth by matrix plagioclase,in the monzogranites(northern subarea),suggest mixing of peralkaline granitic magma with mafic *** the north of the southern subarea,the presence of magmatic microdioritic enclaves (MMEs)in the I subgroup granitoids,transfer of plagioclase phenocrysts and homblendes between host granodiorite and the MME across the boundary and a prominent resorption surface in the plaginclase phenocrysts indicate mixing of crustal magma(I subgroup granitoids)with mafic magma,Magma mix

关键词： A-type granite I-type granitoid East Junggar oceanic crust Magma mixing Underplating

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oceanic crustal structure and tectonic origin of the southern Kyushu-Palau Ridge in the Philippine Sea

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Acta Oceanologica Sinica 2022年第1期41卷 39-49页

作者： Xiongwei Niu Pingchuan Tan Weiwei Ding Wei Wang Yao Wei Xiaodong Wei Aiguo Ruan Jie Zhang Chunyang Wang Yong Tang Jiabiao Li Key Laboratory of Submarine Geosciences Ministry of Natural Resources/Second Institute of OceanographyMinistry of Natural ResourcesHangzhou 310012China School of Oceanography Shanghai Jiao Tong UniversityShanghai 200240China Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai) Zhuhai 519080China

A new high-resolution velocity model of the southern Kyushu-Palau Ridge(KPR) was derived from an activesource wide-angle seismic reflection/refraction profile. The result shows that the KPR crust can be divided into the upper crust with the P-wave velocity less than 6.1 m/s, and lower crust with P-wave velocity between 6.1 km/s and 7.2 km/s. The crustal thickness of the KPR reaches 12.0 km in the center, which gradually decreases to 5.0–6.0 km at sides. The velocity structure of the KPR is similar to the structures of the adjacent West Philippine Basin and Parece Vela Basin(PVB), indicating a typical oceanic crust. Isostatic analysis shows that some regional compensation occurs during the loading of the KPR, which implies that the KPR was built mainly by magmatism during the splitting of the Izu-Bonin-Mariana arc and the following back-arc seafloor spreading of the PVB during30–28 Ma BP. The absence of the thick middle crust(6.0–6.5 km/s) and high velocity lower-crustal layers(7.2–7.6 km/s) suggest that arc magmatism plays a less important role in the KPR formation.

关键词： P-wave crustal structure ocean bottom seismometer Kyushu-Palau Ridge oceanic crust

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The transport of water in subduction zones

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Science China Earth Sciences 2016年第4期59卷 651-682页

作者： ZHENG YongFei CHEN RenXu XU Zheng ZHANG ShaoBing School of Earth and Space Sciences University of Science and Technology of China

The transport of water from subducting crust into the mantle is mainly dictated by the stability of hydrous minerals in subduction zones. The thermal structure of subduction zones is a key to dehydration of the subducting crust at different depths. oceanic subduction zones show a large variation in the geotherm, but seismicity and arc volcanism are only prominent in cold subduction zones where geothermal gradients are low. In contrast, continental subduction zones have low geothermal gradients, resulting in metamorphism in cold subduction zones and the absence of arc volcanism during subduction. In very cold subduction zone where the geothermal gradient is very low(?5?C/km), lawsonite may carry water into great depths of ?300 km. In the hot subduction zone where the geothermal gradient is high(>25?C/km), the subducting crust dehydrates significantly at shallow depths and may partially melt at depths of crust but also cause hydration of the mantle wedge. Nevertheless, there are still minor amounts of water to be transported by ultrahigh-pressure hydrous minerals and nominally anhydrous minerals into the deeper mantle. The mantle wedge overlying the subducting slab does not partially melt upon water influx

关键词： Subduction zones oceanic crust Mantle wedge Thermal structure Hydrous minerals Water transport Arc magmatism

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A subduction channel model for exhumation of oceanic-type high-pressure to ultrahigh-pressure eclogite-facies metamorphic rocks in SW Tianshan,China

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Science China Earth Sciences 2016年第12期59卷 2339-2354页

作者： LI JiLei GAO Jun WANG XinShui Key Laboratory of Mineral Resources Institute of Geology and GeophysicsChinese Academy of Sciences

High-pressure(HP) and ultrahigh-pressure(UHP) eclogites exposed in collisional orogens are widely regarded to record the history of crustal rocks that were subducted to mantle depths and exhumed back to the *** into subduction and exhumation processes plays an important role in understanding the nature and evolution of subduction zones,geodynamics and plate *** contrast to continental-type HP to UHP metamorphic rocks that are dominated by felsic lithology,oceanic-type HP to UHP metamorphic rocks are dominated by mafic eclogites and thus have greater density,and their exhumation needs to overcome large barriers and may involve complicated tectonic *** exhumation of HP to UHP rocks is mainly influenced by the internal buoyancy,however,the external tectonic forces(such as channel flow) also act as effective exhumation drivers;in addition,effects of tectonic settings(such as slab rollback and breakoff) should take into *** HP-UHP metamorphic terrane in Southwestern Tianshan,which mainly comprises of metasediments with interlayered metamafic lenses and blocks,represents a typical accretionary melange associated with deep subduction of oceanic ***,the exhumation mechanisms of these once deeply buried HP-UHP rocks are still under *** on the field occurrences,petrographic features,peak metamorphic P-T conditions and ages of the eclogites/blueschists and their metasedimentary country rocks,a "sediment-type subduction channel" model is advocated in this study to appraise/decipher the formation and evolution of Southwestern Tianshan HP-UHP metamorphic ***-cyclic metamorphic eclogites record the multistage burial-exhumation cycling manipulated by convective flow in a channel-like interface between the plates,giving robust evidence for the presence of a subduction *** addition,this study summarizes some remaining geotectonic problems and research perspectives concerning the Southwestern Tianshan HP-UHP me

关键词： Eclogite High-pressure metamorphism oceanic crust Exhumation Subduction channel Southwestern Tianshan

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Faulting, magmatism and crustal oceanization of the Okinawa Trough

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Acta Oceanologica Sinica 2009年第3期28卷 40-49页

作者： GAO Jinyao ZHANG Tao FANG Yinxia YANG Chuanguo MEI Sai Key Laboratory of Submarine Geosciences of State oceanic Administration Hangzhou 310012 China Second Institute of Oceanography State Oceanic Administration Hangzhou 310012 China

The paper focuses on the characteristics of faulting and magmatism of the Okinawa Trough and the relation between them. En-echelon grabens are ranked oblique to the continental shelf edge uplift, and the Longwang uplift, the rifting block ridge in the northern segment and the ＂Mianhua uplift＂ in the southern segment have possibly preserved characteristics of volcanism and magmatism occurring with those rifting phases. The clockwise rotation of the southern Ryukyu Islands, driven by collision between Luzon and Taiwan, has played a key role in the crustal oceanization, enhancing the crustal extension of the southern segment and inducing volcanic magmatism in those grabens, among which the Yaeyama graben is a typical example of the presence of oceanic crust. Faulting and magmatism were mainly migrating towards the island arc asymmetrically. The crustal oceanization of the Okinawa Trough is difficultly interpreted by the linear magnetic anomaly model, which is fit for the symmetric spreading of the mid-oceanic ridges.

关键词： Okinawa Trough fault graben uplift oceanic crust volcanic magma

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The formation mechanism of accretionary wedge at Karamay in West Junggar,NW China

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Science China Earth Sciences 2017年第3期60卷 546-556页

作者： YANG GaoXue LI YongJun TONG LiLi LI GanYu Earth Science and Resources College Chang'an UniversityXi'an 710054China

Accretionary wedge is the typical product of subduction-zone processes at shallow depths. Determining the location, composition and mechanism of accretionary wedge has important implications for understanding the tectonism of plate subduction. The Central Asian Orogenic Belt （CAOB） is one of the world＇s largest accretionary orogenic belts, and records the bulk evolution of Paleo-Asian Ocean from opening to closure, with multi-stages and multi-types of crust-mantle interaction in the Paleozoic. West Junggar （western part of Junggar Basin）, located in the core area of CAOB, is characterized by a multiple intra-oceanic subduction system during the Paleozoic. In its eastem part crop out Devonian-Carboniferous marine sedimentary rocks, Darbut and Karamay ophiolitic m61anges, alkali oceanic island basalts, island arc volcanic rocks and thrusted nappe structure. Such lithotectonic associations indicate the occurrence of accretionary wedge at Karamay. In order to decipher its formation mechanism, this paper presents a synthesis of petrography, structural geology and geochemistry of volcanic rocks. In combination with oceanic subduction channel processes, it is suggested that the accretionary wedge is a composite melange with multiple stages of formation. The application of oceanic subduction channel model to the Karamay accretionary wedge provides new insights into the accretion and orogenesis of CAOB.

关键词： oceanic crust Subduction zone Geochemistry oceanic island basalt Ophiolitic melange Accretionary wedge West Junggar

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Global distribution of geothermal gradients in sedimentary basins

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Geoscience Frontiers 2023年第6期14卷 478-495页

作者： Folarin Kolawole Jonathan C.Evenick Lamont-Doherty Earth Observatory at Columbia University New YorkNYUSA INPEX Corporation TokyoJapan

The heat budget of sedimentary basins is determined by heat transfer across the lithosphereasthenosphere boundary and lithospheric heat sources,such that the tectonic evolution of their host continental and oceanic lithosphere ultimately impact the present-day heat flow and average geothermal *** increase in availability of publicly-accessible geothermal gradient measurements across the world provides an opportunity to globally assess the dominant controls on the thermal regime of sedimentary ***,we compile a global dataset of152,000 unique data points with constrained bottomhole temperature measurements and assess the relationships between geothermal gradient and selected independent tectonic variables,including crustal and lithospheric thicknesses,crustal age,sediment thickness,and basin *** results show that in both oceanic and continental settings,geothermal gradients exhibit a non-linear,systematic variation with the tectonic *** find that oceanic geothermal gradients decrease with increasing crustal age and lithospheric *** gradients in the continents show no clear relationships with thermotectonic crustal age,but decrease with increasing crustal and lithospheric *** drop significantly at 1.5 km sediment-cover thickness,likely reflecting the effect of high sedimentation rates,but show a striking rise at>12 km thicknesses,potentially influenced by thinned lithosphere and thermal blanketing *** commonly-assumed‘normal’gradient of 25℃/km for continents is only valid for a narrow range(1.5–12.5 km)of sedimentary cover-thickness,and oceanic‘normal’gradient may be as high as 50–75℃/km for>20 Ma crustal age and>50 km-thick *** show that,conditionally,crustal age may best predict average geothermal gradients in oceanic settings,and lithosphere thickness in ***,we observe that tectonic basin types exhibit distinct ranges of gradients that reflect their prevalent tec

关键词： Geothermal gradient oceanic crust Continental crust Lithosphere Tectonics

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Five-Stage Model of the Palaeozoic crustal Evolution in Xinjiang

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Acta Geologica Sinica(English Edition) 1998年第4期72卷 339-349页

作者： LIU Dequan TANG Yanling ZHOU Ruhong Xinjiang Bureau of Geology and Mineral Exploration and Development No. 2 W. Karamay Rd Urumqi Xinjiang 830000

Abstract: The great majority of the Palaeozoic orogenic belts of Central Asia are of the intercontinental type, whose evolution always follows a five-stage model, i.e. the basal continental crust-extensional transitional crust-oceanic crust-convergent transitional crust-new continental crust model. The stage for the extensional transitional crust is a pretty long, independent and inevitable phase. The dismembering mechanism of the basal continental crust becoming an extensional continental crust is delineated by the simple shear model put forward by Wernike (1981). The continental margins on the sides of a gently dipping detachment zone and moving along it are asymmetric: one side is of the nonmagmatic type and the other of the magmatic type with a typical bimodal volcanic formation. In the latter case, however, they were often confused with island arcs. This paper discusses the five-stage process of the crustal evolution of some typical orogenic belts in Xinjiang.

关键词： crustal evolution extensional transitional crust oceanic crust new continental crust five-stage model Xinjiang

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A Global Perspective on crustal Structure and Evolution based on A New crustal Classification

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Acta Geologica Sinica(English Edition) 2021年第S1期95卷 48-50页

作者： Irina M.ARTEMIEVA Alexey SHULGIN School of Earth Sciences China University of GeosciencesWuhan 430074China Marine Geodynamics GEOMAR Helmholtz Center for Ocean ResearchKielGermany Department of Geophysics Stanford UniversityCAUSA CEED University of OsloNorway

Knowledge of the crustal structure is the key for understanding physical and chemical conditions of its formation and later modification by geodynamic *** has long been recognized that crustal structure is controlled by tectonic settings,and that the crustal thickness is one of the most important parameters that reflects the geodynamic origin of the crust.A long tectonic life of continental crust leads to its significant reworking by plate tectonics processes and crust-mantle interaction,which include mechanical extension.

关键词： crustal delamination granitization basin subsidence orogenic processes continental rifting hotspots continental shelves failed oceans oceanic crust

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