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首页> 外文期刊>Contributions to Mineralogy and Petrology >Ultrahigh pressure metamorphic rocks from the Chinese Continental Scientific Drilling Project: I. Petrology and geochemistry of the main hole (0–2,050 m)
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Ultrahigh pressure metamorphic rocks from the Chinese Continental Scientific Drilling Project: I. Petrology and geochemistry of the main hole (0–2,050 m)

机译：中国大陆科学钻探项目的超高压变质岩：I.主孔的岩石学和地球化学（0–2050 m）

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摘要

The main hole (MH) of the Chinese Continental Scientific Drilling Project (CCSD) in southern Sulu has penetrated into an ultrahigh-pressure (UHP) metamorphic rock slice which consists of orthogneiss, paragneiss, eclogite, ultramafic rock and minor schist. Recovered eclogites have a UHP metamorphic mineral assemblage of garnet + omphacite + rutile ± phengite ± kyanite ± coesite ± epidote. Ultramafic rocks contain garnet + olivine + clinopyroxene + orthopyroxene ± Ti-clinohumite ± phlogopite. Gneisses and schists contain an amphibolite-facies paragenesis, but their zircons have coesite, garnet, omphacite (or jadeite) and phengite inclusions, indicating that eclogites and gneisses have been subjected to in situ UHP metamorphism. Using available geothermobarometers, P–T estimates of 3.1–4.4 GPa and 678–816°C for eclogites were obtained. If surface outcrops and neighboring shallow drill holes are considered together, we suggest that a huge supracrustal rock slab (> 50 km long × 100 km wide × 5 km deep) was subducted to a depth > 100 km and then exhumed to the surface. The depth interval (0–2,050 m) of the CCSD-MH can be divided into six lithological units. Unit 1 consists of alternating layers of quartz-rich and rutile-rich eclogites, with thin interlayers of gneiss and schist. Eclogites of unit 1 are characterized by Nb, Ta, Sr and Ti depletions, low Mg number and general LREE enrichment. Unit 2 comprises rutile- and ilmenite-rich eclogite and minor “normal” eclogite and is characterized by high TiO2, total Fe, V, Co and Sr, and very low SiO2, alkali, Zr, Ba, Nb, Ta and total REE contents, and LREE-depleted REE patterns with slightly positive Eu anomalies. Unit 3 contains ultramafic rock and minor MgO-rich eclogite. Protoliths of UHP rocks from units 1, 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth. Units 4 and 6 consist of interlayered eclogite and paragneiss; the eclogites are characterized by Th, U, Nb, Ta and Ti depletion and K enrichment and LREE-enriched REE patterns. Paragneisses show Nb, Ta, Sr and Ti depletions and LREE-enriched REE patterns occasionally with slightly negative Eu anomalies, indicating that their protoliths represent metamorphic supracrustal series. Unit 5 consists mainly of orthogneisses, showing distinct Nb, Ta, Sr and Ti depletions, and LREE-enriched REE patterns with pronounced negative Eu anomalies, suggesting granitic protoliths. In conclusion it is proposed that the southern Sulu UHP belt consists of a series of meta-supracrustal rocks, a layered mafic–ultramafic complex and granites.
机译：苏鲁南部的中国大陆科学钻探项目（CCSD）的主孔（MH）已渗透到超高压（UHP）变质岩片中，该变质岩片由原片麻岩，石长石，榴辉岩，超镁铁质岩和次片岩组成。回收的榴辉岩具有石榴石+绿辉石+金红石±辉石±蓝晶石±堇青石±附子的UHP变质矿物组合。超镁铁质岩石包含石榴石+橄榄石+斜辉石+邻辉石±钛斜辉石±金云母。片麻岩和片岩具有闪长岩相的共生作用，但其锆石具有堇青石，石榴石，绿辉石（或硬玉）和辉石包裹体，表明榴辉岩和片麻岩已经历了原位UHP变质作用。使用可用的地热气压计，获得的榴辉岩的P–T估计值为3.1–4.4 GPa，678–816°C。如果同时考虑地表露头和邻近的浅钻孔，我们建议将一块巨大的表壳上岩石板（长> 50 km×宽100 km×深5 km）俯冲至深度> 100 km，然后将其掘出。 CCSD-MH的深度间隔（0–2,050 m）可以分为六个岩性单元。第1单元由富含石英和金红石的榴辉岩交替层组成，中间夹有片麻岩和片岩。单元1的榴辉岩的特征是Nb，Ta，Sr和Ti的耗竭，低Mg值和一般的LREE富集。第2单元由富金红石和钛铁矿的榴辉岩和少量的“普通”榴辉岩组成，其特征是TiO2高，总Fe，V，Co和Sr高，而SiO2低，碱，Zr，Ba低，Nb，Ta和总REE含量，以及带有少量Eu异常的LREE耗尽REE模式。第3单元包含超镁铁质岩石和少量富含MgO的榴辉岩。来自1号，2号和3号单元的UHP岩石的原石代表着地壳深度的层状镁铁质至超镁铁质侵入体。单元4和单元6由层状榴辉岩和石阶组成。榴辉岩的特征是Th，U，Nb，Ta和Ti的耗尽，钾的富集和富LREE的REE模式。 Paragneisses偶尔会显示Nb，Ta，Sr和Ti的耗竭以及富含LREE的REE模式，且Eu异常略微为负，表明它们的原生石代表变质的上壳系列。第5单元主要由直生片麻岩组成，表现出明显的Nb，Ta，Sr和Ti损耗，以及富含LREE的REE模式和明显的Eu负异常，表明为花岗岩原生岩。总之，建议苏鲁南极高压带由一系列超表壳岩石，层状镁铁质-超镁铁质复合体和花岗岩组成。

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  • 来源
    《Contributions to Mineralogy and Petrology》 |2006年第4期|421-441|共21页
  • 作者

    Zeming Zhang; Yilin Xiao; Jochen Hoefs; J. G. Liou; Klaus Simon;

  • 作者单位

    Institute of Geology Chinese Academy of Geological Sciences;

    Geowissenschaftliches Zentrum der Universität Göttingen;

    Geowissenschaftliches Zentrum der Universität Göttingen;

    Department of Geological and Environmental Sciences Stanford University;

    Geowissenschaftliches Zentrum der Universität Göttingen;

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