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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（0-2,050 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 + orthopy-roxene + - 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 metamor-phism. Using available geothermobarometers, P-T estimates of 3.1-4.4 GPa and 678-816 deg 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 x 100 km wide x 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 TiO_2, total Fe, V, Co and Sr, and very low SiO_2, 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+-锂铁矿+-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+邻苯二酚+-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（或翡翠）和锂铁矿包裹体，表明榴辉岩和片麻岩已被原位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和678-816℃。如果将地表露头和邻近的浅钻孔一起考虑，我们建议将一块巨大的壳上岩石板（> 50 km长x 100 km宽x 5 km深）俯冲到> 100 km的深度，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耗竭，低Mg值和一般的LREE富集。第2单元包含富金红石和钛铁矿的榴辉岩和少量的“普通”榴辉岩，其特征是TiO_2含量高，总Fe，V，Co和Sr含量高，而SiO_2，碱金属，Zr，Ba，Nb，Ta和REE含量极低，以及具有轻微正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1,2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。第4和第6单元由夹层的榴辉岩和paragneiss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的耗尽以及富含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单元主要由正长片麻岩组成，显示出明显的Nb，Ta，Sr和Ti损耗，以及富含LREE的REE模式，具有明显的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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