南阿尔金高压-超高温麻粒岩变质作用:大陆地壳超深俯冲与折返过程的记录

董杰; 魏春景; 张建新

doi:10.3799/dqkx.2019.233

南阿尔金高压-超高温麻粒岩变质作用:大陆地壳超深俯冲与折返过程的记录

doi: 10.3799/dqkx.2019.233

董杰^1, ,,
魏春景^1, , ,,
张建新²

1.
北京大学地球与空间科学学院, 北京 100871
2.
中国地质科学院地质研究所, 北京 100037

基金项目:

科技部“973”项目 2015CB856105

详细信息

作者简介:
董杰(1993-), 男, 博士, 岩石学专业

通讯作者:
魏春景

中图分类号: P581
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- 被引次数: 0
出版历程
- 收稿日期: 2019-08-19
- 刊出日期: 2019-12-15

Metamorphism of High Pressure-Ultrahigh Temperature (HP-UHT) Granulites from South Altyn Orogen: Records for Ultradeep Subduction and Exhumation of Continental Crust

Dong Jie^{1
,
,},
Wei Chunjing^{1
, ,
,},
Zhang Jianxin²

1.
School of Earth and Space Sciences, Peking University, Beijing 100871, China
2.
Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

摘要

摘要: 南阿尔金造山带是目前报道的具有最深俯冲记录的大陆超高压变质带，其内出露有高压-超高温麻粒岩，它们对深入理解大陆地壳岩石超深俯冲与折返过程具有重要意义.介绍了对南阿尔金巴什瓦克地区长英质麻粒岩和基性麻粒岩的岩相学、矿物化学、相平衡模拟及锆石U-Pb年代学研究成果.其中基性麻粒岩主要记录了深俯冲大陆地壳折返过程的变质演化：包括高压榴辉岩相、高压-超高温麻粒岩相、低压-超高温麻粒岩相及随后的近等压降温演化阶段；长英质麻粒岩除了记录与基性麻粒岩相似的折返过程外，还记录了从角闪岩相到超高压榴辉岩相的进变质演化过程.结合已有研究资料，确定超高压榴辉岩阶段峰期条件> 7~9 GPa和>1 000℃，可达到斯石英稳定域.锆石年代学显示两种岩石类型的原岩和变质年龄均分别在900 Ma和500 Ma左右.变质作用与年代学研究表明，南阿尔金大陆地壳岩石在早古生代发生超深俯冲至200~300 km后，折返至加厚地壳底部发生高压-超高温变质作用，随后被快速抬升至地壳浅部发生低压-超高温变质作用并经历迅速冷却.
- 高压-超高温变质作用 /
- 长英质麻粒岩 /
- 基性麻粒岩 /
- 大陆超深俯冲 /
- 南阿尔金 /
- 岩石学
Abstract: The South Altyn orogen is a typical continental ultrahigh-pressure (UHP) belt which is claimed to host the deepest subducted crustal rocks. HP-UHT granulites occurred in the belt are of significance for understanding the ultradeep subduction and exhumation of continental crust. This paper presents the results of petrography,mineral chemistry,phase equilibria modelling and zircon U-Pb dating for felsic and mafic granulites from Bashiwake area. Mafic granulites have mainly recorded the exhumation process of ultradeep continental crust,with metamorphic evolution from HP eclogite facies to HP-UHT granulite facies,further to low-pressure (LP)-UHT granulite facies conditions and the subsequent isobaric cooling. In addition to the similar exhumation to that of mafic granulites,felsic granulites have also preserved the early prograde history from amphibolite facies to UHP eclogite facies conditions. Combing previous studies,the peak conditions of UHP eclogite facies is estimated to be > 7-9 GPa and > 1 000℃,covering the stishovite-stability field. Zircon age dating suggests that both felsic and mafic granulites have similar protolith ages of~900 Ma and metamorphic ages of~500 Ma. Metamorphic and dating studies indicate that the South Altyn continental crust was subducted to ultradeep depths of 200-300 km during the Early Paleozoic and exhumed to the bottom of a thicken crust where HP-UHT metamorphism occurred. Then the crust was uplifted rapidly to the shallow crustal level and experienced LP-UHT metamorphism followed by subsequent isobaric cooling.
- HP-UHT metamorphism /
- felsic granulite /
- mafic granulite /
- continental ultradeep subduction /
- South Altyn orogen /
- petrology

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图 1 长英质麻粒岩(a)、含假蓝宝石基性麻粒岩(b，c)及普通石榴单辉麻粒岩(d)镜下特征显微照片

Grt.石榴石；Cpx.单斜辉石；Amp.角闪石；Ky.蓝晶石；Bi.黑云母；Spr.假蓝宝石；Spl.尖晶石；Rt.金红石；Pl.斜长石；Ilm.钛铁矿；Crn.刚玉；Qz.石英；据Dong et al., 2018, 2019(修改)

Fig. 1. Microtextures of felsic granulites (a), sapphirine-bearing mafic granulites (b, c) and common garnet-clinopyroxene mafic granulites (d)

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图 2 南阿尔金长英质麻粒岩石榴石核-幔-边成分环带特征

X_Prp.镁铝榴石；X_Grs.钙铝榴石；X_Alm.铁铝榴石；X_Sps.锰铝榴石；据Dong et al. (2018)修改

Fig. 2. Chemical zoning profiles of the garnet porphyroblast from a felsic granulite in South Altyn orogen

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图 3 南阿尔金长英质麻粒岩(a)和基性麻粒岩(b)4阶段(I~IV)P-T演化轨迹

L05、L07代表的温压条件/轨迹分别引自Liu et al.(2005, 2007)；图a花岗岩干固相线引自Stern et al.(1975)；图b玄武岩干固相线，石榴石、斜长石消失线引自Green and Ringwood(1967)；矿物相变反应线及固相线引自Dong et al.(2018, 2019)中THERMOCALC计算结果；AM.角闪岩相；(H)GN.(高压)麻粒岩相；EC.榴辉岩相；UHP.超高压榴辉岩相；LP/HP-UHT.低压/高压-超高温麻粒岩相；Hol.Hollandite；Wa.K-wadeite；Kfs.钾长石；Omp.绿辉石；Sil.矽线石；Coe.柯石英；Sti.斯石英；Dia.金刚石；Gr.石墨；其他矿物缩写见图 1；据Dong et al.(2018, 2019)修改

Fig. 3. Metamorphic P-T paths of felsic granulites (a) and mafic granulites (b) from South Altyn orogen

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