Early Mesozoic retrograded eclogite and mafic granulite from the Badu Complex of the Cathaysia Block, South China: Petrology and tectonic implications
Early Mesozoic retrograded eclogite and mafic granulite from the Badu Complex of the Cathaysia Block, South China: Petrology and tectonic implications
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华南华夏地块八都杂岩早中生代退变榴辉岩和镁铁质麻粒岩：岩石学及构造意义
DOI：
10.1016/j.gr.2016.10.002
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发表时间：
2017
影响因子：
6.1
通讯作者：
Zhou Xiwen
中科院分区：
文献类型：
--
作者：
Zhao Lei;Zhai Mingguo;Santosh M.;Zhou Xiwen
华南华夏地块东北部沿着八都地区的高级变质杂岩中保存有退变质榴辉岩和镁铁质麻粒岩。本文介绍了这些岩石的岩石学特征、矿物相平衡、P-T条件和锆石U-Pb年龄。矿物结构和反应关系表明，退变质榴辉岩经历了4个变质阶段：榴辉岩相阶段（M1），单斜辉石退变质阶段（M2），角闪石退变质阶段（M3），角闪石退变质阶段（M4）。镁铁质麻粒岩可划分为三个阶段：（1）斜长石缺失阶段（M1），（2）麻粒岩相阶段（M2）和（3）角闪岩相阶段（M3）。两类岩石的变质演化均遵循顺时针P-T轨迹。传统的地质温度计和地质压力计结合相平衡模型得出榴辉岩每个变质阶段的变质P-T条件为500-560 °C、23-24 kbar（M1）、640-660 °C、14-16 kbar（M2）、730-750 °C和11-13 kbar（M3）。退变质阶段（M4）被推断为发生在角闪岩到绿片岩相的条件下。镁铁质麻粒岩的相平衡模拟表明，在角闪岩相条件下，各变质阶段的P-T条件为600-720 °C，> 13 kbar（M1）和860-890 °C，5-6 kbar（M2和M3）。LA-ICPMS锆石U-Pb定年和微量元素分析表明，高压变质作用发生在245-251 Ma。该麻粒岩的原岩年龄为997 Ma，与广泛分布于华夏地块和沿着江南带的镁铁质-超镁铁质岩石的原岩年龄相近。中生代古大洋岩石圈物质的俯冲（或地壳增厚）和榴辉岩的形成，表明华夏地块当时可能处于特提斯洋域。麻粒岩的形成可能与中生代基性岩浆底侵作用有关，伴随着岩石圈拆沉、加热和榴辉岩的退积，同时伴随着快速的抬升。
The high-grade metamorphic terrane in the Badu region along the northeastern Cathaysia Block in South China preserves retrograded eclogites and mafic granulites. Here we present the petrology, mineral phase equilibria and P-T conditions based on pseudosection computations, as well as zircon U-Pb ages of these rocks. Mineral textures and reaction relationships suggest four metamorphic stages for the retrograded eclogite as follows: (1) eclogite facies stage (M1), (2) clinopyroxene retrograde stage (M2), (3) amphibole retrograde stage (M3), and (4) chlorite retrograde stage (M4). For the mafic granulite, three stages are identified as: (1) plagioclase-absent stage (M1), (2) granulite facies stage (M2) and (3) amphibolite facies stage (M3). Metamorphic evolution of both of the rock types follows clockwiseP-Tpath. Conventional geothermometers and geobarometers in combination with phase equilibria modelling yield metamorphicP-Tconditions for each metamorphic stage for the eclogite as 500–560 °C, 23–24 kbar (M1), 640–660 °C, 14–16 kbar (M2), 730–750 °C, and 11–13 kbar (M3). The chlorite retrograde stage (M4) is inferred to have occurred at lower amphibolite to greenschist facies conditions. Phase equilibria modelling of the mafic granulite showsP-Tconditions for each metamorphic stage as 600–720 °C, > 13 kbar (M1) and 860–890 °C, 5–6 kbar (M2) and M3 at amphibolite facies conditions. LA-ICPMS zircon U-Pb dating and trace element analysis show that the high pressure metamorphism occurred at 245–251 Ma. Protolith age of the mafic granulite is 997 Ma, similar to that of the mafic to ultramafic rocks widely distributed in the Cathaysia Block and also along the Jiangnan belt. Subduction of ancient oceanic lithospheric materials (or crustal thickening) during Mesozoic and formation of eclogites suggest that the Cathaysia Block was perhaps in the Tethyan oceanic domain at this time. The granulite formation might have been aided by Mesozoic mafic magma underplating associated with lithospheric delamination, heating and retrogression of the eclogite accompanied by rapid uplift.