北大别木子店石榴辉石岩的麻粒岩相退变质作用

张泽明; 钟增球; 游振东; 胡开明

北大别木子店石榴辉石岩的麻粒岩相退变质作用

1.
中国地质科学院地质研究所, 北京 100037
2.
中国地质大学地球科学学院, 武汉 430074
3.
浙江省区域地质调查院, 萧山 311203

基金项目:

国家自然科学基金重大项目 4979404

面上项目 49772142

面上项目 49772146

详细信息

作者简介:
张泽明, 男, 副教授, 博士后, 1961年生, 1996年毕业于中国地质大学, 获博士学位, 现主要从事岩石学与变质地质学研究

中图分类号: P588.3
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出版历程
- 收稿日期: 1999-09-30
- 刊出日期: 2000-05-25

GRANULITE-FACIES RETROGRADE METAMORPHISM OF GARNET PYROXENITE IN MUZIDIAN, NORTHERN DABIE MOUNTAINS

1.
Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
2.
Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China
3.
Zhejiang Institute of Regional Geological Survey, Xiaoshan 311203, China

摘要

摘要: 详细的岩相学、矿物化学、岩石化学和变质作用温压条件计算表明, 大别变质地体北部角闪二辉麻粒岩是石榴辉石岩在其抬升过程中经历麻粒岩相退变质作用的产物, 峰期变质作用至少是发生在高压榴辉岩相条件下, 而且地温梯度较低.石榴辉石岩的退变质作用p-t轨迹以早期的近等温降压、中期的近等压升温和晚期的降温降压为特征.这一结果表明北大别变质地体的峰期变质作用并非仅达麻粒岩相.
- 麻粒岩 /
- 石榴辉石岩 /
- 榴辉岩相 /
- P-T轨迹 /
- 北大别地体
Abstract: The detailed investigation into the amphibole two-pyroxene granulite in the north of Dabie metamorphic terrain in terms of petrography, mineral chemistry, petrochemistry, and estimated p-t conditions for metamorphism indicates that this rock is a product of the garnet pyroxenite that experienced the granulite-facies retrograde metamorphism during its uplift. The peak metamorphism occurred at least in the high-pressure eclogite facies at a lower temperature gradient. The retrograde metamorphism p-t path of the garnet pyroxenite was characterized by the near isothermal decompression in the early stage, the near isobaric temperature rise in the middle stage and the temperature fall and decompression in the late stage. These features suggest that the p-t conditions of peak metamorphism in the northern Dabie terrain are higher than that of granulite facies.
- granulite /
- garnet pyroxenite /
- eclogite facies /
- p-t path /
- northern Dabie terrain

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图 1 大别地体简化地质图(据文献[1]修改)

UAF.高角闪岩相; LAF.低角闪岩相; EAF.绿帘角闪岩相.1.随县群; 2.宿松群; 3.大别杂岩; 4.花岗岩; 5.断裂; 6.剪切带; 7.麻粒岩/样品位置

Fig. 1. Sketch geological map of Dabie terrain

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图 2 角闪二辉麻粒岩和石榴辉石岩残留体显微照片

A.角闪二辉麻粒岩, 由斜方辉石(Opx)、斜长石(Pl)、角闪石(Amp)和少量单斜辉石(Cpx)组成; B.角闪二辉麻粒岩中的石榴石后成合晶假象(Sym); C.石榴辉石岩的残留体石榴石(Grt)和单斜辉石(Cpx), 石榴石发育由斜方辉石和斜长石组成的后成合晶冠状体(Sym); D. 石榴辉石岩的石榴石残留体(Grt)及其由斜方辉石和斜长石组成的后成合晶冠状体(Sym).A, B和C为单偏光, 长边为3.3 cm, D为正交偏光, 长边3.3 cm

Fig. 2. Photomicrographs of amphibole two-pyroxene granulite and relic of garnet pyroxenite

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图 3 石榴石的化学成分环带

分析点间距为0.03 mm

Fig. 3. Chemical compositional zoning of garnet

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图 4 石榴辉石岩稀土元素球粒陨石标准化分配型式

Fig. 4. Chondrite-normalized REE distribution pattern of garnet pyroxenite

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图 5 石榴辉石岩变质作用p-t轨迹

图中变质相界据Evans^[19].E.榴辉岩相; G.麻粒岩相; A.角闪岩相; EA.绿帘角闪岩相; B.蓝片岩相; GS.绿片岩相.Al₂O₅多型转变反应据Holdaway^[20]; 图中轨迹为石榴辉石岩变质作用p-t轨迹.Ⅰ.石榴辉石岩阶段; Ⅱ.后成合晶阶段; Ⅲ.麻粒岩相阶段; Ⅳ.角闪岩相阶段; 轨迹为南大别地区超高压变质岩的p-t轨迹^{[21, 14]}; 温压计单变线分别为: BT Blundy和Holland角闪石-斜长石温度计, BTB Brey和Kokler的二辉石温度计, BTC Brey和Kokler的斜方辉石中Ca含量温度计, HP Harley石榴石-斜方辉石压力计, HT Harley石榴石-斜方辉石温度计, N P Newton和Parkins石榴石-斜方辉石-斜长石-石英反应压力计, PAP Paria等石榴石-单斜辉石-斜方辉石-斜长石-石英反应Fe端元压力计, PBP Paria等石榴石-单斜辉石-斜方辉石-斜长石-石英反应Mg端元压力计, PT Powell石榴石-单斜辉石温度计, S T Sen和Bhattacharya石榴石-斜方辉石温度计.Ky.蓝晶石; And.红柱石; Sill.夕线石; Grt.石榴石; Cpx.单斜辉石; Opx. 斜方辉石; Pl.斜长石; Qtz.石英

Fig. 5. Metamorphic p-t path of garnet pyroxenite

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表 1 北大别木子店石榴辉石岩的代表性矿物电子探针分析结果

Table 1. Representative mineral analyses of garnet pyroxenite of Muzidian of northem Dabie

表 2 各阶段变质温压条件估算

Table 2. Estimated p-t conditions for various stages of metamorphism

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