印度东高止山脉安格尔麻粒岩组下地壳变质作用的对比风格:对印度-南极洲对比的启示

IF 3.5 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Aparupa Banerjee, Proloy Ganguly, Kaushik Das, Nilanjana Sorcar, Sankar Bose
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引用次数: 0

摘要

摘要本文研究了东高盖特省(EGP)北缘元古界安格尔域的一套高品位岩石,包括基性麻粒岩、铝质麻粒岩、孔雀岩、绿硝子岩和奥根片麻岩,以及含橄榄变质岩、辉长岩和斑岩花岗岩等中品位岩石。根据岩石学和地温压资料,确定了两个不同的变质事件。早期事件(MA1)的印记保存在基性麻粒岩、铝质麻粒岩、孔雀岩、奥根片麻岩和细粒绿粒岩中,但在基性麻粒岩和铝质麻粒岩中保存最好。镁质麻粒岩在MA1峰条件下稳定为正辉石+斜辉石+斜长石±石榴石+钛铁矿±石英组合,MA1峰条件下稳定为Fe3+-石榴石+赤铁矿+磁铁矿+堇青石+ k长石+斜长石+硅线石+石英+铝质麻粒岩熔体。相平衡模型和热气压数据表明,该事件的P-T条件为>850°C, 7至8kbar。逆行变质作用(MA1R)包括轻微的减压(降至~5 kbar)和随后的冷却,分别在铝质麻粒岩和基性麻粒岩中形成含黑云母和含角闪石的矿物组合。原岩结构约束的单殖石(U-Th-total Pb)和锆石(U-Pb)数据表明,MA1变质作用的年龄约为1200 Ma,与花岗质和绿砾质岩浆作用有关,受长根片麻岩和细粒绿砾岩中振荡带锆石域的约束。整体岩石受MA2次较年轻变质事件的影响,其结构特征为角闪石(MA1R期发育)部分置换为基性麻粒岩中的正辉石±斜辉石+斜长石±钛铁矿+熔体组合。铝质麻粒岩中的黑云母经脱水熔融形成石榴石+堇青石组合。上述组合中的石榴石未形成成斑岩阶段,并生长于MA1石榴石之上。MA2事件遵循逆时针的P-T轨迹,导致加热(高达800°C)和相关负载(从4.0到5.8 kbar)沿着前进路径。铝质麻粒岩和孔石的独居石U-Th-total Pb数据显示,MA2年龄分别为987±12 Ma和975±16 Ma。细粒绿帘岩和长片麻岩也记录了MA2事件的印记,形成了薄到厚的扇形带过度生长,群体年龄分别为979±12和982±29 Ma。962±13 Ma形成的基性麻粒岩中锆石过度生长。MA2事件与粗粒绿帘石(983±22 Ma)和斑状花岗岩(960±10 Ma)的结晶一致。因此,地质年代学资料表明,安格尔域在约990 ~ 960 Ma经历了MA2变质作用和伴生岩浆作用。MA1事件(~ 1200ma)在EGP的大部分地区明显缺失,而其在安格尔域占主导地位,表明后者可能是约1200ma的外来块体,约960ma后才与EGP的其余部分结合。我们进一步认为,安圭尔地区的变质史与东南极洲Prydz湾地区的变质史有着显著的不同,但与东南极洲Prydz湾地区的变质史非常吻合。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Contrasting styles of lower crustal metamorphism from a granulite suite of rocks from Angul, Eastern Ghats Belt, India: Implications for the India-Antarctica correlation
Abstract The present work is focussed on a suite of high-grade rocks including mafic granulite, aluminous granulite, khondalite, charnockite, and augen gneiss along with medium-grade rocks like olivine-bearing metanorite, gabbro, and porphyritic granite of the Angul domain at the northern margin of the Proterozoic Eastern Ghats Province (EGP). Based on the petrological and geothermobarometric data, two distinct metamorphic events have been identified. The imprints of the earlier event (MA1) are preserved in the mafic granulite, aluminous granulite, khondalite, augen gneiss, and fine-grained charnockite, but those are best preserved in mafic granulite and aluminous granulite. In mafic granulite, orthopyroxene + clinopyroxene + plagioclase ± garnet+ ilmenite ± quartz assemblage was stabilised at the peak MA1 conditions, whereas the peak MA1 assemblage is represented by Fe3+-garnet + hematite + magnetite + cordierite + K-feldspar + plagioclase + sillimanite + quartz + melt in aluminous granulite. Phase equilibria modelling and thermobarometric data suggest the P–T conditions of >850°C, 7 to 8 kbar for this event. The retrograde metamorphism (MA1R) involved minor decompression (down to ~5 kbar) and subsequent cooling to form biotite- and hornblende-bearing mineral assemblages in aluminous granulite and mafic granulite, respectively. Texturally constrained monazite (U–Th–total Pb) and zircon (U–Pb) data from the former rock suggest ca. 1200 Ma age of the MA1 metamorphism, which was associated with granitic and charnockitic magmatism as constrained from oscillatory-zoned zircon domains in the augen gneiss and fine-grained charnockite. The rock ensemble was affected by a younger metamorphic event (MA2), which is texturally characterised by partial replacement of hornblende (developed during MA1R) to orthopyroxene ± clinopyroxene + plagioclase ± ilmenite + melt assemblage in mafic granulite. Moreover, biotite of aluminous granulite has undergone dehydration melting to produce garnet + cordierite-bearing assemblage. Garnet in the above assemblage did not form as porphyroblastic phase and overgrew the MA1 garnet. The MA2 event followed a counterclockwise P–T trajectory, causing heating (up to 800°C) with associated loading (from 4.0 to 5.8 kbar) along the prograde path. Monazite U–Th–total Pb data from aluminous granulite and khondalite suggest MA2 ages of 987 ± 12 and 975 ± 16 Ma, respectively. Fine-grained charnockite and augen gneiss also recorded the imprints of MA2 event by developing thin to thick sector-zoned overgrowth yielding group ages of 979 ± 12 and 982 ± 29 Ma, respectively. Zircon overgrowth in mafic granulite formed at 962 ± 13 Ma. The MA2 event coincides with the crystallisation of coarse-grained charnockite at 983 ± 22 Ma and porphyritic granite at 960 ± 10 Ma. Geochronological data, thus, indicate that the Angul domain underwent the MA2 metamorphism and associated magmatism at ca. 990 to 960 Ma. The apparent absence of MA1 event (~1200 Ma) in the greater part of the EGP and its dominance in the Angul domain suggest that the latter was possibly an exotic block at ca. 1200 Ma and joined with the rest of the EGP only after ca. 960 Ma. We further suggest that the metamorphic history of the Angul domain is strikingly different from the rest of the EGP, but matches well with that of the Prydz Bay region of the East Antarctica.
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来源期刊
Journal of Petrology
Journal of Petrology 地学-地球化学与地球物理
CiteScore
6.90
自引率
12.80%
发文量
117
审稿时长
12 months
期刊介绍: The Journal of Petrology provides an international forum for the publication of high quality research in the broad field of igneous and metamorphic petrology and petrogenesis. Papers published cover a vast range of topics in areas such as major element, trace element and isotope geochemistry and geochronology applied to petrogenesis; experimental petrology; processes of magma generation, differentiation and emplacement; quantitative studies of rock-forming minerals and their paragenesis; regional studies of igneous and meta morphic rocks which contribute to the solution of fundamental petrological problems; theoretical modelling of petrogenetic processes.
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