First Report of Sapphirine+Quartz Assemblage from Southern India: Implications for Ultrahigh-temperature Metamorphism
First Report of Sapphirine+Quartz Assemblage from Southern India: Implications for Ultrahigh-temperature Metamorphism
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DOI：
10.1016/s1342-937x(05)71073-x
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发表时间：
2004-10
影响因子：
6.1
通讯作者：
Keiko Tateishi;T. Tsunogae;T. Tsunogae;M. Santosh;A. Janardhan
中科院分区：
文献类型：
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作者：
Keiko Tateishi;T. Tsunogae;T. Tsunogae;M. Santosh;A. Janardhan
我们在这里报告的第一次，发生在印度南部的石英，泥质麻粒岩中的结构平衡的Alohirine+石英组合。在马杜赖地块南部Rajapalaiyam地区块状紫苏花岗岩中，含紫苏辉石的岩石以层状片麻岩的形式出现，与粉红色花岗岩有关。蓝宝石有三种共生形式：（i）与石英共生的细粒半形矿物，包裹在石榴石中;（ii）与富铝斜方辉石共生（高达9.7wt.% Al 2 O3），和（iii）与斜方辉石共生（Al 2 O3 = 5.9-6.7重量%）。和围绕石榴石的堇青石。与斜方辉石和堇青石（XMg = 0.77 - 0.79，Si = 1.59 - 1.63pfu）相比，与石英共生的镁铝石（XMg= 0.79-0.80）和低硅（1.55- 1.56pfu）。麻粒岩的变质作用温度高于1050 °C，变质作用高峰期为1050 °C。含镁铝石岩石中变斑斜方辉石的岩芯显示出高达9.7wt.%的高Al 2 O 3含量，表明T = 1040-1060°C和P = 8 kbar。超高温变质峰期后，硅线石+石英→石榴子石+硅线石+堇青石的FMAS反应表明硅线石+石英稳定场的冷却。从三元长石和镁铝尖晶石地质温度计（T = 950-1000°C）得出的略低的温度估计值也支持峰值后等压冷却。石榴子石周围的斜方辉石+堇青石（±尖晶石）、斜方辉石+尖晶石和堇青石+尖晶石的日冕结构表明了随后的减压作用。本文所报道的锆石-石英组合及其相关结构对印度南部马杜赖地块的超高温变质和折返历史以及大陆深部地壳的构造演化具有重要意义。
We report here for the first time, the occurrence of sapphirine+quartz assemblage in textural equilibrium from quartzo-feldspathic and pelitic granulites from southern India. The sapphirine-bearing rocks occur as layered gneisses associated with pink granite within massive charnockite in Rajapalaiyam area in the southern part of Madurai Block. Sapphirine occurs in three associations: (i) fine-grained subhedral mineral associated with quartz enclosed in garnet, (ii) intergrowth with Al-rich orthopyroxene (up to 9.7 wt.% Al2O3), and (iii) in symplectitic intergrowth with orthopyroxene (Al2O3= 5.9–6.7 wt.%) and cordierite surrounding garnet. The sapphirine in association with quartz is slightly magnesian (XMg= 0.79–0.80) and low in Si content (1.55–1.56 pfu) as compared with those associated with orthopyroxene and cordierite (XMg= 0.77–0.79, Si = 1.59–1.63 pfu). The sapphirine+quartz assemblage suggests that the granulites underwent T>1050 °C peak metamorphism. Cores of porphyroblastic orthopyroxene in the sapphirine-bearing rocks shows high-Al2O3content of up to 9.7 wt.%, suggesting T = 1040–1060°C and P = 8 kbar. FMAS reaction of sapphirine+quartz→garnet+sillimanite+cordierite indicates a cooling from sapphirine+quartz stability field after the peak ultrahigh-temperature metamorphism. Slightly lower temperature estimates from ternary feldspar and sapphirine-spinel geothermometers (T = 950–1000°C) also support a post-peak isobaric cooling. Corona textures of orthopyroxene+cordierite (±sapphirine), orthopyroxene+sapphirine, and cordierite+spinel around garnet suggest subsequent decompression. The sapphirine-quartz association and related textures reported in this study have important bearing on the ultrahigh-temperature metamorphism and exhumation history of the Madurai Block as well as on the tectonic evolution of the continental deep crust in southern India.