Delineating crustal domains in Peninsular India: Age and chemistry of orthopyroxene-bearing felsic gneisses in the Madurai Block
Delineating crustal domains in Peninsular India: Age and chemistry of orthopyroxene-bearing felsic gneisses in the Madurai Block
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DOI：
10.1016/j.precamres.2011.12.013
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发表时间：
2012-03-01
影响因子：
3.8
通讯作者：
Clark, Chris
中科院分区：
文献类型：
--
作者：
Plavsa, Diana;Collins, Alan S.;Clark, Chris
印度南部的马杜赖地块富含花岗质正片麻岩，其中大部分含有斜方辉石（角辉岩）。这项研究发现，马杜赖地块西北部（广义上指 Karur-Kambam-Painavu-Trichur 线的北部和西部）的正片麻岩与马杜赖地块东南部的正片麻岩有很大不同。在马杜赖地块的北部和西北部，卡诺岩记录了新太古代（类似于 2.7-2.5Ga）的变质结晶年龄。套印温度与 535 Ma 相似。他们的太古宙 Nd 贫乏地幔模型年龄 (2.51-3.01 Ga)、高 epsilon Nd-(T) 值 (-3.28 和 +4.55 之间) 和低到中等的初始 Sr-87/Sr-86 比率 (0.7017-0.7106) 表明主要源自地幔，并涉及太古代地壳物质的不同程度。东南部马杜赖地块样本的结晶年龄要小得多，分别为 1007 +/- 23 Ma 和 784 +/- 18 Ma，一系列贫 Nd 地幔模型年龄在 1.38 至 1.69 Ga 之间，表明该地体的同位素演化存在显着不同。这些硫镁辉石的同位素特征（ε Nd-(T) = +2.58 至 -3.28，初始 Sr-87/Sr-86 = 0.7054-0.7084）表明地幔源参与了来自当代地壳的可变输入。所有样本都显示出由于埃迪卡拉纪-寒武纪变质作用（类似于 535 Ma）而导致的后续锆石生长或同位素扰动。正片麻岩的原生火成岩 U-Pb 年龄形成鲜明对比，识别出两个不同的地体；马杜赖地块北部和西部为太古代基底地体，南部和东部为以变沉积岩为主的元古代地体。两者之间的同位素边界在这里被定义为 Karur-Kambam-Painavu-Trichur (KKPT) 线状线以南的广阔区域，并表现为一系列向南倾斜的地震反射体。与马达加斯加中部进行了对比，那里的元古代沉积岩被冲断到塔那那利佛地块的新太古代正片麻岩之上。 (C) 2012 Elsevier B.V. 保留所有权利。
The Madurai Block of southern India is rich in granitic orthogneiss, much of which is orthopyroxene-bearing (charnockite). This study has identified that orthogneiss from the northwest of the Madurai Block (broadly defined as north and west of the Karur-Kambam-Painavu-Trichur lineament) has a very different origin from that in the south-eastern Madurai Block.To the north and north-west of the Madurai Block, charnockites record Neoarchaean (similar to 2.7-2.5Ga) crystallization ages with metamorphic overprinting at similar to 535 Ma. Their Archaean Nd depleted mantle model ages (2.51-3.01 Ga), high epsilon Nd-(T) values (between -3.28 and +4.55) and low to moderate initial Sr-87/Sr-86 ratios (0.7017-0.7106) indicate a primarily mantle-derived origin with variable involvement of Archaean crustal material. The south-east Madurai Block samples have much younger crystallization ages of 1007 +/- 23 Ma and 784 +/- 18 Ma and a range of Nd depleted mantle model ages between 1.38 and 1.69 Ga, suggesting a significantly different isotopic evolution of this terrane. The isotopic signature of these charnockites (epsilon Nd-(T) = +2.58 to -3.28, initial Sr-87/Sr-86 = 0.7054-0.7084) suggests the involvement of a mantle source with variable input from the contemporary crust. All samples show subsequent zircon growth, or isotopic disturbance, due to Ediacaran-Cambrian metamorphism (similar to 535 Ma).The sharply contrasting primary igneous U-Pb ages of orthogneisses identify two distinct terranes; an Archaean basement terrane to the north and west and a Proterozoic terrane dominated by metasedimentary rocks to the south and east of the Madurai Block. The isotopic boundary between the two is here defined as a broad zone south of the Karur-Kambam-Painavu-Trichur (KKPT) lineament and appears as a southerly dipping series of seismic reflectors. A correlation is made with central Madagascar where Proterozoic metsedimentary rocks are thrust over Neoarchaean orthogneisses of the Antananarivo Block. (C) 2012 Elsevier B.V. All rights reserved.