Mesoproterozoic granulites of the Shillong-Meghalaya Plateau: Evidence of westward continuation of the Prydz Bay Pan-African suture into Northeastern India
Mesoproterozoic granulites of the Shillong-Meghalaya Plateau: Evidence of westward continuation of the Prydz Bay Pan-African suture into Northeastern India
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DOI：
10.1016/j.precamres.2006.08.011
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发表时间：
2007-01-05
影响因子：
3.8
通讯作者：
Saikia, R. R.
中科院分区：
文献类型：
--
作者：
Chatterjee, Nilanjan;Mazumdar, A. C.;Saikia, R. R.
澳-南极地区的热年代学研究表明，东南极洲的Prydz湾泛非缝合线继续向西进入印度。然而。由于缺乏足够的热年代学资料，到目前为止，东印度境内的缝合线的位置还不确定。本文报道了罗迪尼亚超大陆新元古代-寒武纪古地磁重建中，位于印度盾极东北端靠近澳南极地块的西隆-梅加拉亚片麻岩杂岩（SMGC）两个区域的麻粒岩相变质岩的电子显微（EPMA）单脱石日期和矿物共长作用。在Garo-Goalpara Hills地区，1596 +/- 15 Ma （n = 103）的中元古代年龄与逆时针的压力-温度路径相关，近峰值条件为7-8 kbar和850℃，稀有的matrix monazite边缘记录了更年轻的年龄（1032-1273 Ma）。在Sonapahar地区，Garo-Goalpara山以东50公里处，麻粒岩相变质岩中的均质独居石颗粒产生的EPMA日期紧密聚集在500 +/- 14 Ma (n = 36)，而与它们在退火良好的矿物基质中的结构背景无关。在一些分带的独居石颗粒中，岩心的年龄为1078 +/- 31 Ma （n = 10）和1472 +/- 38 Ma （n = 13）。500 Ma的测年与880 ~ 480 Ma的斑岩花岗岩Rb-Sr测年相对应，斑岩花岗岩主要侵入SMGC的中东部。我们认为，寒武纪-奥陶纪在SMGC中逐渐向东的优势表明，印度板块与澳-南极板块最终合并为泛非板块，Prydz湾缝合线通过SMGC向北延伸，缝合线的西部边界可能位于Garo-Goalpara山和Sonapahar地区之间。(c) 2006 Elsevier B.V.版权所有
Thermo-chronologic considerations in the Australo-Antarctic domains suggest that the Prydz Bay Pan-African suture of East Antarctica continues westward into India. However. the location of the suture within Eastern India has so far been uncertain because of a lack of adequate thermo-chronological information. In this study, electron microprobe (EPMA) monazite dates and mineral paragenesis of granulite facies metapelites are reported from two areas of the Shillong-Meghalaya gneissic complex (SMGC), a crustal block located in the extreme northeast of the Indian shield close to the Australo-Antarctic block in Neoproterozoic-Cambrian paleomagnetic reconstructions of the Rodinia supercontinent. In the Garo-Goalpara Hills region, a well constrained Mesoproterozoic age of 1596 +/- 15 Ma (n = 103) is correlated with a counterclockwise pressure-teniperature path with near peak conditions of 7-8 kbar and 850 degrees C. Rare matrix monazite rims record younger ages (1032-1273 Ma). At Sonapahar region, 50 kin ESE of Garo-Goalpara Hills, homogenous monazite grains in granulite facies metapelites yield EPMA dates tightly clustered at 500 +/- 14 Ma (n = 36) irrespective of their textural setting in a well-annealed mineral matrix. In a few zoned monazite grains, the cores yield older ages of 1078 +/- 31 Ma (it = 10) and 1472 +/- 38 Ma (n = 13). The 500 Ma date corresponds with the ca. 880-480 Ma Rb-Sr dates of porphyritic granites that predominantly intruded the east-central part of the SMGC. We propose that the progressively eastward dominance Of Cambro-Ordovician ages in the SMGC indicates a Pan-African final amalgamation of the Indian plate with the Australo-Antarctic plate and a northward extension of the Prydz Bay suture through the SMGC, with the western boundary of the suture possibly located between the Garo-Goalpara Hills and Sonapahar areas. (c) 2006 Elsevier B.V. All rights reserved.