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Structure and chronology across the Achankovil terrain boundary shear zone system (South India), and its Madagascar connection in the Gondwanaland
International Journal of Earth Sciences ( IF 2.3 ) Pub Date : 2021-03-30 , DOI: 10.1007/s00531-021-02029-5
P. Praharaj , S. Rekha , A. Bhattacharya

In South India, the WNW-striking ~ 130-km-long Achankovil Shear Zone (AKSZ) separating the Trivandrum Block and the Madurai Block is speculated to continue within southern Madagascar in the East Gondwanaland. Two aspects continue to be debated, whether the AKSZ is a terrain boundary shear zone, and if so, when the accretion occurred. We present, for the first time, a detailed field-based analysis of contrasting mesoscale structures and deformation kinematics in the granulite facies rocks across the AKSZ. The mineralogical segregation layering (S2T) in the Trivandrum Block is sub-horizontal to gently inclined and describes F3T regional-scale open asymmetric WNW-trending sub-horizontal folds. By contrast, the S2M granulite facies layering in the Madurai Block describes regional-scale steeply plunging F3M folds. Both blocks share the NNW/NNE-trending sub-parallel sinistral and dextral S3 shears of the AKSZ. Deformation microstructures and garnet-bearing melt-hosted syn-S3 extensional shears attest to the persistence of high temperature during D2–D3 deformations. Monazite chemical dates and existing Pb–Pb zircon dates are overwhelmingly Pan-African in and across the AKSZ, but the Paleoproterozoic (2.1–1.8 Ga) dates in the Trivandrum Block, equivalent to those reported in Anosyan and Androyan domains of southern Madagascar, are lacking in the Madurai Block. By contrast, the Mid Neoproterozoic (800–750 Ma) Pb–Pb zircon dates in the Madurai Block, equivalent to the Antananarivo domain (Central Madagascar), are lacking in the Trivandrum Block. The structural–chronological contrasts between the two blocks suggest the AKSZ to be a Pan-African terrain boundary shear zone system that is continuous with the Ranotsara shear zone in Madagascar. [248]



中文翻译:

横跨Achankovil地形边界切变带系统(印度南部)的结构和年代,及其在冈瓦纳大陆的马达加斯加连接

在印度南部,WNW引人注目〜130公里长的Achankovil剪切带(AKSZ)分隔了Trivandrum区块和Madurai区块,预计将在东部Gondwanaland的马达加斯加南部继续延伸。仍在争论两个方面,AKSZ是否为地形边界剪切带,如果是,则何时发生积聚。我们首次提出了基于现场的详细分析,该分析对整个AKSZ的粒岩相岩石中的中尺度结构和形变运动学进行了对比。Trivandrum区块中的矿物分离层(S 2T)为近水平至平缓倾斜,并描述了F 3T区域规模的开放性非对称WNW趋势亚水平褶皱。相比之下,S 2MMadurai区块中的粒岩相分层描述了区域规模的急剧下降的F 3M褶皱。两个模块共享AKSZ的NNW / NNE趋势次平行的左旋和右旋S 3剪切机。变形微观结构和含石榴石的熔体承载的syn-S 3拉伸剪切机证明了D 2 –D 3期间的高温持续存在变形。在AKSZ及其整个地区,独居石化学日期和现有的Pb-Pb锆石日期绝大多数是泛非洲的,但是Trivandrum区块中的古元古代(2.1–1.8 Ga)日期与马达加斯加南部Anosyan和Androyan域报道的日期相同。马杜赖街区缺乏。相比之下,特里凡得琅地块缺少在马杜赖地块中的新元古代中期(800-750 Ma)Pb-Pb锆石,相当于安塔那那利佛地域(马达加斯加中部)。两个区块之间的结构-时间顺序对比表明,AKSZ是一个泛非洲地形边界剪切带系统,与马达加斯加的Ranotsara剪切带连续。[248]

更新日期:2021-03-30
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