Journal of Earth System Science ( IF 1.9 ) Pub Date : 2021-06-09 , DOI: 10.1007/s12040-021-01607-0 Riya Dutta , Harsh Bhu , Ritesh Purohit , Kamal Kant Sharma
Abstract
Granitoids from Pindwara–Abu Road Belt (PARB) are studied to characterize their tectonostratigraphic status in relation to the associated metasediments. The PARB lies along the southern swathes of the Mesoproterozoic Delhi Supergroup (DSG) in the Aravalli Delhi Mobile Belt (ADMB) of the northwestern Indian Shield. The outcrop scale granitoids of the study area are categorized into massive and gneissic variants. The former variety is being prominently exposed as leucocratic variant intrusive into the melanocratic gneisses as well as associated metasediments. Massive intrusive granitoids have been dated previously representing three major regional thermal events of 1000, 850, and 750 Ma. These multiple tectono-thermal events have led to diminished preservation of pristine gneissic character in the granitoids outcropping as dismembered bodies in the PARB. Consequently, the field relationship between the granitoids and associated metasediments is extremely obliterated. The present study, with the help of regional and detailed mapping on different scales and petrography, has attempted to establish basement–cover relationship between the gneissic granitoids and the associated metasediments. Quartzite outcrops are delineated as marker horizons characterizing the contact lithounit between the two. The cover rocks have sheared contact with the gneissic basement, which has a limited patchy outcrop pattern as ‘Remnants’. These ‘Remnant’ outcrops, conceivably behaved as primitive relicts, perhaps acted as a cradle for the proximal metasediments. Earlier studies, based on heavy carbon isotope character, have given an age span of ~1200–1300 Ma for the associated calcareous metasediments of the PARB. The gneissic granitoid, basement to these metasediments, is hence considered to be pre-1300 Ma, older than the massive granitoids (1000–750 Ma). The span of events reveals that the southern terrane of the DSG of rocks, especially the PARB has a younger geological history as compared to the northern terrane of the Delhi Supergroup which has records of 1700–1400 Ma. The events recorded from the PARB of the DSG are younger in age and indicate Meso-Neoproterozoic transition (~1300–750 Ma). Globally, these are correlatable with the Grenvillian orogeny followed by Rodinia Supercontinent, amalgamation, and splitting tectonism in the northwestern Indian Shield.
Research highlights
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Granitoids from Pindwara-Abu Road Belt (PARB) are studied to characterize their tectonostratigraphic status in relation to the associated metasediments and are attempted to establish the basement-cover relationship between the granitoids and the associated country rocks.
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Granitoids of the study area are categorized into massive and gneissic variants.Massive granitoid emplacement pertains to the three major Neoproterozoic thermal events that led to diminished preservation of pristine gneissic character.
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Gneissic Granitoids preserve pristine characters, conceivably behaved as primitive relicts that perhaps acted as a cradle for the proximal metasediments. These gneissic granitoids are henceforth considered to be pre-1300 Ma, older than the massive granitoids (1000 Ma to 750 Ma).
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Quartzite outcrops are delineated as marker horizons, characterizing the contact lithounit between the gneissic granitoids and metasediments. These granitoids and associate quartzite display regional scale enêchelon pattern of distribution reflecting impact of transpressional shearing.
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The events recorded from the PARB of the Delhi Supergroup are younger in age and indicate Meso-Neoproterozoic transition (~1300–750 Ma) that are globally correlatable with the Grenvillian orogeny followed by Rodinia Supercontinent amalgamation and splitting in the north-western Indian Shield.
中文翻译：
来自中元古代德里超群的 Pindwara-Abu 公路带花岗岩地质：构造意义
摘要
研究来自 Pindwara-Abu 公路带 (PARB) 的花岗岩，以表征与相关变质沉积物相关的构造地层状态。PARB 位于印度地盾西北部阿拉瓦利德里移动带 (ADMB) 中元古代德里超群 (DSG) 的南部。研究区露头规模花岗岩分为块状变体和片麻岩变体。前一种变体作为侵入黑质片麻岩以及相关变质沉积物的白斑变体而显着暴露。先前已经确定了大量侵入花岗岩的年代，它们代表了 1000、850 和 750 Ma 的三个主要区域热事件。这些多重构造热事件导致在PARB中作为肢解体露头的花岗岩中原始片麻岩特征的保存减少。因此，花岗岩类与相关变质沉积物之间的现场关系被极大地消除了。本研究借助不同尺度的区域详细绘图和岩相学，试图建立片麻质花岗岩与相关变质沉积物之间的基底-覆盖关系。石英岩露头被描绘为标记层，表征两者之间的接触岩石单元。覆盖岩与片麻岩基底发生剪切接触，片麻岩基底具有作为“残余物”的有限的片状露头模式。这些“残余”露头，可以想象作为原始遗迹，也许是近端变质沉积物的摇篮。早期的研究基于重碳同位素特征，给出了 PARB 相关钙质变沉积物的年龄跨度约为 1200-1300 Ma。片麻质花岗岩是这些变质沉积物的基底，因此被认为是 1300 Ma 之前的，比块状花岗岩（1000-750 Ma）更古老。事件的跨度表明，与记录为 1700-1400 Ma 的德里超群的北部地体相比，岩石 DSG 的南部地体，尤其是 PARB 具有更年轻的地质历史。从 DSG 的 PARB 记录的事件年龄较小，表明中-新元古代过渡（~1300-750 Ma）。在全球范围内，这些与格伦维尔造山运动、罗迪尼亚超大陆、合并、
研究亮点
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研究来自 Pindwara-Abu 公路带 (PARB) 的花岗岩以表征其与相关变质沉积物相关的构造地层状态，并试图建立花岗岩与相关围岩之间的基底-覆盖关系。
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研究区的花岗岩分为块状变体和片麻岩变体。大规模花岗岩侵位属于导致原始片麻岩特征保存减弱的三大新元古代热事件。
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片麻岩花岗岩保留了原始特征，可以想象其表现为原始遗迹，可能充当了近端变质沉积物的摇篮。这些片麻岩花岗岩被认为是 1300 Ma 之前的，比块状花岗岩（1000 Ma 到 750 Ma）更古老。
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石英岩露头被描绘为标志层，表征片麻质花岗岩和变质沉积物之间的接触岩石单元。这些花岗岩和伴生石英岩显示出区域尺度的分布格局，反映了挤压剪切的影响。
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从德里超群的 PARB 记录的事件年龄较小，表明中-新元古代过渡（~1300-750 Ma）与 Grenvillian 造山运动相关，随后是 Rodinia 超大陆合并和印度地盾西北部的分裂。
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