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      https://www.ias.ac.in/article/fulltext/jess/130/0118

    • Keywords

       

      Granitoids; remnants; pristine character; Pindwara–Abu Road Belt (PARB); Delhi Supergroup (DSG); Meso-Neoproterozoic transition.

    • 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 ${\sim}$1200–1300 Ma for the associated calcareous metasediments of the PARB. The gneissic granitoid, basement to these metasediments, is hence considered to be pre-1300 Ma, older than the massive granitoids (1000–750 Ma). The span of events reveals that the southern terrane of the DSG of rocks, especially the PARB has a younger geological history as compared to the northern terrane of the Delhi Supergroup which has records of 1700–1400 Ma. The events recorded from the PARB of the DSG are younger in age and indicate Meso-Neoproterozoic transition (${\sim}$1300–750 Ma). Globally, these are correlatable with the Grenvillian orogeny followed by Rodinia Supercontinent, amalgamation, and splitting tectonism in the northwestern Indian Shield.

      $\bf{Highlights}$

      $\bullet$ 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.

      $\bullet$ Granitoids of the study area are categorized into massive and gneissic variants.Massive granitoid emplacement pertains to the threemajor Neoproterozoic thermal events that led to diminished preservation of pristine gneissic character.

      $\bullet$ 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).

      $\bullet$ 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.

      $\bullet$ The events recorded from the PARB of the Delhi Supergroup are younger in age and indicate Meso-Neoproterozoic transition (${\sim}$1300–750 Ma) that are globally correlatable with the Grenvillian orogeny followed by Rodinia Supercontinent amalgamation and splitting in the north-western Indian Shield.

    • Author Affiliations

       

      RIYA DUTTA1 HARSH BHU1 RITESH PUROHIT1 KAMAL KANT SHARMA2

      1. Department of Geology, M. L. S. University, Udaipur, Rajasthan 313 001, India.
      2. Department of Geology, Government College, Sirohi, Rajasthan 307 001, India.
    • Dates

       
  • Journal of Earth System Science | News

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