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      https://www.ias.ac.in/article/fulltext/jess/128/03/0051

    • Keywords

       

      Pseudotachylyte; cataclasite; survivor clasts; roundness; melting.

    • Abstract

       

      Roundness of survivor clasts (mineral/rock fragments) in fault rocks (e.g., pseudotachylyte and cataclasite/gouge) has been used by some workers to distinguish melt-origin from crush-origin of such rocks. Keeping in view the large overlap in the published data on the roundness of fault rocks, the reliability of such a discriminator appears somewhat uncertain. The present study attempts to reappraise the aforesaid criterion through roundness analysis of quartz and feldspar clasts in melting-dominated pseudotachylyte (M-Pt), crushing-dominated pseudotachylyte (C-Pt) and fault-related cataclasite (F-Ct) collected from Sarwar–Junia Fault Zone in Rajasthan and from Gavilgarh–Tan Shear Zone in central India. Our analysis shows that roundness of clasts cannot reliably distinguish between fault rocks of melt-origin and crush-origin (especially M-Pt and F-Ct) as the roundness values overlap and a distinct limit of roundness value for each rock type cannot be established. While the roundness of clasts in M-Pt and C-Pt may be enhanced due to melt-induced rounding off of the initially angular clasts, rounding of clasts can also occur by abrasion during rolling of crushed material in F-Ct. Furthermore, anomalous thermal expansion of clasts in melt-origin pseudotachylyte may cause disintegration of larger clasts into smaller angular fragments, thereby increasing the percentage of angular clasts in melt-origin fault rocks. Therefore, roundness of survivor clasts cannot be solely used as a discriminator between melt-origin and crush-origin fault rocks.

    • Author Affiliations

       

      Arindam Sarkar1 Anupam Chattopadhyay1 Tusharika Singh1

      1. Department of Geology, University of Delhi, Delhi 110007, India.
    • Dates

       
  • Journal of Earth System Science | News

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