GEOLOGY OF THE WESTERN ARUNACHAL HIMALAYA IN PARTS OF TAWANG AND WEST KAMENG DISTRICTS, ARUNACHAL PRADESH DISCUSSION

摘要

The authors mention that the rapakivi texture in Bomdila gneiss and tongues and apophyses of Bomdila gneiss in the low-grade metasedimentaries are the evidences for intrusive origin of Bomdila gneiss. On the contrary in the same area, Srinivasan and Vikram Rai (1996) recorded many field evidences for granitisation of metasedimentaries (para gneiss origin) for Bomdila gneiss. Based on my extensive field experience in eastern Bhutan and western Arunachal Pradesh (Srinivasan, et al. 1995; Srinivasan and Vikram Rai, 1996; Srinivasan, 1999; Srinivasan, 2001), I can definitely state that the so-called tongues and apophyses are nothing but detached rafts and fold closures of this highly deformed gneiss. This Bomdila gneiss (para gneiss) with the associated metasedimentaries is involved in complex folding (Srinivasan and Vikram Rai, 1996; Srinivasan, 1999; Srinivasan, 2001) and the outcrop pattern of this gneiss in a map even gives the wrong impression of intrusive nature. I want to know whether the authors observed cross cutting relationship of this gneiss with the bedding contacts of metasedimentaries. If so, they may kindly provide photo evidence for cross cutting relationship and also for rapakivi texture.