Parh Group basalts of northeastern Balochistan, Pakistan; precursors to the Deccan Traps; Himalaya and Tibet; mountain roots to mountain tops
Special Paper - Geological Society of America
The Late Cretaceous Parh Group basalts of northeastern Balochistan, Pakistan, crop out in a northeast-trending linear belt of more than 300 km, from Kach in the southwest to Waziristan Northwest Frontier Province in the northeast. The base of the Parh Group volcanic rocks generally consists of pillow basalt, grading upward into volcanic agglomerate, breccia, and tuff. Cherty limestone is associated with both the pillow basalts and the agglomerates. The volcanic rocks in the Parh Group are predominantly alkali olivine basalt, and have lesser olivine tholeiite and very minor quartz tholeiite. With the exception of one quartz tholeiite unit, which has a mid-ocean ridge basalt composition, the Parh Group basalts have whole-rock major and trace element compositions similar to those of hotspot-related oceanic-island basalts of the Southern Hemisphere, such as Reunion and Tristan Da Cunha. The compositions of the Parh Group volcanic rocks and their geological setting suggest that the source for the volcanic rocks was oceanic islands on the continental shelf or slope along the boundary between the Indo-Pakistan plate and the Tethys sea, before they were thrust into their present position in the India-Eurasia suture. The ages of the Parh Group volcanics precede and slightly overlap those of the nearby Deccan Traps, suggesting that they represent the earliest magmas generated from the rising Reunion hotspot plume, which would have been below the Tethyan ocean floor before the main pulse of Deccan volcanism. Therefore, these early Parh Group lavas probably are the northernmost and oldest of the Reunion hotspot trail. The low volume and generally alkaline nature of all of these lava flows suggest that they represent small-degree melts associated with cooler edges of the thermal plume that created the immense Deccan Traps.
Published Article/Book Citation
Special Paper - Geological Society of America, 328 (1999) pp.59-74.