Characterizing crustal melt episodes in the Himalayan orogen

Abstract

Extensive studies have been undertaking in exploring the tectonic evolution of the Himalayan Orogen. Various tectonic models were developed to explain and constraint spatially and temporally critical events including the collision of Indian Plate with the Eurasia Plate, crustal thickening in association with the indentation, crustal spreading of the Tibetan Plateau. Recent study by King et al., 2011 identified two distinct leucogranite suites which were formed by contrasting tectonic actions at Sakya. They are Equigranular Anastomosing Leucogranite (AEG) formed under prograde fluidpresent condition while the Discrete Porphyritic Pluton Leucogranite (DPP) formed with retro-grade fluid-absent environment. Based on the characteristics of AEG and DPP, this study started with the acquisition of geochemistry data of rock samples collected for researches at various locations of the Himalaya Orogen. The two leucogranite suites were characterized through the study of their geochemistry comprised major elements, trace elements and rare earth elements models. Results of the studies concluded the existence of AEGs and DPPs distributed over the eastern area of the Himalaya Orogen beyond longitude 85 degree East. DPPs are also found at the far West location of the orogen. AEGs are typically formed from around 38Ma to 23Ma, while DPPs are of young age from 23Ma to 15Ma. Based on the observation of missing, or paucity in data for AEG and DPPs available to the west of longitude 85 degree East, it is hypothesized that recent collision of the Arabia plate to the Iran Domain inhibited the northward indentation movement of the Indian plate that not only caused the anticlockwise rotation of the Indian plate but also decreased the rate of tectonic movement of the Indian plate in the West relative to Eurasia plate. The slow rate of tectonic movement may result in insufficient thickening/energy developed within the crustal layer to cause any melting. Further studies to examine and development of the hypothesis is recommended.