Health & Environmental Research Online (HERO)


Print Feedback Export to File
7153395 
Journal Article 
Cenozoic crustal anatexis and the leucogranites in the Himalayan collisional orogenic belt 
Zeng LingSen; Gao LiE; , 
2017 
SCIENCE PRESS 
BEIJING 
1420-1444 
WOS:000403701000004 
Since the India-Eurasian continental collision, the Himalayan orogenic belt has experienced major tectonic transitions from earlier crustal compression and thickening to later extension and rapid exhumation, which induced pronounced changes in the pressure-temperature-composition (P-T-X) of high-grade metamorphic rocks. Consequently, the mid to lower crustal rocks has undergone correspondingly different partial melting processes and produced a wide spectrum of melts of leucogranitic compositions. Such granites show substantial differences in ages of crystallization, mineral compositions, whole-rock element as well as radiogenic isotope (Sr and Nd) compositions. The earliest anatexis is represented by the Eocene (similar to 43 Ma) high Sr/Y granites from melting of mafic rocks under thickened crustal conditions, followed by the melting of metasedimentary rocks in the Oligocene time, possibly induced by the initiation of rapid exhumation of the Himalayan high grade basements. A majority of leucogranites formed from similar to 25Ma to similar to 10Ma were derived either from fluxed melting of muscovite (A-type) or from muscovite dehydration melting (B-type) of metasediments. These two modes of crustal anatexis, possibly from vastly similar source rocks, generated granitic melts with substantial differences in major and trace element as well as Sr isotope geochemistry due to the coupled differences in the melting behavior of the major minerals (muscovite, feldspar) and accessory phases (zircon and monazite) during different modes of crustal anatexis. Each phases of leucogranite production are accompanied by various degrees of differentiation and the formation of highly fractionated leucogranites. Some of such leucogranites are highly enriched in key metal elements (Sn, Nb, Ta, and Be) and thus could be potential targets for future exploration of precious metals. Data summarized in this contribution suggests a strong coupling of granite chemical compositions with the changes in tectonic regimes, which in turn implies that leucogranites, by sorting out their original melt compositions, could serve as a valuable probe to investigate the physical and chemical behavior of deep crustal rocks in collisional orogenic belts worldwide.