PALEOMAGNETIC STUDY OF THE EOCENE QUXU PLUTON OF THE GANGDESE BELT - CRUSTAL DEFORMATION ALONG THE INDUS-ZANGBO SUTURE ZONE IN SOUTHERN TIBET

Forty-five samples have been collected at nine sites on the 42.5 Ma Quxu pluton (90-degrees 50'E, 29-degrees 20'N) in the Gangdese batholith. Westerly declination (D = -48-degrees and -83-degrees) is observed in primary magnetizations from two sites about 25 km from the Indus-Zangbo suture zone after thermal demagnetization. This direction is consistent with the westerly paleomagnetic directions of the crustal blocks in other areas along the Indus-Zangbo suture zone. The Quxu pluton of the Gangdese Belt was rotated in a "domino style" deformation process as a part of a long (840 km) and narrow (less than 100 km) deformed zone between the India-Eurasia continents associated with the collision of India since 42.5 Ma. The pluton, between 11 km and 14 km from the suture acquired the secondary magnetization (D = -28-degrees and -39-degrees) during a cataclastic metamorphic process at sometime during the 'domino style' deformation. The primary magnetization was completely destroyed in the pluton within 11 km of the suture during slow cooling at the uplift stage and was replaced by thermoviscous remanent magnetization parallel to the present axial dipole field.