Miocene-Pleistocene crustal anatexis in the Namche Barwa massif, southern Tibet

Abstract

位于喜马拉雅东构造结的南迦巴瓦地块经历了复杂的构造变形、强烈的变质和深熔作用，是研究碰撞造山过程中地壳深熔作用的重要对象。完整地厘定新生代晚期岩浆作用期次对于揭示南迦巴瓦地区的构造演化历史和深部过程具有重要意义。南迦巴瓦地块3件淡色花岗岩样品的锆石U-Pb定年结果显示该地块经历了11.30±0.16Ma和2.59±0.04Ma两期地壳深熔作用，可能与南迦巴瓦地块晚新生代快速隆升和剥蚀相关。南迦巴瓦地块保存了大量的~11Ma变质作用和地壳深熔作用记录指示该时间段为构造活动剧烈期。上新世晚期的淡色花岗岩表明，穹窿的隆升和剥蚀所导致的岩浆作用至少持续到了~2.59Ma，代表了南迦巴瓦地区一次年轻的构造岩浆事件。;The Namche Barwa massif, located in the eastern tectonic junction of Himalayan Orogen, has experienced complex tectonic deformation, intensive metamorphism and anatexis which resulted in various types of leucogranites to investigate the nature of crustal anatexis during the tectonic evolution of collision orogenic belts. Knowledge of the timing of such crustal anatexis in rapidly exhumed high grade metamorphic terranes like the Namche Barwa is important to understand the feedback of rapid near-surface processes (erosion and denudation) and those relatively deep processes (high-T metamorphism and partial melting). Zircon U-Pb dating of three leucogranite samples from the Namche Barwa yields that this block has experienced two episodes of young crustal anatexis (11.30±0.16Ma and 2.59±0.04Ma, respectively), which may be related to rapid denudation and uplift of the Namche Barwa in the Late Cenozoic. A number of studies have demonstrated that various rock types in the Namche Barwa have experienced a major episode of metamorphism and crustal anatexis at~11Ma, indicating intense tectonic activities in this period. Occurrence of leucogranite of late Pliocene in age further suggests that the anatectic processes caused by rapid denudation and uplift in this massif lasted at least to~2.59Ma.