Thermochronological constraints on two pulses of Cenozoic high-K magmatism in eastern Tibet

• 作 者: 王江海 尹安 周江羽 张玉泉 解广轰
• 机 构: Guangzhou Institute of Geochemistry, Chinese Academy of Sciences,Department of Earth & Space Science
• 出 处: Science in China(Series D:Earth Sciences)
• 发表日期: 2003年07期
• 关键词: Cenozoic Tibet eastern mantle magmatic younger isotopic volcanic enriched constr

The previously published U-Pb and 40Ar/39Ar ages and our 21 newly-obtained 40Ar/39Ar ages suggest that the Cenozoic magmatism in eastern Tibet and Indochina occurred in two episodes, each with distinctive geochemical signatures, at (40—28) Ma and (16—0) Ma. The older rocks are localized along the major strike-slip faults such as the Jinsha-Red River fault system and erupted synchronously with transpression. The younger rocks are widely distributed in rift basins and coeval with the east-west extension of Tibet and eastern Asia. Combining with their geochemical data, we consider that the earlier magmatic phase was generated by continental subduction, while the later volcanic phase was caused by decompression melting of a recently meta- somatically-altered, depleted mantle source. The magmatic gap between the two igneous pulses represents an important geodynamic transition in the evolution of eastern Tibet, from the processes controlled mainly by crustal deformation to those largely dominated by mantle tectonics.

The previously published U-Pb and 40Ar / 39Arges and our 21 newly-obtained 40Ar / 39Arches suggest that the Cenozoic magmatism in eastern Tibet and Indochina occurred in two episodes, each with distinctive geochemical signatures, at (40-28) Ma and (16-0) Ma. The older rocks are localized along the major strike-slip faults such as the Jinsha-Red River fault system and erupted synchronously with transpression. The younger rocks are distributed in rift basins and coeval with the east-west extension of Tibet and eastern Asia. Combining with their geochemical data, we consider that the earlier magmatic phase was generated by continental subduction, while the later volcanic phase was caused by decompression melting of a recently meta- somatically-altered, depleted mantle source. The magmatic gap between the two igneous pulses represents an important geodynamic transition in the evolution of eastern Tibet, from the processes controlled mainly by crustal deformation to those largely dominated by mantle tectonics.