ISOTOPIC AGES OF THE I TYPE GRANITESIN WEST JUNGGAR SAWUER REGION

Abstract

Sawuer region is located in west Junggar, Jimunai County of Altay district and Hefeng county of Tacheng district, Xinjiang. The region is along the north margin of Kazakstan-Junggar plate. The intrusions (mainly acid) are widespread. The Sentasi intrusion, the Wokensala intrusion and the Tasite intrusion are mainly adamellite. According to SHRIMP U-Pb age analysis results, the crystallization age of Sentasi intrusion is 328.2±5.7Ma(1σ) and that of Wokensala intrusion is 323.8±6.2Ma(1σ), and the age of Tasite intrusion is 313.6±3.2Ma(1σ) with 40Ar/39Ar age analysis results, corresponding to the afternoon of early Carboniferous. The intrusions belong to I type granite and are the partial alkali rock. The Nd, Sr, Pb isotope compositions of the intrusions indicate a mantle source, while the δ18O values are normal. The intrusions belong to post-collisional granite, indicating that the Sawuer region indeed west Junggar was in the post-collisional setting in the afternoon of early Carboniferous. They might form in the extrusion to extension period of the post-collisional stage. The geochemistry characteristics of the Sentasi, Wokensala and Tasite intrusions are similar to those of known I type granites formed at about 300Ma in Junggar. The post-collisional I type granites must begin to form in the afternoon of early Carboniferous in Junggar. The confirmation of post-collisional I type granites of afternoon of early Carboniferous in the Sawuer region provides new evidence for the regional vertical continental growth in late Paleozoic.