西藏多龙矿集区发现早白垩世流纹岩夹层

The discovery of Early Cretaceous rhyolite interlayer in the Duolong ore concentration area,Tibet

继西藏冈底斯成矿带之后,新近探明的具有超大型远景的典型斑岩型铜金矿区——多龙矿集区地处西藏改则县西北部,班公湖-怒江缝合带北缘多不扎地区。早先西藏1∶25万物玛幅区调工作对多龙矿集区做过详细调查,填补了该缝合带北部研究的空白。近来区域地质调查发现,该区原先厘定的下侏罗统曲色组内出露早白垩世流纹岩夹层。流纹岩LA-ICP-MS锆石U-Pb年龄为118.8±1.4Ma,表明该套夹火山岩沉积地层的形成时代为早白垩世。这一发现补充了南羌塘早白垩世岩浆活动记录,为研究多龙矿集区成矿地质背景和班公湖-怒江洋演化提供了重要线索。初步研究认为,在中生代增生杂岩广泛出露的多龙矿集区,该套地层很可能代表一套早白垩世增生杂岩,同时也可能是同时期区域伸展环境下重沉积的产物。

A typical gold-rich porphyry copper ore district with large potential called the Duolong ore concentration area was recent?ly discovered after the discovery of the Gangdise metallogenic belt. It is located in northwest Gerze County in Tibet and lies withinthe Duobuzha part on the northern margin of the Bangong Co-Nujiang suture zone (BNSZ). 1∶250000 Wuma regional geologicalsurvey was carried out in detail previously, which filled the gap of the study of northern BNSZ. The authors recently found that anEarly Cretaceous rhyolite interlayer is exposed in the Quse Formation which was believed to have been formed in the Lower Jurassic.The weighted mean value of zircon U-Pb age measured by LA-ICP-MS from rhyoliteis is 118.8±1.4Ma, which suggests that thesedimentary strata with volcanic rock should have been formed in the Early Cretaceous. The discovery not only complements recordsof Early Cretaceous magmatic activity in southern Qiangtang block but also provides important clues for the study of the metallogenicgeological setting of the Duolong ore concentration area and the evolution of the Bangong Co-Nujiang Ocean. A preliminary studysuggests that the strata may represent Early Cretaceous accretionary complexes in Duolong where Mesozoic accretionary complexesare widely distributed. Meanwhile, it might be the contemporaneous product of re-deposition in the environment of regional exten?sion.