地质学报2017，Vol.91Issue(1)：132-150,19.
西藏班公湖—怒江缝合带美日切错组中酸性火山岩锆石U-Pb年龄、Sr-Nd-Hf同位素、岩石成因及其构造意义
Petrogenesis, Zircon U-Pb Geochronology and Sr-Nd-Hf Isotopes of the Intermediate-felsic Volcanic Rocks from the Duolong deposit in the Bangonghu-Nujiang Suture Zone, Tibet, and Its Tectonic Significance
摘要
Abstract
The Bangonghu-Nujiang suture zone in Tibet of China.has been is an important porphyry copper gold metallogenic belt,with superior geological condition of mineralization,The Duolong ore-concentrated deposit,the first superlarge epithermal porphyry Cu-Au deposit discovered in the western BangonghuNujiang suture zone,is widely covered with plenty of effusive volcanic rocks.However,the petrogenesis,magma source and geodynamic setting of the granitoids are still constrained loosely.In this paper,LAICP-MS zircon date yields U-Pb age of 108.2±2.6Ma(MSWD=0.39) for the dacite,regarding to the similar geochronological data of 109.3±2.2Ma(MSWD=1.70) for the rhyolite.The dacite and rhyolite are characterized by high silica (SiO2 =60.89 ％ ～ 72.00 ％),potassium-rich (K2O =3.08 ％ ～ 5.53 ％),alkali-rich (K2O+Na2 O=6.88％ ～ 8.96％),peralkaline to peraluminous (A/CNK =0.92 ～ 1.28) and High calc-alkaline to shoshonitic.The rocks are systematically more enriched in large-ion lithophile elements (LILE:Th、U、K、Pb and Rb) and LREE,relatively deplted in high strength elements (HFSE:Ta、Nb、Ti and Zr) and HREE.Total Coneentartion of REE range from 141.52 × 10-6 ～ 236.05 × 10-6,with LREE/HREE of 8.54～9.30,LaN/YbN of 10.42～11.05 and middle negative Eu anomalies(δEu=0.65～0.80).Besides,trace elements compositions indicate that the magma is contaminated by crustal mantle when it rise and The isotopes of these rocks are characterized by high(87 Sr/86 Sr)i (from 0.7050 to 0.7053),low (mNd/144Nd)i(from 0.5124 to 0.5126,low εNd(t)(from-1.51 to 1.29).The positive εHf (t) values of zircons from rhyolite whose second stage Hf mode mean ages are 288.0Ma vary from +11.6 to +15.5,contrasted with εHf (t) values of +3.4～+8.0 from dacite whose second stage Hf mode mean ages are 813.1Ma.Based on the above discussions,we proposed that the geochemical characteristics of these volcanic rocks are consistent with those of arc-type magmas worldwide and the arc volcanic rocks magma were all generated by partial melting of mantle wedges replaced by the fluid which is formed the dehydration of the oceanic crust subduction plate,and its rock-forming resulted from the mixing between the juvenile lower crust-derived melts and mantle-derived mafic melts under the background of BangonghuNujiang Tethys subducting northward to Qiangtang massif.In addition,the volcanic activity suggests Bangonghu-Nujiang ocean was subducting at least during approximate 108～109Ma,and the closure time of this ocean should be later than early Cretaceous(108～109Ma),which is different from early recognition of closure time of late Jurassic to early-Cretaceous.关键词
闭合时限/岛弧火山岩/美日切错组/班公湖—怒江成矿带西段/西藏Key words
Closure time/Island-arc volcano rock/Early Cretaceous/Duolong ore-concentrated district/western Bangonghu-Nujiang suture zone/Tibet引用本文复制引用
韦少港,唐菊兴,宋扬,刘治博,王勤,林彬,贺文,冯军..西藏班公湖—怒江缝合带美日切错组中酸性火山岩锆石U-Pb年龄、Sr-Nd-Hf同位素、岩石成因及其构造意义[J].地质学报,2017,91(1):132-150,19.基金项目
本文受国土资源部公益性行业专项“斑岩-浅成低温热液成矿系统研究及勘查评价示范-以西藏多龙整装勘查区为例”(编号:201511017)、国家自然科学青年基金“西藏羌塘地体南缘铁格龙南超大型浅成低温热液型铜(金)矿床保存条件研究”(编号:41402178)及科技基础性工作专项(项目编号:2014FY121000)共同资助. （编号:201511017）
