Zircon U-PbSHRIMP age and origin of post-orogenic Lamazhao granitic pluton from Altai orogen: its implications for vertical continental growth.

喇嘛昭岩体是阿尔泰造山带典型的后构造岩体,其时代问题一直没有解决。本次锆石SHRIMP定年给出 206Pb／238U年龄276±9Ma(MSWD=1．1),代表其形成年龄。这为阿尔泰后造山花岗岩和后造山作用提供了一个可靠的年代学证据。主量、微量元素地球化学特征显示该岩体具有I-A过渡的高钾钙碱性或高分异钙碱性花岗岩的特点。依据岩体构造特征、年代学、地球化学和地质背景综合分析,该岩体应为后造山岩体。该岩体Sr初始值变化于0．704-0．71659之间。εNd(T) 值为正值(+1．3-+2．8),模式年龄TDM-2为0．93-0．81Ga,与中亚造山带典型的高(正)εNd(T)值花岗岩相同。而且...The Lamazhao pluton is a typical post-tectonic pluton in the Altai orogen, but its emplacement time is still conclusively undetermined. This paper presents a zircon SHRIMP Pb-206/U-238 age of 276 +/- 9Ma (MSWD = 1.1), which is interpreted as his emplacement age. This provides an evidence for post-orogenic granitic magmatism and post orogeny. Major and trace elements show that the pluton has transition features from high-K calc-alkaline or high-fractionated I-type granites to A-type granites. Integration analysis of structural pattern, geochronology, geochemistry, and geological setting suggest that this pluton is post orogenic. Its Sr( T)(i) values are between 0.704 and 0.71659, epsilon(Nd) (T) values between +1.3 and +2.8, and TDM-2 from 0.93 to 0.81 Ga, which are similar to those of high ( positive) -epsilon(Nd) (T) value granites from the Central Asian Orogenic Belt. Importantly, its epsilon(Nd) ( T) values are slightly higher than these of syn-orogenic granites in the same area. This suggests that new juvenile mantle-derived materials, beside subducted juvenile ocean crust or arc rocks, probably contributed to the generation of the granites during post orogen in Altai orogen with Precambrian basement. This study provides an evidence for vertical continental crustal growth in the Central Asian Orogenic Belt.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000231179000006&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701SCI(E)中文核心期刊要目总览(PKU)中国科技核心期刊(ISTIC)5903640-6502