大兴安岭全胜林场地区晚石炭世岩浆活动研究:对兴安地块与松嫩地块拼合时间的限定  

Late Carboniferous Magmatic Activities in the Quanshenglinchang Area,Great Xing'an Range:Constrains on the Timing of Amalgamation between Xing'an and Songnen Massifs

作　　者：崔芳华[1] 郑常青[1] 徐学纯[1] 姚文贵[1] 施璐[1] 李娟[1] 徐久磊[1] 

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《地质学报》2013年第9期1247-1263,共17页Acta Geologica Sinica

基　　金：中国地质调查局地质调查工作项目(编号1212011120654);国土资源部公益性行业科研专项经费项目(编号201011083SinoProbe-09-06)共同资助的成果

摘　　要：大兴安岭全胜林场地区位于兴蒙造山带东段的兴安地块,出露的晚古生代花岗岩主要由中粒黑云母二长花岗岩和中粗粒黑云母正长花岗岩组成,岩石未遭受变质作用。岩石地球化学特征显示两类花岗岩高硅（SiO_2=75.72%~76.28%）、富碱（Na_2O＋K_2O=7.78%~8.89%）、弱过铝（Al_2O_3=12.42%~13.01%）,TiO_2、Fe_2O_3、FeO、MnO、MgO、CaO、P_2O_5等含量很低,标准矿物分子中石英、钠长石、正长石含量较高,出现少量刚玉分子和极少量的锆石、磷灰石、磁铁矿和钛铁矿等,但未见有碱性暗色矿物;稀土元素总量中等略偏高,轻重稀土分馏明显且轻稀土富集,具中等—较强的负铕异常;大离子亲石元素Rb、K、Pb较富集而Ba、Sr、Eu明显亏损,强烈亏损Nb、Ta、Ti等高场强元素（HFSE）和P元素。岩石所具有的A/CNK〈1.1、标准矿物刚玉分子〈1%、A/NK〉1.0、P_2O_5与SiO_2负相关、较高的分异指数（DI=92.49~97.26）等特征以及偏低的锆石饱和温度（730~834℃）,均显示其具有类似于高分异I型花岗岩的特点。岩石中锆石呈半自形—自形柱状,振荡环带较发育,Th/U比值较高（大多介于0.36~1.35）,为岩浆成因锆石;4个样品的锆石U-Pb加权平均年龄分别为322.2±1.2 Ma、305.9±2.4Ma、301.3±2.6Ma和294.8±1.6Ma,代表其岩浆侵位时代为晚石炭世至早二叠世,研究区内出露的二长-正长花岗岩为晚石炭世—早二叠世岩浆侵位活动的产物。岩相学、岩石地球化学、年代学研究以及区域构造演化表明,大兴安岭全胜林场地区晚石炭世岩浆侵位活动可能发生在兴安地块和松嫩地块碰撞拼合所造成的造山晚期—造山后伸展构造背景下,二者最晚于早石炭世末已经完成碰撞拼合。Late Paleozoic granitoids without undergoing metamorphism in Quanshenglinchang area, Great Xing＇ an Range mainly consist of medium biotite adame[lite and medium-coarse biotite syenogranite. The study area lies in Xing＇an Massif which is an eastern part of the Xing＇an Mongolian orogenic belt. Geochemical data suggest that these rocks are rich in SiO2 （SiO2-- 75.72%~76.28%）, alkalis （Na20-K20-7.78%- 8.89%） and are charactered by slightly peraluminous （A12Oa = 12.42 % -13.01 %） and the low content of TiO2, Fe2O3, FeO, MnO, MgO, CaO, P2O3. They have high contents of normative quartz, albite, orthoclase and little corundum, zircon, apatite, magnetite, ilmenite, but do not contain alkaline melaminerals. These granitic rocks are slightly high in total REE and LREE contents, and show obvious fractionation of LREE from HREE with significant negative Eu anomalies. They are also characterized by enrichment in Rb, K, Pb, depletion in Ba, Sr, Eu , severe depletion in Nb, Ta,Ti（HFSE）and P. The features of A/CNK ~ 1. 1, normative corundum contents ~1~, A/NK ~ 1. 0, negative correlation between P20s and SiO2, higher differentiation index （DI--92.49~97.26）, lower saturation temperatures of zircon（730~834~C ） manifest that these granites belong to highly fractionated I-type. Zircons from these rocks exhibit hypautomorphic-automorphic crystal, clear oscillatory zoning, higher Th/U ratios （most in 0.36~1. 35）, these characters indicate that they are magmatic in origin. The weighted average ages of zircon U-Pb isotope of these four samples are （322.2!1.2） Ma, （305.9-＋-2.4） Ma, （301.3_42.6） Ma and （294.8~＋1.6） Ma, indicating that they formed during Late Carboniferous to early Permian. So, adamellite and syenogranite in the study area are considered as products of magmatic emplacement. The petrography, petrogeochemistry, chronology study and regional tectonic evolution reveal that these late Carboniferous intrusions in Quanshenglinchang area, Great Xing＇ an Range formed under a te

关 键 词：高分异Ⅰ型花岗岩 锆石U-PB测年 晚石炭世 碰撞拼合 大兴安岭全胜林场地区 

分 类 号：P588.11[天文地球—岩石学]