【摘要】：論文選取廣泛發(fā)育于內(nèi)蒙古根多河地區(qū)的早白堊世花崗質(zhì)侵入巖為研究對象,通過野外調(diào)研、測試分析和綜合研究,確定了其形成的時代,地球化學(xué)特征,探討了該時期花崗巖的巖漿源區(qū)性質(zhì)、巖石成因以及形成的構(gòu)造背景,為大興安嶺地區(qū)早白堊世侵入巖的活動時間及構(gòu)造演化歷史提供了新的資料。野外調(diào)研結(jié)果表明,根多河地區(qū)以新立屯巖體為代表的花崗閃長巖集中分布于新立屯林場一帶,總體呈近南北向巖基展布,切割了區(qū)內(nèi)北東、北北東向斷裂,由11個侵入體組成,出露面積45.12km2;以根多河巖體為典型代表的二長花崗巖主要分布在根多河林場、濟(jì)沁河林場一帶及零星出露于研究區(qū)東部、東南部,根多河巖體總體呈近北東向巖基展布,由11個侵入體組成,出露面積59.07km2。采用鋯石LA-ICPMS U-Pb測年方法,測得新立屯巖體形成時代為135.6±1.3Ma、根多河巖體形成時代為130.3±2.4Ma,表明其形成時代為早白堊世,而非前人認(rèn)為的印支期或燕山早期。不同巖體主量元素、微量元素和稀土元素測試結(jié)果表明,新立屯巖體的SiO2含量65.64%~67.09%;里特曼指數(shù)(σ)2.40~2.92,屬鈣堿性巖石;A/CNK值在0.92~0.97之間,呈準(zhǔn)鋁質(zhì)特點;稀土元素總量(ΣREE)102.3~159.13×10-6,平均值為122.86×10-6,輕稀土元素分餾作用較強(qiáng),重稀土元素分餾作用相對較弱。Tm出現(xiàn)弱的正異常,Er、Yb、Eu呈負(fù)異常,δEu值0.61~0.80,為弱虧損,說明源區(qū)巖漿發(fā)生過斜長石的分離結(jié)晶,導(dǎo)致殘余熔體中Eu的虧損。根據(jù)Sr和Yb的富集和虧損程度,可將本區(qū)花崗閃長巖定為高Sr低Yb型花崗巖,Sr462μg/g,Yb2.04μg/g。根多河巖體SiO2含量66.88~76.53%;里特曼指數(shù)(σ)2.27~3.13,屬鈣堿性巖石;A/CNK值在1.05~1.17之間,為鋁過飽和巖石;稀土元素總量(ΣREE)141.53~194.03×10-6,輕重稀土分餾明顯,為輕稀土富集型;Ce、Gd出現(xiàn)相對明顯的正異常;δEu值0.23~0.92,暗示源區(qū)殘留相存在斜長石;微量元素球粒具有貧Ba、Nb、C、P、Ti,富K、Rb、Th、Nd的特點;Ba相對于Rb、Th明顯虧損。上述地球化學(xué)特征顯示本區(qū)白堊紀(jì)中酸性侵入體的源區(qū)存在斜長石而缺乏石榴石和角閃石,表明本期巖漿源區(qū)比較淺。Nb顯負(fù)異常,表明其與消減有關(guān)。綜合研究發(fā)現(xiàn),新立屯巖體的花崗閃長巖為準(zhǔn)鋁質(zhì)、高鉀鈣堿性系列的I型花崗巖,呈高Sr低Yb型,形成于較高壓的下地殼,具有類似于活動大陸邊緣花崗巖的巖石組合特征,暗示其可能形成于活動大陸邊緣構(gòu)造背景,即與古太平洋板塊的俯沖有關(guān)。根據(jù)構(gòu)造判別推測,該地區(qū)的根多河二長花崗巖形成于造山后的拉張環(huán)境,地殼減薄,促使軟流圈的物質(zhì)上涌和幔源巖漿的底侵作用,導(dǎo)致地殼的溫度升高,減壓熔融形成該地區(qū)的二長花崗巖。
[Abstract]:In this paper, the early Cretaceous granitic intrusive rocks, which are widely developed in Gendohe area, Inner Mongolia, are selected as the research object. Through field investigation, test analysis and comprehensive research, the age and geochemical characteristics of granitic intrusive rocks in this period are determined, and the magmatic origin, petrogenesis and tectonic background of granites in this period are discussed. It provides new data for the activity time and tectonic evolution history of early Cretaceous intrusive rocks in Daxinganling area. The results of field investigation show that the granodiorite represented by Xinlitun rock mass in Gendohe area is concentrated in the area of Xinlitun Linchang, which is distributed in the north-south direction, and cuts the north-east and north-east faults in the area, which is composed of 11 intrusions and the exposed area is 45.12 km ~ 2. The monzonitic granite represented by the Gentuohe rock mass is mainly distributed in the Gentuohe forest farm. The JiQinhe forest farm area and sporadic exudation in the eastern part of the study area. In the southeast, the Gentuohe rock mass is distributed in the near-east-eastward rock base, which is composed of 11 intrusions with an exposed area of 59.07km2.The Gentuohe rock mass is distributed in the east of the study area in the east and southeast of the study area. By using zircon LA-ICPMS U-Pb dating method, the formation age of Xinlitun rock mass is 135.6 鹵1.3 Ma, and that of Gendohe rock mass is 130.3 鹵2.4 Ma, indicating that its formation age is early Cretaceous, rather than the Indochina or early Yanshanian period. The test results of main elements, trace elements and rare earth elements of different rock masses show that the SiO2 content of Xinlitun rock mass is 65.64% 鈮，

本文編號：2500732