【摘要】：系統(tǒng)總結(jié)并分析了近年來獲得的額爾古納地塊中生代花崗巖的年代學(xué)、地球化學(xué)和Hf同位素?cái)?shù)據(jù),以便從Hf同位素時(shí)空變異角度揭示額爾古納地塊陸殼增生及再造過程,為造山帶地殼演化提供證據(jù).基于花崗巖鋯石U-Pb定年結(jié)果,額爾古納地塊中生代花崗質(zhì)巖漿作用至少可劃分五個(gè)階段:早-中三疊世(249~237Ma)、晚三疊世(229~201Ma)、早-中侏羅世(199~171Ma)、晚侏羅世(155~149Ma)和早白堊世(145~125Ma).其中,前三個(gè)侵入階段的花崗巖主要為I型花崗巖,而后兩個(gè)階段為A型花崗巖,反映中生代蒙古-鄂霍茨克大洋板塊俯沖-碰撞-伸展過程導(dǎo)致額爾古納地塊陸殼由加厚向減薄變化的特征.中生代花崗巖中鋯石Hf同位素分析結(jié)果表明,額爾古納地塊陸殼增生主要發(fā)生于中元古代及新元古代,并且這些中生代花崗巖具有隨時(shí)代變新εHf(t)值逐漸升高、二階段模式年齡(TDM2)逐漸下降的變化趨勢(shì),揭示額爾古納地塊中生代不同期次花崗質(zhì)巖漿的產(chǎn)生經(jīng)歷了從古老陸殼物質(zhì)熔融至新增生陸殼物質(zhì)熔融的變化過程.此外,鋯石Hf同位素組成在空間上還具有隨緯度增加εHf(t)值逐漸下降、二階段模式年齡(TDM2)逐漸升高的變化特征,顯示出研究區(qū)深部陸殼物質(zhì)組成中古老陸殼成分由南向北增多的趨勢(shì).而在同一緯度范圍內(nèi),鋯石Hf同位素組成也存在差異.這些結(jié)果表明額爾古納地塊深部陸殼在橫向和垂向上均存在明顯的不均一性.綜合上述特征,本文提出了額爾古納地塊下部陸殼的結(jié)構(gòu)模型.
[Abstract]:The geochronological, geochemical and Hf isotopic data of the Mesozoic granites in the Erguna massif obtained in recent years are systematically summarized and analyzed in order to reveal the process of crustal accretion and reconstruction in the Erguna block from the point of view of Hf isotopic temporal and spatial variation. Provide evidence for crustal evolution of orogenic belts. Based on the U-Pb dating of granite zircon, the Mesozoic granitic magmatism in the Erguna block can be divided into at least five stages: early and Middle Triassic (249~237Ma), late Triassic (229~201Ma), early and Middle Jurassic (199~171Ma). Late Jurassic (155~149Ma) and early Cretaceous (145~125Ma). Among them, the granites in the first three intrusive stages are mainly I-type granites, and the last two stages are A-type granites. The results show that the Mesozoic Mongolian-Okhotsk oceanic plate subducted collision-extensional process leads to the change from thickening to thinning of the Erguna block continental crust. The Hf isotopic analysis of zircon from Mesozoic granites shows that the continental crust accretion occurred mainly in Mesoproterozoic and Neoproterozoic, and these Mesozoic granites have gradually increased 蔚 Hf (t) value. The decreasing trend of the two-stage model age (TDM2) reveals that the generation of granitic magma in the Erguna massif experienced a process from the melting of the ancient continental crust to the melting of the newly formed continental crust. In addition, the Hf isotopic composition of zircon has the characteristics of decreasing 蔚 Hf (t) value and increasing TDM2 with the increase of latitude. It is shown that the composition of the ancient continental crust in the deep continental crust in the study area is increasing from south to north. In the same latitudes, the Hf isotopic compositions of zircon are also different. These results indicate that the deep continental crust of the Erguna block has obvious heterogeneity both horizontally and vertically. Based on the above characteristics, a structural model of the lower continental crust of the Erguna block is proposed.
【作者單位】： 吉林大學(xué)地球科學(xué)學(xué)院;
【基金】：國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(編號(hào):2016YFC0600403) 國(guó)家自然科學(xué)基金項(xiàng)目(批準(zhǔn)號(hào):41330206)資助
【分類號(hào)】：P542

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相關(guān)期刊論文 前10條

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本文編號(hào)：2422907