本文關鍵詞：南部拉薩地塊晚白堊世花崗巖類年代學與地球化學　出處：《中國地質(zhì)大學(北京)》2017年博士論文　論文類型：學位論文

  更多相關文章： 青藏高原 拉薩地塊 晚白堊世 埃達克巖 巖石成因

【摘要】：南部拉薩地塊中生代巖漿巖大面積分布,對其成因與源區(qū)信息及構(gòu)造環(huán)境、地球動力學背景的探討還需進一步進行。本文報道了拉薩地塊南緣克曲-松卡一帶侵入于葉巴組火山巖中的中-酸性侵入巖的鋯石U-Pb年代學、鋯石Hf同位素及全巖地球化學,并結(jié)合南部拉薩地塊已有成果,探討了中生代至新生代以來,南部拉薩地塊花崗巖類巖石成因和區(qū)域巖漿-構(gòu)造演化。鋯石U-Pb年齡結(jié)果顯示,本文中酸性侵入巖的侵入年代為晚白堊世(90.3~98.7Ma)。鋯石Hf同位素方面,εHf(t)為較大正值(+9.4~+15.7),變化范圍不大,顯示虧損源區(qū)的地球化學特征。TDM=135~380Ma,TDMC=150~557Ma,地幔模式年齡和地殼模式年齡較年輕。全巖Sr-Nd同位素給出類似結(jié)果,εNd(t)=+3.6~+4.3,Nd同位素地幔模式年齡屬新元古代-早古生代階段(476~728Ma),為新生地殼的源區(qū)特征�？饲�-松卡地區(qū)的花崗巖類總體富堿、富鉀,屬于高鉀鈣堿性-鉀玄質(zhì)巖石系列。A/CNK=0.66~1.03,屬于偏鋁質(zhì)-弱過鋁質(zhì)巖石。巖石鎂含量偏低,Mg O=0.25~3.82%(Mg#=24.33~40.68)。微量元素方面,富集輕稀土元素、虧損重稀土元素,輕重稀土分異不強([La/Yb]N=8.0~25.6)。δEu=0.57~1.10,多數(shù)樣品顯示輕微Eu負異常,少數(shù)為Eu正異常。巖石富集大離子親石元素(LILE)而虧損高場強元素(HFSE)。本文晚白堊世花崗巖類巖石主要來源于新特提斯大洋板片俯沖消減過程中,新生鎂鐵質(zhì)地殼的部分熔融,中部拉薩地塊基底物質(zhì)混入極少。與此形成對比的是,南部拉薩東段與西段的花崗巖類,則有更為富集的同位素特征和更為古老的地幔、地殼模式年齡,顯示明顯的古老地殼物質(zhì)混入特征。晚白堊世侵入巖具有埃達克質(zhì)巖石親緣性,新特提斯洋大洋地殼部分熔融來源的埃達克巖以早白堊時期的馬門安山巖和南部拉薩地塊東段晚白堊世紫蘇花崗巖為代表;而本文拉薩地塊南緣晚白堊世埃達克質(zhì)巖石及始新世以來的,在南部拉薩地塊廣泛出露的埃達克巖及含礦的埃達克質(zhì)斑巖,則來源于在新特提斯洋俯沖背景下,增厚下地殼的部分熔融。
[Abstract]:The Mesozoic magmatic rocks in the southern Lhasa block are widely distributed, and the origin, source information and tectonic environment are discussed. This paper reports the zircon U-Pb geochronology of the intermediate-acid intrusive rocks in the volcanic rocks of the Yeba formation in the southern margin of the Lhasa massif. Zircon HF isotopes and whole-rock geochemistry, combined with the results of the Lhasa block in the south, have been discussed from Mesozoic to Cenozoic. Genesis and regional magmatic tectonic evolution of granitic rocks in the Lhasa block, southern China. Zircon U-Pb age shows. The intrusive age of the intermediate-acid intrusive rocks in this paper is the late Cretaceous (90.3n) 98.7 Ma.The zircon HF isotopes, 蔚 Hfct), are relatively positive (9.4 ~ 15.7). The range of variation is not large, indicating that the geochemical characteristics of the source area of Changzhangyuan... TDM 135T ~ (38) Ma ~ (38) TDMCN ~ (150) ~ (557) Ma. The mantle model age and the crustal model age are younger. The Sr-Nd isotopes of the whole rock show similar results, 蔚 Ndt0 = 3.6 ~ 4.3. The ND isotopic mantle model age belongs to Neoproterozoic to early Paleozoic stage, which is the source of the new crust. The granitoids in Kechu-Songka area are rich in alkali and potassium. It belongs to the high-potassium calc-alkaline-potash rock series. A / CNK = 0.661.03, belongs to the metaluminum-weak peraluminous rock, and its magnesium content is on the low side. MgO 0.25 ~ 3.82% mg #Li 24.33 ~ 40.68%. In respect of trace elements, they are enriched in light rare earth elements, depleted in heavy rare earth elements, and have little difference between light and heavy rare earth elements (P < 0.05). [La/Yb > 8. 0 ~ 25. 6. 未 EU 0. 57 ~ 1. 10, and most of the samples show slight negative EU anomalies. A few are EU positive anomalies. The rocks are enriched with large ion lithophile elements (LILE) and are depleted of high field strength elements (HFSEs). The late Cretaceous granitic rocks in this paper are mainly derived from the subduction process of the new Tethys oceanic plate. In contrast, the granitoids of the eastern and western Lhasa sections in the south of Lhasa, by contrast, are partially melted in the newly formed magnesia-ferric crust, and the basement material of the Lhasa block in the central part of the region is very little. There are more enriched isotopic characteristics and older mantle, crustal model ages, indicating obvious characteristics of the mixing of ancient crustal materials. The late Cretaceous intrusive rocks are related to adakian rocks. The early Cretaceous Maman andesite and the late Cretaceous Perilla granites in the eastern Lhasa block are the representative of the adakite which originated from the partial melting of the oceanic crust of the NeoTethys Ocean. However, the late Cretaceous adakitic rocks in the southern margin of the Lhasa massif and the adakite widely exposed in the southern Lhasa block and the mineral-bearing adakitic porphyry originated from the new Tethys subduction background. Thickening the partial melting of the lower crust.
【學位授予單位】：中國地質(zhì)大學(北京)
【學位級別】：博士
【學位授予年份】：2017
【分類號】：P597.3;P588.121
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本文編號：1417644