【摘要】：位于藏南的拉薩地體普遍發(fā)育晚漸新世-中新世埃達(dá)克質(zhì)巖石,而雅魯藏布江縫合帶以南的特提斯喜馬拉雅帶中卻鮮有同類巖石的報(bào)道,關(guān)于他們的時(shí)空聯(lián)系上存在著爭(zhēng)議。本文報(bào)道了緊鄰縫合帶以南的群讓地區(qū)新發(fā)現(xiàn)的二長(zhǎng)斑巖年代學(xué)和地球化學(xué)數(shù)據(jù),通過對(duì)其研究為藏南地區(qū)構(gòu)造-巖漿活動(dòng)及演化提供約束。通過全巖地球化學(xué)分析,群讓斑巖呈現(xiàn)為酸性(Si O2=66-68.3%),鉀質(zhì)(K2O/Na2O=1.0-1.38,Na2O-2.0K2O),高鋁(Al2O3=15.85-16.20%),低鎂(Mg O=0.44-1.27%),低相容元素(Cr=14.81-24.62 ppm,Ni=8.79-12.28 ppm),相對(duì)虧損重稀土元素和Y元素(Y=12.23-17.18 ppm,Yb=0.78-1.05 ppm),高Sr(822.2-1386 ppm),具有高的Sr/Y和(La/Yb)N比值(Sr/Y=64.56-81.30、(La/Yb)N=95.1-138.4),無明顯負(fù)銪異常(δEu=0.73-1.11),明顯具有埃達(dá)克質(zhì)巖的特征。獲得的鋯石LA-ICP-MS U-Pb加權(quán)平均年齡為10.02±0.33 Ma,與報(bào)道的特提斯喜馬拉雅以及拉薩地塊上的晚漸新世-中新世埃達(dá)克質(zhì)巖時(shí)代一致。地化特征表明群讓斑巖可能來自增厚的鐵鎂質(zhì)下陸殼的部分熔融,源區(qū)深度約為50 km,源巖巖性可能為石榴角閃巖或角閃巖。結(jié)合區(qū)域地質(zhì)情況,表明群讓斑巖可能是晚中新世由藏南拆離系的活動(dòng)造成鐵鎂質(zhì)下地殼的減壓和脫水,部分熔融形成了埃達(dá)克質(zhì)熔體,在10 Ma左右侵位形成了東西走向的巖脈。在斑巖中發(fā)現(xiàn)的大量的黑云母片麻巖捕擄體表明熔漿在上升過程中捕擄了上部的地殼物質(zhì)。關(guān)于藏南晚漸新世-中新世埃達(dá)克質(zhì)巖的巖石成因,普遍認(rèn)為是由下部巖石圈的減薄作用引起形成的,本文首次提出群讓埃達(dá)克質(zhì)巖是由藏南拆離系的活動(dòng)而形成,為埃達(dá)克質(zhì)巖巖石成因提供新的解釋,同時(shí)對(duì)藏南拆離系的活動(dòng)時(shí)限提供約束條件。
[Abstract]:Late Oligocene-Miocene Adakitic rocks are generally developed in Lhasa terrane in southern Tibet, while there are few reports of similar rocks in the Tethys Himalayan belt south of the Yarlung Zangbo River suture belt, and their temporal and spatial links are controversial. This paper reports the geochronology and geochemistry data of the two long porphyry discovered in the south of the suture zone, which provides the constraints for the tectonic-magmatic activity and evolution in the south of Tibet. According to the geochemical analysis of the whole rock, the porphyry is characterized by acid (Si O2O 66-68.3%), potassium (K _ 2O / Na _ 2O 1.0-1.38) Na _ 2O-2.0K _ 2O, high aluminum (Al2O3=15.85-16.20%), low magnesium (Mg O _ 2O _ (0.44-1.27%). Low compatible elements (Cr=14.81-24.62 ppm,Ni=8.79-12.28 ppm), relatively depleted heavy rare Earth elements and Y elements) (Y 12.23-17.18 ppm,Yb=0.78-1.05 ppm), High Sr (822.2-1386 ppm),) It has a high ratio of Sr/Y to (La/Yb) N (Sr/Y=64.56-81.30, (La/Yb) N95.1-138.4), no obvious negative europium anomaly (未 Eu=0.73-1.11), and has the characteristics of adakitic rocks. The zircon LA-ICP-MS U-Pb weighted average age is 10.02 鹵0.33 Ma, which is consistent with the reported age of the Tethys Himalayas and the late Oligocene Miocene Adakitic rocks in the Lhasa massif. The geochemical characteristics indicate that the porphyry may originate from the partial melting of the thickened ferromannesite lower continental crust, and the source depth of 50 km, source rocks may be pomegranate amphibolite or amphibolite. Combined with the regional geological conditions, it is suggested that the porphyry may have been caused by the activities of the late Miocene detachment system in southern Tibet, resulting in the decompression and dehydration of the lower crust of ferromagnesite and partial melting of the adakitic melt. The emplacement formed east-west vein at about 10 Ma. A large number of biotite gneiss captives found in porphyry indicate that the magma captured the upper crust material during the rising process. As to the petrogenesis of the late Oligocene to Miocene adakitic rocks in southern Tibet, it is generally believed that they were formed by the thinning of the lower lithosphere. It provides a new explanation for the rock genesis of the adakite, and also provides the constraint conditions for the time limit of the activity of the southern Tibetan detachment system.
【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P588.1;P597.3

【參考文獻(xiàn)】

相關(guān)期刊論文 前10條

1 李光明,芮宗瑤;西藏岡底斯成礦帶斑巖銅礦的成巖成礦年齡[J];大地構(gòu)造與成礦學(xué);2004年02期

2 芮宗瑤,李光明,張立生,王龍生;西藏斑巖銅礦對(duì)重大地質(zhì)事件的響應(yīng)[J];地學(xué)前緣;2004年01期

3 張旗,錢青,王二七,王焰,趙太平,郝杰,郭光軍;燕山中晚期的中國(guó)東部高原:埃達(dá)克巖的啟示[J];地質(zhì)科學(xué);2001年02期

4 張進(jìn)江;郭磊;張波;;北喜馬拉雅穹隆帶雅拉香波穹隆的構(gòu)造組成和運(yùn)動(dòng)學(xué)特征[J];地質(zhì)科學(xué);2007年01期

5 曲曉明,侯增謙,國(guó)連杰,徐文藝;岡底斯銅礦帶埃達(dá)克質(zhì)含礦斑巖的源區(qū)組成與地殼混染:Nd、Sr、Pb、O同位素約束[J];地質(zhì)學(xué)報(bào);2004年06期

6 李祥輝;王尹;徐文禮;孫勇;孔慶友;曾慶高;謝饒武;毛國(guó)政;尼瑪次仁;周勇;劉玲;;試論西藏南部上三疊統(tǒng)復(fù)理石郎杰學(xué)群與涅如組[J];地質(zhì)學(xué)報(bào);2011年10期

7 李德威;藏南成礦條件及找礦遠(yuǎn)景分析[J];桂林冶金地質(zhì)學(xué)院學(xué)報(bào);1994年02期

8 陳文寄 ,李齊 ,郝杰 ,周新華 ,萬(wàn)京林 ,孫敏;Postcrystallization thermal evolution history of Gangdese batholithic zone and its tectonic implication[J];Science in China(Series D:Earth Sciences);1999年01期

9 趙志丹 ,莫宣學(xué) ,張雙全 ,郭鐵鷹 ,周肅 ,董國(guó)臣 ,王勇;Post-collisional magmatism in Wuyu basin,central Tibet:evidence for recycling of subducted Tethyan oceanic crust[J];Science in China(Series D:Earth Sciences);2001年S1期

10 侯增謙,曲曉明,王淑賢,高永豐,杜安道,黃衛(wèi);西藏高原岡底斯斑巖銅礦帶輝鉬礦Re-Os年齡:成礦作用時(shí)限與動(dòng)力學(xué)背景應(yīng)用[J];中國(guó)科學(xué)(D輯:地球科學(xué));2003年07期

，

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