本文選題：雅江縫合帶 + 輝長(zhǎng)巖�。� 參考：《中國(guó)地質(zhì)大學(xué)(北京)》2015年碩士論文

【摘要】：在雅江縫合帶南側(cè)加查到郎縣一帶產(chǎn)出有一套走向近東西的基性-超基性巖帶,與雅魯藏布江蛇綠巖帶平行共生,基性-超基性巖帶中主要為輝長(zhǎng)巖輝綠巖,普遍發(fā)生蝕變,本文對(duì)加查到郎縣一帶的輝長(zhǎng)巖進(jìn)行了詳細(xì)的野外觀測(cè),選擇典型的野外露頭采集了樣品。整個(gè)研究區(qū)的輝長(zhǎng)巖地球化學(xué)特征基本相同,系統(tǒng)的巖石學(xué)、地球化學(xué)分析和研究表明該輝長(zhǎng)巖的Si02含量均45.80%-50.89%,與正常的洋中脊玄武巖SiO2含量(N-MORB,48.77%)相當(dāng),Mg0的含量在4.23%～7.8%,平均為5.74%。Mg#為41.31～63.55平均為48.85,低于原生巖漿范圍,推測(cè)其在巖漿演化過(guò)程中存在與其他物質(zhì)的混染作用。輕稀土和重稀土元素比值(LREE/HREE)的含量范圍在2.08到8.09之間,平均為3.4,輕重稀土無(wú)明顯分餾。σEu變化范圍在0.72～1.15,平均值在0.98,說(shuō)明巖石存在輕微的Eu負(fù)異常或無(wú)異常,未發(fā)生明顯的斜長(zhǎng)石分離結(jié)晶作用。從微量元素原始地幔標(biāo)準(zhǔn)化蛛網(wǎng)圖可以看出,樣品曲線分布位置和走勢(shì)與E-MORB(富集型地幔)類似,說(shuō)明巖漿可能來(lái)源于富集地幔,也有可能是來(lái)源于正常的虧損地幔,在巖漿的形成或者演化過(guò)程中收到了外來(lái)溶液的影響,使得樣品相對(duì)的富集輕稀土。由SHRIMP鋯石U-Pb年齡表明該輝長(zhǎng)巖形成于55.5～56Ma,與雅江洋的閉合時(shí)間一致。由此本文認(rèn)為當(dāng)大洋板塊俯沖到最終階段,因重力等作用,大洋板塊與其南的喜馬拉雅地塊之間發(fā)生斷裂,軟流圈減壓發(fā)生部分熔融,形成超基性基性熔漿,俯沖作用持續(xù)斷裂位置向北移動(dòng)至增生楔之下,同時(shí)雅江洋閉合兩側(cè)碰撞,其熔漿底侵上升,不同程度地與地殼物質(zhì)發(fā)生混染,在此條件下形成這套基性巖巖脈。
[Abstract]:On the south side of the Yagang suture belt, there is a set of basic-ultrabasic rock belt with the direction of east-west, which is parallel to the Yalu Zangbo ophiolite belt, and the basic-ultrabasic rock belt is mainly gabbro diabase, which is generally altered. In this paper, a detailed field observation of gabbro in Longlong County is carried out, and a typical outcrop is selected to collect samples. The geochemical characteristics of gabbro in the whole study area are basically the same. Geochemical analysis and study show that the content of SiO2 in the gabbro is 45.80-50.89, which is equivalent to the normal SiO2 content of mid-oceanic ridge basalt (N-MORBN 48.77g).) the content of Mg0 is 4.2377.8G, with an average of 5.74g 路Mg# 41.3163.55, 48.85, which is lower than that of the primary magma. It is inferred that the magma is mixed with other materials during the evolution of magma. The content range of LREE / HREE is between 2.08 and 8.09, with an average of 3.4, and there is no significant fractionation of REE. The variation range of 蟽 EU is 0.72 ~ 1.15 and the average value is 0.98, which indicates that there are slight EU negative anomalies or no anomalies in rocks. There was no obvious segregation and crystallization of plagioclase. It can be seen from the trace element primitive mantle-normalized spider web that the distribution of the sample curve is similar to that of E-MORBB, indicating that the magma may originate from the enriched mantle or from the normal depleted mantle. In the process of magma formation or evolution, the samples are relatively enriched with LREE due to the influence of external solutions. The shrimp zircon U-Pb age indicates that the gabbro was formed at 55.5 ~ 56 Ma, which is consistent with the closing time of the Yajiang Ocean. It is concluded in this paper that when the ocean plate subducts to the final stage, the fault occurs between the oceanic plate and its southern Himalayan block due to the action of gravity, and the subduction of the asthenosphere occurs partial melting, forming ultrabasic melts. The subduction continues to move northward below the accretive wedge, and at the same time the two sides of the Yajiang ocean close collide with each other, and its melting-bottom transgression rises, and mixed with the crustal material to varying degrees, the basic rock vein is formed under this condition.
【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)】：P588.124

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本文編號(hào)：2015108