本文關(guān)鍵詞： 蛇綠巖 蛇綠混雜巖 玉石溝 構(gòu)造演化 北祁連　出處：《中國地質(zhì)大學(xué)(北京)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：北祁連加里東造山帶位于中祁連板塊與華北板塊西南緣(阿拉善地塊)之間,呈北西—南東走向,東與右行走滑的同心一固原斷裂相鄰,西被左行走滑的阿爾金斷裂所截切,北祁連造山帶自南向北可以劃分為托萊南山北坡的消減洋殼殘片、托萊山北坡的俯沖形成的高壓變質(zhì)巖以及增生雜巖、河西走廊南山的島弧火山巖以及河西走廊弧后盆地等不同的構(gòu)造單元。根據(jù)收集的資料顯示,玉石溝蛇綠巖向東可與川刺溝、扎麻什、小八寶蛇綠巖相連,一起構(gòu)成了大洋擴(kuò)張脊型蛇綠巖帶。通過對玉石溝地區(qū)蛇綠混雜巖的野外地質(zhì)特征、巖石鏡下觀察、巖石地球化學(xué)特征、堆晶輝長巖測年等多方面的詳細(xì)研究,并結(jié)合前人對玉石溝蛇綠混雜巖的研究成果,初步得出以下幾點認(rèn)識:研究區(qū)蛇綠混雜巖由堆晶輝長巖、早奧陶世陰溝群基性火山巖、變質(zhì)橄欖巖、輝長輝綠巖墻及早奧陶世陰溝群深海沉積巖等組成;蛇綠混雜巖北側(cè)逆沖推覆于二疊系窯溝群紅泉組(P3h)之上,南側(cè)由北向南逆沖推覆于石炭系羊虎溝組(C2y)與二疊系八音河群大黃溝組(P1—2d)地層之上,西側(cè)與古元古界托賴巖群(Pt1Tb)片巖段成斷層接觸,向東沿出工作圖區(qū)外;在蛇綠混雜巖內(nèi)部不同巖片之間的接觸關(guān)系為斷層接觸;獲得堆晶輝長巖年齡為513.4±6.4Ma,表明蛇綠巖形成時間大約為早寒武紀(jì)到早奧陶世;玉石溝蛇綠混雜巖單元內(nèi)枕狀玄武巖在Zr/Y-Zr和Zr/4-Y-Nb/2的構(gòu)造判別圖解上,均落入洋脊玄武巖區(qū),從N-MORB標(biāo)準(zhǔn)化微量元素配分模式顯示出“局部凸起、總體相對平坦”的特征,即在Rb、Ba、Th、Ta、Nb處局部隆起,其他所有元素的豐度相對于N-MORB值不太富集,與典型的洋中脊玄武巖相似(Pearce,1982),總體均表明玉石溝蛇綠混雜巖中的玄武巖是在擴(kuò)張脊條件下生成的。
[Abstract]:The Caledonian orogenic belt in North Qilian is located between the Middle Qilian plate and the southwestern margin of the North China Plate (Alashan Block), with a NW-SE strike, adjacent to the right-strike-slip concentric Guyuan fault in the east, and cut by the Altun fault of the left strike-slip in the west. The North Qilian orogenic belt can be divided from south to north into subducted oceanic crust fragments on the northern slope of Tolai Mountains, high-pressure metamorphic rocks and accretive complex formed by subduction of the northern slope of Tulaishan. The volcanic rocks of the island arc in the South Mountain of the Hexi Corridor and the back-arc basin of the Hexi Corridor are different tectonic units. According to the collected data, the Yushigou ophiolite can be connected to the Chuan Caigou, Zamashi and Xiaobabao ophiolite to the east. Through the detailed study of the field geological characteristics of ophiolite melange in Yushigou area, the microscopic observation of rocks, the geochemical characteristics of rocks, the dating of heap gabbro, etc. Combined with the previous research results of the Yushigou ophiolite melange, it is concluded that the ophiolite in the study area is composed of heaped gabbro, early Ordovician trench group basic volcanic rocks, metamorphic peridotite. The pyroxene dike is composed of deep-sea sedimentary rocks of the early Ordovician trench group, and the northern side of the ophiolitic melange is thrust over the Hongquan formation of the Permian Yaogou group (P3h). The southern side is thrust from north to south, which is overlaid by the Yanghugou formation of Carboniferous (C2y2) and the P1-2d formation of the Bayinhe Group of Permian. The west side is in contact with the Paleoproterozoic Towlaiyan group (Pt1Tb) schist in fault contact, and out of the working map area along the eastward direction. The contact relationship between different pieces of ophiolitic melange is fault contact, the age of heaped gabbro is 513.4 鹵6.4 Ma. it indicates that the ophiolite was formed from early Cambrian to early Ordovician. The occipital basalts in the Yushigou ophiolite melange unit fall into the oceanic ridge basalt area on the structural discriminant diagram of Zr/Y-Zr and Zr/4-Y-Nb/2. From the N-MORB standardized trace element distribution model, the characteristics of "local bulge, overall relatively flat" are shown. In other words, the abundance of all other elements is not enriched relative to N-MORB value at the local uplift of Rb#en0# Ba-Ba-Th Ta-TaNb, and is similar to that of typical mid-oceanic ridge basalts, which shows that the basalts in the Yushigou ophiolite melange were formed under the condition of extensional ridges.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)(北京)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P588

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