發(fā)布時(shí)間：2018-05-15 03:07

  本文選題：寬坪巖群 + 碎屑巖��； 參考：《西北大學(xué)》2015年碩士論文

【摘要】：北秦嶺造山帶主要由寬坪巖群、二郎坪巖群、秦嶺巖群和丹鳳巖群四個(gè)巖石地層單元組成,準(zhǔn)確限定各個(gè)組成單元的形成時(shí)代和構(gòu)造背景,對(duì)于研究和重建北秦嶺造山帶的形成和演化過(guò)程具有重要意義。本文在大量文獻(xiàn)閱讀和野外考察的基礎(chǔ)上,選擇北秦嶺西段甘肅天水-陜西寶雞地區(qū)的寬坪雜巖為研究對(duì)象,對(duì)研究區(qū)東岔、固川溝、斜峪關(guān)和大鎮(zhèn)溝多條剖面出露的淺變質(zhì)碎屑巖、變鎂鐵質(zhì)巖和片麻狀花崗巖進(jìn)行了詳細(xì)的野外地質(zhì)、巖石學(xué)、地球化學(xué)和鋯石U-Pb年代學(xué)研究,獲得了以下初步認(rèn)識(shí)：1、北秦嶺西段寬坪雜巖主要由淺變質(zhì)的碎屑巖、變鎂鐵質(zhì)巖和片麻狀花崗巖體組成。其中,碎屑巖主要為成熟度較高的長(zhǎng)石石英砂巖,形成于被動(dòng)大陸邊緣環(huán)境；變鎂鐵質(zhì)巖石的原巖為中基性火成巖,形成于大陸裂谷環(huán)境；東岔花崗巖顯示了A型花崗巖的特征,而固川溝花崗巖為一套強(qiáng)過(guò)鋁的S型花崗巖。2、鋯石年代學(xué)研究結(jié)果顯示,研究區(qū)寬坪雜巖淺變質(zhì)碎屑巖的形成時(shí)代530Ma；變鎂鐵質(zhì)巖石原巖的形成時(shí)代為1771±15Ma；東岔和固川溝花崗巖的形成時(shí)代分別為1775±14Ma和2197±19Ma。變鎂鐵質(zhì)巖石原巖以及花崗質(zhì)巖石的結(jié)晶年齡遠(yuǎn)大于寬坪碎屑巖的沉積年齡,說(shuō)明它們并不構(gòu)成一個(gè)統(tǒng)一巖石地層單位,這些古老的火成巖體應(yīng)該是卷入造山帶的華北板塊南緣物質(zhì),應(yīng)從寬坪巖群中剔除。3、碎屑鋯石的定年結(jié)果顯示,北秦嶺西段寬坪巖群碎屑巖主要存在～600-800Ma、～950-1100Ma、-2500Ma和～3400Ma四組年齡峰值,其中-2500Ma和～3400Ma與華北板塊的年齡譜系吻合,-950-1100Ma與北秦嶺的巖漿事件吻合,～600-800Ma與南秦嶺/揚(yáng)子板塊的年齡分布一致,指示寬坪碎屑巖同時(shí)接受了華北板塊、北秦嶺以及揚(yáng)子板塊北緣的碎屑物質(zhì),也間接證明,寬坪碎屑巖沉積環(huán)境應(yīng)該是在華北地塊和北秦嶺陸塊之間的一個(gè)裂陷盆地。
[Abstract]:The North Qinling orogenic belt is mainly composed of four lithostratigraphic units: Kuanping rock group, Erlangping rock group, Qinling rock group and Danfeng rock group. It is of great significance to study and reconstruct the formation and evolution of the North Qinling orogenic belt. Based on a large number of literatures and field investigations, this paper selects the Kuanping complex in Tianshui-Baoji area of Gansu Province in the western part of the North Qinling Mountains as the research object, and studies the Dongcha and Guchuan gully in the study area. The shallow metamorphic clastic rocks, metamorphic mafic rocks and granitic granites from several sections of Xiaoyuguan and Dazhenggou have been studied in detail in field geology, petrology, geochemistry and zircon U-Pb chronology. It is shown that the Kuanping complex in the western part of the North Qinling Mountains is mainly composed of shallow-metamorphic clastic rocks, metamorphic mafic rocks and granitic bodies. Among them, clastic rocks are mainly feldspar quartz sandstone with high maturity, which are formed in passive continental margin environment, and metamorphic mafic rocks are intermediate basic igneous rocks formed in continental rift environment. The Dongcha granite shows the characteristics of A-type granite, while the Guchuanggou granite is a set of S-type granite. The age of formation of shallow metamorphic clastic rocks in Kuanping complex, Kuanping complex is 530Ma. the age of formation of metamorphic rocks is 1771 鹵15Ma. the age of formation of Dongcha and Guchuangou granites is 1775 鹵14Ma and 2197 鹵19Marespectively. The age of crystallization of metamorphic mafic rocks and granitic rocks is much greater than that of clastic rocks, indicating that they do not constitute a unified lithostratigraphic unit. These ancient igneous bodies should be the material in the southern margin of the North China plate involved in the orogenic belt, and should be excluded from the Kuanping rock group. The dating results of the detrital zircon show that the clastic rocks of the Kuanping rock group in the western part of the North Qinling Mountains mainly have the age peaks of Y600-800 Mahuan950-1100Ma-2500Ma and 3400Ma. The age spectrum of -2500Ma and Yi-3400Ma coincides with the age distribution of the North China plate from -950-1100Ma to the North Qinling magma event, indicating that the Kuanping clastic rocks accept the North China plate at the same time, and the age distribution of the South Qinling / Yangtze plate is the same as that of the North Qinling Plate. The detrital materials of the northern Qinling and the northern margin of the Yangtze plate also indirectly prove that the depositional environment of the clastic rocks in Kuanping is a rift basin between the North China block and the North Qinling continental block.
【學(xué)位授予單位】：西北大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類(lèi)號(hào)】：P597.3;P548

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