【摘要】：蘇尼特左旗地區(qū)位于內(nèi)蒙古中北部,屬于中亞造山帶東段的興蒙造山帶,研究區(qū)構(gòu)造上位于二連-賀根山弧增生帶上。該二連-賀根山弧增生帶呈北東東向伸展,南北邊界分別為二連-賀根山斷裂帶和查干敖包-阿榮旗斷裂帶。區(qū)內(nèi)發(fā)育密集的巖脈群,侵位于泥盆系泥鰍河組的砂巖和礫巖和石炭系寶力高廟組火山巖、石炭紀(jì)花崗閃長巖、二長花崗巖等晚古生代巖漿巖中。巖脈群整體呈平行分布,走向?yàn)楸睎|東向,與區(qū)域構(gòu)造線走向一致。在地貌上,巖脈大多數(shù)呈“S”型彎曲,部分巖脈被北北東向斷裂錯斷。由于巖脈具有強(qiáng)抗風(fēng)化能力,與圍巖存在明顯風(fēng)化差異而形成山脊,在遙感影像中顯示為密集的條帶狀凸起。相鄰脈體間隔主要集中在70-100米,密集區(qū)最小間隔約10-20m,單條巖脈出露長度可達(dá)數(shù)公里,寬度主要在20-30m之間,走向在75°-90°之間,近于直立。巖脈種類主要為酸性的花崗斑巖脈和流紋巖脈,另外還有少量的閃長玢巖脈,由于其數(shù)量很少,沒有太多的實(shí)際研究意義,將不在本文的研究范圍之內(nèi)。花崗斑巖脈和流紋巖脈均為斑狀結(jié)構(gòu),花崗斑巖脈斑晶主要為鉀長石和石英及部分斜長石,流紋巖脈斑晶為石英和少量長石,并且流紋巖脈發(fā)育特征的流紋構(gòu)造和球粒構(gòu)造。通過LA-ICP-MS法測得花崗斑巖的鋯石U-Pb諧和年齡為289.2±2.8Ma,流紋巖的鋯石U-Pb諧和年齡為282.4±7.4Ma,由此可確定本區(qū)巖脈群的侵位時代為早二疊世。在巖石地球化學(xué)方面,花崗斑巖脈與流紋巖脈特征相似,主量元素上表現(xiàn)為富硅、富堿、富鋁和貧鈣的特征;微量元素上具有輕稀土元素較富集以及重稀土元素平坦的分布特征,銪顯示弱的負(fù)異常。另外,巖石富集Rb、Ba、Th、U、K及Pb,而Nb、Ta、Ti、P呈明顯的負(fù)異常。這些地球化學(xué)特征顯示該巖脈群是由島弧巖漿巖地殼部分熔融形成的。西伯利亞板塊南緣發(fā)育的巨型A型花崗巖帶(年齡為276Ma-286Ma)及雙峰式火山巖線(年齡為270Ma-281Ma)均代表著伸展構(gòu)造環(huán)境,與之相比,本研究區(qū)巖脈群更能代表區(qū)域伸展構(gòu)造環(huán)境,并且比上述的A型花崗巖帶和雙峰式火山巖線的年齡略早,提高了西伯利亞板塊南緣伸展構(gòu)造環(huán)境的年齡上限。綜上所述,本文認(rèn)為研究區(qū)巖脈群為早二疊世的伸展構(gòu)造背景下島弧巖漿巖地殼局部熔融的產(chǎn)物。
[Abstract]:The Sunita Zuo Banner area is located in the central and northern part of Inner Mongolia and belongs to the Xingmeng orogenic belt in the eastern part of the Central Asian orogenic belt. The arc-accretive zone of Erlian-Hegenshan extends in the north and west direction, and the north and south boundary is the Erlian-Hegenshan fault zone and the Chagan Aobo-Aronqi fault zone. There are dense vein groups in the area, which are located in late Paleozoic magmatic rocks, such as sandstone and conglomerate of the Loach River formation of Devonian, volcanic rock of Baoligaomiao formation of Carboniferous, granodiorite of Carboniferous, monzogranite and other late Paleozoic magmatic rocks. The whole vein group is distributed in parallel with the strike of east-west direction, which is consistent with the regional tectonic line. In geomorphology, most of the veins are "S" curved, and some of them are faulted in NNE direction. Because of the strong weathering resistance of the vein and the obvious difference between the rock and the surrounding rock, the ridge is formed, which is shown to be a dense banded protuberance in remote sensing images. The distance between adjacent veins is mainly 70-100 m, the minimum interval in dense area is about 10-20 m, the length of single vein is several kilometers, the width is mainly between 20-30 m, and the strike is between 75 擄-90 擄, which is nearly vertical. The main types of veins are acidic granitic porphyry veins and rhyolite veins, and a small amount of diorite-porphyrite veins, due to the small number of diorite-porphyrite veins, there is not much practical significance, so it will not be within the scope of this study. The granitic porphyry vein and the rhyolite vein are both porphyry structure. The porphyry crystals of the granitic porphyry vein are mainly potash feldspar, quartz and some plagioclase, while the rhyolite vein porphyry is quartz and a little feldspar. The zircon U-Pb harmonic age of granitic porphyry is 289.2 鹵2.8 Ma. and the zircon U-Pb harmonic age of rhyolite is 282.4 鹵7.4 Ma.Therefore, the emplacement age of the vein group in this area is determined to be early Permian. In the aspect of rock geochemistry, the characteristics of granitic porphyry vein and rhyolite vein are similar, and the main elements are silicon-rich, alkali-rich, aluminum-rich and calcium-poor. The trace elements are relatively rich in light rare earth elements and flat in the distribution of heavy rare earth elements. Europium shows weak negative anomalies. In addition, the rocks are enriched in Rb,Ba,Th,U,K and Pb, but Nb,Ta,Ti,P is obviously negative abnormal. These geochemical characteristics indicate that the vein group was formed by the partial melting of the crust of island arc magmatic rocks. The giant A-type granite belt (age 276Ma-286Ma) and the bimodal volcanic rock line (age 270Ma-281Ma) developed on the southern edge of the Siberian plate represent the extensional tectonic environment. In this study area, the vein group is more representative of the regional extensional tectonic environment, and the age limit of the extensional tectonic environment in the southern edge of the Siberian plate is raised slightly earlier than that of the A-type granite belt and the bimodal volcanic line mentioned above. To sum up, the study area is considered as the product of local melting of island arc magmatic rock crust in the early Permian extensional tectonic setting.
【學(xué)位授予單位】：石家莊經(jīng)濟(jì)學(xué)院
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P597.3;P583

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