西昆仑造山带早中生代花岗岩成因与古特提斯构造演化

发布时间：2018-07-09 15:46

本文选题：花岗岩 + 暗色微粒包体　；参考：《南京大学》2015年博士论文

【摘要】：西昆仑造山带位于位于青藏高原西北缘,是古亚洲构造域与特提斯构造域结合、转换地带,北以乌依塔克-库地缝合带与塔里木地块相接,南以麻扎-康西瓦缝合带为界与甜水海地体拼接。目前可以接受的观点是西昆仑造山带经历了多期造山作用,但有关其具体构造演化过程还存在很大的争论。此外,西昆仑造山史还关系到对欧亚大陆与羌塘地块碰撞并最终焊接历史的认识。西昆仑造山带发育两条醒目的中-酸性深成岩带,即西昆仑北岩带和西昆仑南岩带。其中北岩带分布于乌依塔克-库地缝合带南侧,形成于古生代(以早古生代为主),而南岩带分布于麻扎-康西瓦缝合带北侧,形成于早中生代。本论文主要选择了西昆仑南岩带中的花岗质岩体及其中暗色微粒包体为研究对象,采用锆石SHRIMP定年以及矿物化学、元素地球化学和Sr-Nd-Hf同位素示踪相结合的方法,阐明了它们的源区和岩浆演化过程,探讨其形成的构造环境和动力学机制,从而为西昆仑造山带长期争论的构造演化模式提供新的制约。本次工作对南岩带中六个代表性岩体(玉其卡帕、慕士塔格、塔尔、库地南、阿卡阿孜和麻扎岩体)及其中暗色微粒包体开展了研究。除麻扎岩体分布于甜水海地体外,其余岩体均分布于西昆仑地体内。本次SHRIMP锆石U-Pb定年结果表明,这些岩体及其中暗色微粒包体形成于三叠纪(～243-209 Ma)。玉其卡帕岩体侵位于中三叠世安尼西期(Anisian) (-243 Ma),主要由二云母花岗岩组成,其岩石组合为二长花岗岩-正长花岗岩-碱长花岗岩,主要造岩矿物为钾长石、石英、斜长石、黑云母和白云母,部分样品中含有微量石榴子石,中粒花岗结构,片麻状构造。这些花岗岩属于高钾钙碱性系列并且是过铝质的。它们的初始87Sr/86Sr、εNd(T)和锆石εHf(T)分别为0.7071-0.7077、-4.4--6.3和-3.3。详尽的元素和同位素地球化学研究结果表明,这些花岗岩是在陆-陆碰撞过程中通过前寒武纪基底变质岩“湿”的深熔作用形成的。慕士塔格和塔尔岩体侵位于晚三叠世卡尼期(Carnian) (234-227 Ma),主要由花岗闪长岩和二长花岗岩组成,主要造岩矿物为斜长石、钾长石、石英、角闪石和黑云母,中粒花岗结构,块状构造,局部片麻状构造。这两个岩体含有一系列暗色微粒包体,其SHRIMP锆石U-Pb年龄(233-226 Ma)与寄主岩一致。寄主花岗岩也属于高钾钙碱性系列,但主要是准铝质的,少量弱过铝质。它们的初始87Sr/86Sr、εNd(T)和锆石SHf(T)分别为0.7052-0.7104、-3.6-7.3和-3.3N-1.0。详尽的元素和同位素地球化学研究表明这些花岗质岩石都是由底侵的包体岩浆诱发下地壳中前寒武纪变质岩石发生部分熔融而形成的。其中,对于慕士塔格岩体(邻近麻扎-康西瓦缝合带)来说,部分熔融作用发生在正常厚度(40 km)的下地壳,而对于塔尔岩体(远离麻扎-康西瓦缝合带)来说,部分熔融则发生在加厚(～40-50 km)的下地壳。暗色微粒包体主要是基性的(SiO2=48.0-51.6 wt.%),少量具有中性成分(SiO2= 53.0-54.6 wt.%),并且它们都是钾质的,其地球化学特征与碰撞后钾质岩浆相似。这些暗色微粒包体具有与寄主岩相似的εNd(T)值,但是它们的初始87Sr/86Sr比寄主岩低,而锆石εHf(T)值比寄主岩高。详尽的元素和同位素地球化学研究结果表明,包体岩浆起源于受到俯冲组分改造过的岩石圈地幔的部分熔融,其中对于慕士塔格岩体中的包体来说,部分熔融作用发生在尖晶石相地幔区域(60 km),而对于塔尔岩体中的包体来说,部分熔融作用则发生在尖晶石-石榴子石相过渡带(～60-80 km)。中三叠世安尼西期和晚三叠世卡尼期花岗岩及暗色微粒包体岩石成因特征表明,西昆仑地体和甜水海地体之间的古特提斯洋盆最终闭合发生在中三叠世安尼西期(Anisian) (-243 Ma),而到了晚三叠世卡尼期(Carnian) (-234-227 Ma),该区域已进入碰撞后阶段,古特提斯洋壳断离(Slab break-off)是形成卡尼期花岗岩及其暗色微粒包体的动力学机制。库地南、阿卡阿孜和麻扎岩体均侵位于晚三叠世诺瑞期(Norian) (215-209 Ma),并且呈现出向南逐渐变年轻的趋势。库地南岩体(215 Ma)主要由高钾钙碱性花岗闪长岩和二长花岗岩组成,其初始87Sr/86Sr、εNd(T)和锆石εHf(T)分别为0.7093-0.7099、-4.9-5.4和0.3。元素和同位素数据表明该岩体可能是由玄武质岩浆底侵诱发下地壳中前寒武纪基底变质岩发生部分熔融而形成的。阿卡阿孜岩体(213 Ma)位于库地南岩体南侧,主要由高钾钙碱性二长花岗岩、正长花岗岩和碱长花岗岩组成,该岩体含有大量暗色微粒包体。寄主花岗岩的初始87Sr/86Sr、 εNd(T)和锆石εHf(T)与库地南岩体相似,分别为0.7071-0.7085、-3.7--4.8和-0.7。因此,该岩体同样是由包体岩浆底侵诱发下地壳中前寒武纪基底变质岩发生部分熔融而形成的。包体主要成分是基性的(Si02含量为48.0-54.9wt.%),并且是钾质的,显示陆缘弧钾质岩浆的地球化学特征。它们的初始87Sr/86Sr和εNd(T)分别为0.7071-0.7080和-2.6～-4-5。元素和同位素数据表明包体岩浆起源于尖晶石-石榴子石过渡相地幔楔(-60-80 km)的部分熔融。麻扎岩体(209 Ma)位于甜水海地体中,由高钾钙碱性英云闪长岩和花岗闪长岩组成,其初始87Sr/86Sr、εNd(T)和锆石εHf(T)分别为0.7087-0.7097、-6.3～-6.5和-2.8。元素和同位素数据表明该岩体是由幔源岩浆与壳源岩浆发生混合作用而形成的。晚三叠世诺瑞期花岗岩及暗色微粒包体岩石成因特征表明,西昆仑-甜水海联合地体在晚三叠世诺瑞期(215-209 Ma)处于活动大陆边缘环境,与甜水海地体和喀喇昆仑地体之间的古特提斯洋的北向俯冲有关。同时结合甜水海地体自早侏罗世开始发生陆源红层磨拉石堆积,我们认为欧亚大陆与喀喇昆仑地体(羌塘地块)最终拼贴作用发生在早侏罗世。
[Abstract]:Located in the northwest margin of the Qinghai Tibet Plateau, the western Kunlun orogenic belt is located in the northwest margin of the Qinghai Tibet Plateau. It is a combination of the ancient Asian tectonic domain and the Tethys tectonic domain, the transition zone, the north of the Tarim block suture zone and the Tarim block in the north. The south is spliced with the sweet water Haiti body with the mazaja suture suture zone. The view that the West Kunlun orogenic belt has experienced many periods is acceptable. In addition, the history of the western Kunlun orogenic history is also related to the collision of the Eurasian continent with the Qiangtang block and the final welding history. The West Kunlun orogenic belt developed two wake acid deep diagenetic belts, namely the West Kunlun northern rock belt and the western Kunlun Southern rock belt. It is distributed in the southern side of the ulitac kuldi suture belt, formed in the Paleozoic (mainly in the early Paleozoic), and the Southern rock belt is distributed in the northern side of the Mazha Connecticut suture belt and formed in the early Mesozoic. This paper mainly selected the granitic rock mass in the Southern rock belt of West Kunlun and its dark particle inclusion body as the research object, and adopted zircon dating for SHRIMP years as well. The combination of mineral chemistry, elemental geochemistry and Sr-Nd-Hf isotope tracer illustrates their source and magma evolution processes, and discusses the tectonic setting and dynamic mechanism of their formation, thus providing a new system for the long debated tectonic evolution model of the western Kunlun orogenic belt. Yuch Kappa, moussata, tal, cutan, a CAD and Mazha rock mass and its dark microparticle inclusions were studied. Except the Mazha rock mass distributed in the sweet water Haiti in vitro, the rest of the rock mass were distributed in the West Kunlun area. The SHRIMP zircon U-Pb dating results showed that these rocks and its dark microparticle inclusions were formed in the Triassic period ( ~ 243-209 Ma). The jade kappa pluton invades the middle three epoch (-243 Ma), mainly composed of two mica granite, and its rock assemblage is two granite - syenite alkali granite. The main rock forming minerals are potash feldspar, quartz, plagioclase, biotite and muscovite, and some of the samples contain a small amount of pomegranite in some samples. These granites belong to the high potassium calc alkaline series and are peraluminous. Their initial 87Sr/86Sr, epsilon Nd (T) and zircon epsilon Hf (T) are 0.7071-0.7077, -4.4--6.3 and -3.3. detailed elemental and isotopic geochemical studies show that these granites are through the cold front during land land collisions. The "wet" deep melting of the basilar metamorphic rocks of the martial arts was formed. The moustagg and the Al plutons were invaded in the late three Carney period (Carnian) (234-227 Ma), mainly composed of granodiorite and two granitic granite. The main rock forming minerals were plagioclase, potassium feldspar, quartz, amphibolite and biotite, medium granitic structure, lump structure, and local flax. The two rocks contain a series of dark particle inclusions, and the SHRIMP zircon U-Pb age (233-226 Ma) is the same as the host rock. Host granite also belongs to the high potassium calc alkaline series, but it is mainly quasi aluminous and a small amount of weakly peraluminous. Their initial 87Sr/86Sr, epsilon Nd (T) and zircon SHf (T) are 0.7052-0.7104, -3.6-7.3 and -3.3N-1.0., respectively. The elemental and isotopic geochemical studies have shown that these granitic rocks are formed by partial melting of the Precambrian metamorphic rocks in the lower crust induced by the underclad magma, and the partial melting of the moustigg rock (adjacent to the Mazha connecticw suture zone) occurs below the normal thickness (40 km). For the shell, for the tar rock mass (far away from the Mazha Connecticut suture zone), the partial melting occurs in the lower crust of thickening (to 40-50 km). The dark colored particles are mainly based on the base (SiO2=48.0-51.6 wt.%), a small amount of SiO2= 53.0-54.6 wt.%, and they are all potassium, and their geochemical characteristics and post collisional potassic magma Similar. These dark particle inclusions have the values of epsilon Nd (T) similar to host rocks, but their initial 87Sr/86Sr is lower than the host rock, and the zircon epsilon Hf (T) values are higher than the host rocks. The partial melting occurs in the spinel phase mantle region (60 km) in the pluton pluton, while the partial melting occurs in the transition zone of the spinel - Garnet (~ 60-80 km) for the peritenite in the Tuli rock mass. In the middle three, the Carney period and the late three fold phase of the granite and the dark particle perittite The Shi Chengyin characteristics indicate that the final closure of the ancient Tethys oceanic basin between the West Kunlun and the sweet water Haiti body occurred in the middle three epoch (Anisian) (-243 Ma), and to the late three fold Carnian (-234-227 Ma), the region had entered the post collision stage, and the Gut Tis oceanic crust (Slab break-off) was a Carney stage. The kinetic mechanism of rock and its dark colored particulate inclusions. The Kutan, Al Kuda and Mazha intrusions are all invaded in the late three period (Norian) (215-209 Ma), and present a trend towards the south. The Kutan rock mass (215 Ma) is mainly composed of high potassium calc alkaline granodiorite and two granitic granite, and its initial 87Sr/86Sr, Nd (T). The zircon epsilon Hf (T), respectively, 0.7093-0.7099, -4.9-5.4 and 0.3. elements and isotopic data indicate that the rock mass may be formed by partial melting of the Precambrian basement metamorphic rocks in the lower crust of the basaltic magma. The alkamia rock mass (213 Ma) is located on the south side of the Kutan rock mass, mainly from the high potassium calc alkaline two granitic granite. The granite and alkali feldspar are composed of a large number of dark particle inclusions. The initial 87Sr/86Sr, epsilon Nd (T) and the zircon epsilon Hf (T) of host granite are similar to the cutan rock mass, respectively, 0.7071-0.7085, -3.7--4.8 and -0.7., therefore, the rock mass also occurred in the Precambrian basement metamorphic rock in the lower crust of the lower crust induced by the Bao Tiyan pulp underplating. The main components of the inclusions are based on the base (Si02 content 48.0-54.9wt.%) and are potassium, indicating the geochemical characteristics of the epicontinental arc potassic magma. Their initial 87Sr/86Sr and epsilon Nd (T) are 0.7071-0.7080 and -2.6 to -4-5. elements and isotopic data, respectively, indicating that the inclusion magma originated from the spinel garnet. The partial melting of the crossing mantle wedge (-60-80 km). The Mazha rock mass (209 Ma) is located in the sweet water Haiti body and consists of high potassium calc alkaline diorite and granodiorite. Its initial 87Sr/86Sr, epsilon Nd (T) and zircon epsilon Hf (T) are 0.7087-0.7097, -6.3 to -6.5, and -2.8. elements and isotopes, indicating that the rock mass was derived from the mantle derived magma and Ke Yuanyan. The formation of the mixture of the pulps. The formation of the late three Permian granite and dark granitic xenoliths showed that the West Kunlun - the sweet water Sea joint body was in the active continental margin in the late three fold (215-209 Ma), related to the North subduction of the ancient Tethys ocean between the sweet water Haiti body and the Karakoram. Combined with the early Jurassic, the Haiti body of sweet water began to accumulate in the early Jurassic. We believe that the final collage of the Eurasian continent and the Karakoram block (Qiangtang block) occurred in the early Jurassic.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P588.121;P548

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