西秦岭中川花岗岩体年代学、地球化学、岩浆混合成因

发布时间：2018-12-13 10:32

【摘要】：西秦岭造山带位于中国腹心地带秦岭造山带的西段,是中国中央造山带的重要组成部分。中川花岗岩体位于西秦岭构造带东部礼县-罗坝-锁龙口断裂和礼县-洮坪断裂两大断裂之间,主要侵位于泥盆系舒家坝群和西汉水群中。其岩石类型主要为中粗粒似斑状黑云二长花岗岩、中粒含斑黑云二长花岗岩以及中细粒黑云二长花岗岩,这些岩石由外向内依次呈同心圆状分布。岩体中岩浆暗色包体发育,同时也发育后期侵入的细粒花岗岩脉。LA-ICPMS锆石U-Pb定年显示,似斑状黑云二长花岗岩的年龄为221±1Ma(MSDW=0.26),细粒黑云二长花岗岩为217±1Ma(MSDW=0.107);含斑晶岩浆暗色包体为220±1Ma(MSDW=0.107),细粒岩浆暗色包体为216±1Ma(MSDW=0.26);细粒花岗岩脉为207±1Ma(MSDW=0.29)。这表明该岩体从边部到中心年龄有逐渐变新的趋势,暗色包体和寄主岩石的形成年龄基本一致,岩脉的形成时间最晚。中川岩体中不同寄主岩石类型在矿物组成上基本一致,为碱性长石+斜长石+石英+黑云母±角闪石组合,暗色矿物以黑云母为主,可见少量角闪石,不含石榴子石、堇青石等富铝矿物,岩体中心晚期的细粒黑云二长花岗岩不含角闪石,并有极少量的白云母出现。岩浆暗色包体主要分布于岩体边部,矿物组成为黑云母、角闪石、石英、斜长石、碱性长石,岩石类型为细粒石英闪长岩,部分包体内部包裹钾长石巨晶。中川岩体寄主岩石的A/CNK=0.99~1.15,具高硅、铝和富碱的特点,属高钾钙碱系列,准铝质-弱过铝质I型花岗岩,同时细粒黑云二长花岗岩A/CNK大于1.1,铁镁含量较低,出现少量白云母,为高分异I型花岗岩。岩浆暗色包体具低硅、富铝和富碱的特点,属钾玄岩-高钾钙碱系列,准铝质岩。寄主岩石和岩浆暗色包体均表现出轻稀土相对富集的右倾的特征,轻、重稀土元素分馏明显,具弱的负铕异常;均富集LREE、Rb、Ba、K等大离子亲石元素,亏损HREE、Zr、Hf、Ta、Nb、P、Ti等高场强元素。同位素组成上,寄主岩石与暗色包体的εNd(t)分别变化于-7.31~-8.73和-5.32~-5.69之间,TDM2分别变化于1.59~1.71Ga和1.43~1.46Ga之间,εHf(t)值分别为-7.02~-0.31和-3.0~0,TDMC为1.27~1.70Ga和1.2~1.5Ga,暗色包体发育淬冷边和针状磷灰石,反映寄主花岗岩和岩浆暗色包体分别来源于不同源区,寄主岩石主要是古老地壳物质部分熔融的结果,暗色包体岩浆可能是来自岩石圈地幔,但与寄主花岗质岩浆已发生了一定的混合。该岩体外围金矿床的成矿年龄(171~210Ma)稍晚于岩体形成年龄,并且岩体、矿区岩脉以及金矿床年龄相近,金矿与岩体时空上联系密切,结合前人成矿物质来源的研究,认为成矿物质与成岩物质具有相似性。这表明该岩体与其周围的金矿可能具有同源性和继承性演化的特点。
[Abstract]:The West Qinling orogenic belt is an important part of the central orogenic belt of China, which is located in the western part of the Qinling orogenic belt in the ventral heart of China. The Zhongchuan granite body is located between the Lixian-Luoba-Suolongkou fault and the Lixian-Taoping fault in the eastern part of the western Qinling structural belt, and mainly transgressions in the Devonian Shujiaba group and the western Han water group. The rock types are mainly medium-coarse porphyry bifeldite, mesomorphic porphyry bifeldite and medium-fine-grained black cloud monzogranite. These rocks are distributed in concentric circles from outside to inside. LA-ICPMS zircon U-Pb dating shows that the age of porphyry bifeldspar granite is 221 卤1Ma (MSDW=0.26). The fine grained bifeldite is 217 卤1Ma (MSDW=0.107); The dark color inclusion of porphyry magma is 220 卤1Ma (MSDW=0.107), the dark color inclusion of fine-grained magma is 216 卤1Ma (MSDW=0.26), and the vein of granitic granite is 207 卤1Ma (MSDW=0.29). This indicates that the age from the edge to the center of the rock body is gradually changing, the age of formation of the dark inclusion is basically the same as that of the host rock, and the formation time of the vein is the latest. The mineral composition of different host rocks in Zhongchuan rock mass is basically the same, which is composed of alkaline feldspar plagioclase quartz biotite 卤hornblende assemblage, dark mineral is mainly biotite, a small amount of hornblende and no garnet is found. Cordierite and other aluminum-rich minerals, the late fine-grained biotite monzonitic granites in the center of the rock body do not contain amphibole, and a very small amount of Muscovite appears. The magmatic dark inclusion is mainly distributed at the edge of the rock body, and the mineral composition is biotite, hornblende, quartz, plagioclase, alkaline feldspar, the rock type is fine quartz diorite, and some inclusions contain potassium feldspar megacrystals. The A / CNK ~ (0.99) ~ (1.15) of the host rocks of the Zhongchuan rock body is characterized by high silicon, aluminum and alkali, belonging to the high potassium calcium alkali series, quasi-aluminum-weakly peraluminous I-type granite, and the fine grained black cloud monzomorphic granite (A/CNK > 1.1). The content of Fe and mg is low and a small amount of Muscovite, which is a high differentiation I type granite. The magmatic dark inclusion is characterized by low silicon, rich in aluminum and alkali. It belongs to the series of potash-high potassium calcium alkali, quasi-aluminous rock. The dark inclusions of host rocks and magma show the characteristics of relative enrichment of LREE to the right, light and heavy REE fractionation is obvious, with weak negative europium anomaly. All of them are rich in large ion lithophile elements such as LREE,Rb,Ba,K and depleted high field strength elements such as HREE,Zr,Hf,Ta,Nb,P,Ti. In isotopic composition, 蔚 Nd (t) of host rocks and dark inclusions varied from -7.31 to 8.73 and -5.32 to 5.69, and TDM2 to 1.59~1.71Ga and 1.43~1.46Ga, respectively. The 蔚 Hf (t) values were -7.02 ~ (-0.31) and -3.0 ~ 0 ~ (-1) 1.27~1.70Ga, respectively. The dark inclusion developed quenching edge and acicular apatite, which indicated that the host granite and magmatic dark inclusion originated from different source regions, respectively. The host rocks are mainly the result of partial melting of ancient crustal materials. The dark inclusion magma may come from the lithospheric mantle, but has been mixed with the host granitic magma to some extent. The metallogenic age (171~210Ma) of the peripheral gold deposit is slightly later than that of the rock mass, and the age of the ore body, the vein and the gold deposit is similar, and the gold deposit is closely related to the rock mass in time and space. It is considered that the ore-forming material is similar to the diagenetic material. This indicates that the rock may have the characteristics of homology and succession evolution with the gold deposits around it.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121;P597.3

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