云南凤庆西老黄坟花岗岩体成因机制分析
发布时间：2018-11-19 22:12
【摘要】：滇西三江地区位于喜马拉雅-特提斯构造域的东端与环太平洋构造域的汇合部,受到太平洋板块、印度洋板块和欧亚板块的共同影响,经历了特提斯形成演化、印度-欧亚大陆碰撞以及高原隆升的复杂过程。区内发育的临沧复式花岗岩基是区域出露面积最大的复式岩基,是古特提斯构造域中的重要单元,本文在野外调研的基础上,对位于临沧复式花岗岩基北缘的云南凤庆西老黄坟中酸性侵入岩岩石学、元素地球化学等方面的研究,结合区域上已有成果,旨在对其成因和形成时代以及区域构造岩浆演化提供约束。研究发现凤庆西老黄坟岩体位于大勐龙变质带上,主要岩性为黑云母石英闪长岩,局部间夹有花岗闪长岩,呈不规则状、孤岛状或条带状分布于主岩体中,燕山晚期花岗岩呈小岩体侵位其中。岩石表面风化较重,主要表现为绿泥石化、硅化、钾化、钠黝帘石化、绢云母化。部分地段受韧性剪切的变形变质作用影响尚有部分糜棱岩化、初糜棱岩化岩石。矿物化学分析显示,岩石中的斜长石为中酸性斜长石;黑云母为镁质黑云母,但具有向铁质黑云母过渡的趋势;角闪石主要为阳起石和镁钠闪石,为变质及交代成因的角闪石。以上特征表明该岩体在结晶成岩过程中一定程度上受到富硅碱流体交代蚀变及燕山期浅动力变质作用。元素地球化学分析显示,该岩体的SiO2含量为64.2%~69.56%,平均为66.83%,K2O/Na2O为1.51~27.42,平均为9.25,A/CNK为1.025~2.906,平均为1.87,总体显示SiO2含量偏高,该岩体为过铝质高钾钙碱性花岗岩,具有明显的轻稀土富集,重稀土亏损,大离子亲石元素相对富集,过渡元素相对亏损的特征。以上特征进一步表明该岩浆过程与板片俯冲碰撞过程中伴随深部流体交代作用有关。结合Zr-TiO2、黑云母TFeO/(TFeO+MgO)-MgO、1000Ga/Al2O3-K2O/MgO、CaO/Na2O-Al2O3/TiO2、Rb/Ba-Rb/Sr和La/Sm-La等图解判断凤庆西老黄坟岩体并非单一壳源岩浆经简单结晶分异而来,而是经历了复杂构造-岩浆作用,分离结晶作用很明显,由此推测该岩体是由地壳部分熔融的钙碱性花岗岩浆,先经过分离结晶作用,再经过多次脉动和伴随快速运移的低程度结晶分异形成的,在结晶过程中受到了一定程度的地幔流体的交代作用。凤庆西老黄坟岩体与其他地区临沧花岗基印支期及二叠纪岩体有着不同的岩相学特征,但有着相似的地球化学特征,进一步推测三者可能为相同或相近源区的岩浆作用的产物。其源岩为杂砂岩。形成环境为后碰撞。综合研究认为,凤庆西老黄坟岩体可能形成于二叠纪,属临沧复式花岗岩基过渡演化的岩体组成部分,是昌宁-孟连洋闭合,兰坪-思茅陆块与保山陆块碰撞过程的产物。其主体形成机制上表现为在洋壳板块俯冲消减导致大陆对接后碰撞条件下引发深部上地壳部分熔融的陆壳改造产物。
[Abstract]:The Sanjiang area in western Yunnan is located at the eastern end of the Himalayan Tethys tectonic domain and the confluence of the circum-Pacific tectonic domain. It is influenced by the Pacific plate, the Indian Ocean plate and the Eurasian plate, and has undergone the Tethys formation and evolution. Complex processes of India-Eurasia collision and plateau uplift. Lincan-type granite base developed in this area is the largest outcropping area and an important unit in the paleoTethys tectonic domain. The petrology and elemental geochemistry of acidic intrusive rocks in Laowangfen, Fengqing County, Yunnan Province, located in the northern margin of Lincang complex granite base, have been studied. The purpose of this paper is to provide constraints on the origin and formation of magma and the evolution of regional tectonic magma. It is found that the Laowangfen rock body in the west of Fengqing is located in the Damenglong metamorphic belt. The main lithology is biotite quartz diorite, and there is a granodiorite intercalated locally, which is irregular, isolated island or striped in the main rock mass. The late Yanshanian granite emplaced in small rock mass. The weathering of the rock surface is heavy, mainly manifested as green mud fossilization, silicification, potassium, sodium tetrahedrite and sericite. Some mylonitization and primary mylonitization are affected by ductile shear deformation and metamorphism. The mineral chemistry analysis shows that the plagioclase in the rocks is intermediate acid plagioclase, the biotite is magnesia biotite, but has the tendency of transition to ferric biotite, and the amphibole is mainly actinolite and magnesium sodium amphibole, which are metamorphic and metasomatic hornblende. The above characteristics indicate that the rock mass is subjected to the metasomatic alteration of silicon-rich fluid and the shallow dynamic metamorphism of Yanshanian period to some extent during the process of crystallization and diagenesis. The element geochemistry analysis shows that the SiO2 content of the rock mass is 64.2 ~ 69.56, the average value is 66.83K _ 2O / Na _ 2O = 1.51n 27.42, and the average value is 9.25% A / C / N = 1.025 / 2.906, with an average value of 1.87, respectively. The SiO2 content is relatively high, and the rock mass is peraluminous high potassium calc-alkaline granite with obvious characteristics of light rare earth enrichment, heavy rare earth deficiency, relative enrichment of large ion lithophile elements and relative depletion of transition elements. The above characteristics further indicate that the magmatic process is related to the metasomatism of deep fluids during plate subduction and collision. Combined Zr-TiO2, biotite TFeO/ (TFeO MgO)-MgO,1000Ga/Al2O3-K2O/MgO,CaO/Na2O-Al2O3/TiO2, Rb/Ba-Rb/Sr and La/Sm-La diagrams show that the Xihuangfen rock body is not a single crust magma through simple crystallization differentiation, but experienced complex tectonic-magmatism, and the separation and crystallization process is very obvious. It is inferred that the rock mass is formed by the calc-alkaline granite magma partially melted in the crust, which is separated and crystallized first, then through multiple pulsations and low-degree crystallization differentiation accompanied by rapid migration. In the process of crystallization, the mantle fluid is responsible for the metasomatism to some extent. The Laowangfen pluton in the west of Fengqing has different lithofacies characteristics from other Lincang granitic and Permian rocks, but it has similar geochemical characteristics. It is further speculated that the three bodies may be the product of magmatism of the same or similar source area. The source rock is complex sandstone. The forming environment is a rear collision. It is considered that the Laowangfen rock body in the west of Fengqing may have been formed in the Permian period and is a part of the transitional evolution of the Lincang complex granite base. It is the result of the Changning-Menglian ocean closure and the collision process between the Lanping-Simao continental block and the Baoshan block. Its main formation mechanism is the product of continental crust transformation which caused partial melting of deep upper crust under the condition of subduction and subduction of oceanic crust plate resulting in collision after continental docking.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121
本文编号：2343577
[Abstract]:The Sanjiang area in western Yunnan is located at the eastern end of the Himalayan Tethys tectonic domain and the confluence of the circum-Pacific tectonic domain. It is influenced by the Pacific plate, the Indian Ocean plate and the Eurasian plate, and has undergone the Tethys formation and evolution. Complex processes of India-Eurasia collision and plateau uplift. Lincan-type granite base developed in this area is the largest outcropping area and an important unit in the paleoTethys tectonic domain. The petrology and elemental geochemistry of acidic intrusive rocks in Laowangfen, Fengqing County, Yunnan Province, located in the northern margin of Lincang complex granite base, have been studied. The purpose of this paper is to provide constraints on the origin and formation of magma and the evolution of regional tectonic magma. It is found that the Laowangfen rock body in the west of Fengqing is located in the Damenglong metamorphic belt. The main lithology is biotite quartz diorite, and there is a granodiorite intercalated locally, which is irregular, isolated island or striped in the main rock mass. The late Yanshanian granite emplaced in small rock mass. The weathering of the rock surface is heavy, mainly manifested as green mud fossilization, silicification, potassium, sodium tetrahedrite and sericite. Some mylonitization and primary mylonitization are affected by ductile shear deformation and metamorphism. The mineral chemistry analysis shows that the plagioclase in the rocks is intermediate acid plagioclase, the biotite is magnesia biotite, but has the tendency of transition to ferric biotite, and the amphibole is mainly actinolite and magnesium sodium amphibole, which are metamorphic and metasomatic hornblende. The above characteristics indicate that the rock mass is subjected to the metasomatic alteration of silicon-rich fluid and the shallow dynamic metamorphism of Yanshanian period to some extent during the process of crystallization and diagenesis. The element geochemistry analysis shows that the SiO2 content of the rock mass is 64.2 ~ 69.56, the average value is 66.83K _ 2O / Na _ 2O = 1.51n 27.42, and the average value is 9.25% A / C / N = 1.025 / 2.906, with an average value of 1.87, respectively. The SiO2 content is relatively high, and the rock mass is peraluminous high potassium calc-alkaline granite with obvious characteristics of light rare earth enrichment, heavy rare earth deficiency, relative enrichment of large ion lithophile elements and relative depletion of transition elements. The above characteristics further indicate that the magmatic process is related to the metasomatism of deep fluids during plate subduction and collision. Combined Zr-TiO2, biotite TFeO/ (TFeO MgO)-MgO,1000Ga/Al2O3-K2O/MgO,CaO/Na2O-Al2O3/TiO2, Rb/Ba-Rb/Sr and La/Sm-La diagrams show that the Xihuangfen rock body is not a single crust magma through simple crystallization differentiation, but experienced complex tectonic-magmatism, and the separation and crystallization process is very obvious. It is inferred that the rock mass is formed by the calc-alkaline granite magma partially melted in the crust, which is separated and crystallized first, then through multiple pulsations and low-degree crystallization differentiation accompanied by rapid migration. In the process of crystallization, the mantle fluid is responsible for the metasomatism to some extent. The Laowangfen pluton in the west of Fengqing has different lithofacies characteristics from other Lincang granitic and Permian rocks, but it has similar geochemical characteristics. It is further speculated that the three bodies may be the product of magmatism of the same or similar source area. The source rock is complex sandstone. The forming environment is a rear collision. It is considered that the Laowangfen rock body in the west of Fengqing may have been formed in the Permian period and is a part of the transitional evolution of the Lincang complex granite base. It is the result of the Changning-Menglian ocean closure and the collision process between the Lanping-Simao continental block and the Baoshan block. Its main formation mechanism is the product of continental crust transformation which caused partial melting of deep upper crust under the condition of subduction and subduction of oceanic crust plate resulting in collision after continental docking.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121
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