【作者】 王刚；

【导师】 王宗起；

【作者基本信息】 中国地质大学（北京） ， 构造地质学， 2014， 博士

【摘要】 北大巴山是南秦岭的重要组成部分之一，经历了俯冲-增生造山和碰撞造山以及陆内造山等多个构造演化阶段，对其构造属性不同地质学家仍存在不同的认识。火山-沉积序列和火山岩石组合具有构造专属性，是识别古板块构造格局，追溯其构造演化历史的有效手段。本文选择北大巴山腹地滔河口组玄武质火山-沉积岩和斑鸠关组粗面质火山-沉积岩为研究对象，开展火山-沉积岩石组合类型及序列特征研究，并结合岩石学、岩石地球化学、同位素地质年代学等对火山岩成因与形成构造背景进行了研究，并探讨地球动力学过程。此外，对滔河口组赋存的小镇铜矿床进行了矿床成因与成矿时代等的研究。根据野外路线调查和地质剖面实测与修测，本文对滔河口组和斑鸠关组火山沉积岩进行了火山相划分和古火山机构的恢复。研究表明滔河口组可能存在榨溪、笔架山等多个火山喷发口，建立的理想火山-沉积序列表明榨溪地区具有典型的海山环境特征；斑鸠关组粗面质火山岩在红椿坝断裂南北各有分布，野外共生岩石和岩石结构、构造特征显示，它们为两期不同岩浆活动产物，其中岚皋地区古火山机构位于四季河附近。岩石学、岩石地球化学、同位素测年及古生物化石等研究表明：滔河口组玄武质火山岩为晚古生代早泥盆世（408Ma）碱性玄武岩系列，主要由苦橄岩+碱性玄武岩+碱玄岩+碧玄岩+霞石岩组成，其中蔺河-笔架山发育为钾质类型，西部小镇-榨溪发育为钠质类型，它们为同源岩浆但经历了不同程度的分离结晶作用；均起源于软流圈地幔，早期古老大洋岩石圈底部的橄榄岩和少量陆源沉积物俯冲至软流圈提供了物源，源区发生了地幔交代作用。岚皋地区粗面岩为早古生代中志留世（432Ma）钾质碱性系列，紫阳地区粗面岩为晚古生代早泥盆世（~410Ma）钾玄岩系列。它们均发生了强烈的分离结晶作用，但经历了不同矿物的结晶分异；部分熔融是它们各自岩浆形成的主要过程，但它们为两种不同的母岩浆；岚皋地区粗面岩起源于独立的地幔源，且源区存在地幔交代作用，而紫阳地区粗面岩起源于受铁镁质岩浆的底侵引起下地壳部分熔融。通过火山-沉积序列、火山岩石组合及岩石地球化学等研究表明岚皋地区粗面岩与滔河口玄武质火山岩分别形成于弧后板内环境和弧后盆地海山环境；而紫阳地区粗面岩形成于与俯冲有关的造山环境，表明北大巴山地区发生了向南的俯冲作用。矿物学、矿床地球化学和成矿年代学等研究表明，小镇铜矿为中低温岩浆期后热液型矿床，形成于154Ma，赋矿钠长岩为岩浆成因。因此，北大巴山地区存在燕山期成岩成矿地质事件。更多还原

【Abstract】 The Northern Daba Mountain, as an important component of the South Qinling orogen, has experienced a variety of tectonic evolutionary stages, for instance, subduction-accretion orogenesis, collisional orogenesis, and intracontinental orogenesis, and different geologists hold different perspectives on the tectonic attributes of the mountains. The volcani-sedimentary sequence and volcanic rock assemblages have tectonic speciality, and they are an effective measure for identifying patterns of ancient plate tectonics and tracing the tectonic evolution history. With the basaltic volcanic-sedimentary rocks of Taohekou Formation and the trachytic volcanic-sedimentary rocks of Banjiuguan Formation in the hinterland of the northern Daba Mountains as the research objects, a research is conducted on the assemblage type and the sequence characteristics of the volcanic-sedimentary rocks; moreover, in combination with petrology, geochemistry, isotopic geochronology, researches were carried out to explore the tectonic background of the cause and formation of the volcanic rocks, meanwhile, the geodynamic processes are also investigated. In addition, the deposit genesis and metallogenic epochs are also conducted on the Xiaozhen copper deposit occurring in Taohekou Formation.According to the field investigation and the actual and revisional surveys of the geological profile, this paper classifies the volcano facies and reconstructs the palaeo-volcanic mechanisms of the volcanic-sedimentary rocks of Taohekou and Banjiuguan Formations. The research suggests that many volcano vents, such as Zhaxi, Bijiashan, possibly exist in Taohekou Formation. And the establishment of the ideal volcano-sedimentary sequence indicates that Zhaxi area has the features typical environment characteristics of seamounts; besides, the trachytic volcanic rocks of Banjiuguan Formation occur in both the north and the south of Hongchunba Fault. Judging from the field symbiotic rock, rock structures and the structure characteristics, they are products of two different magmatic activities, among which the palaeo-volcanic mechanisms in Langao area is located in the vicinity of the Siji River.Based on petrology, geochemistry, isotope dating and fossils, the studies show that the basaltic volcanic-sedimentary rocks of Taohekou Formation erupted in early Devonian (408Ma) of Late Paleozoic and mainly composed of the picrites, alkaline basalts, tephrites, basanites and nephelinites which is an alkaline basalt series. The eastern of Linhe to Bijiashan area develop the potassic type while the western of Xiaozhen to Zhaxi area develop sodic type, they are comagmatic but have experienced fractional crystallizations of different degrees; they are all originated from the asthenosphere mantle. Early stage of the peridotite at the bottom of the ancient oceanic lithosphere and a small amount of terrigenous sediment will subduct to the asthenosphere, which provided the material source, especially when the mantle metasomatism took place in the source region. The trachytic volcanic-sedimentary rocks in Langao area belong to the potassic-alkali series as formed in middle Silurian (432Ma)of Early Paleozoic, while the trachytic volcanic-sedimentary rocks in Ziyang area are of the shoshonite series and they formed in early Devonian (-410Ma) of Late Paleozoic. They all underwent the strong fractional crystallization, but experienced the crystallization differentiation of different minerals; partial melting is the main process of their magmatic formations, but they are two different kinds of parental magmas; the trachytic rocks in Langao area originated from the independent mantle source,also, the source area has mantle metasomatism, while the trachytic rocks in Ziyang area originated from the partial melting of the lower crust, which is caused by the under plating of the femic magma.Through researches into the volcano-sedimentary sequences, volcanic rock assemblages as well as geochemistry, it can be indicated that the basaltic volcanic rocks of Taohekou Formation and the trachytic rocks in Langao Area are respectively formed in the intraplate environment of back-arc and seamount of back-arc basin setting, while the trachytic rocks in Ziyang Area were developed in the subduction-related orogenic environment, which shows that southward subduction had ever happened in the Northern Daba Mountain.Moreover, based on mineralogy, deposit geochemistry and metallogenic geochronology, the researches indicate that the Xiaozhen copper deposit, formed in154Ma, is a hydrothermaldeposit after the magmatic stage with middle or low temperature, and the ore-bearing albitites are taken as the magma genesis. Therefore, there exist such geological events as diagenesis and mineralization in Yanshanian in the Northern Daba Mountain.更多还原