【作者】 冯佐海；

【导师】 梁金城； 戴塔根；

【作者基本信息】 中南大学 ， 矿产普查与勘探， 2003， 博士

【摘要】 近年来，由于南岭花岗岩带的研究为揭示华南大地构造属性、演化及地球动力学背景提供了重要的岩石学与地球化学等方面的证据而倍受瞩目。但研究多集中在其东段和中段，对其西段、特别是在花岗岩侵位过程及相关构造研究方面尤显薄弱。本文在野外地质调查基础上，运用岩石有限应变测量、现代构造解析、岩石地球化学以及岩浆动力学等研究方法和手段，研究了位于南岭花岗岩带西段的广西姑婆山-花山花岗岩体的构造样式、变形特征、侵位过程及其与大地构造环境关系；分析了与该岩体侵位相关构造的运动学、几何学和动力学。取得了以下主要成果或认识： 1．对姑婆山-花山花岗岩体的岩石谱系单位进行了重新厘定。将该岩体解体为26个侵入体，归并成牛庙和杨梅山2个独立侵入体，以及桂岭、里松、望高、新路、白水带和华美6个单元。在此基础上，建立了牛庙超单元、姑婆山超单元和银平超单元。这3个超单元是华南中生代构造—岩浆旋回中虽有间断但却关系密切的3次岩浆热事件的产物，并均具有渐进式的同源岩浆演化规律。 2．岩浆动力学研究显示，姑婆山-花山花岗岩体形成于中深成环境，岩浆粘度较大、上升速度较慢、密度小于围岩；且总体上看，在岩浆侵位过程中从早期(超)单元到晚期(超)单元岩浆粘度由低到高，上升速度、密度、温度及压力由大到小。 3．研究表明，姑婆山-花山花岗岩体的主体单元在塑性、半塑性状态下，甚至在次岩浆状态时就遭受(或产生)了一定的气球膨胀作用；同时也对其围岩产生了强力挤压和拖拽作用，具有主动侵位的特征。但岩体所具有的独特“拖尾”构造样式也表明，岩体的部分侵位空间还来自岩体边部区域断裂走滑剪切作用所“诱导”的空间，因此也具有被动侵位的特征。 4．岩石有限应变测量和应变分析显示，姑婆山-花山花岗岩体及其热接触变质围岩主要为压扁型应变，应变程度弱—中等。但应变类型及应变程度的时空分布呈明显的非均一性。应变类型方面，早期的牛庙和杨梅山独立侵入体及里松、望高单元以压扁型应变为主，晚期的新路单元主要为拉长型应变；空间上，各单元(或独立侵入体)边部以压扁和平面型应变为主，中部主要为拉长型应变。应变程度方面，从早期单元到晚期单元应变程度递减；围岩内的应变程度向岩体接触 面方向增强，且存在明显的应变梯度。上述应变特征表明，岩体及其 热接触变质围岩的变形与岩浆脉动侵位密切相关，显示出主、被动侵位机制兼具，但以主动侵位为主的特征。 5.岩体的冷却与隆升史研究表明，本区中生代地壳曾经历过3次快速隆升，它们分别发生在牛庙超单元(210.5 Ma一190 Ma)、姑婆 山超单元(162.2 Ma一145.67 Ma)和银平超单元(129.1 Ma一121.2Ma)侵位期间，上升速率分别为0.69 mm/a、0.40 mH订a不口o.30m而a，比晚三叠世以来本区0.10 mm/a的地壳平均上升速率快约3一7倍。地壳的这种快速隆升—热折返，表明本区中生代存在强烈的壳一慢作用。 6.研究表明，姑婆山一花山花岗岩体形成于印支运动后由碰撞挤压向板内裂解拉张转化的地球动力学背景。其中牛庙和姑婆山两超单元为后碰撞花岗岩，形成于晚三叠世扬子板块与华夏板块最终拼合的主碰撞期后由挤压体制向拉伸体制转变的后碰撞构造环境;而银平超单元则形成于伸展体制为主的板内环境。本区后碰撞期约经历了65m·y.。 7.侵位机制的量化研究表明，在姑婆山一花山花岗岩体现有的空间里，主动膨胀作用为岩体拓展了23%一38%的空间;构造扩展约为岩体定位提供了21%的空间;剩下的41%一56%的空间是由岩浆侵吞作用获取的，故姑婆山一花山花岗岩体为复合侵位机制。从各单元看，牛庙和杨梅山独立侵入体以及桂岭单元为气球膨胀侵位机制;里松和望高单元以气球膨胀侵位机制为主，局部为岩墙扩展机制侵位;新路、白水带和华美单元则主要为岩墙扩展侵位机制。即从早至晚，随侵位深度由深至浅、构造环境由挤压向伸展转换，岩体侵位机制明显的表现出从主动向被动转化的趋势。 8.岩体的生长方式研究表明，牛庙、杨梅山两独立侵入体为侧向式;桂岭、里松、望高和新路单元为中心式或偏心式;白水带、华美单元为中心多点式。虽然多数单元表现为极性生长，但除杨梅山独立侵入体侵位时岩浆通道可能出现的有限偏移外，在近90 m.y.的岩体缓慢生长过程中，姑婆山和花山花岗岩体始终都是通过各自深部相对稳定的主通道上侵。暗示在姑婆山一花山花岗岩体侵位的有限时、空间内，其所在的块体构造变动不大，为一相对稳定块体。更多还原

【Abstract】 Attention has recently been paid to fruitful studies of Nanling granite belt that have provided important petrologic, geochemical, and other evidences for understanding the tectonic nature and evolution history and geodynamic setting of south China. The problem is, however, that these studies have only focused on the east and middle sections of the granite belt, and that few workers have made enough efforts on its west section, not even to say on the emplacement mechanisms and related structures of the plutons within the belt.This study thoroughly and systematically deals with the huge Gupuoshan-Huashan granite batholith located on the west section of Nanling granite belt and in Guangxi Province. The dissertation is based on intensive geologic mapping. Methods of finite strain measurement, modern structural analysis, petro-geochernistry, and magma dynamics have been employed. The structural style, deformational features, and emplacement process of Gupuoshan-Huashan batholith, and their relationships with tectonic environment are discussed, and the structural geometry, kinematics, and dynamics associated with granitic emplacement are analyzed. Conclusions are made as follows:1.Twenty-six individual intrusions have been identified within the Gupuoshan-Huanshan granitic batholith. They are classified into and named as Niumiao independent intrusion, Yangmeishan independent intrusion, and Guiling, Lisong, Wanggao, Xinlu, Baishuidai, and Huamei Units respectively. These granitic intrusions/units are grouped into three super-units: Niumiao Super-unit, Gupuoshan Super-unit, and Yinping Super-unit. Detailed study demonstrates that these three super-units are products of three periodic magmatic thermal events occurred during South China’s Mesozoic tectonic-magmatic cycle, and that they were evolved sequentially from the same magma source.2. Study of magmatic dynamics of the Gupuoshan-Huashan pluton shows that the pluton crystallized within middle-deep crust with relatively high viscosity, slow ascend rate, and lower-than-its-country-rock density. The early sequences have lower viscosities and greater ascend rates, densities, temperature and pressure than late sequences.3. The major intrusive units were already subjected tocompressional force produced by ballooning when the magmas were at plastic and half-plastic states, and even at half-molten state. The ballooning also exerted a strong compression and a shear force to country rocks, suggesting an active emplacement mechanism. The unique "tail" shape and deformation features of the pluton, however, imply that a regional strike-slip wench faulting would also contribute to the opening of the space for the magma emplacement, therefore suggesting a passive emplacement mechanism as well.4. Strain analyses from 155 finite strain measurement stations within the pluton and its aureole also demonstrate that the strain is mainly characterized by a flattening pattern, and that the strain types and strain intensities are heterogeneously distributed from time to time. The early sequences such as Niumiao and Yangmeishan intrusions and Lisong and Wanggao Units show mostly flattening strain patterns, whereas the late sequences such as Xinlu Unit stretching strain patterns. Spatially, the flattening and planar strain patterns exist along the margins of each unit and independent intrusion, whereas the stretching patterns appear in their central area. From early sequences (units) to late sequences (units), the average strain intensity decreases. A strain gradient exists from the aureole to the contact due to an increasing strain intensity measured from the aureole to the contact. The strain heterogeneity and strain patterns imply that periodic pulsating emplacement could account for the deformation of the pluton and its aureole country rocks, suggesting an active emplacement mechanism for the pluton.5. The cooling and exhumation history of the pluton is re-constructed. It is found that the Mesozoic crust of the region has experienced three fast exhumation events更多还原