陕南安康断裂两侧早古生代镁铁-超镁铁质岩浆杂岩带地质特征及Fe-Ti矿化机制研究

发布时间：2019-06-30 20:40

【摘要】：研究区位于陕西省南部,为南秦岭造山带的重要组成部分。近年来在安康断裂南北两侧分别发现了两条镁铁—超镁铁质岩浆杂岩带,镁铁—超镁铁质岩浆杂岩往往内部Fe-Ti矿化特征明显,赋含大量含Ti-Fe矿物。本论文从岩石学、岩石地球化学、矿物化学和同位素年代学等方面对安康断裂南北两侧镁铁—超镁铁质岩浆杂岩带进行了系统研究,进而探讨Fe-Ti矿化机制,取得的认识和成果如下。1、断裂南北两侧镁铁—超镁铁质岩浆杂岩带岩石组成十分复杂,镁铁—超镁铁质侵入岩类和喷出岩类都有发育。其中两侧的喷出岩岩性组合具明显差异,断裂北侧的岩石受较强的变形变质作用改造,岩性主要为斜长角闪岩、榴闪岩、变质凝灰岩;而断裂南侧基本无变形变质作用,岩性以玄武岩、火山碎屑岩为主。两侧侵入岩岩性组合基本相同,主要为(变)角闪辉石岩、(变)辉石角闪岩、(变)辉长岩、(变)辉绿玢岩和(变)辉绿岩等。2、镁铁—超镁铁质岩浆杂岩的TiO2含量变化较大,可分为成矿镁铁—超镁铁质岩浆杂岩和非成矿镁铁—超镁铁质岩浆杂岩两种类型。岩石地化显示成矿镁铁—超镁铁质岩浆杂岩与非成矿镁铁—超镁铁质岩浆杂岩原岩类型存在明显区别,成矿镁铁—超镁铁质岩浆杂岩显示出高碱、高钛特征,微量元素和稀土元素模式曲线基本类似于典型的OIB模式,轻重稀土分异显著,具明显的Eu正异常,非成矿镁铁—超镁铁质岩浆杂岩的微量元素和稀土元素模式曲线则介于E-MORB型玄武岩与洋岛玄武岩之间,Eu异常不明显。3、镁铁—超镁铁质岩浆杂岩的矿物成分主要为角闪石、长石、石榴子石、辉石等,副矿物有钛铁矿、榍石等。矿物学与矿物化学特征表明,断裂两侧含Ti矿物与主要造岩矿物之间的共生组合及结构特征形式多样且差异明显,断裂北侧Ti-Fe氧化物主要为变质成因,而南侧Ti-Fe氧化物主要为岩浆后期分异作用形成。此外,研究区钛铁矿具富锰贫镁的特征与攀枝花、红格及勉略构造带上已发现的岩浆型钛铁矿床富镁贫锰的特征正好相反,这与前人对该区钛铁矿成因的认识截然不同。4、获得断裂北侧变质镁铁—超镁铁质岩浆杂岩的LA-ICP-MS锆石U-Pb谐和年龄为429.5±9.9Ma~447.0±2.5Ma之间,表明其形成于早古生代,即形成晚奥陶纪—早志留世之间。断裂南侧镁铁—超镁铁质岩浆杂岩形成时代同为早古生代(421.9±2.0Ma~436.0±4.5Ma),测年结果表明断裂两侧镁铁—超镁铁质岩浆杂岩与研究区已发现的含钛磁铁矿岩体及近年来北大巴山镁铁质岩体所测成岩年龄基本上一致,可能为同源、同期岩浆作用的产物。
[Abstract]:The study area is located in the south of Shaanxi Province and is an important part of the South Qinling orogenic belt. In recent years, two mafic-ultra-mafic magmatic complex belts have been found on the north and south sides of Ankang fault. The mafic-ultra-mafic magmatic complex is often characterized by Fe-Ti mineralization and contains a large number of Ti-Fe minerals. In this paper, the mafic-ultra-mafic magmatic complex belt on the north and south sides of Ankang fault is systematically studied from the aspects of petrology, petrogeochemistry, mineral chemistry and isotopic chronology, and then the Fe-Ti mineralization mechanism is discussed. 1. The rock composition of the mafic-ultra-mafic magmatic complex belt on the north and south sides of the fault is very complex, and the mafic-ultra-mafic intrusive rocks and exhaled rocks are developed. The lithologic assemblages of the ejected rocks on both sides are obviously different, and the rocks on the north side of the fault are transformed by strong deformation and metamorphism, and the lithology is mainly plagioclastic hornblende, eclogite and metamorphosed tuff, while there is basically no deformation metamorphism on the south side of the fault, and the lithology is mainly basalt and pyroclastic rock. The lithologic assemblages of the intrusive rocks on both sides are basically the same, mainly including (variable) hornblende, (variable) gabbro, (variable) diabase and (variable) diabase. 2. The TiO2 content of mafic-ultra-mafic magmatic complex varies greatly, which can be divided into two types: ore-forming mafic-ultra-mafic magmatic complex and non-ore-forming mafic-ultra-mafic magmatic complex. The rock geochemistry shows that there is obvious difference between ore-forming mafic-ultra-mafic magmatic complex and non-metallogenic mafic-ultra-mafic magmatic complex. The metallogenic mafic-ultra-mafic magmatic complex shows high alkali and high titanium characteristics, trace elements and rare earth elements model curve is basically similar to the typical OIB model, the differentiation of heavy and heavy rare earth elements is significant, and there is obvious Eu positive anomaly. The trace elements and rare earth element model curves of non-metallogenic mafic-ultra-mafic magmatic complex are between E-MOB basalt and oceanic island basalt, and Eu anomaly is not obvious. 3, the mineral composition of mafic-ultra-mafic magmatic complex is mainly hornblende, feldspar, garnet, pyroxene and so on, and the accessory minerals are ilmenite, sphene and so on. Mineralogical and mineral chemical characteristics show that the symbiotic assemblages and structural characteristics between Ti minerals and main diagenetic minerals on both sides of the fault are diverse and obviously different. The Ti-Fe oxides on the north side of the fault are mainly metamorphosed, while the Ti-Fe oxides on the south side are mainly formed by late magmatic differentiation. In addition, the characteristics of manganese-rich and magnesium-poor ilmenite in the study area are opposite to those of magmatic ilmenite deposits found in Panzhihua, Hongge and Mian structural belts, which is quite different from the previous understanding of the genesis of ilmenite in this area. 4. The LA-ICP-MS zircon U-Pb harmonic age of metamorphosed mafic-ultra-mafic magmatic complex on the north side of the fault is 429.5 卤9.9 Ma~447.0 卤2.5Ma. It shows that it was formed in the early Paleozoic, that is, between the late Ordovician and the early Silurian. The formation age of mafic-ultra-mafic magmatic complex on the south side of the fault is the same as that of early Paleozoic (421.9 卤2.0 Ma~ 436.0 卤4.5 Ma),). The results show that the magmatic complex on both sides of the fault is basically the same diagenetic age as that of the titanium-bearing magmatic complex found in the study area and the mafic rock mass of North Dabashan in recent years, which may be the product of magmatism at the same time.
【学位授予单位】：桂林理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.1;P618.31;P618.47

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