【作者】 黄贻梅；

【导师】 袁峰；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2010， 硕士

【摘要】 繁昌盆地是长江中下游地区重要的陆相火山断陷盆地之一。本文对繁昌火山岩盆地中分村组粗安岩、赤沙组黑云母粗安斑岩、蝌蚪山组流纹岩、三梁山组黑云母粗面岩进行了锆石LA-ICPMS U-Pb测年,获得其年龄分别为134.4±2.9、131.3±1.8、130.8±2.2、128.1±3.1Ma,显示盆地内火山岩浆活动的时限约在135-128Ma之间,火山岩均为早时白垩世岩浆活动的产物。古老年龄的出现为繁昌盆地可能存在太古宙基底提供了证据。通过火山岩地球化学特征研究表明,繁昌盆地内4组火山岩具有岩浆同源性关系,其岩浆源区为富集地幔。岩浆演化经历了岩浆分异、分离结晶作用和同化混染作用。早期的中分村组、赤沙组火山岩岩浆分异程度相对较低,而晚期的蝌蚪山组、三梁山组火山岩的岩浆分异程度较高。繁昌盆地早期岩浆岩形成于挤压—拉张过渡的构造背景,而晚期岩浆岩则形成于典型的拉张构造背景,构造背景的转换时间约在130.8Ma左右。对比研究表明,长江中下游地区繁昌盆地、庐枞盆地和宁芜盆地的4个旋回火山活动的时限可以完全对应。繁昌盆地与庐枞盆地可能具有相似的地质过程、成岩过程和构造背景。135 Ma可以作为长江中下游地区陆相火山断陷盆地早白垩世火山岩浆活动全面展开的时间。盆地内中生代火山活动期(135-128 Ma)处于中国东部岩石圈减薄的高峰期,繁昌盆地火山岩正是这一地球动力背景下深源岩浆活动的产物。对桃冲铁矿矿石矿物的岩石地球化学研究表明,矽卡岩与围岩区别较大,包裹体研究显示,成矿流体具有高温高盐特征,且同位素数据表明岩浆热液与早期的矽卡岩形成有关,石英硫化物阶段成矿作用与大气降水和岩浆热液混合流体有关。因此,桃冲铁矿为层控矽卡岩矿床。更多还原

【Abstract】 The Fanchang basin is one of the important continental volcanic fault basins in the Middle-Lower reaches of Yangtze River, where the volcanic rocks can be generally subdivided into four Formations, i.e., Zhongfencun Formation, Chisha Formation, Kedoushan Formation and Sanliangshan Formation. The LA-ICPMS U-Pb ages of zircons from trachyandesite of Zhongfencun Formation, biotite trachytic porphyry of Chisha Formation, rhyolite of Kedoushan Formation and biotite trachyte of Sanliangshan Formation are 134.4±2.9Ma,131.3±1.8Ma,130.8±2.2Ma and 128.1±3.1Ma respectively. Hence, the ages of volcanic rocks in the Fanchang basin range from 134-128Ma, corresponding to the Early Cretaceous. Many inherited or captured zircons occur in the volcanic rocks, the oldest one is 2894Ma age which may correspond to the 2.7Ga peak age of global magma activities and continental developments. It is implies the existence of Archean basement under the Fanchang basin. The forming period of volcanic rocks in the Fanchang basin is nearly similar to those in the other continental volcanic basins in Middle-Lower reaches of Yangtze River, and the four volcanic circles of Fanchang basin can entirely correspond with those of Luzong basin and Ningwu basin. The four formations of volcanic rocks of Fanchang Basin had homologous magma, which is from the enrichment mantle. Magma evolution included the magmatic differentiations, fractional crystallizations and assimilation of contaminations. The early Zhongfencun Formation and Chisha Formation was relatively low level of magmatic differentiation, but there were high level during the late Kedoushan Formation and Sanliangshan Formation. Early magmatic rocks formed in compression-extensional tectonic setting, while the late magmatic rocks were formed in the typical extensional tectonic setting at about 130.8Ma. Comparison shows that Fanchang basin and Luzong Basin may have similar geological processes, diagenetic processes and tectonic setting. The 135Ma is considered as the beginning of the early Cretaceous volcanic activities in the continental volcanic fault basins in Middle-Lower reaches of Yangtze River. The period of Mesozoic volcanic activities,135-128 Ma, in the Fanchang basin, correspond to the fastigium of the lithospheric thinning in eastern China, which constrained the volcanic activities in the Fanchang basin.The studies of lithogeochemistry on Taochong iron ore have shown that skarns were different with wall rocks.The inclusions shown the mineral characteristics had high temperature and high salt,and isotope datas show the magmatic hydrothermal formed related with the early skarn, the mixture of magmatic arid hydrothermal water related to the later mineralization forming. Therefore, the Taochong iron ore deposit is stratabound skarn deposit. Quartz sulfide mineralization stage relatively mixed magmatic-meteoric fluids.更多还原