【作者】 史志刚；

【导师】 李廷栋； 丁孝忠；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2014， 博士

【摘要】 位于扬子块体东南部的“江南造山带”是扬子与华夏两个古老块体于元古代时期碰撞而形成的巨型构造带。庐山地区是“江南造山带”构造体系中最复杂的区域之一,对于分析整个“江南造山带”的构造演化至关重要。以同位素年代学研究为框架,采用沉积学、层序地层学、岩石学与地球化学、同位素年代学相结合的研究方法,在收集分析前人研究成果的基础上,通过野外调查及实验测试,系统解决了庐山地区新元古代地层与构造演化问题。本论文的研究取得了许多新认识,其中主要结论和创新性成果如下：利用LA-ICP-MS锆石U-Pb定年方法限定了星子岩群原岩的沉积下限是806Ma,定位于武陵运动(820±Ma)构造转换面之上,属于板溪期沉积地层。本文最新的研究结果改变了前人将星子岩群作为扬子古块体东南缘出露的古老变质结晶基底的观点,也基本否定了将星子岩群作为“庐山变质核杂岩”的古老变质核的前提。同时,此最新成果也证实前人关于观音桥片麻状花岗岩与星子岩群之间的侵入关系需要重新审视。利用SHRIMP锆石U-Pb定年方法精确测定了汉阳峰组的成岩年龄为838+4Ma,将汉阳峰组定位在武陵运动(820±Ma)构造转换面之下的双桥山群下部层位。结合筲箕洼组和汉阳峰组的年代测定结果及地球化学成分和产出构造环境分析,将筲箕洼组与汉阳峰组统一划分为一个多期喷发的新元古代早期滨海-陆相裂谷型玄武岩-安山岩-流纹岩组合,可以与皖南溪口群下部,以及湘东冷家溪群下部相对比。庐山垄筲箕洼组细碧角斑岩化岩石组合从构造环境到形成时代与“江南造山带”中皖南伏川蛇绿岩、鄣源超基性岩、湖南文家市基性岩类似,可以相互对比。首次根据野外观测以及地球化学分析确定庐山地区在～840Ma正处于大陆边缘弧后裂谷火山口附近的位置,属滨海到陆相环境,是火山弧向弧后小洋盆的过渡区。火山喷发以裂隙式间歇喷溢为主,伴有强烈的爆发作用。庐山地区出露双桥山群横涌组和计林组。双桥山群横涌组以上层位原岩形成时限稍晚,最可能在832～823之间。横涌组原生沉积构造特征表明本组沉积环境属较为活动的海盆环境。计林组属海进体系域至早期高水位体系域形成期间沉积的凝缩层。庐山地区保留的南华系地层不全,较明确的只有莲沱组与南沱组。莲沱组基本层序特征构成海进相序,南沱组反映冰川后退-前进交替特征。对庐山地区局限出露的新元古代仰天坪组粉砂质泥岩首次开展了较深入研究。根据有限的同位素定年结果结合野外层位关系将仰天坪组初步划定为横涌组与莲沱组之间的新元古代地层。通过对仰天坪组野外特征分析,结合地球化学成分构造环境投图的结果,推断仰天坪组沉积环境是新元古代板溪期火山弧后的深水海盆。在总结前人“江南造山带”研究成果的基础上,结合本文最新的高精度同位素年代学结果,重建了庐山地区自新元古代早期至南华纪的年代地层格架,提出了“江南造山带”中、东段包括庐山地区在内的新元古代构造演化模式。更多还原

【Abstract】 The "Jiangnan Orogen" is a large-scale tectonic belt, which was formed when the Yangtze Block collided with the Cathaysia Block during Proterozoic. The Lushan area is one of the most complex regions in the "Jiangnan Orogen", and is crucial for understanding the tectonic evolution of whole "Jiangnan Orogen". In the framework of the isotope chronology, the sedimentology, sequence stratigraphy, petrology, geochemistry and isotopic dating were employed to study the Neoproterozoic geological issues of Lushan area and "Jiangnan Orogen" in this thesis. Combined the field investigation and the experimental measurement with the results of other researchers, a few of geological puzzles on the Neoproterozoic strata and tectonic evolution of the Lushan area was systematacially resolved.A lot of original understandings were obtained in this thesis, and the main conclusions and innovative results were listed as follows:The LA-ICP-MS zircon U-Pb dating was employed to constraint the lower depositional time limit of the protolith of the Xingzi complex to be806Ma, and the Xingzi complex is located above Wuling Movement (820±Ma) tectonic transformation plane. Therefore, the Xingzi complex belongs to the "Banxi period" stratum. The latest research result of this thesis rejected the conclusion that the Xingzi complex was the ancient metamorphic crystalline basement of the Yangtze Block proposed by the previous researchers, and denied the theoretical premise that the Xingzi complex was the old metamorphic core of the "Lushan metamorphic core complex" as well. This result verified that the relationship between the Guanyinqiao gneissic granite and the Xingzi complex group need be reexamined.The diagenetic age of the Hanyangfeng Formation was accurately determined to be838±4Ma by SHRIMP zircon U-Pb dating. The latest research result positioned the Hanyangfeng Formation to the lower part of the Shuangqiaoshan group under Wuling Movement (820±Ma) tectonic transformation plane. Combining the dating results and geochemical composition with the formational tectonic setting of the Shaojiwa Formation and the Hanyangfeng Formation, this study classified the Shaojiwa Formation and the Hanyangfeng Formation into a unified rift-type early Neoproterozoic multi-cycles eruptional coastal-continental facies basalt-andesite-rhyolite assemblage. This assemblage may correlate with the lower Xikou Group in Southern Anhui and the Lower Lengjiaxi Group in Eastern Hunan. From the tectonic setting to the diagenetic age, the spilite-keratophyre assemblage of the Shaojiwa Formation is similar with the Fuchuan ophiolite in Southern Anhui, the ultrabasic rocks in Zhangyuan and the Wenjiashi basic rock in Hunan, therefore, they may correlate each other.For the first time, according to the field observation and the geochemical analysis, the Lushan area was confirmed to be a volcanic crater during-840Ma. At that time this volcanic was located in the continental marginal back-arc rift, and belonged to the coastal to continental setting. The zone ought to be a transitional zone between the volcanic arc and a little back-arc ocean basin. The volcanic eruption is mainly an intermittent fissure one accompanied a strong outbreak.The Hengyong Formation and Jilin Formation of the Shuangqiaoshan Group outcrop in Lushan area. The protolith of the strata above the hengyong formation probably deposited during from832to823Ma. The primary sedimentary structural feature of the Hengyong Formation indicates that its sedimentary environment is a relatively fluctuant ocean basin. The Jilin Formation was a stratum which deposited in the transgression system to the early high water system. In Lushan area. The Nanhua System is not complete, and only reserves the Liantuo Formation and the Nantuo Formation. The basic features of the sequence of the Liantuo Formation display the transgression facies, and the Nantuo Formation performs the features of the alternant glacial retreat-progress.For the first time, this thesis intensively researched the Yangtianping Formation, which only locally outcrops in Lushan area. The Yangtianping Formation is the Neoproterozoic silty mudstone. According to a few of the isotope dating results and the field bedding relation, the Yangtianping Formation was preliminarily classified as one between the Hengyong Formation and the Liantuo Formation. Through analyzing the field features of the Yangtianping Formation and the tectonic setting discrimination of the geochemical compositions, the sedimentary environment of the Yangtianping Formation was inferred as the later Qingbaikou period deep back-arc sea basin.Through summarizing the studying results of other researchers on the "Jiangnan Orogen" and the latest high precise isotope chronology data attained by this thesis, the chronostratigraphy framework was reestablished. The Neoproterozoic tectonic evolution pattern of the middle and eastern segment of "Jiangnan Orogen" including Lushan area was built as well.更多还原