湖南冷家溪群划分及同位素年龄约束

依据区域岩石组合特征,参照岩石地层的划分原则,对冷家溪群进行重新划分:下部为海相深水盆地沉积细碎屑岩系,划分出易家桥组、潘家冲组、雷神庙组;上部为盆地斜坡相浊流(扇)沉积粗碎屑岩系,分为黄浒洞组、小木坪组、大药菇组。在冷家溪群各岩组中的凝灰岩夹层内取得一批新的SHRIMP锆石U-Pb测年数据,对其沉积时代归属提供了新的约束。锆石SHRIMP年龄数据表明其沉积时限介于820～>862 Ma之间,时代属于新元古代早期。     

谈谈冷家溪群坪原组,“杨林冲组”和大药姑组的归属

作者在野外考察与室内综合研究的基础上 ,新建“杨林冲组”取代 1988年创建的坪原组作为冷家溪群最上部的地层单位 ,并将原大药姑组分解为两部分 ,分别划归震旦系下统洪江组和富禄组。     

沧水铺群的演替及其岩石地层学问题──论湖南新元古界底部岩石地层序列

本文通过介绍沧水铺群创建和演绎的过程以及因其被演替后所面临的岩石地层学问题，认为《湖南省岩石地层》（ 1997）中，新元古界底部──冷家溪群与板溪群马底绎组之间──的宝林冲组火山岩→横路冲组砾岩序列是主观虚拟的，沧水铺群林家湾组砾岩→银珠坝组火山岩序列是客观存在不容置疑替代的，并从砾石成分、变质特征、地质剖面、区域分布、专家检验以及钻探地质工程难验证等方面予以论证。     

湘东北岳阳地区冷家溪群和板溪群凝灰岩SHRIMP锆石U-Pb年龄——对武陵运动的制约

对冷家溪群及其上覆板溪群斑脱岩中的锆石进行研究,测得冷家溪群小木平组斑脱岩SHRIMP锆石U-Pb年龄（822Ma±10Ma）和上覆板溪群张家湾组斑脱岩锆石U-Pb年龄（802.6Ma±7.6Ma）,结合＂江南造山带＂东部变质基底双桥山群和西南地区四堡群、下江群的SHRIMP锆石U-Pb年龄,将冷家溪群与其相应的江南古陆变质地层明确定位于新元古界。该年龄对重新界定＂武陵运动＂的时限和进行同期地层的区域对比、构造演化研究都有重要意义。冷家溪群与双桥山群、梵净山群、四堡群、双溪坞群一样,均为低变质绿片岩系,构成了江南古陆地区的变质基底。多年来冷家溪群一直划归中元古界,并且视为＂武陵运动＂的主体,其时代的定位将影响整个江南古陆变质基底的地层划分和对比,也将制约江南造山带的地质背景和成矿条件解疑。上述锆石U-Pb年龄不仅标示了湘东地区新元古代地层的时代,也为江南古陆中部变质基底提供了新的、精确的年代学数据。     

两广云开地区前震旦纪地层

云开地区前震旦纪地层由青白口纪－蓟县纪的云开群和长城纪的高州岩群组成，其中高州岩群新建黄岭岩组、莞塘组和新安组３个岩石地层单位。区域上，高州岩群与桂东南的四堡群、海南的抱板群相当；云开群的沙湾坪组与丹洲群和石碌群相当；而处于裂谷盆地中心的云开地区在蓟县纪沉积了罗罅组、丰垌口组及兰坑组。     

湘东北岳阳地区冷家溪群和板溪群凝灰岩 SHRIMP 锆石U-Pb年龄 ——对武陵运动的制约

对冷家溪群及其上覆板溪群斑脱岩中的锆石进行研究,测得冷家溪群小木平组斑脱岩SHRIMP锆石U-Pb年龄(822Ma±10Ma)和上覆板溪群张家湾组斑脱岩锆石U-Pb年龄(802.6Ma±7.6Ma),结合“江南造山带”东部变质基底双桥山群和西南地区四堡群、下江群的SHRIMP锆石U-Pb年龄,将冷家溪群与其相应的江南古陆变质地层明确定位于新元古界。该年龄对重新界定“武陵运动”的时限和进行同期地层的区域对比、构造演化研究都有重要意义。冷家溪群与双桥山群、梵净山群、四堡群、双溪坞群一样,均为低变质绿片岩系,构成了江南古陆地区的变质基底。多年来冷家溪群一直划归中元古界,并且视为“武陵运动”的主体,其时代的定位将影响整个江南古陆变质基底的地层划分和对比,也将制约江南造山带的地质背景和成矿条件解疑。上述锆石U-Pb年龄不仅标示了湘东地区新元古代地层的时代,也为江南古陆中部变质基底提供了新的、精确的年代学数据。     

两广云开地区前震旦纪地层

云开地区前震旦纪地层由青白口纪－蓟县纪的云开群和长城纪的高州岩群组成，其中高州岩群新建黄岭岩组、莞塘组和新安组３个岩石地层单位。区域上，高州岩群与桂东南的四堡群、海南的抱板群相当；云开群的沙湾坪组与丹洲群和石碌群相当；而处于裂谷盆地中心的云开地区在蓟县纪沉积了罗罅组、丰垌口组及兰坑组     

湘东北中元古代冷家溪群的解体及其地质意义

近年来1：5万和1：25万区域地质调查研究发现，湘东北地区原中元古代冷家溪群实际上包含了时代更老的不同构造环境的物质建造，其应予以解体，分离出基本无序的变质沉积-火山岩系，使之与区域上中元古代冷家溪群原有的基本属性能对比。根据对这些变质沉积-火山岩系的岩石组合、岩石学、同位素年代学等研究，初步厘定出“涧溪冲岩群”、“仓溪岩群”和“连云山杂岩”3个群级构造-岩石地层单位，属绿片岩-角闪岩相，其原岩形成地质时代是新太古-古元古代。     

平江万古金矿床地球化学研究

平江万古金矿床，成矿物质来源于容矿地层中元古界冷家溪群坪原组，矿床继承了容矿地层富Ａｓ、Ｓｂ、Ｗ等微量元素的特点，成矿流体为与区域浅变质作用有关的ＨＣＯ＿３－－Ｃｌ－－Ｎａ￣＋－Ｃａ￣（２＋）型建造水热液，成矿过程中Ａｕ主要以ＡｕＡｓＳ＿２、ＡｕＡｓＳ＿３￣（２－）络合物形式迁移，矿床形成于中一低温，弱碱性、还原环境。     

临湘干港晏家金矿区构造变形特征研究

研究区冷家溪群浅变质岩系沉积后至少经历了加里东期、燕山期和喜山期3期构造运动，劈理、面理、线理、小褶皱等发育，构造置换强烈、构造变形复杂，大多数情况下很难通过产状测量来确定原始层序及其划分。查明矿区以紧闭褶皱为主，处于一叠加倾伏向斜核部，并发现了长约790m的F2韧性剪切带。指出《湖南省岩石地层》（1997.6）将冷家溪群划分为5个组可能有误，各个组也不可能有那么大的地层厚度。     

Geochronology and Tectonic Evolution of the West Section of the Jiangnan Orogenic Belt

As an important part of South China Old Land, the Jiangnan Orogenic Belt plays a significant role in explaining the assembly and the evolution of the Upper Yangtze Block and Cathaysia, as well as the structure and growth mechanism of continental lithosphere in South China.The Lengjiaxi and the Banxi groups are the base strata of the west section of the Jiangnan Orogenic Belt.Thus, the research of geochronology and tectonic evolution of the Lengjiaxi and the Banxi groups is significant.The maximum sedimentary age of the Lengjiaxi Group is ca.862 Ma, and the minimum is ca.822 Ma.The Zhangjiawan Formation, which is situated in the upper part of the Banxi Group is ca.802 Ma.The Lengjiaxi Group and equivalent strata should thus belong to the Neoproterozoic in age.The Jiangnan Orogenic Belt consisting of the Lengjiaxi and the Banxi groups as important constituents is not a Greenville Orogen Belt(1.3 Ga–1.0 Ga).The Jiangnan Orogenic Belt is a recyclic orogenic belt, and the prototype basin is a foreland basin with materials derived from the southwest and the sediments belong to the active continental sedimentation.By combining large amounts of dating data of the Lengjiaxi and the Banxi groups as well as equivalent strata, the evolutionary model of the western section of the Jiangnan Orogenic Belt is established as follows: Before 862 Ma, the South China Ocean was subducted beneath the Upper Yangtze Block, while a continental island arc was formed on the side near the Upper Yangtze Block.The South China Ocean was not closed in this period.From 862 Ma to 822 Ma, the Upper Yangtze Block was collided with Cathaysia; and sediments began to be deposited in the foreland basin between the two blocks.The Lengjiaxi Group and equivalent strata were thus formed and the materials might be derived from the recyclic orogenic belt.From 822 Ma to 802 Ma, Cathaysia continued pushing to the Upper Yangtze Block, experienced the Jinning-Sibao Movement(Wuling Movement); as result, the folded basement of the Jiangnan Orogenic Belt was formed.After 802 Ma, Cathaysia and the Upper Yangtze Block were separated from each other, the Nanhua rift basin was formed and began to receive the sediments of the Banxi Group and equivalent strata.These large amounts of dating data and research results also indicate that before the collision of the Upper Yangtze Block with Cathaysia, materials of the continental crust became less and less from the southwest to the east in the Jiangnan Orogeneic Belt; only island arc and neomagmatic arc were developed in the eastern section.Ocean-continent subduction or continent-continent subduction took place in the western and southern sections, while intra-oceanic subduction occurred in the eastern section.Comprehensive analyses on U-Pb ages and Hf model ages of zircons, the main provenance of the Lengjiaxi Group is Cathaysia.     

湘东北涧溪冲新太古代变质沉积-火山岩岩石矿物学和岩石地球化学研究

通过区域地质调查研究,在湘东北文家市涧溪冲村原中元古代冷家溪群新发现一套基本无序的变质沉积-火山岩系。根据岩石矿物学、岩石地球化学研究表明,涧溪冲变质沉积-火山岩系为变质火山岩夹变质粘土质沉积岩,属绿片岩—高绿片岩相。变质火山岩的原岩为大洋拉张环境下形成的以低钾拉斑玄武岩为主,低钾玄武安山岩次之的火山-次火山岩系,其物源为亏损地幔。变火山岩Sm-Nd全岩等时线年龄为(2594±48)Ma,其形成时代可能是新太古代。因此,与传统的中元古代冷家溪群的岩石组合、形成环境、形成时代、变质变形都具有明显不同的特征,原冷家溪群应予以解体。     

江南古陆中段沧水铺群锆石U-Pb年龄和构造演化意义

江南古陆中段湖南益阳地区沧水铺群发育在冷家溪群和板溪群之间,其在地层柱中的位置一直是中国地质学家解疑江南造山带何时启动的关键层位。笔者在沧水铺群中的火山集块岩中获得锆石SHRIMP U-Pb年龄(821±13)Ma,再次验证了沧水铺群中的火山岩是820 Ma武陵运动之前的火山事件的产物,与武陵运动的启动有关,也说明该期火山岩与冷家溪群中大量的火山凝灰岩为同一构造运动的产物。     

赣中周潭群副变质岩碎屑锆石U-Pb年代学

对赣中周潭群副变质岩中的碎屑锆石开展了LA-ICP-MS U-Pb定年工作,两个石榴黑云母片岩和一个黑云母片岩三个样品中碎屑锆石给出的最年轻的年龄峰值分别为834±11Ma、830±11Ma和809±15Ma.这些碎屑锆石具有与江南造山带内冷家溪群及其相当地层类似的年龄谱型式和相近的最年轻的年龄峰值,表明周潭群应与它们有相似的形成历史和源区,产生于相似的构造环境.因此,周潭群在新元古代扬子地块与华夏地块拼接的过程中,应与冷家溪群、双桥山群等地层一样靠近扬子一侧,而不应属华夏地块.从黑云母片岩部分碎屑锆石的变质边获取的年龄分别为444±11Ma和438±11Ma,表明周潭群地层的变质作用发生在加里东期,与华夏地块其他地区的角闪岩相变质岩的变质年龄一致.相反,与周潭群同期的双桥山群、冷家溪群等地层均未达到角闪岩相变质.这表明,在扬子和华夏地块新元古代的拼接之后,二块体在(现在的)赣中地区又裂开,从而导致了周潭群和相邻的冷家溪群及双桥山群在加里东时期有不同的变质响应.     

湘西金矿地质地球化学特征

通过湘西金矿的矿区地质特征、微量元素地球化学特征等研究,认为赋矿层位为冷家溪群和板溪群马底驿组;导矿和控矿构造为东西向构造;板岩、砂质板岩和变质砂岩的主要成矿元素丰度相对较高;板岩、砂质板岩、变质砂岩曲线具有相似趋势,说明成矿物质来源具有共同特征。     

Distribution Characteristics of Gold and Other Trace Elements in the Proterozoic Lengjiaxi Group,Northeastern Hunan Province

Systematic geochemical studies of the Proterozoic Lengjiaxi Group in northeastern Hunan Province suggest that the Lengjiaxi Group is a Au-As-Sb-W association-type Au-bearing turbidite formation.The contents of Au,As,Sb,W,Cr,Mn,Pb and Zn in the turbidite formation are more than two times as high as the average contents of trace elements in the upper continental crust.The low abundance of Ag and the close correlation between Au and As are two important characteristic features.In the Au-bearing turbidite formation the enrichment of gold is due to the extensive occurrence of Au-bearing pyrites.Higher contents of Au,W,Sb and Ag in the greywacke indicate that they also exist in the form of heavy minerals.Au,Ag,As,Sb,W and REE in the Au-bearing turbidite formation have a close genetic relation with the chemistry of the gold deposits.     

Petrogenesis and tectonic evolution of Lianyunshan complex,South China: Insights on Neoproterozoic and late Mesozoic tectonic evolution of the central Jiangnan Orogen

The Yangtze and Cathaysia blocks in South China are separated by the ca. 1500 km long Jiangnan Orogen. The Lianyunshan complex, located in the central segment of Jiangnan Orogen, includes wide exposures of late Mesozoic granites. Here we report geological, geochronological and geochemical data from the Lianyunshan late Mesozoic granites and their Neoproterozoic host rocks belonging to the Lengjiaxi Group. Detrital zircon U–Pb ages reveal a single prominent peak at ca. 840 Ma in the metamorphosed and deformed Lengjiaxi Group samples. Ten of the youngest zircon grains in these rocks have a weighted mean age of 828.8 ± 7.1 Ma, which is tentatively interpreted as the maximum depositional age of the Lengjiaxi Group. Two stages of late Mesozoic S-type granites are dated at ca. 150 Ma and ca. 140 Ma from the Lianyunshan domain. From early to late, these rocks show decreasing MgO, CaO, Fe₂O₃^T, TiO₂ contents and increasing SiO₂, K₂O, Eu/Eu*, Rb/Sr ratios and differentiation index, suggesting continuous magmatic evolution dominated by fractional crystallization. The εHf(t) values of zircons with late Mesozoic ages are all negative, with their two-stage model ages mainly ranging from 1.9 to 1.4 Ga, which is significantly different from the model age of the host rocks belonging to the Lengjiaxi Group. These results indicate that the late Mesozoic granites were mainly derived from the partial melting of Paleo-Mesoproterozoic basement rocks that are older than Lengjiaxi Group. Major and trace element features suggest that the protoliths of these early stage granites in Lianyunshan are probably mixed greywacke and shale. The arc-like trace elements signature of all the late Mesozoic granites were possibly inherited through crustal contamination during the magma genesis caused by slab rollback associated with Paleo-Pacific subduction during 150- to 140 Ma beneath the central Jiangnan belt.