SHRIMP baddeleyite age for the Fraser Dyke Swarm,southeast Yilgarn Craton,Western Australia     

M. T. D. Wingate  I. H. Campbell  L. B. Harris 《Australian Journal of Earth Sciences》2013,60(2):309-313

Recent high‐resolution aeromagnetic data have delineated an extensive swarm of undeformed northeast‐trending dolerite dykes in the southeastern Yilgarn Craton, known previously only from isolated exposures in surface mining operations. Owing to parallelism of the dykes to the Fraser Mobile Belt, the eastern segment of the Albany‐Fraser Orogen, the swarm is referred to here as the Fraser Dyke Swarm. Ion‐microprobe dating of baddeleyite from a granophyric segregation in the centre of one dyke yields a mean ²⁰⁷Pb/²⁰⁶Pb age of 1212 ± 10 Ma (95% confidence limits). The location of the Fraser Dyke Swarm, adjacent and parallel to the Fraser Mobile Belt, suggests that the dykes may have been emplaced into lines of weakness that originated during tectonic loading and downwards flexure of the craton margin. This is the first evidence of ca 1210 Ma mafic dykes and associated crustal‐scale extension in the southeast Yilgarn Craton, although the age is similar to those reported recently for dolerite and quartz diorite dykes in the central and southern part of the craton, suggesting that a genetic relationship may exist between intrusions in the two areas.  相似文献   

Geochronology and geochemistry of Grenville-aged (1063 ± 16 Ma) metabasalts in the Shennongjia district,Yangtze block: implications for tectonic evolution of the South China Craton     

《International Geology Review》2012,54(1):76-96

To better understand the evolution of the South China Craton (SCC), we have determined the geochronological and geochemical compositions of newly recognized Grenville-aged metabasalts in the Shennongjia region of the northern Yangtze block. LA-ICP-MS U-Pb dating of zircons indicates that the metabasalts formed at 1063 ± 16 Ma. The rocks are calc-alkaline, are characterized by SiO₂ contents (50.50 to 55.62 wt.%), and have moderate-to-high MgO contents (7.25–9.60 wt.%). They display light rare earth element enrichment ((La/Yb)_N = 7.0–9.8) with slightly negative Eu anomalies (Eu/Eu* = 0.82–0.90) and have pronounced depletion in high-field strength elements as well as positive Pb anomalies in the primitive mantle-normalized trace element pattern. They possess high initial Sr isotopic ratios of 0.7092–0.7107, large negative ε_Nd(t) values of ?12.1 to ?11.0, and a relatively narrow range of initial Pb isotope ratios (²⁰⁶Pb/²⁰⁴Pb = 16.503–17.019, ²⁰⁷Pb/²⁰⁴Pb = 15.259–15.452, and ²⁰⁸Pb/²⁰⁴Pb = 36.169–36.994). These isotopic characteristics are typical of basalts derived from an EM2 source region and suggest a subcontinental lithospheric mantle source that was metasomatized by subducted components (fluids and melts). Integrating our new data with documented igneous and metamorphic events during late Mesoproterozoic to early Neoproterozoic time in the region and western segments of the Yangtze block, we suggest that the Shennongjia area might be a microcontinent that was independent of the continental nucleus of the Yangtze block and was accreted to the Yangtze block at the end of Mesoproterozoic time. This study thus argues against the traditional view that the SCC was formed simply by Yangtze–Cathaysia collision and supports a hypothesis in which the Yangtze block was a collage of microcontinents accreted during the Grenvillian period accompanying the assembly of the Rodinia supercontinent.  相似文献   

中元古代微指状叠层石: 超微组构和有机矿化过程     

汤冬杰  史晓颖  蒋干清  张文浩 《地质论评》2012,58(6):1001-1016

微指状叠层石(microdigitate stromatolites,以下简称MDS)是新太古代—中元古代一种重要的沉积构造。由于其内部以纤维状组构为重要特征,而缺乏直接的微生物化石证据,被认为代表特定海洋化学条件下形成的一种海底碳酸盐沉淀,属无机成因。本文对华北中元古代雾迷山组硅化MDS的显微组构研究发现,其柱体由亚毫米级浅色微亮晶纹层(平均厚约65μm)和暗色微晶纹层(平均厚约680μm)交互叠加而成。前者含较少细菌残余,重结晶显著;后者富含细菌残余、微晶多面体及微球粒,并进一步分为具密集连续次级微纹层的(平均厚约380μm)和具稀疏断续微纹层的(平均厚约300μm)两种暗纹层。这三种纹层在纵向上的规律性交互可能反映了季节性变化。毛发状垂向纤维贯穿于整个柱体,但在亮纹层内稀疏。这种纤维可能由垂向生长的丝状菌束(宽<10μm)矿化而成,有些由微球粒(粒径为10～30μm)定向富集构成。微球粒富含细菌残余、胞外聚合物(EPS)以及与之密切共生的纳米颗粒(粒径<45nm)。纳米颗粒可粘结形成亚μm级多面体,构成碳酸盐晶体生长的基点。包围微球粒的微亮晶环边和纤维组构间的微亮晶条带内少细菌残余,可能属微生物影响的矿化成因,而纤维体和微球粒则是微生物诱发矿化的结果。故中元古代MDS属微生物成因,它所展现的有机矿化过程可能也适用于更古老的叠层石。此外,MDS内有机矿物从纳米颗粒到微球粒的有序聚合可能代表了有机矿化的普遍过程,并可用作判定微生物成因碳酸盐岩的重要标识。  相似文献   

Zircon U–Pb–Hf isotopes and bulk-rock geochemistry of gneissic granites in the northern Jiamusi Massif,Central Asian Orogenic Belt: implications for Middle Permian collisional orogeny and Mesoproterozoic crustal evolution     

《International Geology Review》2012,54(9):1109-1125

  相似文献   

震动变形构造所表征的震积岩:以河北宣化中元古界高于庄组第三段为例   总被引：1，自引：0，他引：1       下载免费PDF全文

梅冥相 《地学前缘》2012,19(2):239-247

地震变形构造主要包括小级别的张性或压性断层、不协调的软沉积物变形褶皱等,这些变形构造以震动变形作用为特点从而成为识别和定义地震岩的主要标志。在河北宣化一带的高于庄组第三段下部的白云质灰岩或灰质白云岩层之中,发育了极为典型的地震变形构造,包括层内断层、层内褶皱以及极为典型的碎裂角砾岩等。高于庄组第三段地震变形构造的发现,为探索和研究地震作用对沉积岩层的破坏和改造而区分于其他的事件沉积如海啸沉积和风暴沉积提供了极为重要的实例,也为更加深入理解高于庄组第三段非叠层石碳酸盐岩沉积序列的产出背景提供了重要资料。  相似文献   

扬子克拉通西南缘中元古代通安组的形成时代——锆石LA-ICPMS U-Pb年龄   总被引：5，自引：0，他引：5  

耿元生  柳永清  高林志  彭楠  江小均 《地质学报》2012,86(9):1479-1490

通安组是扬子克拉通西南缘褶皱基底的组成部分,可分为5个岩性段。本文利用凝灰质粉砂岩(样品100620-1)中碎屑锆石和侵入通安组的辉长-闪长岩脉(样品100620-1-1和样品100620-2-2)中岩浆锆石的LA-ICP-MSU-Pb年龄探讨通安组的形成时代。通安组三段中凝灰质粉砂岩的碎屑锆石有两个主要的峰值年龄,分别为1.8～1.9Ga和2.28～2.38Ga,这表明通安组三段的沉积物来自不同的物源区。该凝灰质粉砂岩中最年轻的3粒锆石的207Pb/206Pb平均年龄为1806Ma。从侵入到通安组第三段的辉长-闪长岩的岩浆锆石中获得了1513±13Ma的207Pb/206Pb加权平均年龄(样品100620-2-1)和1531±18Ma的上交点年龄(样品100620-2-2)。这些新获得的年龄数据可以限定通安组的形成时限为1.8～1.5Ga。辉长-闪长岩脉1513Ma和1531Ma的年龄数据与东川群黑山组火山凝灰岩1503±7Ma的年龄结果相似,表明侵入到通安组三段中的辉长-闪长岩脉与东川群黑山组的火山凝灰岩形成于一个岩浆旋回的同一阶段。因此,通安组三段大致相当于云南东川群的黑山组。  相似文献   

华北地台西缘中元古界蓟县系墩子沟群特征及其地质意义   总被引：1，自引：0，他引：1  

许安东  姜修道 《地球科学与环境学报》2003,25(4):27-31

华北地台西缘龙首山中元古界墩子沟群是一套基本没有变质的盖层性质的沉积,根据岩性可划分为三个组下组以砾岩为主,具底砾岩性质;中组是以灰岩为主的浅海碳酸盐沉积;上组是一套细粒的陆源碎屑岩.其下与古元古界龙首山岩群的角度不整合面代表吕梁运动,与华北地台主体相比缺失长城系和青白口系.墩子沟群分布特征是中组分布广,厚度和岩相都比较稳定,下组的陆源粗碎屑岩东部区域较厚,分选磨圆都比较好,岩相厚度稳定,粒度较细,如金昌的河西堡、永昌的韩母山一带.西部区域厚度薄分选磨圆均差,岩相厚度不稳定,有的部位缺失此组沉积或以很薄的底砾岩产出,如张掖东大山、山丹独峰顶一带.说明当时海侵自东向西侵进,反映出华北地台在蓟县纪中期形成海进,明显向西超覆的特点.墩子沟群虽然变质轻微但变形却十分强烈,其原因一方面内部有滑塌形成的同生角砾岩和层间小褶皱、揉皱等准同生构造,说明当时的地形有一定的坡度;另一方面后期又受到祁连运动的影响所致.  相似文献   

贺兰山地区中元古代微生物席成因构造   总被引：23，自引：2，他引：21  

史晓颖  王新强  蒋干清  刘典波  高林志 《地质论评》2008,54(5):577-586

贺兰山中段中元古界黄旗口组石英砂岩中发现丰富的微生物席成因构造(MISS),包括由微生物席生长、破坏和腐烂过程形成的3种类型、9种不同形态的构造;与华北大红峪组发现的同类构造在成因类型与多样性方面具有很强的可对比性.砂岩中发育双向交错层理、冲洗层理、高角度单斜层理系和波痕,泥质粉砂岩夹层中发育波痕与泥裂,表明微生物席主要发育于潮间带上部至潮上带下部环境.MISS构造在华北地台长城系下部砂岩中的广泛存在表明在1.6 Ga前以蓝细菌为主的微生物群在环潮坪碎屑环境也很活跃.可能代表了微生物由海洋向陆地环境发展的过渡阶段.具光合作用功能的制氧蓝细菌的蓬勃发展可能是引发中元古代海洋化学条件发生转变、含氧量增高的重要原因,并为真核生物及宏观藻类的兴起创造了条件.研究表明,黄旗口组与华北大红峪组大致同时,反映了Columbia超大陆裂解期华北地台开始拉伸-张裂、缓慢沉降的构造古地理背景.  相似文献   

Microbial Mats in the Mesoproterozoic Carbonates of the North China Platform and Their Potential for Hydrocarbon Generation   总被引：2，自引：0，他引：2  

史晓颖  张传恒  蒋干清  刘娟  王议  刘典波 《中国地质大学学报(英文版)》2008,19(5):549-566

The well-preserved Mesoproterozoic succession in the North China platform consists mainly of three llthological associations including peritidal quartz sandstone, shallow marine and lagoonai dark to black shales, and shallow epeiric carbonates, with a total thickness of up to 8 000 m. In addition to well-documented microplants, macroalgae, and microbial buildups, abundant microbially induced sedimentary structures (MISS) and mat-related sediments have been recognized in these rocks. Intensive microbial mat layers and MISS are especially well preserved in the carbonates of the upper Gaoyuzhuang (高于庄) (ca. 1.5 Ga) and lower Wumishan (雾迷山) (ca. 1.45 Ga) formations, Indicating diversified microbial activities and a high organic production. In these petrified blomats, putative microbial fossils (both coccoidal and filamentous) and framboidal pyrites have been identified. The abundance of authigenic carbonate minerals in the host rocks, such as, acicular aragnnites, rosette barites, radial siderites, ankerites, and botryoidai carbonate cements, suggests authigenlc carbonate precipitation from anaerobic oxidation of methane (AOM) under anoxic/euxinic conditions. Warm climate and anoxic/euxinic conditions in the Mesoproterozoic oceans may have facilitated high microbial productivity and organic burial in sediments. Although authigenic carbonate cements may record carbonate precipitation from anaerobic methane oxidation, gas blister (or dome) structures may indicate gas release from active methanogenesls during shallow burial Bituminous fragments in mat-related carbonates also provide evidence for hydrocarbon generation. Under proper conditions, the Mesoproterozoic mat-rich carbonates will have the potential for hydrocarbon generation and serve as source rocks. On the basis of petrified biomats, a rough estimation suggests that the Mesoproterozoic carbonates of the North China platform might have a hydrocarbon production potential in theorder of 10×108t.  相似文献   

华北克拉通北缘裂谷渣尔泰群LA-ICP-MS碎屑锆石U-Pb测年及地质意义   总被引：6，自引：3，他引：3  

公王斌  胡健民  李振宏  董晓朋  刘洋  刘绍昌 《岩石学报》2016,32(7):2151-2165

华北克拉通自1.85Ga形成之后,经历了广泛的拉伸,形成了一系列中-新元古代裂谷。其中北缘裂谷由渣尔泰群、白云鄂博群及化德群组成,发育了一系列大型-超大型多金属矿床。该裂谷系形成演化的研究对认识华北克拉通中-新元古代演化及区域找矿具有重要意义。但是对于该裂谷系中渣尔泰群的时代,一直存在争议。早期认为渣尔泰群属于中元古代,主要分布于狼山地区和渣尔泰山地区。但最新的研究已将狼山地区的渣尔泰群限定为新元古代,更名为狼山群,并据此确定华北克拉通北缘存在新元古代裂谷。因此,必须对渣尔泰山地区渣尔泰群的时代进行重新限定。在此基础上可综合分析华北克拉通北缘裂谷的形成与演化。系统的LA-ICP-MS锆石U-Pb测年结果表明,渣尔泰山地区渣尔泰群碎屑锆石年龄峰值主要为1.8~1.9Ga和2.5Ga。与北缘裂谷长城系,包括白云鄂博群下部及化德群下部的碎屑锆石年龄组成特征一致。而蓟县系、待建系及青白口系存在1.1~1.35Ga、1.5~1.6Ga等较年轻的碎屑锆石年龄峰值,如白云鄂博群上部、新元古代狼山群及化德群上部。因此,渣尔泰山地区渣尔泰群整体可与长城系对比。碎屑锆石年龄组成特征表明,渣尔泰群物质主要来自华北克拉通内部的太古宙-古元古代结晶基底。综合前人对白云鄂博群、化德群及狼山群地层年龄及岩浆岩的研究成果,可确定北缘裂谷是中-新元古代多期裂解事件形成的复杂裂谷。  相似文献