南秦岭武当山群变质酸性火山岩锆石U-Pb年代学   总被引：4，自引：0，他引：4  

张永清  张健  李怀坤  陆松年 《地质学报》2013,87(7):922-930

对武当山群3个变质酸性火山岩样品的锆石U-Pb定年结果表明,武当山群变质酸性火山岩形成年龄为675.2±3.1 Ma,说明武当山群存在新元古代南华纪的地层组成.武当山群变质变形复杂,具多期岩浆活动,可能由不同时代火山岩和少量沉积岩组成,部分变质火山岩具有与耀岭河群火山岩和侵入到武当山群中的基性侵入岩相似的形成年龄,指示了武当山群变质酸性火山岩可能与基性侵入岩群和耀岭河群火山岩存在成因联系.基于现有同位素定年数据,武当山群火山岩数据具有年龄跨度大(太古宙至中生代)的显著特征,但总的趋势是新近取得的年龄数据多数比早期获得的数据要年轻.  相似文献   

四川会东新田金矿矿床地质特征及找矿远景   总被引：1，自引：0，他引：1  

周邦国 《地质与勘探》2013,49(5):872-881

四川会东县新田金矿是本项目组在康滇中东部地区取得的重要找矿成果。在矿产资源调查评价时,已圈定2个铜金矿体,其中K1矿体控制长1200m,平均厚1.88m,矿石平均品位Au 2.53g/t,Cu 0.45%;K2矿体控制长400m,平均厚2.65m,矿石平均品位Au 4.56g/t,Cu 0.74%。初步估算(3341)金属量Au 5218 kg,Cu 1.27万t。本文详细介绍了新田金矿床成矿地质背景、矿床地质特征,通过对控矿因素的研究,认为新田金矿属于构造蚀变岩型金矿床,其成矿时代、矿床成因与紧邻的播卡金矿床类似,受喜山期南北向的韧性剪切带控制。结合区内化探异常成果,提出在新田矿区及外围地区,具有继续寻找同类型矿床的潜力。  相似文献   

康滇地轴北缘新台子金矿区矿床地质特征及找矿方向浅析     

杨钻云 《地质与勘探》2013,49(5):846-854

新台子金矿区在成矿区带上属于海西期构造剪切带金成矿带,该带受丹巴弧形构造、大渡河韧性剪切构造及海西期基性-超基性岩浆活动的共同影响,以分布丰富的矿产资源为特征,是扬子地块西缘重要的贵金属成矿带。文章综合分析了区内矿床地质、控矿构造、矿石矿物、蚀变组合等成矿地质条件,将区内矿床成因类型确定为浅层低温热液石英脉型和构造破碎带蚀变岩型。两种矿床类型均受到地层、构造、岩浆岩的控制,具备形成小-中型规模金矿床的有利条件:①新台子金矿区及其邻区贵金属成矿带的成矿物源主要是前震旦系康定群;②深大断裂是多源成矿物质迁移的主要通道,壳源岩浆活动为成矿物质活化提供了热源;③泥盆系危关群炭质绢云板岩、千枚岩等黑色岩系作为有机化学障,使自下而上的含矿流体内的金元素沉淀、聚集成矿。  相似文献   

柴北缘欧龙布鲁克地块寒武系-奥陶系的重新厘定   总被引：1，自引：0，他引：1  

陈青 《地质与勘探》2013,49(5):825-835

通过对柴达木盆地北缘欧龙布鲁克地区的野外地质调查和精细剖面测量,根据岩石组合、沉积构造、地层接触关系及新发现的生物化石特征,对分布于该地区的早古生代寒武纪-奥陶纪岩石地层进行了详细的划分对比和重新厘定:①欧龙布鲁克群只发育寒武系的第三统和顶部的芙蓉统,缺失底部的纽芬兰统和第二统;②多泉山组为下奥陶统,石灰沟组属于中奥陶统;③原划分的中奥陶统大头羊沟组属于构造改造的断片,不符合建组原则,应弃用;④通过柴达木盆地周缘分布的早古生界地层的区域对比,认为欧龙布鲁克地块之上出露的寒武系-奥陶系(海相碳酸盐岩沉积建造)与滩间山群、祁慢塔格群和纳赤台群(中基性火山岩建造)分别代表了不同构造背景-沉积环境的产物。本研究工作一方面为建立该地区合理和行之有效的岩石地层和年代地层系统提供依据,另一方面为柴达木盆地北缘寒武系-奥陶系地层层序-岩相古地理演化及油气资源潜力评价等研究提供详实的资料,同时也为深化塔里木东南缘陆块群的构造演化提供科学依据。  相似文献   

华北克拉通西南缘汝阳群沉积时代及其地质意义：来自碎屑锆石U-Pb年龄的证据   总被引：4，自引：0，他引：4       下载免费PDF全文

李猛  王超  王钊飞 《地质科学》2013,48(4):1115-1139

汝阳群分布在华北克拉通西南缘,位于河南-陕西-山西交界地区,主要为一套未变质的碎屑岩及碳酸盐岩地层,不整合于熊耳群火山岩系之上,其上被洛峪群整合覆盖。长期以来,其地质时代一直存有较大的争议。本文通过对汝阳群下部白草坪组4个石英砂岩样品中的碎屑锆石进行LA-ICP-MS U-Pb年龄测定,获得的²⁰⁷Pb/²⁰⁶Pb年龄分布范围为3 000～1 800 Ma,主要集中在2 600～2 400 Ma之间(约占67%),年龄主峰值为2 550～2 500 Ma,说明其沉积物质主要来源于新太古代末以及古元古代的地质体。其中,最年轻锆石的²⁰⁷Pb/²⁰⁶Pb谐和年龄值分别为1 817±22 Ma、1 838±23 Ma、1 924±17 Ma和1 829±28 Ma,说明汝阳群沉积时代不老于1 800 Ma,与其上覆洛峪群中近期获得1 611±8 Ma的年龄相吻合,因此其形成时代应为中元古代早期。  相似文献   

Some problems of slope development     

C. R. Twidale 《Australian Journal of Earth Sciences》2013,60(2):131-147

Slopes are the fundamental unit of the physiographic landscape. Yet the reasons for variations in their morphology and inferred mode of development are not well understood. The problem is complex, but the slope budget, which results primarily from the interplay of climatically induced factors and structure is significant: where the erosion of the upper slope elements surpasses that on the lower, parallel retreat prevails, but when the reverse is the case, slope decline is dominant. Complications are introduced by such factors as climatic change and fluctuations of baselevel, both local and general. But structural factors can and do override all others.

A knowledge of geomorphic history, and of processes and their effectiveness under various circumstances, in advance of that usually at our disposal at present is necessary before slopes can satisfactorily be analysed. It appears unlikely that there is a universal law of slope development..  相似文献   

The Somerset Dam Layered basic intrusion,Southeastern Queensland     

C. I. Mathison 《Australian Journal of Earth Sciences》2013,60(1):57-86

The Somerset Dam Layered Basic Intrusion is probably a sub‐volcanic magma chamber, and it consists of 20 saucer‐shaped layers composed of troctolites, olivine gabbros, ferrigabbros, and leucogabbros. The layered sequence is 1650 ft (500 m) thick, and comprises several repetitions of a standard pattern termed a zone. Each zone is generally composed of four layers, and successive mineral assemblages from the base upwards are: plagioclase‐olivine, plagioclase‐augite‐olivine, plagioclase‐augite‐magnetite‐ilmenite, and plagioclase‐uralite. Pronounced modal and textural changes define the boundaries between these layers. Within a zone, systematic variation in the proportions and compositions of minerals is thought to be the result of a slight decrease in temperature, and an increase in the partial pressures of water vapour and oxygen from the base to the top.

Repetition of zones is explained by a mechanism involving periodic renewals of magma. Lack of progressive changes in mineral compositions and proportions from the base to the top of the layered sequence is also a consequence of the magma composition, the control of water vapour pressure, and the limited range of crystallisation temperatures. Gravitational settling of early minerals does not explain the variation within a zone, or the small‐scale rhythmic layering that is locally developed, and it is concluded that diffusion has been an important control.  相似文献   

Inliers of banded iron‐formation in the Proterozoic Wyloo Group sediments near Paraburdoo,Western Australia     

Desmond F. Lascelles 《Australian Journal of Earth Sciences》2013,60(1-2):161-165

Two inliers with a total outcrop length of 3000 m and a maximum width of 200 m, consisting of a sedimentary klippe (olistolith) and an olistostrome (both composed of banded iron‐formation and shale belonging to the Hamersley Group) occur within the Mininer Turbidite Member of the Wyloo Group, south of Paraburdoo, W.A., 2500 m from the top of the Hamersley Group proper. The olistostrome is a typical debris slide produced by slumping of unconsolidated material. The klippe was rafted into position as a solid block by a turbidity current.

The pattern of mineralisation within the banded iron‐formation part of the klippe, which is identified as being from the Brockman Iron Formation, together with evidence from the basal conglomerate of the Wyloo Group, shows that the formation of the Hamersley iron ore deposits commenced prior to the deposition of the Wyloo Group sediments.  相似文献   

Geological significance of middle Cambrian trilobites from near Melba Flats,western Tasmania     

J. B. Jago  C. J. Bentley 《Australian Journal of Earth Sciences》2013,60(4):469-481

In western Tasmania, near Melba Flats, a basalt within the Serpentine Hill Complex is overlain unconformably by Dundas Group sediments (Hodge Slate). About 32 m above the unconformity, a siltstone contains agnostoid and polymerid trilobites that indicate correlation with the middle Cambrian Ptychagnostus punctuosus Zone (Drumian Stage of unnamed Epoch 3 of the Cambrian). This provides an upper limit of about 505.2–504.5 Ma to the emplacement of ultramafic allochthons in western Tasmania. Other fossils present include dendroids, inarticulate brachiopods, hyolithids, helcionellids and sponges. The widespread agnostoid trilobite Ptychagnostus affinis (Brøgger 1878) and the holocephalinid trilobites Meneviella and Holocephalina are recorded for the first time in Tasmania.  相似文献   

Coupled asteroid impacts and banded iron-formations,Fortescue and Hamersley Groups,Pilbara, Western Australia     

A.Y. Glikson  A.H. Hickman 《Australian Journal of Earth Sciences》2013,60(5):689-701

Asteroid impact spherule layers and tsunami deposits underlying banded iron-formations in the Fortescue and Hamersley Groups have been further investigated to test their potential stratigraphic relationships. This work has included new observations related to the ca 2.63 Ga Jeerinah Impact Layer (JIL) and impact spherules associated with the 4th Shale-Macroband of the Dales Gorge Iron Member (DGS4) of the Brockman Iron Formation. A unit of impact spherules (microkrystite) correlated with the ca 2.63 Ga JIL is observed within a >100 m-thick fragmental-intraclast breccia pile in drill cores near Roy Hill. The sequence represents significant thickening of the impact/tsunami unit relative to the JIL type section at Hesta, as well as relative to the 20–30 m-thick ca 2.63 Ga Carawine Dolomite spherule-bearing mega-breccia. The ca 2.48 Ga-old Dales Gorge Member of the Brockman Iron Formation is underlain by an ?0.5 m-thick rip-up clast breccia located at the top of the ca 2.50 Ga Mt McRae Shale, and is interpreted as a tsunami deposit. We suggest that the presence of impact ejecta and tsunami units stratigraphically beneath a number of banded iron-formations, and units of ferruginous shale in the Pilbara and South Africa may result from a genetic relationship. For example, it could be that under Archean atmospheric conditions, mafic volcanism triggered by large asteroid impacts enriched the oceans in soluble FeO. If so, seasonal microbial and/or photolytic oxidation to ferric oxide could have caused precipitation of Fe₂O₃ and silica. In view of the possible occurrence of depositional gaps and paraconformities between impact ejecta units and overlying ferruginous sediments, these relationships require further testing by isotopic age studies.  相似文献