The Tashisayi nephrite deposit from South Altyn Tagh,Xinjiang,northwest China   总被引：1，自引：0，他引：1  

Kong Gao  Guanghai Shi  Meili Wang  Gen Xie  Jian Wang  Xiaochong Zhang  Ting Fang  Weiyan Lei  Yan Liu 《地学前缘(英文版)》2019,10(4):1597-1612

The Tashisayi nephrite deposit is located in South Altyn Tagh.in Qiemo County,Xinjiang Province,northwest China.It is a recent discovery in the vast,well-known Kunlun-Altyn nephrite belt distributed along the south of the Tarim Basin,producing more than half of the nephrite from the whole belt in 2017.Field investigations revealed that it is a dolomitic marble-related(D-type)nephrite deposit,but little is known about its age of formation and relationships between the granites and marble.Here we report field investigations,petrography of the neph rite,as well as petrography,geochemistry,geochronology of the zoisite-quartz altered intrusive rock and adjacent granites.An A-type granite is identified with a SHRIMP U-Pb zircon age of 926± 7 Ma,suggesting it was emplaced in an extensional tectonic environment at that time.The altered intrusive rock has a cluster of U-Pb zircon age of 433± 10 Ma.with similar trace element features to the A-type granite,suggesting it was formed in an extensional regime at this later time.Nephrite formed because of the metasomatism of dolomite marble by hydrothermal fluids.It is inferred that Ca~(2+) was released from the dolomitic marble by metasomatism forming Ca-rich fluids,which caused alteration of both the intrusive rocks(6.00-8.22 wt.% CaO)and granite(1.76-3.68 wt.% CaO)near the nephrite ore bodies.It is also inferred that Fe2+ from the granite migrated towards the dolomite marble.The fluids gave rise to the formation of Ca-minerals.such as zoisite,in the nephrite and altered intrusive rock,and epidote in the granite.Based on the contact relationships.similarity in hydrothermal processes,and consumption of Ca~(2+),the Tashisayi nephrite is considered to have formed at the same time as the alteration of the intrusive rocks,i.e.～433 Ma.The geochronological similarity(～926 Ma.433 Ma)of South Altyn and North Qaidam may suggest that tectonically they belong to one single complex in the past,which was offset by the Altyn Tagh fault(ATF).The similar formation ages of the nephrites from Altyn Tagh(433 Ma)and the previously studied areas of West Kunlun(378-441 Ma)and East Kunlun(416 Ma)indicate that these nephrites formed during the closure of Proto-Tethys and in the accompanving post-collisional.extensional environment.  相似文献   

A locally calibrated,late glacial 10Be production rate from a low-latitude,high-altitude site in the Peruvian Andes     

《Quaternary Geochronology》2015

Well-dated records of tropical glacier fluctuations are essential for developing hypotheses and testing proposed mechanisms for past climate changes. Since organic material for radiocarbon dating is typically scarce in low-latitude, high-altitude environments, surface exposure-age dating, based on the measurement of in situ produced cosmogenic nuclides, provides much of the chronologic information on tropical glacier moraines. Here, we present a locally calibrated ¹⁰Be production rate for a low-latitude, high-altitude site near Quelccaya Ice Cap (∼13.95°S, 70.89°W, 4857 m asl) in the southeastern Peruvian Andes. Using an independent age (12.35 +0.2, −0.02 ka) of the late glacial Huancané IIa moraines based on thirty-four bracketing radiocarbon ages and twelve ¹⁰Be concentrations of boulders on the moraines, we determine a local production rate of 43.28 ± 2.69 atoms gram⁻¹ year⁻¹ (at g⁻¹ yr⁻¹). Reference ¹⁰Be production rates (i.e., production rates by neutron spallation appropriate for sea-level, high-latitude sites) range from 3.97 ± 0.09 to 3.78 ± 0.09 at g⁻¹ yr⁻¹, determined using scaling after Lal (1991) and Stone (2000) and depending on our assumed boulder surface erosion rate. Since our boulder surface erosion rate estimate is a minimum value, these reference production rates are also minimum values. A secondary control site on the Huancané IIIb moraines suggests that the ¹⁰Be production rates are at least as low as, or possibly lower than, those derived from the Huancané IIa moraines. These sea-level, high-latitude production rates are at least 11–15% lower than values derived using the traditional global calibration dataset, and they are also lower than those derived from the late glacial Breque moraine in the Cordillera Blanca of Peru. However, our sea-level, high-latitude production rates agree well with recently published, locally calibrated production rates from the Arctic, New Zealand, and Patagonia. The production rates presented here should be used to calculate ¹⁰Be exposure ages in low-latitude, high-altitude locations, particularly in the tropical Andes, and should improve the ability to compare the results of studies using ¹⁰Be exposure-age dating with other chronological data.  相似文献   

Spring time sources and sinks of Peroxyacetyl Nitrate in the UK and its contribution to acidification and nitrification of cloud water     

G. G. McFadyen  J. N. Cape 《Atmospheric Research》1999,50(3-4)

During spring the atmospheric concentration of Peroxyacetyl Nitrate, PAN, in the UK varies over three orders of magnitude due to long range transport and local photochemical production. An experiment at Great Dun Fell was used to determine which of these sources of PAN controlled spring time concentrations and to quantify the contribution of PAN to oxidised nitrogen in cloud water. The gas phase mixing ratio of a wide range of trace gas pollutants, including PAN, along with cloud water chemical composition and aerosol/cloud droplet distributions were measured. A chemical model was developed to determine the contribution of PAN hydrolysis to cloud water nitrification and to quantify the sink strengths of PAN. Chemical reaction following thermal decomposition was found to be the dominant sink mechanism in the model but transport was the most important factor controlling PAN concentration. During cloud episodes PAN concentrations varied from 100 ppt to over 1 ppb but the calculated inorganic oxidised nitrogen loading in the cloud due to PAN dissolution and hydrolysis was an insignificant fraction of the observed total oxidised nitrogen loading of the cloud. Extrapolation of the model to persistent cloud in marine conditions showed that PAN has a negligible effect on cloud nitrification. It was concluded that PAN concentrations were heavily influenced by regional concentrations and that the hydrolysis of PAN in cloud water was an insignificant source of oxidised nitrogen in cloud water.  相似文献   

白云石镁水泥材料的初步研究   总被引：4，自引：4，他引：0       下载免费PDF全文

王明英  肖学英  王继东  张全有  常成功  王海平 《盐湖研究》2012,20(1):44-48

以活性较高的苛性白云石粉和氯化镁溶液制备白云石镁水泥材料。研究氧化镁、氯化镁和水不同配比条件下对白云石镁水泥材料的抗压强度、相组成以及形貌的影响。在所研究的配比条件下,以氧化镁、氯化镁和水摩尔比为3.38∶1.00∶16.86和3.24∶1.00∶16.26配比的镁水泥样块强度较高,结构致密,水化物胶凝相稳定;氯化镁加入量较低,水的加入量较高会使镁水泥试块强度不高;氯化镁加入量较高,水的加入量较低会使镁水泥试块吸潮返卤现象严重,导致强度逐渐下降。  相似文献   

Dolomite Mountains and the origin of the dolomite rock of which they mainly consist: historical developments and new perspectives   总被引：3，自引：0，他引：3  

JUDITH A. MCKENZIE  CRISOGONO VASCONCELOS 《Sedimentology》2009,56(1):205-219

Beginning in the late 18th Century, the Dolomite Mountains in Northern Italy have been the location for major sedimentological developments, from the discovery of the mineral dolomite to the formulation of the coral-reef hypothesis to explain the origin of the massive dolomite structures that define the splendid scenery of the region. Further, the Dolomite Mountains have inspired voluminous research into the origin of dolomite, questioning whether dolomite is a primary precipitate or a secondary replacement product. Recently, with the recognition that microbes can mediate dolomite precipitation, a new geomicrobiological approach, combining the study of modern natural environments with bacterial culture experiments, is now being used to calibrate or interpret microbial evidence derived from the dolomite rock record. This three-pronged methodology applied to the study of dolomite formation holds great promise for future research into the 'Dolomite Problem' and provides a new impetus to revisit the Dolomite Mountains in the 21st Century.  相似文献   

“白云岩问题”与“前寒武纪之谜”研究进展   总被引：8，自引：0，他引：8  

王勇 《地球科学进展》2006,21(8):857-862

白云岩的成因是沉积学界倍受关注的研究主题;众多的白云岩化模式可以用来解释各种成岩白云岩的成因;然而原生白云岩的成因一直是困扰沉积学界的难题,被称为“白云岩问题”。究其原因主要在于：在近地表环境的常温、常压实验条件下不能生成完美有序的白云石矿物。近年来,野外观测和实验模拟研究发现某些微生物的生命活动可导致白云石于地表常温、常压条件下发生沉淀。如硫酸盐还原细菌和产烷菌的调节作用可以克服白云石晶核形成的动力学障碍,在这些厌氧菌的参与下,白云石晶核形成和沉淀并不需要高镁离子和过饱和状态的溶液环境。这种微生物学和沉积学的结合代表了一个新的研究方向,同时也为解决“白云岩问题”带来了新希望。泥晶白云岩化作用（mimetic dolomization）可以保留原矿物（文石或方解石）的晶形、原岩的微细组构,对解释地史时期保存原生构造的白云岩具重要的启示。“前寒武纪之谜”是指前寒武纪叠层石中缺乏钙化蓝细菌化石的现象。参与碳酸盐岩叠层石建造的微生物群组成可能随着地质历史的演化发生变化,蓝细菌在显生宙的叠层石建造过程中起主导作用,细胞体积更小的真细菌很可能是参与前寒武纪叠层石建造的主要微生物。  相似文献   

2005.0年代中国地区地磁场及其长期变化球冠谐和分析   总被引：4，自引：0，他引：4       下载免费PDF全文

陈斌  顾左文  高金田  袁洁浩  狄传芝 《地球物理学报》2011,54(3):771-779

国家地磁图作为描述一个国家领域内地磁场空间分布的基础科技产品,其选用的模型计算方法应准确合理地反映标准年代上地磁场空间分布及未来5年的地磁场长期变化趋势.本文应用球冠谐和(SCH)方法,对中国地区1119个野外地磁测点和36个地磁台的观测数据进行了计算,获得了2005.0标准地磁年代中国地区地磁正常场及其异常场空间分布...  相似文献   

Microbialites of the Neoproterozoic Beck Spring Dolomite,Southern California     

CARA L. HARWOOD  DAWN Y. SUMNER 《Sedimentology》2011,58(6):1648-1673

Ancient microbialites reflect interactions between microbial communities and environmental conditions. However, evaluating the relative roles of microbial community processes and environmental influences on microbialite morphology and internal fabric in the rock record can be challenging. The Neoproterozoic Beck Spring Dolomite preserves diverse microbialites, and thus provides an opportunity to explore the factors that influenced microbialite development locally. Stromatolitic, thrombolitic and composite microbialites are abundant in subtidal to upper intertidal carbonates in the Beck Spring Dolomite. Thrombolitic and composite microbialites have not been recognized previously in this unit, but compose much of the newly defined thrombolitic member. Stratigraphic relationships demonstrate that these three types of microbialites formed in close spatial and temporal association in subtidal to intertidal environments. The relative proportions and distributions of stromatolitic and thrombolitic microbialites vary with depositional environment; stromatolitic microbialites dominate in deeper intertidal to subtidal facies, whereas thrombolitic textures are more abundant in upper intertidal facies. Composite microbialites, composed of intermingled clotted and laminated textures, formed in all environments but are most abundant in intertidal facies. The broad environmental distribution of stromatolitic, thrombolitic and composite microbialites and the intermingling of textures suggest that laminated and clotted textures reflect diverse microbial community morphologies rather than environmental variations. Furthermore, the ca 750 Ma age of thrombolitic microbialites in the Beck Spring Dolomite requires that they formed without the influence of calcimicrobes or metazoans colonizing and grazing the microbial mat surface. Thus, these thrombolites provide further evidence that the biostratigraphic distribution of thrombolites cannot be uniquely attributed to evolution of calcifying and grazing organisms in the earliest Cambrian, and that older microbial communities were capable of producing clotted textures.  相似文献   

巴西坎普斯盆地油气地质特征     

朱毅秀  高兴  杨程宇  宋玲 《海相油气地质》2011,16(3):22-29

坎普斯盆地为典型的被动大陆边缘拉伸裂谷盆地,由前裂谷期(非海相)、同裂谷期(过渡相)及后裂谷期(海相)三个构造层组成.含盐层序为区域盖层,盐下层序泥页岩和盐上层序坎普斯组泥页岩为局部盖层;主要烃源岩为下白垩统拉高亚费耶组湖相黑色钙质页岩;古近系和新近系浊积砂岩为主力储集体,上白垩统浊积岩也是重要储层,下白垩统尼欧克姆阶...  相似文献   

Extensive carbonate cementation of fluvial sandstones: An integrated outcrop and petrographic analysis from the Upper Cretaceous, Book Cliffs, Utah   总被引：1，自引：0，他引：1  

Kevin G. Taylor  Philip G. Machent 《Marine and Petroleum Geology》2011,28(8):1461-1474

Extensive, large-scale pervasive cementation in the form of cement bodies within fluvial strata has rarely been documented although fluvial strata commonly act as important hydrocarbon reservoirs, as well as groundwater aquifers. Here, we present outcrop, petrographic and geochemical data for pervasive ferroan dolomite cement bodies up to 250 m in size from Upper Cretaceous Desert Member and Castlegate Sandstone fluvial strata exposed in the Book Cliffs in Utah. These cement bodies are present with coastal plain fluvial strata within both the Desert and Castlegate lowstand sandstones and are most abundant in the thin, distal fluvial strata. Cement bodies are almost entirely absent in updip, thicker, fluvial strata. Petrographic observations suggest a predominantly early diagenetic timing to the mildly ferroan dolomite, with a component of later burial origin. δ¹³C values for the cement (+4.8 to −5.7‰ V-PDB) suggest a marine-derived source for the earliest phase with a burial organic matter source for later cement. δ¹⁸O data (−6.3 to −11.8‰ V-PDB) suggest precipitation from freshwater dominated fluids. It is proposed here that dolomite was derived from leaching of detrital dolomite under lowstand coals and cementation took place in coastal aquifers experiencing mixed meteoric-marine fluids as a result of base-level fluctuations. This data presented here shows that large cement bodies can be an important component within fluvial sandstones with a potentially significant impact upon both reservoir quality and fluid flow within reservoirs, especially at the marine-non-marine interface.  相似文献