川西理塘断裂带奔戈- 村戈段古地震事件及其非均匀性活动特征     

张克旗  吴中海  周春景  田婷婷  李跃华  李家存 《地质学报》2020,94(4):1295-1303

在对青藏高原东南缘地区的理塘左旋走滑活动断裂带野外调查研究中，在其奔戈- 村戈段开挖了两个探槽LT1301和SLT1204。在对两个探槽上所揭示出的古地震事件进行详细划分的基础上，结合所获得的10个OSL年代样品和13个14C年代样品的测试年龄，对理塘断裂带北段的古地震事件发生时代进行了厘定。结果表明2个探槽共揭示出至少4次古地震事件，其中小规模的探槽LT1301仅揭示出1次古地震，可能为发生于公元1729年的历史地震，或是可能发生于距现在950a~1. 0ka之间的一次大地震，由于关键部位年代数据不足，上述两种可能性尚无法明确。较大的探槽SLT1204揭示出包含有探槽LT1301中古地震事件在内的古地震4次，最早的古地震事件I发生于9. 9ka之前，而事件II、III和IV则发生在公元1729年~4. 8kaBP之间，复发间隔为约1. 6ka。川西理塘断裂带北段的古地震研究结果表明，该断裂的大地震复发具有非线性特征，不符合特征地震模式，其中全新世晚期的大地震活动频率明显增大，表明它正处于丛集活动阶段。  相似文献   

High‐Precision,High‐Accuracy Oxygen Isotope Measurements of Zircon Reference Materials with the SHRIMP‐SI     

Janaína N. vila  Trevor R. Ireland  Peter Holden  Peter Lanc  Andrew Latimore  Norm Schram  John Foster  Ian S. Williams  Liane Loiselle  Bin Fu 《Geostandards and Geoanalytical Research》2020,44(1):85-102

Analytical protocols for SHRIMP‐SI oxygen isotope analysis (δ¹⁸O) of a suite of zircon reference materials (RMs) are presented. Data reduction involved a robust estimate of uncertainties associated with the individual spot as well as for groups where the spot data are combined. The repeatability of δ¹⁸O measurements is dependent on both the analytical conditions and the choice of the primary reference material. Under optimised conditions, repeatability was often better than 0.4‰ (2s) allowing sample uncertainties to be obtained to better than 0.2‰ (at 95% confidence limit). Single spot uncertainty combined the within‐spot precision with the scatter associated with repeated measurements of the primary zircon reference material during a measurement session. The uncertainty for individual spots measured under optimised conditions was between 0.3 and 0.4‰ (at 95% confidence). The analytical protocols described were used to assess a variety of zircon RMs that have been used for geochronology and for which laser fluorination oxygen isotope data are available (Temora 2, FC1, R33, QGNG and Ple?ovice), as well as zircons that have been used as RMs for trace element or other types of determination (Mud Tank, Monastery, 91500, AS57, AS3, KIM‐5, OG1, SL13, CZ3 and several other Sri Lankan zircons). Repeated analyses over nine sessions and seven different mounts show agreement within analytical uncertainty for Temora 2, FC1, R33, QGNG, Ple?ovice and 91500, when normalised to Mud Tank. For existing ion microprobe mounts with these materials, an appropriate δ¹⁸O can be determined. However, care should be taken when using zircons from the Duluth Complex (i.e., FC1, AS57 and AS3) as reference materials as our data indicated an excess scatter on δ¹⁸O values associated with low‐U zircon grains.  相似文献   

Geochemical and geochronological characteristics of the Um Rus granite intrusion and associated gold deposit,Eastern Desert,Egypt     

Basem Zoheir  Richard Goldfarb  Astrid Holzheid  Hassan Helmy  Ahmed El Sheikh 《地学前缘(英文版)》2020,11(1):325-345

The Um Rus tonalite-granodiorite intrusion(~6 km2)occurs at the eastern end of the Neoproterozoic,ENE-trending Wadi Muba rak shear belt in the Central Eastern Desert of Egypt.Gold-bearing quartz veins hosted by the Um Rus intrusion were mined intermittently,and initially by the ancient Egyptians and until the early 1900 s.The relationship between the gold mineralization,host intrusion,and regional structures has always been unclear.We present new geochemical and geochronological data that help to define the tectonic environment and age of the Um Rus intrusion.In addition,field studies are integrated with EPMA and LA-ICP-MS data for gold-associated sulfides to better understand the formation and distribution of gold mineralization.The bulk-rock geochemical data of fresh host rocks indicate a calc-alkaline,metaluminous to mildly peraluminous,I-type granite signature.Their trace element composition reflects a tectonic setting intermediate between subduction-related and within-plate environments,presumably transitional between syn-and post-collisional stages.The crystallization age of the Um Rus intrusion was determined by in situ SHRIMP 206 Pb/238 U and 207Pb/235U measurements on accessory monazite grains.The resultant monazite U-Pb weighted mean age(643±9 Ma;MSWD 1.8)roughly overlaps existing geochronological data for similar granitic intrusions that are confined to major shear systems and are locally associated with gold mineralization in the Central Eastrn Desert(e.g.,Fawakhir and Hangaliya).This age is also consistent with magmatism recognized as concomitant to transpressional tectonics(D2:~650 Ma)during the evolution of the Wadi Mubark belt.Formation of the gold-bearing quartz veins in NNE-SSW and N-S striking fault segments was likely linked to the change from transpressional to transtensional tectonics and terrane exhumation(D3:620-580 Ma).The development of N-S throughgoing fault arrays and dike swarms(~595 Ma)led to heterogeneous deformation and recrystallization of the mineralized quartz veins.Ore minerals in the auriferous quartz veins include ubiquitous pyrite and arsenopyrite,with less abundant pyrrhotite,chalcopyrite,sphalerite,and galena.Uncommon pentlandite,gersdorffite,and cobaltite inclusions hosted in quartz veins with meladiorite slivers are interpreted as pre-ore sulfide phases.The gold-sulfide paragenesis encompasses an early pyrite-arsenopyrite±loellingite assemblage,a transitional pyrite-arsenopyrite assemblage,and a late pyrrhotite-chalcopyrite-sphalerite±galena assemblage.Free-milling gold/electrum grains(10 sμm-long)are scattered in extensively deformed vein quartz and in and adjacent to sulfide grains.Marcasite,malachite,and nodular goethite are authigenic alteration phases after pyrrhotite,chalcopyrite,and pyrite and arsenopyrite,respectively.A combined ore petrography,EPMA,and LA-ICP-MS study distinguishes morphological and compositional differences in the early and transitional pyrites(PyⅠ,PyⅡ)and arsenopyrite(ApyⅠ,ApyⅡ).Py I forms uncommon small euhedral inclusions in later PyⅡand Apy II.PyⅡforms large subhedral crystals with porous inner zones and massive outer zones,separated by narrow As-rich irregular mantles.The Fe and As contents in PyⅡare variable,and the LA-ICP-MS analysis shows erratic concentrations of Au(<1 to 177 ppm)and other trace elements(e.g.,Ag,Te,and Sb)in the porous inner zones,most likely related to discrete sub-microscopic sulfide inclusions.The outer massive zones have a rather homogenous composition,with consistently lower abundances of base metals and Au(mean 1.28 ppm).The early arsenopyrite(Apy I)forms fine-grained euhedral crystals enriched in Au(mean 17.7 ppm)and many other trace elements(i.e.,Ni,Co,Se,Ag,Sb,Te,Hg,and Bi).On the other hand,ApyⅡoccurs as coarsegrained subhedral crystals with lower and less variable concentrations of Au(mean 4 ppm).Elevated concentrations of Au(max.327 ppm)and other trace elements are measured in fragmented and aggregated pyrite and arsenopyrite grains,whereas the undeformed intact zones of the same grains are poor in all trace elements.The occurrence of gold/electrum as secondary inclusions in deformed pyrite and arsenopyrite crystals indicates that gold introduction was relatively late in the paragenesis.The LAICP-MS results are consistent with gold redistribution by the N-S though-going faults/dikes overprinted the earlier NNW-SSE quartz veins in the southeastern part of the intrusion,where the underground mining is concentrated.Formation of the Um Rus intrusion and gold-bearing quartz veins can be related to the evolution of the Wadi Mubarak shear belt,where the granitic intrusion formed during or just subsequent to D2 and provided dilatation spaces for gold-quartz vein deposition when deformed by D3 structures.  相似文献   

Chronological and geochemical constraints on the pre-variscan tectonic history of the Erzgebirge,Saxothuringian Zone     

《Gondwana Research》2020

A combined U–Pb zircon geochronological and whole-rock isotopic and geochemical study has been carried out on high-grade orthogneiss, meta-basite, and meta-sediments from the Erzgebirge. The results indicate multiple pulses of Ediacaran–Ordovician magmatism in a transitional volcanic-arc to rift-basin setting. Orthogneiss from high-pressure nappes exhibit a step-like pattern of inherited zircon ages and emplacement ages of 500–475 Ma. In contrast, granite gneiss from the medium-pressure core of the Erzgebirge is characterised by three pulses of magmatism in the Early Cambrian, Late Cambrian, and Early Ordovician. A trend of decreasing Th/U ratios in zircon is observed to c.500 Ma, after which significant increases in the trend and variability of the data is inferred to mark the transition from arc-related to rift-related magmatism. Sediments deposited in the Early Cambrian have continental island arc affinity. Major detrital peaks in the Ediacaran and subordinate Tonian, Palaeoproterozoic, and Neoarchaean data are consistent with an Avalonian-Cadomian Arc and West African Craton derivation. The Early Cambrian sediments were locally reworked by a thermal event in the Ordovician resulting in leucocratic banding and recorded in Ordovician zircon rims characterised by systematically lower Th/U ratios. Ptygmatically folded leucocratic bands containing Ordovician zircon rims, associated with low Th/U ratios, are further observed in the granite gneiss core of the Erzgebirge. Variscan ages are rare, except in a fine-grained high-pressure micaschist, which contains exclusively small, structure-less, zircon with a weighted mean age of 350 ± 2 Ma. These data, along with a re-evaluation of previously published data, have been interpreted as the product of flattening subduction during the Early Cambrian; followed by the opening of slab windows in the Late Cambrian; and finally delamination in the Early Ordovician. Delamination of the orphaned slab led to asthenospheric upwellings triggering extension, bimodal magmatic pulses, recycling of fertile crust, high-temperature metamorphism, and cratonisation of relatively young crust.  相似文献   

基于MS60的BIM放样与施工结果精度分析     

邓明镜  冉东  杨忠轩  黄恒  李昌义 《测绘通报》2019,(3):145-147,162

随着各种异形建筑的不断出现，传统施工放样方法及检测技术已不能完全满足施工要求，因此需要引进新的施工放样及检测技术。本文结合重庆仙桃数据谷金融大楼项目，运用MS60的BIM放样与三维激光扫描技术，探究其在异形建筑施工放样及结果检测中的高效性、可靠性。在施工放样过程中，首先通过在BIM模型上选取放样点，利用MS60全站扫描仪自动搜索与追踪，简化施工放样流程；然后运用BIM模型与点云数据相结合的表面偏差分析对施工结果进行高精度分析，从而为后续施工提供参考。  相似文献   

Source and supply of sediment to a shoreline salient in a fringing reef environment     

Michael V.W. Cuttler  Jeff E. Hansen  Ryan J. Lowe  Julie A. Trotter  Malcolm T. McCulloch 《地球表面变化过程与地形》2019,44(2):552-564

Reef-associated landforms are coupled to the health of the reef ecosystem which produces the sediment that forms and maintains these landforms. However, this connection can make reef-fronted coastlines sensitive to the impacts of climate change, given that any decline in ecosystem health (e.g. decreasing sediment supply) or changes to physical processes (e.g. sea level rise, increasing wave energy) could drive the sediment budgets of these systems into a net erosive state. Therefore, knowledge of both the sediment sources and transport mechanisms is required to predict the sensitivity of reef-associated landforms to future climate change. Here, we examine the benthic habitat composition, sediment characteristics (composition, texture, and age), and transport mechanisms and pathways to understand the interconnections between coastal morphology and the reef system at Tantabiddi, Ningaloo Reef, Western Australia. Benthic surveys and sediment composition analysis revealed that although live coral accounts for less than 5% of the benthic cover, coral is the dominant sediment constituent (34% on average). Sediment ages (²³⁸U/²³⁰Th) were mostly found to be thousands of years old, suggesting that the primary sediment source is relic reef material (e.g. Holocene reef framework). Sediment transport across the lagoon was quantified through measurements of ripple migration rates, which were found to be shoreward migrating and responsible for feeding the large shoreline salient in the lee of the reef. The derived sediment fluxes were comparable with previously measured rates of sediment production by bioerosion. These results suggest that sediment budgets of systems dependent on old (>10³ years) source materials may be more resilient to climate change as present-day reef health and community composition (i.e. sources of ‘new’ carbonate production) have limited influence on sediment supply. Therefore, the vulnerability of reef-associated landforms in these systems will be dictated by future changes to mechanisms of sediment generation (e.g. bioerosion) and/or physical processes. © 2018 John Wiley & Sons, Ltd.  相似文献   

赣南狮吼山硫铁多金属矿区花岗岩地球化学、年代学特征及其成因     

贺根文  路思明  彭琳琳  于长琦  李伟  刘翠辉 《吉林大学学报(地球科学版)》2020,50(5):1491-1504

狮吼山矿区是江西省内规模最大的矽卡岩型硫铁多金属矿床，伴生W、Cu、Au多种成矿元素，成矿作用与矿区出露的茶山迳复式花岗岩体有关。岩体主要包括茶山迳似斑状黑云母二长花岗岩和莲湖细粒二长花岗岩两期，为研究成矿岩体的侵位时代、岩石成因及与成矿的关系，本次工作进行了U-Pb锆石定年、岩相学和岩石地球化学等测试分析。结果表明：岩体具有高硅、高钾、富铝的特征，属高钾钙碱性系列花岗岩；轻重稀土元素分馏明显，均为右倾型，弱Eu负异常，以富集Cs、Rb、Th、U、Pb，亏损Ba、Nb、Sr、和Ti等元素为主要特征，属于低Ba-Sr壳源花岗岩类；锆石具较好晶形，具典型岩浆锆石特征，利用LA-ICP-MS进行U-Pb测年，获得谐和年龄为（162.4±0.6）Ma（MSWD=1.8），加权平均年龄为（162.4±1.4）Ma（MSWD=1.4），谐和年龄与加权平均年龄在误差范围内高度一致，表明茶山迳复式岩体侵位于燕山早期中侏罗世；综合考虑岩体矿物组合、主微量元素及高分异特征，认为其成因分类应属于S型花岗岩；对比中国花岗岩成矿元素平均含量，茶山迳两期花岗岩均具有较高的W、Mo、Bi、Pb等成矿元素含量，可同时为成矿作用提供热源、流体及物质。  相似文献   

华北板块北缘勃隆克A型花岗岩锆石U-Pb定年及其地质意义     

李春麟  王宗秀  陶涛 《地质通报》2020,(1):40-50

内蒙古翁牛特旗勃隆克岩体位于华北板块北缘,侵位于上侏罗系火山岩地层中。详细的岩相学研究显示,勃隆克花岗岩具有粒状结构、蠕虫结构和文像结构,块状构造,部分斜长石已绢云母化、泥化。对勃隆克花岗岩进行了LA-ICP-MS锆石U-Pb定年,获得134.0±1.8Ma和134.9±4.1Ma的侵位年龄,表明其形成于早白垩世。地球化学特征显示,花岗岩属于高钾钙碱性系列,有较高的SO2(74.1%~75.6%)、Na2O+K2O(8.98%~9.2%)、Rb(210×10-6~225×10-6)含量和10000×Ga/Al(2.69~2.80)、Rb/Sr(5.8~18.9)值,具有较低的CaO、MgO、Ba和Sr含量。铝饱和指数A/CNK=0.99~1.03,属于偏铝质或过铝质A型花岗岩。稀土元素球粒陨石标准化图解显示,轻稀土元素相对富集,负Eu异常明显;在原始地幔标准化图解上,Ba、Sr、Nb、Ta、P、T强烈亏损,富集Rb、Th、K、Hf等元素,与华北板块北缘早白垩世A型花岗岩类似。结合区域构造演化,认为勃隆克花岗岩形成于伸展构造背景。晚中生代,华北板块北缘构造体制经历了重大的转变,地壳从挤压体制转为岩石圈减薄和地壳伸展体制,软流圈物质上涌导致上覆地壳长英质物质的部分熔融形成勃隆克A型花岗岩。  相似文献   

Metamorphism and geochronology of garnet amphibolite from the Beishan Orogen,southern Central Asian Orogenic Belt:Constraints from P-T path and zircon U-Pb dating     

《地学前缘(英文版)》2020,11(4):1189-1201

Numerous lenses of garnet amphibolite occur in the garnet-bearing biotite-plagioclase gneiss belt in the Baishan area of the Beishan Orogen,which connects the Tianshan Orogen to the west and the Mongolia-Xing'anling Orogen to the east.The study of metamorphism in Beishan area is of great significance to explain the tectonic evolution of Beishan orogen.According to the microstructures,mineral relationships,and geothermobarometry,we identified four stages of mineral assemblages from the garnet amphibolite sample:(1) a pre-peak stage,which is recorded by the cores of garnet together with core-inclusions of plagioclase(Pl_1);(2) a peak stage,which is recorded by the mantles of garnet together with mantle-inclusions of plagioclase(Pl_2)+amphibole(Amp_1)+Ilmenite(Ilm_1)+biotite(Bt_1),developed at temperature-pressure(P-T) conditions of 818.9-836.5℃ and7.3-9.2 kbar;(3) a retrograde stage,which is recorded by garnet rims + plagioclase(Pl_3)+amphibole(Amp_2)+orthopyroxene(Opx_1)+biotite(Bt_2)+Ilmenite(Ilm_2),developed at P-T conditions of 796.1-836.9℃ and5.6-7.5 kbar;(4) a symplectitic stage,which is recorded by plagioclase(Pl_4)+orthopyroxene(Opx_2)+amphibole(Amp_3)+biotite(Bt_3) symplectites,developed at P-T conditions of 732 ±59.6℃ and 6.1 ±0.6 kbar.Moreover,the U-Pb dating of the Beishan garnet amphibolite indicates an age of 301.9 ±4.7 Ma for the protolith and 281.4±8.5 Ma for the peak metamorphic age.Therefore,the mineral assemblage,P-T conditions,and zircon U-Pb ages of the Beishan garnet amphibolite define a near-isothermal decompression of a clockwise P-T-t(Pressure-Temperature-time) path,indicating the presence of over thickened continental crust in the Huaniushan arc until the Early Permian,then the southern Beishan area underwent a process of thinning of the continental crust.  相似文献   

Geochemistry,detrital zircon geochronology and Hf isotope of the clastic rocks in southern Tibet: Implications for the Jurassic-Cretaceous tectonic evolution of the Lhasa terrane     

《Gondwana Research》2020

In order to reconstruct tectonic evolution history of the southern margin of Asia (i.e., Lhasa terrane) before the India-Asia collision, here we present a comprehensive study on the clastic rocks in the southern Lhasa terrane with new perspectives from sedimentary geochemistry, detrital zircon geochronology and Hf isotope. Clasts from the Jurassic-Early Cretaceous sedimentary sequences (i.e., Yeba and Chumulong Formations) display high compositional maturity and experienced moderate to high degree of chemical weathering, whereas those from the late Early-Late Cretaceous sequences (Ngamring and Shexing Formations) are characterized by low compositional maturity with insignificant chemical weathering. Our results lead to a coherent scenario for the evolution history of the Lhasa terrane. During the Early-Middle Jurassic (∼192-168Ma), the Lhasa terrane was speculated to be an isolated geological block. The Yeba Formation is best understood as being deposited in a back-arc basin induced by northward subduction of the Neo-Tethys ocean with sediments coming from the interiors of the Lhasa terrane. The Middle Jurassic-Early Cretaceous Lhasa-Qiangtang collision resulted in the formation of a composite foreland basin with southward-flowing rivers carrying clastic materials from the uplifted northern Lhasa and/or Qiangtang terranes. During the late Early-Late Cretaceous (∼104-72Ma), the Gangdese magmatic arc was uplifted rapidly above the sea level, forming turbidites (Ngamring Formation) in the Xigaze forearc basin and fluvial red beds (Shexing Formation) on the retro-arc side. At the end of Late Cretaceous, the Lhasa terrane was likely to have been uplifted to high elevation forming an Andean-type margin resembling the modern South America before the India-Asia collision.  相似文献