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1.
New data on the age, composition, sources, and formation conditions of the Early Precambrian granitoids of the Batomga inlier of the southeastern Siberian Platform basement are discussed. Geochronological SRHIMP II U–Pb study of the zircons reveals that the calc-alkaline granitoids of the Khoyunda Complex are 2056–2057 Ma in age and their formation was related to the Early Proterozoic stage in the development of the Batomga granite–greenstone domain. It is established that the primary melts for these rocks formed in subduction settings through melting of the depleted mantle source with some contribution of ancient crustal material. In terms of temperature, partial melting followed by crystallization of the granitoids under peak metamorphic conditions corresponds to the transition between amphibolite and granulite facies at elevated pressure; high temperature and high-grade metamorphism are subduction-related phenomena reflected in the back-arc settings of the active continental margin. The protoliths of calc-alkaline metavolcanics of the Batomga Group are found to be chronologically and compositionally analogous to the subduction granitoids of the Khoyunda and Dzhagdakan complexes; i.e., these granitoids are coeval with the Batomga island arc. The lower age limit of the Batomga Group is estimated at 2.2 Ga and its upper age limit is defined by the age of the intruded Khoyunda granitoids. The formation of the rocks of the Batomga Group and associated granitoids of the Khoyunda and Dzhagdakan complexes reflects the formation of the continental crust at the Early Paleoproterozoic stage of the evolution of the Batomga lithosphere block (2.2–2.0 Ga ago).  相似文献   

2.
The Neoproterozoic Wadi Kid metamorphic belt in southeastern Sinai in Egypt represents a structurally and metamorphically complex assemblage of metasedimentary and metavolcanic rocks folded into a series of ENE–WSW-trending antiforms and synforms. Geological mapping in this region is challenging, primarily due to difficult access, complexity of structures, and lack of resolution and areal integrity of lithological differentiation using conventional mapping techniques. Spectral ratioing of selected bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data of the area, in synergy with geological field observation, proved effective in resolving geological mapping problems in the region. A new ASTER band-ratio image 4/7-4/6-4/10 is applied successfully for lithological mapping in the Wadi Kid area, showing improvement over previous techniques in detailing the main rock units. These are gneiss and migmatite, amphibolite, volcanogenic sediments with banded iron formation, meta-pelites, talc schist, meta-psammites, meta-acidic volcanics, meta-pyroclastics volcaniclastics, albitites and granitic rocks. Validating the use of the new ASTER band-ratio image relied on both calculating statistical optimum index factor (OIF) and matching interpreted lithological boundaries to field data and previously published geologic maps. The adopted ASTER band-ratio image demonstrates the benefit of using ASTER remote sensing data in lithological mapping of the Wadi Kid area and therefore for lithological mapping in the Arabian–Nubian shield and other arid areas.  相似文献   

3.
阿尔泰造山带变质岩系时代问题的讨论   总被引：26，自引：1，他引：26  
针对目前阿尔泰地区变质岩系时代划分中年龄数据应用的一些问题,提出如下认识:富蕴县城西的石榴石片麻岩中锆石UPb上交点年龄2349±226Ma(2σ),初步确证了该区古元古代大陆地壳岩石的存在;克木齐群和富蕴群变质岩全岩SmNd等时线年龄代表其母岩形成时代。变质岩系和显生宙花岗岩类的Nd模式年龄,以及各种类型岩石中长石Pb二阶段模式t1年龄仅指出存在前寒武纪大陆地壳的可能性,没有真正的年龄意义,不能作为划分地层时代的依据。阿尔泰造山带是否存在1400Ma和700～900Ma的变质岩系岩石,至今仍缺乏可靠年龄数据的佐证  相似文献   

4.
We studied geology and main rock assemblages of the Precambrian Kan, Arzybei, and Derba terranes of the Central Asian Fold Belt which border the Siberian craton in the southwest. The Precambrian terranes include three isotopic provinces (Paleoproterozoic, Mesoproterozoic, and Neoproterozoic) distinguished from the Sm-Nd isotope compositions of granitoids, felsic metavolcanics, and metasediments. The terranes formed in three stages of crustal evolution: 2.3–2.5, 0.9–1.1, and 0.8–0.9 Ga. Proterozoic juvenile crust was produced by subduction-related magmatism; it was originally of transitional composition and transformed into continental crust by potassic plutonism as late as the Late Vendian-Cambrian. Terrigenous sediments in the Arzybei and Derba terranes vary in T(DM) Nd model ages from 1.0 to 2.0 Ga. The Nd ages of the underlying metavolcanics and lowest T(DM) of metasediments indicate that terrigenous sedimentation started in the Neoproterozoic. It was maintained by erosion of Mesoproterozoic-Neoproterozoic crust and, to a lesser extent, of Early Precambrian rocks on the craton margin or in Paleoproterozoic terranes. Ar-Ar dating of amphiboles and biotites from metamorphic rocks and U-Pb dating of zircons from granitoids yielded 600–555 and 500–440 Ma, respectively, corresponding to the Vendian and Early Paleozoic stages of nearly synchronous metamorphism and plutonism. Accretion and collision events caused amalgamation of the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic terranes in the Vendian and their collision with the Siberian craton. The lateral growth of the paleocontinent completed in the Late Ordovician.  相似文献   

5.
澜沧江构造带南段变质岩系锆石U-Pb年代学及构造涵义   总被引：4，自引：3，他引：1  
澜沧江构造带南段的古老变质岩系因临沧花岗岩基的大面积出露而呈零星分散状出露,该地区是否存在前寒武纪结晶基底和变质岩系的精确时代以及澜沧江构造带变质岩系的变质时限等问题还不是很清楚。本文以变质岩系为研究对象,挑选出锆石颗粒进行U-Pb SHRIMP定年,获得锆石核部U-Pb年龄是1802Ma、1404Ma、1092Ma、906~961Ma、812Ma和727~623Ma,时代为古元古代、中元古代和新元古代,揭示研究区存在前寒武纪的结晶基底,三叠纪(~230Ma)发育区域性岩浆作用事件,破坏改造了其结晶基底;昌宁-耈街剖面近澜沧江岸边花岗质片麻岩的锆石U-Pb谐和年龄为73.9±1.8Ma(MSWD=1.3,N=6),记录澜沧江构造带变质岩经历了晚白垩世变质事件。综合研究认为澜沧江构造带南段存在区域性前寒武纪结晶基底,构造带中昌宁段之变质岩系的变质时间为晚白垩世(85~74Ma),并一直持续到36Ma,约32Ma之后构造带发生走滑运动,变质事件明显早于走滑运动事件。  相似文献   

6.
The U–Pb age of zircons from Ediacaran sandstones of the cover of the Tuva–Mongolian microcontinent and the rocks of its Early Precambrian basement (Gargan block) was analyzed by the LA–ICP–MS method. The major stages of tectonomagmatic activity of this block include the Neoarchean, Paleoproterozoic (no younger than 2 Ga), and Neoproterozoic. Comparison of the age of zircons from Ediacaran terrigenous rocks of the Tuva–Mongolian microcontinent and sandstones of the reference sections of the Ediacaran shelf of the Siberian platform undeniably indicates their independent accumulation.  相似文献   

7.
西昆仑地区元古宙岩浆侵入作用及构造-岩浆演化过程   总被引：2，自引：0，他引：2  
通过对西昆仑地区元古代侵入岩的岩石类型、形成时代和岩石地球化学资料的综合分析,探讨各个构造单元侵入岩形成期次、岩石成因及构造-岩浆演化过程。铁克里克断隆带元古宙中酸性侵入岩以A型花岗岩为主,是塔里木板块古老基底在高温低压条件下发生部分熔融的产物。西昆仑造山带古元古代和中元古代早期中酸性侵入岩为钙碱性I型花岗岩,是变玄武岩在低温条件下部分熔融条件下形成的,而古元古代晚期和新元古代中酸性侵入岩则是高温条件下老基底岩系部分熔融而形成的A型花岗岩。甜水海地块仅发育新元古代侵入岩,为S型花岗岩,是高温高压环境下甜水海地块古老基底部分熔融而形成。根据侵入岩岩浆演化规律,将西昆仑地区元古宙划为4个演化阶段:12 426~1 567Ma:以铁克里克断隆带A型花岗岩为代表的塔里木板块陆内演化,以西昆仑造山带钙碱性-拉斑质I型花岗岩为代表的陆缘弧。21 301~1 000Ma:铁克里克断隆带和西昆仑造山带均以陆内演化性质的A型花岗岩为主。31 000~851 Ma:甜水海地块S型花岗岩可能是陆-陆碰撞导致地壳加厚的产物,指示甜水海地块可能作为Rodinia超大陆的一员发生聚合拼接作用。4815~644 Ma:铁克里克断隆带和西昆仑造山带均存在碱性基性岩浆岩和A型花岗岩的双峰式侵入岩组合,指示塔里木地块和西昆仑地块可能作为Rodinia超大陆组成部分,在该阶段发生了裂解作用。通过对元古宙侵入岩的系统分析,西昆仑地区不同构造单元地壳演化有一定差异,经历了不同演化过程。  相似文献   

8.
周文孝  葛梦春 《地球科学》2013,38(4):715-724
通过大比例尺填图和剖面研究, 将内蒙古锡林浩特地区的"锡林郭勒杂岩"解体分为3大部分: 一套表壳岩、晚元古代基性-超基性侵入岩和早古生代酸性侵入岩.在此基础上根据变质岩的岩性组合和变形变质特点, 可将其中的表壳岩化分为4个岩性段: 黑云(石榴石)斜长片麻岩, 间夹多层条纹状斜长角闪岩, 在其顶部多见薄层含磁铁石英岩; 中粗粒黑云斜长片麻岩和细粒长英质片麻岩; 混合岩化条带状黑云(角闪)斜长片麻岩, 含石榴石黑云二长片麻岩夹条纹状斜长角闪岩组合; 夕线石黑云斜长片麻岩, 条纹状黑云斜长片麻岩, 间夹含石榴石黑云母石英片岩.通过对比区域内宝音图群、艾勒格庙组、白乃庙群等古老地块的岩石组合, 发现在原岩建造、变质级别、沉积环境等特征上均有区别, 应将这套表壳岩单独厘定为锡林浩特岩群, 它们组成了锡林郭勒微陆块前寒武变质基底岩系, 其地质特征的研究对锡林郭勒微陆块基底的形成和演化及华北板块与西伯利亚板块的构造关系演化有重要意义.   相似文献   

9.
白云鄂博位于华北克拉通北缘,是阴山地块的重要组成部分。本文对该区变质基底的5个花岗质岩石样品进行了锆石SHRIMP U-Pb定年,获得了2.63Ga和1.89~2.20Ga的岩浆锆石年龄以及2.47~2.51Ga和1.86~1.94Ga的变质锆石年龄。新太古代早期片麻状英云闪长岩的岩浆锆石εHf(t)值和tDM2(CC)(Hf)年龄分别为3.57~8.36和2.59~2.88Ga,古元古代中晚期花岗质岩石的岩浆锆石εHf(t)值和tDM2(CC)(Hf)年龄分别为-17.20~8.58和2.11~3.70Ga。变质锆石与岩浆锆石具有类似的Hf同位素组成。结合前人研究成果,表明:白云鄂博地区存在新太古代早期到古元古代晚期岩浆作用;在每一岩浆作用过程中,地幔添加和壳内再循环都起了重要作用;白云鄂博地区变质基底经历了新太古代晚期-古元古代早期和古元古代晚期构造热事件;阴山地块与南侧孔兹岩带具有类似的早前寒武纪地质演化历史。  相似文献   

10.
The purpose of this study was to examine the efficiency of Advanced Space Borne Thermal Emission and Reflection Radiometer (ASTER) data in the discrimination of geological formations and the generation of geological map in the northern margin of the Tunisian desert. The nine ASTER bands covering the visible (VIS), near-infrared (NIR) and short-wave infrared (SWIR) spectral regions (wavelength range of 400–2500 nm) have been treated and analyzed. As a first step of data processing, crosstalk correction, resampling, orthorectification, atmospheric correction, and radiometric normalization have been applied to the ASTER radiance data. Then, to decrease the redundancy information in highly correlated bands, the principal component analysis (PCA) has been applied on the nine ASTER bands. The results of PCA allow the validation and the rectification of the lithological boundaries already published on the geologic map, and gives a new information for identifying new lithological units corresponding to superficial formations previously undiscovered. The application of a supervised classification on the principal components image using a support vector machine (SVM) algorithm shows good correlation with the reference geologic map. The overall classification accuracy is 73 % and the kappa coefficient equals to 0.71. The processing of ASTER remote sensing data set by PCA and SVM can be employed as an effective tool for geological mapping in arid regions.  相似文献   

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