Timing of deformation in the Norseman-Wiluna Belt, Yilgarn Craton, Western Australia     

Roberto F. Weinberg  Louis Moresi  Peter van der Borgh 《Precambrian Research》2003,120(3-4):219-239

Establishing relative and absolute time frameworks for the sedimentary, magmatic, tectonic and gold mineralisation events in the Norseman-Wiluna Belt of the Archean Yilgarn Craton of Western Australia, has long been the main aim of research efforts. Recently published constraints on the timing of sedimentation and absolute granite ages have emphasized the shortcomings of the established rationale used for interpreting the timing of deformation events. In this paper the assumptions underlying this rationale are scrutinized, and it is shown that they are the source of significant misinterpretations. A revised time chart for the deformation events of the belt is established. The first shortening phase to affect the belt, D₁, was preceded by an extensional event D_1e and accompanied by a change from volcanic-dominated to plutonic-dominated magmatism at approximately 2685–2675 Ma. Later extension (D_2e) controlled deposition of the ca 2655 Ma Kurrawang Sequence and was followed by D₂, a major shortening event, which folded this sequence. D₂ must therefore have started after 2655 Ma—at least 20 Ma later than previously thought and after the voluminous 2670–2655 Ma high-Ca granite intrusion. Younger transcurrent deformation, D₃–D₄, waned at around 2630 Ma, suggesting that the crustal shortening deformation cycle D₂–D₄ lasted approximately 20–30 Ma, contemporaneous with low-volume 2650–2630 Ma low-Ca granites and alkaline intrusions. Time constraints on gold deposits suggest a late mineralisation event between 2640–2630 Ma. Thus, D₂–D₄ deformation cycle and late felsic magmatism define a 20–30 Ma long tectonothermal event, which culminated with gold mineralisation. The finding that D₂ folding took place after voluminous high-Ca granite intrusion led to research into the role of competent bodies during folding by means of numerical models. Results suggest that buoyancy-driven doming of pre-tectonic competent bodies trigger growth of antiforms, whereas non-buoyant, competent granite bodies trigger growth of synforms. The conspicuous presence of pre-folding granites in the cores of anticlines may be a result from active buoyancy doming during folding.  相似文献   

Petrographic of Northwestern Sudan     

NafiM AbdullatifM 《中国地质大学学报(英文版)》2003,14(2):137-143

The sedimentology of the Northwestern Sudan consists of lower, middle and upper cycles. The lower and upper cycles are composed of intercalated fluvial and shallow marine facies, whereas the middle cycle consists entirely of fluvial and glaciofluvial facies. The petrographic analysis shows that the lower and upper cydes consist of quartz and lithic arenite sandstones, whereas the middle cycle consists of arkosic and lithic arenite sandstones. The lower and upper cycle sandstones reflect derivation mainly from recycled orogens with minor contribution from craton interior provenances. However, the middle cycle sandstones indicate derivation from basement uplift, transitional and mainly recycled orogens provenances.  相似文献   

云南宁蒗地区喜山期斑岩带地质特征与成矿   总被引：1，自引：0，他引：1  

胡受权  郭文平 《地质与勘探》1996,32(3):7-13

斑岩带受近南北向的包都－波罗弧形断裂控制，由混源型岩浆被动侵位而成，属钙碱性系列，中酸性岩。研究表明为含铜或铜（钼）斑岩，具良好的成矿前景。  相似文献   

Tectonometamorphic evolution of the Himalayan metamorphic core between the Annapurna and Dhaulagiri, central Nepal   总被引：12，自引：0，他引：12  

J.-C. VANNAY  & K. V. HODGES 《Journal of Metamorphic Geology》1996,14(5):635-656

The metamorphic core of the Himalaya in the Kali Gandaki valley of central Nepal corresponds to a 5-km-thick sequence of upper amphibolite facies metasedimentary rocks. This Greater Himalayan Sequence (GHS) thrusts over the greenschist to lower amphibolite facies Lesser Himalayan Sequence (LHS) along the Lower Miocene Main Central Thrust (MCT), and it is separated from the overlying low-grade Tethyan Zone (TZ) by the Annapurna Detachment. Structural, petrographic, geothermobarometric and thermochronological data demonstrate that two major tectonometamorphic events characterize the evolution of the GHS. The first (Eohimalayan) episode included prograde, kyanite-grade metamorphism, during which the GHS was buried at depths greater than c. 35 km. A nappe structure in the lowermost TZ suggests that the Eohimalayan phase was associated with underthrusting of the GHS below the TZ. A c. 37 Ma ⁴⁰Ar/³⁹Ar hornblende date indicates a Late Eocene age for this phase. The second (Neohimalayan) event corresponded to a retrograde phase of kyanite-grade recrystallization, related to thrust emplacement of the GHS on the LHS. Prograde mineral assemblages in the MCT zone equilibrated at average T =880 K (610 °C) and P =940 MPa (=35 km), probably close to peak of metamorphic conditions. Slightly higher in the GHS, final equilibration of retrograde assemblages occurred at average T =810 K (540 °C) and P=650 MPa (=24 km), indicating re-equilibration during exhumation controlled by thrusting along the MCT and extension along the Annapurna Detachment. These results suggest an earlier equilibration in the MCT zone compared with higher levels, as a consequence of a higher cooling rate in the basal part of the GHS during its thrusting on the colder LHS. The Annapurna Detachment is considered to be a Neohimalayan, synmetamorphic structure, representing extensional reactivation of the Eohimalayan thrust along which the GHS initially underthrust the TZ. Within the upper GHS, a metamorphic discontinuity across a mylonitic shear zone testifies to significant, late- to post-metamorphic, out-of-sequence thrusting. The entire GHS cooled homogeneously below 600–700 K (330–430 °C) between 15 and 13 Ma (Middle Miocene), suggesting a rapid tectonic exhumation by movement on late extensional structures at higher structural levels.  相似文献   

Metamorphic evolution of garnet-spinel peridotites from the Variscan Schwarzwald (Germany)   总被引：1，自引：0，他引：1  

A. Kalt  R. Altherr 《International Journal of Earth Sciences》1996,85(2):211-224

Garnet-spinel peridotites form small, isolated, variably retrogressed bodies within the low-pressure high-temperature gneisses and migmatites of the Variscan basement of the Schwarzwald, southwest Germany. Detailed mineralogical and textural studies as well as geothermobarometric calculations on samples from three occurrences are presented. Two of the garnet-spinel peridotites have equilibrated at 680–770°C, 1.4–1.8 GPa within the garnet-spinel peridotite stability field, one of the samples having experienced an earlier stage within the spinel peridotite stability field (790°C, <1.8 GPa). The third sample, with only garnet and spinel preserved, probably equilibrated within the garnet peridotite stability field at higher pressures. These findings are in line with the distinction of two groups of ultramafic garnet-bearing high-pressure rocks with different equilibration conditions within the Schwarzwald (670–740°C, 1.4–1.8 GPa and 740–850°C, 3.2–4.3 GPa) which has previously been established (Kalt et al. 1995). The equilibration conditions of 670–770°C and 1.4–1.8 GPa for garnet-spinel peridotites from the Central Schwarzwald Gneiss Complex (CSGC) are similar to those for eclogites of the Schwarzwald and also correspond quite well to those for garnet-spinel peridotites from the Moldanubian zone of the Vosges mountains and of ecologites from the Moldanubian s.str. of the Bohemian Massif.  相似文献   

大陆层控构造论盆－山系与造山带成因及演化新模式   总被引：1，自引：0，他引：1  

李扬鉴  张星亮 《化工矿产地质》1996,18(3):149-155

大陆构造以受中地壳塑性层控制的盆－山系和冲叠造山带厚皮构造为主要构造类型，而与中生代以来才出现的受软流层控制的大洋岩石圈板块构造截然不同。由上地壳正断层上盘断陷盆地和下盘断隆山所组成的盆－山系，与地球自转速度逐渐变慢派生不同性质水平力和重力的共同作用有关。当地球自转速度突然变化时，将派生强烈的侧压力，使升降幅度较大、具有侧向应变空间的断陷盆地与断隆山之间的上地壳发生冲叠运动，盆－山系由此演变成冲叠造山带。后者对前者存在着严格的继承关系，服从于“升降－冲叠律”。中生代以来的盆－山系和冲叠造山带有的是板块活动产物  相似文献   

Geochemical constraints on the petrogenesis of basalts from eastern Jiangnan orogen, South China   总被引：2，自引：0，他引：2  

Hongfeng Tang  Xinmin Zhou 《中国科学D辑(英文版)》1997,40(6):627-633

The basalts crop out widely in the eastern part of late Proterozoic Jiangnan orogen. In terms of their petrographical and geochemical characteristics, they can be divided into two distinct types: low- and high-Ti. basalts. They crystallized from the magmas derived from the depleted upper mantle differing in partial melting degree. Project supported by the National Natural Science Foundation of China.  相似文献   

秦岭造山带地壳构造与楔入成山   总被引：23，自引：3，他引：23       下载免费PDF全文

袁学诚 《地质学报》1997,71(3):227-235

横穿秦岭的河南叶县至湖北南漳的反射地震剖面揭示，秦岭造山带地壳由一系列由南向北楔入到中地壳的鳄鱼式构造所组成。南北溱岭上地壳分别形成南秦岭和北秦岭推覆系。北秦岭推覆系是组成基底的地壳沿脆转换面拆离冲叠形成的一个推覆系，可以分出栾川推覆体，瓦穴子推覆体，二郎坪推覆体及朱夏推覆体。  相似文献   

Tectonic Evolution of the Himalayan Collision Belt   总被引：5，自引：0，他引：5  

Cui Junwen Institute of Geology  Chinese Academy of Geological Sciences  Beijing 《《地质学报》英文版》1997,71(2):133-143

This paper discusses the tectonic divisions of the Himalayan collision belt anddeals with the tectonic evolution of the collision belt in the context of crustal accretion in thefront of the collision belt, deep diapirism and thermal-uplift extension and deep material flow-ing of the lithosphere-backflowing. Finally it proposes a model of the tectonic evolution-progressive intracontinental deformation model-of the Himalayan belt.  相似文献   

Timing and geochemical characters of the Sanchazi magmatic arc in Mianlüe tectonic zone, South Qinling     

LI Shuguang  HOU Zhenhui  YANG Yongcheng  Sun Weidong  ZHANG Guowei  LI Qiuli 《中国科学D辑(英文版)》2004,47(4)

The Sanchazi mafic-ultramafic complex in Mianlue tectonic zone, South Qinling can be subdivided into two blocks, i.e. Sanchazi paleo-magmatic arc and Zhuangkegou paleo-oceanic crust fragment (ophiolite). The Sanchazi paleo-magmatic arc is mainly composed of andesite, basaltic and basalt-andesitic gabbro (or diorite), andesitic dyke, plagiogranite and minor ultramafic rocks, which have typical geochemical features of island arc volcanic rocks, such as high field strength element (e.g. Nb, Ti) depletions and lower Cr, Ni contents. The Light rare earth element (LREE) and K enrichments of these rocks and zircon xenocrystals of 900 Ma from plagiogranite suggest that this magmatic arc was developed on the South active continental margin of the South Qinling micro-continent. The U-Pb age of (300 ± 61)Ma for zircons from plagiogranite indicates that the Mianlue paleo-oceanic crust was probably subducted underneath the South Qinling micro-continent in Carboniferous. This is consistent with the formation time (309Ma) of the Huwan eclogite originating from oceanic subduction in Dabie Mountains, suggesting that the Mianlue paleo-ocean probably extended eastward to the Dabie Mountains in Carboniferous. The high-Mg adakitic rocks in Sanchazi paleo-magmatic arc suggest that the subducted oceanic crust was relatively young (＜25Ma) and hot.  相似文献