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61.
《地学前缘(英文版)》2020,11(6):2243-2269
The Gurupi Belt, in north-northeastern Brazil, is a mobile belt developed in the south-southwestern margin of the São Luís cratonic fragment and crops out as a tectonic and erosional window within the Phanerozoic cover. Field, petrographic, geochemical, geochronological, and Nd isotopic information (new and published) constrain the timing and types of magmatic associations present in the belt and the tectonic settings in which they formed. The Rhyacian was the main period of magmatic activity, which can be grouped into two main stages. (1) ~2185–2130 Ma: pre-collisional, juvenile, calc-alkaline magnesian and calcic ferroan granitoid suites, and minor calc-alkaline and tholeiitic mafic plutonism (now amphibolites), formed in intra-oceanic to transitional/continental arcs; and intra- or back-arc volcano-sedimentary basin. (2) ~2125–2070 Ma: syn- (two-mica granites) to late-collisional (potassic to shoshonitic granites and quartz-syenite) plutonic suites produced after crustal thickening and melting, with localized migmatization, that intruded during the compressive D1 deformational phase and concomitantly with greenschist to amphibolite metamorphism. There is a zonation of the Rhyacian episodes, with intra-oceanic stages occurring to the northeast, and the continental arc and collisional phases occurring to the southwest, indicating the presence of an active continental margin to the southwest, and subduction from NE to SW (present-day configuration). This magmatic framework is a continuation to the south of what is described for the São Luís cratonic fragment to the north, and the orogenic scenario is identical to what is observed for the same period in the West African Craton (Eburnean/Birrimian orogen), which additionally supports previous geological correlations. In the Neoproterozoic, a few magmatic occurrences are recognized. An extensional event allowed the intrusion of an anorogenic, nepheline syenite at ca. 730 Ma, which was followed by the intrusion of a crustal, calc-alkaline microtonalite, of uncertain tectonic setting, at 624 Ma. Both intrusions underwent greenschist to amphibolite facies metamorphism between 580 Ma and 529 Ma. This metamorphic event is probably related to crustal thickening, which produced crustal melting and intrusion of two-mica granites between 595 Ma and 549 Ma. The absence of oceanic and arc-related assemblages, along with geophysical information about the basement of the Phanerozoic cover indicates an intracontinental setting for the Neoproterozoic–Early Cambrian evolution of the Gurupi Belt, with rifting and posterior closure of the basin, without oceanization. Rifting and closure correlate in time with the onset of Rodinia breakup and West Gondwana assembly, respectively, but we interpret the events in the Gurupi Belt as having no direct role in these two global supercontinent-related events, but, instead, as being related to orogenic events occurring in the periphery of the West African and Amazonian cratons at that time. 相似文献
62.
Wei-Cui Ding Ting-Dong Li Xuan-Hua Chen Jian-Ping Chen Sheng-Lin Xu Yi-Ping Zhang Bing Li Qiang Yang 《地学前缘(英文版)》2020,(2):651-663
The West Junggar Orogenic Belt(WJOB)in northwestern Xinjiang,China,is located in the core of the western part of the Central Asian Orogenic Belt(CAOB).It has suffered two stage tectonic evolutions in Phanerozoic,before and after the ocean–continental conversion in Late Paleozoic.The later on intracontinental deformation,characterized by the development of the NE-trending West Junggar sinistral strike-slip fault system(WJFS)since Late Carboniferous and Early Permian,and the NW-trending Chingiz-Junggar dextral strike-slip fault(CJF)in Mesozoic and Cenozoic,has an important significance for the tectonic evolution of the WJOB and the CAOB.In this paper,we conduct geometric and kinematic analyses of the WJOB,based on field geological survey and structural interpretation of remote sensing image data.Using some piercing points such as truncated plutons and anticlines,an average magnitude of^73 km for the left-lateral strike-slip is calculated for the Darabut Fault,a major fault of the WJFS.Some partial of the displacement should be accommodated by strike-slip fault-related folds developed during the strike-slip faulting.Circular and curved faults,asymmetrical folds,and irregular contribution of ultramafic bodies,implies potential opposite vertical rotation of the Miao’ergou and the Akebasitao batholiths,resulted from the sinistral strike-slipping along the Darabut Fault.Due to conjugate shearing set of the sinistral WJFS and the dextral CJF since Early Mesozoic,superimposed folds formed with N–S convergence in southwestern part of the WJOB. 相似文献
63.
本研究根据2017年8月和2018年8月在东海北部杭州湾和三门湾大型底栖动物的拖网采集资料,对这两个海域的大型底栖动物群落结构和多样性进行了研究。杭州湾的10个站位和三门湾的6个站位共获得61种大型底栖动物,其中甲壳动物最多(22种),其次是鱼类(20种)、软体动物(14种)、棘皮动物(2种)、刺胞动物(2种),多毛类最少(1种)。杭州湾大型底栖动物优势种出现3种,三门湾出现8种,脊尾白虾Palaemoncarinicauda是两个海域唯一的共同优势种。相比2017年,杭州湾和三门湾在2018年鱼类的种类和数量都有明显的增长。根据大型底栖群落的多样性指数,杭州湾不同区域的生物多样性差异较大,而三门湾则较为平均。对杭州湾和三门湾大型底栖动物进行聚类分析和nMDS排序分析,结果表明,杭州湾不同站位大型底栖动物相似度低,Q8、Q9、Q10站位群落结构与三门湾的站位更为接近,三门湾的底栖群落在2017年和2018年存在较大差异。杭州湾和三门湾大型底栖动物群落的变化可能与环境因子、人类活动、厄尔尼诺事件等的变化相关。 相似文献
64.
湖相介形类壳体微量元素(本文主要指Mg和Sr)是重建古环境的重要指标之一,可以定性或定量地反映湖水信息。自20世纪80年开始应用以来,经过30余年的发展取得了很大进展。在古环境重建过程中主要存在两类影响因素:(1)其宿生水体中M/Ca比值(M主要指Mg和Sr)的影响因素:季节变化、微环境差异和湖泊演化过程,这类因素通过对宿生水体中M/Ca比值来影响介形虫壳体中的M/Ca比值,进而造成古环境重建结果的误差增大或可靠性降低;(2)介形类壳体微量元素分配系数的影响因素:宿生水体中M/Ca比值、温度、碱度等,这类因素能够直接影响介形类壳体分泌、钙化的生命-化学过程的因素,是定量重建的重要影响因素。加强现代介形类生活习性和微量元素组成变化过程的研究可以消除或减小以上影响因素对古环境重建的影响,提高介形类壳体化石中微量元素组成在古环境重建研究中的精度和可靠性。 相似文献
65.
Anthony Bouton Emmanuelle Vennin Philippe Amiotte-Suchet Christophe Thomazo Jean-Pierre Sizun Aurélien Virgone Eric C. Gaucher Pieter T. Visscher 《Basin Research》2020,32(5):1005-1034
Most source-to-sink studies typically focus on the dynamics of clastic sediments and consider erosion, transport and deposition of sediment particles as the sole contributors. Although often neglected, dissolved solids produced by weathering processes contribute significantly in the sedimentary dynamics of basins, supporting chemical and/or biological precipitation. Calcium ions are usually a major dissolved constituent of water drained through the watershed and may facilitate the precipitation of calcium carbonate when supersaturating conditions are reached. The high mobility of Ca2+ ions may cause outflow from an open system and consequently loss. In contrast, in closed basins, all dissolved (i.e. non-volatile) inputs converge at the lowest point of the basin. The endoreic Great Salt Lake basin constitutes an excellent natural laboratory to study the dynamics of calcium on a basin scale, from the erosion and transport through the watershed to the sink, including sedimentation in lake's waterbody. The current investigation focused on the Holocene epoch. Despite successive lake level fluctuations (amplitude around 10 m), the average water level seems to have not been affected by any significant long-term change (i.e. no increasing or decreasing trend, but fairly stable across the Holocene). Weathering of calcium-rich minerals in the watershed mobilizes Ca2+ ions that are transported by surface streams and subsurface flow to the Great Salt Lake (GSL). Monitoring data of these flows was corrected for recent anthropogenic activity (river management) and combined with direct precipitation (i.e. rain and snow) and atmospheric dust income into the lake, allowing estimating the amount of calcium delivered to the GSL. These values were then extrapolated through the Holocene period and compared to the estimated amount of calcium stored in GSL water column, porewater and sediments (using hydrochemical, mapping, coring and petrophysical estimates). The similar estimate of calcium delivered (4.88 Gt) and calcium stored (3.94 Gt) is consistent with the premise of the source-to-sink approach: a mass balance between eroded and transported compounds and the sinks. The amount of calcium deposited in the basin can therefore be predicted indirectly from the different inputs, which can be assessed with more confidence. When monitoring is unavailable (e.g. in the fossil record), the geodynamic context, the average lithology of the watershed and the bioclimatic classification of an endoreic basin are alternative properties that may be used to estimate the inputs. We show that this approach is sufficiently accurate to predict the amount of calcium captured in a basin and can be extended to the whole fossil record and inform on the storage of calcium. 相似文献
66.
Land subsidence in densely urbanized areas is a global problem that is primarily caused by excessive groundwater withdrawal. The Kathmandu Basin is one such area where subsidence due to groundwater depletion has been a major problem in recent years. Moreover, on 25 April 2015, this basin experienced large crustal movements caused by the Gorkha earthquake (Mw 7.8). Consequently, the effects of earthquake-induced deformation could affect the temporal and spatial nature of anthropogenic subsidence in the basin. However, this effect has not yet been fully studied. In this paper, we applied the SBAS-DInSAR technique to estimate the spatiotemporal displacement of land subsidence in the Kathmandu Basin before and after the Gorkha earthquake, using 16 ALOS-1 Phased Array L-band Synthetic Aperture Radar (PALSAR) images during the pre-seismic period and 26 Sentinel-1 A/B SAR images during the pre- and post-seismic periods. The results showed that the mean subsidence rate in the central part of the basin was about ?8.2 cm/year before the earthquake. The spatial extents of the subsiding areas were well-correlated with the spatial distributions of the compressible clay layers in the basin. We infer from time-series InSAR analysis that subsidence in the Kathmandu basin could be associated with fluvio-lacustrine (clay) deposits and local hydrogeological conditions. However, after the mainshock, the subsidence rate significantly increased to ?15 and ?12 cm/year during early post-seismic (108 days) and post-seismic (2015–2016) period, respectively. Based on a spatial analysis of the subsidence rate map, the entire basin uplifted during the co-seismic period has started to subside and become stable during the early-post-seismic period. This is because of the elastic rebound of co-seismic deformation. However, interestingly, the localized areas show increased subsidence rates during both the early-post- and post-seismic periods. Therefore, we believe that the large co-seismic deformation experienced in this basin might induce the local subsidence to increase in rate, caused by oscillations of the water table level in the clay layer. 相似文献
67.
Protected areas are increasingly prone to violent extremism spillover, with dramatic consequences for both local people and wildlife populations. Due to the influence of violent extremist groups, science and policy generally fade away. We outline the case of the W-Arly-Pendjari complex of protected areas in West Africa (Burkina Faso, Benin, and Niger), 62% of which is currently under the control of violent extremist groups. The last large population of West African elephants may soon disappear if no action is taken. We discuss the roles of conservation science and policy in protected areas under violent extremism spillover, namely (i) maintaining and reinforcing international support, (ii) authentically engaging local communities in conservation and management strategies, and (iii) planning long-term conservation and security strategies. 相似文献
68.
基于中国区域逐日降雪、降水、气温、相对湿度、气压和风速等观测数据,构建了中国区域的Logistic降雪判定方法,并对该方法和当前广泛应用的其他降雪判定方法在中国区域的适用性展开对比研究。结果表明,单温度阈值法和S曲线法对[-3,4] ℃气温区间内的降雪模拟不确定性相对较大。比较而言,Logistic拟合的系列方法成功率更高,对中国不同区域降雪识别也更为稳健,尤其是对青藏高原地区降雪事件的识别效果明显优于其他方法。在Logistic方法中,温度和相对湿度对降雪判定起决定作用,而气压和风速的影响相对较小。Logistic湿球温度方案(LogTw)和气温+相对湿度方案(LogTaHR)均能很好地再现降雪量的空间分布和年际变化特征,且相应偏差均小于其他方法;总体上,这两种方案对降雪量识别效果差别不大。因此,可使用LogTw方案或LogTaHR方案对中国区域降雪事件进行判别,尤其是对模式中降雪事件的识别。 相似文献
69.
70.
利用1961—2016年山西盛夏(7—8月)平均降水和同期NOAA重构海温资料,分析了山西盛夏降水分别与赤道中东太平洋海温和西太平洋暖池海温相关性的变化。结果表明:山西盛夏降水和赤道中东太平洋海温之间呈现稳定的显著负相关;和西太平洋暖池海温呈现正相关,并在20世纪70年代末到80年代初之后相关性加强,通过了0.05显著性检验。进一步分析表明,这种西太平洋暖池海温对20世纪80年代以来山西盛夏降水指示意义加强的事实,主要体现在赤道中东太平洋海温偏冷的背景下。西太平洋暖池海温异常通过影响与山西盛夏降水密切相关的大气环流、季风槽位置和东亚夏季风,导致山西盛夏降水异常。盛夏赤道中东太平洋海温偏冷时,西太平洋暖池海温偏暖(冷),通过遥相关引起中高纬度大气欧亚—太平洋型遥相关(EUP)和负太平洋—日本(PJ)波列,通过影响季风槽位置偏西偏北(偏东偏南),引起西太平洋副热带高压偏北(南)和季风指数偏小(大),导致山西盛夏降水偏多(少)。 相似文献