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1.
攀西裂谷存在吗？ 总被引：12，自引：0，他引：12
大陆裂谷以地幔上隆、岩石圈伸展、减薄、断陷和沉降为特征，伸展构造环境是大陆裂谷形成的必要条件和本质特征。中国学者以前所认为攀枝花-西昌裂谷的主要标志是海西期层状堆晶杂岩、晚二叠世峨眉山玄武岩、印支期环状碱性杂岩和晚三叠世裂谷盆地沉积。最近一系列研究成果表明攀西地区海西期-印支期构造岩浆热事件是地幔柱和岩石圈相互作用的结果，不是裂谷作用的产物。进一步对上扬子西缘二叠纪-三叠纪的沉积作用和构造特征综合分析表明攀西地区不存在裂谷盆地沉积。该区晚二叠世-中三叠世为古陆隆起遭受剥蚀，晚三叠世断陷型类磨拉石建造是前陆走滑复合盆地的产物。本文根据对攀西地区二叠纪-三叠纪的岩浆活动、沉积作用、构造特征和地球物理资料等方面综合研究对攀西裂谷的存在提出质疑，并以峨眉山地幔柱活动为主线探讨了攀西地区古生代和中生代的地质构造演化历史。 相似文献
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提要：扬子地块西缘新元古代岩浆岩分布广泛,目前对其成因和构造背景的认识还存在很大争议。本文报道了川西康滇裂谷北段康定—丹巴地区新元古代基性岩墙的岩石学、元素地球化学和Sm-Nd同位素特征,探讨其岩石成因、岩浆源区性质和岩浆熔融深度。结果表明岩石样品属拉斑系列,形成于板内裂谷环境,岩浆在上升侵位过程中受到了初生岛弧地壳物质不同程度的混染。岩浆起源于亏损地幔源区,是尖晶石地幔橄榄岩部分熔融的产物,很可能与导致Rodinia超级大陆裂解的新元古代地幔柱事件有关。 相似文献
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《矿物岩石地球化学通报》2017,(2)
碳酸岩是揭示地幔地球化学动力学的"探针岩石",迄今有关碳酸岩的研究集中在裂谷环境,而鲜见造山带地区碳酸岩研究的报道。在四川攀西喜马拉雅期造山带、秦岭造山带和华北中央造山带内均有碳酸岩产出,且蕴藏了大型稀土和钼矿床,是研究深俯冲、壳-幔作用和深部碳循环的理想实验室。传统观念认为碳酸岩形成于裂谷环境与地幔柱活动相关,而造山带碳酸岩很可能是陆源富碳沉积物俯冲至地幔低程度熔融的产物。中国造山带内碳酸岩地球化学研究均显示了地壳物质对碳酸岩地幔源区的贡献,这暗示地表碳俯冲至深部地幔,交代地幔发生熔融,这不仅为较还原的地幔源区提供富氧成分,还可以使碳酸岩的母体岩浆更富集稀土,形成稀土矿床。 相似文献
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鲁西前寒武纪基性岩墙群 总被引：16，自引：0，他引：16
鲁西地区发育大规模的中元古代基性岩墙群,侵位于早前寒武纪结晶基底内,未变形未变质,以北北西向和近南北向为主,是鲁西前寒武纪最引人注目的一种伸展构造标志。鲁西基性岩墙群属于板内大陆裂谷拉斑玄武岩系列,与板内大陆裂谷活动密切相关,代表一种非造山岩浆活动。该岩墙群富集大离子亲石元素(L IL E) ,略亏损高场强元素(HFSE) ,比较富集Cr、Ni,明显亏损Th。稀土元素配分模式为轻稀土略富集的右倾曲线。鲁西基性岩墙群的微量元素和稀土元素特征反映源区为略富集的地幔。从时空分布特征、构造特征、岩石化学相关性、岩浆源区和古构造应力场分析,鲁西基性岩墙群与燕辽—中条拗拉槽系有一定的成生联系。 相似文献
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在川、滇、黔三省晚二叠世峨眉山玄武岩省的中部，产于攀西古裂谷内的龙帚山火山岩建造自下而上有4个喷发旋回：拉斑玄武岩、碱玄响岩、钾粗面玄武岩以及拉斑玄武岩。上下两个玄武岩旋回的岩性与该裂谷带以外大面积展布的高钛玄武岩岩性相同；而其碱玄响岩旋回主要由响碱玄岩—碱玄响岩—响岩岩系组成，夹粗安岩和安粗岩层，此旋回厚达千米，类似于非洲肯尼亚裂谷带的高原溢流响岩岩系。龙帚山晚二叠世火山岩建造的层序和岩石组合不同于古裂谷带外正常的大陆板内暗色岩喷出相的层序和岩浆演化规律，可能是地幔热柱和裂谷背景下岩石圈拉张复合作用的结果。 相似文献
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对扬子地块西缘康滇裂谷北段的丹巴变质玄武岩进行了系统的岩石学、元素-Nd同位素地球化学研究,结果表明该岩石为碱性玄武岩,样品相对富MgO、富TiO2,Mg#值介于0.51～0.59之间.稀土总量较高,轻重稀土分馏较明显,Th、Nb、Ta、Zr、Hf和LREE等不相容元素富集,Y和HREE明显亏损,地球化学特征与洋岛玄武岩(OIB)类似.岩浆形成于板内裂谷环境,起源于类似OIB的地幔源区,并在上升过程中受到了大陆岩石圈地幔(SCLM)物质不同程度的混染,同时还可能有少量下地壳物质的混染.样品在岩石化学上表现出地幔柱岩浆作用的痕迹,很可能与导致Rodinia超级大陆裂解的新元古代地幔柱事件有关. 相似文献
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攀西茨达和太和层状岩体时代 总被引：7，自引：0，他引：7
由于对攀西层状岩体中的同一岩体采用不同的定年方法获得的年龄结果有较大差异,导致对层状岩体的成岩时代产生争议。对攀西古裂谷带内茨达和太和两个层状辉长岩体进行了黑云母^40Ar/^39Ar法和锆石ELA-ICP-MS法定年研究,结果表明：茨达不含矿层状辉长岩中黑云母^40Ar/^39Ar坪年龄为256Ma,太和含矿层状辉长岩中锆石U-Pb年龄为215Ma,其年龄范围在256-215Ma,相当于晚二叠世—晚三叠世,属于海西晚期—印支期,而且不含矿层状辉长岩侵位时间在前,含矿层状岩体侵位时间在后。此外,根据此次层状岩体同位素地质年龄测定,表明其早期侵位时间并非在裂谷张裂之前的成穹阶段,而是和峨眉山玄武岩在晚二叠世—晚三叠世张裂阶段的喷溢具有同步性,亦显示层状辉长岩的岩浆作用与地幔柱活动,以及断裂构造的密切关系。 相似文献
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本文主要讨论穹窿-火山型攀西裂谷的成因,岩浆深成作用与火山作用过程;穹窿构造的发生、发展的演化历史;岩浆分异趋势及双峰式岩浆演化系列及其成因。 攀西裂谷曾经历了岩石圈穹窿—陆壳穹窿一次火山穹窿三个发展演化阶段。碱性岩浆作用与地壳隆升、地幔去气、热流汇聚作用有着密切的成因联系,成穹作用最盛,岩浆碱度最高。随着陆壳破裂、开放、挥发分散逸,岩浆性质从强碱质—弱碱质—碱酸性转化。 穹窿构造的发展演化阶段有机地控制了岩浆源和二次岩浆房的深度和岩浆演化特点,随着穹窿构造的发展演化,岩浆活动由深成幔源→中浅成幔源加陆壳轻微混染→超浅成壳幔混合源逐渐演化,因而可以认为:穹窿-火山型裂谷发育的各个阶段,存在有低位→中位→高位的二次岩浆房。 攀西裂谷属不发育的夭折裂谷,以演化时间长为特点,有利于岩浆深源(二次岩浆房内)结晶分异、液体不混容性分离作用和陆壳的同化混染作用等得以彻底进行,最终形成“双峰式”岩浆组合。 相似文献
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Continental rift evolution: From rift initiation to incipient break-up in the Main Ethiopian Rift, East Africa 总被引：2，自引：0，他引：2
The Main Ethiopian Rift is a key sector of the East African Rift System that connects the Afar depression, at Red Sea–Gulf of Aden junction, with the Turkana depression and Kenya Rift to the South. It is a magmatic rift that records all the different stages of rift evolution from rift initiation to break-up and incipient oceanic spreading: it is thus an ideal place to analyse the evolution of continental extension, the rupture of lithospheric plates and the dynamics by which distributed continental deformation is progressively focused at oceanic spreading centres.The first tectono-magmatic event related to the Tertiary rifting was the eruption of voluminous flood basalts that apparently occurred in a rather short time interval at around 30 Ma; strong plateau uplift, which resulted in the development of the Ethiopian and Somalian plateaus now surrounding the rift valley, has been suggested to have initiated contemporaneously or shortly after the extensive flood-basalt volcanism, although its exact timing remains controversial. Voluminous volcanism and uplift started prior to the main rifting phases, suggesting a mantle plume influence on the Tertiary deformation in East Africa. Different plume hypothesis have been suggested, with recent models indicating the existence of deep superplume originating at the core-mantle boundary beneath southern Africa, rising in a north–northeastward direction toward eastern Africa, and feeding multiple plume stems in the upper mantle. However, the existence of this whole-mantle feature and its possible connection with Tertiary rifting are highly debated.The main rifting phases started diachronously along the MER in the Mio-Pliocene; rift propagation was not a smooth process but rather a process with punctuated episodes of extension and relative quiescence. Rift location was most probably controlled by the reactivation of a lithospheric-scale pre-Cambrian weakness; the orientation of this weakness (roughly NE–SW) and the Late Pliocene (post 3.2 Ma)-recent extensional stress field generated by relative motion between Nubia and Somalia plates (roughly ESE–WNW) suggest that oblique rifting conditions have controlled rift evolution. However, it is still unclear if these kinematical boundary conditions have remained steady since the initial stages of rifting or the kinematics has changed during the Late Pliocene or at the Pliocene–Pleistocene boundary.Analysis of geological–geophysical data suggests that continental rifting in the MER evolved in two different phases. An early (Mio-Pliocene) continental rifting stage was characterised by displacement along large boundary faults, subsidence of rift depression with local development of deep (up to 5 km) asymmetric basins and diffuse magmatic activity. In this initial phase, magmatism encompassed the whole rift, with volcanic activity affecting the rift depression, the major boundary faults and limited portions of the rift shoulders (off-axis volcanism). Progressive extension led to the second (Pleistocene) rifting stage, characterised by a riftward narrowing of the volcano-tectonic activity. In this phase, the main boundary faults were deactivated and extensional deformation was accommodated by dense swarms of faults (Wonji segments) in the thinned rift depression. The progressive thinning of the continental lithosphere under constant, prolonged oblique rifting conditions controlled this migration of deformation, possibly in tandem with the weakening related to magmatic processes and/or a change in rift kinematics. Owing to the oblique rifting conditions, the fault swarms obliquely cut the rift floor and were characterised by a typical right-stepping arrangement. Ascending magmas were focused by the Wonji segments, with eruption of magmas at surface preferentially occurring along the oblique faults. As soon as the volcano-tectonic activity was localised within Wonji segments, a strong feedback between deformation and magmatism developed: the thinned lithosphere was strongly modified by the extensive magma intrusion and extension was facilitated and accommodated by a combination of magmatic intrusion, dyking and faulting. In these conditions, focused melt intrusion allows the rupture of the thick continental lithosphere and the magmatic segments act as incipient slow-spreading mid-ocean spreading centres sandwiched by continental lithosphere.Overall the above-described evolution of the MER (at least in its northernmost sector) documents a transition from fault-dominated rift morphology in the early stages of extension toward magma-assisted rifting during the final stages of continental break-up. A strong increase in coupling between deformation and magmatism with extension is documented, with magma intrusion and dyking playing a larger role than faulting in strain accommodation as rifting progresses to seafloor spreading. 相似文献
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自中生代末期以来,东北地区形成了以松辽地堑为主体,联合下辽河裂谷、伊通-依兰裂谷、抚顺-密山裂谷以及邻近断陷盆地的大陆裂谷系,并向南北两端延伸,在亚洲东部构成一条大的裂谷带。这个大陆裂谷系的形成和发展是由中央向两侧展开的,与板块俯冲、弧后扩张密切相关。 相似文献
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Non‐uniform splitting of a single mantle plume by double cratonic roots: Insight into the origin of the central and southern East African Rift System 
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下载免费PDF全文 Using numerical thermo‐mechanical experiments we analyse the role of an active mantle plume and pre‐existing lithospheric thickness differences in the structural development of the central and southern East African Rift system. The plume‐lithosphere interaction model setup captures the essential features of the studied area: two cratonic bodies embedded into surrounding lithosphere of normal thickness. The results of the numerical experiments suggest that localization of rift branches in the crust is mainly defined by the initial position of the mantle plume relative to the cratons. We demonstrate that development of the Eastern branch, the Western branch and the Malawi rift can be the result of non‐uniform splitting of the Kenyan plume, which has been rising underneath the southern part of the Tanzanian craton. Major features associated with Cenozoic rifting can thus be reproduced in a relatively simple model of the interaction between a single mantle plume and pre‐stressed continental lithosphere with double cratonic roots. 相似文献
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V. V. Yarmolyuk A. M. Kozlovsky V. M. Savatenkov V. P. Kovach I. K. Kozakov A. B. Kotov V. I. Lebedev G. Eenjin 《Petrology》2016,24(5):433-461
Data on the composition, inner structure, and magma sources of giant batholith in the Central Asian Orogenic Belt are analyzed with reference to the Khangai batholith. The Khangai batholith was emplaced in the Late Permian–Early Triassic (270–240 Ma) and is the largest accumulations (>150000 km2) of granite plutons in central Mongolia. The plutons are dominated by granites of normal alkalinity and contain subalkaline granites and more rare alkaline granites. The batholith is hosted in the Khangai zonal magmatic area, which consists of the batholith itself and surrounding rift zones. The zones are made up of bimodal basalt–trachyte–comendite (pantellerite) or basalt-dominated (alkaline basalt) volcanic associations, whose intrusive rocks are dominated by syenite and granite, granosyenite, and leucogranite. Both the batholith and the rift zones were produced within the time span of 270–240 Ma. Although the rocks composing the batholith and its rift surroundings are different, they are related through a broad spectrum of transitional varieties, which suggests that that the mantle and crustal melts could interact at various scale when the magmatic area was produced. A model is suggested to explain how the geological structure of the magmatic area and the composition of the magmatic associations that make up its various zones were controlled by the interaction between a mantle plume and the lithospheric folded area. The mantle melts emplaced into the lower crust are thought to not only have been heat sources and thus induced melting but also have predetermined the variable geochemical and isotopic characteristics of the granitoids. In the marginal portions of the zonal area, the activity of the mantle plume triggered rifting associated with bimodal and alkaline granite magmatism. The formation of giant batholiths was typical of the evolution of the active continental margin of the Siberian paleocontinent in the Late Paleozoic and Early Mesozoic: the Khangai, Angara–Vitim, and Khentei batholiths were formed in this area within a relatively brief time span between 300 and 190Ma. The batholiths share certain features: they consist of granitoids of a broad compositional range, from tonalite and plagiogranite to granosyenite and rare-metal granites; and the batholiths were produced in relation to rifting processes that also formed rift magmatic zones in the surroundings of the batholiths. The large-scale and unusual batholith-forming processes are thought to have occurred when the active continental margin of the Late Paleozoic Siberian continent overlapped a number of hotspots in the Paleo- Asian Ocean. This resulted in the origin of a giant anorogenic magmatic province, which included batholiths, flood-basalt areas in Tarim and Junggar, and the Central Asian Rift System. The batholiths are structural elements of the latter and components of the zonal magmatic areas. 相似文献
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《地学前缘(英文版)》2016,7(2)
The East African Rift system(EARS)provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches,the eastern,magma-rich,and the western,magma-poor,on either sides of the old thick Tanzanian craton embedded in a younger lithosphere.Data on the pre-rift,syn-rift and post-rift far-field volcanic and tectonic activity show that the EARS formed in the context of the interaction between a deep mantle plume and a horizontally and vertically heterogeneous lithosphere under far-field tectonic extension.We bring quantitative insights into this evolution by implementing high-resolution 3D thermo-mechanical numerical deformation models of a lithosphere of realistic rheology.The models focus on the central part of the EARS.We explore scenarios of plumelithosphere interaction with plumes of various size and initial position rising beneath a tectonically pre-stretched lithosphere.We test the impact of the inherited rheological discontinuities(suture zones)along the craton borders,of the rheological structure,of lithosphere plate thickness variations,and of physical and mechanical contrasts between the craton and the embedding lithosphere.Our experiments indicate that the ascending plume material is deflected by the cratonic keel and preferentially channeled along one of its sides,leading to the formation of a large rift zone along the eastern side of the craton,with significant magmatic activity and substantial melt amount derived from the mantle plume material.We show that the observed asymmetry of the central EARS,with coeval amagmatic(western)and magmatic(eastern)branches,can be explained by the splitting of warm material rising from a broad plume head whose initial position is slightly shifted to the eastern side of the craton.In that case,neither a mechanical weakness of the contact between the craton and the embedding lithosphere nor the presence of second plume are required to produce simulations that match observations.This result reconciles the passive and active rift models and demonstrates the possibility of development of both magmatic and amagmatic rifts in identical geotectonic environments. 相似文献
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中国东北晚中生代-新生代盆山体系构造演化及成因探讨 总被引：1，自引：0，他引：1
中国东北盆山体系主要形成和发展于晚侏罗世晚期-新近纪,经历了晚侏罗世晚期-早白垩世小盆山（盆岭）和晚白垩世-新近纪大盆山（盆山）两个阶段的构造发展过程.盆岭阶段起始于东北高原向盆岭体系转换的张家口期,全盛于义县-九佛堂期,萎缩于盆岭向盆山体系构造转换的沙海-阜新期,结束于张老公屯期（东山期）.盆山阶段经历了晚白垩世早期大规模拗陷、晚白垩世晚期拗陷萎缩、古近纪大规模裂谷和新近纪后裂谷拗陷.认为太平洋板块对盆山体系形成和发展有巨大的影响,但无论是板块、地幔柱和超级地幔柱均不太可能形成如此规模,又具北北东向的中-新生代岩浆岩带和盆山体系,更可能是超级地幔热带、地幔柱和东亚多向板块汇聚背景下,西太平洋板块俯冲共同作用的结果. 相似文献
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The Roer Valley Rift System (RVRS) is located between the West European rift and the North Sea rift system. During the Cenozoic, the RVRS was characterized by several periods of subsidence and inversion, which are linked to the evolution of the adjacent rift systems. Combination of subsidence analysis and results from the analysis of thickness distributions and fault systems allows the determination of the Cenozoic evolution and quantification of the subsidence. During the Early Paleocene, the RVRS was inverted (Laramide phase). The backstripping method shows that the RVRS was subsequently mainly affected by two periods of subsidence, during the Late Paleocene and the Oligocene–Quaternary time intervals, separated by an inversion phase during the Late Eocene. During the Oligocene and Miocene periods, the thickness of the sediments and the distribution of the active faults reveal a radical rotation of the direction of extension by about 70–80° (counter clockwise). Integration of these results at a European scale indicates that the Late Paleocene subsidence was related to the evolution of the North Sea basins, whereas the Oligocene–Quaternary subsidence is connected to the West European rift evolution. The distribution of the inverted provinces also shows that the Early Paleocene inversion (Laramide phase) has affected the whole European crust, whereas the Late Eocene inversion was restricted to the southern North Sea basins and the Channel area. Finally, comparison of these deformations in the European crust with the evolution of the Alpine chain suggests that the formation of the Alps has controlled the evolution of the European crust since the beginning of the Cenozoic. 相似文献
19.
Evolution of calc-alkaline to alkaline magmatism through Carboniferous convergence to Permian transcurrent tectonics,western Chinese Tianshan 总被引：7，自引：0，他引：7
Bo Wang Dominique Cluzel Liangshu Shu Michel Faure Jacques Charvet Yan Chen Sebastien Meffre Koen de Jong 《International Journal of Earth Sciences》2009,98(6):1275-1298
Continuous magmatic activity occurred in the western Chinese Tianshan, Central Asia, from the Carboniferous to the Permian,
i.e. before and after the Late Carboniferous amalgamation of Junggar and the Yili Blocks. Zircon U–Pb LA-ICPMS and Ar–Ar data
reveal a coincidence in time between regional wrench faulting and granitoid emplacement. Permian post-collisional granitoids
crop out within or at the margins of large-scale dextral strike-slip shear zones, some of them show synkinematic fabrics.
The whole rock geochemical features of the Early-Middle Permian granitoids indicate an evolution from high-K calc-alkaline
towards alkaline series. In other places of the North Tianshan, alkaline magmatism occurred together with deep marine sedimentation
within elongated troughs controlled by wrench faults. Therefore, in contrast with previous interpretations that forwarded
continental rift or mantle plume hypotheses, the coexistence of diverse magmatic sources during the same tectonic episode
suggests that post-collisional lithosphere-scale transcurrent shearing tightly controlled the magmatic activity during the
transition from convergent margin to intraplate anorogenic processes. 相似文献
20.
Devana Chasma is a rift system on Venus formed in association with the Beta Regio and Phoebe Regio volcanic highlands, which are interpreted as mantle plumes. We present a new analysis of a 2500-km-long segment of Devana. Based on the rift topography, the horizontal extension across the rift boundary faults is 3–9 km. This is a lower bound on the total rift extension because the altimetry does not resolve the topographic relief across the numerous faults that are visible in radar images of the rift floor. The total extension across Devana is approximately 20 km, similar in magnitude to continental rift systems on Earth. Rift flank elevations are up to 3.1 km in the regions nearest the mantle plumes and decay strongly with increasing distance from the plumes, indicating a strong thermal component to the rift flank topography, unlike the situation usually reported for terrestrial rifts. As on Earth, there is also a flexural uplift component to the flank topography. Rift depths are up to 2.5 km below the surrounding plains, with considerable along-strike variability. There is a 600 km lateral offset along Devana Chasma near the mid-point between the two mantle plumes. Devana most likely formed as two distinct rifts due to the horizontal stresses created by outflow from the upwelling plumes. The offset zone formed as a result of the interaction between the two rift tips, which requires that upwelling at the two mantle plumes overlapped in time. 相似文献