桂北元宝山地区超镁铁岩的年代、源区及其地质意义   总被引：8，自引：0，他引：8  

周继彬  李献华  葛文春  刘颖 《地质科技情报》2007,26(1):11-18

桂北元宝山地区超镁铁岩的SHRIMP锆石U-Pb年龄为(841±22)Ma(2σ),与桂北三防-何家湾地区出露的镁铁-超镁铁侵入岩年龄(约825 Ma)接近,表明桂北地区出露的镁铁-超镁铁侵入岩具有基本一致的结晶年龄.超镁铁岩的岩石学和主量元素特征表明超镁铁岩是堆晶岩,其微量元素质量分数较低(＜NMORB),蛛网图上除了Nb、Ta、Zr、Hf亏损外,一般表现为平坦的分配曲线.超镁铁岩εNd(t)的变化范围为-1.0～6.5,表明超镁铁岩的母岩浆遭受了一定程度的地壳混染.元宝山地区超镁铁岩低的w(Th)/w(Nb)比值与原始地幔非常类似,而与大陆弧玄武岩浆的比值明显不同,推测元宝山地区超镁铁岩应形成于板内环境,而不是活动大陆边缘,其形成很可能与导致新元古代Rodinia超大陆裂解的发生于约825 Ma的华南地幔柱有关.  相似文献   

A deformed alkaline igneous rock–carbonatite complex from the Western Sierras Pampeanas, Argentina: Evidence for late Neoproterozoic opening of the Clymene Ocean?   总被引：1，自引：0，他引：1  

C. Casquet  R.J. Pankhurst  C. Galindo  C. Rapela  C.M. Fanning  E. Baldo  J. Dahlquist  J.M. Gonzlez Casado  F. Colombo 《Precambrian Research》2008,165(3-4):205-220

A deformed ca. 570 Ma syenite–carbonatite body is reported from a Grenville-age (1.0–1.2 Ga) terrane in the Sierra de Maz, one of the Western Sierras Pampeanas of Argentina. This is the first recognition of such a rock assemblage in the basement of the Central Andes. The two main lithologies are coarse-grained syenite (often nepheline-bearing) and enclave-rich fine-grained foliated biotite–calcite carbonatite. Samples of carbonatite and syenite yield an imprecise whole rock Rb–Sr isochron age of 582 ± 60 Ma (MSWD = 1.8; Sri = 0.7029); SHRIMP U–Pb spot analysis of syenite zircons shows a total range of ²⁰⁶Pb–²³⁸U ages between 433 and 612 Ma, with a prominent peak at 560–580 Ma defined by homogeneous zircon areas. Textural interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525 ± 7 Ma (Pampean orogeny) and at ca. 430–440 Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic ⁸⁷Sr/⁸⁶Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd₅₇₀ values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neo-proterozoic lower continental crust.  相似文献   

华南新元古代裂谷盆地演化——Rodinia超大陆解体的前奏   总被引：26，自引：0，他引：26  

王剑  刘宝珺  潘桂棠 《矿物岩石》2001,21(3):135-145

沉积学研究表明，华南新元古代沉积盆地具典型裂谷盆地沉积演化特征。代表裂谷盆地早期形成阶段的成因相组合有：冲洪积相组合、陆相（或海相）火山岩及火山碎屑岩相组合、滨浅海相沉积组合、淹没碳酸盐台地及欠补偿盆地黑色页岩相组合；而代表中、后期形成阶段的成因相组合有：滨岸边缘相至深海相组合，冰期冰积岩相组合、碳酸盐岩及碳硅质细碎岩相组合。华南裂谷盆地岩相古地理演化经历了5个重要的时期，整体上反映了一个由陆变海、由地堑－地垒相间盆地变广海盆地、由浅海变深海、盆地上小变大的演化过程。裂谷盆地的形成经历了裂谷基的形成、地幔柱作用与裂谷体的形成，被动沉降（下坳）与裂谷盖的形成三个阶段。华南裂谷盆地的形成演化与Rodinia超大陆在新元古代时期的裂解作用密切相关，它是超大陆解体过程的一个重要组成部分。  相似文献   

构造旋回与大地构造年表   总被引：1，自引：0，他引：1  

任纪舜  徐芹芹  邓平  肖黎微 《地球学报》2016,37(5):528-534

构造旋回的划分是大地构造研究的基础之一。但板块学说兴起以来,一些学者基于均变论的哲学思想,却试图抛弃构造旋回的概念。然而,随着时间的推移,地球系统科学的提出,大规模、多学科地学观测,人们已认识到突变与灾变的重要性,认识到渐变与突变相结合的螺旋式向前发展的旋回演化论,才是更全面、更深刻地认识地质规律的有力武器。在大地构造研究中,一些学者常用地层年表,而不用构造旋回。然而,以生物地层学为主要依据的显生宙地层年表与构造旋回和构造岩浆事件并不完全耦合。这是因为,地层年表是在研究地球表生作用,即岩石圈、水圈、大气圈、生物圈之间相互作用的基础上建立的;而构造旋回则是地球内生作用,即壳、幔、核以及壳、幔、核不同层次间多层圈相互作用的历史记录。一些学者在研究大地构造时,只用同位素年龄表示的构造事件,不使用构造旋回。然而,"事件"只是单个现象的呈现,只是构造发展的片段,旋回则阐明过程,反映事物发展中各"事件"(片段)之间的内在联系,反映事物演化的本质。事实上,威尔逊旋回的建立,已为构造旋回和构造事件之间的联系赋予了全新的科学内涵,这也是地质科学发展过程中,正确处理继承与创新关系的一个光辉范例。一些学者由于对全球造山运动是否是同时性的质疑,认为建立全球统一构造年表是不可能的,也是不必要的。可是,地球作为一个整体,其动态活动应该基本上同时的,在受同一地球动力系统控制的一个大区域内,构造运动在各地虽然不是完全同时,但却大致是同时的。北美、欧洲、亚洲加里东、华力西旋回的各次构造运动基本上可以互相对比,就是证明。既然如此,我们就可以按照优先原则,将早古生代的构造旋回称为加里东旋回,将晚古生代的构造旋回称为华力西(海西)旋回。超大陆和超大陆旋回的提出,深化了构造旋回的研究,同时也为建立构造年表开辟了道路。目前已初步提出古元古代哥伦比亚、中元古代罗丁尼亚、新元古代冈瓦纳和显生宙潘吉亚等几个超大陆旋回,这样,我们便可以用超大陆旋回作为构造年表中最大一级的时间单位,每个超大陆旋回又可进一步分为几个旋回,如潘吉亚旋回可分为加里东、华力西两个旋回。我们相信,随着地质学、地球化学、地球物理学研究的深入,随着对固体地球系统和全球地质构造更加深入、全面、系统的观测研究,不久的将来我们将会像建立显生宙地层年表一样,建立起大区域以至全球的构造年表。  相似文献   

Multiple P–T–d–t paths reveal the evolution of the final Nuna assembly in northeast Australia     

Silvia Volante  Amaury Pourteau  William J. Collins  Eleanore Blereau  Zheng-Xiang Li  Matthijs Smit  Noreen J. Evans  Adam R. Nordsvan  Chris J. Spencer  Brad J. McDonald  Jiangyu Li  Christina Günter 《Journal of Metamorphic Geology》2020,38(6):593-627

The final assembly of the Mesoproterozoic supercontinent Nuna was marked by the collision of Laurentia and Australia at 1.60 Ga, which is recorded in the Georgetown Inlier of NE Australia. Here, we decipher the metamorphic evolution of this final Nuna collisional event using petrostructural analysis, major and trace element compositions of key minerals, thermodynamic modelling, and multi-method geochronology. The Georgetown Inlier is characterised by deformed and metamorphosed 1.70–1.62 Ga sedimentary and mafic rocks, which were intruded by c. 1.56 Ga old S-type granites. Garnet Lu–Hf and monazite U–Pb isotopic analyses distinguish two major metamorphic events (M1 at c. 1.60 Ga and M2 at c. 1.55 Ga), which allows at least two composite fabrics to be identified at the regional scale—c. 1.60 Ga S1 (consisting in fabrics S1a and S1b) and c. 1.55 Ga S2 (including fabrics S2a and S2b). Also, three tectono-metamorphic domains are distinguished: (a) the western domain, with S1 defined by low-P (LP) greenschist facies assemblages; (b) the central domain, where S1 fabric is preserved as medium-P (MP) amphibolite facies relicts, and locally as inclusion trails in garnet wrapped by the regionally dominant low-P amphibolite facies S2 fabric; and (c) the eastern domain dominated by upper amphibolite to granulite facies S2 foliation. In the central domain, 1.60 Ga MP–medium-T (MT) metamorphism (M1) developed within the staurolite–garnet stability field, with conditions ranging from 530–550°C at 6–7 kbar (garnet cores) to 620–650°C at 8–9 kbar (garnet rims), and it is associated with S1 fabric. The onset of 1.55 Ga LP–high-T (HT) metamorphism (M2) is marked by replacement of staurolite by andalusite (M2a/D2a), which was subsequently pseudomorphed by sillimanite (M2b/D2b) where granite and migmatite are abundant. P–T conditions ranged from 600 to 680°C and 4–6 kbar for the M2b sillimanite stage. 1.60 Ga garnet relicts within the S2 foliation highlight the progressive obliteration of the S1 fabric by regional S2 in the central zone during peak M2 metamorphism. In the eastern migmatitic complex, partial melting of paragneiss and amphibolite occurred syn- to post- S2, at 730–770°C and 6–8 kbar, and at 750–790°C and 6 kbar, respectively. The pressure–temperature–deformation–time paths reconstructed for the Georgetown Inlier suggest a c. 1.60 Ga M1/D1 event recorded under greenschist facies conditions in the western domain and under medium-P and medium-T conditions in the central domain. This event was followed by the regional 1.56–1.54 Ga low-P and high-T phase (M2/D2), extensively recorded in the central and eastern domains. Decompression between these two metamorphic events is ascribed to an episode of exhumation. The two-stage evolution supports the previous hypothesis that the Georgetown Inlier preserves continental collisional and subsequent thermal perturbation associated with granite emplacement.  相似文献   

Financial statement as at 31 December 1969     

N. G. Direen  A. J. Crawford 《Australian Journal of Earth Sciences》2013,60(4):491-502

The Tasman Line, a much‐discussed concept in the geology and tectonics of eastern Australia, has a long and chequered history of interpretation. This extends to current debates regarding the age and position of the Tasman Line in Gondwana‐Rodinia reconstructions. We present constraints, from mapping, geochemistry and geophysics, on the interpretation of gravity and magnetic lineaments attributed to the Tasman Line in New South Wales, South Australia, Victoria and Tasmania. These pieces of evidence suggest a protracted and complex latest Neoproterozoic to Carboniferous geological history that produces a variety of geophysical responses, rather than a simple ‘Line’. We also find no evidence of Rodinian breakup age activity responsible for any of the anomalies. In light of these findings, our preference is that the Tasman Line concept be abandoned as misleading, especially with regard to models of Rodinia‐Gondwana breakup, which must have occurred elsewhere, possibly well to the east. Instead, the rocks preserved in the westernmost part of the Tasmanides are consistent with previously proposed ‘Southwest Pacific’‐style models for Neoproterozoic continental breakup, margin formation and reaccretion of continental fragments in the Early Palaeozoic.  相似文献   

塔里木盆地碎屑锆石年龄分布对前寒武纪基底的指示   总被引：7，自引：0，他引：7  

邬光辉  孙建华  郭群英  唐涛  陈志勇  冯晓军 《地球学报》2010,31(1):65-72

应用碎屑锆石LA-ICP-MS U-Pb定年方法研究塔里木盆地前寒武纪基底与超大陆的关系, 对盆地内部不同地区井下11个碎屑岩样品进行锆石年代学分析。塔里木盆地南部与北部分别检测到早元古代、中元古代产生的物源, 结合周边造山带测年资料分析佐证了早中元古代塔里木南北块体演化有差异, 北部大量的中元古代早期年代数据可能预示塔北微块体存在与Columbia超大陆裂解时间相近的构造－热事件。南北塔里木在新元古代早期才发生碰撞拼合形成统一的基底与演化进程, 所有样品都检测到南华纪年龄数据证实塔里木板块及其周缘在此期发生大规模裂解事件, 南华纪大规模火成岩活动形成了盆地显生宙碎屑岩最主要的蚀源, 塔里木板块存在与Rodinia超大陆裂解时间相当的构造－热事件。碎屑锆石测年资料为研究塔里木板块与超大陆的关系提供了来自盆地内部的证据。  相似文献   

扬子地台西缘对Rodinia形成期地质响应   总被引：7，自引：0，他引：7  

王康明  阚泽忠 《华南地质与矿产》2001,(4):22-27

扬子地台西缘冕宁－会理地区在中新元古代Rodinia形成期地质响应强烈，地质记录丰富，在中元古代时期，本区自北而南、自东而西由克拉通边缘盆地演变陆缘拗陷盆地（南部）和陆间裂谷盆地（西部）；自新元古代以来，盆地构造演化分异更为明显，其北部会理天宝山地区形成岛弧（906Ma），而冕宁地区演变为弧后盆地，同时伴有广泛低绿片岩相区域动力变质，岛弧南部会理菜子园、西南部盐边荒田地区产生地块碰撞拼贴，形成混杂岩带（856Ma）；西侧形成双成岩带（800．9－815Ma），沿该岩带产生高绿片岩相－麻粒岩相区域低压热流变质；随汇聚继续向陆块推进，产生新生火山弧（812Ma），并相继产生弧－陆碰撞，导致S型岩浆侵位（669－687Ma）。至此，本区陆块汇聚作用结束，至晚震旦世，重新拗陷转入被动大陆边缘盆地演化时期。  相似文献   

Palaeomagnetic constraints on the position of the Kalahari craton in Rodinia     

C. McA. Powell  D. L. Jones  S. Pisarevsky  M. T. D. Wingate 《Precambrian Research》2001,110(1-4)

A comparison of late Mesoproterozoic palaeomagnetic poles from the Kalahari craton and its correlative Grunehogna craton in East Antarctica shows that the Kalahari–Grunehogna craton straddled the palaeo-Equator and underwent no azimuthal rotation between ca. 1130 and 1105 Ma. Comparison of the Kalahari palaeopoles with the Laurentia APWP between 1130 and 1000 Ma shows that there was a latitudinal separation of 30±14° between Kalahari and the Llano–West Texas margin of Laurentia at ca. 1105 Ma. The Kalahari craton could have converged with southwestern Laurentia between 1060 and 1030 Ma to become part of Rodinia by 1000 Ma. In Rodinia, the Kalahari craton lay near East Antarctica with the Namaqua–Natal orogenic belt facing outboard and away from the Laurentian craton.  相似文献   

Structure and Evolution of the East Antarctic Lithosphere: Tectonic Implications for the Development and Dispersal of Gondwana   总被引：1，自引：0，他引：1  

Masaki Kanao  Masahiro Ishikawa  Mikiya Yamashita  Katsutada Kaminuma  Larry D. Brown   《Gondwana Research》2004,7(1):31

Lithospheric evolution of the Antarctic shield is one of the keystones for understanding continental growth during the Earth's evolution. Architecture of the East Antarctic craton is characterized by comparison with deep structures of the other Precambrian terrains. In this paper, we review the subsurface structure of the Lower Paleozoic metamorphic complex around the Lützow-Holm area (LHC), East Antarctica, where high-grade metamorphism occurred during the Pan-African orogenic event. LHC is considered to be one of the collision zones in the last stage of the formation of Gondwana. A geoscience program named ‘Structure and Evolution of the East Antarctic Lithosphere (SEAL)’ was carried out since 1996-1997 austral summer season as part of the Japanese Antarctic Research Expedition (JARE). Several geological and geophysical surveys were conducted including a deep seismic refraction/wide-angle reflection survey in the LHC. The main target of the SEAL seismic transect was to obtain lithospheric structure over several geological terrains from the western adjacent Achaean Napier Complex to the eastern Lower Paleozoic Yamato-Belgica Complex. The SEAL program is part of a larger deep seismic profile, LEGENDS (Lithospheric Evolution of Gondwana East iNterdisciplinary Deep Surveys) that will extend across the Pan-African belt in neighboring fragments of Gondwana.  相似文献