Zircon U–Pb age and Sr–Nd–Hf isotopic constraints on the age and origin of Triassic mafic dikes,Dalian area,Northeast China     

《International Geology Review》2012,54(2):249-262

Post-orogenic mafic rocks from Northeast China consist of swarms of dolerite dikes. We report a new U–Pb zircon age, as well as whole-rock geochemical and Sr–Nd–Hf isotopic data. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb zircon analysis yielded an age of 210.3 ± 1.5 million years (i.e. Triassic) for these mafic dikes. Most Dalian mafic rocks exhibit low K₂O + Na₂O contents, and span the border between alkaline and calc-alkaline rock associations in the total alkali–silica diagram. The investigated dikes are also characterized by relatively high (⁸⁷Sr/⁸⁶Sr)_i ratios (0.7061–0.7067) and negative ?_Nd (t) (?4.7 to??4.3) and ?_Hf (t) values (?4.1 to??1.1), implying that they were derived from an enriched lithospheric mantle source. The mafic dikes are characterized by relatively low MgO (4.65–5.44 wt.%), Mg^# (41–44), and compatible element content [such as Cr (89.9–125 ppm) and Ni (56.7–72.2 ppm)], which are the features of an evolved mafic magma. No evidence supports the idea that the mafic rocks were affected by significant assimilation or crustal contamination during emplacement. We conclude that the dolerites formed in a post-orogenic extensional setting, related to lithospheric delamination or ‘collapse’ of the Central Asian Orogenic Belt (CAOB), also termed the Xingmeng Orogenic Belt in China.  相似文献   

Geochemical behaviours of chemical elements during subduction-zone metamorphism and geodynamic significance     

《International Geology Review》2012,54(10):1253-1277

ABSTRACT

Seafloor subduction and subduction-zone metamorphism (SZM) are understood to be the very cause of both subduction-zone magmatism and mantle compositional heterogeneity. In this article, we compile geochemical data for blueschist and eclogite facies rocks from global palaeo-subduction-zones in the literature, including those from the Chinese Western Tianshan ultrahigh pressure (UHP) metamorphic belt. We synthesize our up-to-date understanding on how chemical elements behave and their controls during subduction-zone metamorphism. Although the compositional heterogeneity of metamorphic minerals from subducted rocks has been recently reported, we emphasize that the mineral compositional heterogeneity is controlled by elemental availability during mineral growth, which is affected by the protolith composition, the inherited composition of precursor minerals, and the competition with neighbouring growing minerals. In addition, given the likely effects of varying protolith compositions and metamorphic conditions on elemental behaviours, we classify meta-mafic rocks from global palaeo-subduction-zones with varying metamorphic conditions into groups in terms of their protolith compositions (i.e. ocean island basalt (OIB)-like, enriched mid-ocean ridge basalt (MORB)-like, normal [N]-MORB-like), and discuss geochemical behaviours of chemical elements within these co-genetic groups rather than simply accepting the conclusions in the literature. We also discuss the geochemical consequences of SZM with implications for chemical geodynamics, and propose with emphasis that: (1) the traditionally accepted ‘fluid flux induced-melting’ model for arc magmatism requires revision; and (2) the residual subducted ocean crust cannot be the major source material for OIB, although it can contribute to the deep mantle compositional heterogeneity. We also highlight some important questions and problems that need further investigations, e.g. complex subduction-zone geochemical processes, different contributions of seafloor subduction and resultant subduction of continental materials, and the representativeness of studied HP–UHP metamorphic rocks.  相似文献   

Age and geochemistry of the Carboniferous-Permian magmatism and Fe-Ti-V oxide metallogeny in the Eastern Tianshan Orogen,NW China: evidence from the Yaxi mafic-ultramafic complex     

《International Geology Review》2012,54(7):853-867

ABSTRACT

The Eastern Tianshan Orogen (Xinjiang, NW China) in the Central Asian Orogenic Belt (CAOB) is featured by its many Carboniferous-Triassic mafic-ultramafic intrusions and associated magmatic Fe-Ti-V oxide mineralization. In this study, we present the first systematic data comparison on the age and whole-rock geochemistry of the ore-forming mafic-ultramafic complexes at Yaxi, Niumaoquan, Xiangshanxi, and Weiya. Our new age dating on the Yaxi complex indicates that the mineralized gabbro (zircon SHRIMP U-Pb dated 297.3 ± 4.9 Ma) formed in the latest Carboniferous-Early Permian, similar to the diorite (LA-ICP-MS zircon U-Pb dated 308.3 ± 8.6 Ma) and granodiorite (LA-ICP-MS zircon U-Pb dated 304.9 ± 1.7 Ma). The Yaxi complex is the oldest late Palaeozoic mafic-ultramafic intrusion reported so far in the Eastern Tianshan. The mineralized gabbro at Yaxi contains higher average Fe₂O_3T (20.83 wt.%), TiO₂ (5.91 wt.%), and V (523 ppm) contents than its ore-barren counterpart (7.45 wt.%, 0.99 wt.%, and 133 ppm, respectively). These Eastern Tianshan mafic rocks are mildly large ion lithophile element (LILE) enriched and high field-strength element (HFSE) depleted, and with LREE/HREE enrichment (Yaxi: (La/Yb)_N = 2.7 ~ 5.37) and subtle positive Eu anomalies (Yaxi: Eu/Eu* = 0.94 to 3.31). This suggests that the Eastern Tianshan mafic-ultramafic magmas were likely derived from an arc/subduction-modified magma source. The E-W trending crustal-scale faults (e.g. the Aqikkuduk fault) may have acted as magma conduits and controlled the magma emplacement. The spatial-temporal distribution of the Eastern Tianshan Fe-Ti-V ore-forming mafic-ultramafic complexes and their petrologic and geochemical features suggest that the latest Carboniferous-Early Permian magmatic phase was likely emplaced in a collision-related compression setting following the Junggar Ocean closure, whereas the late Early Permian phase may have been related to a post-collisional orogenic setting.  相似文献   

Nd-isotope and geochemistry of an early Palaeoproterozoic high-Si high-Mg boninite–norite suite of rocks in the southern Bastar craton,central India: petrogenesis and tectonic significance     

《International Geology Review》2012,54(13):1596-1615

ABSTRACT

Nd-isotope and lithogeochemistry of an early Palaeoproterozoic high-Si high-Mg boninite–norite (BN) suite of rocks from the southern Bastar craton, central India, are presented to understand their nature, origin, and tectonic setting of emplacement. Various types of evidence, such as field relationships, radiometric metamorphic ages, and the global distribution of BN magmatism, suggest emplacement in an intracratonic rift setting, commonly around 2.4–2.5 Ga. On the basis of geochemistry these high-Si high-Mg rocks are classified as high-Ca boninites, high-Mg norites, and high-Mg diorites. Nd-isotope data indicate that the high-Mg norite and the high-Mg diorite samples are similar, whereas the high-Ca boninites have a different isotopic character. The high-Mg norite and the high-Mg diorite samples have younger T_DM model ages than the high-Ca boninites. Geochemical and Nd-isotopic characteristics of the studied rocks indicate some prospect of crustal contamination; however, the possibility of mantle metasomatism during ancient subduction event cannot be ignored. Trace-element modelling suggests that the high-Ca boninites may have crystallized from a magma generated by a comparatively greater percentage of melting of a lherzolite mantle source than the source for the other two varieties. Furthermore, the high-Ca boninite rocks are most likely derived from an Archaean subduction process (the Whundo-type), whereas the other two types are the products of the interaction of subduction-modified refractory mantle wedge and a plume, around the Neoarchaean–Palaeoproterozoic boundary. The emplacement of the high-Mg norites and the high-Mg diorites may be linked to crustal thickening and associated cratonization at the end of the Archaean.  相似文献   

华南地区中生代岩浆成矿作用的四大问题   总被引：14，自引：1，他引：13  

陈毓川  王登红 《大地构造与成矿学》2012,36(3):315-321

通过对矿床成矿系列30多年的长期研究,认为华南是我国与中生代岩浆岩有关有色、稀土、稀有金属、铀等矿床成矿系列发育最完善的成矿省之一,并且形成了以武夷-云开构造-岩浆-成矿带为中心、向东、西两侧对称分布、成岩成矿时代逐渐变年轻的区域性分带格局。这样的分带格局受到了区域性水平方向构造运动和垂直方向壳幔物质相互作用的共同制约,而壳幔相互作用程度的不同和表壳构造的差异也是华南出现不同成矿系列(亚系列)以及成矿系列叠合的重要原因。  相似文献   

华南构造演化的基本特征   总被引：95，自引：11，他引：84  

舒良树 《地质通报》2012,31(7):1035-1053

华南至少经历了4期区域规模的大陆动力学过程,除新元古代和晚中生代具有活动陆缘背景外,均在板块内部发生并完成。华夏块体是一个以新元古代岩石为主体构成的前南华纪基底,不是稳定的克拉通古陆,经历了聚合-裂解-再聚合的复杂构造演化。志留纪发生的板内碰撞-拼合事件使华夏块体与扬子块体再次缝合,形成真正统一的中国南方大陆。在震旦纪—早侏罗世期间,整个华南基本处于陆内滨海-浅海-斜坡环境,内部没有切穿岩石圈的断层,没有大规模幔源岩浆和火山喷发的记录,多次构造变形与岩浆活动均在统一的华南岩石圈之上进行。经过早—中侏罗世的构造体制转换,才演化成为晚中生代西太平洋活动大陆边缘的一部分。从早到晚,华南岩石圈经历了多期、幕式的生长,以侧向增生为主(块体拼合),垂向生长为辅(岩浆上侵)。到晚中生代,在古太平洋板块俯冲和陆内伸展的背景下,形成了独特的华南盆岭构造。长期的板内构造演化和多期的花岗岩浆活动使华南具有很好的成矿条件,成为各种矿产与资源的富集区。新元古代南华纪和晚中生代晚侏罗世—早白垩世是华南最有利的成矿期,尤以后者矿种最多、储量最大。  相似文献   

Break Up of Australia-India-Madagascar Block, Opening of the Indian Ocean and Continental Accretion in Southeast Asia With Special Reference to the Characteristics of the Peri-Indian Collision Zones   总被引：7，自引：0，他引：7  

S.K. Acharyya 《Gondwana Research》2000,3(4):425-443

Linear belts of Gondwana basins developed in the Indian continent since Late Palaeozoic along favoured sites of Precambrian weak zones like cratonic sutures and reactivated mobile belts. The Tibetan and Sibumasu - West Yunnan continental blocks, that were located adjacent to proto-Himalayan part of the Indian continent, rifted and drifted from the northern margin of the East Gondwanic Indo-Australian continent, during Late Palaeozoic, when the said northern margin was under glacial or cool climatic condition and rift-drift tectonic setting. The Indo-Burma-Andaman (IBA), Sikule, Lolotoi blocks were also rifted and drifted from the same northern margin during Late Jurassic. This was followed by the break-up of the Australia-India-Madagascar continental block during the Cretaceous. The activity was associated with hot spot related volcanism and opening up of the Indian Ocean. The Late Cretaceous and Tertiary phases of opening of the Arabian Sea succeeded the Early Cretaceous phase of opening of the Bay of Bengal, part of the Indian Ocean. The Palaeo- and Neo-Tethyan sutures in Tibet, Yunnan, Laos, Thailand and Vietnam reveal the complex opening and closing history of the Tethys. The IBA block rotated clockwise from its initial E-W orientation because of 90°E and adjacent dextral transcurrent fault movements caused due to faster northward movement of the Indian plate relative to that of Australia. The India-Tibet terminal collision during Early-Middle Eocene initiated Himalayan orogenesis and contemporaneously there was foreland basin development that was accompanied with sporadic but laterally extensive continental-flood-basalt (CFB) type and related volcanism. The Paleogene rocks of the Himalayan foreland basin are involved in tectonism and are mostly concealed under older rocks.

The Mesozoic-Early Eocene ophiolite terrane on IBA does not represent the eastern suture of the Indian plate but occurs as klippe on IBA, caused due to oblique collision between Sibumasu and IBA during Late Oligocene. Post-collisional indentation of Y-shaped Indian continent into the Asian collage produced Himalayan syntaxes, clockwise rotation of the Sibumasu block which was then sutured to the Tibetan and SE Asian blocks, and tectonic extrusion of the Indochina block along the Ailao Shan Red River (ASRR) shear zone. Highly potassic magmatic rocks were emplaced during Late Palaeogene at the oroclinally flexed marginal parts of the South China continental lithosphere. These magmatic bodies were dislocated by the ASRR left lateral shear zone soon afterwards. Petrogenetic and tectonic processes that generated the Eocene CFB volcanics at the Himalayan foreland basin may have also produced Late Palaeogene magmatism from outer parts of the Namche-Barwa Syntaxis. Their site-specific location and time sequence suggest them to be genetically related to the India-Asia collision process and Indian continent's indentation-induced syntaxial buckling. Deep mantle-reaching fractures were apparently produced during India-Asia terminal collision at the strongly flexed leading brittle edge of the Indian continental lithosphere, and possibly later in time at the outer oroclinally bent marginal parts of the rigid South China continental lithosphere, generating typical magma.

The subduction zone that developed along the western margin of IBA due to oblique convergence between the IBA and the Indian plate is still active. The northern end of IBA ultimately collided with the NE prolongation of the Indian continent and was accreted to it during Mio-Pliocene. The Shillong massif was uplifted and overthrust over the Bengal Basin located over its passive margin to the south, whereas, the Eocene distal shelf sediments of IBA were overthrust over the Tertiary shelf of the Indian continent.  相似文献   

Genesis of intermediate igneous rocks at the end of the Sveconorwegian (Grenvillian) orogeny (S Norway) and their contribution to intracrustal differentiation     

Jacqueline Vander Auwera  Michel Bogaerts  Olivier Bolle  John Longhi 《Contributions to Mineralogy and Petrology》2008,156(6):721-743

Abundant ferroan, metaluminous granitoids (970–950 Ma) emplaced at the end of the Sveconorwegian collisional orogeny (1130–900 Ma) are dominated by intermediate to silicic compositions with rare mafic facies. Both 73% fractional crystallization of an amphibole-bearing gabbroic cumulate substracted from the parent mafic composition and 30% non-modal batch melting of an amphibolitic source equivalent in composition to the mafic facies produce a monzodioritic liquid with appropriate trace element composition. A better fit is obtained for the partial melting process. Both processes could have occurred simultaneously to produce mafic cumulates and restites. As there is no evidence for large volumes of dense mafic rocks in the Sveconorwegian upper crust, these dense mafic rocks were probably produced in the lower crust. Formation of these granitoids, thus, contributed to the vertical stratification of the Proterozoic continental crust and also to the transfer of water from the lower crust to the surface.  相似文献   

大兴安岭中生代岩浆岩及岩浆作用研究进展     

杨斌  邓丽军  仲雪辰 《安徽地质》2016,(2):87-91

大兴安岭地区位于中国雄伟版图的东北部,属于兴蒙造山带的东延部分。本区在地质历史时期曾发生过多期次、多阶段岩浆活动,其中尤以中生代岩浆活动最为强烈,分布最为广泛,与成矿关系最为密切。在总结前人资料的基础上,从构造地质背景入手结合锆石同位素测年资料探讨该区中生代岩浆岩和岩浆作用。研究本区中生代岩浆岩及其岩浆作用有助于我们还原其地质历史演化过程并掌握其地质演化发展规律,为该区科研及矿产勘查工作提供借鉴。  相似文献   

冀东黄柏峪—羊崖山地区太古宙岩浆作用和变质作用——SHRIMP锆石U-Pb定年   总被引：4，自引：0，他引：4  

孙会一  颉颃强  刘守偈  董春艳  刘敦一  万渝生 《地质通报》2016,35(1):27-42

报道了冀东黄柏峪—羊崖山地区太古宙变质辉长岩、黑云斜长片麻岩、片麻状二长花岗岩、片麻状富钾花岗岩等不同类型变质岩浆岩(8个样品)的SHRIMP锆石U-Pb定年结果。首次发现3.1Ga二长花岗岩,黑云斜长片麻岩形成时代约为3.0Ga。变质辉长岩的侵入时代很可能为新太古代晚期,存在少量3.2~3.6Ga捕获锆石。几乎所有岩石样品都记录了约2.5Ga的变质锆石年龄。结合前人资料认为,(1)冀东地区新太古代晚期构造热事件十分发育,被认为与地幔软流圈上涌导致的岩浆板底垫托有关;(2)冀东地区中太古代以前的陆壳物质广泛分布,黄柏峪—羊崖山地区很可能存在一古老陆核。  相似文献