Decoding Provenance and Tectonothermal Events by Detrital Zircon Fission‐Track and U‐Pb Double Dating: A Case of the Southern Ordos Basin

Multi-dating on the same detrital grains allows for determining multiple different geo-thermochronological ages simultaneously and thus could provide more details about regional tectonics. In this paper, we carried out detrital zircon fission-track and U-Pb double dating on the Permian-Middle Triassic sediments from the southern Ordos Basin to decipher the tectonic information archived in the sediments of intracratonic basins. The detrital zircon U-Pb ages and fission-track ages, together with lag time analyses, indicate that the Permian-Middle Triassic sediments in the southern Ordos Basin are characterized by multiple provenances. The crystalline basement of the North China Craton (NCC) and recycled materials from pre-Permian sediments that were ultimately sourced from the basement of the NCC are the primary provenance, while the Permian magmatites in the northern margin of NCC and Early Paleozoic crystalline rocks in Qinling Orogenic Collage act as minor provenance. In addition, the detrital zircon fission-track age peaks reveal four major tectonothermal events, including the Late Triassic-Early Jurassic post-depositional tectonothermal event and three other tectonothermal events associated with source terrains. The Late Triassic-Early Jurassic (225–179 Ma) tectonothermal event was closely related to the upwelling of deep material and energy beneath the southwestern Ordos Basin due to the coeval northward subduction of the Yangze Block and the following collision of the Yangze Block and the NCC. The Mid-Late Permian (275–263 Ma) tectonothermal event was associated with coeval denudation in the northern part of the NCC and North Qinling terrane, resulting from the subduction of the Paleo-Asian Ocean and Tethys Ocean toward the NCC. The Late Devonian-early Late Carboniferous (348±33 Ma) tectonothermal event corresponded the long-term denudation in the hinterland and periphery of the NCC because of the arc-continent collisions in the northern and southern margins of the NCC. The Late Neoproterozoic (813–565 Ma) tectonothermal event was associated with formation of the Great Unconformity within the NCC and may be causally related to the Rodinia supercontinent breakup driven by a large-scale mantle upwelling.     

Petrogenesis of the Early Jurassic Nandaling flood basalts in the Yanshan belt, North China Craton: A correlation between magmatic underplating and lithospheric thinning

Integrated geochemical and Sr–Nd–Pb isotopic studies of the Early Jurassic Nandaling flood basalts (NFB) in the Yanshan belt, northern margin of the North China Craton (NCC), are presented in this paper. These sub-alkaline basalts evolved from a more magnesium-rich parental magma through fractional crystallization of olivine and clinopyroxene. The primitive magma of the NFB originated from 2–5% partial melting of spinel to garnet transitional peridotite at about 70–80 km depth in the Mesozoic lithosphere mantle. The NFB contain a distinctive lithospheric component, characterized by Nb (Ta), Th, U and Ti depletions, LREE enrichments, moderate Sr, and low Nd and Pb initial isotopic ratios, as a result of an interaction between lower crust (15–25%) and primitive magma evoked by magmatic underplating at crust–mantle boundary. The Early Jurassic NFB extruded in an intraplate extensional setting related to post-orogenic collapse in the northern margin of the NCC, indicating an event of lithospheric modification earlier than that in the southern margin (Early Cretaceous). The temporal similarity of the Jurassic–Cretaceous mantle-derived mafic rocks to lower crust replacement, and the decoupling of surface shortening with lithospheric thinning during the Late Jurassic–Early Cretaceous, suggest the important role of magmatic underplating and subsequent crust–mantle interaction accompanied by asthenosphere upwelling on the evolution of the Mesozoic lithosphere of the NCC. The correlation between lithospheric thinning and magmatic underplating may be an important process in continental rifting.     

Mafic microgranular enclaves in Late Paleozoic granitoids in the Burgasy quartz syenite massif, western Transbaikalia: Composition and petrogenesis

The paper presents original data on the inner structure, mineralogy, and geochemistry of the Late Paleozoic Burgasy quartz syenite massif in western Transbaikalia and mafic microgranular enclaves (MME) in its rocks. The composition of the mafic microgranular enclaves is close to that of phase-1 monzonitoids of this pluton, but the enclaves are not xenoliths of these rocks but were produced by the crystallization of an individual portion of dispersed hybridized basalt melt. The basaltoid nature of the enclaves follows, first of all, from the relict assemblage of calcic plagioclase (An _73–60) and clinopyroxene and from the magmatic dolerite and microgabbro textures of the rocks. The monzonitoid composition of the enclaves was caused by hybridism, which was responsible for the crystallization of quartz, potassic feldspar, and sodic plagioclase due to the introduction of silica, potassium, and some other components. Hybridism was restricted to a boundary crystallization layer in the deep portion of the magmatic chamber (near its bottom). The scatter of the enclaves throughout the whole volume of the pluton is explained by the density inversion of the hybrid layer and material transfer by convective flows. The mafic enclaves crystallized from basaltic melt of within-plate geochemical type. In spite of intense hybridism, the enclaves preserved typical compositional signatures of mafic magma related to the generation of granites in western Transbaikalia in the Late Paleozoic. The basaltoid nature of the mafic enclaves of the Burgasy Massif testifies that magma was simultaneously generated in the mantle and crust during the development of the Late Paleozoic province in the area.     

Late Triassic Granites From the Quxu Batholith Shedding a New Light on the Evolution of the Gangdese Belt in Southern Tibet

The Gangdese magmatic belt formed during Late Triassic to Neogene in the southernmost Lhasa terrane of the Tibetan plateau. It is interpreted as a major component of a continental margin related to the northward subduction of the Neo-Tethys oceanic slab beneath Eurasia and it is the key in understanding the tectonic framework of southern Tibet prior to the India-Eurasia collision. It is widely accepted that northward subduction of the Neo-Tethys oceanic crust formed the Gangdese magmatic belt, but the occurrence of Late Triassic magmatism and the detailed tectonic evolution of southern Tibet are still debated. This work presents new zircon U-Pb-Hf isotope data and whole-rock geochemical compositions of a mylonitic granite pluton in the central Gangdese belt, southern Tibet. Zircon U-Pb dating from two representative samples yields consistent ages of 225.3±1.8 Ma and 229.9±1.5 Ma, respectively, indicating that the granite pluton was formed during the early phase of Late Triassic instead of Early Eocene(47–52 Ma) as previously suggested. Geochemically, the mylonitic granite pluton has a sub-alkaline composition and low-medium K calc-alkaline affinities and it can be defined as an I-type granite with metaluminous features(A/CNK1.1). The analyzed samples are characterized by strong enrichments of LREE and pronounced depletions of Nb, Ta and Ti, suggesting that the granite was generated in an island-arc setting. However, the use of tectonic discrimination diagrams indicates a continental arc setting. Zircon Lu-Hf isotopes indicate that the granite has highly positive εHf(t) values ranging from +13.91 to +15.54(mean value +14.79), reflecting the input of depleted mantle material during its magmatic evolution, consistent with Mg~# numbers. Additionally, the studied samples also reveal relatively young Hf two-stage model ages ranging from 238 Ma to 342 Ma(mean value 292 Ma), suggesting that the pluton was derived from partial melting of juvenile crust. Geochemical discrimination diagrams also suggest that the granite was derived from partial melting of the mafic lower crust. Taking into account both the spatial and temporal distribution of the mylonitic granite, its geochemical fingerprints as well as previous studies, we propose that the northward subduction of the Neo-Tethys oceanic slab beneath the Lhasa terrane had already commenced in Late Triassic(~230 Ma), and that the Late Triassic magmatic events were formed in an active continental margin that subsequently evolved into the numerous subterranes, paleo-island-arcs and multiple collision phases that form the present southern Tibet.     

Mantle‐derived and crustal melts dichotomy in northern Greece: spatiotemporal and geodynamic implications

Two distinct groups of subduction‐related (orogenic) granitoid rocks, one Jurassic and the other Tertiary, occur in the area between the Vardar (Axios) Zone and the Rhodope Massif in northern Greece. The two groups of granitoids differ in many respects. The first group shows evolved geochemical characters, it is not associated with mafic facies, and evidence of magmatic interaction between mantle‐ and crustal‐derived melts is lacking. The second group has less evolved geochemical characters, it is associated with larger amount of mafic facies, and magmatic interaction processes between mantle‐derived and crustal melts are ubiquitous as evidenced by mafic microgranular enclaves and synplutonic dykes showing different enrichment in K₂O, Ti, and incompatible elements. This kind of magmatism can be attributed to the complex geodynamic evolution of the area. In particular, we suggest that two successive subduction events related to the closure of the Vardar and the Pindos oceans, respectively, occurred in the investigated area from Late Jurassic to Tertiary. We relate the genesis of Jurassic granitoids to the first subduction event, whereas Tertiary granitoids are associated with the second subduction. Fluids released by the two subducted slabs induced metasomatic processes generating a ‘leopard skin’ mantle wedge able to produce mafic melts ranging from typical calc‐alkaline to ultra‐potassic. Such melts interacted in various amounts with crustal calc‐alkaline anatectic melts to generate the wide spectrum of Tertiary granitoids occurring in the study area. Copyright © 2004 John Wiley & Sons, Ltd.     

Geochemistry of middle-late Mesozoic mafic intrusions in the eastern North China Craton: New insights on lithospheric thinning and decratonization

We present detailed geochronological, geochemical and Sr-Nd-Pb isotopic data for late Mesozoic mafic intrusions in the Taili region (western Liaodong Province) of the eastern North China Craton (NCC). We obtained laser-ablation inductively-coupled plasma mass spectrometry U-Pb zircon ages from lamprophyres with ages ranging from 139 to 162 Ma and diorites with clusters of ages at 226 ± 11 Ma, 165 ± 5.8 Ma and 140 ± 4.8 Ma. We interpret the Triassic zircons in diorites to be inherited from the Paleo-Asian Ocean slab. Both the lamprophyres and diorites contain abundant inherited grains (2644–2456 Ma) that were likely derived from the ancient NCC basement, reflecting a contribution from old lower crustal material. Like contemporaneous late Mesozoic mafic rocks in the Jiaodong and Liaodong Peninsula areas of the NCC, the Taili lamprophyres reveal a strong subduction signature in their normalized trace element patterns, including depletion of high field strength elements and enrichment of large ion lithophile elements. The rare-earth element patterns of the Taili intermediate-mafic intrusions are best explained if they were principally derived from partial melting of amphibole-bearing lherzolite in the spinel-garnet transition zone. Slab-derived melts likely contributed to the formation of late Mesozoic mafic rocks along three margins of the craton: due to accretion of the Yangtze Block along the southern margin of the craton, subduction of the Paleo-Asian Ocean along the northern margin, and subduction of the Paleo-Pacific oceanic plate along the eastern margin of NCC. We present a synthesis of the geochemical, spatial, and temporal patterns of magmatic rocks and periods of deformation that contributed to decratonization of the NCC in response to the Mesozoic tectonic evolution of adjacent plates along its northern, southern, and eastern margins.     

Geochemistry, Nd Isotopic Characteristics of Metamorphic Complexes in Northern Hebei： Implications for Crustal Accretion

The middle segment of the northern margin of the North China Craton （NCC） consists mainly of metamorphosed Archean Dantazi Complex, Paleoproterozoic Hongqiyingzi Complex and unmetamorphosed gabbro-anorthosite-meta-alkaline granite, as well as metamorphosed Late Paleozoic mafic to granitoid rocks in the Damiao-Changshaoying area. The -2.49 Ga Dantazi Complex comprises dioritic-trondhjemitic-granodoritic-monzogranitic gneisses metamorphosed in amphibolite to granulite facies. Petrochemical characteristics reveal that most of the rocks belong to a medium- to high-potassium calc-alkaline series, and display Mg^# less than 40, right-declined REE patterns with no to obviously positive Eu anomalies, evidently negative Th, Nb, Ta and Ti anomalies in primitive mantlenormalized spider diagrams, εNd（t）=＋0.65 to -0.03, and depleted mantle model ages TDM=2.78-2.71 Ga. Study in petrogenesis indicates that the rocks were formed from magmatic mixing between mafic magma from the depleted mantle and granitoid magma from partial melting of recycled crustal mafic rocks in a continental margin setting. The 2.44-2.41 Ga Hongqiyingzi Complex is dominated by metamorphic mafic-granodioritic-monzogranitic gneisses, displaying similar petrochemical features to the Dantazi Complex, namely medium to high potassium calc-alkaline series, and the mafic rocks show evident change in LILEs, negative Th, Nb, Ta, Zr anomalies and positive P anomalies. And the other granitiod samples also exhibit negative Th, Nb, Ta, P and Ti anomalies. All rocks in the Hongqiyingzi Complex show right-declined REE patterns without Eu anomaly. The metamorphic mafic rocks with εNd（t） = -1.64 may not be an identical magmatic evolution series with granitoids that have εNd（t） values of ＋3.19 to ＋1.94 and TDM ages of 2.55-2.52 Ga. These granitic rocks originated from hybrid between mafic magma from the depleted mantle and magma from partial melting of juvenile crustal mafic rocks in an island arc setting. All the -311 Ma Late Paleozoic metamorphic mafic rocks and related granitic rocks show a medium-potassium calc-alkaline magmatic evolution series, characterized by high Mg^#, obviously negative Th, Nb, Ta anomalies and positive Sr anomalies, from no to strongly negative Ti anomalies and flat REE patterns with εNd（t） = ＋8.42, implying that the maflc magma was derived from the depleted mantle. However the other granitic rocks are characterized by right-declined REE patterns with no to evidently positive Eu anomalies, significantly low εNd（t） = -13.37 to -14.04, and TDM=1.97-1.96 Ga, revealing that the granitoid magma was derived from hybrid between maflc magma that came from -311 Ma depleted mantle and granitoid magma from Archean to Early Paleoproterozoic ancient crustal recycling. The geochemistry and Nd isotopic characteristics as well as the above geological and geochronological results indicate that the middle segment of the northern margin of the NCC mainly experienced four crustal growth episodes from Archean to Late Paleozoic, which were dominated by three continental marginal arc accretions （-2.49, -2.44 and 311 Ma）, except the 1.76-1.68 Ga episode related to post-collisional extension, revealing that the crustal accretion of this segment was chiefly generated from arc accretion and amalgamation to the NCC continental block.     

Early Cretaceous Magma Mingling in Xiaocuo, Southeastern China Continental Margin: Implications for Subduction of Paleo-Pacific Plate

Magma mingling has been identified within the continental margin of southeastern China.This study focuses on the relationship between mafic and felsic igneous rocks in composite dikes and plutons in this area,and uses this relationship to examine the tectonic and geodynamic implications of the mingling of mafic and felsic magmas.Mafic magmatic enclaves(MMEs) show complex relationships with the hosting Xiaocuo granite in Fujian area,including lenticular to rounded porphyritic microgranular enclaves containing abundant felsic/mafic phenocrysts,elongate mafic enclaves,and back-veining of the felsic host granite into mafic enclaves.LA-ICP-MS zircon U-Pb analyses show crystallization of the granite and dioritic mafic magmatic enclave during ca.132 and 116 Ma.The host granite and MMEs both show zircon growth during repeated thermal events at-210 Ma and 160-180 Ma.Samples from the magma mingling zone generally contain felsic-derived zircons with well-developed growth zoning and aspect ratios of 2-3,and maficderived zircons with no obvious oscillatory zoning and with higher aspect ratios of 5-10.However,these two groups of zircons show no obvious trace element or age differences.The Hf-isotope compositions show that the host granite and MMEs have similar ε_(Hf)(t) values from negative to positive which suggest a mixed source from partial melting of the Meso-Neoproterozoic with involvement of enriched mantlederived magmas or juvenile components.The lithologies,mineral associations,and geochemical characteristics of the mafic and felsic rocks in this study area indicate that both were intruded together,suggesting Early Cretaceous mantle—crustal interactions along the southeastern China continental margin.The Early Cretaceous magma mingling is correlated to subduction of Paleo-Pacific plate.     

Field evidence,mineral chemical and geochemical constraints on mafic-felsic magma interactions in a vertically zoned magma chamber from the Chotanagpur Granite Gneiss Complex of Eastern India

The Nimchak granite pluton (NGP) of Chotanagpur Granite Gneiss Complex (CGGC), Eastern India, provides ample evidence of magma interaction in a plutonic regime for the first time in this part of the Indian shield. A number of outcrop level magmatic structures reported from many mafic-felsic mixing and mingling zones worldwide, such as synplutonic dykes, mafic magmatic enclaves and hybrid rocks extensively occur in our study domain. From field observations it appears that the Nimchak pluton was a vertically zoned magma chamber that was intruded by a number of mafic dykes during the whole crystallization history of the magma chamber leading to magma mixing and mingling scenario. The lower part of the pluton is occupied by coarse-grained granodiorite (64.84–66.61?wt.% SiO₂), while the upper part is occupied by fine-grained granite (69.80–70.57?wt.% SiO₂). Field relationships along with textural and geochemical signatures of the pluton suggest that it is a well-exposed felsic magma chamber that was zoned due to fractional crystallization. The intruding mafic magma interacted differently with the upper and lower granitoids. The lower granodiorite is characterized by mafic feeder dykes and larger mafic magmatic enclaves, whereas the enclaves occurring in the upper granite are comparatively smaller and the feeder dykes could not be traced here, except two late-stage mafic dykes. The mafic enclaves occurring in the upper granite show higher degrees of hybridization with respect to those occurring in the lower granite. Furthermore, enclaves are widely distributed in the upper granite, whereas enclaves in the lower granite occur adjacent to the main feeder dykes.Geochemical signatures confirm that the intermediate rocks occurring in the Nimchak pluton are mixing products formed due to the mixing of mafic and felsic magmas. A number of important physical properties of magmas like temperature, viscosity, glass transition temperature and fragility have been used in magma mixing models to evaluate the process of magma mixing. A geodynamic model of pluton construction and evolution is presented that shows episodic replenishments of mafic magma into the crystallizing felsic magma chamber from below. Data are consistent with a model whereby mafic magma ponded at the crust-mantle boundary and melted the overlying crust to form felsic (granitic) magma. The mafic magma episodically rose, injected and interacted with an overlying felsic magma chamber that was undergoing fractional crystallization forming hybrid intermediate rocks. The intrusion of mafic magma continued after complete solidification of the magma chamber as indicated by the presence of two late-stage mafic dykes.     

华北克拉通北缘三叠纪金矿床地质特征、物质来源与控制因素SCIEI北大核心CSCD

三叠纪是华北克拉通重要的成矿期,三叠纪金矿主要分布在华北克拉通北缘,构成一条近东西向延伸、长约1500km的金成矿带,其中包括乌拉山-大青山、张家口、冀东-辽西、青城子及夹皮沟等多个金矿集中区。华北克拉通北缘三叠纪金矿带的赋矿围岩主要为新太古代-中元古代变质岩系和中生代花岗岩类,金矿床以石英脉型矿化为主,伴随蚀变岩型矿化;中、西段金矿集中区矿化组合表现为金或金钼矿化,东段则以金多金属矿化为主。同位素年代学资料表明,该带金矿主要形成于晚三叠世(240~220Ma);流体包裹体特征表明,成矿流体具中温、低盐度、低密度特征,属于H_(2)O-NaCl-CO_(2)±CH_(4)体系,相分离作用可能是石英脉型金矿金沉淀的主要机制;氢-氧同位素组成进一步表明,成矿流体早期为岩浆水或变质水,后期混入了大气降水。矿石碳、硫、铅、氦-氩同位素及金矿集中区内成矿相关岩体的钕、铪同位素组成表明,华北克拉通北缘三叠纪金矿床的成矿流体和成矿物质均与壳-幔混合作用有关,其中,幔源物质及流体的贡献与区域三叠纪岩浆活动有关,壳源组分的贡献主要来自前寒武纪变质围岩。金矿床形成的构造背景整体上与中亚造山带造山后伸展作用有关:晚三叠世,华北北缘受中亚造山带碰撞后伸展作用的影响,发生岩石圈首次减薄事件,同时发育多条深大断裂及碱性花岗岩-碱性岩的侵入活动,为大规模区域金矿的形成提供了优越条件。金矿带的东段可能同时受扬子克拉通与华北板块碰撞作用的影响,是造成其与中、西段金矿集中区成矿特征有一定差异的主因。     

小兴安岭东南金山屯一带晚三叠世二长花岗岩成因及其地质意义

在小兴安岭东南端金山屯一带,广泛发育近南北向展布的晚三叠世似斑状二长花岗岩岩石组合,岩石中普遍见有暗色微细粒闪长质包体和中-基性脉岩群。对岩体及其包体、中-基性脉岩的宏观、微观特征和地球化学特征的研究表明,包体形态多呈浑圆的外形,显示出明显的塑性流变特点,具典型的岩浆结构包体中见针状磷灰石和含寄主岩钾长石、石英巨晶,具有明显的岩浆混合成因的包体特征;岩体的中-基性脉岩（群）形态多样,与花岗岩的界面或呈小波浪状或呈平直状,并见寄主岩长石斑晶,表现出壳幔混合作用形成的同深成岩墙群特征。该区晚三叠世二长花岗岩具显著的岩浆混合成因特征,其形成可能与碰撞后伸展动力学机制下的基性岩浆底侵作用有关。     

华北克拉通北缘张家口-宣化地区古生代-中生代岩浆构造活动与成矿作用

河北省张家口-宣化地区(张宣地区)位于华北克拉通北缘中段,区内自显生宙以来构造活动频繁,并产出大量岩浆岩和金矿床,是研究华北克拉通北缘岩浆-构造-成矿演化体系的重要对象。本文通过对张宣地区的水泉沟正长岩、响水沟似斑状花岗岩、井儿洼粗安岩-英安岩、象山花岗闪长岩、青羊沟黑云母二长花岗岩和张家口组流纹岩的锆石年龄、Lu-Hf同位素和地球化学组成进行研究,结合前人研究成果,获得区内古生代-中生代岩浆岩的侵位时期主要为海西期(峰值398Ma和373Ma)、印支期(峰值234Ma)和燕山期(峰值143Ma和130Ma)。张宣地区在古生代-中生代经历了古亚洲洋俯冲、华北克拉通破坏及古太平洋俯冲过程。早古生代时期,古亚洲洋向华北克拉通俯冲;到泥盆纪,白乃庙岛弧带和华北克拉通北缘发生弧陆碰撞,张宣地区处于弧陆碰撞后的伸展环境,富集地幔岩浆上涌并经历了地壳的同化混染和分离结晶的共同作用,形成大量碱性岩;二叠纪末期-三叠纪,各微陆块相互碰撞,张宣地区处于碰撞后伸展阶段,地幔岩浆引起加厚下地壳的部分熔融,基性、酸性岩浆混合,导致区内的基性岩与酸性岩共存;侏罗纪-白垩纪时期,华北克拉通发生减薄,形成区内大范围的侵入岩和火山岩。张宣地区产有大量金矿、铅锌矿、银矿及少量铜矿和钼矿,金矿集中产于宣化-崇礼-赤城交界处,而银铅锌多金属矿则成群成带环绕金矿化集中区分布。成矿时间主要为海西期和燕山期,印支期成矿尚未明确,但成矿潜力巨大。根据地质特征和同位素组成,可将张宣地区的金矿床划分为"东坪式"、"小营盘式"和"张全庄式"三类。古生代-中生代各时期岩浆活动对金成矿均有贡献,大部分金矿床与海西期和燕山期岩浆活动联系密切,多期次成矿及成矿叠加是形成张宣地区大量金矿床的重要因素。     

Origin of two contrasting latest Permian–Triassic volcanic rock suites in the northern North China Craton: implications for early Mesozoic lithosphere thinning

New geological, geochronological, and geochemical results on volcanic rocks and cobbles from early Mesozoic sedimentary rocks identify two contrasting latest Permian–Triassic volcanic rock suites in the northern North China Craton (NCC). The early rock suite erupted during the latest Permian–Early Triassic at ca. 255–245 Ma and was probably widely distributed in the northern NCC prior to the Early Jurassic. It comprises rhyolitic welded tuff, rhyolite, and tuffaceous sandstone and is characterized by high contents of SiO₂ and K₂O, moderate initial ⁸⁷Sr/⁸⁶Sr, low negative ε_Nd(t) and ε_Hf(t) values, and old Nd-Hf isotopic model ages. It was likely produced by fractional crystallization of lower crustal-derived magmas due to underplating by lithospheric mantle-derived magmas near the crust–mantle boundary in syncollisional to post-collisional/post-orogenic tectonic settings. The late rock suite, erupted during the Middle–Late Triassic at ca. 238–228 Ma, displays adakitic geochemical signatures and consists of intermediate volcanic rocks such as andesite, trachyandesite, and autoclastic trachyandesite breccia, with minor felsic rocks. This suite is characterized by high Al₂O₃, MgO, Sr, Ba, Cr, V, and Ni concentrations; high Mg# values; low Y and Yb concentrations and high Sr/Y ratios; low initial ⁸⁷Sr/⁸⁶Sr; high negative ε_Nd(t) and ε_Hf(t) values; and young Nd-Hf isotopic model ages. The younger suite was generated by mixing of magmas derived from melting of upwelling asthenosphere, with melts of ancient lower crust induced by underplating of basaltic magmas in an intraplate extensional setting. Strong upwelling of asthenospheric mantle and significant involvement of the asthenospheric mantle materials indicate that the lithospheric mantle beneath the northern NCC was partially delaminated during Middle–Late Triassic time, representing the initial destruction and lithospheric thinning of the northern NCC. Lithospheric thinning and delamination are likely the most important reasons for the Triassic tectonic transition and change of magmatism and deformation patterns in the northern NCC.     

内蒙古解放营子花岗闪长岩岩浆混合机制——来自斜长石和角闪石的矿物化学证据

为揭示华北克拉通北缘中晚三叠世解放营子花岗闪长岩的岩浆混合机制,对寄主岩石和镁铁质包体中斜长石和角闪石开展了电子探针分析.分析结果显示,多斑和少斑包体边部的斜长石斑晶发育An值增加的突变环带,环带的An值为32～46,明显高于核部和边部斜长石的An值(18～31),而核部的An值与寄主岩石中斜长石的An值一致,该特征指...     

西秦岭天水地区晚三叠世柴家庄二长花岗岩及其暗色包体地球化学——岩石成因及岩浆混合作用

晚三叠世花岗岩类在秦岭-大别造山带西端广泛分布,其成因机制及地球动力学背景的研究对于反演华北、扬子两大板块沿秦岭-大别造山带在三叠纪时期的拼合历史具有重要意义.本文选择西秦岭天水地区柴家庄晚三叠世二长花岗岩及其中的暗色包体进行精细的岩石学和地球化学研究.暗色包体中普遍发育针状磷灰石及斜长石捕掳晶,暗示岩浆混合作用;暗色包体具有较低的SiO₂（60.27%~60.38%）、高的Mg#（54~55）和Nb/Ta比值（14.8~16.6）,表明其来源于富集岩石圈地幔的部分熔融作用;寄主二长花岗岩表现出典型埃达克岩的地球化学特征,其富集Sr、Ba,亏损Y和HREE,岩石的Sr/Y比值介于88~98之间,Y/Yb比值介于13~15之间,暗示源区有石榴石残余.结合前人的研究结果,提出柴家庄二长花岗岩可能为增厚的造山带下地壳在碰撞后伸展环境下发生部分熔融作用的产物,可能与晚三叠世时期秦岭造山带的板片断离作用有关     

内蒙古狼山地区石炭纪-三叠纪岩浆作用及其构造意义

华北地块北缘广泛发育石炭纪-三叠纪岩浆岩,岩浆岩的时空展布及反映的构造背景对研究古亚洲洋的俯冲增生作用具有重要的意义.然而,目前的研究集中在华北地块北缘中东部,该期岩浆活动的向西延伸有待深入研究.通过对狼山地区近年来获得的晚古生代-早中生代岩浆岩岩石学、地球化学、锆石U-Pb年龄及Hf同位素数据的综合分析,结果表明该区经历了早石炭世-晚二叠世、中-晚三叠世两期构造岩浆作用.其中,早石炭世-晚二叠世岩浆活动时限在338~251 Ma,岩性主要为辉长岩、角闪辉长岩、闪长岩、石英闪长岩、花岗闪长岩及二长花岗岩,辉长岩类的微量元素蛛网图及稀土元素配分型式与岛弧火山岩的曲线类似,花岗岩类具高Sr（>250×10-6,平均值为425×10-6）低Y（6.89×10-6~24.30×10-6）的特点.中-晚三叠世岩浆活动时限在245~228 Ma,岩性主要为正长花岗岩,花岗岩具高K₂O/Na₂O（1.48~1.58）、低Sr（154×10-6~49×10-6）低Yb（1.01×10-6~1.38×10-6）的特点,稀土配分曲线表现为轻稀土略富集、Eu负异常中等-强（Eu*=0.54~0.23）、重稀土平坦的近似海鸥型,总体反映了后造山花岗岩的地球化学特征.结合构造判别图解及区域地质资料,结果表明狼山地区早石炭世-晚二叠世为俯冲挤压的构造背景,中-晚三叠世则进入了后造山伸展的构造阶段.狼山地区晚古生代-早中生代发育的两期构造岩浆作用与华北陆块北缘中东部（330~265 Ma及250~200 Ma）类似,古亚洲洋的向南俯冲形成了华北陆块北缘近东西向延伸的晚古生代岩浆岩带,华北陆块与其北缘增生造山带拼贴作用的时限为二叠纪末-三叠纪初.      

Neoproterozoic calc‐alkaline peraluminous granitoids of the Deleihimmi pluton,Central Eastern Desert,Egypt: implications for transition from late‐ to post‐collisional tectonomagmatic evolution in the northern Arabian–Nubian Shield

The widely distributed late‐collisional calc‐alkaline granitoids in the northern Arabian–Nubian Shield (ANS) have a geodynamic interest as they represent significant addition of material into the ANS juvenile crust in a short time interval (∼630–590 Ma). The Deleihimmi granitoids in the Egyptian Central Eastern Desert are, therefore, particularly interesting since they form a multiphase pluton composed largely of late‐collisional biotite granitoids enclosing granodiorite microgranular enclaves and intruded by leuco‐ and muscovite granites. Geochemically, different granitoid phases share some features and distinctly vary in others. They display slightly peraluminous (ASI = 1–1.16), non‐alkaline (calc‐alkaline and highly fractionated calc‐alkaline), I‐type affinities. Both biotite granitoids and leucogranites show similar rare earth element (REE) patterns [(La/Lu)_N = 3.04–2.92 and 1.9–1.14; Eu/Eu* = 0.26–0.19 and 0.11–0.08, respectively) and related most likely by closed system crystal fractionation of a common parent. On the other hand, the late phase muscovite granites have distinctive geochemical features typical of rare‐metal granites. They are remarkably depleted in Sr and Ba (4–35 and 13–18 ppm, respectively), and enriched in Rb (381–473 ppm) and many rare metals. Moreover, their REE patterns show a tetrad effect (TE_1,3 = 1.13 and 1.29) and pronounced negative Eu anomalies (Eu/Eu* = 0.07 and 0.08), implying extensive open system fractionation via fluid–rock interaction during the magmatic stage. Origin of the calc‐alkaline granitoids by high degree of partial melting of mafic lower crust with subsequent crystal fractionation is advocated. The broad distribution of late‐collisional calc‐alkaline granitoids in the northern ANS is related most likely to large areal and intensive lithospheric delamination subsequent to slab break‐off and crustal/mantle thickening. Such delamination caused both crustal uplift and partial melting of the remaining mantle lithosphere in response to asthenospheric uprise. The melts produced underplate the lower crust to promote its melting. The presence of microgranular enclaves, resulting from mingling of mantle‐derived mafic magma with felsic crustal‐derived liquid, favours this process. The derivation of the late‐phase rare‐metal granites by open system fractionation via fluid interaction is almost related to the onset of extension above the rising asthenosphere that results in mantle degassing during the switch to post‐collisional stage. Consequently, the switch from late‐ to post‐collisional stage of crustal evolution in the northern ANS could be potentially significant not only geodynamically but also economically. Copyright © 2011 John Wiley & Sons, Ltd.     

Isotopic constraints on crustal architecture and Permo‐Triassic tectonics in New Guinea: Possible links with eastern Australia

New U–Pb zircon ages and Sr–Nd isotopic data for Triassic igneous and metamorphic rocks from northern New Guinea help constrain models of the evolution of Australia's northern and eastern margin. These data provide further evidence for an Early to Late Triassic volcanic arc in northern New Guinea, interpreted to have been part of a continuous magmatic belt along the Gondwana margin, through South America, Antarctica, New Zealand, the New England Fold Belt, New Guinea and into southeast Asia. The Early to Late Triassic volcanic arc in northern New Guinea intrudes high‐grade metamorphic rocks probably resulting from Late Permian to Early Triassic (ca 260–240 Ma) orogenesis, as recorded in the New England Fold Belt. Late Triassic magmatism in New Guinea (ca 220 Ma) is related to coeval extension and rifting as a precursor to Jurassic breakup of the Gondwana margin. In general, mantle‐like Sr–Nd isotopic compositions of mafic Palaeozoic to Tertiary granitoids appear to rule out the presence of a North Australian‐type Proterozoic basement under the New Guinea Mobile Belt. Parts of northern New Guinea may have a continental or transitional basement whereas adjacent areas are underlain by oceanic crust. It is proposed that the post‐breakup margin comprised promontories of extended Proterozoic‐Palaeozoic continental crust separated by embayments of oceanic crust, analogous to Australia's North West Shelf. Inferred movement to the south of an accretionary prism through the Triassic is consistent with subduction to the south‐southwest beneath northeast Australia generating arc‐related magmatism in New Guinea and the New England Fold Belt.     

Timing of Magma Mixing in the Gangdisě Magmatic Belt during the India-Asia Collision： Zircon SHRIMP U-Pb Dating

Abstract  Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdisê giant magmatic belt, within which the Qüxü batholith is the most typical MME‐bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U‐Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±1 Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions. Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge‐scale magma mixing in the Gangdisê belt took place 15–20 million years after the initiation of the India‐Asia continental collision, genetically related to the underplating of subduction‐collision‐induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass‐energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.     

冀东晚古生代东湾子岩体的岩石成因研究

冀东晚古生代东湾子岩体由角闪石岩、少量辉石岩和辉长岩组成.典型的堆晶结构、全岩和镁铁质矿物(透辉石、角闪石)的上凸型稀土分布模式、相容元素含量低且变化范围大(如:角闪石岩中V=296×10-6～673×10-6)的特征表明了岩体的堆晶成因.计算得到的与辉石岩中的透辉石相平衡的熔体具有很高的稀土含量,轻重稀土分馏较为明显,富集大离子亲石元素(如:Sr,Ba,K),亏损高场强元素(如:Nh,Zr,Ti),具有典型的弧岩浆特征.透辉石和角闪石的矿物成分也具有弧岩浆的特征.高钙透辉石、大量的角闪石与黑云母的存在说明母岩浆富水.透辉石在高PH2O的状态下与熔体反应,生成角闪石的结构特征也证明了这一点.结合岩体的球化学特征,认为岩浆来源于富集的含有角闪石的尖晶石橄榄岩的部分熔融,母岩浆具有富水的特征(>3%).考虑到岩体形成时代(～300Ma;Zhao et al.,2007)和地质背景,认为东湾子岩体与位于华北北缘的其它晚石炭-早二叠世的岩体形成于同一构造背景下,都是晚古生代时期古亚洲洋向华北板块之下俯冲的产物.