The Middle Jurassic Yungang Formation in the Datong Basin, located in North China, is a prime example of braided fluvial depositional systems, offering an alternative to the homogeneous subsurface oil and gas reservoirs prevalent across the country. In this study, mineralogical, petrographic, and geochemical analyses were conducted to identify the type and extent of diagenesis and its evolution in the sandstones of the Yungang Formation. The sandstones primarily consist of medium-grained, moderately sorted lithic arkose and feldspathic litharenite, featuring secondary dissolution pores as their dominant pore type. During the eodiagenetic stage, the primary processes include (i) mechanical compaction; (ii) cementation by early calcite, dolomite, limonite, chlorite and kaolinite, and (iii) feldspar dissolution by leaching from atmospheric precipitation. Mesodiagenetic processes include (i) further mechanical and chemical compactions; (ii) cementation by late calcite and dolomite; (ii) kaolinite and illitization of kaolinite; (iv) quartz overgrowth; and (v) feldspar dissolution. Compaction and carbonate cementation during both diagenetic stages are the primary factors controlling porosity reduction. Whereas, feldspar dissolution enhances porosity by creating valuable secondary pore spaces. Therefore, the relatively high-quality sandstones in the Yungang Formation are characterized by coarser-grained with better sorting and a high feldspar content. This research provides valuable diagenetic insights for the exploration and development of high-quality reservoirs for oil and gas resources.

Regional heat flow provides a direct surface indication of the thermal state and energy balance of the lithosphere. Heat flux in the Tibetan Plateau remains poorly studied due to the lack of adequate information on heat flow. In this study, we investigated granitoids from the Gonghe-Guide district located in the NE Tibetan Plateau, which have important significance as hot and dry rocks with potential for geothermal resources. Samples from granitoid rocks as well as felsic dikes were collected from this area, and their geochemical data were combined with regional geophysical and drilling core data to evaluate a high-heat-flow anomaly. Our data show that granitoid rocks, including granodiorite, monzogranite, and syenogranite, crystallized at ca. 253−240 Ma, while felsic dikes formed ca. 230 Ma. The former were emplaced during the oceanic subduction process, whereas the latter formed in the syncollisional stage associated with the closure of the paleo-Zongwulong Ocean. Geochemically, these granitoid rocks are metaluminous to slightly peraluminous, with an average differentiation index (DI) value of 80, and they are classified as weakly to moderately fractionated I-type granites. The felsic dikes are peraluminous with high DI values (average of 95), typical of highly fractionated I-type granites. In terms of their high K and especially U and Th abundances, the calculated radioactive heat generation produced by the granodiorite, monzogranite, syenogranite, and felsic dikes is 1.85, 2.91, 6.85, and 3.02 μW/m3, respectively. Their moderate to high heat production generates a local heat-flow anomaly of 14.8−22.2 mW/m2 above the regional value of subduction zones, accounting for 11%−18% of the total regional heat flow. In combination with regional magnetotelluric data, the high-heat-flow anomaly may be attributed to an additional heat-flow contribution from a partial melt layer beneath this region. Furthermore, there is a significant positive correlation between the radioactive heat generation and magmatic fractionation, indicating that the enrichments of heat-producing elements are controlled by fractional crystallization and subsequently source composition. The granitoid rocks with high heat generation correspond to the large-scale intermediate-felsic magmatism during the subduction stage. We propose a model wherein a continuous subduction process during the closure of the paleo-Zongwulong Ocean and protracted cooling and crystallization processes resulted in the enrichment in heat-producing elements.

The Western Qinling Orogen is marked by secular Triassic magmatism, a thorough understanding of the mechanism of which could provide critical insights into the reconstruction of the Palaeo-Tethys tectono-magmatic activity. Here, we present new geochemical, geochronological and Lu-Hf isotopic data for three batholiths and review regional data. These batholiths have similar rock assemblages (mainly granodiorite and monzogranite), which are characterized by dominantly plagioclase, quartz, and K-feldspar, subsequently amphibole and biotite. Zircon U-Pb data reveal that they represent the long-duration magmatism during the Triassic (ca. 251–223 Ma). Mineralogical characteristics and geochemical affinities manifest that these rocks in the Zeku district can be explicitly delineated as high-K, calc-alkaline, weakly fractionated I-type granites. They yield significantly negative εHf(t) values ranging from −12.81 to −1.26 with old two-stage mantle depleted model ages between 2054 and 1319 Ma. In tandem with Th/Nb (0.98), Th/La (0.39) and La/Nb (2.40) ratios and moderate pressure conditions (ca. 7–10 kbar), the studied granites were derived from partial melting of the Middle Paleoproterozoic to Middle Mesoproterozoic lower crust source region with minor mafic hydrous magma addition. Our new understandings, in conjunction with the temporal-spatial distribution characteristics of magmatism in the West Qinling Orogen, as well as the regional tectonic evolution, suggest that the superimposed orogeny evolved from the northward subduction of the Palaeo-Tethys Ocean (264–225 Ma) through syn-collision (225–215 Ma) to post-collision (beginning at ca.215 Ma) between the North China Craton and South China Block. In this scenario, at the convergent continental margin, the oceanic plate may have undergone melting producing the melts parental to the Zeku granites.

The central Inner Mongolia stretches across the Central Asian Orogenic Belt and northern margin of the North China Craton, where magmatic Cu-Ni sulfide deposits are widely distributed. The Kebu Cu-Ni sulfide deposit,located in the southwest part of the Bayan Obo rift zone in central Inner Mongolia, is a newly discovered high grade Cu-Ni deposit. It is important to determine the formation age of the Kebu mafic-ultramafic intrusion and identify its petrogenesis and mineralization process, so as to guide the deep prospecting breakthrough of the Kebu deposit and mineralization evaluation of similar mafic-ultramafic intrusions within the region. The Kebu intrusion is mainly composed of dominant peridotites and ore-bearing gabbros, both of which show enrichment of light rare earth elements, Rb, Sr, Ba but depletions of heavy rare earth elements, Nb and Ta. The olivine-gabbro of the Kebu pluton yields a LA-ICP-MS zircon U-Pb weighted.mean age of 267. 5 +/- 1. 8Ma, indicating that it was generated by Middle Permian magmatism. The zircon epsilon(Hf)(t)values, (Sr-87/Sr-86)(i) values and epsilon(Nd)(t)values of the Kebu intrusion range from - 4. 67 similar to 2. 84,0. 7062 similar to 0. 7071 and -10. 6 similar to - 5. 65, respectively. PGE geochemical characteristics show that the Kebu ore samples have relatively low Ni/ Cu values and high Pd/ Ir and Cu/ Pd values. The above suggests that the Kebu intrusion was formed under a post-collision extensional setting after the closure of the Paleo-Asian Ocean. The source magma was high Mg basaltic magma that derived from the subducted-metasomatic EMI type lithospheric mantle and experienced crustal material mixing during emplacement process. It is worth noting that the addition of crustal sulfur played a key role in promoting sulfide segregation and final mineralization of the Kebu mafic-ultramafic magma. Combining with the latest prospecting finding,we propose that the Kebu deposit has high potential for Cu-Ni mineralization in its deep section,and the later stage ultramafic rocks and deep magma channel should be the focus of the following mineral exploration work.

内蒙古中部地区横跨中亚造山带与华北陆块北缘,区内广泛分布岩浆铜镍硫化物矿床(点).额布图铜镍硫化物矿床是区域规模较大、品位较高的岩浆铜镍硫化物矿床之一.以额布图铜镍硫化物矿床中含长橄榄辉石岩为主要研究对象,开展了系统的矿物学、岩相学、矿相学、锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素等方面的研究,探讨了额布图镁铁—超镁铁质岩体的成岩成矿时代及岩石成因;在此基础上,综合区域地质资料简要分析了矿床找矿潜力,为实现进一步铜镍找矿突破提供指导.结果表明:额布图镁铁-超镁铁质岩体中含长橄榄辉石岩LA-ICP-MS锆石U-Pb年龄为(326.0±2.1)Ma,属早石炭世,形成于古亚洲洋向华北陆块俯冲的岛弧环境.含长橄榄辉石岩SiO2含量(质量分数,下同)为44.62％～55.81％(平均含量为51.60％),MgO含量为27.45％～33.10％(平均含量为30.32％),CaO含量为1.15％～2.22％(平均含量为1.61％);具有轻稀土元素富集、重稀土元素亏损的右倾型球粒陨石标准化稀土元素配分模式以及Eu弱负异常;Sr-Nd同位素地球化学研究结果表明,额布图镁铁—超镁铁质岩体(87Sr/86Sr)i值为0.708 5～0.712 3(平均值为 0.710 6),(143Nd/144 Nd)i值为 0.511 7～0.511 8(平均值为 0.511 8),εNd(t)值为-10.57～-8.07(平均值为-8.91).综合上述研究,额布图镁铁—超镁铁质岩体的原始岩浆为经历了俯冲板片流体交代的富集岩石圈地幔部分熔融的产物,原生岩浆主要为高镁玄武质岩浆,同时在上升侵位过程中经历了较强的地壳物质混染.由于地壳硫的加入以及富硅地壳混染,促进了硫化物熔离成矿.结合区域地质资料及最新探矿工程控制情况,额布图镁铁—超镁铁质岩体深边部有较好的找矿潜力,应将理清岩浆流动方向、寻找隐伏岩体及深部岩浆通道作为下一步找矿重点.

The Gonghe geothermal basin is situated in the westernmost part of the western Qinling orogen and possesses the supreme potentials to explore and develop hot dry rock (HDR) geothermal resources in China. The basal rock of HDR reservoir in Gonghe basin is composed of granitoids. In this contribution, in order to constrain the formation mechanism of the Gonghe HDR, granitic samples from outcropping have been collected and drilling core samples data from the archives also been compiled. The studied results show that the obtained zircon U-Pb ages of 255.1 +/- 1.9 Ma and 253.9 +/- 2.6 Ma for granodiorite and monzogranite, respectively. All granitoids from both outcropping and drilling core have the similar rock associations and their major and trace elements possess the consistent evolved patterns, such as relative enrichment of LILEs (e.g., K, Rb), depletion of HFSEs (e.g., Nb, Ti), and negative Eu anomalies (0.32-0.66), indicating that they share the same magma sources and evolutional processes. And they have the affinity of I-type granites. They were derived from the mixture of partial melting of metabasaltic rocks in the lower crust and a small amount of mantle-derived magma and formed in a subductionrelated setting relative to the southward subduction of the Zongwulong oceanic crust beneath the west Qinling terrane. The heat production values of rocks around the Gonghe basin were calculated and all basal granitic rocks ranges from 0.35 to 8.51 mu W/m3, yielding an arithmetic mean value of 1.97 mu W/m3, indicating that the radioactive heat generation capacity of granitoids in the Gonghe basin is slightly lower. The HDR reservoir in the Gonghe basin was probably due to an allied thermal effect of the radiogenic heat production in the thickening continental crust and the heat contributed by a deep magma chamber below the basin. The early Triassic granitoids with a higher thermal conductivity serve as the conductive medium of the geothermal heat; whilst the sedimentary rocks marked by lower thermal conductivity above the granitic batholiths act as the reservoir cap. This contribution provides a relatively rational understanding for the mechanism of the HDR reservoir in Gonghe geothermal basin from the petrological and geochemical perspectives, which is conducive to the geothermal potential assessment and estimation, and to-be implementation of the Enhanced Geothermal System demonstration project in China.

Precise timing of granitoids and constraints of their magma sources are critical to understanding the subduction–collision tectonic evolution of the Altun orogenic belt (AOB), a vital part of the Qinghai-Tibet plateau in northwestern China. We provide in-situ zircon U–Pb age, Hf isotopic composition and whole-rock geochemistry of the Yusupualeke granitic pluton in the South Altun orogenic belt (SAOB), an integral unit of the AOB, to determine the tectono-magmatic evolution of the SAOB at early Palaeozoic. The Yusupualeke granitic pluton comprises the medium-coarse grained porphyritic monzogranite and medium-fine grained granodiorite. The monzogranite sample yielded a weighted mean 206Pb/238U age of 476.8 ± 3.6 Ma (MSWD = 0.59), while the granodiorite yielded a weighted mean 206Pb/238U age of 453.2 ± 4.7 Ma (MSWD = 0.013). Zircon U–Pb ages suggest that the subduction–collision process of the SAOB remained from the middle stage of the early Palaeozoic to the end. Both of the studied granitoids belong to metaluminous to weakly peraluminous series and show typical I-type granite characteristics with depletions in Ba, Nb, Sr, P, and Ti, and enrichments in light rare earth elements (LREEs), Rb, Th, K, and slightly negative Eu anomalies. Based on the geochronological data and regional geological background, we believe that the porphyritic monzogranites were formed during the northward subduction process of the South Altun ocean (SAO), while the granodiorites were formed during the tectonic regime transition stage. Besides, combing the previous research achievements with our newly obtained data, we put forward a new division and geodynamic model of the early Palaeozoic tectono-magmatic evolution for the South Altun orogenic belt.

The Xiangpishan complex in the Zongwulong‐Qinghainanshan Tectonic Belt, Northeast (NE) Tibetan Plateau, is a composite concentric pluton consisting of a felsic core (granodiorite) surrounded by quartz diorite in the middle to diorite and minor gabbro at the margin with locally less volume of monzogranite. Many dioritic enclaves are unevenly distributed within host granitoids. We evaluate the petrogenesis of the complex by geochemical, geochronological, and Hf isotopic data in tandem with regional data in the belt. The results show that felsic rocks were emplaced during the Late Permian (ca. 262–256 Ma); whilst gabbros yielded a younger age of ca. 249 Ma. As the hybrid phase from mixing between felsic and mafic magmas, enclaves and diorites have analogous ages (ca. 257–254 Ma) to both. Zircons from gabbro and enclaves are marked by higher εHf(t) value up to +1.82; whilst granodiorites have lower εHf(t) value of −5.48, consistent with hybrid diorites possessing intermediate εHf(t) values of −3.14 to 0.34. Furthermore, the quantitative calculation from Mass Balances Modelling suggests that the mass of mafic magma (ca. 67%–79%) is involved to achieve the hybridization. Geochemically, these rocks crystallized from calc‐alkaline magma with different sources, but demonstrated consistent arc‐like signatures, as they are enriched in large‐ion lithophile elements and light rare earth element (LREE), and depleted in high‐ field‐strength elements and heavy rare earth element (HREE). Besides, they present negative Nb–Ta anomalies together with significant P and Ti troughs. Finally, an evolutional model has been proposed that the asthenosphere‐lithosphere interaction played an important role during the emplacement of the complex, where the limited volumes of mantle‐derived melt act as the suppliers of heat and mass (mainly volatile components) to induce partial melting of the juvenile mafic lower crust and mixed (or mingled) with the produced crust‐derived magma during the oceanic subduction, which led to the generation of diorites as well as mafic microgranular enclaves.

The western Gonghe basin in the NE Tibetan Plateau, witnessed extensive magmatism during the Triassic, whereas only few magmatic flare-up events occurred during the Permian. Understanding the geodynamic setting of these magmatic pulses is important in the reconstruction of the Paleo-Tethys tectonic history. In this contribution, we present in-situ zircon U-Pb geochronological and Lu-Hf isotopic data, as well as whole-rock major and trace elements data from monzogranite and syenogranite dyke in the western Gonghe region to constrain their petrogenesis and tectonic implications. Zircon U-Pb data show that the monzogranite (253-260 Ma) and syenogranite dyke (247-261 Ma) were formed during the Late Permian, rather than the Jurassic as presumed in previous studies. Mineralogical characteristics and geochemical affinities reveal that these rocks are high-K calcalkaline, metaluminous to weakly peraluminous (ASI = 0.95-1.02), moderately-highly fractionated (DI = 81-95) I-type granites. The major and trace element characteristics (including Mg#, Ni, Cr, Zr/Hf, Nb/Ta, and Th/U contents), together with the zircon epsilon Hf(t) values (-5.90 to 1.22, TDMC = 845-1250 Ma) and 176Hf /177Hf ratios (0.282481 to 0.282674) suggest that the magmas were derived through partial melting of the Early Mesoproterozoic metagreywacke in the lower crust with minor juvenile crust addition. Extensive fractional crystallization of plagioclase and subordinate K-feldspar as well as apatite is inferred. Our findings in this study, in conjunction with those from previous studies, suggest that the magmatic flare-up event during the Late Permian in the western Gonghe area is related to local extension concomitant with the break-off of the subducting slab associated with the northward subduction of the Paleo-Tethys oceanic lithosphere.

[研究目的]玉苏普阿勒克塔格花岗岩体位于阿尔金造山带南部茫崖蛇绿混杂岩带内,主要由中粗粒似斑状黑云二长花岗岩及中细粒含斑黑云二长花岗岩组成.玉苏普阿勒克塔格岩体的形成时代、成因类型和岩浆物质来源尚不明确,制约了我们进一步认识该岩体形成的地球动力学背景以及南阿尔金造山带早古生代构造演化过程.[研究方法]因此,本文对玉苏普阿勒克塔格岩体进行了岩石学、锆石U-Pb年代学、全岩地球化学、黑云母矿物化学及Hf同位素组成等方面的研究.[研究结果]锆石U-Pb年代学研究结果表明该岩体中粗粒似斑状黑云二长花岗岩的锆石U-Pb加权平均年龄为451～447 Ma.结合前期工作获得该岩体中细粒含斑黑云二长花岗岩的年龄(430～423 Ma),笔者认为玉苏普阿勒克塔格花岗岩体属于早古生代岩浆活动的产物.黑云母矿物化学研究结果表明,玉苏普阿勒克塔格岩体形成于温度较低压力较高环境.根据玉苏普阿勒克塔格岩体两期花岗岩的矿物组成、全岩地球化学特征及形成的物理化学环境,认为该岩体属于I型花岗岩.Hf同位素组成研究结果表明,玉苏普阿勒克塔格岩体两期花岗岩具有相似的Hf同位素组成,暗示它们具有相似的物质来源:源岩以新生地壳的部分熔融为主,在侵位过程中经历了部分古老地壳物质的混染.[结论]综合玉苏普阿勒克塔格花岗岩体的形成时代、成因类型、物质来源,结合区域构造演化资料,本文认为玉苏普阿勒克塔格岩体形成于与南阿尔金洋北向俯冲有关的活动大陆边缘环境.

The Altun orogenic belt (AOB) was the site of complex subduction of oceanic crust and continental collision during the Paleozoic. The North Altun ophiolitic mélange belt (NAB) is a one of the key tectonic units of the AOB and contains abundant subduction- and collision-related rocks. In this paper, we report the petrography, zircon U–Pb ages, geochemistry, and zircon Hf isotopes of the Bashikaogong S-type granitic rocks from the North Altun ophiolitic mélange belt (NAB) to constrain their petrogenesis and tectonic setting. The granitic rocks consist of three types of granites, i.e., (1) gray, medium- to coarse-grained porphyritic granite; (2) gray, medium-grained granite; and (3) pink, medium- to coarse-grained granite. Zircon U–Pb dating yielded ages of 483–477, 458–453, and 447–445 Ma for type 1, type 2, and type s3 granites, respectively. All the three types of granites share similar strongly peraluminous (A/CNK > 1.1), contain muscovite mineral, have K2O/ Na2O ratios of > 1, and display negative zircon εHf(t) values, which are similar to typical S-type granites. On the basis of our data and results of previous studies, we infer that type 1 granites (483–477 Ma) are related to subduction of North Altun oceanic lithosphere, type 2 granites (458–453 Ma) are syn-collision granites related to continental collision between the Central Altun and Dunhuang Blocks, and type 3 granites (447–445 Ma) are from the late-collision stage. The Bashikaogong S-type granitic rocks recorded early Paleozoic subduction and collision in the North Altun region and were generated by the partial melting of the protolith of the metasedimentary Paleoproterozoic–Mesoproterozoic basement in the CAB due to the collapse of the overthickened subduction orogen.

AbstractThe South Altyn Orogenic Belt (SAOB) is one of the most important orogenic belts in NW China, consisting of the South Altyn Continental Block and the Apa–Mangya Ophiolitic Mélange Belt. However, its Palaeozoic tectonic evolution is still controversial. Here, we present petrological, geochemical, zircon U–Pb and Lu–Hf isotopic data for the Mangya plutons with the aim of establishing the Palaeozoic tectonic evolution. We divide the Early Palaeozoic magmatism in the Apa–Mangya Ophiolitic Mélange Belt into four episodes and propose a plate tectonic model for the formation of these rocks. During 511–494 Ma, the South Altyn Ocean (SAO) was in a spreading stage, and some shoshonite series, I-type granitic rocks were generated. From 484 to 458 Ma, the oceanic crust of the SAO subducted northward, accompanied by large-scale magmatic events resulting in the generation of vast high-K calc-alkaline series, I-type granitic rocks. During 450–433 Ma, the SAO closed, and break-off of the subducted oceanic slab occurred, with the generation of some high-K calc-alkaline series, I–S transitional type granites. The SAOB was in post-orogenic extensional environment from 419 to 404 Ma, and many A-type granites were generated.

The Altun orogenic belt, located on the northern margin of the Tibetan Plateau, records the assembly and breakup of the Rodinia supercontinent. In this paper, we report the petrography, zircon U–Pb ages and Hf isotope data, and bulk geochemistry of the Hongliugou alkali feldspar granites from the Altun orogenic belt to constrain their petrogenesis and tectonic implication. Zircon U–Pb dating yielded ages of 857–851 Ma, interpreted as the emplacement ages of the granites. The granites are metaluminous; have high SiO2, K2O, and rare‐earth element (REE) contents; low CaO and P2O5 contents; high FeOt/MgO ratios; and high 10,000 × Ga/Al values. They show marked depletion in heavy REEs, enrichment in light REEs, and pronounced negative Eu anomalies. These rocks are enriched in high‐field‐strength elements, depleted in Ba, Sr, P, and Ti, and lack Nb and Ta anomalies. These petrological and geochemical characteristics are consistent with those of A‐type granites. The samples plot in the A1‐type field in a discrimination diagram for A‐type granites. Zircon εHf(t) values vary from +1.76 to +7.40 with two‐stage Hf model ages of 1.27 to 1.63 Ga, implying that the granites were derived mainly from juvenile crust. On the basis of these and previous results, we propose that the Hongliugou alkali feldspar granites formed in an intraplate rift setting related to the initial breakup of Rodinia.

南阿尔金造山带位于柴达木盆地和祁连-昆仑造山带之间,是一条重要的大陆俯冲-碰撞造山带,带中分布的大量早古生代花岗岩蕴含着造山带构造演化的重要信息.茫崖A型碱长花岗岩对限定南阿尔金进入造山后伸展环境的时限以及壳幔相互作用具有指示意义,然而该岩体的成因类型、物质来源和形成的构造环境缺乏详细研究.因此,本文利用岩相学、岩石地球化学、LA-ICP-MS U-Pb年代学和Lu-Hf同位素分析对碱长花岗岩进行系统的研究,并探讨岩浆活动对造山带构造演化的响应.碱长花岗岩显示高硅、富铁、富碱、贫钙和镁的特点,并强烈亏损Ba、Sr、P、Eu和Ti,属于A2型花岗岩;岩体的结晶年龄为403～424Ma,是中—新元古代新生地壳(新生长英质物质或钙碱性花岗岩类)部分熔融的产物,岩浆源区可能存在少量富Ca斜长石残留相;南阿尔金造山带在424M a之后进入造山后的伸展环境,不同块体之间的均衡调整导致深部幔源物质持续上涌,造成地壳的部分熔融,形成了这一期A型花岗岩.

The Altun orogenic belt in northwest China is part of the northern margin of the Tibetan Plateau. The North Altun ophiolitic melange belt is an important tectonic unit within the Altun orogenic belt that contains voluminous early Paleozoic granitoids. In this study, we report the petrological features, geochemical compositions, and zircon U-Pb and Hf isotope data of three granitic plutons from the western segment of the North Altun ophiolitic melange belt. Zircon U-Pb dating yields magmatic crystallization ages of 499, 493 and 496 Ma for samples of granodiorite, quartz diorite and syenogranite, respectively. The granitoids have metaluminous to weakly peraluminous and medium-K to high-K calc-alkaline characteristics and display relative enrichments in large ion lithophile elements (Rb, Th, U, K) and light rare earth elements (LREE) and relative depletions in Nb, Ta, Sr, P and Ti, suggesting an arc-related origin. The granodiorites (499 Ma) have positive zircon epsilon(Hf)(t) values ranging from +1.87 to +6.59 with two-stage Hf model ages (T-DMC) of 1.05 to 1.35 Ga, implying that the granodiorites were derived from juvenile crust. The quartz diorites (493 Ma) have similar Hf isotopic characteristics to the granodiorites (epsilon(Hf)(t) = +2.59 to +6.04, T-DMC = 1.08 to 1.30 Ga), indicating derivation from juvenile crust. The syenogranites (496 Ma) have high total REE and K2O contents, and low zircon epsilon(Hf)(t) values (-1.69 to +1.54), suggesting that they were derived mainly from juvenile crust mixed with ancient crustal materials. Combined with data from previous studies, we conclude that magmatism in the North Altun ophiolitic melange belt can be subdivided into three episodes: Episode 1 (520-470 Ma) granitoids are related to subduction; Episode 2 (460-425 Ma) granitoids formed in a continent-continent collisional setting; and Episode 3 (<420 Ma) granitoids are post-collisional granites. Our results are consistent with south-directed subduction of the North Altun oceanic lithosphere beneath the Central Altun Block during the early Paleozoic (520-460 Ma), which was followed by collision with the Dunhuang Block. (C) 2019 Elsevier B.V. All rights reserved.

安徽省铜陵地区是中国著名的以矽卡岩和斑岩型矿床为主的铜-金多金属矿集区,区内广泛产出的中酸性侵入岩与成矿关系十分密切.沙滩脚矿田位于该矿集区的东部,出露沙滩脚、桂花冲和姚家岭岩体及其不同规模、不同矿化类型的铜、金、锌等矿床,岩体对成矿起了重要的控制作用.本文在前人研究的基础上,对该矿田内的沙滩脚、姚家岭、桂花冲3个岩体进行了详细的岩石学、地球化学和锆石U-Pb年代学研究,以期查明沙滩脚矿田中酸性侵入岩的成因及成岩构造环境.岩石地球化学分析表明,3个岩体具有准铝质特征,均属于高钾钙碱性I型花岗岩类,轻稀土富集,重稀土亏损,具有弱的负Eu异常,富集Rb、Th等元素,亏损Nb、Ta等高场强元素.姚家岭岩体的锆石U-Pb年龄为140.4～140.9 Ma,沙滩脚岩体形成时代相对较早(141.4～144.1 Ma),桂花冲岩体形成相对较晚(138.3 Ma).结合区域地质背景,笔者认为沙滩脚矿田的这些岩体形成于早白垩世伸展环境,是由来自于富集地幔的分异的碱性玄武质岩浆与地壳易熔组分部分熔融形成的花岗质岩浆混合后分期侵位形成的.

Abundant intermediate-acid intrusions were widely outcropped in the western segment of North Altyn. In order to investigate the petrogenesis and formation environment of the granitoids in the western segment, and the features of magmatic activity, the syenogranite and diorite from the western segment of North Altyn were chosen to study by means of petrology, geochemistry, zircon U-Pb chronology and Hf isotope. The results show that the zircon U-Pb ages for the syenogranite are 495. 7 similar to 502. OMa. These rocks show signatures of I-type granite, with aluminum saturation index (A/CNK = 0. 86 similar to 1. 09) less than 1. 1 and a negative correlation between P2O5 and SiO2. The syenogranite samples show steep REE patterns, with LREE enrichment relative to HREE, and pronounced negative Eu. They also show characteristic distribution, with pronounced enrichments in Rb, Ba, Th, U, K and depletions of Nb, Ta, P, Ti. Geochemistry and zircon Hf isotopic characteristics suggest that the composition of the source is heterogeneous. The source rocks of the syenogranite were mainly intermediate-basic metaigneous rocks of the juvenile crust (0. 95 similar to 1. 4Ga), and minor ancient crust (1. 42 similar to 1. 83Ga). The diorite was emplaced in 497. 1 +/- 3Ma, with LREE enrichment relative to HREE, slightly negative Eu, enrichments in Rb, Ba, Th, U, K and depletions of Nb, Ta, P, Ti. The zircon epsilon(Hf) (t) values of the diorite rang from- 1. 61 similar to +2. 16. The two-stage model age (t(DM2)) are varied in 1. 34 similar to 1. 56Ga. These characteristics indicate that the source rocks probablely derived from the juvenile crust and a small amount of ancient crust. The syenogranite and diorite were formed in the Early Paleozoic. They have the characteristics of the arc granites. In combination with the regional tectonic setting, these rocks were probablely formed in continental arc setting related to the subduction of oceanic crust.

阿克提山花岗岩体位于阿尔金断裂南缘,其形成时代与区域内其他花岗岩体差异较大,该岩体走向明显地受阿尔金断裂带分支断裂控制.锆石LA-ICP-MS U-Pb年代学分析表明,该岩体结晶年龄约为262Ma,其形成可能与南阿尔金地区在华力西期-印支期发生的大规模线性构造运动有关.岩体的岩性主要为石英闪长岩、花岗闪长岩,其暗色矿物以角闪石、黑云母为主,岩石A/CNK值均小于1.1,显示准铝质—弱过铝质特征,属于高钾钙碱性系列;大离子亲石元素Rb、Th、K相对富集,高场强元素Nb、Ta、P、Sr、Ti明显呈负异常;稀土元素配分曲线具有中等负Eu异常,δEu的平均值为0.73,(La/Yb)N平均值为14.57,说明该花岗岩体岩浆部分熔融程度较高.根据岩石学及地球化学特征可判断该岩体为I型花岗岩.锆石Lu-Hf同位素分析表明,锆石εHf(t)值为+1.46～+9.14,均为正值,二阶段模式年龄的峰值平均为943Ma,表明其源岩主要为新元古代新生地壳物质的部分熔融.阿尔金断裂在印支期的走滑运动是从地壳深部的韧性变形开始的,随后在浅地表发生脆性断裂形成大规模走滑断裂带.阿克提山岩体的形成与地壳深部减压熔融有关.

玉苏普阿勒克塔格岩体是南阿尔金出露面积较大的花岗岩体之一.为了查明该岩体的成因与形成的构造环境,探讨南阿尔金地区的岩浆演化过程,对该岩体进行了岩石学、地球化学及锆石U-Pb年代学方面的研究.研究结果表明玉苏普阿勒克塔格岩体主要由中粗粒似斑状黑云二长花岗岩及中细粒含斑黑云二长花岗岩组成.本次研究获得中粗粒似斑状黑云二长花岗岩的锆石U-Pb年龄为442～448 Ma,中细粒含斑黑云二长花岗岩的锆石U-Pb年龄为423～430 Ma.岩石地球化学显示,早期花岗岩具有准铝质特征(A/CNK=0.97),晚期花岗岩具有弱过铝质特征(A/CNK=1.04).两期花岗岩均属于高钾钙碱性I型花岗岩,轻稀土富集重稀土亏损,具有Eu的弱负异常.两期花岗岩都富集Rb、Th、K等元素,亏损Ba、P、Sr、Ti等元素.根据两期花岗岩的形成时代,结合区域地质背景认为玉苏普阿勒克塔格岩体形成于活动大陆边缘环境,是早古生代南阿尔金洋向北俯冲碰撞,在构造体制转换阶段幔源岩浆上涌新生地壳发生部分熔融形成.

Yemaquan monzogranite pluton is the largest outcrop in North Altyn,with a medium-coarse grain and porphyritic texture.This paper aims to discuss the genesis and diagenesis environment of the monzogranite,and the tectonic evolution of North Altyn.Thus,it is necessary to study petrology,geochemistry,zircon U-Pb chronology and Hf isotope of the pluton. The zircon U-Pb age data suggest that the monzogranite was generated at 450—453 Ma.The rock shows significant features of I-type granite with high ratio of Na2O/K2O(1.72—2.29),aluminum saturation index(A/CNK=0.99—1.10)and negative correlation between P2O5% and SiO2%.The REE pattern shows depletion of HREE,relative enrichment of LREE,and slightly negative Eu anomaly.In the primitive mantle-normalized trace-element diagram,the rock shows strong enrichment of Rb,Ba,Th,U,K and depletion of Nb,Ta,P,Ti.The values ofεHf(t)range in 5.52—10.75.The two-stage model ages (tDM2)vary from 0.75 to 1.09 Ga.These characteristics indicate that the source rock was formed from the juvenile crust (basites).Considering the regional tectonic setting,it is concluded that the monzogranite was generated by partial melting of the basites at the root of the orogenic belt in the syn-collision to post-collision environment.