Late Permian to Early Triassic subduction and retreating of the Paleopacific slab: Constraints from continental arc magmatism in Hainan IslandSCIEI北大核心CSCD

海南岛大规模二叠-三叠纪侵入岩的形成是与古特提斯洋有关,还是与古太平洋俯冲闭合有关还存在巨大争议。本文对琼中金波两处辉绿岩脉及其围岩花岗岩的研究显示,露头1辉绿岩脉的锆石U-Pb年龄为245.4±3.8Ma,TiO_(2)含量(1.07%~1.18%)低,而MgO(8.60%~9.41%)和Mg^(#)值(62.31~65.02)较高,为钙碱性系列,球粒陨石和原始地幔标准化配分曲线中具有明显的Eu、Nb、Ta、Ti和Ba负异常,以及显著Th、U、Zr、Rb和Pb等正异常,(^(87)Sr/^(86)Sr)_(i)=0.707138~0.712797,(^(143) Nd/^(144)Nd)_(i)=0.511884~0.511965,ε_(Nd)(t)值为-7.01~-8.58,指示其形成于大陆岛弧环境。相比之下,露头2辉绿岩锆石U-Pb年龄为242.8±3.1Ma,但其TiO_(2)(2.65%~3.06%)含量较高,而MgO(4.24%~5.39%)和Mg^(#)值(40.09~45.86)较低,具有Eu、Rb、Pb、Nb、Ta和Ti弱正异常和Th负异常,(^(87)Sr/^(86)Sr)_(i)=0.690244~0.717031,(^(143) Nd/^(144)Nd)_(i)=0.512886~0.512915,ε_(Nd)(t)值为+6.41~+7.93,具有板内玄武岩的特征,指示其形成于板内裂解环境。辉绿岩脉围岩二长花岗岩的锆石U-Pb年龄为255.3±3.0Ma和255.7±3.2Ma,含少量角闪石和黑云母,具有较高的SiO_(2)(71.62%~73.72%)、Na_(2)O+K_(2)O(6.60%~9.17%)和Al_(2)O_(3)(平均14.88%)含量,A/CNK值(0.97~1.03)较低,亏损Nb、Ta、Ti、Sr和Ba,富集Rb、Th、U和Pb,为高分异I型岛弧花岗岩。总的来看,二长花岗岩和辉绿岩形成于大陆岛弧挤压向伸展过渡的构造环境。对比二叠-三叠纪侵入岩体的走向、碰撞前-同碰撞-碰撞后岩浆岩的时代以及榴辉岩的变质年龄等,发现海南岛侵入岩与哀牢山-松马造山带明显不同,而与日本和朝鲜半岛的岛弧岩浆岩类似,由此我们认为海南岛大规模晚二叠-早三叠世岩浆岩为古太平洋板片向欧亚板块俯冲后撤的产物,后撤过程受到古特提斯俯冲板片的影响。     

Genesis and geological significance of sulfide bearing mafic enclaves and host syenite in Heishishan,East Kunlun: Evidence from geochronology,mineralogy, geochemistry and Sr-Nd-Hf isotopesSCIEI北大核心CSCD

黑石山铜铅锌矿床位于东昆仑造山带中段的五龙沟地区,矿区内的石英二长岩-正长岩发育有暗色微粒包体,本研究在包体中发现了硫化物。锆石U-Pb定年显示,正长岩形成于239.4±1.0Ma,具有富Si和K,贫Mg、Cr、Ni,明显的Eu负异常,富集大离子亲石元素、亏损高场强元素,较为富集的Sr-Nd-Hf同位素特征。暗色微粒包体由斜长石和角闪石组成,可见角闪石堆晶,贫硅、富钙、铝、碱和铁,Mg#值为38.37,具有明显的Eu负异常,轻重稀土分馏弱。结合宿主正长岩和暗色包体的矿物成分相似性和岩相学特征,本文认为暗色微粒包体与正长岩来自同一个岩浆房,属于同源岩浆包体,是岩浆房早期分离结晶相,被中酸性岩脉携带上升至正长岩熔体中,一起侵位至浅部地壳。综合岩石地球化学、同位素和矿物成分,本文认为正长岩是下地壳含水镁铁质岩石在压力较低条件下部分熔融的产物。暗色微粒包体中发育硫化物,且包体岩浆的硫含量远高于正长岩岩浆,指示岩浆房的早期分离结晶相带走了硫,使残余熔体贫硫。     

Migration-circulation processes and enrichment-mineralization mechanism of lithium-beryllium elements in the continental crust.SCIEI北大核心CSCD

锂铍金属是世界关键金属资源,矿床类型多样,成矿作用发生在大陆地壳。但大陆地壳中锂铍元素的迁移-循环规律及不同锂铍矿床间的成因联系尚不清楚。本文系统地总结与梳理了大陆地壳结构与物质循环特征和不同类型锂铍金属矿床间的成因联系,提出大陆地壳锂铍循环-成矿系统的概念与模型,并将大陆地壳锂铍的迁移与循环划分为四个过程:变质过程、深熔过程、花岗岩浆过程、花岗质岩浆岩风化、淋滤与蚀变的浅-表生过程。沉积岩中锂铍元素在变质过程中可富集到一些变质矿物中,一些富锂铍黏土矿物也在变质过程转变成新的富锂铍变质矿物(如绿泥石、云母与堇青石);地壳深熔过程使得锂铍元素从变质矿物中释放出来并聚集在花岗岩浆中,麻粒岩相深熔(如黑云母脱水熔融与堇青石分解熔融)可能是锂铍大规模成矿的主要熔融方式;绝大多数锂铍矿床与花岗岩浆及其岩浆岩有关,是花岗岩浆与花岗质岩浆岩在不同演化阶段与不同方式富集成矿的结果;浅-表生过程对锂铍花岗岩-伟晶岩和流纹岩与流纹质凝灰岩的物理化学改造,可形成盐湖卤水型锂矿床、黏土型锂矿床以及各种次生锂铍矿床。变质过程中锂铍的迁移与富集机制,大型-超大型花岗岩-伟晶岩型锂铍矿床形成条件与关键控制因素等问题,是亟待研究与思考的科学问题。     

Evidences from zircon U-Pb geochronology,whole -rock geochemistry and Hf isotope of Early Cretaceous magmatic rocks in Baishan area,southern Jilin Province: Constraints on destruction of the North China CratonSCIEI北大核心CSCD

This paper reports new geochemical data including zircon U-Pb ages with Hf isotopic data, whole -rock major and trace isotopic compositions for the Early Cretaceous magmatic rocks in the northeastern North China Craton ( NCC), with the purpose of constraining its petrogenesis and tectonic setting. It also provides a basis for further discussion on the formation and evolution of the lithosphere in the northeastern NCC during the Late Mesozoic. Zircons in the Xinglin granite porphyry, Hongtuya andesitic crystal tuff and Jiangyuan rhyolitic breccia-bearing crystal-lithic tuff all show magmatic origin. Zircon U-Pb dating yield age are 130 +/- 1Ma, 128 +/- 1Ma and 120 +/- 1Ma, respectively. The Xinglin granite porphyry and the Hongtuya andesitic crystal tuff have high content of SiO2, Al2O3 Sr, high Na2O/K2O, Sr/Y and ( La/Yb)(N) ratios. In addition, they exhibit low Y and Yb. They are enriched in LILE ( e. g., Ba, Th and U), depleted in HFSE ( e. g., Nb, Ti and P) with weak negative Eu anomalies (delta Eu =0. 82 similar to 0. 94), showing they are typical of adakitic rocks. The Xinglin granite porphyry has high content of total -alkali, low content of TiO2, characterized by peraluminous-weakly peraluminous granite A/CNK = 1. 06 similar to 1. 14, the zircon saturated temperature values of 798 similar to 815 degrees C and a distribution pattern of LREE enrichment with incline to the right, which indicates it is I -type granite. The zircon ( t) values in the Xinglin granite porphyry ranged 17. 96 0. 19, and the two -stage model ages yield t(DM2) = 1197 similar to 2313Ma, which imply that the Xinglin granite porphyry is derived from partial melting of the thickened mafic lower crust of Paleoproterozoic to Mesoproterozoic. The zircon epsilon(Hf)( t) values in the Hongtuya andesitic crystal tuff ranged 3. 37 similar to 5. 47, and the two -stage model ages yield t(DM2) = 830 similar to 967Ma, indicating that the Hongtuya andesitic crystal tuff is a metasomatism product of the Neoproterozoic delaminated eclogite lower crust partial melting and mantle peridotite. Combined with the epsilon(Hf)( t) values in the Jiangyuan rhyolitic breccia-bearing crystal-lithic tuff ranged 2. 69 1. 00, and the two -stage model ages yield t(DM2) = 1115 similar to 1349Ma, we conclude that the epsilon(Hf)( t) values of magmatic rocks are heterogeneous in the southern Jilin Province, and the magmatic source area is characterized by multi -component origin, including both ancient crust and juvenile crust. We supposed that there were two accretion evolution events in the continental crust of the northeastern NCC during Proterozoic. Comprehensive studies have shown that subduction and slab roll -back of the Paleo-Pacific plate ( Izanagi) led to the thickened the northeastern NCC being in an extensional tectonic setting during the Early Cretaceous, and the destruction of the northeastern NCC by delamination occurred spatially from west to east. The partial melting of delaminated lower continental crust resulted in a wide distribution of adakitic rocks.     

Evolution of the eastern segment of the northern margin of the North China Craton in the Triassic: Evidence from the geochronology and geochemistry of magmatic rocks in Kaiyuan area,North LiaoningSCIEI北大核心CSCD

To constrain the evolution of the eastern segment of the Paleo-Asian Ocean (PAO), petrography, geochemistry and zircon U-Pb dating analyses were conducted over the gabbro and rhyolite in the Kaiyuan area, North Liaoning, in the eastern segment of the northern margin of the North China Craton (NCC). Zircon dating results indicate that the gabbros and rhyolite were formed in the Trassic (246 +/- 2Ma, 241 +/- 2Ma, 226 +/- 3Ma and 241 +/- 2Ma). The three gabbros of Triassic have similar geochemical characteristics, originated from the mantle, and were contaminated by crust materials in the process of ascending and emplacement. The Early Triassic gabbro (246Ma) originated from the enriched mantle source metasomatized by fluid. It was formed by 1% partial melting of garnet spinel lherzolite in the extensional environment caused by breaking off slab. The Middle Triassic gabbro (241Ma) was derived from a transitional mantle metasomatized by fluid and melt, and was formed by 1% to 2% partial melting of garnet spinel peridotite. The Late Triassic gabbro (226Ma) was derived from a transitional mantle metasomatized by fluid and melt, and was formed by 3% similar to 4% partial melting of garnet spinel lherzolite in the post-orogenic extensional environment. The Middle Triassic rhyolite (241Ma) has the characteristic of post collisional I-type granite, that enriched in light rare earth elements and large ion lithophile elements, depleted in high field strength elements, and negative Nb, Ti, P and Sr anomaly. The low content of Sr and Yb suggested a 30 similar to 40km depth source. The Middle Trassic "bimodal" igneous rocks implied an extensional environment caused by the remainder oceanic crust breaked away at the bottom of the crust. Based on the lithologic association, regional strata information and the chronological data in this paper and published by predecessors, the Triassic magmatism in the eastern segment of the northern margin of the NCC can be divided into five stages: 252 similar to 246Ma, 246 similar to 242Ma, 242 similar to 240Ma, 240 similar to 230Ma and 230 similar to 215Ma. These five magmatic events were the results of the southward subduction and extinction of the PAO: (1) The transformation from active continental margin to syn-collisional setting resulted in the final closure of the PAO (252 similar to 246 Ma); (2) Continuous pushing resulted in orogenic uplift (246 similar to 242Ma); (3) Extension caused by the detachment of the remainder subduction oceanic crust at the bottom of the crust (242 similar to 240Ma); (4) Rapid uplift and crustal thickening (240 similar to 230Ma); (5) Extension of post-orogenic(230 similar to 215Ma).     

Metallogeny of the Longtangou-Huoyangou Sn deposit in North Qinling Orogeny: Geochronological and petrogeochemical evidence from Sn-bearing granite-pegmatiteSCIEI北大核心CSCD

北秦岭卢氏官坡地区龙潭沟-火炎沟锡矿床是近年来在豫西地区实现的重大找矿突破,然而前人对该矿床的形成时代以及成矿作用研究较少。本文以与锡成矿关系密切的白云母电气石钠长石花岗伟晶岩(以下称含锡花岗伟晶岩)为研究对象,开展了岩相学,岩石地球化学,以及锡石、铌钽铁矿和磷灰石LA-ICP-MS U-Pb年代学研究,探讨了花岗伟晶岩的源区性质、成岩成矿时代和构造环境。结果显示:(1)含锡花岗伟晶岩的锡石、铌钽铁矿和磷灰石U-Pb年龄分别为408.1±1.5Ma、391.5±2.0Ma和387.0±2.1Ma;锡石年龄代表早期锡矿化的时间,铌钽铁矿和磷灰石代表晚期铌钽矿化的时间;结合区域研究成果,认为官坡-丹凤地区存在两期锡铌钽等稀有金属成矿作用。(2)含锡花岗伟晶岩富硅和铝,贫碱,富集Rb、Cs、Nb、Ta和Hf,亏损Ba、P和Ti,相对富集重稀土元素,亏损轻稀土元素,具明显的Eu负异常,暗示其源岩应为陆壳物质。(3)龙潭沟-火炎沟锡矿床形成于造山后由挤压到伸展转换的构造背景。通过与秦岭造山带的灰池子复式岩体,以及成铀伟晶岩和稀有金属伟晶岩进行对比,我们认为,龙潭沟-火炎沟锡矿床的成锡伟晶岩地球化学特征既有相似性又有差异性,具更高的结晶分异演化程度;沉积源岩物质组成可能是龙潭沟-火炎沟伟晶岩成锡矿的关键。卢氏官坡地区龙潭沟-火炎沟锡矿床的发现,对于在昆仑-秦岭-大别地区找早泥盆世的稀有金属矿床,尤其是锡矿床,具有重要意义。     

Mantle property of Hegenshan ophiolite in Inner Mongolia: Constrains from element geochemistry and Re-Os isotopes of harzburgiteSCIEI北大核心CSCD

贺根山蛇绿岩带是中亚造山带东部出露面积最大的晚古生代蛇绿岩带,然而研究者对它是大洋岩石圈的残余还是陆内岩石圈地幔伸展的产物仍存在较大争议,主要归因于一直缺少橄榄岩Re-Os同位素的有效制约。基于此,本文对贺根山蛇绿岩中方辉橄榄岩进行了系统的岩石学、地球化学和Re-Os同位素研究。方辉橄榄岩主要由橄榄石、斜方辉石、粗粒的铬尖晶石和少量单斜辉石组成。贺根山方辉橄榄岩具有难熔地球化学特征,显示出高的MgO(45.1%~48.1%)含量,低的CaO(0.09%~0.26%)和Al 2O 3(0.58%~0.90%)含量及Tb/Yb比值,低于原始上地幔的^(187)Os/^(188)Os(0.1236~0.1263)同位素组成;橄榄石具有较高的Fo值(91.0~91.7)和NiO含量(0.26%~0.48%),而且单斜辉石具有低的重稀土含量,暗示了贺根山方辉橄榄岩是尖晶石相陆下岩石圈地幔高程度(20%~30%)部分熔融的难熔残余。另外,方辉橄榄岩相对富集LREE和大离子亲石元素,亏损高场强元素(例如Nb、Ta),且单斜辉石具有高Ti/Eu值和低的La/Yb,揭示了地幔源区受到硅酸盐熔体交代作用的改造。另一方面,方辉橄榄岩显示出相对年轻的Re亏损模式年龄,t RD为454~825Ma,表明贺根山地区岩石圈地幔形成的时代应该在0.8Ga之前,而后经历过多期熔体抽离和交代,与区域上大规模地壳增生时代吻合,可能是罗迪尼亚超大陆裂解的响应。结合蛇绿岩中大量深源矿物(金刚石等)和捕获锆石的存在、南北两侧一致的地质记录,本文认为贺根山方辉橄榄岩可能是陆内伸展环境下深部地幔物质上涌减压熔融的产物。     

Tectonic nature of the NE Asian continental margin during the Late Jurassic–Early Cretaceous: constraints from the geochronology and geochemistry of igneous rocks in the NE North China Craton

ABSTRACT

This paper presents geochronological, geochemical, and zircon Hf–O isotope data for late Mesozoic intrusive rocks from the northeastern North China Craton (NCC), with the aim of constraining the late Mesozoic tectonic nature of the NE Asian continental margin. U–Pb zircon data indicate that the Late Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Jurassic (161 ? 156 Ma) and Early Cretaceous (125 ? 120 Ma). Late Jurassic magmatism consists mainly of monzogranites. These monzogranites display high Sr/Y ratios and the tetrad effect in their REE, respectively, and have negative ε_Hf(t) values (?22.6 to ?15.8). The former indicates that the primary magma was generated by partial melting of thickened NCC lower crust, the latter suggests that the monzogranites were crystallized from highly fractionated magma, with the primary magma derived from partial melting of lower continental crust. Combined with the spatial distribution and rock associations of the Late Jurassic granitoids, we conclude that the Late Jurassic magmatism in the eastern NCC formed in a compressional environment related to oblique subduction of the Paleo-Pacific Plate beneath the Eurasia. The Early Cretaceous magmatism consists mainly of granitoids and quartz diorites. The quartz diorites formed by mixing of melts derived from the mantle and lower crust. The coeval granitoids are classified as high-K calc-alkaline and metaluminous to weakly peraluminous series. Some of the granitoids are similar to A-type granites. The granitoid ε_Hf(t) values and T_DM2 range from ?14.3 to ?1.4 and 2089 to 1274 Ma, respectively. These values indicate that their primary magma was derived from partial melting of lower crustal material of the NCC, but with a contribution of mantle-derived material. We therefore conclude that Early Cretaceous magmatism in the northeastern NCC occurred in an extensional environment related to westward subduction of the Paleo-Pacific Plate beneath Eurasia.     

Geochemistry and Zircon U–Pb–Hf Isotopic Systematics of the Sanchahe Quartz Monzonite Intrusion in the North Qinling Tectonic Zone,Central China： Implications for its Petrogenesis and Tectonic Setting

The Sanchahe quartz monzonite intrusion is situated in the middle segment of the North Qinling tectonic belt, Central China mainland, and consists chiefly of sanukitoid–like and granodioritic-monzogranitic rocks. The sanukitoid–like rocks are characterized by quartz monzonites, which display higher Mg#（55.0–59.0）, and enrichments in Na2 O＋K2 O（7.28–8.94 %）, Ni（21-2312 ppm）, Cr（56-4167 ppm）, Sr（553-923 ppm）, Ba（912-1355 ppm） and LREE（（La/Yb）N =9.47–15.3）, from negative to slightly positive Eu anomalies（δEu=＋0.61 to ＋1.10）, but also depletion in Nb, Ta and Ti. The granodioritic-monzogranitic rocks diaplay various Mg#of 6.00-53.0, high Na2 O＋K2 O（7.20– 8.30%）, Sr（455–1081 ppm） and（La/Yb）N（27.6–47.8）, with positive Eu anomalies（δEu=1.03–1.57） and depleted Nb, Ta and Ti. Laser ablation inductively coupled plasma mass spectrometry（LA-ICPMS） zircon U-Pb isotopic dating reveals that the sanukitoid-like rocks were emplaced at two episodes of magmatism at 457±3 Ma and 431±2 Ma, respectively. The monzogranites were emplaced at 445±7Ma. Sanukitoid–like rocks have their εHf（t） values ranging from ＋0.3 to ＋15.1 with Hf–depleted mantle model ages of 445 to 1056 Ma, and the monzogranite shows its εHf（t） values ranging from 21.6 to ＋10.8 with Hf–depleted mantle model ages of 635 to 3183 Ma. Petrological, geochemical and zircon Lu –Hf isotopic features indicate that the magmatic precursor of sanukitoid–like rocks was derived from partial melting of the depleted mantle wedge materials that were metasomatized by fluids and melts related to subduction of oceanic slab, subsequently the sanukitoid magma ascended to crust level. This emplaced mantle magma caused partial melting of crustally metamorphosed sedimentary rocks, and mixing with the crustal magma, and suffered fractional crystallization, which lead to formations of quartz monzonites. However, the magmatic precursor of the granodioritic-monzogranitic rocks were derived from partial melting of subducted oceanic slab basalts. Integrated previous investigation for the adackitic rocks in the south of the intrusion, the Sanchahe intrusion signed that the North Qinling tectonic zone was developed in an early Paleozoic transitionally tectonic background from an island arc to back–arc.     

Tectonic evolution of the Late Paleozoic Early Mesozoic orogenic belt in the eastern segment of the northern margin of the North China Block: Evidence from meta volcanic rocks of Jianshanzi,northern Liaoning ProvinceSCIEI北大核心CSCD

LA-ICP-MS U-Pb dating, whole -rock geochemistry and Hf isotopic analyses for the Jianshanzi volcanic rocks in the Kaiyuan area are presented to explore the Late Paleozoic -Early Mesozoic tectonic evolution history of the eastern segment of the northern margin of the North China block. The detailed research indicates that the protolith of Jianshanzi metamorphic volcanic rocks includes rhyolite, dacite and andesite, they are calc-alkaline series and metaluminous-weak peraluminous rocks. According to the zircon U-Pb dating, the metamorphic rhyolite and metamorphic andesite formed in the Late Permian (256. 1 +/- 1. 5Ma, 252.4 +/- 1. 7Ma) and the Late Triassic (222. 4 +/- 1. 8Ma, 227. 9 +/- 1. 2Ma), respectively. They are characteristized by enrichment in light rare earth elements and large ion lithophile elements, and depletion of heavy rare earth elements and high field strength elements. Metamorphic rhyolite has an obvious negative Eu anomaly with epsilon(Hf) ( t) values of 10. 83 + 8. 10 and the second -stage model are 698 similar to 1967Ma. They are mainly due to the partial melting of the juvenile basaltic lower crust and the contamination of a small amount of ancient crustal materials. Metamorphic andesite has no obvious Eu anomaly, and the epsilon(Hf)( t) value and the second -stage model are +4.54 similar to + 6. 79 and 825 similar to 968 Ma, which may be the product of partial melting of basic lower crust. There are two periods of magmatism in Jianshanzi volcanic rocks: Late Permian -Early Triassic (247 similar to 256Ma) and Late Triassic (similar to 225Ma). The material composition of the Jianshanzi volcanic rocks is characterized by different times and different tectonic backgrounds. It is comprehensively believed that the eastern segment of the northern margin of the North China block was in an active continental margin tectonic environment during the Permian, and the Palaeo-Asian Ocean subducted in both directions; Mantle -derived magma ascends and emplaces, forming a nascent crust and causing crustal thickening. The Paleo-Asian Ocean finally closed in the early Middle Triassic, and the impact of collisional orogeny may have continued until the early Late Triassic.     

Metallogenic age and fluid evolution of the Kangshan Au-polymetallic deposit in the southern margin of the North China Craton: Constraints from monazite U-Pb age,and in-situ trace elements and S isotopes of pyriteSCIEI北大核心CSCD

小秦岭-熊耳山金矿集区位于华北克拉通南缘,发育众多伴生铅锌银等金属的金矿,成为揭示克拉通破坏型金矿成因的天然实验室。产于小秦岭-熊耳山金矿集区内的康山金多金属矿床受控于北东向的中生代脆性断裂,赋存于新太古代变质岩和中元古代火山岩中。成矿过程可分为4个热液阶段:石英±黄铁矿阶段、石英-黄铁矿-黄铜矿-自然金阶段、多金属硫化物-自然金-石英-铁白云石阶段、石英-方解石±萤石阶段。本文获得康山金多金属矿床金成矿阶段热液独居石LA-ICP-MS U-Pb年龄为131.7±4.6Ma,与晚中生代华北克拉通破坏有关的岩浆热液成矿作用时代一致。本次研究开展的各阶段黄铁矿原位微量元素单点和扫面分析,发现第2阶段Au与Co、Ni、As呈正相关关系,且有明显的振荡环带,Cu、Ag、Sb、Pb、Bi这几种元素从黄铁矿颗粒的核部向边缘含量逐渐降低,且黄铁矿颗粒中出现富含这些元素的矿物包裹体,说明该阶段发生流体沸腾作用;而第3阶段黄铁矿中各微量元素含量为所有阶段中最低,黄铁矿无振荡环带且裂隙中有富含各微量元素的硫化物充填,说明各种元素在该阶段均得到充分卸载,且成矿流体的化学性质较稳定。结合前人关于该矿床各阶段流体包裹体分析结果,表明流体沸腾是Au的主要沉淀机制,而流体混合是Pb、Zn、Ag的主要沉淀机制。黄铁矿中微量元素含量指示,从第1阶段到第3阶段流体温度依次降低;第2和第3阶段流体fO2比第1阶段高且后两者相差不大。根据黄铁矿Co、Ni含量及比值的计算,认为第1和第2阶段黄铁矿为岩浆热液成因,第3阶段黄铁矿受围岩物质影响。黄铁矿原位S同位素分析得到第1至第3阶段黄铁矿δ34S分别为+6.6‰-+8.9‰、+5.0‰-+7.2‰和+6.0‰-+8.7‰,均与区域花岗岩类的S同位素值类似。综上所述,本文得出康山金多金属矿床形成于早白垩世与华北克拉通破坏有关的岩浆热液成矿作用。     

Genesis of the Maka Pb-Zn-W deposit in southeastern Yunnan" Constraints from sphalerite Rb-Sr dating,cassiterite U-Pb dating and in -situ S,Pb isotopes of sulfideSCIEI北大核心CSCD

马卡铅锌钨矿床地处云南省马关县与麻栗坡县的南温河交界处,位于燕山晚期老君山复式花岗岩体北缘。野外地质调查发现,该矿床主要发育矽卡岩型、石英脉型铅锌矿化和萤石石英脉型白钨矿化,但它们的形成机制仍缺乏系统研究。本文通过闪锌矿Rb-Sr、锡石原位U-Pb同位素定年和硫化物原位S、Pb同位素分析,厘定了马卡矿床不同类型铅锌矿化年龄,并探讨了其成矿物质来源及成因机制。矽卡岩型和石英脉型铅锌矿石中闪锌矿分别获得了88.9±1.9Ma(MSWD=4.5)和85.18±0.72Ma(MSWD=1.2)的Rb-Sr等时线年龄,同时获得石英脉型铅锌矿石中锡石LA-ICP-MS U-Pb年龄为84.3±4.7Ma(MSWD=0.66)。结果指示锌、锡矿化时代为晚白垩世,矽卡岩型和石英脉型铅锌矿化分别与该区广泛出露的老君山花岗岩(-90Ma)和花岗斑岩年龄(80-86Ma)一致。矿石硫化物原位硫同位素测试结果显示,δ34S值范围为2.53‰-9.65‰,均值为4.7‰,与老君山花岗岩中硫化物硫同位素组成(4.07‰)相似,表明硫主要来源于老君山花岗岩,少部分源自沉积地层;原位铅同位素组成特征也表明矿石铅主要源自老君山花岗岩。综合研究认为,老君山花岗岩体南北缘地区具有相似的成矿地质条件。马卡矿床的形成主要与燕山晚期老君山复式花岗岩体有关,可能经历了与花岗岩有关的矽卡岩型矿化和与花岗斑岩有关的热液充填、交代成矿过程。     

Genesis and tectonic setting of Late Jurassic-Early Cretaceous granites in Nachatang area,Central Lhasa Terrane: Constraints from geochemistry,chronology and Hf isotopesSCIEI北大核心CSCD

西藏中拉萨地块东段大规模侏罗纪-白垩纪花岗岩类的成因类型及构造背景尚未得到有效约束,该时期岩浆作用的时空分布、岩石成因以及深部动力学机制等问题亟需新的深入研究。本文对中拉萨地块东段南缘那茶淌地区的花岗岩类进行了系统的岩相学、元素地球化学、年代学和锆石Hf同位素研究。LA-MC-ICPMS锆石U-Pb定年结果显示,那茶淌地区黑云母二长花岗岩成岩年龄为147±1.4Ma,花岗闪长岩年龄为140.6±1.3Ma,系晚侏罗世-早白垩世中酸性岩浆活动的产物。在元素地球化学组成上,黑云母二长花岗岩和花岗闪长岩的主量元素组成具有富SiO₂(分别为71.02%～71.81%和65.17%～66.73%)、Al₂O₃(分别为13.45%～13.57%和14.43%～15.20%)、碱金属(Na₂O+K₂O)(分别为6.79%～7.48%和6.55%～7.37%),贫TiO₂(分别为0.15%～0.21%和0.10%～0.13%)等特征,显示I型准铝-弱过铝质(A/CNK=0...     

Genesis of the titanian andradite in alkaline rocks and their petrological and mineralization significance:A study example of the garnet from the Fanshan ultramafic. syenitic complex in North China CratonSCIEI北大核心CSCD

富钛钙铁榴石是硅不饱和碱性火成岩中的特征矿物,其Ti含量和Ti进入石榴石的方式可直接反映岩浆体系的硅饱和度和氧逸度。河北矾山超镁铁岩-正长岩杂岩体是华北克拉通北缘东西向展布三叠纪碱性岩带的重要岩体之一,其岩石中发育三种类型的富钛钙铁榴石:类型Ⅰ发育于岩体外带的石榴石辉石正长岩中,与辉石、黑云母呈岩浆共生关系,端元组成为Adr_(25-65)Mmt_(15-37)Slo_(8-28)Grs_(10-14),以高TiO_(2)含量(6.08%~18.61%)、较低的SiO_(2)含量(25.46%~33.26%)为特征,为原生岩浆成因;类型Ⅱ见于各类岩石,呈细粒他形充填于其他矿物颗粒之间,端元组成为Adr_(57-69)Mmt_(5-19)Slo_(0-6)Grs_(19-27),以高Al_(2)O_(3)含量(3.95%~5.56%)为特征,为岩浆演化后期熔体富Al_(2)O_(3)时结晶而成;类型Ⅲ亦见于各类岩石,主要呈细粒他形或细碎状发育于其他矿物内,端元组成为Adr_(68-79)Mmt_(8-14)Slo_(0-5)Grs_(6-14),以低的Al_(2)O_(3)含量(1.18%~2.89%)和较高的FeO含量(21.65%~24.62%)为特征,为岩浆期后热液成因。在矾山杂岩体的富钛钙铁榴石中,Ti主要以Si→Ti^(4+)和2Fe^(3+)→Ti^(4+)+Fe^(2+)/Mg替代方式进入到晶体结构中,反映了矾山杂岩体的母岩浆体系为二氧化硅不饱和的碱性岩浆,并具有较高的氧逸度。受石榴石的主量元素组成和相应的晶体结构控制,在微量元素组成上,矾山杂岩体中的富钛钙铁榴石富集轻稀土或中稀土、亏损重稀土,大离子亲石元素(Rb、Ba、Pb和Sr)含量较低或极低,而高场强元素(如Th、U、Nb、Ta、Zr和Hf等)含量普遍较高。本文对石榴石的成因研究结果支持矾山杂岩体不同类型的岩石形成于封闭体系下同一母岩浆系统充分的结晶-分异和堆晶作用;此演化模式可以较好地解释矾山杂岩体的同心环状特征和韵律层状结构,以及磁铁矿和磷矿的成因。