Geochemistry and zircon U–Pb–Hf isotopes of the 780 Ma I-type granites in the western Yangtze Block: petrogenesis and crustal evolution

ABSTRACT

Neoproterozoic I-type granites could provide vital insights into the crust–mantle interaction and the crustal evolution along the western Yangtze Block, South China. This paper presents new zircon U–Pb ages, bulk-rock geochemistry, and in situ zircon Lu–Hf isotope on the Dalu I-type granites from the southwestern Yangtze Block. Zircon U–Pb dating show the crystallization ages of 781.1 ± 2.8 Ma for granodiorites and 779.8 ± 2.0 Ma for granites, respectively. The Dalu granodiorites are Na-rich, calc-alkaline, metaluminous to slightly peraluminous (A/CNK = 0.94–1.08). Zircons from granodiorite have positive εHf(t) values (+2.16 to +7.39) with crustal model ages of 1.21–1.54 Ga, indicating juvenile mafic lower crust source. The Dalu granites are high-K calc-alkaline, peraluminous rocks. They have variable zircon εHf(t) values (?4.65 to +5.80) with crustal model ages of 1.31–1.97 Ga, suggesting that they were derived from the mature metasediment-derived melts by the mixing of newly formed mafic lower crust-derived melts. The geochemical variations in Dalu pluton is dominated not only by the different source rocks but also by the different melting temperatures. Combining with the geochemistry and isotopic compositions of I-type granitoids and tectonic setting in the western Yangtze Block, we propose that the Dalu I-type granodiorites–granites associations are the magmatic response from different crustal levels, which were induced by the heat anomaly due to the asthenosphere upwelling in the subduction-related setting.     

Timing of granitic magma mixing in the southeastern Gyeongsang Basin,Korea: SHRIMP-RG zircon data

Late Cretaceous calc-alkaline granites in the Gyeongsang Basin evolved through the mixing of mafic and felsic magmas. The host granites contain numerous mafic magmatic/microgranular enclaves of various shapes and sizes. New SHRIMP-RG zircon U–Pb ages of both granite and mafic magmatic/microgranular enclaves are 75.0?±?0.5 Ma and 74.9?±?0.6 Ma, respectively, suggesting that they crystallized contemporaneously after magma mixing. The time of injection of mafic melt into the felsic magma chamber can be recognized as approximately 75 Ma by field relations, petrographic features, geochemical evolution, and SHRIMP-RG zircon dating. This Late Cretaceous magma mixing event in the Korean Peninsula was probably related to the onset of subduction of the Izanagi (Kula)–Pacific ridge.     

Petrogenesis and tectonic implications of early Silurian high-K calc-alkaline granites and their potassic microgranular enclaves,western Kunlun orogen,NW Tibetan Plateau

The western Kunlun orogen occupies a key position along the tectonic junction between the Pan-Asian and Tethyan domains, reflecting Proto- and Palaeo-Tethys subduction and terrane collision during early Palaeozoic to early Mesozoic time. We present the first detailed zircon U–Pb chronology, major and trace element, and Sr–Nd–O–Hf isotope geochemistry of the Qiukesu pluton and its microgranular enclaves from this multiple orogenic belt. SHRIMP zircon U–Pb dating shows that the Qiukesu pluton was emplaced in the early Silurian (ca. 435 Ma). It consists of weakly peraluminous high-K calc-alkaline monzogranite and syenogranite, with initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7131–0.7229, ?_Nd(T) of –4.1 to –5.7, δ¹⁸O of 8.0–10.8‰, and ?_Hf(T) (in situ zircon) of –4.9. Elemental and isotopic data suggest that the granites formed by partial melting of lower-crustal granulitized metasedimentary-igneous Precambrian basement triggered by underplating of coeval mantle-derived enclave-forming intermediate magmas. Fractional crystallization of these purely crustal melts may explain the more felsic end-member granitic rocks, whereas such crustal melts plus additional input from coeval enclave-forming intermediate magma could account for the less felsic granites. The enclaves are intermediate (SiO₂ 57.6–62.2 wt.%) with high K₂O (1.8–3.6 wt.%). They have initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7132–0.7226, ?_Nd(T) of –5.0 to –6.0, δ¹⁸O of 6.9–9.9‰, and ?_Hf(T) (in situ zircon) of –8.1. We interpret the enclave magmas as having been derived by partial melting of subduction-modified mantle in the P–T transition zone between the spinel and spinel-garnet stability fields. Our new data suggest that subduction of the Proto-Tethyan oceanic crust was continuous to the early Silurian (ca. 435 Ma); the final closure of the Proto-Tethys occurred in the middle Silurian.     

东天山卡瓦布拉克地区片麻状花岗岩形成时代及地质意义

东天山卡瓦布拉克地区发育大量片麻状花岗岩,据野外特征分为含斑片麻状花岗岩和不含斑片麻状花岗岩,片麻理属后期韧性剪切叠加改造结果.本文获得含斑片麻状花岗岩LA-ICP-MS锆石U-Pb年龄为(942.1±7.2)Ma和(941.9±4.9)Ma;不含斑晶的片麻状花岗岩年龄为(424.2±3.4)Ma,这些年龄数据表明片麻状花岗岩分别形成于新元古代和中志留世.野外调查表明,片麻状花岗岩侵入于长城系星星峡群和卡瓦布拉克群中,被块状石炭纪花岗岩侵入.研究区西侧上覆泥盆纪地层未发生明显韧性变形.据此限定区内韧性剪切变形发生于晚志留世(约424 Ma)之后至泥盆纪之前.     

Emplacement Ages and Petrogenesis of the Molybdenum–bearing Granites in the Jinduicheng Area of East Qinling, China: Constraints from Zircon U–Pb Ages and Hf Isotopes

The Mesozoic porphyry assemblage in the Jinduicheng area is a special molybdenum area in China, the Mo deposits, including the Jinduicheng, Balipo, Shijiawan, Huanglongpu, are distributed. The emplacement age and geochemical features of the granites in the Jinduicheng area can provide essential information for the exploration and development of the porphyry molybdenum deposit. In this study, we report LA–ICP–MS zircon U–Pb age and zircon Hf isotopic compositions of granite porphyries from the Jinduicheng area, and provide insights on the petrogensis and source characteristics of the granites. The results show that the zircon U–Pb ages of the Jinduicheng granite porphyry (143±1 Ma) and the Balipo granite (154±1 Ma), agree well with the Re–Os ages of molybdenite in the Jinduicheng molybdenum polymetallic deposit (139±3 Ma) and the Balipo molybdenum polymetallic deposit (156±2 Ma), indicating that the emplacement of granite porphyries occurred between Late Jurassic and Early Cretaceous. Zircons granite from the Jinduicheng area give the εHf(t) values mainly ranging from ?10 to ?16, and ?20 to ?24, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.86–2.0 Ga, and 2.2–2.6 Ga, respectively) of zircons of the granite from the Jinduicheng values. The ore–forming materials are mainly derived from crust, with minor mantle substances. Zircons of the granite from the Balipo area give εHf(t) values ranging from ?18 to ?20, ?28 to ?38, and ?42 to ?44, respectively, corresponding to two–stage model ages (tDM2: mainly focused on 1.88–3.0 Ga, and 3.2–3.90 Ga, respectively). the εHf(t) values of the Jinduicheng porphyry more than that of the Balipo porphyry, and two–stage model ages (tDM2) less than that of the Balipo porphyry, shows that he source of the porphyries originated from ancient lower crustal materials in the Jinduicheng area, and mixed younger components, more younger components contributed for the source of the Jinduicheng porphyry.     

江南隆起带中段新元古代花岗岩锆石U-Pb年代学和Hf同位素组成研究

对江南隆起带中段湘东西园坑岩体和赣西九岭岩体的LA-ICPMS锆石U-Pb年代学测定和LA-MC-ICPMS锆石Hf同位素原位分析测试表明:西园坑岩体形成于(804±3)Ma,赣西九岭岩体的年龄为(813±4)Ma和(823±2)Ma,均为新元古代花岗岩.上述三个样品的εHf(t)的加权平均值分别为0.68±0.71,...     

江西省峡江铀矿床两期印支期花岗岩的年代学、岩石地球化学和岩石成因——对华南印支期构造背景和产铀花岗岩成因的指示

位于江西省的峡江铀矿床为华南一个典型的花岗岩型铀矿床,铀矿体产在金滩花岗岩体中。野外地质调查和锆石U-Pb同位素定年工作表明金滩花岗岩体主要由两期的印支期花岗岩组成,其中含矿的等粒状二云母花岗岩形成于239±1Ma,而主体的斑状黑云母花岗岩则形成于226±2Ma。二云母花岗岩具有较高的SiO₂含量（74.09%~74.53%）和明显低的TiO₂、CaO和MgO含量,铝饱和指数为1.20~1.46,含有白云母和石榴子石等过铝质矿物,属于典型的强过铝S型花岗岩。斑状黑云母花岗岩的地球化学特征略微不同于二云母花岗岩,相对富集高场强元素和稀土元素,具有明显更低的Rb/Sr比值以及更小的Eu负异常,铝饱和指数变化为1.05~1.13,属于弱过铝到强过铝花岗岩。同位素组成上,两者都具有较低的ε_Nd（t）值（二云母花岗岩：-9.0~-8.8;斑状黑云母二长花岗岩：-9.8~-9.4）和古元古代的模式年龄（二云母花岗岩：1.73~1.75Ga;斑状黑云母二长花岗岩：1.77~1.80Ga）。地球化学和同位素特征表明金滩岩体中的这两期印支期花岗岩应该都为S型花岗岩。较高的Rb/Sr比值和较低的CaO/Na₂O比值表明二云母花岗岩主要由富粘土的泥质沉积岩部分熔融而来,而斑状黑云母二长花岗岩则主要由贫粘土的碎屑沉积岩部分熔融而来。金滩岩体中的两期印支期花岗岩分别对应于华南印支期同碰撞挤压和碰撞后伸展期的岩浆作用。二云母花岗岩含有更高的U含量,矿物学以及地球化学特征与华南其他的典型产铀花岗岩类似。对比研究表明,华南印支期产铀花岗岩的形成应与同碰撞期挤压背景下的泥质沉积岩的部分熔融有关。     

纳米比亚欢乐谷地区斑状花岗岩成因及构造背景

对纳米比亚欢乐谷地区斑状花岗岩进行系统的地球化学及 Sr--Nd 同位素研究,并对其岩石成因及构造意义进行了讨论。结果表明,该斑状花岗岩为高钾钙碱性-钾玄岩系列的准铝质花岗岩; 岩石富碱、轻稀土和 Ｒb、Th、U、K、Pb 等大离子亲石元素,贫 Nb、Ta、Ti、Zr、Hf 等高场强元素,具有中等铕负异常。岩石锶初始值为 0. 715 61 ～0. 722 07,εNd( t) 为 －13. 9 ～ －12. 7,Nd 同位素模式年龄为2 025 ～2 153 Ma。揭示欢乐谷地区斑状花岗岩为同碰撞 S 型花岗岩,主要来源于古老地壳物质的重熔,是 Kalahari 克拉通和 Congo 克拉通碰撞造山的产物。     

南岭地区钨矿床共（伴）生金属特征及其地质意义初探

南岭是世界上最重要的钨矿产地,南岭钨矿床中与钨共（伴）生的有色、稀有及贵金属种类很多,数量可观,也是我国重要的矿产资源。论述了南岭及其邻近地区众多钨矿床中与钨共生或伴生的锡、钼、铋、铌钽、铜、铅锌、金银、稀土等元素的不同状况和特征,其中锡、钼、铋是南岭钨矿床中最普遍最重要的共（伴）生元素,铌钽只在演化程度较高的花岗岩相关的钨矿床中伴生产出,铜、金作为钨矿床伴生金属的意义较小,而钨矿床中伴生的银、铅锌具有相当重要的意义。从元素地球化学性质、南岭的区域地背景、花岗岩演化、多期多阶段成矿作用等方面出发,分析和解释了它们之间相互共（伴）生的原因及差异性,探讨了其地质意义。     

Deformation features of garnet-bearing granites from Huwan,western Dabie Mountains

Foliated garnet-bearing granite, usually associated with high pressure and ultrahigh -pressure (UHP) metamophic rocks, is a particular rock-type extensively exposed in the Mesozoic Dabie-Sulu orogenic belt of China. This study focuses on deformation features and SHRIMP zircon dating of foliated garnet granite in a high-pressure metamorphic unit from Huwan, western Dabie Mountains in order to resolve discrepancies in current versions of its petrogenesis and structural evolution. SHRIMP dating reveals a zircon age of 762 ± 15 Ma (MSWD=1.7) for Huwan granites, representing the Middle to Late Neoproterozoic age of intrusion and crystallization. Field and microstructural studies show that the Huwan granite body underwent multiple-stage deformation. The deformation was manifested by an early stage of rootless folding and imposition of relict foliation (S₁); an Indosinian main stage marked by imposition of north-dipping penetrative gneissosity (S₂) and development of ductile shear zones under NNE-SSW directed compression; and a final Indosinian stage of southward thrusting of the Huwan high-pressure unit. Shallow level extension prevailed after the Late Triassic, giving rise to south-dipping thrust faults and north-dipping normal faults. Supported by the National Natural Science Foundation of China (Grant Nos. 40802046 and 40334037) and the Project of Science & Technology Research and Development from Sinopec (Grant No. P02009)