胶东半岛黄崖剖面早白垩世火山岩古地磁结果及其构造意义

对采自于胶东半岛黄崖剖面火山岩样品进行了系统的岩石磁学和古地磁学研究,结果表明HY1和HY2熔岩流样品的载磁矿物主要为磁铁矿和赤铁矿的混合,HY3熔岩流的样品主要为磁铁矿。系统热退磁实验从40块样品中分离出了稳定的特征剩磁方向,获得古地磁偏角/倾角平均方向为12.8°/62.4°(α95=4.8°),对应的平均虚地磁极位置为76.7°N/162.6°E(A95=6.2°)。40Ar/39Ar同位素定年结果显示,HY3火山岩的喷出年龄约为115.3±1.3 Ma~115.6±1.6 Ma(2σ)。比较结果显示,未发现研究区相对于华北块体在早白垩世有较大幅度的旋转或位移。对比山东、辽宁地区以及朝鲜半岛南部已有的晚中生代古地磁数据,发现侏罗-白垩纪期间古地磁的偏角随时间变化规律具有相似性,说明块体的旋转运动具有较一致规律性,指示东亚东缘构造运动可能受到古太平洋俯冲运动方向调整的影响。     

胶东半岛早白垩世地壳隆升剥蚀及其动力学意义

地壳大规模的隆升剥蚀通常是重大地质事件的响应，是地球动力学研究的重要内容之一。本文总结了胶东半岛中生代燕山期不同阶段的花岗岩侵位和金矿形成深度并以此估算了胶东半岛地壳隆升-剥蚀的厚度。结果表明胶东半岛在中生代旱白垩世140—110Ma期间，地壳隆升-剥蚀厚约7km，而从早白垩末期至今的110Ma以来，地壳隆升一剥蚀厚度不足4km。这表明胶东半岛早白垩世140—110Ma期间曾发生了一次重大地质事件，从而导致了胶东半岛整体快速隆升和剥蚀。该事件与中国东部岩石圈减薄的峰期时限耦合，应是岩石圈减薄的深部动力学过程的浅部响应。隆升-剥蚀的深部过程可能与该区造山加厚地壳的拆沉有关，同时还伴有因古太平洋斜向加速俯冲所引起的地幔上涌共同作用有关。     

Early Cretaceous A-type granites and Mo mineralization,Aershan area,eastern Inner Mongolia,Northeast China: geochemical and isotopic constraints

The Jiazishan porphyry-type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. Mineralization occurs mainly as veins, lenses, and layers within the host porphyry. To better understand the link between mineralization and host igneous rocks, we studied samples from underground workings and report new SHRIMP II zircon U–Pb and Re–Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Seven molybdenite samples yield a Re–Os isochron weighted mean age of 135.4 ± 2.1 Ma, whereas the porphyry granite samples yield crystallization ages of 139 ± 1.5 Ma (Jiazishan deposit) and 133 ± 1 Ma (Taolaituo deposit). The U–Pb and Re–Os ages are similar, suggesting that the mineralization is genetically related to Early Cretaceous porphyry emplacement. Re contents of the molybdenite range from 21.74 ppm to 52.08 ppm, with an average of 35.92 ppm, whereas δ³⁴ S values of the sulphide vary from 1.3‰ to 4.2‰. The ores have ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.178–18.385, 15.503–15.613, and 37.979–38.382, respectively. We also obtained a weighted mean U–Pb zircon age of 294.2 ± 2.1 Ma for the oldest granite in Jiazishan area. All granites are A-type granites. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Jiazishan deposit occurred contemporaneously with Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra-continental extension in Northeast China.     

胶东早白垩世高镁闪长岩类的发现及其构造背景

胶东地区发育大规模早白垩世壳幔混合源花岗岩类,但一直未发现与花岗岩类相关的独立的幔源侵入体,给深入理解早白垩世壳幔演化带来了困惑。胶东的柳林庄和夏河城岩体以往被认为是三叠纪闪长岩类,本文在详细的野外地质工作基础上,通过年代学、岩石地球化学、同位素地球化学分析,发现这2个岩体为早白垩世高镁闪长岩。样品的SiO₂含量在53.29%~62.54%之间,MgO含量为3.60%~8.10%,Mg^#主要介于0.47~0.68之间;富集Ba、Rb、K等大离子亲石元素,亏损Nb、Ta、Zr等高场强元素;初始⁸⁷Sr/⁸⁶Sr值为0.7082~0.7083,与地幔平均值接近;ε_Nd（t=113Ma）值很低（-20.5~-16.8）,与胶东地区的基性脉岩同位素组成一致。2个岩体相比而言,柳林庄岩体富K₂O、Fe₂O₃^T,REE、LILE、HFSE含量较高,而MgO、Ni和Cr含量偏低。3件样品的锆石LA-ICP-MS U-Pb同位素加权平均年龄值分别为120.1±1.6Ma、118.3±1.7Ma和122.3±4.0Ma,与壳幔混合源的伟德山型花岗岩及胶东金矿的成岩、成矿时代一致,指示他们形成于统一的地球动力学背景。高镁闪长岩的地球化学特征介于高镁埃达克岩与赞岐岩及埃达克岩与Piip型高镁安山岩之间,指示其形成于古太平洋板块俯冲的地幔楔环境,为富集岩石圈地幔部分熔融的产物。夏河城岩体的岩浆直接来源于含角闪石的富集岩石圈地幔源区,而柳林庄岩体岩浆源区为含金云母的岩石圈地幔并且在岩浆上侵过程中混染了部分地壳物质。     

Incremental growth and origin of the Cretaceous Renjiayingzi pluton,southern Inner Mongolia,China: Evidence from structure,geochemistry and geochronology

The Renjiayingzi intermediate-acid pluton is located along a pre-existing ENE–WSW-trending dextral shear zone that forms part of the Xar Moron suture zone that marks the final closure of the Paleo-Asian Ocean. The pluton is composed of three small intrusions, which from northwest to southeast, are named the Shuangjianshan (SI), the Qianweiliansu (QI) and the Xingshuwabeishan (XI) intrusions. LA-ICPMS zircon U–Pb dating of a pyroxene diorite from the SI yields an age of 138 ± 1 Ma; the SHRIMP zircon U–Pb age of a tonalite from the QI records an age of 134 ± 2 Ma, whereas LA-ICPMS zircon U–Pb dating of a monzogranite from the XI has an age of 126 ± 1 Ma, suggesting the entire pluton was built up by three separate emplacement events that young to the ESE: this is further supported by the contact relations. Incremental growth of plutons by amalgamation of repeated small magma pulses is the most viable emplacement model. The pluton was probably emplaced by updoming of the roof along previous tensile fractures and by upward stacking of the three intrusions. The SI and QI have similar U–Pb ages and geochemical characteristics, and most likely had the same magma source and underwent similar petrogenetic processes. They have high MgO concentrations at low silica contents, are enriched in large ion lithophile elements, depleted in high field strength elements, have negative ε_Nd(t) values of −1.8 to −3.7, with Nd model ages of 1.07–1.19 Ga. Pyroxene diorites of the SI also have variable zircon ε_Hf(t) values (from −0.8 to +6.1), indicating that they were mainly derived from juvenile crust with minor crustal contamination and clinopyroxene-dominated fractional crystallization. The late monzogranites from the XI show weak negative ε_Nd(t) values of −2.3 to −2.5, young Nd model ages of 0.99–1.00 Ga, positive zircon ε_Hf(t) values (+1.3 to +4.6) and higher SiO₂ and K₂O contents, with strong depletion in Eu, P and Ti, indicating derivation from a distinct petrogenetic process from the two earlier intrusions. The monzogranites were the result of partial melting of juvenile crust in response to mantle-derived magma underplating, together with plagioclase-dominated fractional crystallization.     

Gold-hosting high Ba-Sr granitoids in the Xincheng gold deposit,Jiaodong Peninsula,East China: Petrogenesis and tectonic setting

The Xincheng deposit is the only large gold deposit with a proven reserve of >200 t gold hosted by the Early Cretaceous granitoids in northwest Jiaodong Peninsula, East China. The granitoids hosting this ore deposit comprise an inner medium- to fine-grained quartz monzonite and an outer medium- to coarse-grained monzogranite with distinctive K-feldspar megacrysts. LA–ICP–MS zircon dating yields U–Pb ages of 128 ± 1 to 132 ± 1 Ma and 127 ± 2 to 129 ± 1 Ma, for the quartz monzonite and the monzogranite, respectively. The Early Cretaceous ages obtained in our study are comparable with the 126–130 Ma age range reported for the Guojialing granitic suite. The monzogranites, typical high Ba–Sr granites, possess high SiO₂ (70.89–73.35%), K₂O (3.85–4.32%), total alkalis (K₂O + Na₂O = 8.08–8.68%), Sr (634–888 ppm), Ba (1395–2111 ppm) and LREE (59.43–145.88), with low HREE and HFSE contents and insignificant Eu anomalies. The rocks display markedly high Sr/Y (114–297) and (La/Yb)_N (20–79) ratios. They have low MgO (0.23–0.62%), Cr (0.4–8.33 ppm) and Ni (0.47–2.92 ppm) contents. The typical high Ba–Sr signatures of the outer acidic monzogranites are also shared by the inner intermediate-acidic quartz monzonites, with a relatively higher abundance of these elements. The plagioclases in the quartz monzonites and monzogranites are oligoclase–andesine with An contents of 11.7–44.5%, and oligoclase with An contents of 12.9–29.3%, respectively, which both show the reverse zoning texture. The quartz monzonites have zircon ε_Hf(t) values of −21.3 to −13.9 (average −18.7), which are less negative and show larger variations than those of the monzogranites (ε_Hf(t) = −24.7 to −18.1, average −19.5). Detailed elemental, mineralogical and isotopic data suggest that the high Ba–Sr quartz monzonites and monzogranites were most likely generated by partial melting of the basement rocks of the Jiaobei terrane accompanied by crustal assimilation, with minor addition of the intermediate magma derived from the partial melting of juvenile mafic lower crust formed by the earlier underplating of mantle magma, and the quartz monzonites may represent the path of intermediate magma inputting into felsic magma. In combination with previous investigations, we suggest subduction of the paleo-Pacific slab beneath the North China Craton (NCC) and associated asthenosphere upwelling were most likely the mechanism associated with the generation of the high Ba–Sr granites.     

胶东崂山早白垩世A型花岗岩成因及对区域构造演化的意义

早白垩世崂山花岗岩位于苏鲁超高压变质带中部, 是中国东部典型的A型花岗岩之一。其岩浆源区和岩石成因目前还存在一定的争议, 而且其成岩过程中的物理化学条件及相关研究也比较缺乏。本文在详细的野外工作和岩相学研究的基础上, 采用角闪石、黑云母的成分估算了成岩的温度、压力和氧逸度条件, 并开展了岩石地球化学、Sr-Nd同位素分析, 探讨岩石的源区和成因。结果显示, 崂山花岗岩的岩浆形成于高温(>850℃)和高氧逸度条件。岩浆在地壳浅部压力较低的条件下结晶, 岩浆固结温度在700℃左右, 随后经历了快速降温的过程。岩石地球化学方面, 崂山花岗岩富SiO2、富碱, 贫Ca、Mg; 高场强元素Th、Zr、Nb、Y和大离子亲石元素Rb、K含量高, 而Ba、Sr含量低; 稀土元素含量高, 且具有显著的Eu负异常, 呈右倾"海鸥型"分配特征。同位素方面, 所有样品均显示出富集的Sr、Nd同位素特征, (87Sr/86Sr)i=0.706447~0.707876, εNd(117Ma)值为-14.8~-17.4, 全岩Nd两阶段模式年龄(tDM2)为2112~2325Ma。结合胶东地区前人的研究成果, 本文认为崂山A型花岗岩是由地壳中富K的碱性岩重熔而成, 其岩浆源区很可能与该区三叠纪碱性岩浆活动有关。崂山A型花岗岩的形成标志着碰撞造山带底部的扬子板块已经垮塌完毕, 同时岩石圈减薄达到高峰。     

Identification of the Early Jurassic mylonitic granitic pluton and tectonic implications in Namling area,southern Tibet

A number of studies revealed that the Gangdese magmatic belt of southern Tibet was closely related to the northward subduction of the Neo-Tethys oceanic lithosphere and Indo-Asian collision.However,pre-Cretaceous magmatism is still poorly constrained in the Gangdese magmatic belt,southern Tibet.Here,we conducted systematically geochronology and geochemistry studies on a newly-identified granitic pluton in the middle Gangdese magmatic belt(Namling area),southern Tibet.Zircon SHRIMPⅡU-Pb dating for one representative sample gives a weighted age of 184.2±1.8 Ma(MSWD=±1.11),corresponding to emplacement and crystallization age of the granitic pluton in the Early Jurassic(Pliensbachian).High SiO2(68.9-72.1 wt.%)contents and intermediate Mg#values(35-38)together suggest that the newly-identified granitic pluton was probably formed by partial melting of crustal material with minor injection of mantle-derived magma,precluding an origin from melting of metasedimentary rocks that are characterized by low Mg#and high zirconδ^18O values(>8‰).Geochemically,the newly-identified granitic pluton belongs to typical I-type granitic affinity,whereas this is inconsistent with aluminium saturation index(ASI=A/CNK ratios)and geochemical signatures.This suggests that zircon oxygen isotopes(4.30‰-5.28‰)and mineral features(lacking Al-rich minerals)are reliable indicators for discriminating granitic origin.Significantly depleted whole-rock Sr-Nd-Hf isotopic compositions and zirconεHf(t)values indicate that the granitic pluton was derived from partial melting of depleted arc-type lavas.In addition,the granitic pluton shows zirconδ^18O values ranging from 4.30‰to 5.28‰(with a mean value of 4.77‰)that are consistent with mantle-derived zircon values(5.3‰±0.6‰)within the uncertainties,indicating that the granitic pluton might have experienced weak short-living high-temperature hydrous fluid-rock interaction.Combined with the Sr-Nd-Hf-O isotopes and geochemical signatures,we propose that the newly-identified granitic pluton was originated from partial melting of depleted mafic lower crust,and experienced only negligible wall-rock contamination during ascent.Integrated with published data,we also propose that the initial subduction of the Neo-Tethys oceanic lithosphere occurred no later than the Pliensbachian of the Early Jurassic.     

胶东文登长山南花岗闪长岩体的岩浆混合成因：闪长质包体及寄主岩石的地球化学、Sr-Nd同位素和锆石Hf同位素证据

胶东昆嵛山杂岩文登长山南花岗闪长岩体中广泛分布具有火成结构的闪长质包体,这些包体主要为椭圆形或纺锤形,定向排列,大小不等（几cm至几m）,颜色较寄主岩深,粒度较细,包体具有与寄主岩石相似的矿物组合,但铁镁质矿物及斜长石含量明显比寄主岩石高,而石英和钾长石含量低于寄主岩石;镜下包体具有明显的不平衡反应结构,广泛发育针状磷灰石。在地球化学特征上,包体和寄主岩石部富集大离子亲石元素和轻稀土元素,亏损高场强元素,并具有相近的Sr、Nd同位素组成,ISr为0．70784～0．70818,εNd为-15．0～-15．5然而,包体和寄主岩石的主量元素在相关图上呈明显的线性关系,并且岩石学和锆石Hf同位素特征也明显表明文登长山南岩体在成岩过程中发生了镁铁质岩浆和长英质岩浆的混合作用。在岩浆混合作用过程中,全岩Sr、Yd同位素和晚期生成的矿物组成比较快速地达到了均一化,而主量元素和高温矿物锆石Hf同位素组成则残留了原始岩浆的部分特征研究表明,锆石Hf同位素在岩浆混合作用过程中不容易达到同位素平衡,其同位素组成比全岩Sr、Nd同位素更能有效地示踪混合岩浆的源区特征和岩浆混合过程。     

Petrogenesis and tectonic implications of the middle Silurian volcanic rocks in northern West Junggar,NW China

Zircon U–Pb geochronological and geochemical analyses are reported for a suite of the middle Silurian volcanic rocks from northern West Junggar (NW China), southern Central Asian Orogenic Belt (CAOB), with the aim to investigate the sources, petrogenesis, and tectonic implications. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb analysis from an andesite yielded a concordant weighted mean ²⁰⁶Pb/²³⁸U age of 429 ± 3 Ma, indicating the presence of middle Silurian volcanic rocks in northern West Junggar. The andesite is tholeiite series and characterized by minor variations in compositions (SiO₂ = 55.68–59.17 wt.%, Al₂O₃ = 14.56–17.7 wt.%, TiO₂ = 0.55–1.23 wt.%, Na₂O + K₂O = 3.46–7.16 wt.%, and P₂O₅ = 0.15–0.37 wt.%), with wider MgO content (2.18–6.48 wt.%) and Mg# (57.4–77.9). All andesitic rocks are enriched in large-ion lithophile elements (LILEs; e.g. Rb, Ba, K, and Th) and light rare earth elements (LREEs), but strongly depleted in some high field strength elements (HFSEs; e.g. Nb, Ta and Ti), with slight negative Eu anomalies (Eu/Eu* = 0.8–1). These features suggest that the andesitic magmas were derived from 2–8% partial melting of a garnet lherzolite depleted mantle source with subducted sediments metasomatized by slab-derived fluids. Combining the current study with those data in existing literature, we conclude that the middle Silurian volcanic rocks formed in an intra-oceanic subduction setting during consumption of the Irtysh–Zaysan Ocean, and further confirm the eastern extension of the early Palaeozoic Boshchekul–Chingiz volcanic arc of East Kazakhstan in China.     

Cambrian granitic gneiss within the central Qiangtang terrane,Tibetan Plateau: implications for the early Palaeozoic tectonic evolution of the Gondwanan margin

ABSTRACT

The Tibetan Plateau is located in the eastern Himalayan–Alpine orogen, an area where previous research has focused on ophiolites and a high-pressure metamorphic belt, whereas comparatively little research has been undertaken on the Tibetan basement. Cambrian granitic gneiss crops out in the Duguer area of the South Qiangtang terrane in northern Tibet and yields zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb ages of 502–492 Ma, providing insight into the possible existence of basement rocks within the South Qiangtang terrane. The granitic gneisses are geochemically similar to high-K, calc-alkaline S-type granites, and Hf isotopic analysis of zircons within the gneisses yields negative εHf(t) values (–7.4 to – 1.1) and old zircon Hf model ages (T_DM^C = 1757–1406 Ma). These granitic gneisses were generated by partial melting of ancient pelitic rocks, and the resulting melts were contaminated by a small amount of mantle-derived material. Combining our new data with previous research, we conclude that these Cambrian granitic gneisses developed in a post-collisional tectonic setting after Pan-African tectonism. This suggests that the South Qiangtang terrane might have the same early Palaeozoic crystalline basement as the Lhasa, Himalaya, Baoshan, Gongshan, and Tengchong terranes.     

胶东旧店金矿床赋矿岩浆岩岩石成因及其地质意义

胶东地区是我国最重要、规模最大的金矿集区, 其中晚侏罗世玲珑花岗岩分布较为广泛, 是最主要的金赋矿围岩。旧店金矿床位于胶北隆起与胶莱盆地的交界处, 是招平断裂带的重要组成部分, 片麻状二长花岗岩为其主要的赋矿岩体, 对其岩石成因进行研究, 可以为探究金成矿作用提供线索和约束。本文对旧店金矿床周围两处的片麻状二长花岗岩开展LA-ICP-MS锆石U-Pb年代学以及Lu-Hf同位素研究。分析结果显示, 锆石²⁰⁶Pb/²³⁸U年龄为160.1±1.1Ma、160.4±0.7Ma、161±0.4Ma和162.2±0.9Ma, 表明旧店金矿床区域内在晚侏罗世存在较强的岩浆作用。ε_Hf(t)值为-31.9~-20.8, 二阶段Hf模式年龄(t_DM²)为2996~2516Ma, 表明其岩浆来源于下地壳物质部分熔融, 同时二阶段Hf模式年龄(t_DM²)与地幔物质加入和新生地壳产生的岩浆热事件相对应, 因此旧店金矿床的围岩可能由古老镁铁质下地壳物质的部分熔融产生。研究认为二长花岗岩的形成过程可能促使了前寒武纪变质基底中成矿物质活化, 同时岩体发育广泛的断裂为矿床形成提供了良好的围岩条件。

     

Fluid evolution in the Rushan lode gold deposit of Jiaodong Peninsula, eastern China

The Rushan gold deposit in the Jiaodong Peninsula is currently the largest lode gold in China. Gold occurs mainly in pyrite- and polymetallic sulfide–quartz vein/veinlet stockworks. Fluid inclusions in the deposit are divided into three main types, namely CO₂–H₂O, H₂O–CO₂ ± CH₄ and aqueous ones. Microthermometric data show that the pre-gold fluids were CO₂-dominant (X_CO2 up to 0.53), and the total homogenization temperatures fall in the range of 298377 °C. These fluids, modified by fluid/wallrock reactions, gradually evolved into fluids with less CO₂ (X_CO2 = 0.010.19) in the main ore-forming stage, and the total homogenization temperatures range from 170 to 324 °C. Hydrogen and oxygen stable isotope data suggest that ore-forming fluids were mixture of magmatic and meteoritic origin. Co-occurrence of gold and sulfides implies that gold was most likely transported in the form of gold–sulfide complexes. The wide distribution of CO₂ inclusions means that the pH variation during gold transportation was controlled by CO₂ buffering.     

A Study of Sr, Nd and O Isotopes of the K-rich Melanocratic Dykes in the Late Mesozoic Gold Field in the Jiaodong Peninsula

Geologic, petrographic and petrochemical studies of the late Mesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, China, have shown that these dykes are characterized by rich potassium and alkali but poor titanium. They belong to an ultra-high potassic, shoshonitic and high potassic calc-alkaline rock series. The parental magma has relatively high initial strontium ratios ((87Sr/86Sr)i=0.70895-0.71140) and low (143Nd/144Nd)i ratios (varying from 0.51135 to 0.51231); and its δ18OSMow. whole rock values vary from +5.8‰ to +10.6‰ with a mean of+7.1‰. These features suggest that the source region of the magma is an enriched mantle wedge transformed from a continental lithosphere mantle which has experienced metasomatism by mantle-derived fluids with H2O-dominated fluids that were provided during the underthrusting of an ocean crust. The initial magma was generated by low-degree partial melting of the enri     

胶西北新城金矿床二长花岗岩岩石地球化学、锆石U-Pb年龄及Lu-Hf同位素组成

胶东是我国最重要的金矿集区,也是环太平洋中、新生代金成矿系统的重要组成部分,其内花岗质岩石分布广泛,95%以上的金资源储量赋存在晚侏罗世玲珑型花岗岩和早白垩世早期郭家岭型花岗质岩中。关于花岗岩类的成因,尤其是早白垩世花岗质岩的岩石类型及其源区仍存有争议。新城金矿床位于胶东西北部焦家断裂带北段,是迄今为止在胶东矿集区内发现的赋存在早白垩世花岗质岩中最大的金矿床,其内已探明金资源储量大于200t。该金矿床的赋矿围岩为新城花岗岩体,由中细粒石英二长岩和中粗粒似斑状二长花岗岩组成,形成于127~132Ma。进一步的地质观察表明中粗粒似斑状二长花岗岩两侧的岩石粒度逐渐变细,斑晶逐渐变小,长英质矿物增多,明显不同于中粗粒似斑状二长花岗岩,应为中细粒似斑状二长花岗岩。论文对该中细粒似斑状二长花岗岩进行了系统的岩石地球化学、锆石LA-ICP-MS定年和Lu-Hf同位素组成研究,并进一步探讨了该类岩石的地球化学类型、形成时代、岩浆源区性质及其与新城花岗岩体的关系。岩石地球化学研究表明中细粒似斑状二长花岗岩具有高的SiO2(71.18%~73.72%)、全碱(K2O+Na2O=7.07%~8.64%)、Ba(793×10-6)、Sr(729×10-6)和轻稀土含量(71.14×10-6),低的Al2O3(13.57%~15.73%)、MgO(0.22%~0.39%)、Rb(91.7×10-6)、Th(7.4×10-6)、U(4.51×10-6)、Nb(4.49×10-6)、Ta(0.26×10-6)、Y(3.67×10-6)和重稀土含量(7.47×10-6),无明显的铕异常,明显亏损Nb、Ta、P、Ti等高场强元素,显示出典型的高Ba-Sr花岗岩所具有的地球化学特征,属高BaSr花岗岩。锆石LA-ICP-MS定年结果表明中细粒似斑状二长花岗岩形成于123±1Ma,而石英二长岩和中粗粒似斑状二长花岗岩的锆石LA-ICP-MS年龄为127±2Ma~132±1Ma,3种类型岩石具有相似的主量元素组成及稀土和微量元素分布模式,表明新城花岗岩体的形成时代应为123±1Ma~132±1Ma。Lu-Hf同位素测试结果显示中细粒似斑状二长花岗岩岩浆锆石的εHf(t)为-20.76~-18.66,二阶段模式年龄tDM2为2351~2479Ma;在εHf(t)-锆石U-Pb年龄图解中,所有数据点均落在球粒陨石演化线之下的壳源区域。金矿床已有石英二长岩、中粗粒似斑状二长花岗岩和区域玲珑型花岗岩Hf同位素组成及该中细粒似斑状二长花岗岩中2个太古代(2629±14Ma、2402±18Ma)和3个中生代(150±7Ma、151±1Ma、147±1Ma)的继承锆石年龄,表明新城金矿床内中细粒似斑状二长花岗岩应来源于前寒武纪变质基底岩石,岩浆上升过程中遭受了上地壳(主要是玲珑黑云母花岗岩)的混染。     

Petrogenesis and evolution of late Mesozoic granitic magmatism in the Hohhot metamorphic core complex,Daqing Shan,North China

Late Mesozoic granitoid plutons of four distinct ages intrude the lower plate of the Hohhot metamorphic core complex along the northern margin of the North China craton. The plutons belong to two main groups: (1) Group I, deformed granitoids (148 and 140 Ma subgroups) with high Sr, LREE, and Na₂O, low Y and Yb contents, high Sr/Y and La/Yb ratios, weak or no Eu anomalies, low Rb/Ba ratios, similar initial ⁸⁷Sr/⁸⁶Sr values (0.7064–0.7071) and low Mg^# (<37 mostly, 100?×?molar MgO/MgO + FeO _t ); (2) Group II, non-deformed granitoids (132 and 114 Ma subgroups) with low Sr, relatively low Na₂O, high Y and Yb contents, pronounced negative Eu anomalies, high Rb/Ba ratios, and initial ⁸⁷Sr/⁸⁶Sr values (0.7098–0.7161). The two groups share geochemical similarities in ?_Nd(t) (–11.3 to –15.4) and T _DM2 ages (1.85–2.18 thousand million years) as well as Hf isotopic ratios in zircons. Geochemical modelling (using the MELTS code) suggests that similar sources but different depths of magma generation produced the early, high-pressure low-Mg adakitic granitoids and late, low-pressure granitoids with A-type characteristics. The early granitoids likely represent a partially melted, deep-seated, thickened lower continental crust that involved a minor contribution from young materials, whereas the later group partially melted at shallower depths. This granitic magmatic evolution coincided with the tectonic transition from crustal contraction to extension.     

Early Carboniferous volcanic rocks of West Junggar in the western Central Asian Orogenic Belt: implications for a supra-subduction system

The paper presents new U–Pb zircon ages and geochemical data from early Carboniferous volcanic rocks of the Wuerkashier Mountains in the northern West Junggar region, NW China, and of the Char suture–shear zone in East Kazakhstan. The study included analysis of geological setting, major and trace elements, and rock petrogenesis. Both localities host early Carboniferous volcanic units dominated by plagioclase-porphyry andesites and dacites. A West Junggar dacite yielded a ²⁰⁶Pb/²³⁸U age of 331 ± 3 Ma. The Junggar volcanic rocks are tholeiitic, and the Char samples are intermediate between tholeiitic and calc-alkaline. Both the Junggar and Char volcanic units are characterized by LREE enriched rare-earth spectra (La/Sm_n = 1.1–2.4) with Eu negative anomalies (Eu/Eu* = 0.12–1.0) and Nb-Ta minimums (Nb/Th_pm = 0.15–0.35; Nb/La_pm = 0.3–0.7) on multi-element spectra. The Junggar andesites and dacites have higher REE and HFSE (Ti, Nb, Zr, Y, and Th) compared with the Char rocks, suggesting their derivation from a different mantle source. The melting modelling in the Nb-Yb system showed that the Junggar volcanic rocks formed by low- to medium- (2–5%) degree melting of depleted mantle harzburgite and spinel lherzolite. The Char volcanic rocks formed by high-degree melting (15–20%) of spinel lherzolite and garnet-bearing peridotite. The regional geology of West Junggar and East Kazakhstan and the geochemical features of the rocks under study (i.e. depletion in Nb, Ta, and Ti and enrichment in Th, and combination of LREE enrichment and HFSE depletion) all suggest a subduction-related origin of both Junggar and Char volcanic rocks. The early Carboniferous volcanic rocks of West Junggar possibly formed by subduction of the Junggar-Balkhash ocean beneath an active margin of the Kazakhstan continent, whereas those of East Kazakhstan formed by subduction of the Irtysh-Zaisan Ocean beneath an intra-oceanic arc at the active margin of the Siberian continent.     

胶西北大泽山岩体地球化学、锆石U-Pb年代学及Lu-Hf同位素特征

胶东金矿集区是我国最重要的金矿集区, 大规模金成矿作用发生于125~110 Ma。本文选择了与成矿作用同期的早白垩世晚期大泽山岩体为研究对象, 通过详细的岩相学、岩石地球化学、锆石LA-ICP-MS U-Pb年代学研究, 识别出中粒二长花岗岩和细粒二长花岗岩两种主要的侵入岩类型, 它们具有相似的岩相学和岩石地球化学特征, 呈现同源岩浆演化特征。定年结果表明, 中粒二长花岗岩中锆石U-Pb年龄分别为119.8±0.8 Ma和119.3±0.9 Ma, 细粒二长花岗岩中锆石U-Pb年龄分别为109.2±0.7 Ma和109.9±0.7 Ma。岩石地球化学研究表明, 二长花岗岩具有高的全碱(K₂O+Na₂O=8.14%~8.72%), 高的Al₂O₃(12.42%~15.32%), 属过铝质高钾钙碱性系列, 轻稀土(LREE)富集、重稀土(HREE)相对亏损(LREE/HREE=8.46~18.87), 具明显的稀土元素分馏((La/Yb)_N=8.52~24.08)和较强的Eu负异常(δEu=0.33~0.58)。大泽山岩体锆石ε_Hf(t)值为-26.4~-16.2, 亏损地幔二阶段模式年龄(T_DM2)为2 812~2 173 Ma, 物源主要是古元古代和新太古代陆壳的部分熔融, 有少量幔源物质的加入。大泽山岩体成岩期与胶东金矿的主成矿期一致, 暗示岩浆活动与金成矿具有统一的地球动力学背景。

     

胶东三山岛金矿床黄铁矿As富集机制及其对金成矿作用的指示

胶东是中国最大的金矿集区,其金矿成因目前还存在较大争议.作为最重要的载金矿物,黄铁矿显微结构及元素-同位素组成能够很好地示踪成矿物质来源和成矿过程.利用SEM、EPMA和LA-ICP-MS微区原位分析方法对胶东代表性蚀变岩型金矿—三山岛金矿的黄铁矿开展详细的BSE显微结构以及As含量和S同位素耦合关系研究,发现矿区至少...     

青海尕林格南地区火山岩地球化学特征及锆石U-Pb年龄

在东昆仑山脉西段祁漫塔格山中东部的尕林格南地区发育一套火山岩,调查显示火山活动爆发相→溢流相相间的韵律周期较明显,见由玄武质含火山角砾凝灰岩→玄武岩、玄武质凝灰岩→安山岩、安山质角砾凝灰岩→安山岩,以及安山质含火山角砾凝灰岩和安山岩质凝灰岩→玄武岩组成的4个韵律。根据研究区安山质火山角砾凝灰岩的LA-ICP-MS锆石U-Pb年龄222.2±2.1Ma,将该火山岩地层由前人划分的顶志留统—下泥盆统契盖苏组火山岩段重新厘定为上三叠统鄂拉山组。岩石地球化学研究结果表明,该套火山岩属于亚碱性钙碱性系列岩石,具有富钾、同源岩浆演化的特点,并具弧火山岩和碰撞火山岩的地球化学特征,为陆内造山作用下的产物,较好地记录了东昆仑祁漫塔格造山带在晚三叠世岩浆演化的地质信息。