内蒙古东七一山碱长花岗岩的地球化学特征和成因

东七一山碱长花岗岩是内蒙古北山地区规模最大的稀有金属矿化花岗岩,本文在前期岩石学及成矿特征研究基础上,首次对其岩石地球化学、同位素地球化学及年代学进行了分析探讨。岩石富硅、富碱,贫Ti、Fe、Mg、Mn等基性组分,属高钾钙碱性系列岩石。稀土元素配分模式显示Eu强亏损特征,δEu<0.1,Ba、Sr、P、Ti相对地幔显著亏损,而Rb、Nb+Ta、W、Mo、Li等元素明显富集。两类碱长花岗岩的Rb-Sr等时线年龄为128.2±1.1 Ma,相关系数为0.999 9,ISr=0.709 79,说明岩体的物质来源具有明显的壳源特征。147Sm/144Nd值相对亏损地幔值偏高,而143Nd/144Nd值偏低,Pb同位素以富含放射性成因铅为特征。结合岩石学和产出环境研究成果,认为该碱长花岗岩是在燕山晚期,由区域钾长花岗岩浆在壳层挤压-拉伸环境中进一步分异演化形成的,先形成的是碱长花岗斑岩,构成了似斑状碱长花岗岩的外部相,而似斑状碱长花岗岩是在相对封闭且挥发组分和稀有元素进一步富集、结晶分异较缓慢的过程中形成的,由残余流体产生的自交代作用也相对更发育,导致形成与锂云母化、次生钠长石化和硅化关系更密切的铌-钽、钨、锡、铷等稀有金属矿化。以上认识对在北山地区寻找与中生代花岗岩浆活动有关的金属矿产,特别是铌-钽、钨、锡、铷、钼矿产,具有重要的指导意义。     

LA-ICP-MS Zircon U-Pb Geochronology of the Fine-grained Granite and Molybdenite?Re-Os?Dating in the Wurinitu Molybdenum Deposit, Inner Mongolia, China

The Wurinitu molybdenum deposit, located in Honggor, Sonid Left Banner of Inner Mongolia, China, is recently discovered and is considered to be associated with a concealed fine-grained granite impregnated with molybdenite.?The wall rocks are composed of Variscan porphyritic-like biotite granite and the Lower Ordovician Wubin’aobao Formation.?LA-ICP-MS zircon U-Pb dating of the fine-grained granite reveals two stages of zircons,?one were formed at 181.7±7.?4 Ma and?the other at 133.6±3.3 Ma. The latter age is believed to be the formation age of the fine-grained granite, while the former may reflect the age of inherited zircons, based on the morphological study of the zircon and regional geological setting. The Re-Os model age of molybdenite is 142.2±2.5?Ma, which is older than the diagenetic age of the fine-grained granite.?Therefore the authors believe that the metallogenic age of the Wurinitu molybdenum deposit should be?nearly 133.6±3.3 Ma or slightly later, i.e., Early Cretaceous.?Combined with regional geological background research, it is speculated that the molybdenum deposits were formed at the late Yanshanian orogenic cycle in the Hingganling-Mongolian orogenic belt, belonging to the relaxation epoch posterior to the compression and was associated with the closure of the Mongolia-Okhotsk?Sea.     

Granite is an Effective Helium Source Rock: Insights from the Helium Generation and Release Characteristics in Granites from the North Qinling Orogen,China

Global helium(He) shortage is a challenging problem; however, the types of helium source rock and the mechanisms of He generation and release therein remain still poorly understood. In this study, in order to evaluate the potential of granite as an effective helium source rock, we collected granitic samples from the North Qinling Orogen, Central China, in the south of the helium-rich Weihe Basin. The helium generation and release behaviors in granite were studied through analysis of U and Th concentrations, EMPA images, and He and Ar concentrations and isotopic ratios extracted by crushing and stepwise heating. The results indicate that Ar has a better retention and a lower mobility than He. 3 He/4 He ratios released by crushing and stepwise heating are 0.016–0.056 RA and 0.003–0.572 RA, respectively, where RA is the atmospheric 3 He/4 He of 1.4×10-6, reflecting a crustal and radiogenic source. Helium concentrations extracted by the two ways are 0.13–0.95 ucm3 STP/g and 7.82–115.62 ucm3 STP/g, respectively, suggesting that matrix-sited He accounts for more than 98% of total helium preserved in granite. In addition, the total generated He amounts in granites are calculated based on the measured U and Th concentrations in granitic samples. Dividing the preserved He quantities by the generated He amounts, it turned out that less than 10% of He produced since the formation of the granite is preserved in the rock over geological time, suggesting that more than 90% generated He can be transferred to the Weihe Basin. Temperature and fracture are the two critical factors controlling He release. Based on the relationship between He diffusivity of granites and temperature and the He closure temperatures of a variety of U-and Th-rich minerals(27–250°C), we estimate that He can be partially released out of granite at the depths 400 m and totally released at the depths 7800 m. Fractures provide effective transfer of free He from deep source rocks to shallow reservoirs. Finally, a model on granite as an effective helium source rock is established. We suggest exploring He resources in hydrocarbon basins with granitic basement(or adjacent to granite bodies), high geothermal field, and young active fractures.     

乳山金矿煌斑岩的Sm-Nd同位素研究

乳山金矿区发育多种与金矿脉在时空上密切伴生的煌斑岩脉。煌斑岩的稀土元素含量和配分曲线与胶东群残留体和昆嵛山花岗岩的均较相似；三者的εNd(t)、INd(t)和tDM亦甚为相近。胶东群的分异熔融作用，可较好地解释煌斑岩与花岗岩和胶东群残留体在成因上的渊源关系。     

大兴安岭北段巴升河岩体锆石U-Pb年代学及其地质意义

大兴安岭北段扎兰屯地区巴升河岩体由碱长花岗岩组成.采用LA-ICP-MS方法对碱长花岗岩开展锆石U-Pb测年,结果为297.8±3.6 Ma,岩体形成于早二叠世.该岩体4个样品的全岩地球化学等特征显示：巴升河岩体中碱长花岗岩具有富Si、高K、富碱的特征,属于弱过铝质钾玄岩系列,同时,样品∑REE偏高,Eu负异常明显,富集大离子亲石元素,具有A型花岗岩特征,综合前人研究成果及同位素年代学特征,认为兴安地块与松嫩地块拼合的时间早于298 Ma.     

The Late Triassic I–Type Granites from the Longmu Co–Shuanghu Suture Zone in the interior of Tibetan Plateau, China: Petrogenesis and Implication for Slab Break–Off

The Jiangaidarina granitic mass(JM) is an important part of the magmatic belt in Longmu CoShuanghu Suture Zone(LSSZ) in the central Tibetan Plateau. An integrated research involving wholerock geochemistry, zircon LA-ICP-MS U-Pb ages and Hf isotopic compositions was carried out to define the timing, genesis and tectonic setting of the JM. Zircon LA-ICP-MS U-Pb ages have been obtained ranging from 210 to 215 Ma, rather than the Early Jurassic as previously thought. Fifteen granite samples contain hornblendes and show a negative correlation between P_2 O_5 and SiO_2, indicating that the JM is an I-type granite. All the granites are enriched in LREE relative to HREE, with negative Eu anomalies(Eu/Eu*=0.56-0.81), and have similar trace elements patterns, with depletion of Ba, Nb, Sr and P. These suggest that the JM was fractionated, and this is also proved by the characteristic of negative correlations between oxide elements(TiO_2, MgO, FeOt, MnO, CaO) and SiO_2. Almost all ε_(Hf)(t) values of the granites are between-10.3 and-5.8, implying that the JM has a crustal source intimately related with the South Qiangtang Block(SQB), except for one(+10.2), showing a minor contribution from mantle source.Moreover, relatively low Na_2 O/K_2 O ratios(0.42-0.93) and high A/CNK values(0.91-1.50) reflect that the JM was predominately derived from the medium-high potassium basaltic crust, interacted with greywacke. Our new geochemical data and geochronological results imply that the Late Triassic magmas were generated in a post-collisional tectonic setting, probably caused by slab break-off of the Longmu Co-Shuanghu Tethyan Ocean(LSTO). This mechanism caused the asthenosphere upwelling, formed extension setting, offered an enormous amount of heat, and provided favorable conditions for emplacement of voluminous felsic magmas. Furthermore, the LSTO could be completely closed during the Middle Triassic, succeed by continental collision and later the slab broke off in the Late Triassic.     

“三江”云龙锡(钨)成矿带晚白垩世二云母花岗岩LA-ICP-MS锆石U-Pb定年及其地质意义

云龙成矿带位于西南“三江”中段,是该区重要的锡(钨)矿集区.本文利用LA-ICP-MS锆石U-Pb定年方法,对带内与成矿相关的二云母花岗岩进行了年龄测试,获得成岩年龄为72.2±0.8 Ma(MSWD=1.9),属晚白垩世.这是在保山地块首次发现确凿的晚白垩世岩浆岩,表明保山地块经受了该时期构造-岩浆活动的影响.通过锆石微量元素和主微量地球化学特征分析,认为其应属S型花岗岩.结合区域地质背景,认为云龙成矿带该期花岗岩可能与腾冲地块晚白垩世S型花岗岩形成于一致的动力学背景,为新特提斯东向俯冲过程中内陆增厚地壳熔融的产物.本次报道的晚白垩世S型花岗岩与成矿带内一期重要成矿期次时代一致.结合前人研究资料认为,云龙成矿带内三期主要的成矿事件均有同期构造-岩浆事件对应,其中早、晚白垩世成矿活动与同期花岗岩体侵入紧密相关,而新生代成矿活动则与崇山剪切带走滑活动关系密切.这表明本区锡(钨)矿床经历了多期成矿过程,岩浆侵入活动和构造相关混合岩化对矿床形成均有贡献,单一的成因机制(花岗岩相关或混合岩化)可能无法合理解释本区矿床的成因.     

铜陵地区晚古生代岩浆活动的发现：来自凤凰山岩体ZK66钻孔岩心辉绿岩锆石U–Pb定年的证据

凤凰山花岗闪长岩是铜陵地区出露面积最大的岩体,约10 km2,属高钾钙碱性系列.位于该岩体西北角的朱家山附近ZK66钻孔揭示,岩体超覆于三叠纪碳酸盐岩地层之上.除在浅部见到花岗闪长岩之外,深部主要见到晚泥盆世-二叠纪地层.特别是在石炭纪大理岩中见到辉绿岩和花岗斑岩,其锆石LA-ICP-MS U-Pb年龄分别为304 Ma和132 Ma,证明本区存在晚古生代岩浆活动,而中生代花岗质岩浆活动可能持续到132 Ma.晚石炭世辉绿岩的发现,说明该时期海底是一种拉张环境,海底喷流作用可能与岩浆活动有密切的成因关系,为该时期形成大型矿床奠定了基础.     

粤北油洞岩体SHRIMP锆石U-Pb年龄、地球化学特征及其成因研究

油洞岩体位于诸广南部岩体中部,是一个重要的产铀岩体,岩性为中粒小斑状二云母花岗岩。SHRIMP锆石U-Pb年龄为232±4Ma(MSWD=3.2),属于印支早期岩浆活动产物。该岩体在主量元素方面,具有富硅(SiO2平均为72.65%)、富铝(A/CNK值平均为1.12)和高的K2O/Na2O比值(平均为1.79);在微量元素方面,大离子元素富集,Ba、Sr、P、Ti、Nb、Ta亏损明显,具有高的Rb/Sr(平均为8.08)和Rb/Nb比值(平均为20.96);在稀土元素方面,轻稀土明显富集,配分模式呈右倾型,Eu亏损明显;在同位素方面,εNd(t)值低(平均为-11.9),(87Sr/86Sr)i高(平均为0.72330),Nd模式年龄古老(平均为1954 Ma)。这些特征一致表明,油洞岩体属于典型的壳源型花岗岩范畴,是在华南地块和印支地块碰撞结束后不久形成的伸展构造环境中,位于中—下地壳部位的古—中元古代地壳组分由于在地壳缩短之后的伸展、减薄环境下产生的减压、导水和地幔上涌等因素的综合影响下,由泥质岩和砂质岩混合组成的源区发生部分熔融而形成。     

伊通县放牛沟地区早古生代岩浆演化特征及其与矿产关系

伊通县放牛沟早古生代岩浆活动较为强烈,其发展演化与放牛沟多金属硫化物矿床关系极为密切。岩浆活动特点是先喷发后侵入,先期形成钙碱系列的火山—沉积岩系,后期为Ⅰ型中酸性岩浆侵入。该矿床既有火山沉积特征,又有后期岩浆热动力改造特点,其形成受控于岛弧构造环境、火山活动形成的矿源层、后期热动力改造等因素。