Magma Genesis and Mantle Dynamics at the Harrat Ash Shamah Volcanic Field (Southern Syria)     

Krienitz  M.-S.; Haase  K. M.; Mezger  K.; Shaikh-Mashail  M. A. 《Journal of Petrology》2007,48(8):1513-1542

A geochemical and petrological study of Miocene to recent alkalibasalts, basanites, hawaiites, mugearites, trachytes, and phonoliteserupted within the Harrat Ash Shamah volcanic field was performedto reconstruct the magmatic evolution of southern Syria. Themajor element composition of the investigated lavas is mainlycontrolled by fractional crystallization of olivine, clinopyroxene,± Fe–Ti oxides and ± apatite; feldspar fractionationis restricted to the most evolved lavas. Na₂O and SiO₂ variationswithin uncontaminated, primitive lavas as well as variably fractionatedheavy rare earth element ratios suggest a formation by variabledegrees of partial melting of different garnet peridotite sourcestriggered, probably, by changes in mantle temperature. The isotopicrange as well as the variable trace element enrichment observedin the lavas imply derivation from both a volatile- and incompatibleelement-enriched asthenosphere and from a plume component. Inaddition, some lavas have been affected by crustal contamination.This effect is most prominent in evolved lavas older than 3·5Ma, which assimilated 30–40% of crustal material. In general,the periodicity of volcanism in conjunction with temporal changesin lava composition and melting regime suggest that the Syrianvolcanism was triggered by a pulsing mantle plume located underneathnorthwestern Arabia. KEY WORDS: ⁴⁰Ar/³⁹Ar ages; intraplate volcanism; mantle plume; partial melting; Syria  相似文献   

东南极拉斯曼丘陵石榴斜长角闪岩中角闪石的~(40)Ar-~(39)Ar年龄及其地质意义          下载免费PDF全文

仝来喜  刘小汉  张连生  陈海泓  陈福坤  王彦斌  任留东 《极地研究》1998,10(3):4-14

本文对东南极拉斯曼丘陵出露的石榴斜长角闪岩中的角闪石进行了４０Ａｒ－３９Ａｒ年龄测定,分别得到角闪石视年龄１５８６Ｍａ、１０１１～１０８０Ｍａ、７６１Ｍａ和５２９～５８２Ｍａ,角闪石坪年龄１０３６Ｍａ和５５４Ｍａ,角闪石Ａｒ－Ａｒ等时线年龄１０１０Ｍａ,这些同位素年龄证据,首次完整地记录了该区所经历的几乎所有构造变质热事件,为近几年国内外地质学家关于该区构造变质热事件争论的焦点问题,即晚元古代的１０００Ｍａ格林维尔事件（Ｇｒｅｎｖｉｌｉａｎ）与早古生代的５００Ｍａ泛非事件（Ｐａｎ－Ａｆｒｉｃａｎ）孰轻孰重以及前者是否存在,提供了答案。角闪石的４０Ａｒ－３９Ａｒ年龄测定结果表明,拉斯曼丘陵地区经历了复杂的多期变质演化历史,其原岩可能形成于早－中元古代,占主导地位的应该是晚元古代的１０００Ｍａ格林维尔事件,而５００Ｍａ泛非事件则是晚期较强烈的变质热事件。  相似文献   

Post-collision neogene volcanism of the Eastern Rif (Morocco): magmatic evolution through time   总被引：6，自引：0，他引：6  

Samir El Bakkali  Alain Gourgaud  Jean-Louis Bourdier  Herv Bellon  Niyazi Gundogdu 《Lithos》1998,45(1-4):523-543

Neogene volcanism in the Eastern Rif (Morocco) comprises a series of calc-alkaline, potassic calc-alkaline, shoshonitic and alkaline volcanic rocks. According to new stratigraphical, along with new and previous chronological and geochemical data, the orogenic volcanism was successively (1) calc-alkaline (basaltic andesites and andesites: 13.1 to 12.5 Ma, rhyolites: 9.8 Ma), (2) K-calc-alkaline (basaltic andesitic to rhyolitic lavas and granodiorites: 9.0 to 6.6 Ma), and (3) shoshonitic (absarokites, shoshonites, latites, trachytes: 7.0 to 5.4 Ma). The later Pliocene volcanism was basaltic and alkaline (5.6 to 1.5 Ma). The calc-alkaline and K-calc-alkaline series exhibit lower K₂O (0.7–5.3 wt.%), Nb (8–19 ppm) contents and higher ⁸⁷Sr/⁸⁶Sr (0.70773–0.71016) than the shoshonitic series (K₂O: 2.4–7.2 wt.%, Nb: 21–38 ppm, ⁸⁷Sr/⁸⁶Sr: 0.70404–0.70778). Pliocene alkaline basalts have a sodic tendency (Na₂O/K₂O: 1.7–3.5), high Nb content (up to 52 ppm), and low ⁸⁷Sr/⁸⁶Sr ratio (0.70360–0.70413). The variations through time of K₂O, Nb and Sr isotopic ratio reflect different mantle sources: (i) calc-alkaline, potassic calc-alkaline and shoshonitic series are derived from a mantle source modified by older subduction, (ii) alkaline basalts are derived mainly from an enriched mantle source. Through time, incompatible elements such as Nb increased while ⁸⁷Sr/⁸⁶Sr decreased, suggesting a decreasing influence of metasomatized mantle (inherited subduction). Such evolution is related to the post-collision regimes operating in this area, and could be linked to the succession of extensional, compressional and strike-slip fault tectonics.  相似文献   

Age of Saurashtra miliolites by U-Th decay series methods: possible implications to their origin     

N. Hussain  N. Bhandari  K. R. Ramanathan  B. L. K. Somayajulu 《Journal of Earth System Science》1980,89(1):23-29

The miliolite deposits of Saurashtra have been dated by²³⁴U,²³⁰Th,²³¹Pa and¹⁴C methods. Concordant ages of 10⁵ years using the U decay series isotopes are obtained which agree with the ages of the coral reefs of Okha-Dwaraka coast suggesting a contemporaneous origin for both. The lower¹⁴C ages (≤40,000 years) may be due to a recent influx of seawater or ground water. Quartz and clay minerals together constitute only ≤10% by weight, as such the aeolian characteristics of quartz grains may not be relevant to the origin of the miliolites.  相似文献   

Moraine chronosequence of the Donnelly Dome region, Alaska     

A. Matmon  J.P. Briner  P. Bierman 《Quaternary Research》2010,74(1):63-47

We present ¹⁰Be exposure ages from moraines in the Delta River Valley, a reference locality for Pleistocene glaciation in the northern Alaska Range. The ages are from material deposited during the Delta and Donnelly glaciations, which have been correlated with MIS 6 and 2, respectively. ¹⁰Be chronology indicates that at least part of the Delta moraine stabilized during MIS 4/3, and that the Donnelly moraine stabilized ∼ 17 ka. These ages correlate with other dates from the Alaska Range and other regions in Alaska, suggesting synchronicity across Beringia during pulses of late Pleistocene glaciation. Several sample types were collected: boulders, single clasts, and gravel samples (amalgamated small clasts) from around boulders as well as from surfaces devoid of boulders. Comparing ¹⁰Be ages of these sample types reveals the influence of pre/post-depositional processes, including boulder erosion, boulder exhumation, and moraine surface lowering. These processes occur continuously but seem to accelerate during and immediately after successive glacial episodes. The result is a multi-peak age distribution indicating that once a moraine persists through subsequent glaciations the chronological significance of cosmogenic ages derived from samples collected on that moraine diminishes significantly. The absence of Holocene ages implies relatively minor exhumation and/or weathering since 12 ka.  相似文献   

Mineralogical and geochemical investigations of the Dajia Salento-type bauxite deposits,western Guangxi,China     

Xuefei Liu  Qingfei Wang  Jun Deng  Qizuan Zhang  Silei Sun  Jianyin Meng 《Journal of Geochemical Exploration》2010

The Dajia Salento-type bauxite deposit in western Guangxi is hosted within the Quaternary ferrallitic soil profile, and it formed via breaking up, weathering and oxidizing of Permian bauxite orebodies occurring as a semi-continuous layer in the upper Permian. Mineralogical analyses reveal that diaspore, hematite and kaolinite are the major minerals in bauxite ores with small amounts of anatase, chamosite, gibbsite, goethite, illite, zircon, quartz and pyrite. The ore texture and mineral assemblage reveal that the depositional/diagenetic environment of the Dajia bauxite was much close to phreatic environment. Both the ore texture and the morphology of zircon grains also indicate that most of the bauxitic soils were transported a short distance. Diaspore is suggested to be non-metamorphic in origin and mainly formed in a reducing condition of diagenetic environment, while kaolinite is the product of the in situ epigenetic replacement of alumina in diaspore by dissolved silica. Geochemical analyses indicate that Al₂O₃, Fe₂O₃, SiO₂ and TiO₂ are the main components of the bauxite ores and trace elements such as Zr, Hf, Nb, Ta, Th and U were enriched during the bauxitization process. Simultaneously, Zr vs. Hf and Nb vs. Ta show a high correlation. Geochemical indices such as Zr/Hf, Nb/Ta and Eu/Eu* (among others) denote that the magmatic rocks related to the Emeishan plume in western Guangxi and the carbonates in the underlying Maokou Formation provided the main sources of material for the bauxite ores.  相似文献   

长江中下游池州地区矽卡岩-斑岩型W-Mo矿床流体包裹体与H、O、S同位素研究   总被引：7，自引：5，他引：2  

宋国学  秦克章  李光明 《岩石学报》2010,26(9):2768-2782

长江中下游池州地区区域构造上处于下扬子坳陷与江南古陆之间的过渡带上,近年来该区域内以钨钼为主的多金属矿床勘探方面取得了很大突破,鸡头山矽卡岩-斑岩型W-Mo矿、马头斑岩型Mo矿和百丈岩矽卡岩-斑岩型W-Mo矿是其中的三个代表性矿床。在鸡头山矿区和百丈岩矿区钨钼主要赋存于矽卡岩体中,已有工程探明二者的深部都有斑岩型矿体存在;在马头矿区钼主要以含钼石英脉和辉钼矿细脉的形式赋存于近接触带岩体与围岩中。流体包裹体研究表明,池州地区与钨钼矿有关的流体包裹体以水溶液包裹体(L+V)为主,同时发育含子矿物包裹体(L+V+S)和CO2包裹体(L+LCO2+VCO2)。成矿流体演化分为三个阶段:早阶段温度在350～500℃之间,深度约为1.5～2.5km,初始流体盐度为17%～25%NaCleqv,流体富H2O-CO2-CH4等气体,流体发生沸腾作用分离出高盐度流体和富气相低盐度流体;中阶段温度在170～360℃之间,深度约为0.5～1.7km,盐度为2%～24%NaCleqv,富H2O-CO2-CH4-H2S等气体,流体混合作用使得大量钨、钼、铅、锌等金属沉淀成矿;晚阶段温度在100～160℃之间,深度在约0.6km以下,盐度范围为1%～10%NaCleqv,与成矿作用无关。含矿石英脉H-O同位素和硫化物S同位素共同指示,池州地区与钨钼矿有关的成矿流体来自岩浆水、大气水和建造水的混合,流体混合是区域钨-钼-铅-锌成矿的主要机制。  相似文献   

山东金岭金矿床成矿流体地球化学特征   总被引：4，自引：0，他引：4  

王力  孙丰月  王佳良 《岩石学报》2010,26(12):3735-3744

对山东金岭金矿矿石中的流体包裹体进行了岩相学、显微测温及单个包裹体成分激光拉曼光谱研究。结果表明:金矿石中发育含CO2相、气液两相和CO2相等三类包裹体,成矿过程中,流体经历了NaCl-H2O-CO2体系的不混溶作用;成矿流体具有低盐度(6.6%~10.8%NaCleqv)、低密度(0.54~0.93g.cm-3)的特点;成矿温度集中于280~300℃之间,成矿压力为70~119MPa,成矿深度为6.78~9.07km;矿石石英中流体包裹体成分普遍含CO2。结合新近的流体包裹体同位素分析结果和测年数据,认为成矿流体为地幔流体、岩浆流体和大气降水的混合产物,矿床成因类型为幔源流体参与成矿的造山型金矿床中成亚类。  相似文献   

青藏高原西北缘郭扎错断裂~(40)Ar/~(39)Ar年代学研究——阿尔金断裂西延的新证据   总被引：1，自引：0，他引：1  

陈应涛  张国伟  鲁如魁  张永强 《地质通报》2010,29(8):1129-1137

采自阿尔金断裂西南端、沿郭扎错—龙木错—空喀山口一线展布的郭扎错断裂内的糜棱岩样品中同构造黑云母~(40)Ar/~(39)Ar同位素测年的坪年龄分别为105.9Ma±0.5Ma、121.5Ma±0.6Ma、150.4Ma±0.9Ma,表明其早期韧性变形事件发生在晚侏罗世和早白垩世晚期,与阿尔金断裂带主期活动的时期基本一致,为阿尔金断裂带西延提供了新的证据。研究表明,郭扎错断裂与阿尔金断裂带具有一致的变形年代学特征、构造特征等属性,前者是后者的西延部分,二者为同一构造带,均是拉萨地块整体向北运动的动力环境下所产生的脉冲式构造活动的产物。  相似文献   

内蒙古苏尼特左旗地区阿木乌岩体LA-ICP-MS锆石U-Pb年龄及其地球化学特征     

郭支涛  ;孙加鹏  ;梁一鸿  ;邹存铭  ;孙晓  ;周静  ;于泓超  ;赵东明 《世界地质》2014,33(2):311-321

对苏尼特左旗地区阿木乌岩体进行LA-ICP-MS锆石U-Pb测年、主量元素、稀土元素和微量元素测试分析。结果表明,岩体成岩年龄为235.1±3.2 Ma,属中三叠世。岩体具有高SiO2、富K2O、低CaO、低TiO2的特征。强烈亏损Sr、Ba、Ti、P等元素,富集K、Rb、Th等亲石元素,具有右倾"海鸥型"球粒陨石标准化稀土配分型式及强烈的负铕异常等特点。A/CNK=0.77～1.19,A/NK=1.26～1.64,表明阿木乌岩体具有偏铝质A型花岗岩的特征。具有较高的Y/Nb值(2.31～3.001.2),显示出A2型花岗岩的特征,说明岩体形成于造山后的伸展环境。  相似文献