西天山加满特一带早二叠世乌郎组双峰式火山岩锆石U-Pb年代学及Hf同位素组成     

陈邦学  徐胜利  周能武  白权金  黄基汉  郑勇 《高校地质学报》1997,25(3):364

西天山加满特一带基性与酸性火山岩在时空上紧密伴生，其SiO2含量分别为41.89%~52.75%和74.79%~78.51%，具 有明显的Daly间断，属于典型的双峰式火山岩组合，其中的基性单元属于碱性系列，酸性单元属于钙碱性系列。对流纹岩 进行LA-ICP-MS锆石U-Pb法测年和Hf同位素分析，获得其形成年龄为（294.2±0.8） Ma，属于早二叠世，其εHf(t)为较高的 正值（8.0~17.1），二阶段Hf模式年龄TDM2(Hf)平均值为468 Ma。通过对加满特一带双峰式火山岩的地球化学特征和成因类 型进行探讨，表明其不属于同源岩浆演化成因，其中玄武岩是富集石榴石地幔源区发生了尖晶石相橄榄岩向石榴石相橄榄 岩过渡相部分熔融的产物，流纹岩是亏损地幔源底侵新生地壳部分熔融的产物，二者形成于板内伸展环境。结合区域构造 演化，认为西天山在早二叠世已经进入伸展构造背景。  相似文献   

杭州南部新元古代双峰式火山岩的厘定及其构造意义          下载免费PDF全文

卢成忠  顾明光 《中国地质》2007,34(4):565-571

杭州南部新元古界青白口系上墅组火山岩,由基性岩和酸性岩组成,缺乏SiO2在57×10-2～68×10-2的中性及中酸性成分,构成一套双峰式火山岩组合。基性火山岩与酸性火山岩的稀土元素和微量元素特征存在明显差异,表明酸性火山岩并不是由基性岩浆分离结晶产生,而是分别由不同的源区熔融形成,基性火山岩起源于亏损程度较低的地幔或来源于亏损地幔的岩浆受到陆壳物质的混染,酸性火山岩主要由上地壳经不同程度的部分熔融而形成,其形成的构造环境为陆内至陆缘张裂环境。上墅组双峰式火山岩的形成,是华南Rodinia超大陆裂解事件的岩石学记录,揭示了华南Rodinia超大陆裂解始于青白口纪。  相似文献   

峨眉山大火成岩省晚期酸性火山岩的岩石地球化学特征     

邵辉  徐义刚  何斌  黄小龙  罗震宇 《矿物岩石地球化学通报》2007,26(4):350-358

峨眉山大火成岩省出露有少量酸性火山岩,它们与基性火山岩共生,表现出双峰式的特征,为研究峨眉山地幔柱晚期岩浆活动提供了重要的窗口。本文通过对双峰式火山岩主、微量元素和斑晶电子探针分析研究表明,基性火山岩属于碱性玄武岩,酸性火山岩主要由粗面岩组成;相对玄武岩,粗面岩中MgO、Fe2O3、P2O5、TiO2、CaO含量明显降低;粗面岩与玄武岩具有相互平行的REE配分模式,但粗面岩出现明显的Eu负异常,以及Sr、Ti等元素的强烈亏损;粗面岩与玄武岩具有同源的特征,通过稀土元素模拟计算表明粗面岩可以由玄武质岩浆经过80%分离结晶作用(辉石、斜长石和Fe-Ti氧化物)而形成。在峨眉山大火成岩省晚期出现双峰式火山岩,可能与地幔柱活动晚期岩浆供给少,在地壳岩浆房中停留时间长,岩浆发生强烈分离结晶作用有关。  相似文献   

对辽东古元古代地质若干问题的讨论   总被引：21，自引：1，他引：21       下载免费PDF全文

陈荣度李显东  张福生 《中国地质》2003,30(2):207-213

新的区调成果证实上世纪70年代在辽东建立的古元古代辽河群层序以及辽河群存在南北方向相变的认识是正确的。辽河群已全线过鸭绿江分布在狼林地块各处。狼林群的大部分相当于辽河群。辽河群原始沉积盆地主体呈东西向狭带状，它以太古宙陆壳为基底发育双峰式火山岩，构造属性为大陆裂谷，个别中心部分曾发生块体的有限分离而出现洋壳。笔者还对古盆地南、北太古宙陆块间地质差异的原因作了讨论。  相似文献   

福建省中生代双峰式火山岩的特征及成因     

马金清  何文兴  冯宗帜 《地质通报》1998,(3)

福建省中生代双峰式火山岩分别发育于早侏罗世藩坑组、早白垩世石帽山群,二者在剖面上均表现为流纹质火山岩直接覆盖在玄武岩之上。两个时期的双峰式火山岩均发育于断陷带上的火山构造洼地（盆地）内,形成于活动大陆边缘板内拉张环境。玄武岩是上地幔经１０％～２０％部分熔融形成;流纹质岩浆来源于下地壳经１５％～２３％部分熔融,并有较多地幔物质参与。  相似文献   

Chemical Composition and Association of Size-Differentiated Aerosols at a Suburban Site in a Semi-Arid Tract of India     

U. C. Kulshrestha  A. Saxena  N. Kumar  K. M. Kumari  S. S. Srivastava 《Journal of Atmospheric Chemistry》1998,29(2):109-118

Size-differentiated concentrations of SPM, F, Cl, NO₃, SO₄, Na, K, Ca, Mg and NH₄ in atmospheric aerosols were measured in a suburban area of Agra city during December 1992 to March 1993. Except for NH₄, Cl and Na, all components were found to have a bimodal distribution. The fine fraction was dominated by NH₄, K, NO₃ and SO₄, while Na, Ca, Mg, F and Cl contributed to the coarse fraction. Fifty-eight percent of SO₄ and 67% of NO₃ were found in the fine mode and the coarse mode comprised 42 and 33% of SO₄ and NO₃, respectively. SO₄ was found to have a peak above the submicron range at 1.1 µm which has been attributed to secondary sulphate formation by heterogeneous oxidation of SO₂ on alkaline particles of Ca and Mg. The total aerosol was basic in nature and dominated by the soil-derived acid neutralising components (Ca, Mg and Na).  相似文献   

Unusual N—Alkane Distributions in Extracts from Marine Carbonate Rocks at High Levels of Maturity and Overmaturity     

李景贵  R.PAUL PHILP  崔明中 《中国地球化学学报》2002,21(4):322-333

N-alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field of the Sichuan Basin, are characterized by bimodal distributions with the dominant carbon numbers in the range C₁₇-C₂₁ and C₂₅-C₂₉. In most samples, the lower carbon number components are present in greater abundance than the higher carbon number ones. Most samples contain significant concentrations of waxy hydrocarbons (C₂₂₊) with C_21-/C₂₂₊ ratios between 0.50 to 3. 16, and an average value of 1. 34. The n-alkanes in extracts of outcrops and shallow core samples of Upper Proterozoic and Lower Palaeozoic carbonate rocks in the western and southern parts of the North China Basin are of unimodal distributions dominated by n-alkanes maximizing in the C₂₅-C₂₉ range. These extracts have very high concentrations of waxy hydrocarbons with C_21-/C₂₂₊ ratios all < 1. 0, ranging from 0. 14 to 0. 90 and averaging 0. 36. All of the extracts have a marked odd/even predominance in the high molecular weight n-alkane range regardless of whether they are from shallow or deep cores or out-crop samples. Simulation experiments were performed using typical sapropelic-type kerogens from the immature Sinian Lower Xiamalin Formation carbonate-rich shales collected at Jixian, Hebei Province, North China Basin, and the contemporary microplanktonic blue-green algaeSpirulina subsala. Results indicate that the unusual distribution of n-alkanes in the extracts of Upper Proterozoic and Lower Palaeozoic carbonate rocks possibly originated from algae in the source rocks at high levels of maturity and overmaturity. This research project was financially supported by the Chinese Academy of Sciences (Grant No. KZCX2-111 ).  相似文献   

Early Cretaceous rift-related volcanism in the Songliao Basin,NE China – A geochemical study     

Shuang-Qing Li  Yan Wang  Bo-Wen Fang  Jian-Feng He  Fukun Chen  Wolfgang Siebel 《International Geology Review》2019,61(1):39-55

Following the amalgamation of the Siberian and North China Cratons, NE China, as part of the Central Asian Orogenic Belt (CAOB), underwent Late Mesozoic lithospheric extension that was associated with volcanic activity. The Songliao Basin is the most important rift structure formed during these processes and contains voluminous volcanic rocks interlayered with sedimentary infill. Mafic-to-intermediate lavas are associated with felsic ones. This study focusses on the geochemical compositions of the less-widespread Early Cretaceous mafic-to-intermediate lavas in the Songliao Basin and compares them with the more abundant felsic rocks. Two mafic-to-intermediate magma series, one with alkaline and the other with sub-alkaline affinity, were identified. High MgO and Cr contents, low Th/Nb and La/Nb ratios, and variable but depleted Nd isotope compositions indicate that both magma suites were most likely formed by the melting of enriched upper mantle sources. Sub-alkaline mafic-to-intermediate rocks and I-type rhyolites define a co-genetic magma series. This rock suite was produced by the melting of subduction-modified lithospheric mantle and subsequent magma evolution as well as crustal melting during lithospheric extension. Alkaline mafic-to-intermediate rocks and A-type rhyolites form another co-genetic magma suite that was produced under within-plate conditions from an OIB-type mantle source, supposed to be the heterogeneous shallow asthenosphere and/or the lower lithosphere. Decompression partial melting of this mantle source requires a relatively thin lithosphere. The development of alkaline mafic rocks and A-type rhyolites as typical bimodal volcanic assemblage reflects that lithospheric thinning below the Songliao Basin reached its maximum, whereas basin rifting terminated afterwards.  相似文献   

西昆仑塔什库尔干马尔洋岩组的厘定及控矿意义          下载免费PDF全文

贺承广  王世炎  方怀宾  柴建玉  苏建仓  常永伟  王柳林  陈登辉 《中国地质》2019,46(3):517-536

塔什库尔干大型铁矿成矿带位于昆仑造山带西段,原岩恢复表明该区含铁岩系主要为一套双峰式火山岩碎屑岩碳酸盐岩建造组合,岩石普遍遭受绿片岩相变质和多期构造变形。本文报道了在老并一带变安山岩中获得的LA ICP MS锆石U Pb同位素年龄值(603±10)Ma,并结合前人年龄数据,将原划古元古界布伦阔勒岩群的含铁岩系厘定为震旦系寒武系纽芬兰统马尔洋岩组(Z 1m),其内发育典型的双峰式火山岩组合,证实了区内震旦纪早寒武世仍处于拉张伸展背景,变质火山沉积组合特征表明其形成于大陆边缘裂谷构造环境。含铁岩系典型的膏(钡)铁建造很可能为新元古代晚期“Marinoan雪球”冰期后地球系统变化的火山沉积响应。  相似文献   

Three Stages of Mesozoic Bimodal Igneous Rocks and Their Tectonic Implications on the Continental Margin of Southeastern China   总被引：7，自引：0，他引：7  

XING Guangfu  YANG Zhuliang  CHEN Rong  SHEN Jialin  WEI Naiyi  ZHOU Yuzhang Nanjing Institute of Geology  Mineral Resources  Ministry of Land  Resources  Nanjing  Jiangsu 《《地质学报》英文版》2004,78(1):27-39

There are large-scale Mesozoic bimodal igneous rock associations on the continental margin of southeastern China. They aroused extensive attention in the 1980s because of their specific tectonic implications, and have been found frequently during recent geological surveys. This paper reviews the studies of regional Mesozoic bimodal rocks, and concludes that they can be subdivided into three stages, i.e., the Early Jurassic (209-170 Ma, the first (Ⅰ) stage), the Late Jurassic-early Early Cretaceous (154-121 Ma, the second (Ⅱ) stage), and the late Early Cretaceous-Late Cretaceous (115-85 Ma, the third (Ⅲ) stage). These three stages of bimodal rocks were formed in different tectonic settings, and are important indicators for regional Mesozoic tectonic evolution.  相似文献