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1.
This paper re-describes the characteristics of pre-Ordovician (Pt3) metamorphic volcanic rocks in the Huimin-Manlai region of Yunnan Province from the aspects of petrographic characteristics, rock assemblage, petrochemistry, REE, trace elements, lead isotopes and geotectonic setting. The metamorphic volcanic rocks maintain blasto-intergranular and blasto-andesitic textures; the volcanic rocks are characterized by a basalt-andesite-dacite assemblage; the volcanic rocks are basic-intermediate-intermediate-acid in chemical composition, belonging to semi-alkaline rocks, with calc-alkaline series and tholeiite series coexisting, and they are characterized by low TiO2 contents; their REE distribution patterns are of the LREE-enrichment right-inclined type; the volcanic rocks are enriched in large cation elements and commonly enriched in Th and partly depleted in Ti, Cr and P, belonging to the Gondwana type as viewed from their Pb isotopic composition; petrochemically the data points fall mostly within the field of island-arc volcanic rocks. All these characteristics provided new evidence for the existence of original Tethysan island-arc volcanic rocks in the region studied.  相似文献   

2.
The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagzê and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an important volcanic suite for the study of the tectonic evolution of the Gangdise magmatic arc and the Mesozoic Tethys. Based on systematic field investigations, we carried out geochemical studies on representative rock samples. Major and trace element compositions were analyzed for these rock samples by XRF and ICP-MS respectively, and an isotope analysis of Rb-Sr and Sm-Nd was carried out by a MAT 262 mass spectrograph. The results show that the SiO2 contents in lava rocks are 41 %-50.4 % and 64 %-69 %, belonging to calc-alkaline basalt and dacite. One notable feature of the basalt is its low TiO2 content, 0.66 %-1.01 %, much lower than those of continental tholeiite. The ΣREE contents of basalt and dacite are 60.3-135 μg/g and 126.4-167.9 μg/g respectively. Both rocks have similar REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts have depleted Ti, Ta and Nb and slightly negative Nb and Ta anomalies, with Nb*＝0.54-1.17 averaging 0.84. The dacites have depleted P and Ti and also slightly negative Nb and Ta anomalies, with Nb*＝0.74-1.06 averaging 0.86. Major and trace elemental and isotopic studies suggest that both basalt and dacite originated from the partial melting of the mantle wedge at different degrees above the subduction zone. The spinal lherzolite in the upper mantle is likely to be their source rocks, which might have been affected by the selective metasomatism of fluids with crustal geochemistry. The LILE contents of both rocks were affected by metamorphism at later stages. The Yeba bimodal volcanic rocks formed in a temporal extensional situation in a mature island arc resulting from the Indosinian Gangdise magmatic arc.  相似文献   

3.
The Late Archean Fuping Group of the Xiaojiao area in Pingshan Couty,Hebei Province consists mainly of three metamorphic rock types of supracrustal affinity,i.e.,Kfeldspar leucoleptite,biotite leptite-gneiss and hornblendic rocks.Their anatectic derivatives formed in the initial stage of anatexis are petrochemically of K-feldspar granitic trondhjemitic and granodioritic compositions respectively,and in general have inherted the main petrochemical featurews from their parent rock types,Probably due to the fact that they contain less REE rich accessory minerals as compared with their parent rocks,the anatectic derivatives are in general lower in EREE content,But both the derivatives and their parent rocks have similar REE patterns,which serves as an additional indication of the genetic relationship between them.  相似文献   

4.
Field investigations and laboratory integrated research as indicated that ophiolite mélange in the Nan-Uttaradit zone, northern Thailand, consists of fragments of tectonites such as metamorphic peridotite (extremely silicified serpentinite), cumulates (pyroxenolite, gabbro, and gabbro-diorite), ocean-ridge basalt, oceanic-island ba-salt and radiolarian silicalite, and it was formed during D3-P. The rock series, rock types and petrogeochemical characteristics of metamorphic tholeiites in the Nan area of the Nan-Uttaradit zone are similar to those of ocean-ridge basalts (C1) in China's Ailaoshan zone. As for the Hawaiites in the Nan area of the Nan-Uttaradit zone, their major elements, REEs and trace elements are similar to those of oceanic-island basalts in China's Jinshanjiang zone (P11). In the Uttaradit area of this zone the metamorphic alkaline basalts show transitional petrogeochemical characteristics between ocean-ridge basalts and oceanic-island basalts, which were still formed in oceanic-island environments. The above-described basalts are all oceanic volcanic rocks and they are the most important part of the Paleo-Tethys oceanic crust in the Nan-Uttaradit zone.  相似文献   

5.
Recently discovered intermediate-basic volcanic rocks in the Devonian strata at Dachang, Guangxi Zhuang Autonomous Region are dominated by basalts and andesites. Most of them belong to the calc-alkali and alkali series. Petrology and geochemistry data indicate that the volcanic rocks may be formed in a continental rift environment. The volcanic rocks are in conformable contact with the overlying and underlying wall rocks, with such typical sedimentary structures as laminated and striped ones, and the host rocks of the volcanic rocks contain lots of marine fossils such as tentaculite. Many pieces of evidence indicate that the eruption environment of the volcanic rocks is a sea-facies one. The volcanic rocks are of the LREE-enrichment type, with high ratios of light rare-earth elements to heavy rare-earth elements. In addition, they display moderately negative δEu anomalies and moderately negative δCe anomalies with a higher degree of LREE and HREE fractionation. Through the Q-cluster analysis of the REE samples, it is indicated that the ores have a closer relation with the layered volcanic rocks, and also possess a certain inheritance-consistency relationship with the layered volcanic rocks. The source of ore-forming materials may be related with volcanism. It is proposed that the ore deposit in the study area should be genetically explained as the result of marine volcano-sedimentary exhalation of hot water and late superposition-reworking.  相似文献   

6.
During the Late Paleozoic, West Junggar(Xinjiang, NW China) experienced a shift in tectonic setting from compression to extension. Ha'erjiao is an important area for investigating collisional structures, post–collisional structures, and magmatic activities. Based on the petrological and geochemical characteristics of pyroclastic and other volcanic rocks in the Permian Kalagang Formation from the borehole ZKH1205 in the Jimunai Basin, the main types of source rock for the pyroclastic rocks deposited in the basin are identified and their implications for the Early Permian tectonic setting examined. The abundance of basalt and andesite lithic fragments in the pyroclastic rocks, together with the REE characteristics and the contents of transition and high field strength elements show that the source rocks were chiefly intermediate–basic volcanic rocks. High ICV values, low CIA values, low Rb/Sr ratios, low Th/U ratios and the mineralogical features suggest weak chemical weathering of the source rocks; the geochemical patterns of the pyroclastic rocks might not only have been impacted by crustal contamination but also might be related to the nature of the magma from the source area. The geochemical properties of the pyroclastic rocks distinguish them from arc-related ones, and such samples plot in the within-plate basalt(WPB) field in some diagrams. This is consistent with the formation background of the Early Permian volcanic rocks in this region.  相似文献   

7.
The geochemistry of the basic volcanic rocks at the south margin of the Qinling orogenic belt(SMQOB) suggests that they were formed in an intraplate tectonic setting.The REE distribution patterns show these rocks are strongly enriched in LREE with high ∑REE, and their trace elements geochemistry is similar to that of contimental flood basalt.All the above evidence suggests that the Caledonian basic volcanic rocks in the SMQOB were tholeiitic basalts formed in an intraplate spreading-initial rift tectonic setting.The characteristics of regional geology and geochemistry indicate that there was an intraplate spreading-rift tectonic setting between the South Qingling block and the Yangtze block in the Caledonian epoch.The dynamic spreading in this district began in the Early Caledonian and then the intraplate spreadinginitial rifts were formed in the Late Caledonian.As a result of spreading of the Tethys and geodynamic processes in deep mantle ,the Mianlue-Huashan oceanic basin was formed between the Qinling block and the Yangtze block in Devonian,and the Qinling microplate was separated from the northern part of the Yangtze plate.  相似文献   

8.
Bedded cherts occurring in the Early Permian Gufeng Formation in the Lower Yangtze region, eastern China, are nearly 20-80 m in thickness and contain varying amounts of radiolarians and sponge spicules. There are three types of section for the Gufeng Formation: chert, carbonate and chert-carbonate mixing types. Bedded cherts mainly occur in the first and third types of section. The depocentres of silica are marked by some small (not larger than a few thousand square kilometres in area) rhombic or elliptic hollows and their formation was controlled by faults. Argillaceous volcanic rocks in cherts occur as numerous thin layers. Bedded cherts are characterized by higher Fe and lower Al contents, enrichment in such trace elements as As, Sb, Bi, Ga, Au, Ag and Cr, lower total REE abundance, negative Ce anomaly and varying degrees of HREE enrichment. These characteristics are important evidence for hydrothermal cherts. Minor amounts of substances of non-hydrothermal origin are mixed in the cherts. The tempera  相似文献   

9.
Two types of enclaves occur in magmatic plutons in Tongling,Anhui.Enclaves of the first type are residuals of metamorphic rocks of high amphibolite facies,and those of the other type are magmatic rocks ranging from monzonitic to dioritic in composition. A combined petrological and mineralogical study has been carried out on the two types of enclaves in order to estimate their forming conditions and analyze their relations to their hosts.so as to have an insight into the material sources of magmatic rocks and associated mineral deposits and give a clue to better understanding the mechanism of magmatism-metallogeny.This leads us to propose a new metallogenic model for strats-bound skarn-type ore deposits associated with a syntectic type of magmatic rocks.The new model can be simply summarized as partial melting of old metamorphic basement rocks at depth and accumulating,differentiating and positioning of magmas to form deep-level and shallow-level magma chambers,follower by mixing of different magmas associated with their crypto-explosion,migration of gas-bearing ore fluids and precipitation of metals in fluids within the magmas.  相似文献   

10.
The Cenozoic volcanic rock of Shandong Province are mainly alkalic and strongly alkalic basaltic rocks.The Contents of major and trace elements including transitional,incompatible and rare-earth elements were determined.The chemical characterisitics of major and trace elements indicate that these basaltic rocks were derived from a mantle source and probably represent a primary magma,I,e.,unmodifiecd partical melts of mantle peridotite in terms of Mg values,correlatione between P2O5 and Ce,Sr,Ni and Rb concentrations,mantle xenoliths,etc.The abundances of trace elements vary systematically from west to east.The compatible transition elements such as Co,Ni,and Cr show a remarkable depletion,whereas the incompatible and rare-earth elements are abundant as viewed from the chondrite-nor-malized patterns.The chemical composition and correlation are consistent with the tectonic setting.According to the batch and fractional partial melting theory,the trace element contents of Shandong volcanic rocks can be calculated from the two-component mixing model.  相似文献   

11.
龙脖河铜矿床位于滇中地区红河成矿带南段,矿区火山岩发育、与铜矿化时空密切共生。区内火山岩遭受了不同程度的蚀变或区域变质作用,根据矿物组合可分为变安山岩、变次火山岩和变基性火山岩。三类变火山岩均相对富Na,在地球化学分类图解上样品主要位于碱性玄武岩区域。除个别微量元素外,三类岩石的微量元素含量相近,与各种构造环境玄武岩相比,本区变火山岩富集HFSE(Th、Nb等)、亏损LILE(Sr、Ba等),微量元素配分模式出现明显Th、Nb正异常和Sr、Ba负异常。三类岩石的REE含量范围相互重叠,除Eu异常外,其REE配分模式均为相似的LREE富集型。各种地球化学证据表明,本区三类变火山岩为同源岩浆不同演化阶段的产物,其原始岩浆为大陆板内拉张构造环境交代富集地幔部分熔融的产物,结晶分异作用在岩浆演化过程中具有重要地位。  相似文献   

12.
苏海图组火山岩发育自然铜矿化,具有从拉斑玄武岩系列向钙碱性玄武岩系列过渡的特点。依据地球化学特征,表明其TiO2含量较低(1%),玄武岩高的Al2O3含量、低的稀土含量,并且稀土元素曲线具有平缓型到轻稀土低度富集的特点。微量元素原始地幔标准化图解上,它们均富集大离子亲石因素(LILE),亏损高场强元素(HFSE),具有强的Nb和Ta的负异常,Ti的低负异常,以及P和Sm的低正异常。Zr/Nb值和Sm/Nd值接近MORB的范围,Th/Nb值大于0.11,Nb/Zr值小于0.04。以上这些特征均显示出典型岛弧岩浆的特点。所以,苏海图组火山岩为火山弧火山岩,其构造背景为大陆岛弧,源区可能为被流体或沉积物交待改造的亏损地幔。  相似文献   

13.
武当地块耀岭河群中两类不同性质的酸性火山岩研究   总被引：1，自引：0，他引：1  
耀岭河群火山岩中可划分出两类不同性质的酸性火山岩:酸性岩A主要属碱流岩-白碱流岩类,酸性岩B主要属流纹英安岩/英安岩类。总体上看二者主量元素组成差异不大:SiO2含量为65.00%～79.85%,(Na2O+K2O)为5.26%～9.68%。强烈富集Th、Nb、Ta、La、Ce、Nd、Zr、Sm和Hf等微量元素,强烈亏损Ba、K、Sr、P、Ti等元素,稀土元素特征表现为∑REE很高(339.94～1152.85μg/g),具有强烈的铕负异常(δEu=0.18～0.32),与典型的大陆裂谷流纹岩的稀土曲线一致。酸性火山岩B显示K、Rb、Ba、Th和LREE的正异常和Sr、P、Ti和Nb的负异常,Eu具弱负异常(δEu=0.64～0.88),表现出与酸性火山岩A迥然不同的微量元素及稀土元素特征,而与耀岭河群基性火山岩相似,显示其成因可能与之有相同源区。  相似文献   

14.
比利亚谷铅锌银矿位于海拉尔-根河中生代火山盆地北西缘。该矿床赋存于上侏罗统满克头鄂博组酸性火山岩中,受NW向断裂构造控制,主矿体呈脉状产出。火山岩围岩及主要矿石矿物的微量稀土特征相似:具有富集Rb、Th等大离子亲石元素,而亏损Sr、Nb、Ta等高场强元素的特点,表明其均产于板内构造环境。不同之处为:1矿石矿物的稀土微量元素总量明显小于火山岩围岩;2火山岩围岩呈现出明显的负Eu异常,而矿石矿物则具有强弱不等的正Eu异常。综合分析认为比利亚谷铅锌银矿为火山-次火山热液型矿床,其主要成矿作用与晚侏罗世-早白垩世(140Ma左右)火山活动有着密切联系,区域地质背景上对应于构造体制大转折的晚期,但是成矿期后矿体受到了120Ma大规模岩浆活动的影响,本期岩浆活动是区域岩石圈快速减薄引起,产生了一期深变质作用以及壳幔相互作用有关的深部流体活动,受其强烈改造,引起了矿石矿物微量稀土元素含量的改变。  相似文献   

15.
陕西省西南部铧厂沟火山岩以英安岩为主(～ 90vol％),夹玄武岩构造透镜体(～ 10vol％).玄武岩SiO2含量为43.6％ ～ 54.7％,具有低K、Ti,高Na、Mg的特征;稀土总量为24×10-6 ～29×10-6,中稀土轻微富集,Eu、Sr轻微正异常;具有正Rb、Ba异常及负Nb、Zr异常,LaN/YbN值为1.81 ～2.87,Th/Yb值为0.19 ～0.23,Th/Nb值为0.11 ～0.20,Nb/La值为0.26～0.70,Hf/Th值为0.50 ～ 0.67,显示亚碱性弧玄武岩的特征.英安岩SiO2含量为59.5％～ 72.3％,稀土总量较低(116×10-6～187 × 10-6),为右倾式配分模式,Eu负异常,富集大离子亲石元素(如Rb、Ba、Th、K等),亏损高场强元素(如Nb、P、Ti、Ta等),显示弧火山岩地球化学特征.获得玄武岩的锆石SHRIMP U-Pb年龄为801.7±4.7Ma (MSWD=1.18;n=12),英安岩的锆石LA-ICP-MS U-Pb年龄为802.1±5.3Ma (MSWD=1.02;n=19),二者在误差范.内一致.因此,铧厂沟火山岩是一套火山弧环境的亚碱性玄武质-英安质火山岩组合,表明新元古代曾有大洋板块向南俯冲到扬子古板块北缘之下;这套火山岩裹挟于泥盆系沉积地层中,与泥盆系地层一起,共同组成了一套由晚古生代-三叠纪勉略洋闭合所致的构造混杂岩带.  相似文献   

16.
在青藏高原腹地,二叠纪火山岩分布于唐古拉山东段,古地理上位于北羌塘盆地东缘。对唐古拉山东段莫云地区中二叠世栖霞期尕笛考组火山岩的主量元素、微量元素和Sr-Nd同位素进行了分析。岩相学和地球化学指标显示二叠纪火山岩为玄武岩,该套岩石低SiO2、MgO、K2O和Mg#值(0.39～0.48),富Na2O、TFeO、TiO2、P2O5含量,富集LREE和高场强元素(Nb、Ta、Zr、Hf、P、Ti),(La/Yb)N=14.89～23.23,(Gd/Yb)N=2.30～3.58,Eu异常不明显(δEu=0.76～0.99),具有明显的Th正异常和K、Sr负异常,显示与板内碱性玄武岩相似的地球化学特征;同位素组成以低(87Sr/86Sr)i(0.7033～0.7039)、高εNd(t)(+4.2,t=271Ma)为特点,反映岩浆源区既有亏损地幔源(DMM)又有富集地幔源(EMⅠ)的双重属性。岩浆起源可能与地幔柱诱导的软流圈上涌导致含石榴子石橄榄岩的岩石圈地幔部分熔融有关。莫云玄武岩形成于板内伸展环境(初始裂谷),具有主动裂谷作用性质。  相似文献   

17.
新疆金矿火山岩微量及稀土元素地球化学特征   总被引：1，自引：0，他引：1  
刘家远 《黄金地质》2001,7(4):45-51
金矿火山岩微量元素以Th和Zr的明显正异常及Nb和Ti的明显负异常为特征。微量元素比值蛛网图模式曲线均呈微向左倾斜的多峰多谷曲线。过渡元素以Cr和Ni的明显负异常及Sc,Co,Cu明显正常为特征。过渡元素球粒陨石标准化曲线，也均呈微向右倾斜的W形曲线。稀土元素以稀土总量偏低，轻稀土富集，重稀土亏损，Eu具微弱异常至微弱正常为特征。稀土元素配分模式均呈微向右倾斜和近于水平的平滑曲线，陆相火山作用两类成矿岩浆建造－陆相火山岩与潜火山杂岩具有基本一致的微量元素和稀土元素地球化学特征。  相似文献   

18.
Late Permian-Early Triassic (P2-T1) volcanic rocks distributed on the eastern side of ocean-ridge and oceanic-island basalts in the Nan-Uttaradit zone were analyzed from aspects of petrographic characteristics, rock assemblage, REE, trace elements, geotectonic setting, etc., indicating that those volcanic rocks possess the characteristic features of island-arc volcanic rocks. The volcanic rock assemblage is basalt-basaltic andesite-andesite. The volcanic rocks are sub-alkaline, dominated by calc-alkaline series, with tholeiite series coming next. The chemical composition of the volcanic rocks is characterized by low TiO2 and K2O and high Al2O3 and Na2O. Their REE patterns are of the flat, weak LREE-enrichment right-inclined type. The trace elements are characterized by the enrichment of large cation elements such as K, Rb and Ba, common enrichment of U and Th, and depletion of Nb, Ta, Zr and Hf. The petrochemical plot falls within the field of volcanic rocks, in consistency with the plot of island-arc volcanic rocks in the Jinsha River zone of China. This island-arc volcanic zone, together with the ocean-ridge/oceanic island type volcanic rocks in the Nan-Uttaradit zone, constitutes the ocean-ridge volcanic rock-island-arc magmatic rock zones which are distributed in pairs, indicating that the oceanic crust of the Nan-Uttaradit zone once was of eastward subduction. This work is of great significance in exploring the evolution of paleo-Tethys in the Nan-Uttaradit zone.  相似文献   

19.
中心屯地区位于大兴安岭火山岩带中南段,区内岩浆活动强烈,发育有中生代不同时期的基性-酸性火山岩。在野外地质调查的基础上,通过研究晚侏罗世火山岩岩石学特征及岩石化学数据,发现区内晚侏罗世火山岩主要为中性-酸性岩石,属于钙碱性系列;稀土元素大都具有铕负异常,配分曲右倾,显示轻稀土元素富集、重稀土元素亏损的特点;微量元素的过渡元素Cr、Co、Ni含量较低,富集大离子亲石元素Rb、Ba、K等,亏损大离子亲石元素Sr,亏损Nb、Th、Ti、P等高场强元素。综合分析表明,晚侏罗世火山岩岩浆来源于地壳。其形成环境处于亚洲大陆边缘断陷带,受太平洋板块俯冲作用的影响。  相似文献   

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