东昆仑阿克楚克塞地区辉长岩地球化学特征、锆石U-Pb年龄及其构造意义     

杨锡铭  孙丰月  赵拓飞  刘金龙  彭勃 《地质通报》2018,37(10):1842-1852

东昆仑地区基性-超基性岩石的研究较薄弱,缺乏对东昆仑幔源岩浆活动及岩浆演化的整体认识。对阿克楚克塞辉长岩进行了地球化学、锆石U-Pb年代学及Hf同位素研究,结果显示,该岩石形成于晚三叠世早期(219.3±1.1Ma,MSWD=0.80);岩石SiO2含量为49.03%~57.26%,Mg#值为49~57,属于钙碱性系列岩石;稀土元素配分曲线为轻稀土元素富集的右倾型,富集大离子亲石元素Rb、Ba、K,相对亏损高场强元素Nb、Ta、Ti;εHf(t)=-1.81~3.25,锆石Hf模式年龄大于锆石结晶年龄。地球化学特征显示,阿克楚克塞辉长岩岩浆源区应为受俯冲板片流体交代的岩石圈地幔。结合区域构造背景分析,阿克楚克塞辉长岩形成于印支期造山后伸展的构造环境,继承了早期板片俯冲改造的地幔源区特征。  相似文献   

大兴安岭十八站—韩家园地区晚中生代火山岩年龄、地球化学特征及其构造意义     

柴明春  王泉  赵国英  高溯  曹昆 《地质通报》2018,37(10):1866-1881

大兴安岭十八站—韩家园地区发育晚中生代基性-中酸性火山岩。选取粗面安山岩、粗面岩、流纹岩进行年代学和岩石地球化学研究。粗面安山岩LA-ICP-MS锆石U-Pb年龄为125.2±0.9 Ma,为早白垩世火山作用的产物。岩石地球化学特征表明,中酸性火山岩属于高钾钙碱性-钾玄岩系列。岩石稀土元素总量∑REE=121.42×10~(-6)~154.43×10~(-6),轻、重稀土元素分异明显(La/Yb)_N=19.25~31.98,在稀土元素配分图上显示右倾型,除一个流纹岩样品具显著负Eu异常外,多数样品无明显Eu负异常(δEu=0.45~0.90)。岩石具弱富集大离子亲石元素Ba、Sr,明显亏损高场强元素Nb、Ta、Ti的特征。结合区域资料,认为十八站—韩家园地区早白垩世中酸性火山岩形成于蒙古-鄂霍茨克洋闭合机制下后碰撞伸展背景。粗面安山岩、粗面岩和流纹岩系同源岩浆部分熔融与结晶分异作用的结果,岩浆来源于受俯冲流体交代的富集岩石圈地幔。  相似文献   

Geodynamic setting,structure, and composition of continuous trachybasalt-trachyandesite-rhyolite series in the north of Altai-Sayan area: the role of crust-mantle interaction in continental magma formation     

A.A. Vorontsov  O.Yu. Perfilova  N.N. Kruk 《Russian Geology and Geophysics》2018,59(12):1640-1659

The geologic positions and geochemical and isotope parameters of the Ordovician-early Silurian and Early-Middle Devonian continuous volcanic series of the Minusa basin and its mountainous framing are compared. Both series are composed mostly of moderately alkaline rocks with variations in SiO₂ contents from 45 to 77 wt.%. The Ordovician-early Silurian series differs from the Early-Middle Devonian one in lower contents of TiO₂ (< 1.7 wt.%) and Fe₂O_3tot and higher contents of Al₂O₃ in all rock varieties and in the more fractionated REE patterns of trachybasalts. The compositions of both series reflect two simultaneous mechanisms of magma evolution. The main process was fractional crystallization leading to the formation of rocks from trachybasalts to trachyrhyodacites. The accessory mechanism was the contamination of fractionated melts by crustal material, anatectic melting of crust, and mixing of deep-seated magmas with crustal melts. These processes had specifics at each stage and were controlled by the composition of the sources of parental melts. Their geochemical and isotopic parameters (high alkalinity, high contents of lithophile elements, negative anomalies of Nb, Ta, and Ti, and enrichment in radiogenic Sr) point to the interaction of mantle plumes with the lithospheric mantle that was metasomatically transformed during the preceding Vendian-early Cambrian subduction processes.  相似文献   

Ore-bearing fluids of the Eldorado gold deposit (Yenisei Ridge,Russia)     

N.A. Gibsher  A.A. Tomilenko  A.M. Sazonov  T.A. Bul’bak  M.O. Khomenko  M.A. Ryabukha  E.O. Shaparenko  S.A. Sil’yanov  N.A. Nekrasova 《Russian Geology and Geophysics》2018,59(8):983-996

The Eldorado low-sulfide gold-quartz deposit, with gold reserves of more than 60 tons, is located in the damage zone of the Ishimba Fault in the Yenisei Ridge and is hosted by Riphean epidote-amphibolite metamorphic rocks (Sukhoi Pit Group). Orebodies occur in four roughly parallel heavily fractured zones where rocks were subject to metamorphism under stress and heat impacts. They consist of sulfide-bearing schists with veins of gray or milky-white quartz varieties. Gray quartz predominating in gold-bearing orebodies contains graphite and amorphous carbon identified by Raman spectroscopy; the contents of gold and amorphous carbon are in positive correlation. As inferred from thermobarometry, gas chromatography, gas chromatography-mass spectrometry, and Raman spectroscopy of fluid inclusions in sulfides, carbonates, and gray and white quartz, gold mineralization formed under the effect of reduced H₂O-CO₂-HC fluids with temperatures of 180 to 490 °C, salinity of 9 to 22 wt.% NaCl equiv, and pressures of 0.1 to 2.3 kbar. Judging by the presence of 11% mantle helium (³He) in fluid inclusions from quartz and the sulfur isotope composition (7.1-17.4‰ δ³⁴S) of sulfides, ore-bearing fluids ascended from a mantle source along shear zones, where they “boiled”. While the fluids were ascending, the metalliferous S- and N-bearing hydrocarbon (HC) compounds they carried broke down to produce crystalline sulfides, gold, and disseminated graphite and amorphous carbon (the latter imparts the gray color to quartz). Barren veins of milky-white quartz formed from oxidized mainly aqueous fluids with a salinity of < 15 wt.% NaCl equiv at 150-350 °C. Chloride brines (> 30 wt.% NaCl equiv) at 150-260 °C impregnated the gold-bearing quartz veins and produced the lower strata of the hydrothermal-granitoid section. The gold mineralization (795-710 Ma) was roughly coeval to local high-temperature stress metamorphism (836-745 Ma) and intrusion of the Kalama multiphase complex (880-752 Ma).  相似文献   

内蒙古巴林右旗晚二叠世埃达克质火山岩特征及其地质意义     

杨文鹏  张生旭  姜海洋  刘洪大  隋成禹  孙江军  张俭峰  吕石佳  李新鹏 《地质通报》2018,37(9):1710-1721

内蒙古东南部巴林右旗地区发育晚二叠世埃达克质火山岩,岩石组合为安山岩、粗安岩、英安岩及辉石安山岩,其LA-ICP-MS锆石U-Pb测年结果为256.7±2.7Ma,指示其形成于晚二叠世。地球化学特征显示,该套火山岩属准铝质-弱铝质中钾钙碱性岩石系列,具富Si(SiO_256%)、高Al(Al_2O_315%)、富Na、贫K、高Sr、低Yb和Y等特征,Na_2O/K_2O值为2.33~3.90,Mg~#值为35.3~60.8;稀土元素总量为96.69×10~(-6)~192.4×10~(-6)、轻重稀土元素分馏较明显((La/Yb)_N值为6.27~13.82),具正的Eu(δEu=1~1.67)异常,在原始地幔标准化蛛网图中,富集大离子亲石元素Rb、Ba、U,亏损高场强元素Nb、Ta,为O型(大洋型)埃达克质火山岩地球化学特征。综合区域资料,巴林右旗埃达克质火山岩是残留在地幔中的古亚洲洋残余洋壳部分熔融并受到地幔橄榄岩混染形成的,暗示晚二叠世存在古亚洲洋向华北板块俯冲消亡事件。  相似文献   

Formation and evolution of the Archean continental crust of China: A review     

《China Geology》2018,1(1):109-136

The mainland of China is composed of the North China Craton, the South China Craton, the Tarim Craton and other young orogenic belts. Amongst the three cratons, the North China Craton has been studied most and noted for its widely-distributed Archean basement rocks. In this paper, we assess and compare the geology, rock types, formation age and geochemical composition features of the Archean basements of the three cratons. They have some common characteristics, including the fact that the crustal rocks prior to the Paleoarchean and the supracrustal rocks of the Neoarchean were preserved, and Tonalite-Trondhjemtite-Granodiorite (TTG) magmatism and tectono-magmatism occurred at about 2.7 Ga and about 2.5 Ga respectively. The Tarim Craton and the North China Craton show more similarities in their early Precambrian crustal evolution. Significant findings on the Archean basement of the North China Craton are concluded to be: (1) the tectonic regime in the early stage (>3.1 Ga) is distinct from modern plate tectonics; (2) the continental crust accretion occurred mostly from the late Mesoarchean to the early Neoarchean period; (3) a huge linear tectonic belt already existed in the late Neoarchean period, suggesting the beginning of plate tectonics; and (4) the preliminary cratonization had already been completed by about 2.5 Ga. Hadean detrital zircons were found at a total of nine locations within China. Most of them show clear oscillatory zoning, sharing similar textures with magmatic zircons from intermediate-felsic magmatic rocks. This indicates that a fair quantity of continental material had already developed on Earth at that time.  相似文献   

Petrogenesis of the microcrystalline-dioritic enclaves from Jiuling granitoids in the eastern segment of Jiangnan Orogen and constraints on magma source materials     

《China Geology》2018,1(3):374-391

Numerous dark enclaves with different shapes are found in Jiuling Neoproterozoic granitoids. Precise LA-ICP-MS U-Pb dating was conducted on zircons extracted from two microcrystalline enclave samples, yielding crystallization ages of 822.6±5.8 Ma and 822.2±6.2 Ma, respectively. The consistent ages within analytical errors with the host granitoids suggested that they were the products of the same magmatism. The microcrystalline-dioritic enclaves commonly show plastic forms and contain similar plagioclase megacrysts to the host rocks, and both of the enclaves and host granitoids showed a complex composition and structural imbalance in plagioclases. Furthermore, the apatites with a euhedral acicular shape occurred widely in the microcrystalline-dioritic enclaves. All of these petrographic features above imply magma mixing is involved in their diagenesis. The enclaves and host granitoids show a marked zircon trace element difference and Hf isotopic signatures without correlation in zircon trace element pairs but form their own system between enclaves and host granitoids. Additionally, most of the zircons show extremely high ε_Hf (t) with ε_Hf (t) =3.54–11.94 from the southern samples, and ε_Hf (t) =1.0–9.09 from the central region. Some zircons with the higher ε_Hf (t) are similar to the zircons from the juvenile island arc in the eastern segment of Jiangnan Orogen. Integrated geological and Hf isotopic characteristics suggest microcrystalline-dioritic enclaves were derived from the partial melting process of the Mesoproterozoic crust which enriched juvenile island arc materials and mixed with the granitic magma that remelted from the Mesoproterozoic continental crust which relatively enriched ancient sediments and mixed with the host granitoid in diagenesis.  相似文献   

青海湖地区生物中正构烷烃及其氢同位素组成与影响因素     

段毅  吴应忠  吴保祥  孙涛 《地质学报》2018,92(7):1541-1550

青海湖是我国最大的内陆咸水湖泊。本文应用GC-MS和GC-TC-IRMS同位素分析技术,对青海湖水生生物和周围地区陆生生物中正构烷烃及其氢同位素进行了分析,研究了生物中正构烷烃及其同位素组成。结果显示了不同生物中正构烷烃碳数分布范围在C1 5~C33之间,呈单峰型分布;主峰碳数是水生生物(除海韭菜外)相对较低,主要为C23和C25,陆生木本植物次之,为C27;陆生草本植物较高,为C27和C29;CPI值分布在4.0~29.7之间;ACL值为26.0~29.6,分布与植物类型有关。青海湖水生生物中正构烷烃氢同位素组成分布在-209.8‰~-85.6‰之间,平均值为-169.2‰~-121.2‰;陆生植物的正构烷烃δD值为-196.7‰~-84.3‰之间,平均值为-173.0‰~-108.6‰。青海湖不同水生生物和不同陆生生物之间的正构烷烃氢同位素组成差别显著。研究发现,湖泊的含盐量对水生植物的正构烷烃氢同位素具有显著影响,环境湿度和降水量明显影响了陆生植物的正构烷烃氢同位素组成;植物的正构烷烃平均氢同位素组成随着其ACL值增加,具有变轻的趋势;不同种类植物的正构烷烃合成期间具有不同的氢同位素分馏效应,与陆生植物相比较,水生植物的正构烷烃相对于环境水更富集轻氢同位素,并且随着ACL值增加,环境水和正构烷烃之间的氢同位素分馏增大。  相似文献   

柴北缘达达肯乌拉山地区闪长岩锆石LA-ICP-MSU-Pb年龄、岩石地球化学特征及其构造意义   总被引：1，自引：0，他引：1  

刘永乐  刘智刚  张爱奎  何书跃  张大明  毛生元  李兴良  奎明娟 《矿床地质》2018,37(5):1079-1090

达达肯乌拉山位于柴达木盆地北缘中东部,区内发育闪长岩体,以小岩株形式产出。通过对达达肯乌拉山闪长岩岩石LA-ICP-MS锆石U-Pb定年和地球化学特征的研究,获得闪长岩体的年龄为(240.5±1.7) Ma,属早印支期。闪长岩体的w(K_2O)较高,为2.03%～2.30%,w(Na2O)含量较低,为3.2%～3.44%,为一套准铝质及弱过铝质高K、低Na的高钾钙碱性型I型花岗岩。岩石稀土元素总量为158.35×10~(-6)～200.41×10~(-6),球粒陨石标准化曲线向右倾斜,重稀土元素曲线呈水平状,轻稀土元素富集,但负铕异常不明显,岩浆分异程度不高。岩石的La/Ta(54.32～68.51)、Sm/Nd(0.18～0.19)及Rb/Sr(0.11～0.19)比值特征反映该岩体岩浆具有壳幔混合的特点。通过构造判别,反映达达肯乌拉山岩体可能形成于俯冲陆壳断离、幔源岩浆底侵的地球动力学背景,在中央造山带早中生代统一的板块碰撞与挤压构造体制下,以滩间山蛇绿岩带为基础,发生陆壳俯冲和断离作用,并诱发幔源岩浆的底侵和下地壳物质的部分熔融,沿火山机构侵位形成达达肯乌拉山岩体。  相似文献   

豫西崤山东部中河岩体锆石U-Pb年龄、地球化学和Lu-Hf同位素特征     

肖建辉  武广  孟宪锋  范海洋  李铁刚  田强国  徐文超 《矿床地质》2018,37(2):290-310

中河花岗斑岩体位于河南省崤山东部,该岩体是最近发现的中河大型银铅锌矿床的成矿母岩。选取2件花岗斑岩样品进行LA-ICP-MS锆石U-Pb定年,获得2件样品的~(206)Pb/~(238)U年龄加权平均值分别为(129±0.7)Ma(MSWD=0.78)和(131±1.5)Ma(MSWD=1.70),表明中河岩体形成于早白垩世。岩石地球化学特征显示,中河岩体具有高的w(SiO_2)和w(K_2O)、低的w(Na_2O),其A/CNK比值为1.03~1.63,Mg#值介于25~50,总体上属于过铝质-强过铝质的高钾钙碱性系列。岩石具有低的w(Yb),中等-弱的铕负异常,稀土元素配分曲线为轻稀土元素富集型,轻稀土元素分馏相对强烈,但重稀土元素分馏不明显。中河岩体有相对低的w(Sr)和w(Y),且富集大离子亲石元素Rb、Ba、U、K和轻稀土元素,亏损高场强元素Nb、Ta、P、Zr、Hf、Ti和重稀土元素。中河岩体锆石εHf(t)值为-34.4~-23.2,平均为-26.9,Hf同位素二阶段模式年龄介于2485~3182 Ma,平均为2714 Ma。岩石地球化学特征及Hf同位素组成表明中河岩体的岩浆源区主要为新太古代地壳物质,并有少量的中太古代地壳物质,中-新太古代增生的具有弧岩浆特征的地壳物质部分熔融形成了早白垩世的中河岩体。  相似文献