新疆博格达造山带西段石炭纪双峰式火山岩地球化学特征及成因

新疆博格达造山带博格达峰南侧柳树沟组出露大量双峰式火山岩组合.本文对博格达造山带西段石炭纪双峰式火山岩地球化学特征研究结果表明:①玄武岩具有贫K富Na、富Ti富Al和富Mg的特征,w(K2O)/w(TiO2)、w(K2O)/w(P2O5)值较低且范围较小,总体上玄武岩有轻度的地壳物质混染作用;HREE相对富集,轻重稀土...     

西藏冈底斯带叶巴组火山岩地球化学及成因

叶巴组早侏罗世双峰式火山岩分布在拉萨、达孜至墨竹工卡之间, 岩性为浅变质玄武岩、玄武质熔结凝灰岩、英安岩、酸性凝灰岩及火山角砾岩等.火山岩SiO₂含量集中在41%~50.4%和64%~69%两个区间, 为钙碱性系列的玄武岩和英安岩2类.玄武岩的显著特征是TiO₂含量极低, 仅为0.66%~1.01%, 远低于大陆拉斑玄武岩.玄武岩的稀土总量∑REE=60.3~135μg/g, 英安岩的稀土总量∑REE=126.4~167.9μg/g.玄武岩和英安岩具有相似的稀土和微量元素特征, 两者均为轻稀土富集型, 分布特征相似, 轻、重稀土的分馏较明显, Eu异常均不显著; 均表现为LILE、LREE富集, HFS、HREE亏损的特点.玄武岩亏损Ti、Ta、Nb、Zr, Nb和Ta仅略负亏损, Nb*=0.54~1.17, 平均为0.84;英安岩亏损HFS中P、Ti, Ta、Nb略负异常, Nb*=0.74~1.06, 平均为0.86.玄武岩类的ε_Nd(t) =0.96~10.03、(87Sr/86Sr)_i=0.7043~0.7064, 英安岩的ε_Nd(t) =-1.42~1.08、(87Sr/86Sr)_i=0.7038~0.7049.从微量元素和同位素成分看, 玄武岩和英安岩浆起源于俯冲带之上的地幔楔不同程度的部分熔融, 源岩可能是亏损的尖晶石二辉橄榄岩.源区曾受到具地壳成分特征的流体不均匀交代.后期变质作用对岩石大离子亲石元素含量有影响.叶巴组双峰式火山岩形成于成熟岛弧后期的短暂拉张环境, 是印支期冈底斯岩浆弧演化的结果.      

四川青川县青溪铜钼多金属成矿带成矿地质特征

四川省青川县青溪铜多金属成矿带含矿岩系为前震旦通木梁群细碧—石英角斑岩系,具有"上酸下基"的双峰式特点。通过对区域大地构造演化背景、矿区含矿火山岩层序、岩浆活动、后期构造运动等控矿因素与矿床形成的关系,结合已知矿床、矿点的原生晕地球化学特点、成矿条件及成矿规律等研究,并与国际、国内典型块状硫化物矿床的特点进行对比,认为青溪铜多金属成矿带矿床属于"多因复成"的矿床。     

藏北班公湖—怒江缝合带早白垩世双峰式火山岩的确定及其地质意义

班公湖—怒江缝合带及其两侧发育的白垩世岩浆活动记录了大洋俯冲闭合过程的信息,是反演大洋演化的关键。报道了去申拉组火山岩测年结果,并对达查沟地区新发现的去申拉组玄武岩端元进行了详细的地球化学研究。2件火山岩样品的锆石U-Pb年龄分别为104.14Ma和104.95Ma,表明去申拉组火山岩形成于早白垩世晚期。玄武岩地球化学分析结果显示出Nb、Ta、Ti亏损,以及高的Zr含量、Zr/Y和(Th/Nb)N值的特征。研究认为,玄武岩是软流圈地幔部分熔融混染地壳物质的产物。结合已报道的去申拉组酸性岩数据,研究区具有双峰式火山岩特征的去申拉组是班公湖—怒江洋壳南向俯冲过程中,板片断离导致区域伸展背景下岩浆活动的产物。     

Early Mesoproterozoic bimodal plutonism in the southeastern Gawler Craton,South Australia

The Curramulka Gabbronorite on Yorke Peninsula, southeastern Gawler Craton has an emplacement age of 1589 ± 5 Ma. This is similar to previously determined ages for Arthurton Granite (1582 ± 7 Ma), Tickera Granite (ca 1600 – 1575 Ma), regional alteration, the Moonta – Wallaroo mineralisation (ca 1585 Ma) and localised deformation (Tiparra Deformation). Mesoproterozoic bimodal plutonism is interpreted to have resulted from mafic underplating, emplacement of mafic magmas during lithospheric attenuation and enhanced high heat flow assisting in melting of the lower crust to form the broadly A-type Arthurton and Tickera Granites. Plutonism either directly or indirectly created advective fluid-flow to form Cu – Au mineralisation in the Moonta – Wallaroo area. The nature and characteristics of Mesoproterozoic mafic bodies on the Gawler Craton are poorly known. The Curramulka Gabbronorite has a continental tholeiitic composition and igneous layering that is partly of cumulus origin but also contains magmatic segregations formed by fractionation. Some of these segregations have provided zircons for dating. This igneous layering is overprinted by two foliations of tectonic origin: the first is interpreted to be coeval with magma emplacement and the second with conjugate shearing accompanied by retrogression.     

勉略构造带横现河地区张岩沟双峰式火山岩的地球化学特征、LA-ICP-MS锆石U-Pb年龄及其构造意义

提要：横现河地区张岩沟双峰式火山岩位于勉略构造带三岔子—略阳段,由紧密共生的变质基性火山岩和变质中酸性火山岩组成,其原岩为亚碱性玄武岩和亚碱性流纹-英安岩。中酸性火山岩稀土元素含量明显低于玄武岩,表明中酸性火山岩为地壳部分熔融形成,而非分离结晶成因。玄武岩具有较高的Zr含量与较高的Zr/Y值,表现出板内玄武岩特征,其具有的弧印记应为陆壳物质混染所致。LA-ICP-MS锆石U-Pb测试结果表明,流纹岩成岩年龄为(728±10) Ma (n=4,MSWD =0.14)。结合区域地质背景,认为张岩沟双峰式火山岩形成于地壳伸展机制下的大陆裂谷环境,预示着该地区新元古代洋盆的打开。这一新成果,对研究勉略带新元古代的构造演化以及探讨扬子地块北缘对Rodinia超大陆裂解的响应具有重要意义。     

Ordovician sedimentation and bimodal volcanism in the Southern Qiangtang terrane of northern Tibet: Implications for the evolution of the northern Gondwana margin

This article reports our new interpretations of the depositional environment and provenance of the Dawashan Formation in the Longmuco–Shuanghu–Lancangjiang suture zone (LSLSZ), in the Southern Qiangtang terrane of northern Tibet, in order to gain a better understanding of the Ordovician tectonic evolution of the northern margin of Gondwana. The Dawashan Formation is dominated by greywacke and shale, with interlayered bimodal volcanic rocks that were deposited in a bathyal to abyssal marine basin. The detrital zircons in the greywacke of the Dawashan Formation have peak ages of 550, 988, 1640, and 2500 Ma, indicating a northern Gondwana margin provenance. The bimodal metavolcanic rocks from the Dawashan Formation are dominated by metarhyolite with subordinate metabasalt. The results of zircon LA-ICP-MS U–Pb dating indicate that the metarhyolite formed between 470 and 455 Ma. The metavolcanic samples are bimodal (SiO₂ = 45.27–55.05 and 66.09–74.59 wt.%). In comparison, the metabasalt has a wide range of MgO concentrations and Mg^# values, contains variable Cr and low Ni concentrations, is depleted in Rb, Ba, and Sr, and is enriched in TiO₂, Th, U, Nb, and Ta. Geochemical diagrams show that the metabasalt erupted in an intra-plate environment. The metarhyolites have high SiO₂, Th, and U concentrations, low concentrations of MgO, P₂O₅, Nb, Sr, and Ti, and negative Eu anomalies. The metarhyolites yield negative zircon ε_Hf(t) values (–2.08 to – 4.50) and T^C_DM model ages of 1436–1567 Ma. The metarhyolites formed from magma derived from the partial melting of old continental crust. These data indicate that the Dawashan Formation records Middle–Upper Ordovician bathyal to abyssal turbidite deposition in a deep-water rift basin at the northern margin of Gondwana.     

伊宁地块特克斯达坂晚石炭世伊什基里克组双峰式火山岩地球化学特征

伊宁地块特克斯达坂一带出露的晚石炭世伊什基里克组双峰式火山岩主要由玄武岩、流纹岩两大端员组成,其Si O2含量为47. 13%～77. 72%,在53. 62%～72. 15%之间存在明显的间断,具有双峰式火山岩的特征。LAICP-MS锆石U-Pb定年获得流纹岩年龄为302. 8±3. 6 Ma,表明该套火山岩形成于晚石炭世。玄武岩Si O2含量为47. 13%～53. 62%,具有低Si O2、高Fe2O3(TFe2O3=10. 90%～17. 40%)、高MgO(3. 74%～10. 12%,平均为6. 48%)和高Na(Na2O=2. 84%～6. 69%)、低K(K2O=0. 48%～3. 77%)特征(Na2O/K2O=1. 21～12. 18),轻稀土元素富集而重稀土元素亏损[(La/Yb)N=1. 58～4. 94],具有弱的负Eu异常(δEu=0. 30～1. 10),亏损Ta、Nb、Th、Sr等不相容元素。流纹岩Si O2含量为72. 15%～77. 72%,具有高Si O2、高K(K2O=6. 12%～9. 48%)、低Na(Na2O=0. 40%～2. 39%)特征(Na2O/K2O=0. 04～0. 36),K、Rb和LREE显著富集[(La/Yb)N=2. 46～10. 48],相对亏损Ba、Sr、P、Ti,且有基本一致的强负Eu异常(δEu=0. 18～0. 44),具有A2型花岗岩地球化学特征。此外,玄武岩具有相对高的Mg#值和Co、Cr、Ni含量,其εNd(t)值为3. 45、3. 55,表明玄武岩来自于亏损地幔的部分熔融;而流纹岩具有低Mg#和正εHf(t)值,暗示其形成与玄武质岩浆底侵过程中的地壳熔融有关。结合二阶段锆石Hf模式年龄,认为源区可能与元古宙的变质结晶基底重熔有关。根据上述地球化学特征并结合构造判别图解,认为特克斯达坂一带伊什基里克组双峰式火山岩形成于造山后伸展环境,具有板内成因特征。该套典型双峰式火山岩的发现为进一步探讨伊宁地块石炭纪构造演化提供了重要依据。     

云和盆地早白垩世双峰式火山岩特征

本文从岩石学、岩石化学、微量元素及稀土元素等方面，对云和盆地早白垩世馆头组火山岩特征进行了论述，并对其形成环境及成因作了探讨．认为该套火山岩由基性岩及酸性岩构成，缺少SiO2含量在53．17％～68．57％的中性岩，是一套典型的双峰式火山岩组合。指出盆地内火山岩为拉张构造背景下形成，其基性岩和酸性岩具有不同源区，前者源于部分上地幔融熔物质（受陆壳物质混染）；后者来自部分地壳融熔的产物。     

新疆阿舍勒铜矿区双峰式火山岩与成矿背景的初步研究

新疆阿舍勒铜矿是我国近十多年来找到的一个大型海相火山岩型块状硫化物多金属矿床，在经济上和矿床学上都有重要意义。阿舍勒铜矿的容矿岩是早－中泥盆世阿舍勒组海相火山岩，具特征的双峰式组合，缺少含ＳｉＯ２５４％－６１％的中性岩，在地表和钻孔都经常见到基性与酸性火山岩紧密互层现象。稀土和微量元素地球化学表明基性、酸性火山岩来自两个不同的源区。矿石铅同位素组成与细碧岩一致，硫同位素呈典型塔式分布，表明成矿物质