东天山觉罗塔格地区底坎儿组火山岩地球化学特征及构造环境探讨

底坎儿组火山岩是东天山石炭纪火山岩的重要组成部分,其分布范围北至吐-哈盆地南缘,南至沙泉子断裂,其地球化学特征对于探讨觉罗塔格地区的构造环境演化具有重要的意义。本文对底坎儿组火山岩的主量、微量及Sr-Nd同位素进行了研究,以探讨岩石成因及其形成的构造环境。结果表明,底坎儿组火山岩为一套钙碱性的玄武岩-安山岩-流纹英安岩组合,为石榴石-尖晶石橄榄岩地幔部分熔融的产物。玄武岩经历了橄榄石和单斜辉石的结晶分异,安山岩和流纹英安岩则经历了斜长石和磁铁矿的结晶分异。火山岩相对富集轻稀土元素和大离子亲石元素,亏损高场强元素,玄武岩的微量元素配分型式与弧玄武岩相似,而部分安山岩及流纹英安岩的微量元素配分型式与上地壳相似。底坎儿组火山岩的Nd同位素特征[εNd(t)=-0.14~5.69]及微量元素地球化学特征显示其具有中等亏损地幔源区特征,岩浆来自于俯冲流体交代的地幔,岩浆演化过程遭受了有限的地壳混染。基性火山岩微量元素配分型式及构造环境图解表明其可能形成于弧后盆地环境。     

甘肃天祝地区乌鞘岭一带双峰式火山岩 的发现及其构造环境

北祁连乌鞘岭一带出露一套以玄武质岩石为主的双峰式火山岩组合,火山岩岩石类型以变质玄武岩为主,夹少量的流纹岩。玄武质岩石为蚀变玄武岩,属拉斑玄武岩系列,低SiO2、K2O,高Ti,富Na、Th、U等,轻稀土元素亏损—略富集型,无明显Eu异常,微量元素具Nb、Ta负异常。流纹质岩石属钙碱性系列,高SiO2,低K2O,为钠质系列,大离子亲石元素富集,具明显的Nb、P、Ti、Sr负异常和Th、U正异常,轻稀土元素富集,(La/Yb)N为2.98~11.46,Eu负异常明显,δEu介于0.07~0.60之间。结合区域资料分析,乌鞘岭双峰式火山岩可能形成于弧后盆地环境。     

甘肃省榆中地区中元古代兴隆山岩群火山岩地球化学特征及构造环境

分布于甘肃省榆中县兴隆山地区的兴隆山岩群为一套浅变质火山岩与浅变质碎屑岩所组成的岩石组合,其火山岩主要出露于兴隆山岩群中岩组和上岩组。兴隆山岩群火山岩岩性主要为变质玄武岩,具有低w（K2O）、w（Na2O＋K20）和w（TiO2）的特点,且w（TiO2）和w（P2O5）接近于洋中脊玄武岩的平均质量分数,为亚碱性的拉斑玄武岩系列,火山岩稀土元素总量低,轻、重稀土元素分馏不明显,稀土元素配分曲线为轻稀土元素略亏损、重稀土元素平坦型,与洋中脊玄武岩的配分曲线类似,火山岩大离子亲石元素相对富集,高场强元素和重稀土元素平坦,稀土元素、微量元素特征及构造环境判别显示兴隆山岩群的火山岩形成于中元古代秦祁昆多岛洋中部略富集的E型洋中脊的海底扩张环境。     

新疆富蕴县苏普特一带双峰式火山岩的发现及其地质意义

新疆阿尔泰苏普特一带中泥盆统阿勒泰组为一套以玄武质岩石为主的双峰式火山岩组合,下部以变质玄武岩为主,夹少量流纹岩,中部以变质玄武岩、玄武质凝灰岩、沉凝灰岩为主,夹少量酸性火山岩及其碎屑岩,上部流纹质岩石有所增加。玄武质岩石往往变质为角闪片岩、绿帘阳起石片岩等,属拉斑玄武岩系列,低SiO2、K2O,高Ti,富Na、Rb、Ba、Th、U等,轻稀土略富集,无明显铕异常,Nb负异常明显,相似于MORB和岛弧型玄武岩的某些特征,与弧后盆地玄武岩的特征基本一致。流纹质岩石属钙碱性系列,高SiO2,低K2O,为钠质型;大离子亲石元素富集,具明显的Nb、P、Ti负异常和弱的Th正异常,Sr含量较低;稀土元素含量较高,∑REE为135.67×10-6～407.71×10-6,轻稀土略富集,(La/Yb)N为2.55～3.73,铕负异常较明显,δEu值为0.34～0.54。流纹质岩石地球化学特征也与典型弧后盆地双峰式火山岩中的流纹岩相似。结合区域资料分析,苏普特双峰式火山岩是阿尔泰南缘俯冲撕裂型裂谷盆地演化晚期局部形成的类似于弧后环境的产物。     

新疆博格达中段木垒地区七角井组火山岩岩石地球化学特征及构造意义

博格达构造带木垒地区早石炭世七角井组内发育大量双峰式火山岩,火山岩的SiO_2含量在48%～65%之间出现明显的间断,具有Daly成分间断。其玄武岩具有贫K富Na、富Ti、富Al和Mg的特征,K_2O/TiO_2、K_2O/P_2O_5值高且变化范围较大,总体显示玄武质岩浆后期存在轻度地壳混染作用;英安岩具有贫K富Na、低Ti和P,和共生玄武岩的特征不同。玄武岩轻稀土中度富集,轻、重稀土元素之间存在中等分异;英安岩相对于玄武岩,稀土元素总量高于2～3倍,轻重稀土分异明显,显示为右倾且斜率较大的配分模式,具有较强的负Eu异常(δEu=0.89～0.93)。玄武质岩浆可能为亏损地幔的部分熔融作用形成,英安质岩浆可能为地壳物质重熔形成。综合分析认为博格达早石炭世处于弧后裂陷盆地环境。     

阿尔金山拉配泉地区元古宙裂谷火山岩系及其构造意义

阿尔金山拉配泉之北，拉配泉断裂和阿尔金北缘断裂夹持的火山岩片为一套典型的双峰式大陆裂谷火山岩系，基性端员属碱性系列和亚碱性系列，亚碱性系列可分为钙碱性系列和拉斑玄武岩系列，酸性端员均属钙碱性关系，基性火山岩Ｓｍ－Ｎｄ同位素年龄为１７９３±２７０（２σ）Ｍａ，εＮｄ＝６．４±１．４。稀土元素地球化学特征表明，基性火山岩以轻稀土富集配分型式为主，个别样品呈ＭＯＲＢ型平坦配分型式，酸性火山岩以轻稀土高度     

藏南定日白垩纪火山岩岩石学与地球化学初步研究

本文描述了西藏定日白垩纪火山岩的地质、岩石学、岩石地球化学特征和构造造背景。该火山岩岩石类型有蚀变英安岩和蚀变安山岩,其岩石化学成分特征表明岩石为二氧化硅过饱、铝过饱和类型,属亚碱性拉斑玄武岩系列。岩石稀土元素配分曲线呈强烈右倾的轻稀土富集型;微量元素配分模式图呈锯齿状“多隆起”型,类似于岛弧火山岩的微量元素配分模式。综合判定该期火山岩形成于大陆边缘造山带岛弧构造环境。     

甘肃南祁连党河南山中奥陶世火山岩的地球化学特征

甘肃南祁连褶皱带党河南山地区中奥陶世火山岩的岩石学和微量元素、稀土元素的地球化学等研究证明,本区火山岩由基性火山岩和中性火山岩组成。其中,基性火山岩分属碱性玄武岩系列和拉斑玄武岩系列;而中性火山岩为一套钙碱性安山岩,二者均具有低钾、高钠的特点。这些火山岩的稀上元素配分曲线均属于轻稀土富集型,(w(La)／W(Yb))_N=2.73～7777,(w(La)／w(Sm))_N=1.43～3.21,(w(Gd)／w(Yb))_N=1.01～1.92．明显地表现为轻稀土元素配分曲线陡倾,而重稀土元素配分曲线相对平坦的特征。微量元素配分曲线图表现为大离子亲石元素的富集和Nb、Ta、Zr、Hf及Ti不同程度的亏损。这些岩石学和地球化学的特征证明本区火山岩形成于岛弧环境。     

云南主要双峰式火山岩及相关矿产资源

云南双峰式火山岩时空分布较为广泛,贯穿云南及整个西南"三江"地区的地质发展演化过程,并伴有各具特色的矿产。本文基于前人的研究资料,总结了云南主要的双峰式火山岩的时空分布和相关矿产资源的情况,并讨论与双峰式火山岩有关的地质构造背景。总结出在地质历史演化过程中,云南主要分布有:(1)元古宙:滇中地区中元古代大红山群、河口群、东川群、昆阳群中的碱性火山岩及细碧-角斑岩类火山岩组合,新元古代与苏雄组同期的双峰式火山岩;(2)早寒武世梅树村期:扬子地台西缘玄武岩和凝灰岩等火山喷发记录;(3)中—晚志留世:滇西普洱大平掌铜多金属矿区大凹子组(S2+3d)细碧岩-石英角斑岩建造;(4)中—晚泥盆世:滇西北德钦羊拉里农组(D2+3l)碎屑岩夹双峰式火山岩+碳酸盐岩;(5)早三叠世:金沙江造山带攀天阁组(T1p)流纹岩+崔依比组(T1c)玄武岩(细碧岩或蚀变玄武岩)组成的"双峰式"火山岩,滇西洱源岩群双峰式火山岩;(6)中—晚三叠世:澜沧江造山带中南段忙怀组(T2m)流纹岩、流纹英安岩、流纹质火山碎屑岩、少量玄武岩和小定西组(T3x)玄武质火山碎屑岩以及芒汇河组(T3mh)玄武岩、流纹质火山碎屑岩组成的双峰式火山岩;(7)古近纪:剑川组(E2j)碱性玄武岩-粗面质火山角砾岩组合等7个阶段的双峰式火山岩,其地质构造背景各异,并伴有各具特色的矿产。这些双峰式火山岩可以作为制约云南及整个西南"三江"地区关键地质演化和成矿事件的标志性地质现象,是研究其地质构造背景和成矿作用的重要依据。     

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。     

马超营断裂以北熊耳群火山岩系是形成于弧后裂陷盆地环境的基性-酸性双峰态火山岩组合吗?——与胡德祥等同志商榷

中元古界熊耳群火山岩分布于华北地台南缘。本文提出马超营断裂以北火山岩是以安山岩占主导地位的玄武岩—安山岩—英安岩—流纹岩组合,而不是胡德祥等人提出的基性—酸性双峰态组合,它们形成的构造环境为安第斯型火山弧。火山岩上部的粗安岩—粗面岩组合形成的构造环境为弧内盆地。     

塔河地区海西晚期火山岩地球化学特征及地质意义

通过岩心观察,塔河地区海西晚期先后发育基性火山岩和中酸性火山岩两大类。两类火山岩具有不同地球化学组成:基性火山岩K2O+Na2O=3.49%~4.25%,K2O/Na2O=0.18~0.381,为钠质系列玄武岩,富集大离子亲石元素K、Rb、Ba、Th和高场强元素Nb、Ta、Ti、Zr、P,δEu≈1,无明显亏损;中酸性火山岩表现为高场强元素Nb、Ta、Sr、P、Ti亏损,大离子亲石元素K、Rb、Ba、Th较为富集,稀土元素δEu=0.43~0.661,铕具明显负异常特征,K2O+Na2O=6.86%~8.82%,K2O/Na2O=1.25~1.591,为钾玄或高钾钙碱性系列英安岩。强不相容元素Th/Ta、Nb/U比值说明,玄武岩与英安岩成因没有明显亲缘性,玄武岩来源于地幔,英安岩来源于地壳。结合邻区火成岩对比分析,塔河地区发育的玄武岩、英安岩分别与塔中地区玄武岩和南天山分区花岗岩具有相同的地球化学特征,构造判别图解表明,玄武岩形成于板内主裂陷期,英安岩、花岗岩形成于板块边缘岛弧构造环境,作为特殊古构造位置,塔河地区先后发育的玄武岩、英安岩为板内主裂陷盆地边缘和弧火山边缘相互耦合的产物。     

Geochemical behavior of rare earth elements in hydrothermally altered rocks of the Kuroko mining area,Japan

In this study we analyzed the chemical composition of hydrothermally altered dacite and basalt from the Kuroko mining area, northeastern Honshu, Japan, by REE (rare earth element). Features of rare earth element analyses include: (1) altered footwall dacite exhibits a negative Eu anomaly compared with fresh dacite, suggesting preferential removal of Eu²⁺ from the altered dacite via hydrothermal solutions, (2) altered hangingwall dacite and basalt and dacite and basalt adjacent to ore deposits exhibit positive Eu anomalies compared with fresh dacite and basalt, suggesting addition of Eu²⁺ from hydrothermal solutions, (3) LREE ratio (∑LREE/∑REE) from altered dacite of chlorite–sericite zone and K-feldspar zone show a negative relationship with δ¹⁸O, and La/Sm ratios show a positive correlation with the K₂O index. These trends indicate the addition of light rare earth elements such as La to the altered dacite from hydrothermal solution and/or leaching of heavy rare earth elements such as Sm and Yb, (4) Principal component analysis (PCA) indicates that light rare earth elements enrichment is related to the formation of sericite zone near the Kuroko deposits but not to the formations of chlorite and K-feldspar zones, and (5) The correlations among REE features (LREE ratio, MREE ratio, HREE ratio, Eu/Eu?), δ¹⁸O and K₂O index are not found for montmorillonite zone, mixed layer clay mineral zone and mordenite zone. Therefore, it is inferred that sericite, chlorite and K-feldspar alterations are related to the Kuroko and vein-type mineralization, but montmorillonite and mordenite alterations are not related to the mineralizations, and probably they formed at the post-mineralization stage.     

Textural and compositional evidence for magma mixing and its mechanism,Abu volcano group,southwestern Japan

Quaternary basalts, andesites and dacites from the Abu monogenetic volcano group, SW Japan, (composed of more than 40 monogenetic volcanoes) show two distinct chemical trends especially on the FeO^*/MgO vs SiO₂ diagram. One trend is characterized by FeO^*/MgO-enrichment with a slight increase in SiO₂ content (Fe-type trend), whereas the other shows a marked SiO₂-enrichment with relatively constant FeO^*/MgO ratios (Si-type trend). The Fe-type trend is explained by fractional crystallization with subtraction of olivine and augite from a primitive alkali basalt magma. Rocks of the Si-type trend are characterized by partially melted or resorbed quartz and sodic plagioclase phenocrysts and/or fine-grained basaltic inclusions. They are most likely products of mixing of a primitive alkali basalt magma containing olivine phenocrysts with a dacite magma containing quartz, sodic plagioclase and hornblende phenocrysts. Petrographic variation as well as chemical variation from basalt to dacite of the Si-type trend is accounted for by various mixing ratios of basalt and dacite magmas. Pargasitic hornblende and clinopyroxene phenocrysts in andesite and dacite may have crystallized from basaltic magma during magma mixing. Olivine and spinel, and quartz, sodic plagioclase and common hornblende had crystallized in basaltic and dacitic magmas, respectively, before the mixing. Within a lava flow, the abundance of basaltic inclusions decreases from the area near the eruptive vent towards the perimeter of the flow, and the number of resorbed phenocrysts varies inversely, suggesting zonation in the magma chamber.The mode of mixing changes depending on the mixing ratio. In the mafic mixture, basalt and dacite magmas can mix in the liquid state (liquid-liquid mixing). In the silicic mixture, on the other hand, the basalt magma was quenched and formed inclusions (liquid-solid mixing). During mixing, the disaggregated basalt magma and the host dacite magma soon reached thermal equilibrium. Compositional homogenization of the mixed magma can occur only when the equilibrium temperature is sufficiently above the solidus of the basalt magma. The Si-type trend is chemically and petrographically similar to the calc-alkalic trend. Therefore, a calc-alkalic trend which is distinguished from a fractional crystallization trend (e.g. Fe-type trend) may be a product of magma mixing.     

新疆东天山卡拉塔格二叠纪火山岩成因及构造意义

新疆东天山中北部的卡拉塔格地区广泛出露一套二叠纪陆相火山熔岩,本次对其采集的玄武岩和英安岩进行岩相学、锆石U-Pb定年、Lu-Hf同位素和岩石地球化学分析。年代学研究获得2个英安岩样品LA-ICP-MS锆石U-Pb加权平均年龄为（267.5±1.5）Ma和（296.7±1.7）Ma,代表了英安岩的结晶年龄为早二叠世。岩石地球化学数据显示：玄武岩为碱性系列,具有高Al₂O₃质量分数和Na₂O/K₂O值,低TFeO、Cr质量分数和Mg^#值的特征;微量元素Yb标准化的Ta、La和Nb值指示该区玄武质岩浆起源于富集型地幔;低La/Ba值,（Th/Nb）_N>1,Nb/La<1,表明岩浆在上升过程中受到了地壳岩石圈物质的混染;样品w（Zr）>100×10^-6,Zr/Y>5,显示大陆板内玄武岩特征。英安岩为钙碱性系列,富硅铝,Rb、Ba、Th、U、Zr等元素质量分数较高,Ti、Nb、Ta、Sr、P等元素质量分数较低,明显不同于玄武岩元素分布特征,却与地壳元素分布相似;ε_Hf（t） 值（5.4~14.7）为正,表明英安岩源区为新生地壳;w（Rb）-w（Y+Nb）构造环境判别图解表明其形成于大陆伸展环境。结合前人的研究成果,认为卡拉塔格早二叠世火山岩形成于板内伸展环境,为天山石炭纪—二叠纪大火成岩省裂谷火山作用的组成部分,限定了该区古亚洲洋闭合于早二叠世之前。     

新疆阿舍勒盆地阿舍勒组火山岩锆石U-Pb测年及地球化学特征

新疆阿舍勒盆地中阿舍勒组火山岩主要为英安质、流纹质火山角砾岩,凝灰岩、沉凝灰岩等火山角砾岩及火山熔岩,顶部为玄武岩及碧玉岩、灰岩.玄武岩亏损Nb,Ta,Ti等高场强元素,富集Ba,Th,U,Sr等大离子亲石元素,具岛弧玄武岩特征;英安岩为钙碱性系列,富集Rb,Ba,Th,U等大离子亲石元素,Nb,P,Ti亏损十分明显,...     

Petrology of Calc-alkaline Lavas from Ruapehu Volcano and Related Vents, Taupo Volcanic Zone, New Zealand

Most Ruapehu lavas and those of related vents (Taupo VolcanicZone, New Zealand) are calc-alkaline, medium-K basic and acidandesites, though minor volumes of basalt and dacite occur.Nearly all are porphyritic with phenocrysts of plagioclase,augite, olivine (mainly in basalts and basic andesites), orthopyroxene(mainly in acid andesites and dacites), and titanomagnetite(chrome spinel in basic lavas). The lavas have been subdividedinto six groups, each petrographically, geochemically and isotopicallydistinct: Type 1 plagioclase-pyroxene phyric lavas dominate,and range from basalt to dacite. Least squares mass balancecalculations indicate that these lavas were probably generatedfrom low-alumina basalt by combined crystal fractionation (15–55per cent) and crustal assimilation (1–30 per cent). Xenolithstudies indicate that the assimilant is most likely to be apartial melt of gneiss, originally Torlesse terrane greywacke.Crystal accumulation occurs to a minor extent in Type 1 lavasand becomes important in Type 2 (plagioclase-phyric) and Type3 (pyroxene-phyric) lavas. Type 4 lavas are rare and of unknownorigin, though they may be similar to rare hornblende-bearingandesites from nearby Maungakatote volcano. Type 5 lavas areclinopyroxene-olivine-phyric andesites which were probably generatedfrom a primitive basalt by crystal fractionation without crustalassimilation. Type 6 lavas show strong evidence of disequilibriumand were probably generated by mixing Type 5 basalt with Type1 dacite in proportions of between 60:40 and 50:50. The assertion that the assimilant involved in contaminationof most Ruapehu andesites is a partial melt of basement greywackeis a significant departure from previously published theoriesand has important implications for trace element and isotopicmodelling.     

Geochemistry and Petrogenesis of Volcanic Rocks in the Yeba Formation on the Gangdise Magmatic Arc, Tibet

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.     

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.      

塔河油田火山岩的层位归属、火山岩岩石学与岩相学特征

火山岩顶、底地层中的微古化石组合研究表明:塔河油田火山岩的形成时代为二叠纪。岩石学、岩相学、地球物理测井与地震学综合研究结果显示,火山岩主要为英安岩和玄武岩。存在两次火山喷发旋回,形成下部玄武岩、上部英安岩或单一英安岩的垂向火山喷发序列。玄武岩呈带状分布于研究区西部和南部古地貌低洼区,以上平下凸的透镜状河谷充填式地震反射为特点;英安岩分布于北部及东北部地区,以下平上凸的丘形反射形态为特征。可划分出火山爆发相、火山溢流相和火山沉积相3个岩相带。火山爆发相位于火山喷发中心地带,研究区以火山熔岩溢流相为主,火山沉积相布范围局限,位于岩体边缘。火山活动具有喷发频率低、间隔时间短、以宁静的溢流式喷发为主间或伴随较强烈的爆发式喷发为特点。火山活动喷发中心可能是由西南逐渐向东北方向迁移的。