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31.
祁漫塔格构造带是东昆仑造山带的重要组成部分,在青藏高原北部早古生代汇聚板块边缘地质研究中具有重要意义。祁漫塔格构造带在早古生代通常被认为是弧或弧后盆地,但其早期形成阶段的地质记录尚未报道,初始俯冲的时代也有待进一步限定。本文选择了祁漫塔格东段拉陵高里河地区祁漫塔格群火山岩和闪长岩进行岩石学、地球化学、锆石U-Pb年龄学和Hf同位素研究,探讨了岩石成因和构造意义。火山岩以安山岩为主,安山岩SiO2含量中等(54.02%~63.99%),具有低TiO2(0.19%~0.24%)、Al2O3(10.67%~12.86%)、P2O5(0.03%~0.05%)和低FeOT/MgO比值(0.80%~1.04)的特征,具有高的MgO(7.86%~11.44%)和Mg#(63~69);闪长岩SiO2含量为53.62%~55.81%,也具有低TiO2(0.19%~0.25%)、Al2O3(10.58%~11.52%)、P2O5(0.02%~0.04%)和低FeOT/MgO比值(0.9~1.0)的特征,同样具有高的MgO(9.86%~11.63%)和Mg#(64~66)的特点。高镁安山岩和闪长岩微量元素组成相近,Th(0.22~1.23 μg/g)、Rb(4.11~16.11 μg/g)和Ba(66.7~166 μg/g)含量低,Cr(286~668 μg/g)和Ni(57~181 μg/g)含量高,δEu=0.91~1.47,Sr/Y比值(19.7~36.1)较低,∑REE含量介于11.8~27.3 μg/g,(La/Yb)N = 1.3~4.3,轻重稀土分馏弱。在微量元素原始地幔标准化图解上大离子亲石元素Sr、Ba和Pb具明显的正异常,高场强元素Ta、Nb和Ti具有明显的负异常。高镁安山岩LA-ICP-MS 锆石U-Pb同位素年龄为519 Ma;闪长岩LA-ICP-MS 锆石U-Pb同位素年龄为520 Ma和516 Ma,两者锆石Hf同位素组成相似,εHf(t)值分布在+10.5~+15.8。上述研究结果表明,祁漫塔格东段拉陵高里河地区高镁安山岩/闪长岩源于亏损的地幔楔的部分熔融,形成于原特提斯洋俯冲早期的岛弧环境。本研究进一步证明祁漫塔格构造带古洋盆俯冲时代早于520 Ma,该认识也为恢复东昆仑造山带原特提斯洋早期俯冲演化历史提供了重要地质资料。 相似文献
32.
中国东北中生代岩浆活动广泛发育,产于延边的新屯高镁闪长岩(128 Ma)是其中特殊的一类岩石,对于约束构造背景具有重要意义。新屯闪长岩高Mg#,富含LILEs、亏损HFSEs,εHf的范围为3.2~8.9,指示岩浆主要来自同位素亏损的地幔源区。较高的La/Sm和Th/Yb比值,较低的Ba/La比值,暗示俯冲沉积物参与了岩浆的形成。岩石学特征显示普通角闪石、磁铁矿等矿物结晶较早,表明初始岩浆为富水高氧逸度的体系。水饱和条件下斜长石结晶受到抑制、角闪石等矿物发生分离结晶可能是导致演化的岩浆具备高Sr/Y比值的重要原因。在130~110 Ma期间,东北地区在古太平洋板块俯冲后撤影响下发生弧后伸展,软流圈物质上涌改变了地幔楔热状态,导致俯冲沉积物发生部分熔融,交代上覆地幔楔形成了早白垩世高镁闪长岩。 相似文献
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内蒙古梅劳特乌拉SSZ型蛇绿岩中,新发现了早二叠世巴嘎哈尔高镁闪长岩。该闪长岩位于贺根山缝合带内。锆石LA-ICP-MS U-Pb测年表明,巴嘎哈尔闪长岩的侵位年龄为(282±2)Ma,其形成时代为早二叠世。该岩石高镁,MgO含量5.00%~10.94%,Mg#值54~74;SiO_2含量53.52%~58.64%,Al_2O_3含量13.48%~14.98%,Na_2O含量1.36%~3.59%;贫钾,K_2O含量0.48%~1.61%;贫TiO_2(0.28%~0.76%)和P_2O_5(0.080%~0.160%);富Cr(75.00×10~(-6)~555.90×10~(-6))和Ni(26.20×10~(-6)~228.40×10~(-6));富集K、Rb和Sr等大离子亲石元素,亏损Nb、Ta、Zr、Ti和P等高场强元素;稀土元素总量较低(25.16×10~(-6)~83.57×10~(-6)),稀土曲线为略右倾的平坦型。该岩石具有高镁闪长岩的地球化学特征,与赞岐岩相类似,属于俯冲带岛弧型岩浆岩。结合其与梅劳特乌拉SSZ型蛇绿岩中玻安岩和埃达克岩的岩石组合时空分布特征,表明古亚洲洋贺根山洋盆在早二叠世可能仍然处于大洋俯冲消减状态。该高镁闪长岩可能为俯冲洋壳+俯冲深积物来源的硅质熔体交代上覆地幔楔使其部分熔融的产物。 相似文献
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对羌塘地块东北缘甘孜-理塘缝合带南侧日啊日曲石英闪长岩进行了系统的锆石U-Pb年龄、主量-微量元素及Sr-Nd同位素分析, 以探讨其岩石成因及地球动力学意义.LA-ICP-MS锆石U-Pb定年结果表明, 石英闪长岩侵位年龄为218±1 Ma, 为晚三叠世岩浆活动的产物.岩石SiO2含量介于53.02%~62.06%之间, 富Al2O3(15.84%~17.00%)和CaO(6.71%~8.94%), 贫TiO2(0.49%~1.01%)和P2O5(0.04%~0.12%), 具有较高的MgO(3.31%~5.66%)和Mg#(50~62), 属准铝质钙碱性系列; 岩体稀土元素总量较低(38.05×10-6~61.58×10-6), 轻重稀土分馏不明显, LILE富集, HFSE亏损, 具有含量较高的Cr(33.45×10-6~176.64×10-6)和Ni(13.34×10-6~43.62×10-6).全岩(87Sr/86Sr)i比值较为一致(0.706 8~0.707 9), εNd(t)变化于-5.5~-1.6.主微量元素及同位素结果表明日啊日曲石英闪长岩具有高镁闪长岩的特征, 与赞岐岩地球化学特征类似, 为俯冲沉积物来源的熔体交代岩石圈地幔形成的尖晶石相金云母二辉橄榄岩低度(10%~15%)部分熔融的产物, 岩浆演化过程中经历了辉石、角闪石等矿物的分离结晶.微量元素构造判别图解表明岩石为俯冲环境下的弧岩浆岩, 结合区内蛇绿岩、研究区南部陆缘弧火山岩和义敦岛弧埃达克岩的发现, 认为古特提斯洋在晚三叠世时期可能仍处于消减状态, 日啊日曲高镁石英闪长岩形成于甘孜-理塘洋南西向俯冲过程中. 相似文献
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鲁西中生代高Mg闪长岩的成因: 年代学与岩石地球化学证据 总被引：14，自引：0，他引：14
鲁西高Mg闪长岩分布较为广泛, 莱芜铁铜沟岩体和淄博金岭岩体是其典型代表.铁铜沟岩体早期苏长辉长岩和晚期辉石闪长岩、金岭黑云母闪长岩的LA-ICPMS U-Pb谐和加权平均年龄分别为(131.4±4.9)Ma(n=15)、(134.5±2.3) Ma(n=13)和(132.8±4.2)Ma(n=12), 它们代表了岩体的侵位结晶年龄——早白垩世.铁铜沟岩体晚期辉石闪长岩中浑圆状锆石的LA-ICPMS U-Pb谐和年龄为(2 513±54)Ma(n=8), 代表了华北克拉通基底的存在.该类岩石以高Mg# (> 60)、富钠、富含轻稀土元素、贫重稀土元素以及高场强元素(Nb、Ta、Zr、Hf)的明显亏损为特征, 显示埃达克岩(adakite) 的特征.该类岩石中地幔橄榄岩包体的广泛存在以及高Mg的特征表明原始岩浆的地幔成因, 而Sr-Nd同位素组成(Isr为0.704 75-0.707 72和εNd(t)值为-3.95--13.30)和高场强元素(Nb、Ta、Zr、Hf)的亏损以及太古代继承锆石的存在均暗示岩浆源区应有陆壳物质的涉入.铁铜沟岩体和金岭岩体闪长岩成分的差异应归因于岩浆源区性质的差异和部分熔融程度的不同.基于该类岩石的地球化学和所含包体, 同时结合华北克拉通东部中生代早期岩石圈演化历史, 可以认为鲁西中生代早白垩世高Mg闪长岩的形成应为拆沉的岩石圈(地幔+下地壳)与软流圈混熔的产物. 相似文献
36.
The mid‐Cretaceous Spences Bridge Group (SBG) comprises a series of basaltic to rhyolitic lavas and related volcaniclastic rocks (Pimainus Formation) overlain by a succession of mainly amygdaloidal andesites (Spius Formation) related to the closure of the Methow–Tyaughton basin and accretion of the Insular terrane in the North American Cordillera. Geochemical variation in the SBG is related primarily to metasomatic processes in the mantle wedge. Pimainus lavas include low‐ to high‐K, tholeiitic and calc‐alkaline types, and have isotopic compositions (εNd(100Ma) = + 5.2 to + 7.0, εSr(100Ma) = − 10 to − 20, 206Pb/204Pb = 18.82 to 18.91, 207Pb/204Pb = 15.55 to 15.60, 208Pb/204Pb = 38.24 to 38.43) between the ranges for primitive arcs and accreted terrane crust. Crustal sources are identified only for some low–medium K dacite and rhyolite compositions. The occurrence of intermediate compositions with high MgO contents (up to 6 wt%) and the presence of adakitic trace element features in medium–high K felsic lavas attests to metasomatism of the mantle wedge by slab melts during Pimainus volcanism. Spius lavas have comparable K2O and Pb isotopic compositions to the Pimainus, even higher MgO (up to 9.2 wt%), and display a mild intraplate character in having up to 0.6 wt% P2O5, 15 ppm Nb, and 240 ppm Zr. Spius Nd−Sr isotopic compositions (εNd(100Ma) = + 5.3 to + 6.9, εSr(100Ma) = − 14 to − 25) define an array extending from Pimainus to alkaline seamount compositions. The low εSr values, elevated high field strength element contents, and moderate silica contents suggest Spius volcanism was related to the introduction of small melt fractions from the asthenosphere into the mantle wedge which had previously generated Pimainus melts. The range of compositional types in the Pimainus Formation constrains tectonic scenarios to include an elevated slab thermal regime, likely from approach of an ocean ridge system toward the continental margin. Spius volcanism may have been generated by asthenospheric upwelling triggered by slab window development or slab‐hinge roll‐back on closure of the Methow–Tyaughton basin. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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两类埃达克岩的含矿性和成因:东南亚地区与东太平洋带对比 总被引：1，自引：0，他引：1
新生代埃达克岩是一种新型的火成岩(Sr/Y≥20),多产出于大洋岛弧、大陆边缘造山带(东南亚地区)和陆缘火山弧环境(东太平洋带),依据REE配分模式可将其划分为2种成因类型:大洋型(O型)和大陆型(C型)。埃达克岩分别广泛分布于东南亚地区的菲律宾群岛、苏拉威西、中加里曼丹、印度尼西亚几内亚岛、巴布亚新几内亚至所罗门群岛一带,及东太平洋带的北美洲、墨西哥、中美洲、南美洲的北部至南部。研究表明:不同成因类型的埃达克岩具有不同的含矿性,反映各自岩浆源区不同。C型埃达克岩(La/Yb12)是俯冲海洋板块部分熔融叠加增厚的地壳底部部分熔融MASH(熔融-混染-储存-均一化)和AFC(混染-分异-结晶)作用的产物,多半与世界级斑岩铜金矿床共生;O型埃达克岩(La/Yb≤12)则与平缓俯冲的海洋板片部分熔融作用有关,在东南亚地区主要与浅成热泉金矿有成因联系。 相似文献
38.
Reina Nakaoka Soko Kado Shuichi Hasegawa Keiko Suzuki-Kamata Osamu Ishizuka Shun Sekimoto Hiroshi Kawabata Yoshiyuki Tatsumi 《Island Arc》2021,30(1):e12378
Ar-Ar ages, and petrographical and geochemical characteristics of pyroclastics and an overlying lava from Teshima Island, southwest Japan are presented. Although previous geological and age data suggested Teshima pyroclastics were products of magmatism > 3 my prior to lava flows of Setouchi volcanic rocks generated in association with southward migration of the southwest Japan arc sliver during opening of the Sea of Japan backarc basin at ~ 15 Ma, the present results led to the conclusion that a sequence of Setouchi volcanism, induced by slab melting and subsequent melt-mantle reactions, produced both pyroclastics and lava at 14.6–14.8 Ma. This age is oldest among those reported so far and may represent the timing of onset of characteristic Setouchi magmatism immediately posterior to and hence as a result of the mega-tectonic event including rotation of the southwest Japan arc sliver. 相似文献
39.
The Petrology and Geochemistry of Oto-Zan Composite Lava Flow on Shodo-Shima Island, SW Japan: Remelting of a Solidified High-Mg Andesite Magma 总被引：1，自引：0，他引：1
TATSUMI Y.; SUZUKI T.; KAWABATA H.; SATO K.; MIYAZAKI T.; CHANG Q.; TAKAHASHI T.; TANI K.; SHIBATA T.; YOSHIKAWA M. 《Journal of Petrology》2006,47(3):595-629
The Oto-Zan lava in the Setouchi volcanic belt is composed ofphenocryst-poor, sparsely plagioclase-phyric andesites (sanukitoids)and forms a composite lava flow. The phenocryst assemblagesand element abundances change but Sr–Nd–Pb isotopiccompositions are constant throughout the lava flow. The sanukitoidat the base is a high-Mg andesite (HMA) and contains Mg- andNi-rich olivine and Cr-rich chromite, suggesting the emplacementof a mantle-derived hydrous (7 wt % H2O) HMA magma. However,Oto-Zan sanukitoids contain little H2O and are phenocryst-poor.The liquid lines of descent obtained for an Oto-Zan HMA at 0·3GPa in the presence of 0·7–2·1 wt % H2Osuggest that mixing of an HMA magma with a differentiated felsicmelt can reasonably explain the petrographical and chemicalcharacteristics of Oto-Zan sanukitoids. We propose a model wherebya hydrous HMA magma crystallizes extensively within the crust,resulting in the formation of an HMA pluton and causing liberationof H2O from the magma system. The HMA pluton, in which interstitialrhyolitic melts still remain, is then heated from the base byintrusion of a high-T basalt magma, forming an H2O-deficientHMA magma at the base of the pluton. During ascent, this secondaryHMA magma entrains the overlying interstitial rhyolitic melt,resulting in variable self-mixing and formation of a zoned magmareservoir, comprising more felsic magmas upwards. More effectiveupwelling of more mafic, and hence less viscous, magmas througha propagated vent finally results in the emplacement of thecomposite lava flow. KEY WORDS: high-Mg andesite; sanukitoid; composite lava; solidification; remelting 相似文献
40.