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1.
Generation of Porphyritic and Equigranular Mafic Enclaves During Magma Recharge Events at Unzen Volcano, Japan 总被引：5，自引：0，他引：5
BROWNE BRANDON L.; EICHELBERGER JOHN C.; PATINO LINA C.; VOGEL THOMAS A.; DEHN JONATHAN; UTO KOZO; HOSHIZUMI HIDEO 《Journal of Petrology》2006,47(2):301-328
Mafic to intermediate enclaves are evenly distributed throughoutthe dacitic 1991–1995 lava sequence of Unzen volcano,Japan, representing hundreds of mafic recharge events over thelife of the volcano. This study documents the morphological,textural, chemical, and petrological characteristics of theenclaves and coexisting silicic host lavas. The eruptive productsdescribed in this study appear to be general products of magmamingling, as the same textural types are seen at many othervolcanoes. Two types of magmatic enclaves, referred to as Porphyriticand Equigranular, are easily distinguished texturally. Porphyriticenclaves display a wide range in composition from basalt toandesite, are glass-rich, spherical and porphyritic, and containlarge, resorbed, plagioclase phenocrysts in a matrix of acicularcrystals and glass. Equigranular enclaves are andesitic, non-porphyritic,and consist of tabular, medium-grained microphenocrysts in amatrix glass that is in equilibrium with the host dacite magma.Porphyritic enclaves are produced when intruding basaltic magmaengulfs melt and phenocrysts of resident silicic magma at theirmutual interface. Equigranular enclaves are a product of a moreprolonged mixing and gradual crystallization at a slower coolingrate within the interior of the mafic intrusion. KEY WORDS: mafic enclaves; quenched mafic inclusions; magma mingling; Unzen volcano; Unzen Scientific Drilling Project; resorbed plagioclase 相似文献
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在江西相山大型塌陷式火山盆地北部的潜火山岩岩墙中，笔者发现了闪长质的岩石包体，这种包体具典型的反向脉及淬冷边，且淬冷边内含有大量针状磷灰石。在包体内部或包体与寄主岩的边界均见有钾长石及斜长石捕虏晶，这种捕虏晶是包体岩浆从寄主岩岩浆中捕获的，常被熔蚀成筛状或浑圆状。包体与寄主岩（次斑状花岗闪长岩）的稀土元素曲线和不相容元素蛛网图的形态非常相似。因此，相山潜火山岩岩墙中的闪长质岩石包体是不同成分、不同温度的岩浆经对流及不均一岩浆混合作用而形成，在成因类型上属淬冷包体。 相似文献
3.
镇江石马杂岩体中岩石包体的成因研究 总被引：2，自引：0，他引：2
石马杂岩体,为南京—镇江地区出露面积较大的燕山期花岗质杂岩体,具大量暗色、细粒辉石闪长质-石英闪长质岩石包体,岩浆动力学理论的应用和详细的岩相学,岩石地球化学研究表明,该杂岩体中的岩石包体是不同成分岩浆大规模对流、不均一混合机制驱动下形成的,在成因类型上属淬冷包体. 相似文献
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浙江青田花岗岩中岩石包体特征及成因 总被引：7，自引：2，他引：7
浙江青田燕山晚期黑云母花岗岩中有许多石英闪长质岩石包体,它们大小不一,形态各异,以微细粒结构、具冷凝边构造、并发育针状磷灰石为特征。岩石包体与寄主花岗岩的主要氧化物、微量元素的变化趋势呈线性关系。岩石学、矿物学、岩石化学及地球化学等特征的研究表明,石英闪长质岩石包体属淬冷包体,由玄武质岩浆和花岗质岩浆通过不均匀的混合作用而形成。 相似文献
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A variety of low‐ to high‐pressure metamorphic assemblages occur in the metabasic rocks and metachert in the Upper Cretaceous–Eocene ophiolite belt of the central part of the Naga Hills, an area in the northern sector of the Indo–Myanmar Ranges in the Indo–Eurasian collision zone. The ophiolite suite includes peridotite tectonite containing garnet lherzolite xenoliths, layered ultramafic–mafic cumulates, metabasic rocks, basaltic lava, volcaniclastics, plagiogranite, and pelagic sediments emplaced as dismembered and imbricated bodies at thrust contacts between moderately metamorphosed accretionary rocks/basement (Nimi Formation/Naga Metamorphics) and marine sediments (Disang Flysch). It is overlain by coarse clastic Paleogene sediments of ophiolite‐derived rocks (Jopi/Phokphur Formation). The metabasic rocks, including high‐grade barroisite/glaucophane‐bearing epidote eclogite and glaucophane schist, and low‐grade greenschist and prehnite–clinochlore schist, are associated with lava flows and ultramafic cumulates at the western thrust contact. Chemically, the metabasites show a low‐K tholeiitic affinity that favors derivation from a depleted mantle source as in the case of mid‐ocean ridge basalt. Thermobarometry indicates peak P–T conditions of about 20 kb and 525°C. Retrogression related to uplift is marked by replacement of barroisite and omphacite by glaucophane followed by secondary actinolite, albite, and chlorite formation. A metabasic lens with an eclogite core surrounded by successive layers of glaucophane schist and greenschist provides field evidence of retrogression and uplift. Presence of S‐C mylonite in garnet lherzolite and ‘mica fish’ in glaucophane schist indicates ductile deformation in the shear zone along which the ophiolite was emplaced. 相似文献
7.
《International Geology Review》2012,54(11):1241-1270
Origins and positions of gold fields and ores, particularly of placers, in the Yana-Kolyma area and elsewhere in the Northeast, as indicated by the morphostructural analysis and the behavior of gold in endogenic and exogenic processes. – V.P. Sokoloff. 相似文献
8.
Petrogenesis of a Late Jurassic Peraluminous Volcanic Complex and its High-Mg, Potassic, Quenched Enclaves at Xiangshan, Southeast China 总被引：20，自引：0，他引：20
JIANG YAO-HUI; LING HONG-FEI; JIANG SHAO-YONG; FAN HONG-HAI; SHEN WEI-ZHOU; NI PEI 《Journal of Petrology》2005,46(6):1121-1154
A late Mesozoic belt of volcanic–intrusive complexes occursin SE China. Volcanic activity at Xiangshan in the NW of thebelt took place mainly in the Late Jurassic (158–135 Ma).The volcanic rocks from the Xiangshan volcanic complex includerhyolitic crystal tuffs, welded tuffs, rhyolite lavas, porphyriticlavas, and associated subvolcanic rocks. Mineral assemblagesin these magmatic rocks include K-feldspar, plagioclase, quartz,Fe-rich biotite and minor amphibole, orthopyroxene and almandine.Mineral geothermometry indicates a high crystallization temperature(>850°C) for the Xiangshan magmas. The volcanic rocksare generally peraluminous; SiO2 contents are between 65·4%and 76·8% and the samples have high alkalis, rare earthelements (REE), high field strength elements and Ga contentsand high Ga/Al ratios, but are depleted in Ba, Sr and transitionmetals. Trace element geochemistry and Sr–Nd–O isotopesystematics imply that the Xiangshan magmas were probably derivedfrom partial melting of Middle Proterozoic metamorphic lower-crustalrocks that had been dehydrated during an earlier thermal event.These features suggest an A-type affinity. Quenched mafic enclaves,hosted by the subvolcanic rocks, consist mainly of alkali feldspar,plagioclase, clinopyroxene, phlogopite and amphibole. Geothermometrycalculations indicate that the primary magmas that chilled toform the quenched enclaves had anomalously high temperatures(>1200°C). The quenched enclaves have boninitic affinities;for example, intermediate SiO2 contents, high MgO and low TiO2contents, high Mg-numbers and high concentrations of Sc, Ni,Co and V. However, they also have shoshonitic characteristics,e.g. enrichment in alkalis, high K2O contents with high K2O/Na2Oratios, high light REE and large ion lithophile element contents,low initial Nd values (–4·2) and high initial 87Sr/86Srratios (0·7081). We suggest a phlogopite-bearing spinelharzburgitic lithospheric mantle source for these high-Mg potassicmagmas. Underplating of such anomalously high-temperature magmascould have induced granulite-facies lower-crustal rocks to partiallymelt and generate the Xiangshan A-type volcanic suite. A back-arcextensional setting, related to subduction of the Palaeo-Pacificplate, is favoured to explain the petrogenesis of the Xiangshanvolcanic complex and quenched enclaves. KEY WORDS: volcanic complex; quenched enclaves; petrology; geochemistry; back-arc extension setting; Xiangshan; SE China 相似文献
9.
皖南前寒武纪花岗岩类中的岩石包体 总被引：7，自引：0，他引：7
皖南3个著名的强过铝花岗闪长岩岩体,是晚元古代时期以洋壳(包括上覆沉积岩)为主要源岩,经部分熔融形成的侵入体。笔者认为广泛产于其中的岩石包体的成分多种多样,类型复杂,是不同时期岩浆作用的产物,是认识与之相关的寄主花岗岩成因的重要线索。 相似文献
10.
火山岩中玻璃基质或细粒基质在淬火条件下形成,其熔体结构受淬火温压和熔体成分所控制。在已知熔体成分的条件下,淬火温压可根据熔体结构来确定。对于玄武质熔浆有NBO/T=0.098 57+2.77×10~(-4)T+9.13×10~(-10)p;对于粗面安山质熔浆有:NBO/T=-0.465 5+9.10×10~(-4)T+1.14×10~(-9);对于英安质熔浆有:NBO/T=-0.512 3+8.10×10~(-4)T+1.2×10~(-9)p。 相似文献