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首页> 外文期刊>Contributions to Mineralogy and Petrology >The origin of plagioclase phenocrysts in basalts from continental monogenetic volcanoes of the Kaikohe-Bay of Islands field, New Zealand: implications for magmatic assembly and ascent
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The origin of plagioclase phenocrysts in basalts from continental monogenetic volcanoes of the Kaikohe-Bay of Islands field, New Zealand: implications for magmatic assembly and ascent

机译：新西兰Kaikohe-Bay的大陆单一的火山沼泽沼泽的起源：对岩浆装配和上升的影响

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摘要

Late Quaternary, porphyritic basalts erupted in the Kaikohe-Bay of Islands area, New Zealand, provide an opportunity to explore the crystallization and ascent history of small volume magmas in an intra-continental monogenetic volcano field. The plagioclase phenocrysts represent a diverse crystal cargo. Most of the crystals have a rim growth that is compositionally similar to groundmass plagioclase ( similar to An(65)) and is in equilibrium with the host basalt rock. The rims surround a resorbed core that is either less calcic ( similar to An(20-45)) or more calcic ( An(70)), having crystallized in more differentiated or more primitive melts, respectively. The relic cores, particularly those that are less calcic ( similar to An(45)), have Sr-87/Sr-86 ratios that are either mantle-like ( similar to 0.7030) or crustal-like ( similar to 0.7040 to 0.7060), indicating some are antecrysts formed in melts fractionated from plutonic basaltic forerunners, while others are true xenocrysts from greywacke basement and/or Miocene arc volcanics. It is envisaged that intrusive basaltic forerunners produced a zone where various degrees of crustal assimilation and fractional crystallization occurred. The erupted basalts represent mafic recharge of this system, as indicated by the final crystal rim growths around the entrained antecrystic and xenocrystic cargo. The recharge also entrained cognate gabbros that occur as inclusions, and produced mingled groundmasses. Multi-stage magmatic ascent and interaction is indicated, and is consistent with the presence of a partial melt body in the lower crust detected by geophysical methods. This crystallization history contrasts with traditional concepts of low- flux basaltic systems where rapid ascent from the mantle is inferred. From a hazards perspective, the magmatic system inferred here increases the likelihood of detecting eruption precursor phenomena such as seismicity, degassing and surface deformation.
机译：新西兰群岛地区Kaikohe-Bay爆发的卟啉基质爆发了探讨了大陆内遗传岩场内小体积岩浆的结晶和上升历史的机会。 Plagioclase Phenocrysts代表多样化的水晶货物。大多数晶体具有缘生长，其与基族普氏酶（类似于（65））和宿主玄武岩岩石平衡。边缘环围绕着钙的再沉核（类似于（20-45））或更多钙（＆（70）），分别在更分散或更重要的熔体中结晶。遗物核心，特别是那些差的钙（＆类似于（45）），具有SR-87 / SR-86比率，即搭式型（类似于0.7030）或类似地壳状（类似于0.7040 0.7060），表明有些是由富升玄武岩前导者分馏的熔体中形成的抗弯曲，而其他则是来自Greywacke地下室和/或中烯弧菌火山的真正的XenoCrysts。设想侵入式玄武岩先行者产生了一个各种地壳同化和分数结晶的区域。爆发的底座代表了该系统的MAFIC充值，如终端围绕诱捕的抗腊肠和XenoCrystic货物周围的最终晶体边缘生长所示。再充电还涉及夹杂物的同源Gabbros，并产生混合的地面。表明了多级岩浆上升和相互作用，并且与通过地球物理方法检测到的下地壳中的部分熔体体的存在一致。这种结晶历史与传统的低通量玄武岩系统概念形成鲜明对比，其中从地幔中迅速上升。从危险的角度来看，在此推断的岩浆系统增加了检测喷发前体现象的可能性，例如地震性，脱气和表面变形。

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