Plutonic lithics in ignimbrites of Taupo Volcanic Zone, New Zealand: sources and conditions of crystallisation
Plutonic lithics in ignimbrites of Taupo Volcanic Zone, New Zealand: sources and conditions of crystallisation
复制标题
新西兰陶波火山区火成岩中的深成岩屑：结晶来源和条件
DOI：
10.1016/s0009-2541(98)00026-6
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发表时间：
1998
期刊：
影响因子：
3.9
通讯作者：
I. Cartwright
中科院分区：
文献类型：
--
作者：
S. Brown;R. M. Burt;J. Cole;S. Krippner;R. Price;I. Cartwright
在新西兰陶波火山带中部的一些火山口和破火山口杂岩中，深成岩碎屑以罕见的副岩屑的形式出现在一些褐沸石中。深成岩屑的两套主要是：(1)中-细粒花岗岩类和(2)细粒辉绿岩和微闪长岩。花岗岩类大多为中等颗粒岩石，具有等粒和花岗斑共生结构，后者表明在地壳浅层快速结晶。在大多数花岗岩样品中，黑云母是主要的镁铁质相，但也有罕见的角闪石和含斜方辉石的花岗岩类。在Rotoiti褐沸石中的一些花岗岩样品中发现了玻璃，这表明这些样品在喷发前没有完全结晶。辉绿岩和微闪长岩碎屑通常含有丰富的角闪石，以及高达10%的泡状间隙玻璃。花岗岩类中SiO_2丰度在70.3~77.9%之间。它们呈弱铝-弱过铝，富含大离子亲石元素(Rb、K、Ba)，Nb相对MORB亏损，类似于现代TVZ流纹状火山岩。在化学和岩石学上，花岗岩类分为两类：高锶花岗闪长岩(120-205ppm锶)和化学演化程度较高的低锶二长花岗岩(26-65ppm锶)，两者之间存在明显的成分差距。Eu/Eu~*异常和Al_2O_3、CaO、Sr之间的强相关性表明，两个花岗岩类之间的成分变化主要受斜长石分馏的控制。高、低锶组与TVZ流纹岩中观察到的最高、最低锶浓度相吻合。花岗岩类的REE数据和锶、钕、铅、氧同位素比值与已发表的TVZ流纹岩数据相当，因此它们被认为代表了与第四纪TVZ火山活动有关的带状硅质岩浆房的结晶部分，而不是更古老的前TVZ基底的碎片。大多数花岗岩类与其寄主褐辉橄榄岩为同岩浆，但Rotoiti褐辉橄榄岩的矿物组合和全岩化学与其寄主褐辉橄榄岩不同。这些碎片似乎是早期岩浆系统的不完全结晶部分，可能与产生Matahina点火沸石的系统相同。榴辉岩和微闪长岩在地球化学上类似于从TVZ中部喷发的演化的高铝玄武岩，被认为是侵入性的等价物。
Plutonic rock fragments occur as rare accessory lithics within some of the ignimbrites erupted from calderas and caldera complexes in central Taupo Volcanic Zone (TVZ), New Zealand. The two main suites of plutonic lithics are: (1) medium to fine-grained granitoids and (2) fine-grained dolerites and microdiorites. The granitoids are mostly medium-grained rocks with both equigranular and granophyric intergrowth textures, the latter indicating rapid crystallisation at shallow crustal levels. Biotite is the predominant mafic phase in most granitoid samples, although rare hornblende and orthopyroxene-bearing granitoids also occur. Glass occurs in some granitoid samples from Rotoiti ignimbrite, indicating that these samples were incompletely crystallised prior to eruption. Dolerite and microdiorite fragments typically contain abundant hornblende, and up to 10% vesicular interstitial glass. SiO2abundances in the granitoids range between 70.3 and 77.9%. They are weakly metaluminous to weakly peraluminous and show an enrichment in Large Ion Lithophile (LIL) elements (Rb, K, Ba), and a depletion in Nb, relative to MORB, similar to recent TVZ rhyolitic volcanic rocks. Chemically and petrographically the granitoids fall into two distinct groups: high-Sr granodiorites (120–205 ppm Sr), and chemically more evolved low-Sr monzogranites (26–65 ppm Sr), with an apparent compositional gap between the two. Eu/Eu* anomalies and strong correlations between Al2O3, CaO and Sr indicate that compositional variation between the two granitoid groups is dominantly controlled by plagioclase fractionation. The high- and low-Sr groups coincide with the highest and lowest Sr concentrations observed in TVZ rhyolites. REE data and Sr, Nd, Pb and O isotope ratios for granitoids are comparable to published data for TVZ rhyolites, and consequently they are considered to represent crystallised portions of zoned silicic magma chambers associated with Quaternary TVZ volcanic activity, and not fragments of older pre-TVZ basement. Most granitoids are regarded as comagmatic with their host ignimbrites, but those from Rotoiti ignimbrite have different mineral assemblages and whole-rock chemistry to the host ignimbrite. These fragments appear to be incompletely crystallised portions of an earlier magma system, possibly the same system that generated the Matahina ignimbrite. Dolerites and microdiorites are geochemically similar to evolved high alumina basalts erupted from the central TVZ and are considered to be intrusive equivalents.
共轭稳定自由基光激发高自旋有机分子的设计、合成和物理性质，旨在通过光激发态表达复杂功能（IV）
DOI：
--
发表时间：
2005
期刊：
影响因子：
--
作者：
東一 哲也;手木 芳男
通讯作者：
手木 芳男