Trace element composition of quartz from the Variscan Altenberg–Teplice caldera (Krušné hory/Erzgebirge Mts, Czech Republic/Germany): Insights into the volcano-plutonic complex evolution
Trace element composition of quartz from the Variscan Altenberg–Teplice caldera (Krušné hory/Erzgebirge Mts, Czech Republic/Germany): Insights into the volcano-plutonic complex evolution
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DOI：
10.1016/j.chemgeo.2012.07.028
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发表时间：
2012-10
期刊：
影响因子：
3.9
通讯作者：
K. Breiter;M. Svojtka;L. Ackerman;K. Švecová
中科院分区：
文献类型：
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作者：
K. Breiter;M. Svojtka;L. Ackerman;K. Švecová
在这项研究中，内部结构和适当的微量元素分布在石英颗粒内进行了研究，使用激光烧蚀ICP-MS技术结合热阴极和扫描阴极发光分析。所研究的华力西期岩浆岩套位于Altenberg-Teplice破火山口（Krušné hory/Erzebirge东部，沿着捷克共和国/德国边界），由共岩浆火山岩（过铝质基底流纹岩和伴生英安岩，上覆三个亚铝质Teplice流纹岩和花岗斑岩单元）和深成花岗岩（两个A型黑云母和锌华花岗岩侵入体）组成。微量元素在花岗斑岩和流纹岩石英中的分布在阴极发光图像和化学成分上表现出明显的分带性：核部贫Ti，外缘区富Ti，Al的趋势与Ti相反。花岗岩中的石英要么是非常弱的环带，要么是均匀的。根据石英的化学成分及其分带性，我们认为石英晶体是在10 kbar、750°C的原始深源岩浆房中，在Al浓度增高、Ti浓度降低的环境中逐渐结晶的。早期阶段之后是随后的绝热上升到一个浅岩浆房（通过石英中的钛热压法估计在约700°C，2kbar），在此期间，富含钛的晶体边缘形成，然后挤出。破火山口坍塌后，部分岩浆以花岗岩形式侵入，在富含水和熔剂的残余熔体环境中，晚期石英以雪球状石英形式生长，Al含量增加，Ti含量降低。
In this study, the internal structures and appropriate trace-element distributions within quartz grains were investigated using a laser ablation ICP-MS technique combined with a hot-cathode and scanning cathodoluminescence analysis. The studied Variscan magmatic suite is located in the Altenberg–Teplice Caldera (eastern Krušné hory/Erzebirge, along the Czech Republic/Germany border) and composed of co-magmatic volcanics (peraluminous basal rhyolite and associated dacite, overlying three units of subaluminous Teplice rhyolite and granite porphyry) and plutonic granites (two intrusions of A-type biotite and zinnwaldite granites). The trace-element distribution in the granite porphyry and rhyolite quartz demonstrates a distinct zoning in the cathodoluminescence images and chemical compositions: the core is poor in Ti, the outer-rim zones are enriched in Ti, and the trends recorded for Al are opposite to those of Ti. The quartz from granites is either very weakly zoned or homogeneous. Based on the chemical composition of quartz and its zoning, we assume that the quartz crystals began to crystallize gradually in the primary deep-seated magma chamber with a P–T condition of 10kbar and 750°C and in an environment with an increasing concentration of Al and decreasing concentration of Ti. The early stage was followed by the subsequent adiabatic ascent into a shallow magma chamber (estimated by the Ti-in-quartz thermobarometry at approximately 700°C, 2kbar), during which crystal rims rich in Ti formed and then extruded. After the caldera collapse, part of the magma intruded as granite, and in the environment of the residual melt rich in water and flux agents, late quartz grew in the form of snowball quartz with an increased Al content and decreased Ti content.