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首页> 外文期刊>Contributions to Mineralogy and Petrology >Quantitative petrological evidence for the origin of K-feldspar megacrysts in dacites from Taapaca volcano, Chile
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Quantitative petrological evidence for the origin of K-feldspar megacrysts in dacites from Taapaca volcano, Chile

机译：智利塔帕卡火山的Dacits中钾长石超大结晶起源的定量岩石学证据

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摘要

K-feldspar megacrysts are common in granitoids, but relatively rare in chemically equivalent volcanic rocks. Dacites from Taapaca volcano have euhedral sanidine megacrysts up to 5 cm long. Small crystals, where present, are rounded. Growth of the megacrysts engulfed plagioclase and amphibole crystals. Crystal size distributions (CSD) of sanidine megacrysts are hump shaped. All these data show that megacrysts developed from the host magma by coarsening: this was enabled by the cycling of magma temperature around the sanidine liquidus temperature in response to injections of more mafic magma and subsequent magmatic overturns. Plagioclase crystals enclosed in the megacrysts are small and have short, steep, straight CSDs, which contrasts with the CSDs of plagioclase in the groundmass which are shallower and extend to larger sizes. This shows that plagioclase was also coarsened approximately synchronously with sanidine, in response to the same temperature conditions.
机译：钾长石巨晶常见于花岗岩中，但在化学等价的火山岩中相对罕见。塔帕卡火山（Taapaca volcano）火山岩中的达盖特晶体具有正长面体，长达5厘米。存在的小晶体是圆形的。大晶体的生长吞没了斜长石和闪石晶体。 Sanidine大晶体的晶体尺寸分布（CSD）为驼峰形。所有这些数据表明，巨晶从宿主岩浆中通过变粗而形成：这是由于岩浆温度在Sanidine液相线温度附近循环而引起的，这是由于注入了更多的铁镁质岩浆和随后的岩浆倾覆所致。包围在大晶体中的斜长石晶体很小，并且具有短而陡峭的笔直的CSD，这与浅层中斜长石的CSD形成对比，后者更浅并延伸到更大的尺寸。这表明响应于相同的温度条件，斜长石酶也与沙丁胺大致同步地粗化。

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