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首页> 外文期刊>Contributions to Mineralogy and Petrology >Origin of quartz clusters in Vinalhaven granite and porphyry, coastal Maine
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Origin of quartz clusters in Vinalhaven granite and porphyry, coastal Maine

机译：缅因州沿海Vinalhaven花岗岩和斑岩中的石英团簇起源

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We use the crystallographic orientations of quartz crystals, as determined with EBSD, to provide new evidence for the formation of clustered quartz crystals during magma crystallization. Vinalhaven is dominated by granite, with minor porphyry that formed when granite remelted during input of coeval basalt. CL zoning suggests that most quartz clusters in granite and porphyry formed by synneusis, the “swimming together” of preformed crystals. In granite, most quartz pairs in clusters have random orientations—only about 10% have parallel or Esterel twin orientations. Porphyry has fewer quartz clusters, and all pairs have approximately parallel or Esterel twin orientations. CL zoning of quartz pairs in porphyry indicates that they attached prior to a major remelting event. Interpretation of the Vinalhaven quartz clusters leads us to propose that oriented synneusis occurs during crystal accumulation on a magma chamber floor. During hindered settling, some quartz crystals should have come into contact along their dipyramidal faces. Once in contact, continued settling and loss of interstitial melt may have rotated some quartz crystals such that lattices on their dipyramidal faces matched—producing parallel and Esterel twin orientations and creating strong bonds between pairs. Only a small proportion of pairs with matched dipyramidal faces formed in the granite and, during rejuvenation to produce porphyry, only these oriented pairs survived. Hence, the presence of oriented synneusis in a plutonic rock may demonstrate a history of crystal accumulation.
机译：我们使用EBSD确定的石英晶体的晶体学取向，为岩浆结晶过程中簇状石英晶体的形成提供了新的证据。 Vinalhaven主要由花岗岩构成，在古代玄武岩输入期间花岗岩重熔时会形成少量斑岩。 CL分区表明，花岗岩和斑岩中的大多数石英团簇是通过协同作用形成的，即预制晶体的“游动”。在花岗岩中，成簇的大多数石英对具有随机的取向-只有大约10％的石英具有平行或Esterel孪晶取向。斑岩具有较少的石英团簇，并且所有对都具有近似平行或Esterel孪晶取向。斑岩中石英对的CL分区表明，它们在重大重熔事件之前就已附着。 Vinalhaven石英团簇的解释使我们提出定向的协同作用发生在岩浆室底板上的晶体堆积过程中。在受阻沉降过程中，一些石英晶体应沿其金字塔形的面接触。接触后，持续的沉降和间隙熔体的损失可能会使某些石英晶体旋转，从而使其金字塔形面上的晶格匹配-产生平行和Esterel孪晶取向，并在两对之间形成牢固的键合。在花岗岩中只有一小部分成对的具有双锥体表面的成对，并且在复兴以生产斑岩的过程中，只有这些取向的成对得以幸存。因此，在深成岩中定向协同作用的存在可以证明晶体积累的历史。

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