Crystal Settling, In-situ Crystallization, Melt Migration, and Magma Recharge in a Differentiated Mafic Sill, Victoria Island, Canada

晶体沉淀、原位结晶、熔体迁移和岩浆在分化的Mafic Sill中的补充，维多利亚岛，加拿大智力价值。该项目的重点是与加拿大维多利亚岛上暴露的元古界富兰克林火成事件有关的镁铁质岩床中岩浆的演化。通过与加拿大地质调查局的合作，PI参与了这些基岩的实地测绘，并通过其中一个基岩获得了三个完整的钻芯。对这一岩床进行了详细的研究，以破译侵位过程中和侵位后的分化机制。门槛较薄(26~44m厚)，横向较宽(走向长度36公里)，对于如此薄的岩浆体来说，差异显著(MG#S从35到82系统地变化)。上部和下部冷却边缘含有约10%的橄榄石斑晶，突然让位于内部不含橄榄石的辉绿岩，这表明任何悬浮的斑晶迅速沉降，或以某种方式与底缘分离。事实上，在岩床底部附近出现了5到8米厚的橄榄石富集区。自始至终几乎不变的橄榄石成分与橄榄石-玄武岩岩浆的注入一致，随后橄榄石的集体沉降。橄榄石带上方的一层薄(1至2米厚)含有丰富的自面体扇形辉石。占岩床上部80%的辉绿岩，从底部向上，从屋顶向下，逐渐变得贫镁富铁，直到靠近岩床中心的富Fe-Ti元素的“夹心区”。辉绿岩的变化趋势不能用原始岩浆中橄榄石和辉石斑晶的剥离来解释，而一定是辉绿岩就地分异的结果。一个mg#？踢？下部辉绿岩在水平方向上可追踪10多公里，代表岩浆补给事件。尽管基床是元古界的，但初步数据的地球化学模拟表明，常量元素和微量元素都没有发生明显的变化。窗台的合计散装成分与冷藏边框成分非常匹配。岩相学和成分矿物的化学分析被用来解释可能的侵位后压实和晶体碎屑中熔体迁移的岩石结构。将研究CSD的粒度变化，以确定存在的主要矿物的成核和生长历史。拟议研究的目标是评估：[1]富含橄榄石的基底带的起源、压实和再平衡，[2]补给层上下的矿物结构和成分变化，[3]底板和顶板辉绿岩中记录的原地分异趋势的起源，以及压实作用在这两个序列中的作用。更广泛的影响。该项目是与加拿大地质调查局的一项为期五年的区域测绘计划合作进行的。维多利亚岛的岩床在成分和构造环境上与西伯利亚的岩床相似，后者是诺里尔斯克型镍铜铅矿化的发源地；更好地了解它们的侵位和结晶历史可能会改善类似矿床的勘探策略。尽管这些薄的岩床代表了分化岩浆室套间的一个极端终端成员，但它们可能提供了对较大岩浆室的初始结晶过程的关键洞察，在这些岩浆室中，早期结晶历史的记录已被缓慢冷却期间的后来重新平衡所覆盖。该项目也将为学生参与者提供极好的教育机会。

Crystal Settling, In-situ Crystallization, Melt Migration, and Magma Recharge in a Differentiated Mafic Sill, Victoria Island, Canada Intellectual Merit. This project focuses on the evolution of magmas emplaced in mafic sills associated with the Proterozoic Franklin Igneous event as exposed on Victoria Island, Canada. Through cooperation with the Canadian Geological Survey, the PI has been involved in field mapping of these sills and has access to three complete drill cores through one of the sills. Detailed studies of this sill are proposed to decipher the differentiation mechanisms that have operated during and after emplacement of the intrusion. The sill is relatively thin (26 to 44 m thick), laterally extensive (36 kms of strike length), and remarkably differentiated for such a thin magma body (Mg#s vary systematically from 35 to 82). Upper and lower chilled margins with ~10% olivine phenocrysts give way abruptly to olivine-free diabasic rocks in the interior, suggesting that any suspended phenocrysts settled out rapidly, or were segregated in some way from the sill margins. Indeed an olivine-rich zone 5 to 8 m thick occurs near the base of the sills. Near-constant olivine composition throughout isconsistent with injection of an olivine-porphrytic magma, followed by en-masse settling of olivine. A thin (1 to 2 m thick) layer above the olivine zone contains abundant, euhedral, sector-zoned augite. Diabase, which makes up the upper 80% of the sill, becomes progressively Mg-poor and Fe-rich upward from the base and downward from the roof to an Fe-Ti-excluded element rich "sandwich" zone near the center of the sill. The variation trend in the diabase cannot be explained by the removal of olivine and augite phenocrysts from the initial magma, and must have resulted from in-situ differentiation of the diabase. A Mg# ?kick? in the lower diabase can be traced horizontally for over 10 kms, and appears to represent a magma recharge event. Although the sill is Proterozoic, geochemical modeling of preliminary data, suggests that neither major nor trace elements have been significantly altered. The summed bulk composition of the sill very closely matches a chilled margin composition. Petrography and chemical analyses of the constituent minerals is proposed to interpret rock textures with regards to possible post-emplacement compaction and melt migration in the crystal mush. CSD grain size variations will be examined to determine the nucleation and growth history of the major minerals present. Goals of the proposed study are to evaluate: [1] the origin of, and compaction and re-equilibration within, the olivine-rich basal zone, [2] mineral textural and compositional variations above and below the recharge horizon, and [3] the origin of in-situ differentiation trends recorded in the diabase at the floor and roof of the sill, and the role of compaction in these two sequences. Broader Impacts. This project is being carried out in collaboration with a five-year regional mapping program of the Geological Survey of Canada. The Victoria Island sills are similar in composition and tectonic setting to sills in Siberia that host Noril'sk-type Ni-Cu-PGE mineralization; a better understanding of their emplacement and crystallization history may lead to improved exploration strategies for similar deposits. Although these thin sills represent one extreme end-member of the differentiated magma chamber suite, they may provide critical insights into initial crystallization processes in larger magma chambers where the record of the early crystallization history has been overwritten by later re-equilibration during slow cooling. This project will also provide excellent educational opportunities for the student participants.