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

晶体沉降、原位结晶、熔体迁移和岩浆补给：加拿大维多利亚岛。本项目主要研究与加拿大维多利亚岛暴露的元古代富兰克林火成岩事件相关的岩浆的演化。通过与加拿大地质调查局的合作，PI参与了这些技能的实地测绘，并通过其中一个技能获得了三个完整的钻芯。在此基础上提出了详细的研究，以破译在入侵就位期间和之后运作的分化机制。岩台相对较薄（厚度26 ~ 44 m），横向分布广泛（走向长度36 km），对于这样一个薄的岩浆体（Mg#s在35 ~ 82之间系统变化），具有明显的分异。含~10%橄榄石斑晶的上部和下部冷缘突然让位给内部不含橄榄石的辉绿岩，表明任何悬浮斑晶迅速沉降，或以某种方式从基底边缘分离出来。实际上，岩台底部附近有一个5至8米厚的富含橄榄石的地带。几乎恒定的橄榄石组成与橄榄-斑岩岩浆的注入相一致，随后是橄榄石的大量沉降。橄榄石带上方的薄层（1 ~ 2米厚）含有丰富的自面状扇形奥辉石。辉绿岩占基台上部80%，从基底向上、从顶部向下逐渐贫镁富铁，直至基台中心附近形成不含铁钛元素的富“夹心”带。辉绿岩的变化趋势不能用初始岩浆中橄榄石和辉石斑晶的去除来解释，而必须是辉绿岩的原位分异所致。一个Mg踢？在较低的辉绿岩中，可以水平追踪到10公里以上，似乎代表了岩浆补给事件。虽然仍然是元古代，但初步数据的地球化学模拟表明，主要元素和微量元素都没有明显改变。蒸馏器的总体积组成与冷却边缘组成非常接近。提出了岩石学和化学分析的组成矿物，以解释有关可能的侵位后压实和熔融迁移的晶体糊状岩石结构。CSD晶粒尺寸的变化将被检查，以确定主要矿物的成核和生长历史。[1]是富橄榄岩基带的成因、压实作用和内部再平衡作用；[2]是补给层位上下矿物结构和成分的变化；[3]是基底底板和顶部辉绿岩中记录的原位分异趋势的成因，以及压实作用在这两个层序中的作用。更广泛的影响。这个项目是与加拿大地质调查局的一个五年区域制图方案合作进行的。维多利亚岛岩床在组成和构造背景上与西伯利亚岩床相似，具有Noril - sk型Ni-Cu-PGE成矿作用；更好地了解它们的就位和结晶历史，将有助于改进类似矿床的勘探策略。尽管这些薄壁岩代表了分化岩浆房组的一个极端末端成员，但它们可能为更大的岩浆房的初始结晶过程提供重要的见解，在这些岩浆房中，早期结晶历史的记录已被缓慢冷却期间的后期再平衡所覆盖。该项目也将为学生参与者提供良好的教育机会。

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.