The Temagami geophysical anomaly (Ontario, Canada): geological cause and relationship to the 1.85 Ga Sudbury impact event

本项目试图解释北美迄今为止尚未解释的最大磁异常之一的最终地质原因，即加拿大安大略省的天马神地球物理异常。该异常具有突出的科学和经济意义，因为它直接毗邻1.85 Ga萨德伯里杂岩。萨德伯里杂岩是地球上第二大冲击构造，也是世界上最富有的矿区之一，这要归功于广泛的镍铜铂族金属硫化物矿化。天马神异常在形状、大小和强度上都反映了萨德伯里杂岩引起的磁异常。由于缺乏露头，而且直到最近，也没有钻孔，这阻碍了人们对地质的正确认识，而且无论与萨德伯里复合体的遗传联系如何，都仍然是纯粹的猜测。申请人和预期的项目科学家（博士生）对天马神异常中心的第一个深钻孔进行了初步的岩石学研究，发现在2公里深处存在闪长岩，与萨德伯里杂岩及其周围的offset岩脉有相似之处。这增加了与萨德伯里撞击事件的遗传联系的可能性，如果被证明是正确的，将为我们对萨德伯里复合体及其勘探潜力的理解开辟一个全新的视角。因此，该项目的主要目的是测试这种遗传联系，并通过比较从天马神异常地区的岩心和地表样品中获得的岩石学、蚀变史、地球化学、同位素组成和地质年代学的新数据，与萨德伯里杂岩和更广泛地区潜在的等效岩石的现有数据，为地球物理异常提供地质解释。这将包括层状基性和超基性侵入，基性岩脉群，碳酸盐岩库存和沉积铁地层，所有这些都出现在该地区，具有巨大的经济潜力，并且可能是观测到的磁异常的可能候选者。我们的初步观测还揭示了广泛的热液蚀变和角化作用，其成因和与磁异常的关系尚不清楚。因此，该项目的进一步目标将是描述这种蚀变的特征，并根据天马神异常的成因、萨德伯里构造的成因和该地区的成矿作用确定其重要性。

This project attempts to explain the ultimate geological cause of one of the largest, hitherto unexplained, magnetic anomalies in North America, the Temagami geophysical anomaly in Ontario, Canada. The anomaly is of outstanding scientific and economic interest because it is directly adjacent to the 1.85 Ga Sudbury Complex - the second largest impact structure on Earth and one of the world’s richest mining districts thanks to widespread Ni-Cu-PGE-sulfide mineralization. The Temagami Anomaly mirrors the magnetic anomaly caused by the Sudbury Complex in terms of shape, size and intensity. Lack of outcrops and, until recently, of bore holes, prevented a proper geological understanding, and whatever genetic link with the Sudbury Complex has remained pure speculation. Preliminary petrological studies by the applicant and the anticipated project scientist (PhD student) on the first deep drill hole sunk into the centre of the Temagami Anomaly revealed the presence of dioritic rocks at 2 km depth, which bear similarities with offset dykes in and around the Sudbury Complex. This raises the possibility of a genetic link with the Sudbury impact event, which if proved correct, would open up an entirely new perspective on our understanding of the Sudbury Complex and its exploration potential. Thus, the principal aim of this project is to test for such a genetic link and to provide a geological explanation for the geophysical anomaly by comparing new data on the petrology, alteration history, geochemistry, isotopic composition and geochronology to be acquired from drill core and surface samples from the area of the Temagami Anomaly with available data on the Sudbury Complex and potentially equivalent rocks in the wider region. This will include layered mafic and ultramafic intrusions, mafic dyke swarms, carbonatite stocks, and sedimentary iron formations, all of which occur in the area, bear significant economic potential, and could be possible candidates for the observed magnetic anomaly. Our preliminary observations revealed also widespread hydrothermal alteration and brecciation, whose origin and bearing on the magnetic anomaly is unclear. Thus, a further goal of the project will be to characterize this alteration and to establish its significance in terms of the cause of the Temagami Anomaly, the genesis of the Sudbury structure and the metallogeny of the area.