Back-thrusting and overturning of the southern margin of the 1.85Ga Sudbury Igneous Complex at the Garson mine, Sudbury, Ontario
Back-thrusting and overturning of the southern margin of the 1.85Ga Sudbury Igneous Complex at the Garson mine, Sudbury, Ontario
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安大略省萨德伯里 Garson 矿 1.85Ga 萨德伯里火成岩杂岩体南缘的反冲和翻转
DOI：
10.1016/j.precamres.2011.10.020
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发表时间：
2012
影响因子：
3.8
通讯作者：
C. Lesher
中科院分区：
文献类型：
--
作者：
J. Mukwakwami;B. Lafrance;C. Lesher
加尔森矿床是位于1.85Ga萨德伯里构造南段的几个变形岩浆镍铜铂族元素(PGE)矿床之一。矿床沿着褶皱的萨德伯里火成岩杂岩(SIC)的东南翼，位于SIC基岩与下伏的古元古代变基性玄武岩和胡伦超群的变质沉积岩之间的接触处。在Garson矿床中，富含包裹体的角砾岩和浸染型Ni-Cu-PGE硫化物矿石赋存于经历了两次主要韧性变形事件(D1和D2)的陡南倾剪切带和展布带中。D1具有陡峭的南倾S1面理和下倾的L1矿物伸展线理的特征，其特征是变质玄武岩中的铁闪锌矿和褐铁矿中的镁角闪石。变基性玄武岩中铁闪石和寡长石的共存指示了D1期的角闪岩相条件。剪切带形成于1.7-1.6Ga马扎扎尔-拉布拉多造山期，沿或靠近碳化硅-胡隆接触带。在碳化硅的屈曲过程中，由于弯曲滑移，它们形成为层状平行、北倾、北过南的逆冲。由于马扎扎尔-拉布拉多造山期的总体运移方向为自南向北，因此，D1剪切带为逆冲推覆，运移方向相反。逆冲推覆了碳化硅、下伏的胡伦岩和矿带，并将胡伦岩和变质碎屑岩的碎屑侵位到上覆的诺里岩中。与Garson的D1剪切带不同，塞耶-林德斯利剪切带和区域南山剪切带以高角度跨越了SIC-Hurung接触，形成了中等南东倾角的反向剪切带，这是折皱诱导应变在铰链附近局部化的结果，以适应SIC的进一步扁平和紧致，并伴随着D1的逐渐缩短。在Mazatzal-Labradorian造山运动或1.5-1.45GaChieflakian事件期间，D1剪切带与SIC的东南翼一起被翻转成现在的陡峭的南倾，并被重新激活为南北向剪切带，后者与整个劳伦蒂斯东南边缘年轻的安第斯式钙碱性岩浆弧的积累是同时代的。在这次D2重新激活事件中，S1被置换并局部保存在受S2绿泥质剪切面理包围的褶皱中，该面理具有强烈的向下倾斜的L2矿物绿泥石线理和平行的L2韧性滑闪线。
The Garson deposit is one of several deformed magmatic Ni–Cu–platinum group element (PGE) deposits in the South Range of the 1.85Ga Sudbury structure. The deposits occur along the southeast limb of the folded Sudbury Igneous Complex (SIC), at the contact between the SIC basal norite and underlying Paleoproterozoic metabasalt and metasedimentary rocks of the Huronian Supergroup. At the Garson deposit inclusion-rich breccia and disseminated Ni–Cu–PGE sulfide ores are hosted by steeply south-dipping shear zones and splays that underwent two major ductile deformation events (D1and D2). D1is characterized by a steeply, south-dipping, S1foliation and a down-dip L1mineral stretching lineation defined by ferrotschermakite in metabasalt and by magnesiohornblende in norite. Coexisting ferrotschermakite and oligoclase in metabasalt indicate amphibolite facies conditions during D1. The shear zones formed along or near the SIC-Huronian contact during the 1.7–1.6Ga Mazatzal–Labradorian Orogeny. They formed as layer-parallel, north-dipping, north-over-south thrusts in response to flexural slip during buckling of the SIC. As the general transport direction was from south to north during the Mazatzal–Labradorian Orogeny, the D1shear zones are back-thrusts with opposite transport direction. The thrusts imbricated the SIC, underlying Huronian rocks, and ore zones, and emplaced slivers of Huronian rocks and metabreccia into the overlying norite. In contrast to the D1shear zones at Garson, the Thayer Lindsley and the regional South Range shear zones, which transgress the SIC-Huronian contact at a high angle, formed as moderately SE-dipping reverse shear zones as a result of localization of folding-induced strain near the hinge zone in order to accommodate further flattening and tightening of the SIC with progressive D1shortening. Together with the southeast limb of the SIC, the D1shear zones were overturned into their present steep southerly dips and were reactivated as south-over-north shear zones either later during the Mazatzal–Labradorian Orogeny or during the 1.5–1.45Ga Chieflakian event, which was coeval with accretion of juvenile Andean-style, calc–alkaline magmatic arcs along the entire southeastern margin of Laurentia. During this D2reactivation event, S1was transposed and locally preserved in crenulations bounded by a S2chloritic shear foliation, which has a strong down-dip L2mineral chlorite lineation and parallel L2ductile slickenlines.