Archaean quartz arenites in the Canadian shield: examples from the Superior and Churchill Provinces
Archaean quartz arenites in the Canadian shield: examples from the Superior and Churchill Provinces
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DOI：
10.1016/s0037-0738(98)00031-1
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发表时间：
1998-09-01
影响因子：
2.8
通讯作者：
de Kemp, EA
中科院分区：
文献类型：
--
作者：
Donaldson, JA;de Kemp, EA
在加拿大地盾的上级省西北部和西丘吉尔省（雷省）的北方北部，有非常纯净的石英砂屑岩。在上级省的几个绿岩带中，保存完好的是中生代硅质胶结石英砂岩。来自Keeyask湖沉积组合的实例显示了平板状平面和槽状交错层、涟漪、再活化面和卵石滞留沉积。尽管有穿透变形和绿片岩级变质作用，原生结构保存得非常好，显示骨架颗粒非常圆整和分选。Keeyask湖石英砂岩层的继承层上覆有含小规模层状、穹状和柱状叠层石的粉砂岩，推断为浅海沉积环境。碎屑重矿物包括黄铁矿、磁铁矿、锆石、电气石、磷灰石、辉石和黄玉。在西丘吉尔省（Rae省）的北方部分，北东向带中出现了石英砂岩，在这些带中，强烈的构造变形在大多数地方使原生结构和构造变得模糊或消失。这导致了推测，其中一些单位是变粗岩或重结晶脉石英，但当地保存的原生纹理和结构提供了明确的证据，震中起源。在本文所述的实例中，伍德伯恩湖群的石英砂屑岩显示出稀疏的槽和板状平面交错床、通道、涟漪和卵石滞留沉积。这些石英砂岩可能的沉积环境包括河流系统和浅海陆棚设置。在夹层砾岩层中出现的明确的石英-砂屑碎屑提供了至少两个几乎纯石英砂堆积阶段的直接证据。薄片和抛光板揭示了弹性石英颗粒的框架，几乎没有基质（现在主要是白云母），以及辅助重矿物的罕见碎屑颗粒，主要是锆石和不透明的氧化铁。黄铁矿和其他硫化物已被引入沿着裂缝，但一些粒间硫化物颗粒可能是碎屑成因的。这两个地区的石英砂岩的主要来源必须是富含石英的花岗岩。强烈的化学风化的条件表明。在加拿大地盾的西太平洋板块和世界其他地盾中广泛存在的极成熟的石英砂岩，暗示了地球历史早期的地壳稳定性。现在，加拿大地盾的许多太古代绿岩带都发现了石英砂屑岩和超镁铁质岩的组合，这在较年轻的地体中是不典型的。(C)1998 Elsevier Science B. V.保留所有权利。
Units of remarkably pure Archaean quartz arenite occur in the northwestern part of the Superior Province and in the northern terrane of the Western Churchill Province (Rae Province) of the Canadian Shield. In the Superior Province, silica-cemented quartz arenites of Archaean age are well preserved in several greenstone belts. The example from the Keeyask Lake sedimentary assemblage displays tabular-planar and trough cross-beds, ripple marks, reactivation surfaces and pebble lag deposits. In spite of penetrative deformation and greenschist-grade metamorphism, primary textures are extremely well preserved, showing framework grains to be very well rounded and sorted, The succession of Keeyask Lake quartz-arenite beds is overlain by siltstones containing small-scale stratiform, domal and columnar stromatolites, A shallow-marine environment of deposition is inferred. Detrital heavy minerals include pyrite, magnetite, zircon, tourmaline, apatite, sphene and topaz. In the northern part of the Western Churchill Province (Rae Province), Archaean quartz arenites occur in northeasterly trending belts where intense structural deformation has in most places obscured or obliterated primary textures and structures. This has led to speculation that some of these units are metachert or recrystallized vein quartz, but local preservation of primary textures and structures provides clear evidence of epiclastic origin. In the example described herein, quartz arenites of the Woodburn Lake Group display sparse occurrences of trough and tabular-planar cross-beds, channels, ripple marks and pebble lag deposits. Probable environments of deposition for these quartz arenites include fluvial systems and shallow-marine shelf settings. The occurrence of unequivocal quartz-arenite clasts in beds of intercalated conglomerate provides direct evidence of at least two episodes of accumulation of almost pure quartz sand. Thin sections and polished slabs reveal frameworks of elastic quartz grains with little to no matrix (now mainly muscovite), and rare detrital grains of accessory heavy minerals, predominantly zircon and opaque iron oxides. Pyrite and other sulphides have been introduced along fractures, but some intergranular sulphide grains may be of detrital origin. The principal source for the quartz arenites in both areas must have been quartz-rich granitoid rocks. Conditions of intense chemical weathering are indicated. The widespread occurrence of extremely mature quartz arenites throughout Archaean terranes of the Canadian Shield, and in other shields of the world, are suggestive of crustal stability during early Earth history. The association of quartz arenites and ultramafic rocks, uncharacteristic of younger terranes, is now recognized in many Archaean greenstone belts of the Canadian Shield. (C) 1998 Elsevier Science B.V. All rights reserved.