Provenance Determination of Volcaniclastic Rocks: the Nature and Tectonic Significance of a Cambrian Conglomerate from the New England Fold Belt, Eastern Australia
Provenance Determination of Volcaniclastic Rocks: the Nature and Tectonic Significance of a Cambrian Conglomerate from the New England Fold Belt, Eastern Australia
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火山碎屑岩的物源测定：澳大利亚东部新英格兰褶皱带寒武纪砾岩的性质和构造意义
DOI：
10.1306/212f8bc0-2b24-11d7-8648000102c1865d
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发表时间：
1987
影响因子：
2
通讯作者：
Peter A. Cawood
中科院分区：
文献类型：
--
作者：
E. Leitch;Peter A. Cawood
摘要澳大利亚东部新英格兰褶皱带的Murrawong Creek和Pipeclay Creek组是中寒武世为数不多的记录之一-(？)冈瓦那东部边缘的早奥陶世沉积。它们由砾岩、砂岩、粉砂岩和内部海底扇环境中堆积的层状泥质岩组成。砂岩是贫石英的火山石器时代的变体。砾岩碎屑主要是安山岩，但范围从玄武岩到流纹岩；所有这些岩石都是斑岩，斑晶有长石(钙质斜长石之后的钠长石)、辉石，以及罕见的钛磁铁矿。辉石是一种低二氧化钛种类，钛磁铁矿只有适度的二氧化钛含量。蚀变改变了碎屑的岩浆成分，但ESS活动性元素表明它们来自低钾造山套，这与岩石学和矿物学数据一致。西部物源和寒武系以东的下古生界俯冲杂岩的存在-(？)奥陶系单位表明后者是在弧前环境中积累起来的。该分布省可能是西北部东部拉克兰褶皱带的麦夸里火山带的前身，也可能是澳大利亚东南部、维多利亚大陆(南极洲)和新西兰的冈瓦纳边缘碎裂序列中保存的寒武纪洋岛弧之一。
ABSTRACT The Murrawong Creek and Pipeclay Creek Formations of the New England Fold Belt of eastern Australia provide one of the few records of Middle Cambrian-(?) Early Ordovician sedimentation along the eastern Gondwana margin. They comprise conglomerate, sandstone, siltstone, and laminated argillite that accumulated in an inner-submarine-fan environment. Sandstones are quartz-poor volcanolithic varieties. Conglomerate clasts are mainly andesite but range from basalt to rhyolite; all these rocks are porphyritic with phenocrysts of feldspar (albite after calcic plagioclase), augite, and, uncommonly, titanomagnetite. The augite is a low-TiO2 variety, and titanomagnetite has only a modest TiO2 content. Alteration has modified the magmatic composition of the clasts, but the ess mobile elements indicate they were derived from a low-K orogenic suite, in consonance with petrographic and mineralogical data. A western source and the presence of lower Paleozoic subduction-complex rocks to the east of the Cambrian-(?) Ordovician units indicates that the latter accumulated in a forearc setting. The distributive province may have been the precursor of the Macquarie Volcanic Belt of the eastern Lachlan Fold Belt in N.S.W., or one of the Cambrian oceanic island arcs preserved in the fragmented Gondwana margin sequences in southeastern Australia, northern Victoria Land (Antarctica), and New Zealand.