Isotopic characteristics of Ordovician greywacke provenance in the Southern Uplands of Scotland
Isotopic characteristics of Ordovician greywacke provenance in the Southern Uplands of Scotland
复制标题
苏格兰南部高地奥陶纪杂砂岩来源的同位素特征
DOI：
10.1144/gsl.sp.1991.057.01.13
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
J. Floyd
中科院分区：
文献类型：
--
作者：
J. Evans;P. Stone;J. Floyd
摘要南部高地奥陶系杂砂岩的互层成分有明显的差异。Sm-Nd同位素数据，碎屑碎屑岩岩相学和古水流分析的集成允许可能的物源特征和分布推断。波特帕特里克组和加尔德诺赫组含有来自火山源的碎屑：安山岩占波特帕特里克组卡拉多克-阿什吉尔杂砂岩的主要成分，ε Nd 445（沉积时间）在−2.3和−2.9之间，兰代洛-卡拉多克加尔德诺赫组富含角闪石，ε Nd 445在−3.4和−4.4之间。这些值与Llandeilo-Caradoc基尔科姆组灰岩的同位素更贫化的特征形成对比，后者主要含有石英和长石碎屑，ε Nd 445低至−11.2。根据古水流分析，火山岩的物源位于沉积盆地的一侧（现代地理上为南），火山岩的同位素组成符合钙碱性弧或弧后组合，形成于陆壳之上。一个以基尔科姆组碎屑为代表的元古代碎屑岩位于沉积盆地的另一侧。目前暴露于南部高地北部的达尔拉德变质岩显示出比基尔科姆组灰岩更少的放射成因特征，似乎不太可能作为其来源。这可能支持解释的南部高地故障的主要左旋走滑运动的轨迹。
Abstract Interbedded Ordovician greywackes in the Southern Uplands are of markedly different composition. An integration of Sm-Nd isotope data, petrography of detrital clasts, and palaeocurrent flow analyses allows the likely provenance character and distribution to be deduced. The Portpatrick and Galdenoch formations contain detritus from volcanic provenances: andesite dominates the composition of Caradoc-Ashgill greywacke from the Portpatrick Formation which have εNd445 (time of deposition) between −2.3 and −2.9, the Llandeilo-Caradoc Galdenoch Formation is richer in hornblende and has a slightly lower range of εNd445 between −3.4 and −4.4. These values contrast with the more isotopically depleted signature of the Llandeilo-Caradoc Kirkcolm Formation greywackes which contain mainly quartz and feldspar clasts and have εNd445 as low as −11.2. The source of the volcanic rocks, deduced from palaeocurrent analysis, lay on side of the depositional basin (south in terms of modern geography) and the isotopic composition of the volcanic rocks is consistent with a calc-alkaline arc or back-arc assemblage, founded on continental crust. A Proterozoic terrane, represented by detritus from the Kirkcolm Formation, lay on the opposite side of the depositional basin. Dalradian metamorphic rocks currently exposed to the north of the Southern Uplands display a less radiogenic signature than Kirkcolm Formation greywackes and seem unlikely to have acted as their source. This may support interpretations of the Southern Upland Fault as a locus of major sinistral strike-slip movement.