The Southern Uplands Terrane in Scotland – a notional controversy revisited

Development of a regional geological interpretation for the Southern Uplands Terrane has been driven historically by advances in graptolite biostratigraphy, sandstone petrography and turbidite sedimentology (particularly the recognition of reliable way-up criteria), then, more recently, by a growing appreciation of the nature of accretionary processes at active plate margins. The latter has led to the widely held view of the terrane as an archetypal fossil accretionary prism, built up by the accretion at the margin of Laurentia of the sedimentary cover of Iapetus oceanic crust, the cover being stripped from the oceanic crust during its subduction beneath Laurentia. The achievement of this broad consensus has not been without controversy, which still persists in respect of some aspects of the overall model. Suggestions that the northernmost (Ordovician) part of the terrane might have originated in a back-arc basin have been disproved by a combination of mineral dating and basin thermal history analysis utilizing clay mineralogy. Nevertheless, it remains possible for that part of the terrane to have a continental margin, forearc depositional history. The southernmost (mid-Silurian) part of the terrane most probably developed in a foreland basin setting, as a fold-and-thrust belt overriding Avalonia, following the closure of the Iapetus Ocean. Progress in understanding the origins of the Southern Uplands Terrane has been achieved only by the collaborative application of multidisciplinary techniques – biostratigraphic, sedimentary, structural, geochemical and geophysical. This review is a tribute to all those who have contributed.

长期以来，南部高地地体（Southern Uplands Terrane）的区域地质解译工作先后得益于笔石生物地层学（graptolite biostratigraphy）、砂岩岩石学（sandstone petrography）与浊积岩沉积学（turbidite sedimentology）领域的突破——尤其是可靠顶序判别标志的识别——近年来则愈发依赖学界对活动板块边缘增生作用本质的深入认知。后者催生了学界广泛认可的观点：该高地地体属于典型的化石记录增生楔（accretionary prism），由劳伦大陆（Laurentia）边缘对伊阿珀托斯洋（Iapetus Ocean）洋壳沉积盖层的增生作用形成，该盖层在洋壳向劳伦大陆俯冲的过程中被剥离。这一广泛共识的达成并非毫无争议，当前该整体模型的部分方面仍存在持续争论。有观点提出该高地地体最北端的奥陶纪（Ordovician）部分可能形成于弧后盆地（back-arc basin），但通过矿物定年（mineral dating）与结合黏土矿物学（clay mineralogy）的盆地热历史分析（basin thermal history analysis），该假说已被推翻。尽管如此，该部分地体仍有可能具备大陆边缘前弧沉积演化历史。该高地地体最南端的中志留世（mid-Silurian）部分，则极有可能形成于前陆盆地（foreland basin）背景，是伊阿珀托斯洋闭合后覆于阿瓦隆尼亚（Avalonia）之上的褶皱冲断带（fold-and-thrust belt）。目前对南部高地地体成因的认知突破，均依托多学科技术的协同应用——涵盖生物地层学、沉积学、构造地质学、地球化学与地球物理方法。本综述谨向所有为此作出贡献的学者致敬。