Stratigraphic Evolution of the Haslingden Group in the Leichhardt River Fault Trough, Mount Isa Orogen, Australia: Implications for Rift Tectonics

哈斯林登群是伊萨山造山带中最古老的盖层，厚约18千米，于1800~1710 Ma前的莱奇哈特河断槽中堆积，形成于距今约1860 Ma的大陆地壳。火山-沉积Haslingden群以前被解释为单阶段裂谷序列和上覆沉积组合Quilalar组，与随后岩石圈的热收缩有关的凹陷期。我们对哈斯林登群的初步研究表明，这是一个更复杂的演化过程，至少包括两个裂谷阶段。这一假设将通过：1)通过详细的沉积学/古地理分析，包括对可能潮汐成因的浅海沉积物的定量分析，来约束Haslingden群的地层演化；2)将Haslingden群的地层演化与地质记录中记录的裂谷序列进行对比；在地层分析和地质年代学框架的约束下，对左岸的沉降史进行了定量模拟。对哈斯林登群地层演化的了解将加强对北海和基韦纳万裂谷等暴露较少的裂谷以及整个裂谷的了解。这项拟议的研究是澳大利亚矿产资源局对伊萨山造山带进行的多学科调查的一部分，其中包括对左岸造山带的结构分析。作为这一项目的一部分，我们将能够评估LRTT在其自身构造背景下以及在周围构造过程框架内的演变。哈斯林登群的分析结果将与正在进行的构造变质、地质年代学、地球化学和沉积学研究相结合，以形成伊萨山造山带的综合构造模式。在伊萨山造山带构造模型的开发过程中，将进行下沉模拟和不同学科的整合，而PI将在1988年期间在基础设施研究中心学习休假。

The Haslingden Group is the oldest cover sequence in the Mount Isa Orogen; it is ca. 18 km thick and accumulated in the Leichhardt River Fault Trough (LRFT) between 1800 and 1710 Ma ago on ca. 1860 Ma-old continental crust. The volcano- sedimentary Haslingden Group has previously been interpreted as a single-stage rift sequence and an overlying sedimentary package, the Quilalar Formation, as the sag phase associated with subsequent thermal contraction of the lithosphere. Our preliminary work on the Haslingden Group suggests a more complex evolution involving at least two stages of rifting. This hypothesis will be evaluated by: i) constraining the stratigraphic evolution of the Haslingden Group through a detailed sedimentological/paleogeographical analysis including quantitative analysis of shallow marine sediments of probable tidal origin; ii) contrasting the stratigraphic evolution of the Haslingden Group with documented rift sequences in the geologic record; and iii) quantitatively modelling the subsidence history of the LRFT within the constraints of the stratigraphic analysis and the geochronological framework. An understanding of the stratigraphic evolution of the Haslingden Group will enhance the understanding of less well-exposed rifts such as the North Sea and Keweenawan Rifts and of rifts in general. The proposed study is part of a multidisciplinary investigation of the Mount Isa Orogen, including a structural analysis of the LRFT, by the Bureau of Mineral Resources, Australia. As part of this project we will be able to evaluate the evolution of the LRFT within its own tectonic context as well as within the framework of surrounding tectonic processes. The results of the analysis of the Haslingden Group will be integrated with ongoing structural-metamorphic, geochronologic, geochemical and sedimentological studies to formulate a comprehensive tectonic model for the Mount Isa Orogen. Subsidence modelling and integration of various disciplines in developing a tectonic model for the Mount Isa Orogen will be undertaken while the PI is on study leave at the BMR for the duration of 1988.