Structure of the Texas Orocline beneath the sedimentary cover (southeast Queensland, Australia)

Abstract

The New England Orogen in eastern Australia is characterised by orogenic-scale curvatures (oroclines). The largest and most prominent curvature in this system is the Texas Orocline, but its subsurface geometry is still poorly constrained. A large component of the orocline is covered by post-oroclinal sedimentary rocks, which obscure deeper sections of the orocline and make it difficult to understand how the structure is connected to other segments of the New England Orogen. Here, we present geophysical data that elucidate the structure of the Texas Orocline below the sedimentary cover. Using 2D seismic, aeromagnetic TMI (total magnetic intensity) and Bouguer gravity datasets, in combination with outcrop and well data, we identified the depth to the New England ‘basement’ and significant faults intersecting it. We also traced the strongly contorted subsurface continuation of the Peel-Yarrol Fault System, which is characterised by local gravity and magnetic anomalies associated with isolated serpentinite outcrops. Constraints on the timing of oroclinal bending were obtained from the interpretation of seismic transects, which showed that early Permian sedimentary rocks of the Bowen Basin were deposited in a subtrough that deviates from the general north–south trend of the Bowen Basin. The subtrough is oriented approximately parallel to the western limb of the Texas Orocline, thus suggesting that the orocline formed during and/or after early Permian rifting. Our analysis indicates that initial bending occurred contemporaneously with the development of the early Permian rift basins, most likely in the backarc region of a retreating subduction zone. Subsequently, phases of strike-slip and contractional deformation have further tightened the pre-existing curvatures.

澳大利亚东部新英格兰造山带的特点是造山带范围的弯曲（弯曲造山带）。在这个系统中的最大和最突出的弯曲是德克萨斯弯曲造山带，但其地表下的几何特征仍然缺乏了解。该弯曲造山带的很大组成部分被后造山作用沉积岩所覆盖，使我们很难了解这个结构如何与新英格兰造山带的其它部分相连接。在这里，我们提呈地球物理数据来阐明沉积盖层下面德克萨斯弯曲造山带的结构。使用二维地震，航磁TMI（总磁场强度）和布格​​重力数据库，并与露头和钻井资料相结合，我们确定了至新英格兰“地下室”的深度及 与它相交的显著断层。我们还追踪了强烈扭曲的地下Peel-Yarrol断层系统延续体，其特点是与偶然出现的蛇纹岩露头相关的局部重力和磁异常。根据地震断面的解释，我们获得了弯曲造山带弯曲的时间范围，这表明Bowen盆地早二叠世沉积岩沉积于从Bowen盆地一般南北走向分离而来的亚海槽中。该亚海槽取向大致平行于德克萨斯弯曲造山带西部分支，从而表明了弯曲造山带形成于早二叠分裂 期间和/或之后。我们的分析表明，初始弯曲的发生与早二叠世裂谷盆地的发育是同时的，最有可能发生在撤退俯冲带的弧后地区。随后，走滑和收缩变形进一步收紧早先存在的弯曲。

KEY WORDS:

• Texas Orocline
• New England Orogen
• Bowen Basin
• Surat Basin
• eastern Australia
• geophysics

ACKNOWLEDGEMENTS

This project was funded by the Australian Research Council (DP0986762 and DP130100130). Thanks to Origin Energy for providing training, resources and access to data for this project. We are particularly grateful to Thomas Flottmann and Andrew Aouad for assisting with structural and geophysical interpretations. The manuscript benefited from constructive comments by Russell Korsch and Bob Musgrave. We also thank Abbas Babaahmadi for assisting with magnetic and gravity interpretation, and Roberto Weinberg and Uri Shaanan for providing comments on earlier versions of the manuscript.

Shallow 2D seismic data, geological maps, Queensland aeromagnetic data, Queensland Bouguer gravity data and well data used in this project are available through the QDNRM and the Interactive Resource and Tenure Maps database. Deep 2D seismic data, digital elevation model data, national aeromagnetic data and national Bouguer gravity data used in this project are available through Geoscience Australia.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

SUPPLEMENTAL DATA

Table: Names and location data for wells that intersect basement in the Surat and Clarence-Moreton basins.