Geology and geochronology of the Emu Creek Block (northern New South Wales, Australia) and implications for oroclinal bending in the New England Orogen

Abstract

The southern part of the New England Orogen exhibits a series of remarkable orogenic bends (oroclines), which include the prominent Z-shaped Texas and Coffs Harbour oroclines. The oroclines are defined by the curvature of Devonian–Carboniferous forearc basin and accretionary complex rock units. However, for much of the interpreted length of the Texas Orocline, the forearc basin is mostly concealed by younger strata, and crops out only in the Emu Creek Block in the eastern limb of the orocline. The geology of the Emu Creek Block has hitherto been relatively poorly constrained and is addressed here by presenting new data, including a revised geological map, stratigraphic sections and new detrital zircon U–Pb ages. Rocks of the Emu Creek Block include shallow-marine and deltaic sedimentary successions, corresponding to the Emu Creek and Paddys Flat formations, respectively. New detrital zircon U–Pb data indicate that these formations were deposited during the late Carboniferous and that strata were derived from a magmatic source of Devonian to Carboniferous age. The sedimentary provenance and detrital zircon age distribution suggest that the sequence was deposited in a forearc basin setting. We propose that the Emu Creek and Paddys Flat formations are arc-distal, along-strike correlatives of the northern Tamworth Belt, which is part of the forearc basin in the western limb of the Texas Orocline. These results confirm the suggestion that Devonian–Carboniferous forearc basin rocks surround the Texas Orocline and have been subjected to oroclinal bending.

新英格兰造山带南部呈现出一系列显著的造山弯（oroclines），包括著名的Z形德克萨斯造山弯和科夫斯港造山弯。这些造山弯是由泥盆纪-石炭纪弧前盆地的弯弧和增生杂岩地层所圈定。然而，对德克萨斯造山弯的部分长度来说，弧前盆地大部由年轻地层所隐蔽，只在造山弯东枝的鸸鹋溪岩块有出露。鸸鹋溪岩块的地质特征迄今所知甚少，在此通过提供新的数据，包括修订的地质图、地层剖面和新碎屑锆石U-Pb年龄，而对此加以讨论。鸸鹋溪岩块的岩石包括浅海和三角洲沉积序列，相对应的是鸸鹋溪组和Paddys Flat组。新碎屑锆石U-Pb资料表明，这些岩组沉积于石炭纪晚期，地层来源于泥盆纪至石炭纪的岩浆源。沉积物源和碎屑锆石年龄分布表明，地层沉积于弧前盆地环境。我们建议，鸸鹋溪组和Paddys Flat组是岛弧-远端，沿与Tamworth带北部相对应的走向，这是得克萨斯州造山弯西枝的弧前盆地的一部分。这些结果证实了这样的看法，泥盆纪-石炭纪弧前盆地岩石环绕得克萨斯州造山弯，并已受到造山弯弯曲作用的影响。

KEY WORDS:

• forearc basin
• Emu Creek Block
• Tamworth Belt
• New England Orogen
• orocline
• U–Pb geochronology
• detrital zircon

ACKNOWLEDGEMENTS

This work was funded by the Australian Research Council grant DP130100130. The authors thank the residents of the study area, especially Sam and Cara McMurtrie of Four Winds, and Steve and Sharon Ross of Big Fish Flat, for access to their properties and gracious hospitality. We also thank Rob Holm, for his assistance with the processing and interpretation of LA-ICP-MS data, Daniel Wood, for assistance in the field, and Abbas Babaahmadi, for discussions. Peter Cawood and Richard Glen provided helpful and insightful comments, which greatly improved both the manuscript and figures.

SUPPLEMENTARY PAPERS

Table A1 LA-ICP-MS: Detrital zircon U–Pb Geochronology

Figure A1 Large format geological map of the Emu Creek Block and surrounding area.