Switching bulk horizontal shortening directions and regional-scale partitioning of deformation during the Isan Orogeny in the Eastern Fold Belt, Mount Isa Inlier, Australia

Abstract

Prolonged deformation for ca 150 Ma along the Eastern Fold Belt, Mount Isa Inlier, differentially partitioned into three distinct Mesoproterozoic tectonic domains. NW–SE-trending structures dominate the northern domain, whereas E–W- and N–S-trending structures dominate the central and southern domains, respectively.

Changing the direction of bulk horizontal shortening from NE–SW to N–S to E–W shifted the locus of maximum tectono-metamorphic effect. This accounts for the different generations of structures preserved in these three domains. Overprinting relationships and geochronological data reveal a component of deformation partitioning in time as well as space.

Rheological contrasts in the Soldiers Cap Group between a thick interlayered pelitic, psammitic and volcanic units on the one hand, and ca 1686 Ma, competent mafic intrusives and genetically related metasomatic albitite bodies present in its lower part, on the other, enhanced strain localisation during the long-lived Isan Orogeny (ca 1670–1500 Ma).

沿Isa山内围层的东褶皱带为时约150Ma的长期变形作用涉及到三个不同的中元古代构造域。西北-东南向构造在北域占主导地位，而东-西和北-南向的构造分别主宰中部和南部。水平缩短方向从东北至西南到北-南向至东-西的改变转移了最大构造 - 变质作用的重心。这解释了保存在这三个构造域中的不同阶段的构造。叠加关系和年代学数据揭示了变形组分在时间和空间上的作用。在Soldiers Cap 群中,厚的泥质、砂屑和火山岩的互层岩组与约1686Ma的镁铁质侵入岩和成因相关的交代钠长岩体（位于该群下部）之间的流变反差加强了长时间的Isan造山运动（约1670至1500Ma）期间的应力局部化。

KEY WORDS:

• bulk horizontal shortening
• deformation partitioning
• lithological heterogeneities
• Isan Orogeny
• Eastern Fold Belt
• Mount Isa Inlier

ACKNOWLEDGEMENTS

I would like to thank Professor Tim Bell, James Cook University, for invaluable discussions, sincere guidance and critical reading of parts of the manuscript. Doctors Mike Rubenach and Tom Blenkinsop, James Cook University, are greatly acknowledged for fruitful discussions regarding the structure and metamorphism of the Snake Creek anticline. Thanks go to Dr Juergen Reinhardt, University of KwaZulu-Natal, South Africa, for valuable discussion regarding some metamorphic aspects. I would like to thank Dr D. Aerden and one anonymous reviewer for constructive reviewing of the manuscript. Suggestions, comments and editing of the manuscript by Dr D. Aerden improved the manuscript and are greatly appreciated