Contrasts in morphogenesis and tectonic setting during contemporaneous emplacement of S- and I-type granitoids in the Eastern Lachlan Fold Belt, southeastern Australia
Published:January 01, 1999
R. Trzebski, P. Lennox, D. Palmer, 1999. "Contrasts in morphogenesis and tectonic setting during contemporaneous emplacement of S- and I-type granitoids in the Eastern Lachlan Fold Belt, southeastern Australia", Understanding Granites: Integrating New and Classical Techniques, Antonio Castro, Carlos Fernández, Jean Louis Vigneresse
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Integrative gravity and structural modelling of Ordovician-Silurian granitoids in the Eastern Lachlan Fold Belt (southeastern Australia) revealed contrasts in emplacement mode and deformation style between coeval S- and I-type granites. The NNE-SSW directed contraction during the Benambran event of the Lachlan Orogen caused dextral movement along two major strike-slip faults (Carcoar Fault/Copperhannia Thrust) and simultaneous formation of both transtensional pull-apart and transpressional shear zones. The geometry and deformation style of the plutons and country rock, their spatial relationship at depth to adjacent faults and the structural history of both the granites and country rocks suggest a genetic linkage between magma emplacement and synmagmatic deformation. Synchronously, the Carcoar Granodiorite was emplaced into a transtensional pull-apart structure and the Barry Granodiorite and Sunset Hills Granite intruded transpressional shear zones. The I-type Carcoar and Barry granites are square to tabular, wedge-shaped bodies exhibiting a weak deformation; whereas the S-type Sunset Hills Granite is an elongated, tabular to sheet-like pluton showing a moderate deformation degree. The contrasts in 3D shape, emplacement mode and deformation style between the I- and S-type granites are due to differences in nearfield stress regime, geometry of the emplacement sites, intrusion level with respect to thermal and rheological conditions, and in their response to deformation. This response is in part controlled by the proportion of resistant/non-resistant minerals in the granite and host rock. This study demonstrates that distinctive emplacement modes can operate simultaneously in different parts of a fault system under contrasting deformation conditions.
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Understanding Granites: Integrating New and Classical Techniques
Granite magmatism represents a major contribution to crustal growth and recycling and, consequently, is one of the most important mechanisms to have contributed to the geochemical differentiation of the Earth’s crust since Archaean time. Granites are also often associated with ore bodies, and their study therefore has direct commercial relevance.
The modern view of the granite problems requires the application of many different theoretical, experimental and empirical resources provided by geophysics, geochemistry, experimental petrology, structural geology, scale modelling and field geology. Because of the complexity of the granite problem, it is necessary to integrate a variety of techniques and corroborate the findings with field observations.This is the philosophy of this book.
Many chapters are review papers dealing with the development and achievements of a particular technique, whilst other chapters deal with the application of a number of techniques to a specific problem. This volume brings together papers that would otherwise be dispersed in different publications.
The book will be of interest to igneous petrologists, geophysicists, structural geologists and geochemists.