Reply to comment by Brian Stevens on 'Evidence and timing of crnstal extension versus shortening in the early tectonothermal evolution of a Proterozoic continental rift sequence at Broken Hill, Australia'

摘要

Some divergence of opinion about a complexly deformed, high-grade metamorphic terrane like Broken Hill is inevitable. Stevens [2006], however, finds fault with virtually every aspect of our paper, judging in particular that our interpretation of the regional structure is flawed because it does not conform to long-accepted views about the tectonothermal evolution of this important Proterozoic mineral province [e.g., Laing et al., 1978; Marjoribanks et al., 1980; Willis et al., 1983; Stevens et al., 1988; Laing, 1996; Stevens, 1998]. Following the recent identification of early high-temperature shear zones and related mylonitic fabrics in the Willyama Supergroup [White et al., 1995; Gibson and Nutman, 2004], we believe that some of these views are no longer justified and that there is a need for a fundamental change in the way regional structure, stratigraphy and metamorphism in the Broken Hill region are interpreted. Stevens has yet to be persuaded that many of these shear zones exist, let alone have an extensional origin or that they bear any temporal relationship to initial low-P/high-T metamorphism [Gibson and Nutman, 2004; our paper]. Instead, he adheres to the view that all low-P/high-T metamorphism in the Willyama Supergroup is the result of crustal thickening accompanying the 1600 Ma Olary orogeny even though the older nappe-based structural models [Laing et al, 1978; Marjoribanks et al, 1980] cannot adequately explain either the style of metamorphism or why it should postdate the peak of magmatic activity by as much as 70-90 Myr.