New SHRIMP geochronology for the Western Fold Belt of the Mt Isa Inlier: developing a 1800 – 1650 Ma event framework ∗

New SHRIMP age constraints on the timing and duration of magmatism and sedimentation in the Mary Kathleen Fold Belt, Mt Isa Inlier, Australia

“…These maximum depositional age constraints are slightly older than the depositional age of *1755 Ma from Page (1998). Based on the new SHRIMP zircon geochronology data, depositional facies relationships and sequence stratigraphic correlations, the Ballara Quartzite and Corella Formation are time equivalent facies of the *1750 Ma Quilalar Formation, with each of these lithostratigraphic units deposited in the Quilalar Supersequence (Neumann et al 2006). These new datasets confirm the earlier correlations of Derrick et al (1980) andJackson et al (1990), and provide evidence for paleogeographic continuity between depositional systems in the Western and Eastern Successions during the time interval 1760-1745 Ma.…”

“…At of 1773 + 2 Ma (Neumann et al 2006), suggesting that at least minor felsic volcanism also occurred in the Leichhardt River Fault Trough, perhaps recording the waning thermal stages of the Argylla Magmatic Event. Similar ages of *1775 Ma are also identified from two volcaniclastic samples from the Boomarra Horst, northeast of the Mary Kathleen Fold Belt (Page & Sun 1998), although the structural and genetic relationships between these crustal blocks is unclear.…”

“…Holcombe et al (1991) and Pearson et al (1992) described mid-crustal processes operating in the Mary Kathleen Fold Belt of the Eastern Succession from *1760-1720 Ma, including voluminous magmatism associated with extension and the development of crustalscale detachment zones. These processes overlap in time with the development of the *1800-1750 Ma Leichhardt and *1730-1690 Ma Calvert Superbasins in the Western Succession (Neumann et al 2006), leading some researchers (Gibson et al 2008) to conclude that magmatism and extension at these deeper crustal levels were geodynamically linked to basin formation farther west. Here we better constrain the age of magmatism and deep crustal extension in the Mary Kathleen region while, at the same time, providing a more comprehensive temporal framework for the tectonostratigraphic and geodynamic evolution of the Mt Isa Inlier whereby the links between these processes and basin formation may be better understood.…”

“…The basin record is well documented in the Western Succession, where extensive outcrop and low metamorphic grade have allowed detailed description of the development of the Leichhardt, Calvert and Isan Superbasins Southgate et al 2000;Neumann et al 2006). Further, the timing of sedimentation in the Calvert and Isan Superbasins has been well constrained due to the abundance of volcanic and shallow-level intrusive rocks available for geochronological dating (Page & Sweet 1998;Page et al 2000).…”

Hot lithosphere at Mount Isa: implications for Proterozoic tectonics and mineralisation

“…This tectonic denudation leads to pronounced cooling of the metamorphic rocks and melts of the lower plate (Foster et al 1993;Ketcham 1996;Gessner et al 2007). Recent studies have suggested that syn-extensional intrusions in the Mount Isa Inlier such as the Sybella granite and the Wonga granite have been exhumed in the footwall of detachment systems, and created basement highs adjacent to supra-detachment basins (Neumann et al 2006(Neumann et al , 2009Gibson et al 2008). This lateral segmentation differs from the scenario proposed by McLaren et al (1999McLaren et al ( , 2005 where the basement-including highly radiogenic syn-extensional granites-is assumed to be buried below the basin.…”