Evidence for Early Mesoproterozoic Arc Magmatism in the Musgrave Block, Central Australia: Implications for Proterozoic Crustal Growth and Tectonic Reconstructions of Australia B. P. Wade, K. M. Barovich, M. Hand, I. R. Scrimgeour,1 and D. F. Close1 Continental Evolution Research Group, Geology and Geophysics, University of Adelaide, Adelaide, South Australia 5005, Australia (e-mail: [email protected]) ABSTRACT The Musgrave Block in central southern Australia separates the dominantly Paleoproterozoic North Australian Craton from the Late Archean to early Mesoproterozoic Gawler Craton in southern Australia. Geochemical and Nd isotopic data from ∼1.59–1.55-Ga felsic rocks in the Mann Ranges suggest that the early history of the Musgrave Block was linked to the development of subduction along the northern margin of the Gawler Craton. Characteristic geochemical patterns of these felsic rocks include negative anomalies in Nb, Ti, and Y and are accompanied by steep light rare ␧ Ϫ earth element patterns and comparatively juvenile Nd isotopic compositions ( Nd(1550) values from 1.2 to 0.9). The geochemical and isotopic signatures of these early Mesoproterozoic felsic rocks have similarities with island arc systems involving residual Ti-bearing minerals and garnet. We propose that the 1.59–1.55-Ga arclike rocks in the Musgrave Block indicate the presence of an active margin between the North Australian Craton and the South Australian Craton, with subsequent suturing of the Australian continent during the early Mesoproterozoic. The existence of arclike magmatism in the Musgrave Block during the early Mesoproterozoic suggests a period of major crustal growth in the Australian Proterozoic that has important implications for current Proterozoic reconstructions of Australia and Australia’s fit within the supercontinent Rodinia. Introduction Crustal growth models of Late Archean to early cretion of magmatic arc terranes has been viewed Mesoproterozoic Australia (e.g., Rutland 1973; Gee as the primary continent-forming process in many 1979; Etheridge et al. 1987; Wyborn et al. 1988; of the ca. 2.0–1.8-Ga Proterozoic orogenic belts in Oliver et al. 1991) have been dominated by the as- the Northern Hemisphere (e.g., Hoffman 1980, sumption that the Australian lithosphere was a sin- 1988; Lewry 1981; Condie 1982; Park 1985; Patch- gle stabilized mass by the Late Archean. In these ett and Arndt 1986; Dickin and McNutt 1990; Sny- models, crustal formation and growth proceeded by der et al. 1996; Torsvik et al. 1996; Patchett and processes such as vertical accretion involving un- Chase 2002; Steltenpohl et al. 2003). Recent geo- derplating and extensional tectonism driven by chemical and isotopic studies within Australian mantle plumes and delamination. This view of a terrains such as the Arunta Region and the Cap- contiguous Late Archean to Proterozoic Australia ricorn Orogen have recognized, albeit in a some- envisages all tectonic and magmatic activity to be what cryptic way, accreted fragments along con- vergent plate margins (e.g., Zhao 1994; Zhao and intracratonic, independent of plate boundary ele- McCulloch 1995; Scrimgeour et al. 1999; Cawood ments involving driving forces such as subduction and Tyler 2004; Occhipinti et al. 2004). These data zones, with little or no new crustal growth. sets have been used by a number of workers to In contrast to these models for Proterozoic Aus- propose that the evolution of Proterozoic Australia tralia, rapid crustal production by the lateral ac- involved important accretionary and collisional Manuscript received April 1, 2005; accepted August 23, 2005. events (e.g., Myers et al. 1996; Scott et al. 2000; 1 Northern Territory Geological Survey, G.P.O. Box 3000, Betts et al. 2002; Giles et al. 2002, 2004; Tyler 2005). Darwin, Northern Territory 0801, Australia. Identification of Paleoproterozoic arc magma- [The Journal of Geology, 2006, volume 114, p. 43–63] ᭧ 2006 by The University of Chicago. All rights reserved. 0022-1376/2006/11401-0003$15.00 43 44 B. P. WADE ET AL. tism in Australia is restricted to a few cratonic mar- Occhipinti et al. 2004). Felsic orthogneiss from gins of the Archean to Paleoproterozoic terrains, basement to the Isan region have also been sug- such as the North Australian Craton (NAC), in- gested to have magmatic arc affinities (McDonald cluding the eastern Isan margin, the southern mar- et al. 1997). gin of the Arunta Region, and the Halls Creek Oro- This study focuses on the Musgrave Block, which gen (fig. 1; e.g., Foden et al. 1988; Zhao 1994; Zhao is located in central Australia between the NAC and McCulloch 1995; McDonald et al. 1997; Shep- and the South Australian Craton (SAC; fig. 1). Ex- pard et al. 1999; Close et al. 2004), and the West tensive reworking during the Grenvillian Musgrave Australian Craton (WAC), including the Capricorn Orogeny (ca. 1.3–1.1 Ga) and Neoproterozoic- Orogen (fig. 1; e.g., Cawood and Tyler 2004; Oc- Cambrian Petermann Orogeny (ca. 600–530 Ma) chipinti et al. 2004). Mafic and felsic magmatic has resulted in a complexly deformed terrain, with rocks with subduction-related geochemical affini- existing models suggesting that the Albany-Fraser ties from these regions have been viewed as a result Orogeny coincident with the Musgrave Orogeny re- of Paleoproterozoic arc magmatism (e.g., Foden et flects the collision of the NAC with the SAC during al. 1988; Zhao 1992; Zhao and McCulloch 1995; the assembly of Rodinia at ∼1.30–1.10 Ga (fig. 1; Sheppard et al. 1999, 2004; Cawood and Tyler 2004; e.g., Pidgeon 1990; Black et al. 1992; Myers 1993; Figure 1. Map of Australia displaying the locations of Archean cratons and Paleoproterozoic-Mesoproterozoic ter- rains. The rectangle designates the area displayed in figure 2. Journal of Geology MESOPROTEROZOIC ARC MAGMATISM 45 Myers et al. 1996; Clark et al. 1999, 2000; White Lithological and stratigraphic correlations indicate et al. 1999). Alternatively, S¸ ener et al. (2005) have that these felsic rocks may extend into the south- proposed suturing of the NAC with the SAC much ern Musgrave Block; however, the absence of geo- earlier, at ca. 1.73 Ga, with similar suturing of the chronological constraints has hindered their continents between 1.8 and 1.5 Ga proposed by identification. Giles et al. (2004). Recent geochemical studies in the western and Geochronological studies on felsic rocks situated northern Musgrave Block have hinted at major in the northern and western Musgrave Block show crust-forming and magmatic episodes at ca. 1.59– that they are early Mesoproterozoic in age, and to 1.55 Ga, of which the felsic rocks analyzed in this date they represent the oldest recognized crustal study are a part (Glikson et al. 1996; Scrimgeour et material within the Musgrave Block (Gray 1978; al. 1999). These workers tentatively suggest that Maboko et al. 1991; Sun and Sheraton 1992; Ca- the Musgrave Block contains a history of crustal macho and Fanning 1995; Scrimgeour et al. 1999). formation that may involve plate margin processes. The rocks outcrop discontinuously along the Late Proterozoic (ca. 1.08 Ga) mafic dike swarms length of the northern Musgrave Block (fig. 2; Ed- in both the Arunta Region and the Musgrave Block goose et al. 1993, 2004; Scrimgeour et al. 1999). also support episodes of large-scale crustal growth Figure 2. Simplified geological map displaying the Musgrave Block and locations of samples dated by previous workers using SHRIMP (a, Scrimgeour et al. [1999]; b, Young et al. [2002]; c, Camacho and Fanning [1995]). The rectangle shows the approximate location of figure 3. 46 B. P. WADE ET AL. in the early Mesoproterozoic (Zhao and McCulloch are intruded by numerous younger granitoids and 1993). The ∼1.08-Ga high-Mg, low-Ti tholeiites of mafic and felsic dikes (fig. 2). the Stuart Dike Swarm and the Alcurra Dolerite The oldest recognized components of the Mus- (formerly the Kulgera Dikes) of the Arunta Region grave Block are granulite to amphibolite facies fel- and the Musgrave Block, respectively, have isotopic sic rocks, some of which have been dated in the and geochemical signatures that are interpreted as northern Musgrave Block (figs. 2, 3). SHRIMP U- recording modification of the subcontinental lith- Pb analyses on zircon cores from these felsic rocks ospheric mantle by subduction processes during give an age spread of ∼1.59–1.55 Ga, which is in- the Proterozoic (Zhao and McCulloch 1993; Zhao terpreted as representing the crystallization ages of 1994). the intrusive igneous precursor (fig. 2; Edgoose et In this article, we present geochemical and Nd al. 1993, 2004; Camacho and Fanning 1995; Scrim- isotopic data from felsic rocks along the northern geour et al. 1999). Musgrave Block. The combination of the Sm-Nd The ca. 1.59–1.55-Ga felsic rocks from the Mann isotopic system with rare earth elements (REEs) Ranges that are the focus of this study are mig- and geochemistry has proved to be a powerful tool matitic and typically contain orthopyroxene, cli- in the investigation of crustal growth mechanisms nopyroxene, and biotite, with garnet less common. throughout the world (e.g., Johannes et al. 1995; Regions of homogeneous felsic gneiss are likely to Kepezhinskas et al. 1997; Whalen et al. 1999; Hus- have an igneous intrusive precursor (e.g., Scrim- sain et al. 2004). In many orogenic belts, subse- geour et al. 1999). Elsewhere, felsic gneiss is inter- quent tectonic processes have obscured the geo- layered with mafic granulite and, less commonly, chemical and geophysical characteristics of the pelitic gneiss, suggesting a possible bimodal vol- accreted terrane. Robust geochemical tracers and canic precursor or intrusion of mafic sills into a Sm-Nd isotopes can see through accreting tectonic supracrustal sequence (Scrimgeour et al. 1999). events to determine the evolution of the terrane Metamorphic zircon growth in these rocks gives (e.g., Dunphy and Ludden 1998; Whalen et al.