Future Research

This study presents the first tectonic model for the Mesoproterozoic to early Paleozoic evolution of Tasmania within the paleogeographic framework of the supercontinents Nuna, Rodinia, and Gondwana. Although significant progress has been made towards refining the age, stratigraphy, and tectonic setting of Tasmania’s Proterozoic rocks, further work is required to test the new model for the early tectonic evolution of Tasmania. Key questions arising from this study that could test the new model and warrant further research include:

(1) What is the basement to Tasmania?

The unexposed basement to the Rocky Cape Group is assumed to be Paleoproterozoic on the basis of 1800—1600 Ma Nd model ages calculated from late Neoproterozoic to Cambrian intrusive rocks in western Tasmania (Meffre et al., 2004; Berry et al., 2008). A promising opportunity to directly date Tasmania’s basement is presented by gneissic and granitic xenoliths entrained in Tertiary basalts throughout the state (Everard, 2001), which may represent fragments of the lower crust. Understanding the age of Tasmania’s basement would significantly improve the constraints on its Proterozoic position along the margin of Laurentia where the distribution of basement provinces is relatively well established (e.g., Whitmeyer & Karlstrom, 2007).

(2) Was rifting between East Antarctica and southwest Laurentia during the breakup of Nuna successful?

The geological record of Tasmania is consistent with a connection between East Antarctica and southwest Laurentia between the middle Mesoproterozoic and late Neoproterozoic. However, there is little evidence in Tasmania for the closure of a major ocean basin between these continents implied by paleomagnetic data during the late Mesoproterozoic Nuna to Rodinia transition. A persistent connection between East Antarctica and southwest Laurentia during the transition from Nuna to Rodinia could be further tested by:

(A) Additional high-quality paleomagnetic data from Australia-Antarctica between 1500 and 1000 Ma, particularly from the Mawson Continent, which is paleomagnetically unconstrained during this interval.

(B) A detailed study of the architecture of the 1450—1300 Ma basin in Tasmania. The lower-middle Rocky Cape Group can be interpreted as an east-facing passive margin based on the distribution of sedimentary facies and paleocurrent information. However, the distribution of sedimentary facies in the lower-middle Rocky Cape Group may reflect the geometry of a sub-basin within a larger basin system. Understanding the relationship of strata correlative with the lower-middle Rocky Cape Group on King Island and in the Tyennan Region and Clark Group of southwest Tasmania could

help resolve the geometry of the 1450—1300 Ma basin in Tasmania and test its interpretation as an east-facing passive margin produced during the breakup of Nuna.

(3) What is the tectonic setting of Mesoproterozoic metamorphism on King Island and early Neoproterozoic metamorphism on the South Tasman Rise?

Middle Mesoproterozoic (ca. 1290 Ma) and early Neoproterozoic (ca. 920 Ma) metamorphic rocks on King Island and the South Tasman Rise respectively have been interpreted as fragments of orogenic belts related to the assembly of Rodinia (Fioretti et al., 2005; Berry et al., 2005; Li et al., 2008). These interpretations are based largely on the age of these metamorphic rocks, which overlap with Rodinia-forming orogens globally. However, a detailed study of the pressure-temperature- time history of these metamorphic events is required to demonstrate that they record collisional processes. A better understanding of the regional tectonic setting of late Mesoproterozoic (1120— 1050 Ma) magmatic rocks from the South Tasman Rise could also be achieved through a detailed geochemical study including Hf isotopic analysis of zircon, which would help to clarify whether these rocks formed in an arc, collisional, or anorogenic environment. Further work towards understanding these Mesoproterozoic and early Neoproterozoic metamorphic and magmatic events could provide further insight into the position and wider tectonic setting of Tasmania during the transition from Nuna to Rodinia.

(4) Was late Neoproterozoic rifting in Tasmania progressive or sequential?

Late Neoproterozoic rifting in Tasmania is interpreted in this study to be a progressive event that initiated at 780 Ma and led to continental breakup at ca. 580 Ma as Australia-Antarctica separated from western Laurentia. The late Neoproterozoic evolution of Tasmania may instead reflect two distinct rift-drift events, with early rifting at 780—640 Ma recording separation of Australia- Antarctica from western Laurentia (e.g., Li & Evans, 2011) and later rifting at ca. 580 Ma reflecting the separation of Tasmania from either Australia-Antarctica of Laurentia. A key test of the progressive versus sequential rifting models for the late Neoproterozoic separation of Australia-Antarctica from western Laurentia would be to identify rift-related activity in Tasmania at 640—580 Ma. Plausible targets include mafic lava flows in the Robbins Creek Formation that underlie 580 Ma basalts in the Grassy Group, volcaniclastic units in the Success Creek and Crimson Creek Groups, and the numerous Proterozoic mafic dyke suites in northwest Tasmania, which are mostly undated. Refining the duration of late Neoproterozoic rifting in Tasmania would provide important constraints on the timing of final separation of Australia-Antarctica from western Laurentia and a better understanding of the tectonic evolution of Tasmania during the transition from Rodinia to Gondwana.

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