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A Paleozoic subduction complex dominates the Mossman Orogen developed at the northern extremity of the Tasmanides, eastern Australia. Its southern part, displayed in the Broken River Province, is characterised by dismembered ocean-plate stratigraphy in which turbidite-dominated packages and widespread tectonic mélange development are characteristic. The Broken River complex is characterised by formations with quartzose sandstone alternating with those largely formed of sandstone of more labile character. The two compositional groups are considered to reflect separate, age-significant sedimentary regimes, but their ages have hitherto been poorly constrained. With the use of 1082 concordant detrital zircon ages from 13 samples we provide age control for the complex and track its sedimentary provenance. Of quartzose units, the Tribute Hills Arenite and Pelican Range Formation are late Cambrian–Early Ordovician, and the Wairuna Formation is Middle to Late Ordovician, in age. The more labile units (Greenvale, Perry Creek and Kangaroo Hills formations) are collectively of late Silurian–mid-Devonian age. Development of the complex spanned some 130 Myr. Continent-derived sediment involved in accretion of much the complex, from mid-Ordovician to mid-Devonian, was largely sourced from a nearby magmatic arc of late Cambrian–Devonian age, now represented by granitoid plutons of the Macrossan and Pama igneous associations. An older far-field Pacific-Gondwana sediment source is characteristic of early-phase (late Cambrian–Early Ordovician) accretion, in common with sedimentary units of this age generally developed in the Tasmanides. We consider the complex to have grown largely by underplating that positioned younger components beneath those that are older, with out-of-sequence thrust interleaving of these components occurring late in the accretionary history. A Late Devonian contractional folding and cleavage development (Tabberabberan orogenesis) is uniformly expressed across the entire complex and reflects an abrupt change in plate engagement with imposition of a compressional stress regime. [ABSTRACT FROM AUTHOR]

Analysis of detrital zircon from previously geochronologically unconstrained metasedimentary rocks in the eastern Arunta region, using U - Pb LA-ICPMS and SHRIMP, provides ages reconcilable with Australian sources. Maximum depositional ages of the analysed samples fall into two groups, three samples having maximum depositional ages of ca 1780-1760 Ma and two at ca 2510-2490 Ma. Metamorphic monazite from two pelitic rocks provides bimodal age populations of 1773 ± 9 Ma and 325 ± 8 Ma from one sample, and 1719 ± 9 Ma and 341 ± 5 Ma from the second. The age of 1773 ± 9 Ma is the first direct evidence of monazite growth in the interval ca 1780-1770 Ma, and is attributed to high-grade contact metamorphism associated with the proximal emplacement of granodioritic bodies previously thought to be subduction-related. The metamorphic age of 1719 ± 9 Ma is attributed to the Strangways Orogeny (1730-1710 Ma). The Carboniferous ages of 325 ± 8 Ma and 341 ± 5 Ma in both samples are attributed to partial resetting and new growth of monazite during the Alice Springs Orogeny (ca 400-300 Ma). Sm - Nd isotope systematics of the metasedimentary rocks display a large variation ranging from εNd(1760) = - 1.4 to - 8.8 and, when coupled with the detrital-zircon age populations, allow for a locally derived (North Australian Craton) source for the metasedimentary rocks. Analysis of igneous zircon from a felsic layer of the Entia Gneiss Complex intimately interlayered with the metasedimentary rocks yielded a 207Pb/206Pb weighted average age of 1771 ± 10 Ma, interpreted as the crystallisation age of the igneous precursor. This age is indistinguishable within error from that of the granodioritic intrusions (Inkamulla Granodiorite 1773 ± 4 Ma), here thought to be responsible for the high-grade metamorphism in the metasedimentary rocks. Given that the granodioritic bodies have previously been characterised as subduction-related intrusions, the approximately coincident ages of metamorphism, deposition of at least some of the metasedimentary rocks, and the intrusion of voluminous felsic and mafic magmas, suggests that the deposition and metamorphism of the precursor to the metasedimentary rocks may be related to active subduction along the southern margin of the Arunta region. [ABSTRACT FROM AUTHOR]

A fundamental change from thin-skinned to thick-skinned tectonics in the Mt Isa Terrane is interpreted to reflect a westward shift in the locus of crustal thickening during Mesoproterozoic orogenesis in northeastern Australia. Geochronological constraints indicate that west-directed, thin-skinned deformation in the eastern part of the terrane occurred before ca 1540 Ma. This upper crustal system is interpreted to link with deeper crustal thickening in the Georgetown Inlier to the east, where synorogenic granites intruded at ca 1550 Ma. This early system was dissected by basement-cutting reverse faults across the entire Mt Isa Terrane after 1540 Ma. The nature of deeper crustal tectonics within the Mt Isa Terrane is determined by evaluating possible origins for the crustal structure revealed in a seismic-refraction profile. In particular, alignment of shallowly west-dipping, mid-crustal, high-velocity layers is interpreted to reflect tectonic duplication of underplated crust. This crustal stacking fault is inferred to be the controlling structure for the thick-skinned deformation associated with the Isan Orogeny. [ABSTRACT FROM AUTHOR]

The southern margin of the Pilbara Craton in northwestern Australia underwent regional heating, folding, and thrusting as well as extensive fluid flow during collision in the Paleoproterozoic. However, the precise tinting of this event is uncertain. Previous geochronologic studies of Archean basement rocks have yielded a wide range of younger radiometric dates (from ca. 2.4 Ga to ca. 2.0 Ga), interpreted to record multiple hydro- thermal alteration events. In situ U-Pb geochronology of authigenic monazite and xenotime in very low grade Archean metasedimentary rocks from across the craton suggests that the Pilbara was affected by at least two cryptic thermotectonic events, the first between ca. 2430 Ma and ca. 2400 Ma, and the second between ca. 2215 Ma and ca. 2145 Ma. The older event is restricted to three localities in the west, and its cause is unknown. The younger event affected most of the craton (>100,000 km²), spanning a 70 m.y. period from ca. 2215 Ma nearest the collisional margin in the south, to ca. 2145 Ma toward the craton interior in the north. The widespread geographic and stratigraphic distribution of ca 2.2 Ga phosphates suggests that fluid flow was pervasive. This event was probably driven by the northward-advancing Ophthalmian fold-and-thrust belt that developed during protracted collision. The associated low-grade metamorphic front migrated over ∼350 km at an average rate of ∼5.0 mm/yr, placing important constraints on the rate and duration of deformation and metamorphism in orogenic settings. [ABSTRACT FROM AUTHOR]