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Detrital zircon U–Pb age patterns in sandstones from the Triassic–Cretaceous Clarence-Moreton Basin, eastern New South Wales and Queensland, unexpectedly reveal sediment sources overwhelmingly dominated (>70%) by Precambrian–Cambrian zircons, with virtually no input, as was anticipated, from the nearby Carboniferous, Permian or Triassic magmatic arcs and contemporary accretionary wedge associated with the New England Orogen. Some rare, youngest zircons (<5%) are mostly contemporaneous with the estimated depositional age. The older, reworked zircon populations can only be acquired by postulating either (1) an Australian provenance by long overland sediment pathways from the interior to the west, during one or more transport cycles, perhaps from within the Thomson Orogen, and then bypassing or crossing the New England Orogen without any local contribution from that sector or (2) a North Zealandia provenance with a shorter transport distance from a postulated basement block to the east, within the Northern Lord Howe Rise and Kenn Plateau. This would comprise late Mesoproterozoic (1200–1000 Ma) and late Neoproterozoic–Cambrian (700–500 Ma) igneous and metamorphic complexes, similar to that proposed in South Zealandia. Triassic to Jurassic Clarence-Moreton Basin sedimentary rocks have provenances unlike their hinterland time-correlates in New South Wales and Queensland. The latter better share similarities with those in Murihiku Terrane, North Island, New Zealand. The provenance of Clarence-Moreton sediments is similar to that of time-correlates in New Caledonia, and it is postulated that they share a source region on the northern Lord Howe Rise or Kenn Plateau. [ABSTRACT FROM AUTHOR]

The Cretaceous Yuhuashan igneous complex contains abundant xenoliths of high-grade metamorphic rocks, with the assemblage garnet ± hypersthene + biotite + plagioclase + K-feldspar + quartz. The biotite in these samples has high TiO2 (>3.5%), indicating high- T metamorphism (623-778 °C). P-T calculations for two felsic granulites indicate that the peak metamorphism took place at 880-887 °C and 0.64-0.70 GPa, in the low pressure/high temperature ( LP- HT) granulite facies. Phase equilibrium modelling gives equilibrium conditions for the peak assemblage of a felsic granulite of >0.6 GPa and >840 °C, consistent with the P-T calculations, and identifies an anticlockwise P-T-t path. LA- ICPMS U-Pb dating of metamorphic and detrital zircon from one xenolith reveals that the granulite facies metamorphism took place at 273.6 ± 2.2 Ma, and the protolith was a sedimentary rock deposited later than 683 Ma. This represents the first Late Palaeozoic (Variscan) granulite facies event identified in the South China Block ( SCB). Coupled with other geological observations, the LP- HT metamorphic conditions and anticlockwise P-T-t path suggest that Variscan metamorphism probably occurred in a post-orogenic or intraplate extensional tectonic setting associated with the input of external heat, related to the underplating of mantle-derived magma. Based on P-T estimates and the comparison of the protolith composition with mid- to low-grade metamorphic rocks in the area, it is suggested that the mid-lower crust under the Xiangshan-Yuhuashan area consists mainly of these felsic granulites and gneisses, whose protoliths were probably subducted to these depths during the Early Palaeozoic orogeny in the SCB, and underwent two episodes of metamorphism during Early Palaeozoic and Late Palaeozoic time. [ABSTRACT FROM AUTHOR]

Rb-Sr isochron ages and associated initial 87Sr/86Sr ratios of metasedimentary rocks of Caples Group in Southland and Otago, Pelorus Group in Nelson and Marlborough, and their minor North Island correlates in Northland and King Country, reveal the essential continuity of a long Caples Terrane throughout New Zealand. The Rb-Sr ages, in the range 251-117 ma, record post-metamorphic, early Triassic to early Cretaceous uplift and cooling, whilst their associated range of initial 87Sr/86Sr ratios, 0.7039-0.7053, allows a discrimination from analogous datasets of neighbouring Torlesse and Waipapa Terranes. Some petrographically and geochemically anomalous Caples Terrane rocks in east Otago, and Otago Schists of the Aspiring Terrane, all with initial 87Sr/86Sr Sr ratios >0.7055, compare best with datasets of Waipapa Terrane of the North island. Detrital zircon U-Pb ages of greywackes from Caples Terrane metasediments have youngest zircon age components from 251 to 215 ma, and a comparison of dataset patterns from fossiliferous examples suggests that these probably originate from contemporary volcanic sources. Caples volcanism and associated depocentres thus span much of the Triassic. However, their major zircon component, invariably in the range early Triassic to latest Permian, is most persistent, and constitutes an enormous and enduring zircon source thought to be in the New England Orogen of eastern Australia. Minor, late Paleozoic (295-340 ma) zircon components are restricted to (early-middle Triassic) Caples Terrane metasediments with older, minimum zircon age components, perhaps originating in nearby primary sources in the northeasternmost Lachlan Fold Belt and southern part of the New England Orogen. More scattered early Paleozoic-Precambrian zircons are present throughout the Caples Terrane and reflect reworking of zircons from Paleozoic metasediments and plutonic rocks within the New England Orogen (and its immediate hinterland). Caples Terrane metasediments thus represent an offshore, Triassic component of the accretionary prism terranes (late Carboniferous to early Cretaceous) of the eastern Province of New Zealand. Their depocentres were more isolated from the Gondwanaland continental margin than Torlesse and Waipapa Terrane counterparts, and more influenced by substantial contemporary volcanic centres, perhaps located along the Lord Howe Rise. [ABSTRACT FROM AUTHOR]

Detrital zircon U-Pb ages in greywackes and initial 87Sr/86Sr ratios are reported for low-grade metasedimentary rocks from Torlesse Supergroup, Waipapa Group, and Kaimanawa Schist in the central North Island, New Zealand. The data reveal the presence of a hitherto unsuspected, areally extensive, Jurassic part of the Torlesse composite terrane in the Kaimanawa, Kaweka, and Ruahine Ranges, which we name the Kaweka Terrane. Kaweka rocks have initial 87Sr/86Sr ratios (at metamorphism) and detrital zircon patterns that in part are transitional between Rakaia and Pahau Terrane rocks and in part similar to Waipapa Terrane rocks. Combined detrital zircon age data for all Torlesse and Waipapa Terrane data reveal an essential unity, with a long persistence (260-120 Ma) of predominant Permian-Triassic sources in the form of a major Cordilleran-style batholith, a decline in major early Paleozoic-Precambrian sources between 260 and 220 Ma, and presence of minor Early Carboniferous to Late Devonian sources between 180 and 120 Ma. Rb-Sr and K-Ar ages indicate latest Triassic to Early Cretaceous metamorphism in an evolving accretionary wedge. [ABSTRACT FROM AUTHOR]

The petrochemical as well as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Ta0xi Group in eastern Nanling Range, Central Cathaysia indicate that its protolith is the sedimentary rock with low maturation index. The clastic materials are mostly from middle Neoproterozoic (∼736 Ma) granitoid rocks with minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement with the second period of magmatism widespread surrounding the Yangtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recycled Paleoproterozoic mantle-derived crustal materials. The sedimentary rock was deposited in Late Neoproterozoic Era, and carried into low crust in Early Paleozoic. The partial melting of the meta-sedimentary rock took place at about 480 Ma and subsequently granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval (Early Paleozoic) show large Hf isotope variations, and their ϵHf(t) values increase from -13.2 to +2.36 with decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early Paleozoic. Calculation results show that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby Mesozoic high Si peraluminous granites, implying that this kind of granulite facies metamorphic rock is probably the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range. [ABSTRACT FROM AUTHOR]

The Moelv Tillite is the Late Neoproterozoic Varanger glacial deposit recorded in the Hedmark Group, SE Norway. Paired U–Pb and Lu–Hf data collected on detrital zircons in the Rendalen Formation underlying the Moelv Tillite have identified an uncommon 677 ± 15 to 620 ± 14 Ma population, that constrain the deposition of the Moelv Tillite to be younger than 620 ± 14 Ma. The youngest detrital zircons may be derived from granite magmatism related to the 616 ± 3 Ma Egersund dolerite magmatism, situated in the western part of the Sveconorwegian orogen. The Moelv Tillite, which is not overlain by a cap carbonate, possibly correlates with thec. 580 Ma Squantum-Gaskiers glacial deposits of Avalonia. Available palaeomagnetic data for the Late Neoproterozoic suggest that Baltica was located at intermediate to high latitude between 620 and 555 Ma.Terra Nova, 00, 1–9, 2005 [ABSTRACT FROM AUTHOR]

The Paleoproterozoic Mojave and Yavapai crustal provinces in southwestern Laurentia contain evolved and juvenile crust, respectively, but the nature of the province boundary remains uncertain. 1.78-1.35 Ga crystalline basement rocks of the Mojave Province preserve an evolved isotopic signature reflecting an Archean crustal component in several isotopic systems (Nd, Pb, Hf). However, no Archean rocks have been found, and hence the origin and tectonic significance of this Archean component are also unclear. This paper analyzes the U-Pb age and Hf isotopic composition of zircons from both the oldest granodiorite plutons (1.84-1.71 Ga) and the oldest metasedimen-tary rocks (1.75 Ga Vishnu Schist) across a 180-km-long cross-strike transect in Grand Canyon. This transect crosses the Crystal shear zone, which has been proposed as the location of a suture separating the provinces. Our results show that the characteristically bimodal population of detrital zircons in the Vishnu Schist (2.5 Ga and 1.8 Ga modes) yields mixed εHf(t) values, primarily between +5 to -5, that are uniform across the transect. Another new finding is that the 1.84 Ga Elves Chasm pluton, on which the Vishnu Schist was deposited, yields juvenile εHf(t) values of +5 to +12 and was not the dominant source for the ca. 1.85 Ga peak in the 1.75 Ga Vishnu Schist. Instead, the Vishnu Schist was derived from an Archean craton mixed with intermediate to evolved 1.85 Ga crust. Metasediments show no evidence in support of the proposed suture. Paradoxically, plutons east and west of the Crystal shear zone do support models for a crustal suture. Plutons east of the Crystal shear zone dated at 1.74-1.71 Ga yield juvenile εHf(t) values of +5 to +12 that are characteristic of the Yavapai Province. Plutons west of the Crystal shear zone show juvenile to evolved Paleoproterozoic grains (εHf(t) of -5 to +10) as well as xenocrystic Archean and 1.85 Ga grains (εHf(t) of -12 to +10). These data support the proposition that the Crystal shear zone marks a sharp boundary between the Mojave and Yavapai crustal provinces. However, the overlapping Vishnu Schist suggests a more complicated crustal architecture. The depositional setting of the Vishnu Schist remains unclear; however, we interpret the ultimate geometry of the transect to reflect an ~200-km-wide middle-crustal duplex system in which the 1.75 Ga Vishnu Schist was deposited across both Mojave and Yavapai crust. This system was subsequently imbricated in an accretionary complex. The ultimate architecture is of a distributed boundary with slivers of plutons that carry the isotopic signature of their respective provinces imbricated within metasediments. [ABSTRACT FROM AUTHOR]