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Nine Paleozoic sedimentary formations from western Tasmania and two from the Lachlan Orogen—one in northeast Tasmania and one in Waratah Bay in Victoria—contain detrital zircons that fall into major U–Pb age clusters at 2.0–1.4, 1.25–0.95 and 0.62–0.49 Ga. The zircon Th/U ratios and rare earth element (REE) patterns suggest a magmatic origin for detrital zircons in all these rock sequences. The REE geochemical signatures on bivariate discrimination diagrams indicate that most of the zircons originated in continental orogenic settings. The oldest group of zircons have a southwest Laurentian signature previously recognised from Proterozoic metasedimentary rocks in Tasmania. The 1.25–0.5 Ga zircons from all the samples have very similar εHfi values. They are not statistically different from those of typical Lachlan Orogen sandstones and resemble those in Rodinia and early Gondwana orogenic belts. The εHfi values of the Cambrian zircons within the Pioneer Sandstone are similar to the Mount Read Volcanics but cannot be distinguished on εHfi values from other sources in East Gondwana. The detrital zircon provenance of the Bear Gully Chert Bed at the base of the Digger Island Marlstone at Waratah Bay includes the west Tasmanian Proterozoic, the East Gondwana margin and the Macquarie Arc. This mixed provenance provides evidence for the late Cambrian docking of VanDieland with East Gondwana. New zircon Hf isotope data are reported for early Paleozoic sedimentary rocks in Tasmania and Waratah Bay, southern Victoria. The western Tasmania basement was the dominant source for Tasmanian sandstones and a minor source for the Lachlan Orogen sandstones on the northeast margin of VanDieland. The mixed provenance of the Bear Gully Chert supports a late Cambrian accretion of VanDieland to the East Gondwana margin. The youngest zircons in the Bear Gully Chert at Waratah Bay were potentially sourced from the Macquarie Arc. [ABSTRACT FROM AUTHOR]

Extensive crustal anatexis is common during the decompressional exhumation of deeply subducted continental crust and the delamination of a collision‐thickened orogenic lithosphere, indicating that determining the timing of partial melting can provide insights into the possible tectonic evolution during orogenic processes. An integrated study of petrology, zirconology and whole-rock geochemical compositions from migmatites and pegmatites in the Nageng, Langmuri and Wulonggou area of the East Kunlun Orogenic Belt, is presented in this study. The protoliths of these migmatites include Tonian sedimentary rocks and ca. 440 Ma arc-related dioritic rock. Together with previous studies, an extensive crustal anatexis event recorded by anatectic zircons occurred after ca. 410 Ma. In addition, hafnium isotope analyses indicate that the anatectic zircons may or may not inherit their Hf isotope compositions from protolith zircons during partial melting, depending on whether or not the garnet Hf contributes to the Hf budget of anatectic melt. Thus, the most reasonable method to trace the source of granite is to compare the Hf isotope composition of anatectic zircon in migmatite and magmatic zircon in contemporaneous granite. By such method, anatectic melt produced by migmatites in this study could account for both penecontemporaneous A- and I-type granites with high magmatic zircon εHf(t) values and S-type granites with low magmatic zircon εHf(t) values. As the extensive crustal anatexis is later than both metamorphic peak and amphibole-facies retrogression of high-pressure and ultrahigh-pressure (HP-UHP) metamorphic rocks, it is reasonable that post-collision orogenic collapse of the collision‐thickened orogenic lithosphere as a result of delamination and asthenospheric upwelling occurred after ca. 410 Ma, which is also supported by contemporaneous granulite-facies metamorphism, molasse deposition, and magmatic events including Xiarihamu mafic-ultramafic intrusions, A-type granites, and mafic dykes formed in the continental rifting setting. [ABSTRACT FROM AUTHOR]

Several orogenies have shaped the bedrock of southern Sweden. While mafic intrusions represent significant sources of information for reconstructing geodynamics and crustal evolution, the characterization of the various generations of such intrusions in Sweden remains limited. We report in situ zircon U–Pb ages and Hf isotope data from a Fe-Ti eclogite and a coronitic metagabbro from the Eastern Segment in southern Sweden. Crystallisation ages at 1683 ± 17 Ma of the eclogite suggest affiliation with the surrounding 1730–1660 Ma Transscandinavian Igneous Belt intrusions that dominate the Eastern Segment. Secondary zircon growth and Pb-loss in the eclogite sample at 1459 ± 44 Ma and the crystallisation of the metagabbro at 1431 ± 26 Ma overlap and are related to magmatic activity during the Hallandian orogeny. Zircon Hf isotope signatures with chondritic and sub-chondritic values at ~1683 Ma and ~1431 Ma, respectively, correspond to an enriched (or mildly depleted) source in line with a "Mixed Svecofennian Crustal Reservoir". These isotope signatures are more enriched than those in the surrounding gneisses. Zircon isotope data from the herein analysed zircon grains indicate that the eclogite and metagabbro had an enriched mafic source in the mid to lower crust, or within the subcontinental lithospheric mantle below Fennoscandia. [ABSTRACT FROM AUTHOR]

This paper presents major element, trace element, and new zircon Hf isotopic data for the Early Mesozoic intrusive rocks in the south Hunchun, Yanbian area, Northeast China. These data are used to constrain the petrogenesis of these intrusive rocks and their implications for the Phanerozoic continental growth of the Central Asian Orogenic Belt (CAOB). Combining geology, geochronology, and whole-rock geochemistry, we identify three distinct episodes of magmatism as Early-Middle Triassic (249-237 Ma), Late Triassic (224-206 Ma), and Early Jurassic (200-187 Ma). The Early-Middle Triassic (249-237 Ma) adakitic tonalite and granodiorite were produced by the partial melting of subducted oceanic slabs, and the melts were contaminated by mantle peridotite during their ascent, whereas the coeval non-adakitic diorite and monzogranite were most likely derived from partial melting of crustal material. The remarkably high zircon Hf isotopic signature (εHf(t) = + 9.4 - +18.9), the enrichment in large-ion lithophile element and light rare earth elements, and the depletion in high field strength element suggest that these 224 Ma gabbros were derived from the partial melting of depleted mantle modified by subduction-related fluids. The 212 Ma monzogranite was most likely derived from juvenile material mixed with old crustal material as evidenced by their high SiO2, low MgO, and low Cr concentrations and variable εHf(t) values (-4.6 to +10.0). Except for the 197 Ma tonalites with affinity to the high silica adakites, the overall geochemical evolution of Early Jurassic (200-187 Ma) rocks was consistent with fractional crystallization from quartz diorite, granodiorite, and monzogranite to syenogranite. Both the Early Jurassic syn-subduction lateral continental growth by accretion of arc complexes and the Late Triassic post-collisional vertical continental growth by accretion of mantle-derived material played an important role in the Phanerozoic continental growth of the CAOB. [ABSTRACT FROM AUTHOR]

The early tectonic evolution of the Lhasa Terrane remains poorly understood, although evidence for a substantial prehistory has been reported recently. We have carried out in situ zircon U-Pb dating and Hf-O isotopes of late Early Cretaceous monzogranites and get a surprising package of inherited zircons, not only because of their age profile, but also because the oldest Palaeoarchaean zircons are euhedral. The discovery of Palaeoarchaean euhedral zircons in the region suggests the presence of extremely old rocks in Tibet. Zircons from the Nagqu monzogranite yield five age peaks at ~3.45 Ga, ~2.56 Ga, ~1.76 Ga, ~900 Ma, and ~111 Ma. They have large variations in εHf(t) values (−45.1-9.2) and old Hf model ages (924-3935 Ma), with variable δ18O values of −5.80-9.64. Palaeoarchaean zircons (~3.20-3.45 Ga) are euhedral with magmatic zircon characteristics. One of the grains has negative εHf(t) value (−4.8), old Hf model age (3935 Ma), and high positive δ18O value (7.27), which suggests an ancient crustal origin. The source of Palaeoarchaean euhedral zircons should be proximal to prevent long-distance transport and abrasion, whereas the late Early Cretaceous monzogranites are I-type. Thus, Palaeoarchaean euhedral zircons are most likely captured from the country rocks by assimilation at depth or may be relics of previous magmatic zircons. Notwithstanding their exact history, Palaeoarchaean euhedral zircons indicate Palaeoarchaean materials near Nagqu in the Tibetan Plateau. The inherited zircons also experienced a Late Palaeoproterozoic event (~1.76 Ga) likely related to the evolution of the India block. The peak at ~900 Ma suggests affinity to the Qiangtang and Himalaya blocks. [ABSTRACT FROM AUTHOR]

The Mount Somers Volcanic Group (MSVG) forms a large (c. 18,000 km2) calc-alkaline volcanic complex on New Zealand’s Eastern Province. U–Pb secondary ion mass spectrometry (SIMS) spot ages on zircon from the lower glassy ignimbrite in Rakaia Gorge reveal a bimodal distribution of 99.0 ± 0.5 and 96.3 ± 0.5 Ma (2σ). These ages are within error of previous (unpublished) zircon sensitive high resolution ion microprobe ages but have a precision that enables identification of two distinct episodes of zircon crystallisation, indicating magmatic activity over a period of at least 2.5 Ma. The younger age is interpreted to represent the emplacement age of the ignimbrite. The older age may originate from the assimilation of underlying ignimbrites or prolonged magma chamber processes. Combined O and Hf isotopes in zircon indicate that melt compositions for the c. 99 and c. 96 Ma magmatic episodes were very similar and intermediate between the local upper crust and mantle-derived melts, supporting formation through hybridisation of mantle and crustal-derived melts. MSVG magmatism preceded, coexisted with and was succeeded by local mafic alkaline HIMU-type magmatism (97.0 ± 0.5 Ma and younger) on the nearby Pahau Terrane. By contrast, the mafic component of the MSVG was derived from a depleted and potentially subduction-modified source associated with the Rakaia Terrane. [ABSTRACT FROM PUBLISHER]

Zircon U–Pb ages, and geochemical, Sr–Nd and zircon Hf isotopic compositions are reported for the A-type granites and dikes in the Alataw Mountains of the northwestern Tianshan Orogenic Belt (NTOB), with the aim of investigating the sources and genesis of A-type granites and dikes. The laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating of A-type granites yielded a concordant weighted mean206Pb/238U age of 297.4 ± 1.5 and 300.6 ± 0.9 Ma, respectively, defining a late Carboniferous–early Permian magmatic event. Geochemically, the granitic intrusions and dikes are characterized by high SiO2and total alkalies (K2O + Na2O), high Zr, Nb, Ta content, and Ga/Al ratio with prominent negative Ba, Sr, P, Eu, and Ti anomalies. These features indicate that the granitic intrusions and dikes in the eastern Alataw Mountains are of an A-type affinity. The depleted Nd isotope compositions of the granitic intrusions and dikes are consistent with those of the Carboniferous volcanic rocks in the Alataw Mountains, especially Carboniferous adakites (εNd(t) = +3.6 to +6.6), suggesting that they were likely generated by partial melting of less evolved crustal materials, such as oceanic crust stored in the middle and/or lower crust or Carboniferous volcanic arc crust. The widespread late Carboniferous–early Permian magmatism in the NTOB may have been related to a ridge subduction accompanied by slab roll-back of the subducting plate of the North Tianshan Ocean. [ABSTRACT FROM AUTHOR]

In order to constrain the timing and petrogenesis of both the hosting rocks and the inner mafic microgranular enclaves (MMEs) of the Liangnong pluton, SE China, we have performed a series of bulk-rock geochemistry, zircon U–Pb, and Hf isotopic analysis, respectively. Zircon laser ablation–inductively coupled plasma–mass spectrometry U–Pb isotopic analysis yielded ages of 106.3 ± 1.1 Ma for the granodiorite and 103.9 ± 1.6 to 105 ± 1.8 Ma for monzogranite phases within the hosting pluton, as well as an age of 104.7 ± 0.8 Ma for the associated MMEs. The host rocks are metaluminous, have A/CNK values of 0.91–1.09, contain relatively high concentrations of SiO2and K2O, are enriched in Rb, Th, Ba, Zr, and Hf, are depleted of Sr, P, Ti, Nd, and Ta, contain high concentrations of the rare earth elements (REE) and the light REE, and have moderately negative Eu anomalies (Eu /Eu = 0.6–0.8). In comparison, the MMEs contain high concentrations of Al2O3, FeO, MgO, and TiO2, are relatively enriched in Ba, U, and Sr, and are depleted in Th, Nd, and Zr. They have lower total REE concentrations and higher Eu /Eu values than the hosting granites. The zircons within the hosting granites have Hf crustal model ages (TDMC) that show a peak at 1.29–1.85 Ga. Zircons within the MMEs have different εHf(t) values (–3.7 to +4.9) than the zircons within the hosting granites (–10.8 to –1.9). The results indicate that the MMEs and the hosting granites crystallized from magmas with different sources, thereby showing that the Early Cretaceous magmatism in the coastal areas of SE China was generated by the widespread injection of mantle-derived magmas caused by rollback of the subducting palaeo-Pacific Plate. [ABSTRACT FROM AUTHOR]

Widespread granitic intrusions in the northeast part of the Wulonggou area were previously thought to be emplaced into the Palaeoproterozoic Jinshuikou Group during the Neoproterozoic. This contribution presents detailed LA-ICP-MS zircon U–Pb geochronology, major and trace element geochemistry, and zircon Hf isotope systematic on the Wulonggou Granodiorite and Xiaoyakou Granite from the Wulonggou area. Three granodiorite samples yielded U–Pb zircon ages of 247 ± 2, 248 ± 1, and 249 ± 1 Ma, and one granite sample yielded U–Pb zircon age of 246 ± 3 Ma. The granodiorite samples are metaluminous with an alumina saturation index of 0.90–0.96, as well as intermediate- to high-alkali contents of 5.49–6.14 wt.%, and low Zr+Nb+Ce+Y contents, and low Fe2O3T/MgO ratios, which suggest an I-type classical island arc magmatic source. The granite samples are peraluminous with an alumina saturation index of 1.02–1.03, Sr content of 305.00–374.00 ppm, Sr/Y ratios of between 17.68 and 28.77, (La/Yb)Nvalues of 16.98–25.07, low HREEs (Yb = 1.10–2.00 ppm), and low Y (13.00–21.10 ppm), which suggest adakite-like rocks. All granodiorite samples have zirconsεHf(t) values ranging from −2.9 to +3.9, and granite samples have zirconεHf(t) values ranging from −7.8 to +3.2. These Hf isotopic data suggest that the Early Triassic granites were derived from the partial melting of a mafic Mesoproterozoic lower crust, although the degree of ancient crustal assimilation may be higher for the Xiaoyakou Granite. It is suggested here that the ca. 246–248 Ma magma was generated during the northward subduction of the Palaeo-Tethys oceanic plate. [ABSTRACT FROM PUBLISHER]

The isotopic composition of hafnium has been measured in zircons from seven magmatic rocks from the Blekinge region, southeast Sweden, previously dated by the U–Pb zircon method to 1.74–1.76 Ga, with one rock at 1.81 Ga. The results from all samples show limited variation, with a total range in initial ϵHfbetween − 1.5 and +3.2, only slightly more than analytical uncertainty ( ± 1.5 epsilon units). However, taken together with previously published initial ϵNdwhole-rock values of − 0.3 to +1.0 from the same rock samples, a trend with a positive correlation between average initial ϵHf(zr) for each sample and initial ϵNd(WR) can be discerned. This trend could be taken to indicate mixing between a “mildly depleted” component derived from the lithospheric mantle or lower crust, and a slightly more enriched crustal component, either by mixing of separate magmas or by contamination of a mantle-derived magma with crustal material. Such mixing may have occurred both on a regional scale, as indicated by the overall trend, and locally within each intrusion and each rock sample with small-scale variations in isotope composition of the magma during crystallization, indicated by the variation in initial ϵHfbetween the zircons in each sample. The overall results support the presence of a “mildly depleted” lithospheric mantle reservoir, both in terms of Nd and Hf isotopes, also beneath southern Fennoscandia in Proterozoic time. [ABSTRACT FROM AUTHOR]

Large-scale volcanism in the late Mesozoic was a prominent geological event in southeast China. The late Mesozoic volcanic sequences, named the Moshishan Group, are exposed in Zhejiang Province and are predominantly felsic in composition with subordinate mafic magma and rare andesites. To understand the late Mesozoic tectonic evolution of southeast China, we present zircon U–Pb dating, major and trace element analyses, and Hf isotopic compositions from felsic volcanic rocks of the Moshishan Group. Zircon U–Pb dating shows that the Moshishan Group formed between 145 and 129 Ma. The εHf(t) of the analysed zircons ranges from −16.58 to +6.89, and theTDM2age ranges from 753 to 2238 Ma with a major peak at ca. 1870 Ma. Hf isotopic compositions of zircons in Early Cretaceous volcanic rocks are more radiogenic than that of the metamorphic basement rocks, indicating a juvenile component in these magmas. Major element concentrations show that the volcanic rocks mainly belong to the high-K calc-alkaline series. Both zircon saturation temperatures and the εHf(t) values of zircons gradually increased with the evolution of the magma. Trace element data indicates that neither magmatic differentiation of mantle-derived magma nor mixing of magmas from different sources were the predominant magmagenetic processes. Earlier studies suggest that contemporaneous underplating contributed to the heat source that induced crustal melting and to the material origin that inconsistently mixed with the local crustal melts. Magmatic underplating is likely to have occurred because of the southwestward subduction of the Pacific plate with episodic slab rollback. The data obtained in this study suggest that the crust–mantle interaction under the influence of slab rollback played a progressive role in the formation of Early Cretaceous felsic volcanic rocks in southeast China. [ABSTRACT FROM AUTHOR]

The western Qinling region of central China is situated centrally in the Kunlun, Qilian, Qinling, Longmenshan, and Songpan–Ganzi orogens. Late Palaeozoic and Early Mesozoic sediments deposited here may provide keys to understanding the tectonic evolution of the Palaeo-Tethys and collision of the North China and Yangtze Cratons. We conductedin situU–Pb and Lu–Hf isotope analyses of 568 detrital zircons collected from Upper Palaeozoic to Mesozoic sandstones in the central Qinling block, Taohe depression, and Bailongjiang block in western Qinling to constrain the sources of these sandstones. Our results reveal that the Bailongjiang block has affinities with the Yangtze Craton, from which it may have been rifted. Therefore, the Palaeo-Tethyan Animaqen suture between the two cratons lies north of the Bailongjiang block. We identified the North China Craton as the main source for Triassic flysch in central China. It is possible that the Bailongjiang block could have blocked detritus shed from the North China Craton into the main depositional basins in the Songpan–Ganzi area. The dominance of 300–200 Ma detrital zircons of metamorphic origin in Lower Jurassic sandstones indicates that the Dabie–Qinling orogen was elevated during Early Jurassic time. In addition, our Lu–Hf isotopic results also reveal that Phanerozoic igneous rocks in central China were mostly products of crustal reworking with insignificant formation of juvenile crust. [ABSTRACT FROM PUBLISHER]

The location of the suture zone between the South China and Indochina blocks in northwest Vietnam has been under debate for decades. Generally, the boundary between these blocks has been placed along (1) the Ailaoshan–Red River zone or (2) the Song Ma zone. The Sin Quyen Formation, lying between these zones, was previously regarded as a Palaeo- and Mesoproterozoic sequence. It comprises its provenance and tectonic affinity. We analysed detrital zircons from two paragneisses and one migmatite of the Sin Quyen Formation employing laser ablation inductively coupled plasma mass spectrometry U–Pb dating techniques. U–Pb ages of these zircons show three main periods of zircon formation: ∼2.7–3.0, ∼2.2–2.5, and ∼1.8 Ga, suggesting that Sin Quyen rocks were mainly derived from Palaeoproterozoic and Archaean basement units. Inasmuch as the South China basement comprises rocks of similar ages, we conclude that the Sin Quyen Formation belongs to that block. Our new data strengthen the view that the suture between the South China and Indochina blocks is located within the Song Ma zone. In addition, zircons with U–Pb ages >3.0 thousand million years represent the oldest minerals reported in northwest Vietnam so far, indicating the existence of Mesoarchaean crustal remnants in this region. [ABSTRACT FROM AUTHOR]

U-Pb zircon analyses from a series of orthogneisses sampled in drill core in the northern Gawler Craton provide crystallisation ages at ca 1775-1750 Ma, which is an uncommon age in the Gawler Craton. Metamorphic zircon and monazite give ages of ca 1730-1710 Ma indicating that the igneous protoliths underwent metamorphism during the craton-wide Kimban Orogeny. Isotopic Hf zircon data show that 1780-1750 Ma zircons are somewhat evolved with initial εHf values -4 to +0.9, and model ages of ca 2.3 to 2.2 Ga. Isotopic whole rock Sm-Nd values from most samples have relatively evolved initial εNd values of -3.7 to -1.4. In contrast, a mafic unit from drill hole Middle Bore 1 has a juvenile isotopic signature with initial εHf zircon values of ca +5.2 to +8.2, and initial εNd values of ∼+3.5 to +3.8. The presence of 1775-1750 Ma zircon forming magmatic rocks in the northern Gawler Craton provides a possible source for similarly aged detrital zircons in Paleoproterozoic basin systems of the Gawler Craton and adjacent Curnamona Province. Previous provenance studies on these Paleoproterozoic basins have appealed to the Arunta Region of the North Australian Craton to provide 1780-1750 Ma detrital zircons, and isotopically and geochemically similar basin fill. The orthogneisses in the northern Gawler Craton also match the source criteria and display geochemical similarities between coeval magmatism in the Arunta Region of the North Australian Craton, providing further support for paleogeographic reconstructions that link the Gawler Craton and North Australian Craton during the Paleoproterozoic. [ABSTRACT FROM AUTHOR]

Provenance data from Paleoproterozoic and possible Archean sedimentary units in the central eastern Gawler Craton in southern Australia form part of a growing dataset suggesting that the Gawler Craton shares important basin formation and tectonic time lines with the adjacent Curnamona Province and the Isan Inlier in northern Australia. U-Pb dating of detrital zircons from the Eba Formation, previously mapped as the Paleoproterozoic Tarcoola Formation, yields exclusively Archean ages (ca 3300-2530 Ma), which are consistent with evolved whole-rock Nd and zircon Hf isotopic data. The absence of Paleoproterozoic detrital grains in a number of sequences (including the Eba Formation), despite the proximity of voluminous Paleoproterozoic rock units, suggests that the Eba Formation may be part of a Neoarchean or early Paleoproterozoic cover sequence derived from erosion of a multi-aged Archean source region. The ca 1715 Ma Labyrinth Formation, unconformably overlying the Eba Formation, shares similar depositional timing with other basin systems in the Gawler Craton and the adjacent Curnamona Province. Detrital zircon ages in the Labyrinth Formation range from Neoarchean to Paleoproterozoic, and are consistent with derivation from >1715 Ma components of the Gawler Craton. Zircon Hf and whole-rock Nd isotopic data also suggest a source region with a mixed crustal evolution (εNd -6 to -4.5), consistent with what is known about the Gawler Craton. Compared with the lower Willyama Supergroup in the adjacent Curnamona Province, the Labyrinth Formation has a source more obviously reconcilable with the Gawler Craton. Stratigraphically overlying the Eba and Labyrinth Formations is the 1656 Ma Tarcoola Formation. Zircon Hf and whole-rock Nd isotopic data indicate that the Tarcoola Formation was sourced from comparatively juvenile rocks (εNd -4.1 to + 0.5). The timing of Tarcoola Formation deposition is similar to the juvenile upper Willyama Supergroup, further strengthening the stratigraphic links between the Gawler and Curnamona domains. Additionally, the Tarcoola Formation is similar in age to extensive units in the Mt Isa and Georgetown regions in northern Australia, also shown to be isotopically juvenile. These juvenile sedimentary rocks contrast with the evolved underlying sequences and hint at the existence of a large-scale ca 1650 Ma juvenile basin system in eastern Proterozoic Australia. [ABSTRACT FROM AUTHOR]

The integrated in situ microanalysis of Pb and Hf isotopic compositions of zircon (TerraneChron® methodology) has been applied to detrital zircons from locally derived stream sediments in the South Para River, which samples the Houghton Inlier, South Australia. The zircons record two major events: an igneous event at 1718±8 Ma and a metamorphic event at 1625±9 Ma. The igneous event is of broadly similar age to syndepositional magmatism associated with the lower Willyama Supergroup of the Curnamona Province and syn-Kimban Orogeny intrusives of the eastern Gawler Craton. The later metamorphic event is of comparable age to the Olarian Orogeny in the Curnamona Province and to magmatic and metamorphic events in the central to western Gawler Craton. The combination of U – Pb dating and Hf-isotope data provides an additional tool to overcome ambiguities in correlating terranes with similar U – Pb ages. The Hf-isotopic compositions of the Houghton Inlier zircons and their model ages of 2.5 – 2.4 Ga suggest a closer match with the rocks of the Gawler Craton. [ABSTRACT FROM AUTHOR]

Two populations of kimberlitic zircon are present in the Timber Creek kimberlites, Northern Territory. Laser-ablation ICP-MS U–Pb dating yields an age of 1483 ± 15 (2σ) Ma for the main group and an age of 179 ± 2 Ma for the other group. This distinction of two age groups is strongly supported by Hf isotope data on the same zircons. Although the trace-element patterns of both populations are typical of mantle-derived zircons, the ‘young’ population has slightly higher concentrations of most trace elements, but has lower Hf, Nb, Ta and Pb contents. The distinct differences in trace-element contents and Hf isotopic composition of the two zircon populations indicate that they were derived from different magma sources. The dating results indicate that the emplacement age of the Timber Creek kimberlites cannot be older than the age of the ‘young’ zircon population (i.e. 179 ± 2 Ma). This clarifies the inconsistency between the previously reported SHRIMP age of the Timber Creek zircons (1462 ± 53 Ma) and the much younger age (1200 Ma) of the sediments of the Victoria River Basin into which these kimberlites have intruded. The Timber Creek kimberlites are a newly recognised extension of the widespread Jurassic kimberlite activity known in Western Australia and South Australia (Wandagee, Orroroo, Cleve and Eurelia kimberlites). [ABSTRACT FROM AUTHOR]