Detrital Zircon Age Patterns Research Articles

An Australian provenance for the eastern Otago Schist protolith, South Island, New Zealand: evidence from detrital zircon age patterns and implications for the origin of its gold

ABSTRACTUranium–lead age patterns of detrital zircons in Otago Schist meta-sandstones from eastern Otago, including areas of orogenic gold mineralisation, are mostly consistent with a Rakaia Terrane (Torlesse Composite Terrane) accretionary wedge protolith. Southwest of the Hyde-Macraes and Rise & Shine shear zones the depositional age is regarded as Middle–Late Triassic. At the south and west margins, there are two areas in the Late Triassic Waipapa Terrane protolith. Northeast of the Hyde-Macraes Shear Zone, the schist protolith has Middle to Late Triassic and middle to late Permian depositional ages of Rakaia Terrane affinity. At the northeastern margin of the Hyde-Macraes Shear Zone, there is a narrow strip with a mid-Carboniferous protolith, which may be a counterpart of the Carboniferous accretionary wedge in the New England Orogen, eastern Australia. Ordovician–Silurian zircons are a minor but distinctive feature in many of the protolith age patterns and form significant age components at hard-rock gold locations. These constrain the provenance of Rakaia Terrane protolith sediments to Late Triassic time and within the Permian–Triassic magmatic arcs at the northeastern Australian continental margin and partly within the Ordovician–Silurian granitoids of the Charters Towers Province hinterland and environs. The latter have extensive gold mineralisation and thus upon exhumation might be the origin of Otago gold.

Detrital zircon U-Pb and Hf isotopic and whole-rock geochemical study of the Bayan Obo Group, northern margin of the North China Craton: Implications for Rodinia reconstruction

The Zha’ertai-Bayan Obo-Huade rift zone is located in the northern margin of the North China Craton (NCC), where rift-related supracrustal successions are divided into the Langshan, Zha’ertai, Bayan Obo and Huade groups from west to east. The Bayan Obo Group unconformably overlies the Late Neoarchean to Paleoproterozoic basement rocks and has been subdivided into three successions by two prominent unconformities. Depositional ages of the lower, middle and upper succession can be constrained in the period of 1.81–1.65Ga, 1.56–1.35Ga and 1.19–0.92Ga respectively based on ages of the youngest detrital zircons and latter intrusions. Geochemistry of the meta-sedimentary samples suggest that most of them were directly sourced from intermediate to felsic magmatic and metamorphic rocks and only the Halahuogete samples from the middle succession display reworking features. U-Pb ages of detrital zircons from the group yielded age peaks of 2.52–2.48Ga, 1.95–1.85Ga, 1.74–1.61Ga, 1.55–1.53Ga, 1.37–1.34Ga and 1.18–1.13Ga. The late Neoarchean to middle Paleoproterozoic detrital zircons are documented in the lower and middle successions and are derived from the ca. 2.5Ga Guyang and Xi Ulanbulang areas and ca.1.9Ga Halaqin and Liangcheng areas in the Yinshan Block. The late Paleoproterozoic detrital zircons with low εHf(t) values from the Bilute Formation are interpreted to be sourced from the coeval rift-related granitic plutons and volcanic rocks in the northern NCC. On the other way, detrital zircon age patterns of the late Mesoproterozoic to early Neoproterozoic sedimentary units at the northern and southeastern margins of the NCC are similar with those from the western and northern margin of the Fennoscandian shield. Combined with recent paleomagnetic and geological data, we infer that the NCC and Baltica have not separated until 0.89Ga in the Rodinia supercontinent.

Chronological constraints on the tectonic evolution of the Chinese Tianshan Orogen through detrital zircons from modern and palaeo-river sands

ABSTRACTThe Chinese Tianshan Orogen marks prolonged and complicated interactions between the southwestern Palaeo-Asian Ocean and surrounding blocks. New and previously published detrital zircon chronological data from modern and palaeo-river sands were compiled to reveal its tectonic evolution. It is characterized by predominant Palaeozoic as well as minor Mesozoic and Precambrian detrital zircon ages with a multimodal characteristic. The oldest Phanerozoic zircon population (peaking at 475 Ma) is a result of subduction and closure of the early Palaeozoic Terskey Ocean. However, the absence of this peak in the Chinese North and southern South Tianshan suggests that subductions of the North and South Tianshan oceans may not have initiated until the Late Ordovician with subsequent 460–390 and 360–320 Ma arc magmatism. Similar to the magmatic suite in classic collisional orogens, the youngest massive 320–270 Ma magmatism is suggested to be post-collisional. The North and South Tianshan oceans therefore probably had their closure to form the Chinese Tianshan Orogen during the late Carboniferous. The weak Mesozoic intra-plate magmatism further rejects a late Permian–Triassic Tianshan Orogen due to a lack of extensive syn- and post-collisional magmatism. Moreover, diverse Precambrian detrital zircon age patterns indicate that the surrounding blocks have distinct evolutionary processes with short-term amalgamation during the Meso- to Neoproterozoic.

Detrital zircon age patterns and provenance assessment for pre-glacial to post-glacial successions of the Neoproterozoic Macaúbas Group, Araçuaí orogen, Brazil

The Neoproterozoic Macaúbas Group represents the precursor basin system of the Araçuaí–West Congo orogen (SE Brazil – SW Africa), located between the São Francisco and Congo cratons. The Macaúbas basin evolved from continental rift settings to an inland-sea basin (a gulf) partially floored by oceanic crust and connected to aulacogens. Its evolution was coeval with at least one of the major Neoproterozoic glaciations. In this paper, we present more than 450 new U–Pb ages on detrital zircon grains from four units of the Macaúbas Group, covering glacial-related to post-glacial sedimentation stages. The results suggest that the main sedimentary supplies of the Macaúbas basin should have come from secondary sources, located in the São Francisco and Congo cratons. The pre-glacial units of the Macaúbas Group are the only ones that show important contribution from 1100 to 1200Ma sources, and lack Archaean zircons, which are common in younger rocks of the group. These features indicate an important change in the source areas, coherent with the climate change to glacial conditions and with a regional unconformity previously mapped. Sources between 1500–1600Ma are more significant in the continental rift stages, decreasing in the passive margin stage. This suggests changes driven by the end of a glaciation and/or the breakup of the continental lithosphere. Tonian zircons occur throughout all the basin stages, and significantly increase in the late rift and passive margin successions, recording the most abundant rift-related magmatism yet found in the Araçuaí–West Congo orogen. Detrital zircon grains as young as 750Ma reveal contributions from Cryogenian sources to passive margin successions, suggesting sedimentary supplies from the South Bahia Alkaline Province and/or Rio Negro magmatic arc, in Brazil, and/or from rocks found in Africa (e.g., La Louila volcanic rocks). The long lasting evolution of the Macaúbas basin (c. 930Ma to c. 600Ma) would have involved more than one continental rifting event before the onset of an ocean-floor spreading phase around 660Ma.

Identifying Laurentian and SW Gondwana sources in the Neoproterozoic to Early Paleozoic metasedimentary rocks of the Sierras Pampeanas: Paleogeographic and tectonic implications

The provenance of Neoproterozoic to Early Paleozoic sedimentary rocks in the Sierras Pampeanas has been established using U–Pb SHRIMP age determination of detrital zircons in twelve metasedimentary samples, with supplementary Hf and O isotope analyses of selected samples. The detrital zircon age patterns show that the western and eastern sectors of the Sierras Pampeanas are derived from different sources, and were juxtaposed during the Early Cambrian ‘Pampean’ collision orogeny, thus defining initiation of the supercontinent stage of southwestern Gondwana. The Western Sierras Pampeanas (WSP), which extend northwards to the southern Puna (Antofalla) and the Arequipa Massif (Peru), constitute a single large continental basement of Paleoproterozoic age — the MARA block — that was reworked during the Grenvillian orogeny. The MARA block probably extends eastwards to include the Río Apa block (southern Brazil), but in this case without a Mesoproterozoic overprint. Detrital zircons from the WSP and Antofalla yield age peaks between 1330 and 1030Ma, remarkably similar to the range of ages in the Grenville province of eastern Laurentia. The WSP Neoproterozoic sedimentary cover to this basement shows the same 1330–1030 component, but also includes important 1430–1380Ma zircons whose juvenile Hf and O isotopic signatures strongly suggest derivation from the Grenville and the Southern Granite–Rhyolite provinces of eastern Laurentia. In contrast the Eastern Sierras Pampeanas metasedimentary rocks have a typically bimodal detrital zircon pattern with peaks at ca. 1000 and 600Ma, which respectively indicate sources in the Natal–Namaqua belt and the East African orogen and/or the Dom Feliciano belt of SE Brazil and Uruguay. Sedimentary rocks in the Eastern Sierras Pampeanas and Patagonia deposited during the Late Early Cambrian–Early Ordovician interval, after the Pampean orogeny, have detrital patterns common to many sectors along the Terra Australis orogen, reflecting increasingly dominant input to the Paleozoic basins from the Neoproterozoic to Early Cambrian orogenic belts of the Gondwana margin.

Detrital zircon record of the early Paleozoic meta-sedimentary rocks in Russian Altai: Implications on their provenance and the tectonic nature of the Altai–Mongolian terrane

An integrated U–Pb and Hf-isotope study on detrital zircons from the early Paleozoic meta-sedimentary rocks along the Charysh–Terekta–Ulagan–Sayan suture zone in Russian Altai was conducted in order to trace their provenance and tectonic setting. Most of the zircons possess oscillatory zoning and high Th/U ratios (>0.1), indicating their magmatic origin. The investigated samples yield similar zircon populations, i.e., dominant groups with late Neoproterozoic to early Paleozoic ages, followed by those from Mesoproterozoic to late Neoproterozoic and minor ones from Archean to middle Mesoproterozoic, indicating multiple tectono-thermal events in the source area. Comparison with surrounding tectonic units shows that the Tuva–Mongolian terrane and its adjacent island arcs possibly provided substantial materials to the sedimentary basin. These rocks show detrital zircon age patterns and Hf-isotope compositions similar to their counterparts in the Chinese Altai and Tseel terrane in western Mongolia, but different from those in the Gorny Altai terrane. Therefore, the investigated meta-sedimentary units possibly represented the northernmost segment of the Altai–Mongolian terrane. With combination of previous studies in the Chinese Altai and Tseel terrane, our data suggest that the Altai–Mongolian terrane possibly represents a coherent continental arc-accretionary prism system built upon the active margin of the western Mongolia during the Cambrian to Ordovician and thus does not support the micro-continent model with a passive margin.A compilation of U–Pb and Hf-isotope data of detrital zircons from the whole Altai–Mongolian terrane shows that the source area (i.e., the western Mongolia) underwent two most extensive magmatic activities at ca. 1.02–0.67Ga and 0.67–0.43Ga. These zircons possess both positive and negative εHf(t) values, suggesting significant crustal growth and reworking during the magmatic activities. Our study underlines a crucial role of Precambrian micro-continents (e.g., the Tuva–Mongolian terrane) and island arcs surrounding them in the formation of the Central Asian Orogenic Belt.

LA-ICP-MS zircon U–Pb dating of the Langshan Group in the northeast margin of the Alxa block, with tectonic implications

The relationship between the Alxa block and the North China Craton (NCC) is one of the controversial tectonic issues in China. The age spectra of detrital zircons from sedimentary rocks may help resolve the tectonic affinity of the Alxa block. The Langshan terrane is located in the northeast margin of the Alxa block which is connected to the northwest margin of the NCC. Detailed U–Pb dating of zircon from the meta-volcanic rocks and meta-sedimentary rocks of the Precambrian Langshan group shows that the Langshan Group formed in the Neoproterozoic. The evidence includes the zircon age of 804.1±3.5Ma for the meta-volcanic rocks and the youngest detrital zircon age peak at 1187-810Ma for the meta-sedimentary rocks. The detrital zircon age patterns of the Langshan group and Precambrian strata of the Alxa block and the NCC are similar. The older and younger detrital zircon age peaks of the Langshan group are comparable to those of the NCC and the Alxa block, respectively. The 1.7-1.5Ga detrital zircons in the Langshan Group, which might be derived from the “Zhaertai-Bayan Obo-Huade” Mesoproterozoic rift system in the northern margin of the NCC, are not found in the Precambrian strata of the Alxa block. The detrital zircon age peaks of the Langshan group are well correlated to the known Precambrian tectono-thermal events that affected both the Alxa block and the NCC. The development of the Langshan Neoproterozoic rift system is shown by the contemporaneous magmatism in the Alxa block and the adjacent NCC. The results from this study indicate that the Alxa block and the NCC were together in the Neoproterozoic.

Detrital zircon evidence for the reactivation of an Early Paleozoic syn-orogenic basin along the North Gondwana margin in South China

The Early Paleozoic Lian-Shao Basin, South China, is a syn-orogenic basin that developed on the northern margin of Gondwana in response to the Kwangsian orogeny. U–Pb detrital zircon age patterns from Middle Ordovician to Lower Silurian sandstones around the Jiangnan Uplift within the basin provide evidence for exhumation and erosion of the basin basement. The majority of the samples from both east and west of the Jiangnan Uplift display similar age distributions with a dominant peak between 1000 and 900Ma and subordinate peaks at ~2500Ma, ~1700Ma and 600–500Ma. However, the zircon age spectrum of one sample from the west side of the Uplift is distinct with a main peak at 880Ma and lacking grains younger than 650Ma. Combined geochronological and paleocurrent data suggest that detritus within the syn-orogenic basins was derived from the northern segment of East Gondwana but with additional input of detritus from the Jiangnan Uplift by the late Early Silurian. This information together with analysis of time equivalent strata along strike to the northeast suggests that the Jiangnan Uplift was not a continuous barrier to sediment transport from the southeast but represented part of a discontinuous series of islands supplying local detritus that was mixed with sediment transported from northern Gondwana.

U–Pb detrital zircon age patterns of Cenozoic clastic sedimentary rocks in Trinidad and its implications

The Cenozoic evolution of northern South America can be simplified as a diachronous, west-to-east change from north-facing passive margin, to active convergence and transcurrent plate margin. As the current eastern end of the Caribbean-South America plate boundary, the Trinidad area records the most recent tectonic regime transition. Documenting the provenance of Cenozoic clastic rocks in Trinidad provides insights into the spatial and temporal relationships between mountain range uplifting, sediment dispersal, and drainage system development along the eastern end of the Caribbean-South American plate boundary. Four Eocene to Pliocene age outcropping sandstone samples were collected from Trinidad and 545 detrital zircon grains were analyzed using the U–Pb LA-ICP-MS method. A total of 404 analyses with less than 10% discordance were used for the final interpretation. Results show that the age distribution of the Eocene to the Early Oligocene samples is very restricted and dominated by Precambrian age grains with age peaks at ~1400Ma, ~1800Ma, and ~2000Ma, typically derived from the Guyana Shield. In contrast, the Late Oligocene and younger samples show much broader and mixed age distribution that includes Mesozoic, Paleozoic, and Precambrian peaks. This age shift was interpreted as arriving of the Great Caribbean Arc and oblique collision between the South America and Caribbean plates. Continuing collision uplifted the Andes belts to the west. The Eastern Cordillera of Colombia, the Merida Andes, and the northern Venezuela coastal ranges then became the second primary sources. Offshore sedimentation switched from the passive margin with multiple small drainage systems to the active convergent and transcurrent plate margin with a single large river-dominated delivery system.

Detrital zircon U–Pb–Hf and O isotope character of the Cahill Formation and Nourlangie Schist, Pine Creek Orogen: Implications for the tectonic correlation and evolution of the North Australian Craton

Detrital zircon age and Hf isotope patterns for the Cahill Formation and Nourlangie Schist are distinctly different from other Paleoproterozoic successions in the North Australian Craton. The Cahill Formation and Nourlangie Schist comprise the bulk of the Paleoproterozoic strata in the Nimbuwah Domain, the easternmost part of the Pine Creek Orogen on the northern margin of the North Australian Craton. They comprise micaceous and quartzofeldspathic schist, carbonaceous schist, calc-silicate rock, amphibolite and quartzite, deformed and metamorphosed during emplacement of the granitic to dioritic Nimbuwah Complex at 1867–1857Ma. The Cahill Formation hosts several world-class uranium deposits including Ranger, Jabiluka and Nabarlek. U–Pb SHRIMP and LA-SF-ICPMS detrital zircon spectra for four samples of the Cahill Formation and six samples of the Nourlangie Schist show a similar broad spectrum of ages mainly in the range 3300–1900Ma. A ubiquitous dominant peak at 2530–2470Ma matches the age of underlying Neoarchean basement, but is distinct in its dominantly mantle-like Hf and O zircon isotopic character, which shows closer similarity with possible source rocks from the Gawler Craton or alternatively from the Dharwar Craton. Common smaller age peaks occur at 2180Ma, 2080Ma and 2020Ma. The first two have no known magmatic age correlatives in the North Australian Craton. Zircons of the 2020Ma peak have distinctively unradiogenic Hf and elevated δ18O, at variance with local rocks of this age but similar to detrital zircon of the same age from the Gawler Craton. In contrast to younger Proterozoic sedimentary successions within the Pine Creek Orogen, which contain ubiquitous ca. 1870Ma detritus, the detrital spectra for the Cahill Formation and Nourlangie Schist contain almost no ca. 1870Ma detritus. A maximum deposition age of ca. 1866Ma indicates deposition within error of intrusion of the Nimbuwah Complex. We propose that the Cahill Formation and Nourlangie Schist were deposited at a plate margin immediately prior to convergent tectonism. This resulted in their burial, deformation and amphibolite facies metamorphism during orogenesis associated with the Nimbuwah Event. These findings have implications for understanding the Paleoproterozoic evolution of the Pine Creek Orogen within the context of northern Australia.

Drivers for late Paleozoic to early Mesozoic orogenesis in South China: Constraints from the sedimentary record

Unconformity bound Permo-Triassic successions in the Qinfang Basin, South China Craton, reflect tectonic processes associated with tectonothermal activity along the margins of the craton. The provenance record of these successions, based on modal analysis, geochemical composition, detrital zircon U–Pb ages, and paleocurrent data indicate derivation from the adjoining Precambrian Yunkai massif and surrounding Paleozoic sedimentary units. The quartz dominated nature of the siliciclastic units, along with their high Th/Sc and Zr/Sc ratios indicate a recycled orogen source. Detrital zircons from Late Permian to Early Triassic samples display major age groups at 1100–800 Ma, 650–500 Ma, 480–420 Ma, with subordinate age groups at 2800–2400 Ma, 1900–1600 Ma and 1400–1200 Ma. Late Triassic sandstones show a similar detrital zircon age pattern as well as a 300–250 Ma age group. Integration of this provenance data with regional geological information suggests that the unconformity at the base of the Permian succession is related to subduction of the Paleo-Tethys ocean to the south of the craton, whereas the major driver for Triassic tectonic activity corresponds with terrane accretion and the termination of Paleo-Tethys Ocean subduction along the southwest margin of the craton.

Neoproterozoic S-type granites in the Alxa Block, westernmost North China and tectonic implications: In situ zircon U-Pb-Hf-O isotopic and geochemical constraints

The Alxa Block in northern China has been traditionally considered as the westernmost part of the Archean North China Craton (NCC). However, recent studies revealed that there are few Archean rocks exposed in the Alxa Block, and the Paleoproterozoic geology of this block is different from that of the western part of the NCC. Thus, the tectonic affinity of the Alxa Block to the NCC and/or other Precambrian blocks needs further investigations. In this study, we carry out integrated analyses of <i>in situ</i> zircon U–Pb age and Hf–O isotopes as well as whole-rock geochemistry and Nd isotopes for the Neoproterozoic Dabusushan and Naimumaodao granites from central Alxa Block. Secondary ion mass spectrometry (SIMS) U–Pb zircon dating results indicate that the Naimumaodao and Dabusushan granite plutons were formed at <i>ca.</i> 930 Ma and <i>ca.</i> 910 Ma, respectively. These granites are peraluminous (A/CNK value &gt;1.0), and contain peraluminous minerals such as muscovite and tourmaline, similar to those of S-type granites. They are characterized by high zircon δ¹⁸O values of <i>ca.</i> 8.2 to 12.1 permil, corresponding to a calculated magmatic δ¹⁸O value of <i>ca.</i> 10.5 to 14.3 permil, variable zircon ε_Hf(t) values of −6.2 to +3.8 (corresponding to Hf model ages of 2.2 to 1.6 Ga) and whole-rock ε_Nd(t) values of −10.1 to −4.5 (corresponding to Nd model ages of 2.4-1.9 Ga). The petrological and Nd–Hf–O isotopic study indicated that these granites were most probably generated by remelting of dominant (meta)sedimentary rocks in an orogenesis-related compressional environment. There is a clear contrast in the Precambrian geological evolution, including basement rock age data, Precambrian magmatism and detrital zircon age patterns, between the Alxa Block and the NCC. Furthermore, the new <i>in-situ</i> detrital zircon ages on Neoproterozoic (meta)sedimentary rock suggest that Alxa Block is likely related to the Cathaysia Block of South China during the Neoproterozoic, and amalgamated with the NCC since the Early Paleozoic. Thus, our new data suggest that the Alxa Block is most likely a separated Precambrian terrane from the Western Block of the NCC.

Detrital zircon (U–Pb) and Sm–Nd isotope studies of the provenance and tectonic setting of basins related to collisional orogens: The case of the Rio Preto fold belt on the northwest São Francisco Craton margin, NE Brazil

The Rio Preto fold belt (RPFB), in northeastern Brazil, is represented by Precambrian metasedimentary sequences (Canabravinha and Formosa formations) that were accreted to the northwestern São Francisco Craton margin, during the collisional Brasiliano Orogeny (~630–500Ma). The analysis of the detrital zircon age spectra of samples from both formations revealed a broadly distinct sedimentary provenance for each one of them. While the Canabravinha Formation yielded late-Archean to Tonian zircons, the Formosa Formation yielded a relatively simple, bimodal detrital zircon age pattern at 1900–2200Ma and 2500–2650Ma. The Nd isotope compositions of each unit are also broadly distinct. The Canabravinha Formation shows variable TDM model ages ranging from 1.6 to 2.7Ga, with associated εNd(600) values of −8.7 to −19.5, thus reflecting a wide age range in the source areas. The Formosa Formation TDM distribution reflects the bimodal detrital zircon pattern, with two broad TDM peaks of 1.9–2.0 and 2.4–2.6Ga, and εNd(600) values from −12.9 to −26.5. Based on the detrital zircon and Sm–Nd isotope data, we suggest that the Canabravinha and Formosa formations represent two distinct sedimentary sequences in time and space. A sill-like amphibolite body interleaved within the Formosa Formation mica-schists yielded a U–Pb zircon age of 1962.6±9.9Ma that supports this interpretation. Thus, we suggest that the Formosa Formation represents part of the basement of the Neoproterozoic fold belt, presenting a very simple sedimentary provenance derived uniquely from the Cristalândia do Piauí Complex (Archean/Paleoproterozoic) to the north. The Canabravinha Formation, on the other hand, represents the infilling of a Neoproterozoic extensional (rift) basin (~900–600Ma), whose debris came mainly from the São Francisco Craton to the south and from secondary source areas further northeast in the Borborema Province, such as the Cariris Velhos belt (920–1000Ma). During the Brasiliano Orogeny, both the Proterozoic supracrustal sequences and the Archean/Paleoproterozoic basement were tectonically juxtaposed, deformed and metamorphosed under greenschist facies, thus complicating the original stratigraphic relationships between them.

Detrital zircon geochronology from the Bighorn Basin, Wyoming, USA: Implications for tectonostratigraphic evolution and paleogeography

Tectonostratigraphic assemblages record phases of basin history during which the fundamental controls of tectonic setting, subsidence style, and basin geometry are relatively similar. Because these fundamental controls, in combination with climate and eustasy, influence paleogeography and sediment-dispersal patterns, they should also yield similar patterns, or facies, of detrital zircon age spectra. Such age-distribution patterns should be documented on the craton in order to make meaningful comparisons to sedimentary rocks from suspect terranes along continental margins. The Rocky Mountains of western North America provide excellent outcrops of sedimentary rocks that record >500 m.y. of tectonostratigraphic evolution. One such Phanerozoic section is exposed along the margins of the Bighorn Basin in northwest Wyoming, from which we report over 4000 U/Th/Pb detrital zircon ages from 48 samples that span a stratigraphic interval from the Middle Cambrian Flathead Sandstone through the Eocene Willwood Formation. These data provide one of the most complete records of detrital zircon age patterns from this part of cratonic North America. The stratigraphic record of the Bighorn Basin is subdivided into four tectonostratigraphic assemblages (TSA1–TSA4). These assemblages record an initial passive margin, followed by a transition to a convergent margin, followed by a marine-dominated retroarc foreland basin, followed by a retroarc foreland segmented by local basement uplifts. This tectonostratigraphic architecture is expressed as four, first-order patterns within the detrital zircon age distributions. TSA1 represents a Paleozoic–Triassic proximal continental margin assemblage dominated by Proterozoic zircons with abundant grains in the 1600–1950 Ma range, a Grenville population at ca. 1100 Ma, and a Phanerozoic population at ca. 420 Ma. TSA2 is a transitional assemblage associated with the Jurassic–Early Cretaceous organization of a west-facing convergent margin and Cordilleran orogen. The TSA2 detrital zircon age distribution is characterized by the appearance of Mesozoic grains, age peaks at ca. 420 and 600 Ma, and a dominant population of Grenville (1.0–1.1 Ga) grains with a suite of Proterozoic grains diminishing in abundance as age increases to 1.9 Ga. TSA3 sedimentary rocks were deposited in the Cretaceous Interior Seaway in a retroarc foreland basin and are dominated by zircons for which ages are close to the depositional age of the strata, reflecting input from the active Idaho Batholith and Sierran segments of the Cordilleran magmatic arc. The older zircon fractions from TSA3 sedimentary rocks are characterized by a dominant detrital zircon age peak at 1.7–1.8 Ga, which probably reflects reworking of Belt Supergroup metasedimentary rocks from the northwest into the Cretaceous foreland, based on regional paleogeographic patterns. TSA4 reflects the phase of basin fill associated with Paleogene structural segmentation of the retroarc foreland during the Laramide orogeny. Detrital zircon age spectra from this assemblage record erosion and redeposition of all previous sedimentary rocks from surrounding basement uplifts. Patterns of detrital zircon ages reflect fundamental changes in paleogeography and sediment dispersal at the 10–100 m.y. time scale and are clearly related to major tectonic events or phases. Detrital zircon ages also provide evidence for linkages between convergent margin processes such as arc magmatism and sedimentation in the retroarc foreland. During these times of strong arc-retroarc linkage, detrital zircon geochronology provides a potentially useful tool for high-resolution chronostratigraphy.

Provenance connections between late Neoproterozoic and early Palaeozoic sedimentary basins of the Ross Sea region, Antarctica, south-east Australia and southern Zealandia

AbstractThick successions of turbidites are widespread in the Ross–Delamerian and Lachlan orogens and are now dispersed through Australia, Antarctica and New Zealand. U-Pb detrital zircon age patterns for latest Precambrian, Cambrian and Ordovician metagreywackes show a closely related provenance. The latest Neoproterozoic–early Palaeozoic sedimentary rocks have major components, at c. 525, 550, and 595 Ma, i.e. about 40–80 million years older than deposition. Zircons in these components increase from the Neoproterozoic to Ordovician. Late Mesoproterozoic age components, 1030 and 1070 Ma, probably originate from igneous/metamorphic rocks in the Gondwanaland hinterland whose exact locations are unknown. Although small, the youngest zircon age components are coincident with estimated depositional ages suggesting that they reflect contemporaneous and minor, volcanic sources. Overall, the detrital zircon provenance patterns reflect the development of plutonic/metamorphic complexes of the Ross–Delamerian Orogen in the Transantarctic Mountains and southern Australia that, upon exhumation, supplied sediment to regional scale basin(s) at the Gondwana margin. Tasmanian detrital zircon age patterns differ from those seen in intra-Ross Orogen sandstones of northern Victoria Land and from the oldest metasediments in the Transantarctic Mountains. A comparison with rocks from the latter supports an allochthonous western Tasmania model and amalgamation with Australia in late Cambrian time.

Continental Growth and Recycling in Convergent Orogens with Large Turbidite Fans on Oceanic Crust

Convergent plate margins where large turbidite fans with slivers of oceanic basement are accreted to continents represent important sites of continental crustal growth and recycling. Crust accreted in these settings is dominated by an upper layer of recycled crustal and arc detritus (turbidites) underlain by a layer of tectonically imbricated upper oceanic crust and/or thinned continental crust. When oceanic crust is converted to lower continental crust it represents a juvenile addition to the continental growth budget. This two-tiered accreted crust is often the same thickness as average continental crustal and is isostatically balanced near sea level. The Paleozoic Lachlan Orogen of eastern Australia is the archetypical example of a tubidite-dominated accretionary orogeny. The Neoproterozoic-Cambrian Damaran Orogen of SW Africa is similar to the Lachlan Orogen except that it was incorporated into Gondwana via a continent-continent collision. The Mesozoic Rangitatan Orogen of New Zealand illustrates the transition of convergent margin from a Lachlan-type to more typical accretionary wedge type orogen. The spatial and temporal variations in deformation, metamorphism, and magmatism across these orogens illustrate how large volumes of turbidite and their relict oceanic basement eventually become stable continental crust. The timing of deformation and metamorphism recorded in these rocks reflects the crustal thickening phase, whereas post-tectonic magmatism constrains the timing of chemical maturation and cratonization. Cratonization of continental crust is fostered because turbidites represent fertile sources for felsic magmatism. Recognition of similar orogens in the Proterozoic and Archean is important for the evaluation of crustal growth models, particularly for those based on detrital zircon age patterns, because crustal growth by accretion of upper oceanic crust or mafic underplating does not readily result in the addition of voluminous zircon-bearing magmas at the time of accretion. This crust only produces significant zircon when and if it partially melts, which may occur long after accretion.

Provenance comparisons between the Nambucca Block, Eastern Australia and the Torlesse Composite Terrane, New Zealand: connections and implications from detrital zircon age patterns

Detrital zircon U–Pb LAM-ICPMS age patterns for sandstones from the mid-Permian –Triassic part (Rakaia Terrane) of the accretionary wedge forming the Torlesse Composite Terrane in Otago, New Zealand, and from the early Permian Nambucca Block of the New England Orogen, eastern Australia, constrain the development of the early Gondwana margin. In Otago, the Triassic Torlesse samples have a major (64%), younger group of Permian–Early Triassic age components at ca 280, 255 and 240 Ma, and a minor (30%) older age group with a Precambrian–early Paleozoic range (ca 1000, 600 and 500 Ma). In Permian sandstones nearby, the younger, Late Permian age components are diminished (30%) with respect to the older Precambrian–early Paleozoic age group, which now also contains major (50%) and unusual Carboniferous age components at ca 350–330 Ma. Sandstones from the Nambucca Block, an early Permian extensional basin in the southern New England Orogen, follow the Torlesse pattern: the youngest. Early Permian age components are minor (<20%) and the overall age patterns are dominated (40%) by Carboniferous age components (ca 350–320 Ma). These latter zircons are inherited from either the adjacent Devonian–Carboniferous accretionary wedge (e.g. Texas-Woolomin and Coffs Harbour Blocks) or the forearc basin (Tamworth Belt) farther to the west, in which volcaniclastic-dominated sandstone units have very similar pre-Permian (principally Carboniferous) age components. This gradual variation in age patterns from Devonian–late Carboniferous time in Australia to Late Permian–mid-Cretaceous time in New Zealand suggests an evolutionary model for the Eastern Gondwanaland plate margin and the repositioning of its subduction zone. (1) A Devonian to Carboniferous accretionary wedge in the New England Orogen developing at a (present-day) Queensland position until late in the Carboniferous. (2) Early Permian outboard repositioning of the primary, magmatic arc allowing formation of extensional basins throughout the New England Orogen. (3) Early to mid-Permian translocation of the accretionary wedge and more inboard active-margin elements, southwards to their present position. This was accompanied by oroclinal bending which allowed the initiation of a new, late Permian to Early Triassic accretionary wedge (eventually the Torlesse Composite Terrane of New Zealand) in an offshore Queensland position. (4) Jurassic–Cretaceous development of this accretionary wedge offshore, in northern Zealandia, with southwards translation of the various constituent terranes of the Torlesse Composite Terrane to their present New Zealand position.

Constraints of detrital zircon U–Pb ages and Hf isotopes on the provenance of the Triassic Yidun Group and tectonic evolution of the Yidun Terrane, Eastern Tibet

Eastern Tibet to the west of the Yangtze Block consists of the Yidun and Songpan–Ganzi Terranes, separated by the Ganzi–Litang suture zone. The Yidun Terrane includes the Zhongza Massif to the west, but the eastern part of the Yidun terrane is covered by the Yidun Group extending from the south (Shangri-La region) to the north (Changtai region). The Yidun Group, from the base upward, includes the Lieyi, Qugasi, Tumugou and Lanashan formations, which are mainly composed of volcanic-flysch successions. Based on the ages of volcanic interlayers and plutonic intrusions, depositional ages of the Qugasi and Tumugou formations are considered to be slightly older than 230Ma and ca. 220–230Ma respectively, which are prominently older than the previous estimates. The Yidun Group in the Changtai region has two prominent detrital zircon age peaks at 400–480 and 880–980Ma and a minor peak at 2.45–2.50Ga. This pattern suggests a detritus source from the Zhongza Massif, which was a micro-continent separated from the western Yangtze Block. In contrast, the Yidun Group in the Shangri-La region has various zircon age spectra among different formations. The Qugasi Formation in this region has detrital zircon age patterns similar to the Yidun Group in the Changtai region. However, the overlying Tumugou Formation shows distinct age peaks at Triassic (220–240Ma), Neoproterozoic (~720–880Ma), and Paleoproterozoic (~1.75–1.90Ga). This age pattern is similar to that of the Xikang Group of the Songpan–Ganzi Terrane to the east. The detrital zircon age difference between the Qugasi and Tumugou formations in this region indicates a transition of sedimentary sources from the Zhongza Massif to locally distributed Triassic magmatic rocks at ~230Ma. It is thus suggested that the Songpan–Ganzi Terrane may have been connected to or collided with the southern part of the Yidun Terrane during the Late Triassic, whereas the Songpan–Ganzi Terrane and the northern part of the Yidun Terrane were still separated by the Ganzi–Litang Ocean.

The mid-Cretaceous transition from basement to cover within sedimentary rocks in eastern New Zealand: evidence from detrital zircon age patterns

AbstractDetrital zircon U-Pb ages for 30 Late Jurassic and Cretaceous sandstones from the Eastern Province of eastern New Zealand, combined with previously-published geochronological and palaeontological data, constrain the time of deposition in the Pahau and Waioeka terranes of the Cretaceous accretionary margin of Zealandia, and their adjacent cover strata. The zircon age patterns also constrain possible sediment source areas and mid-Cretaceous geodynamic models of the transition from basement accretionary wedge to passive-margin cover successions. Pahau Terrane deposition was mainly Barremian to Aptian but continued locally through to late Albian time, with major source areas in the adjacent Kaweka and Waipapa terranes and minor inputs from the inboard Median Batholith. Waioeka Terrane deposition was mainly Albian, with distinctive and exclusive sediment sources, principally from the Median Batholith but with minor inputs from the Western Province. Alternative tectonic models to deliver such exclusive Median Batholith and Western Province-derived sediment to the mid-Cretaceous Zealandia continental margin are: (1) the creation of a rift depression across Zealandia or (2) sinistral displacement of South Zealandia with respect to North Zealandia, to expose Western Province rocks directly at the Zealandia margin. Detrital zircon age patterns of Cretaceous cover successions of the Eastern Province of eastern New Zealand demonstrate purely local sources in the adjacent Kaweka and Waipapa terranes. Cretaceous zircon components show a decline in successions of late Early Cretaceous age and disappear by late Late Cretaceous time, suggesting the abandonment or loss of access to both the Median Batholith and Western Province as sediment sources.

Provenance variations in the Late Paleozoic accretionary complex of central Chile as indicated by detrital zircons

We present detrital zircon UPb SHRIMP age patterns for the central segment (34–42°S) of an extensive accretionary complex along coastal Chile together with ages for some relevant igneous rocks. The complex consists of a basally accreted high pressure/low temperature Western Series outboard of a frontally accreted Eastern Series that was overprinted by high temperature/low pressure metamorphism. Eleven new SHRIMP detrital zircon age patterns have been obtained for meta-turbidites from the central (34–42°S) segment of the accretionary complex, four from previously undated metamorphic complexes and associated intrusive rocks from the main Andean cordillera, and three from igneous rocks in Argentina that were considered as possible sediment source areas. There are no Mesozoic detrital zircons in the accretionary rocks. Early Paleozoic zircons are an essential component of the provenance, and Grenville-age zircons and isolated grains as old as 3Ga occur in most rocks, although much less commonly in the Western Series of the southern sector. In the northernmost sector (34–38°30′S) Proterozoic zircon grains constitute more than 50% of the detrital spectra, in contrast with less than 10% in the southern sector (39–42°S). The youngest igneous detrital zircons in both the northern Western (307Ma) and Eastern Series (345Ma) are considered to closely date sedimentation of the protoliths. Both oxygen and LuHf isotopic analyses of a selection of Permian to Neoproterozoic detrital zircon grains indicate that the respective igneous source rocks had significant crustal contributions. The results suggest that Early Paleozoic orogenic belts (Pampean and Famatinian) containing material recycled from cratonic areas of South America supplied detritus to this part of the paleo-Pacific coast. In contrast, in the southern exposures of the Western Series studied here, Permian detrital zircons (253–295Ma) dominate, indicating much younger deposition. The northern sector has scarce Early to Middle Devonian detrital zircons, prominent south of 39°S. The sedimentary protolith of the northern sector was probably deposited in a passive margin setting starved of Devonian (Achalian) detritus by a topographic barrier formed by the Precordillera, and possibly Chilenia, terranes. Devonian subduction-related metamorphic and plutonic rocks developed south of 39°S, beyond the possible southern limit of Chilenia, where sedimentation of accretionary rocks continued until Permian times.