Pb Dating Of Detrital Zircons Research Articles

U–Pb detrital zircon ages from the Aguapeí Group (Brazil): Implications for the geological evolution of the SW border of the Amazonian Craton

New U–Pb detrital zircon data of metasedimentary rocks of the Aguapeí Group, SW Amazonian Craton, are presented in this work. Three samples were analyzed by ICPMS laser ablation in order to estimate the age of the source areas of the sediments and the maximum depositional age of the basin. The samples show an Archean age of 2515Ma not yet reported in the region. Paleoproterozoic ages of 2015Ma, 1897Ma and 1812Ma were not reported in this area either, but are observed 1000–1200km to NE, in the Rio Negro-Juruena province. The group of ages ranging from 1655Ma to 1608Ma may represent zircons from the Lomas Maneches orogen, described in Bolivia. The group of zircons with ages of 1544Ma may be related to the Cachoeirinha (in Mato Grosso) or Serra da Providencia (in Rondonia) magmatic suite. The group of ages of ca 1485Ma, 1417Ma and 1411Ma may represent zircons from the adjacent Santa Helena orogen, in Mato Grosso state. Data presented in this work suggest that the maximum depositional age for the Aguapeí sediments is 1.26Ga, the youngest age among the detrital zircons analyzed. The U–Pb ages in zircon define important time constraint for the Aguapei Group sedimentary rocks deposition. In addition, the results here reported define new challenges in order to identify rocks not yet found in the region that may result in a more complete framework for SW Amazonian Craton crustal evolution.

Age and provenance of the Ergunahe Group and the Wubinaobao Formation, northeastern Inner Mongolia, NE China: implications for tectonic setting of the Erguna Massif

Here, we present the results of U–Pb dating of detrital zircons from the Ergunahe Group and the Wubinaobao Formation, within northeastern Inner Mongolia, NE China, with the aim of constraining the tectonic setting of the Erguna Massif. The majority of detrital zircons from five samples collected from the Ergunahe Group and the Wubinaobao Formation are magmatic, although some zircons have metamorphic growth rims. Zircons in two mica schists and in feldspar–quartz sandstone from the Ergunahe Group yield age populations that cluster around 738, 760, 792, 837, 890, 964, and 1050 Ma, whereas zircons from two quartz sandstones within the Wubinaobao Formation yield age populations that cluster at 466, 484, 515, 738, 795, 837, and 894 Ma. These data, combined with detrital zircon age populations (ca. 712 Ma) from the adjacent Xinghuadukou Group, and the fact that the Ergunahe Group intruded by Caledonian gabbros is overlain by upper Silurian units, indicate that the Ergunahe Group formed at 738–712 Ma (i.e. during the Neoproterozoic). In addition, the Wubinaobao Formation is subdivided into two units: a calcareous siltstone unit within the western part of the study area and a quartz sandstone within the eastern part. The calcareous siltstone formed at 712–795 Ma, similar to the Ergunahe Group, whereas the quartz sandstone formed between the 466 Ma and late Silurian. The age spectra of detrital zircons from the Ergunahe Group and the Wubinaobao Formation indicate that sediment in both of these units was derived from terranes that outcrop around the basin. The widespread occurrence of Neoproterozoic detrital zircons within both the Ergunahe Group and the Wubinaobao Formation suggests that Precambrian terranes are present within the Erguna Massif and that the massif has an affinity to the Siberian Craton.

Geochemical zonation across a Neoproterozoic orogenic belt: Isotopic evidence from granitoids and metasedimentary rocks of the Jiangnan orogen, China

In order to understand how Late Mesoproterozoic to Early Neoproterozoic orogenic belts evolved during the assembly and rifting of the supercontinent Rodinia, we have carried out detailed studies on the geochemical compositions of Early Neoproterozoic crust across the Jiangnan orogen (JO) which connects the Yangtze and Cathaysia blocks on the northwestern margin of Rodinia. A gradual geochemical variation is recognized from east to west, based on comparisons of whole-rock Nd isotopes, U–Pb age spectra of detrital zircons, and Hf isotopes in magmatic zircons and detrital zircons from the Neoproterozoic granitoids and metasedimentary basement sequences in the JO. LA-ICP-MS U–Pb dating of detrital zircons from the sediments and magmatic zircons from interlayered volcanic rocks suggests that the folded basement sequences formed within the span 860–825Ma, implying the final amalgamation of the Yangtze and Cathaysia blocks occurred no older than ca 825Ma. The 950–820Ma detrital zircons strongly dominate in the eastern basement sequences, and most of them show moderately to highly positive ɛHf(t). In contrast, many of the Early Neoproterozoic detrital zircons in the western JO have moderately negative ɛHf(t) and more older (>1.0Ga) detrital zircons were found in this area. We suggest that the metasedimentary basement sequences in the JO were deposited in retro-arc foreland basins which originally evolved from back-arc basins, and the change of provenance controlled the variation in crustal geochemistry of crust across the JO. Sediments in the eastern basement sequences have been sourced mainly from the juvenile subduction-related igneous rocks to the east, with a few from the central Yangtze Block, whereas those in the western JO may have been located far from arc terranes to the east and thus received more older recycled detritus from the southern part of the South China Block. Moreover, the Hf isotopes of the detrital zircons imply episodic crustal growth in the provenance of the JO metasedimentary basement sequences, with age peaks at 1.0–0.8Ga, 1.75–1.50Ga and 2.60–2.45Ga. The early crust in South China may have been formed mainly at around 3.8Ga ago, and contains some Hadean components (ca 4.1Ga).

U–Pb detrital zircon provenance of the Saramuj Conglomerate, Jordan, and implications for the Neoproterozoic evolution of the Red Sea region

The latest stage in the evolution of the northernmost Arabian-Nubian Shield is characterized by the development of volcano-sedimentary successions. In Jordan the Saramuj Conglomerate Formation is considered to be one of these post-tectonic basins. It is polymict and poorly sorted with wide range of clast compositions, roundness and size. We present the first SIMS U–Pb dating of detrital zircons from two sandstone samples representative for the conglomerate matrix and of four clasts from the Saramuj Conglomerate for provenance and age determinations. The relative probability curve for the matrix samples indicates a major contribution (85%) from c. 600 to 650Ma, subclusters at 624 and 640Ma, a minor source from 700 to 750Ma, and a clear gap between 650 and 700Ma. These ages are consistent with those obtained from andesitic, rhyodacitic, granitic and gneiss clasts (624, 642, 650 and 734Ma respectively). In contrast to the adjacent volcano-sedimentary successions in the Elat area, Sinai and the Eastern Desert, no ages older than 750Ma were found. The good match between the known ages of the nearby exposed basement with the matrix ages and the immature nature of the sediments implies that the principal input was locally derived erosional detritus. The age of the youngest 10 detrital zircons at c. 615Ma represents the maximum age of deposition, which is consistent with the stratigraphic position of the Saramuj Conglomerate. Clast ages of 642Ma and 650Ma are interpreted as evidence for a magmatic source that has not been recognized in SW Jordan. This study implies that the volcano-sedimentary successions in the northernmost Arabian-Nubian shield may be broadly coeval but have distinct provenance and therefore evolved as isolated basins. Furthermore, U–Pb zircon provenance analysis allows us to recognize igneous products that are no longer preserved and/or exposed in the region.

U–Pb detrital zircon geochronology of the Dalradian Supergroup, Shetland Islands, Scotland: implications for regional correlations and Neoproterozoic–Palaeozoic basin development

U–Pb detrital zircon data show that the East Mainland Succession, the presumed correlative of the Dalradian Supergroup in the Shetland Islands, Scotland, is dominated by Mesoproterozoic and Archaean material, with some Palaeoproterozoic detritus. The data are most consistent with derivation from eastern Laurentia, although western Baltica sources cannot be excluded. A magmatic event at c . 576 Ma supplied detritus to the Clift Hills Group, and was the source of high-temperature fluids that resulted in growth of new metamorphic zircon, and altered old detrital grains within the underlying sedimentary pile. This provides a constraint on the age of the global Shuram–Wonaka event recognized within the Whiteness Group, which underlies the Clift Hills Group. The presence of common Archaean detritus is compatible with broad time-correlation of the East Mainland Succession with the Dalradian Supergroup. However, differences in age, thickness and basin evolution are consistent with deposition in separate basins along the extending Laurentian margin during supercontinent break-up and development of the Iapetus Ocean. Similarities in the detrital zircon records of the East Mainland Succession and the offshore Devonian–Carboniferous Clair Group permit derivation, at least in part, of the latter from the Shetland Islands and proximal sources on the adjacent continental shelf. Supplementary material: SIMS and LA-ICP-MS analytical data, and statistical analyses are available at www.geolsoc.org.uk/SUP18674 .

The Vendian passive continental margin in the southern Siberian Craton: geochemical and isotopic (Sr, Sm–Nd) evidence and U–Pb dating of detrital zircons by the LA-ICP-MS method

Geochemical and isotopic (Sm–Nd and Sr) studies of deposits of the Baikal and Oselok Groups in the southern Siberian Craton and LA-ICP-MS U–Pb dating of detrital zircons show that they accumulated in passive continental-margin settings in the Vendian. The time limits of sedimentation were assessed on the basis of Sr chemostratigraphy of carbonate deposits of the Baikal Group and LA-ICP-MS U–Pb dating of detrital zircons in first-cycle terrigenous deposits of the Oselok Group. The main provenances for rocks of these groups were constant. These were rocks of the cover and basement of the Siberian Craton. Tuffite horizons in upper portions of the groups are the only sign of Late Vendian activation of this block, which is reflected in changes of geochemical indices of terrigenous rocks and their younger Sm–Nd model ages.

Early Carboniferous paleogeography of the northern Verkhoyansk passive margin as derived from U–Pb dating of detrital zircons: role of erosion products of the Central Asian and Taimyr–Severnaya Zemlya fold belts

The first U–Pb dating of detrital zircons from the Lower Carboniferous sandstones in the frontal part of the northern Verkhoyansk fold-and-thrust belt showed that detrital zircon age spectra for the Lower Visean (Krestyakh Formation) and the Upper Visean–Serpukhovian (Tiksi Formation) rocks are quite different. The Early Visean sandstones contain up to 95% detrital zircons of Precambrian age, while those of Late Visean–Serpukhovian age, only 55%. The shape of age distribution plots of Precambrian zircons for both samples is similar, indicating that reworking of terrigenous sediments of the Krestyakh Formation or the same sources dominated in Early Visean time (crystalline basement of the craton, eroded Meso- and Neoproterozoic sedimentary complexes, and igneous rocks of Central Taimyr) contributed significantly to the accumulation of the Late Visean–Serpukhovian deposits. In the rocks of the Tiksi Formation, 45% of detrital zircons are of Paleozoic age, while 24% are Early Paleozoic, with prevailing Cambrian and Ordovician ages. Possible provenance areas with abundant igneous rocks of this age could be the Taimyr–Severnaya Zemlya and Central Asian fold belts extending along the northern, western or southwestern margins of the Siberia. The presence of Middle–Late Devonian zircons is thought to be related to the erosion of granitoids of the Yenisei Ridge and the Altai–Sayan region. Early Carboniferous detrital zircons probably had a provenance in igneous rocks of the Taimyr–Severnaya Zemlya fold belt, on the assumption that collision between the Kara block and the northern margin of the Siberian continent had already occurred by that time. In Early Visean time, sedimentation occurred in small deltaic fans, likely along steep fault scarps that formed as a result of Middle Paleozoic (Devonian–Carboniferous) rifting. The clastic material came from small rivers that eroded the nearby area. Late Visean–Serpukhovian time was marked by a sharp increase in the amount of clastic material and by the appearance of detrital zircons coming from new provenance regions, such as fold belts extending along the northern and southwestern margins of the Siberian continent. A large river system, which was able to transport clastic material over large distances to deposit it in submarine fans on the northern Verkhoyansk passive continental margin, had already existed by that time.

South China continental margin signature for sandstones and granites from Palawan, Philippines

We report results of heavy mineral analysis and U–Pb dating of detrital zircons from metasediments and Cenozoic sandstones, and U–Pb dating of zircons from Cenozoic granites of the North Palawan Continental Terrane (NPCT) and the South Palawan Terrane (SPT). The NPCT metasediments are derived mainly from granitic and metamorphic rocks of continental character. They contain zircons that indicate a maximum depositional age of Late Cretaceous and other age populations indicating a South China origin. The sediments were deposited on the South China margin before rifting of the continental margin during opening of the South China Sea. Miocene SPT sandstones contain similar heavy mineral assemblages suggesting sources that included NPCT metasediments, metamorphic basement rocks at the contact between the SPT and the NPCT, South China Sea rift volcanic and/or minor intrusive rocks, and the Palawan ophiolite complex. The SPT sandstones are very similar to Lower Miocene Kudat Formation sandstones of northern Borneo suggesting a short-lived episode of sediment transport from Palawan to Borneo in the Early Miocene following arc-continent collision. U–Pb dating of zircons shows that the Central Palawan granite is Eocene (42±0.5Ma). The Capoas granite was intruded during a single pulse, or as two separate pulses, between 13.8±0.2Ma and 13.5±0.2Ma. Inherited zircon ages from the Capoas granite imply melting of continental crust derived from the South China margin with a contribution from Cenozoic rift-related and arc material.

Precambrian terrane within the Songnen–Zhangguangcai Range Massif, NE China: Evidence from U–Pb ages of detrital zircons from the Dongfengshan and Tadong groups

The Central Asian Orogenic Belt (CAOB) is a natural laboratory of the Phanerozoic accretionary orogen. The eastern section of the CAOB contains several microcontinental massifs, and it is unknown whether these massifs carry Precambrian basement. Here we present the results of U–Pb dating of detrital zircons from the Dongfengshan and Tadong groups in the eastern margin of the Songnen–Zhangguangcai Range Massif. The Dongfengshan and Tadong groups are subdivided, from bottom to top, into the Liangzihe, Huapigou, and Honglin formations, and the Lalagou and Zhudundian formations, respectively. Zircons from a two-mica quartz schist (sample HCM4-2) in the Liangzihe Formation yielded eight age populations, from 821 to 1802Ma, whereas zircons from a two-mica quartz schist (sample 12HCM3-2) in the Huapigou Formation yielded four age populations (752, 803, 821, and 851Ma). Zircons from a two-mica schist in the Lalagou Formation of the Tadong Group yielded two age populations (450 and 485Ma), and zircons from a biotite-bearing plagioclase gneiss in the lower part of the Zhudundian Formation yielded five main age populations, from 551 to 1815Ma. Samples 11NNA5-1 and 11HNA10-1 from the upper layer of the Zhudundian Formation yielded six main age groups, from 749 to 948Ma. These data, together with the ages of zircons within a tonalite that intrudes the Tadong Group and the overlying Chenming Formation, indicate the presence of a Precambrian terrane associated with sedimentation at various times during the Neoproterozoic, including at ~821–752, ~752–560, and ~750–516Ma, on the eastern margin of the Songnen–Zhangguangcai Range Massif. The Dongfengshan and Tadong groups were previously thought to be Proterozoic, but our study reveals that they constitute a Neoproterozoic–Late Paleozoic tectonic mélange. In addition, the widespread occurrence of detrital zircons with ages of 0.75–0.95, 1.5–1.6, 1.8, and 2.4–2.5Ga provides evidence of a Neoproterozoic magmatic event and the presence of remnant ancient basement material within the Songnen–Zhangguangcai Range Massif.

The tectonic evolution of the Tianshan Orogenic Belt: Evidence from U–Pb dating of detrital zircons from the Chinese southwestern Tianshan accretionary mélange

The Tianshan Orogenic Belt, which is located in the southwestern part of the Central Asian Orogenic Belt (CAOB), is an important component in the reconstruction of the tectonic evolution of the CAOB. In order to examine the evolution of the Tianshan Orogenic Belt, we performed detrital zircon U–Pb dating analyses of sediments from the accretionary mélange from Chinese southwestern Tianshan in this study. A total of 542 analyzed spots on 541 zircon grains from five samples yield Paleoarchean to Devonian ages. The major age groups are 2520–2400Ma, 1890–1600Ma, 1168–651Ma, and 490–390Ma. Provenance analysis indicates that, the Precambrian detrital zircons were probably mainly derived from the paleo-Kazakhstan continent formed before the Early Silurian by amalgamation of the Kazakhstan–Yili microplate, the Chinese central Tianshan terrane and the Kyrgyz North and Middle Tianshan blocks, while detrital zircons with Paleozoic ages mainly from igneous rocks of the continental arc generated by the northward subduction of the south Tianshan paleocean. The age data correspond to four tectono-thermal events that took place in these small blocks, i.e., the continental nucleus growth during the Late Neoarchean–early Paleoproterozoic (~2.5Ga), the evolution of the supercontinents Columbia (2.1–1.6Ga) and Rodinia (1.3–0.57Ga), and the arc magmatism related with the Phanerozoic orogeny. The Precambrian zircons show a similar age pattern as the Tarim and the Cathaysia cratons and the Eastern India–Eastern Antarctica block but differ from those of Siberia distinctly. Therefore, the Tianshan region blocks and the Kazakhstan–Yili microplate have a close affinity to the eastern paleo-Gondwana fragments, but were not derived from the Siberia craton as proposed by some previous researchers. These blocks were likely generated by rifting accompanying Rodinia break-up in late Precambrian times.The youngest ages of the detrital zircons from the subduction mélange show a maximum depositional age of ca. 390Ma. It is coeval with the end of an earlier arc magmatic pulse (440–390Ma) but a bit older than a younger one at 360–320Ma and nearly 70–80Ma older than the HP–UHP metamorphism in the subduction zone (320–310Ma).

Detrital zircons U–Pb SHRIMP ages and provenance of La Modesta Formation, Patagonia Argentina

This paper summarizes the geology of the Paleozoic La Modesta Formation in Patagonia, Argentina, and presents new SHRIMP U–Pb dating of detrital zircons from muscovite-chlorite schist and tourmalinite. Also complementary geochemical and lead isotopic data are presented, indicating that the protoliths were formed from upper crustal rocks by the contribution of a large input from recycled (or felsic) sources. The maximum age of sedimentation of La Modesta Formation is about 446 ± 6 Ma. The basin closure (or eventually a paleocurrent shift) occurs at Lower Devonian before the exhumation of the Middle-Devonian granitoids of the Rio Deseado Complex (Deseado Massif). Many of the detrital zircons are igneous and record Ordovician ages, with a prominent Lower Ordovician-age peak at approximately 473 Ma. Most favourable candidates to provide the younger zircons in the basin would Ordovician granites of the Rio Deseado Complex (Deseado Massif) and Punta Sierra Plutonic Complex (Somun Cura Massif). Older zircons have peaks of different importance (including Brasiliano and Grenvillian ages) between 530 and 700, 750–1500, 1750–2000 and 2550–2700 Ma. La Modesta Formation is also a potential area of materials (detrital zircon) to the basin where the rocks of the Eastern Andean Metamorphic Complex and equivalent formations of the Andean region were generated.

U–Pb ages of detrital zircons within the Inthanon Zone of the Paleo-Tethyan subduction zone, northern Thailand: New constraints on accretionary age and arc activity

U–Pb dating of detrital zircons was performed on mélange-hosted lithic and basaltic sandstones from the Inthanon Zone in northern Thailand to determine the timing of accretion and arc activity associated with Paleo-Tethys subduction. The detrital zircons have peak ages at 3400–3200, 2600–2400, 1000–700, 600–400, and 300–250Ma, similar to the peaks ages of detrital zircons associated with other circum-Paleo-Tethys subduction zones. We identified two types of sandstone in the study area based on the youngest detrital zircon ages: Type 1 sandstones have Late Carboniferous youngest zircon U–Pb ages of 308±14 and 300±16Ma, older than associated radiolarian chert blocks within the same outcrop. In contrast, Type 2 sandstones have youngest zircon U–Pb ages of 238±10 and 236±15Ma, suggesting a Middle Triassic maximum depositional age. The youngest detrital zircons in Type 1 sandstones were derived from a Late Carboniferous–Early Permian ‘missing’ arc, suggesting that the Sukhothai Arc was active during sedimentation. The data presented within this study provide information on the development of the Sukhothai Arc, and further suggest that subduction of the Paleo-Tethyan oceanic plate beneath the Indochina Block had already commenced by the Late Carboniferous. Significant Middle Triassic arc magmatism, following the Late Carboniferous–Early Permian arc activity, is inferred from the presence of conspicuous detrital zircon U–Pb age peaks in Type 2 sandstones and the igneous rock record of the Sukhothai Arc. In contrast, only minimal arc activity occurred during the Middle Permian–earliest Triassic. Type 1 sandstones were deposited between the Late Permian and the earliest Triassic, after the deposition of associated Middle–Late Permian cherts that occur in the same mélanges and during a hiatus in Sukhothai Arc magmatism. In contrast, Type 2 sandstones were deposited during the Middle Triassic, coincident with the timing of maximum magmatism in the Sukhothai Arc, as evidenced by the presence of abundant Middle Triassic detrital zircons. These two types of sandstone were probably derived from discrete accretionary units in an original accretionary prism that was located along the western margin of the Sukhothai Arc.

Tectonic linkage between the Korean Peninsula and mainland Asia in the Cambrian: Insights from U–Pb dating of detrital zircon

The establishment of robust Paleozoic tectonic links between parts of the Korean Peninsula and cratonic blocks within China remains uncertain, despite their important implications for the overall tectonic evolution of East Asia. Here we provide new SHRIMP U–Pb detrital zircon geochronological constraints on correlations between sedimentary rocks of the Taebaeksan Basin (Cambrian–Ordovician) of South Korea and possible source rocks in the North and South China cratons. The detrital grain compositions and whole-rock rare earth element (REE) compositions of sandstones from the Cambrian formations in western (Sambangsan) and eastern (Myeonsan) parts of the Taebaeksan Basin suggest that the sedimentary provenance of these two formations is either a recycled orogen or a magmatic arc. The magmatic (eastern part) versus metamorphic (western part) origins inferred for the youngest populations (ca. 0.5–0.6Ga) of detrital zircon grains from the Cambrian formations collectively indicate that rapid uplift and erosion of the source rocks for the formations took place soon after the associated magmatic and metamorphic events. Thus, we propose that the paleo-sedimentary environments in which these two formations were deposited may have been retroarc basins with the detrital zircons originating from magmatic arcs. The Early Cambrian formation in the eastern Taebaeksan Basin contains populations of detrital zircon grains that show prominent age peaks at ca. 2.0Ga and ca. 1.8Ga, and a distinct lack of Meso- to Neoproterozoic ages, whereas the Middle Cambrian formation in the western Taebaeksan Basin exhibits age peaks at ca. 1.0Ga and ca. 0.7Ga. These age spectra imply that the western Taebaeksan area at the margin of the North China Block may once have been near Gondwana, whereas the eastern Taebaeksan area may have been situated at the margin of the North China Block more distant from Gondwana.

Provenance of lateritic bauxite deposits in the Wuchuan–Zheng’an–Daozhen area, Northern Guizhou Province, China: LA-ICP-MS and SIMS U–Pb dating of detrital zircons

The provenance of the large and super-large scale bauxite deposits developed in the Wuchuan–Zheng’an–Daozhen (WZD) alumina metallogenic province in the Yangtze Block of South China is poorly understood. LA-ICP-MS and SIMS U–Pb dating of detrital zircons from bauxite ores and the underlying Hanjiadian Group in the WZD area provide new constrains on the provenance of the WZD bauxite and provide new insight on the bauxite ore-forming process. The ages of the detrital zircons in the bauxites and the zircons in the Hanjiadian Group are similar suggesting that the bauxites are genetically related to the Hanjiadian sediments. The detrital zircon populations of the four samples studied show four primary age peaks: 2600–2400Ma, 1900–1700Ma, 1300–700Ma and 700–400Ma. The age distribution of detrital zircons indicates that they are probably derived from various sources including Neoproterozoic, Mesoproterozoic, Paleoproterozoic, Archean and some minor Paleozoic sources. The most abundant age population contains a continuous range of ages from 1300 to 700Ma, ages consistent with subduction-related magmatic activities (1000–740Ma) along the western margin of the Yangtze Block and the worldwide Grenville orogenic events (1300–1000Ma). Thus, it is suggested that the main provenances of the WZD bauxite and the Hanjiadian Group are the Neoproterozoic igneous rocks in the western Yangtze Block and the Grenville-age igneous rocks in the southern Cathaysia Block. In addition, this work verifies that the global Grenville orogenic events and subduction-related magmatic activities associated with the Yangtze Block had a significant influence on the formation of the WZD bauxite deposits.

Saps II et valorisation des séjours en unité de surveillance continue : une étonnante inadéquation

We present results of combined in situ U–Pb dating of detrital zircons and zircon Hf and whole-rock Nd isotopic compositions for high-grade clastic metasedimentary rocks of the Slyudyansky Complex in eastern Siberia. This complex is located southwest of Lake Baikal and is part of an early Paleozoic metamorphic terrane in the eastern part of the Central Asian Orogenic Belt (CAOB). Our new zircon ages and Hf isotopic data as well as whole-rock Nd isotopic compositions provide important constraints on the time of deposition and provenance of early Paleozoic high-grade metasedimentary rocks as well as models of crustal growth in Central Asia. Ages of 0.49–0.90 Ga for detrital zircons from early Paleozoic high-grade clastic sediments indicate that deposition occurred in the late Neoproterozoic and early Paleozoic, between ca. 0.62–0.69 and 0.49–0.54 Ga. Hf isotopic data of 0.82–0.69 Ga zircons suggest Archean and Paleoproterozoic (ca. 2.7–2.8 and 2.2–2.3 Ga; Hfc = 2.5–3.9 Ga) sources that were affected by juvenile 0.69–0.82 Ga Neoproterozoic magmatism. An additional protolith was also identified. Its zircons yielded ages of 2.6–2.7 Ga, and showed high positive εHf(t) values of +4.1 to +8.0, and Hf model ages tHf(DM) = tHfc = 2.6–2.8 Ga, which is nearly identical to the crystallization ages. These isotopic characteristics suggest that the protolith was quite juvenile. The whole-rock Nd isotopic data indicate that at least part of the Slyudyansky Complex metasediments was derived from “non-Siberian” provenances. The crustal development in the eastern CAOB was characterized by reworking of the early Precambrian continental crust in the early Neoproterozoic and the late Neoproterozoic–early Paleozoic juvenile crust formation.

Tracing Alpine sediment sources through laser ablation U–Pb dating and Hf‐isotopes of detrital zircons

AbstractAlpine provenance studies based on conventional methods such as sandstone framework grain and heavy mineral analyses are now enhanced by improved techniques in laser ablation inductively coupled plasma mass spectrometry detrital zircon analysis. Although the conventional methods appear to have reached their limits of resolution in palaeogeographic problems, laser ablation inductively coupled plasma mass spectrometry U–Pb dating of detrital zircons adds the time dimension to the provenance analysis. Hafnium‐isotope ratios measured on dated zircons give further information on the origin of the magmas in which the detrital zircons have grown. This study reports detrital zircon U–Pb dating and Hf‐isotope results from sandstone formations related to rifting, drifting and subduction settings at different stages of the Alpine Tethys development. This study is a first evaluation of the correlation between U–Pb age and isotopic features of detrital zircons aimed at describing source terranes in different palaeogeographic domains in the Alpine Tethys area. Pan‐African/Cadomian (Ediacaran–Ordovician), Variscan (Middle Devonian–Carboniferous) and Post‐Variscan (Permian) detrital zircon populations are present in nearly all palaeogeographic settings, but in varying amounts. Single Mesoproterozoic and Palaeoproterozoic detrital zircons are found as minor populations. When comparing the northern and southern margins of the Alpine Tethys, the southern margin detrital sources are characterized mostly by a decreased occurrence or by the absence of Silurian–Devonian zircons. A major distinction between northern (Helvetic, North and Middle Penninic domains) and southern (Austro‐Alpine and South Alpine domains) detrital sources is the occurrence of Triassic zircons at the southern Alpine Tethys margin during rifting and subduction stage sedimentation. Hafnium‐isotope ratios measured on uppermost Permian–Triassic zircons from the South Alpine domain suggest a continental crust derivation of the hosting magmas, as expected in a continental rift environment. In the late stage of Alpine convergence (Late Cretaceous–Palaeogene), the Permian–Triassic zircons are reworked into basins situated on the northern Alpine Tethys margin.

Structural and geochronological constraints on the evolution of the eastern margin of the Tanzania Craton in the Mpwapwa area, central Tanzania

A study of the position, nature and geochronology of the eastern margin of the Tanzania Craton near Mpwapwa yields new constraints on Archaean to Neoproterozoic orogenesis of central Tanzania. The eastern part of the craton comprises typical Neoarchaean grey granodioritic orthogneisses dated with the LA-ICP-MS method by U–Pb zircon at ca. 2.7Ga. A gradual eastward increase in strain in these rocks culminates in a 1–2km wide, locally imbricated, north–south-trending, ductile thrust/shear zone with an oblique top-to-the-NW sense of movement. East of the craton-edge shear zone, high-grade supracrustal rocks are termed the “Mpwapwa Group” in view of uncertain regional correlations. There is an apparent lithological zonation of the Mpwapwa Group parallel to the craton margin shear zone. In the west, the group consists of typical “shelf facies” metasedimentary rocks (marbles, calc-silicates, quartzites, etc.). U–Pb dating of detrital zircons from two quartzites reveal only Archaean detritus, constraining their maximum depositional age to <ca. 2.6Ga. The shelf rocks pass eastwards into semi-pelitic gneisses interlayered with bimodal mafic-felsic gneisses, which may have volcanic protoliths and are intruded by multiple mafic sills. Dating of a felsic gneiss showed it to probably be a Neoarchaean rock which underwent Palaeoproterozoic metamorphism during the Usagaran event at ca. 1930Ma. This date likely represents initial juxtaposition of the (Archaean) Mpwapwa Group against the Tanzania Craton. Consequently the Group are not considered to be stratigraphic correlates of the Usagaran Konse Group or Isimani Suite seen further south, but rather form part of the Neoarchaean crust of the “Western Granulite” terrane of the East African Orogen. The Mpwapwa Group was intruded by weakly foliated biotite granite at 1873±31Ma. Zircons in the granite have metamorphic rims dated between 550 and 650Ma that grew during the East African orogenic event.Distinctive para- and orthogneisses, including charnockite dated at 2707±21Ma, outcrop in the southern part of the area. A sliver of southern tonalitic orthogneiss, entrained in the craton margin shear zone, is an igneous rock of probable early Palaeoproterozoic or Archaean age (>ca. 2300Ma) with a strong metamorphic overprint at ca. 1960Ma (zircon), confirmed by a metamorphic titanite age of ca. 1990Ma, again believed to date the initial phase of craton-margin shearing and juxtaposition of the Archaean crustal blocks. The role of the Neoproterozoic East African orogeny in the evolution of the craton margin is unclear, but the geometry of the shear zone, the presence of Neoproterozoic zircon rims in the Palaeoproterozoic granite and published studies from nearby, all suggest that the latest movements on the shear zone may be Neoproterozoic in age and that the structure may represent the local western front of the East African Orogeny.

Provenance analysis of Permian sandstones in the central and southern Da Xing'an Mountains, China: Constraints on the evolution of the eastern segment of the Central Asian Orogenic Belt

Modal, chemical and U–Pb zircon data from Permian sandstones in the central and southern Da Xing'an Mountains (eastern Inner Mongolia, China) constrain, for the first time, plate collision processes between the northern margin of the North China craton and the composite Erguna–Xing'an–Songliao block. The study area is located between the Ondor Sum-Xar Moron and Hegenshan suture zones of the eastern segment of the Central Asian Orogenic Belt. Modal and geochemical analyses of Permian sandstones suggest derivation from dissected continental arc and recycled orogenic sources. LA-ICP-MS U–Pb detrital zircon data from sandstones indicate Early Permian to earliest Triassic maximum depositional ages (278±4Ma to 249±3Ma). These data also show two uniform age groups of 270–280Ma and 310–320Ma, and we interpret their source to be mainly the Sonidzuoqi–Xilinhot–southern Xi Ujimqin magmatic arc in the north (the southern margin of the Xing'an–Erguna block). The sample from the Upper Permian to lowermost Triassic Linxi Formation in the Linxi area also contains zircons with age groups of ~1800Ma and ~2500Ma, consistent with derivation from the northern margin of the North China craton, which lies to the south. Therefore, the collision between the North China craton and the Xing'an–Erguna block began during the deposition of the Linxi Formation, and the final closure of the intervening oceanic basin occurred during ca. Late Permian–earliest Triassic times, forming the Ondor Sum-Xar Moron suture zone.

On the visualisation of detrital age distributions

Since the development of SIMS and LA-ICP-MS technologies in the 1980s and 1990s, single grain U–Pb dating of detrital zircon has quickly become the most popular technique for sedimentary provenance studies. Currently by far the most widespread method for visualising detrital age distributions is the so-called Probability Density Plot (PDP), which is calculated by summing a number of Gaussian distributions whose means and standard deviations correspond to the individual ages and their respective analytical uncertainties. Unfortunately, the PDP lacks a firm theoretical basis and can produce counter-intuitive results when data quantity (number of analyses) and/or quality (precision) is high. As a more robust alternative to the PDP, this paper proposes a standard statistical technique called Kernel Density Estimation (KDE), which also involves summing a set of Gaussian distributions, but does not explicitly take into account the analytical uncertainties. The Java-based DensityPlotter program (http://densityplotter.london-geochron.com) was developed with the aim to facilitate the adoption of KDE plots in the context of detrital geochronology.

No Paleozoic metamorphics in Palawan (the Philippines)? Evidence from single grain U–Pb dating of detrital zircons

The Palawan Continental Terrane (PCT) is a fragment of the margin of SE China that drifted south as a result of the Cenozoic opening of the South China Sea. This fragment is of great interest as it may contain a record of the early history of the continental margin of SE China that is not exposed on the mainland. The age and potential correlations of meta-sediments exposed on Palawan Island, Philippines, with those exposed on the other islands of Philippine Archipelago and Asia are a long standing problem of the geology of this island. Given the presence of non-metamorphic sedimentary sequences of Permian and Triassic age in the northern part of the island, a Paleozoic age was inferred for the metamorphics but recently also a younger age for these rocks was considered possible. U/Pb dating of detrital zircons by the laser-ablation ICP–MS method reveals the presence of 80–98Ma old zircons in all of the usually distinguished units, hence despite significant differences in degree of metamorphism and tectonic deformation, all meta-sediments appear to be of late Cretaceous or younger age. Thus, in principle, these clastic rocks could be overly derived from the older sequences. However, the relatively higher degree of metamorphism of the younger rocks suggests a tectonic contact with the older sequences.