Early Paleozoic Zircons Research Articles

A Carboniferous to Permian tectono-paleogeographic reconstruction for the southernmost Central Asian Orogenic Belt

The Central Asian Orogenic Belt was formed by the subduction to closure of the Paleo-Asian Ocean (PAO). However, it is highly controversial about the closing time of the PAO, especially its middle segment in the northern Alxa orogenic belt (NAOB). In this study, the new and published zircon U–Pb and Hf data for the Carboniferous to Permian sediments across the NAOB have been integrated to reply the above problem. The depositional ages have been constrained as the Carboniferous to Permian by the detrital zircon ages, fossil assemblages and stratigraphic correlation. The Carboniferous sandstones are dominated by the Paleozoic zircons (mainly around 380–510 Ma) with a few Precambrian zircons. The late Cambrian to early Carboniferous zircons with positive to slightly negative εHf(t) values were probably sourced from the orogen itself. The early Paleozoic zircons with slightly to extremely negative εHf(t) values and the late Archean to Paleoproterozoic zircons were likely derived from the surrounding cratonic blocks in the south. For the Permian samples, the Carboniferous to Permian age signal is enhanced. The Permian zircons yield similar age peaks around 278–279 Ma and similar εHf(t) values, and thus shared a similar source. Thus, the Carboniferous to Permian sediments received detritus across the PAO, indicating the closure of the PAO. Subsequently, the NAOB entered into an extensional setting based on the detrital zircon age patterns, rift-related volcanic rocks and basin analysis. Finally, a tectono-paleogeographic reconstruction from the Carboniferous relic sea and marine transgression to Permian marine regression-transgression-regression with crustal extension was proposed.

Detrital zircons from high-pressure trench sediments (Qilian Orogen): Constraints on continental-arc accretion, subduction initiation and polarity of the Proto-Tethys Ocean

The Qilian Orogen in the northern Tibetan plateau records the tectonic history of the Proto-Tethys Ocean from its initial spreading, subduction to final closure. However, the timing of subduction initiation, subduction polarity and arc volcanic processes of the Proto-Tethys Ocean remain controversial. In this contribution, we present geochronological and Hf isotopic studies for 812 detrital zircons from blueschist- to eclogite-facies metamorphic sedimentary rocks from the trench and accretionary wedge in the Proto-Tethys subduction zone in the North Qilian suture zone. Out of all the U-Pb age data, the Neoproterozoic to Early Paleozoic zircons reveal the timing of opening and closure of the Proto-Tethys Ocean. We show that ∼50 % of the original sediments were derived from the arc-related magmas, with ages ranging from 535 Ma to 441 Ma. This range represents the time from subduction initiation to closure of the Proto-Tethys Ocean in the Qilian Orogen. Based on the closer resemblance of statistical ages to the crust to the north (Alxa) than the south (Central Qilian), we believe the initial subduction polarity of the Proto-Tethys Ocean is northward. The corresponding εHf(t) values (−11 ∼ +15) shows characteristics of continental arc formed by subduction process. The massive intrusion of arc magma during subduction led to a significant crustal growth, and the crustal thickness estimates based on Eu anomalies indicate that the thickness of the continental margin varies from ∼60 km at 500–490 Ma to ∼45 km at ca. 450 Ma, suggesting an evolution process from compression to back-arc extension.

Carboniferous slab-retreating subduction of backarc oceans: the final large-scale lateral accretion of the southern Central Asian Orogenic Belt

During Carboniferous time, tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt (CAOB), although its origin remains unclear. Herein, we presented zircon U-Pb-Hf and whole-rock geochemical and Sr-Nd isotopic data for a suite of volcanic and pyroclastic rocks from the Khan-Bogd area in southern Mongolia. These Carboniferous pyroclastic rocks generally have some early Paleozoic zircons, probably derived from the granitic and sedimentary rocks of the Lake Zone and the Gobi-Altai Zone to the north, indicative of a continental arc nature. In addition, they have a main zircon U-Pb age of ca. 370–330 Ma, positive Hf and Nd isotopes, and mafic-intermediate arc affinity, similar to the coeval arc magmatism. Moreover, the pyroclastic rocks of the northern area have more mafic and older volcanic components with depositional time (ca. 350–370 Ma; Visean and Bashkirian stages) earlier than that in the southern area (mainly ca. 350–315 Ma; Serpukhovian and Bashkirian stages). Combining a preexisting northward subduction supported by the available magnetotelluric data with a slab rollback model of the main oceanic basin of the Paleo-Asian Ocean (PAO) during Carboniferous and Triassic times, we infer that the Carboniferous arc magmatism was probably derived from a backarc ocean triggered by slab rollback. Thus, the juvenile arc volcanism of Mongolia, together with other areas (e.g., Junggar) in the southern CAOB, represented a significant lateral accretion that terminated after the Carboniferous due to a significant contraction of the PAO.

The Duration and Geodynamics of Formation of the Angara–Vitim Batholith: Results of U–Pb Isotope (LA-ICP-MS) Dating of Magmatic and Detrital Zircons

Abstract —We present results of U–Pb (LA-ICP-MS) dating of detrital zircons from the alluvial deposits of the Angarakan River (North Muya Ridge, northern Baikal region), whose drainage basin is composed mainly of granitoids of the Barguzin Complex, typomorphic for the late Paleozoic Angara–Vitim batholith (AVB). Three age clusters with peaks at 728, 423, and 314 Ma have been identified in the studied population of detrital zircons. It is shown that small outliers of igneous and metamorphic rocks, probably similar to the large AVB roof pendants mapped beyond the drainage basin, are the source of Neoproterozoic and early Paleozoic zircons. The late Paleozoic cluster comprises two close peaks at 314 and 28 Ma, which totally “overlap” with the time of the AVB formation and mark a granitoid source of the zircons. The results of detrital-zircon geochronology, together with the data on bedrocks, point to the prolonged (~40 Myr) formation of the AVB, but the intensity of magmatism during this period calls for additional study. Based on the analysis of published geological, geochemical, and geochronological data, we assume that the AVB resulted from the plume–lithosphere interaction that began in the compression setting and gave way to extension 305–300 Ma (the Carboniferous–Permian boundary), which caused replacement of “crustal” granitoids by granitoids formed from a mixed mantle–crustal source.

Three stages of early Paleozoic magmatism in the Tibetan-Himalayan orogen: New insights into the final Gondwana assembly

Earth’s evolution involves deep, hot rocks rising upward by convection to near-surface environments, as well as the unique scenarios such as the formation and breakup of Gondwana and Pangea . These processes have been well recorded by the widely distributed magmatism . To understand the tectonic evolution and Gondwana assembly, we compiled early Paleozoic zircon U–Pb ages (n = 67), in-situ zircon Hf isotopes (n = 1011), and bulk-rock elemental compositions (n = 293) and Sr–Nd isotopes of magmatic rocks in the Tibetan–Himalayan orogen. Three stages of Paleozoic magmatism were identified here, including early (>490 Ma) to middle (490–470 Ma) to late (<470 Ma) stages, in response to the final assembly of the Gondwana supercontinent . Early-stage magmatic rocks are characterized by highly variable SiO 2 (48.0–80.0 wt%) and MgO (0.02–9.65 wt%) contents with Mg# range from 5.4 to 78, K 2 O/Na 2 O ratios ranging from 0.14 to 2.81, and whole-rock Sr–Nd ( 87 Sr/ 86 Sr(i) (0.7035–0.7340), ε Nd (t) (-9.5–+1.0)) and zircon Hf (ε Hf (t) = –15 to + 8.0) isotopic compositions with significant mantle contributions; they could be generated in an Andean-type arc setting along the active northern continental Gondwana margin. Middle-stage magmas were dominated by fertile continental crustal signatures (SiO 2 > 70 wt%, A/CNK > 1.10, MgO < 2.69 wt%) in a crustal thickening setting. Late-stage magmas also have highly variable Si, Mg and isotopic components, with coeval mantle-derived magmas developing in an extensive setting. Importantly, the widespread presence of early Cambrian to late Ordovician peraluminous high-K calc-alkaline magmatism in the Tibetan–Himalayan orogen indicates that the reworking of ancient continental crustal materials played a key role in reconstructing and stabilizing the final Gondwana assembly.

The Carboniferous-Permian tectonic setting for the southernmost Central Asian Orogenic Belt: Constraint from magmatic and sedimentary records in the Alxa area, NW China

The northern Alxa orogenic belt, a junction between the western and eastern Central Asian Orogenic Belt (CAOB), is not well understood, especially in its Carboniferous to Permian tectonic history. In this paper, an integrated study incorporating the geochronology, geochemistry, and isotopes of magmatic rocks and provenance analysis of clastic rocks is conducted to address the above issue. The zircon UPb age data, both in this study and in previous studies, indicates that the Permian magmatic activities in the Alxa Block were intensive and peaked at ca. 276 Ma. The magmatic zircons yield negative εHf(t) values with a wide range, indicating their dominant derivation from the crustal reworking of the Alxa Block with the addition of juvenile materials. The Permian high-K to shoshonitic, I-type granitoids combined with the A-type granitoids/rhyolites were most likely formed in extensional settings. The late Carboniferous sandstones collected along the Badain Jaran fault yield a high proportion of early Paleozoic zircons peaked at ca. 429 Ma with both positive to negative Hf(t) values and a low proportion of Precambrian zircons with positive to negative Hf(t) values. Thus, their provenance were likely the Precambrian to Paleozoic rocks in the Alxa Block and in the terranes in the CAOB. The zircon age spectra with no indicators of Carboniferous zircons approximating their depositional age supports an extensional setting. The Permian A-type granites and volcanic rocks in the Alxa area have some geochemical affinity with the Permian alkaline granitoids in the eastern Tianshan–Beishan and central-north Inner Mongolia regions. These findings support the extension of the Gobi–Tianshan belt in the Alxa area.

Grenvillian and early Paleozoic polyphase metamorphism recorded by eclogite and host garnet mica schist in the North Qaidam orogenic belt

The North Qaidam orogenic belt (NQOB) is generally considered to be an early Paleozoic ultrahigh pressure metamorphic belt, but increasing reports of the Neoproterozoic magmatic and metamorphic events indicate that the NQOB probably also experienced the assembly of the Rodinia. However, the Neoproterozoic evolution of the NQOB is not well constrained due to the sparse records and ambiguous nature of the Neoproterozoic metamorphism. In order to reveal the multi-orogenic history of the NQOB, an integrated study of petrology, phase equilibrium modelling and geochronology was conducted on an epidote eclogite and host garnet mica schist from the Yuka–Luofengpo terrane. New zircon and monazite U–Pb ages show that the protolith of the garnet mica schist was deposited during 994–920 Ma and experienced Neoproterozoic (920–915 Ma) and early Paleozoic (451–447 Ma) polyphase metamorphism together with the enclosed eclogite. Relic omphacite inclusions were first identified in garnet and early Paleozoic zircon domains from the garnet mica schist, which provide solid evidence for the early Paleozoic eclogite facies metamorphism of the mica schist. Similar early Paleozoic peak P–T conditions of >27.4 kbar/613–670 °C and 30.2–30.8 kbar/646–655 °C were obtained for the garnet mica schist and enclosed eclogite, respectively, indicating that eclogites and their host paragneisses in this region underwent continental deep subduction as a coherent metamorphic terrane in early Paleozoic. The peak P–T conditions of the Neoproterozoic metamorphism were roughly constrained at 7.7–12.0 kbar and 634–680 °C for the garnet mica schist, based on stability field of mineral inclusions in Neoproterozoic zircons domains in P–T pseudosection, the relic garnet core composition and Ti-in-zircon thermometer. The high thermal gradients (16–37 °C/km) defined by presently our and previously reported P–T conditions indicate that the Neoproterozoic metamorphism likely occurred in continental collision setting at >945–890 Ma. Since the Grenvillian syn-orogenic granitic magmatism and metamorphism (ca. 1.0–0.9 Ga) in the NQOB are much younger than the Grenvillian orogeny in the central part of Rodinia, the Qaidam Block was probably located at the north margin of Rodinia in Neoproterozoic.

Provenance and tectonic implications of the Carboniferous sediments in the Bainaimiao arc belt, northern margin of the North China Craton: evidence from detrital zircon U–Pb–Hf isotopes and trace elements

Sedimentological and zircon U–Pb–Hf isotopic analyses of the Carboniferous strata in the Bainaimiao arc belt (BAB) provide provenance information for the northern margin of the North China Craton (NCC). The late Carboniferous strata in the eastern BAB were dominantly shallow marine carbonate-clastic deposits. Detrital zircon data show that: (1) sandstone from lower Sidaozhangpeng Formation displays two major age peaks of 369 Ma and 2522 Ma, with eHf (t) values of − 25.9 to − 20.4 and 2.2–6.4, respectively; (2) sandstone from upper Sidaozhangpeng Formation shows a significant age peak at 384 Ma, with eHf (t) values of − 25.3 to − 14.5. Determination of detrital zircon parent rock types based on trace element proxies suggests that the protolith rock types consist of felsic (73%) and mafic rocks (22%), with minor alkaline rocks (5%), implying a continental arc setting. The U–Pb–Hf dating of the Carboniferous strata in the western and eastern BAB shows different provenances: the Carboniferous sediments in the western BAB were derived from early Paleozoic magmatic rocks, micro-block (Hunshandake Block) and the NCC basement; the provenances of the Carboniferous strata from the eastern BAB were mainly local Devonian magmatic rocks, with subordinate input of the Neoarchean NCC basement rocks. The early Paleozoic zircon grains recorded by the early Devonian rhyolitic tuff and late Carboniferous sandstone indicate that the early Paleozoic arc magmatic activities also occurred in the eastern BAB.

Early to mid-Paleozoic magmatic and sedimentary records in the Bainaimiao Arc: An advancing subduction-induced terrane accretion along the northern margin of the North China Craton

The early to mid-Paleozoic subduction-induced terrane accretion along the northern margin of the North China Craton is not well understood. To address this issue, we investigate the magmatic and sedimentary records, including both new and previously published geochemical, Sr–Nd isotopic, and zircon U–Pb–Hf isotopic data from the Bainaimiao Arc. The collected gabbro–diorites and granitoids have been dated to 431–453 Ma. The gabbro–diorites have high Mg/(Mg + Fe) molar ratios (44.41–73.39); depleted Nb, Ta and Ti; and negative εNd(t) values (-9.43–-6.80). They were derived from a mantle wedge metasomatized by subduction-derived fluids with crustal contamination. The granitoids are characterized by high silica, low to high K, low Fe and Mg contents, strong fractionation of rare earth elements, and positive εHf(t) values (+1.42–+8.19). They were derived from crustal melts with juvenile additions. The clastic rocks from the Baoerhantu Group and Xibiehe Formation are dominated by early Paleozoic zircons, whereas those from the Bainaimiao Group are dominated by early Paleozoic and Precambrian zircons. Detrital zircon geochronology and field geology confirm their deposition in early to mid-Paleozoic. The U–Pb ages and petrographic and geochemical analyses indicate that the clastic rocks were deposited in arc-related basins with felsic sources from the Bainaimiao Arc. The xenocrystic and detrital zircons in the magmatic and clastic rocks, respectively, imply a Precambrian basement for the Bainaimiao Arc. The early Paleozoic magmatic rocks of the Bainaimiao Arc show secular changes with decreasing age: increasing K2O contents and Sr/Y ratios and decreasing Fe2O3T + MgO contents and εHf(t) and εNd(t) values. This is likely in response to advancing subduction and related crustal thickening. Accordingly, the following tectono-paleogeographic model was proposed for the Bainaimiao Arc: (a) ∼500–455 Ma initial subduction and juvenile arc development, (b) ∼455–415 Ma continuous subduction with mature arc development, and (c) ∼415–400 Ma accretion to the North China Craton.

Early Paleozoic zircon ages of the Higher Himalayan Gneisses of the Everest region and their Pan-African/Proto-Himalayan orogenic signature

The U-Pb analysis of zircons from two independent leucosome bodies belonging to the paragneiss of the Higher Himalayan Crystallines Sequence (HHCS) in the Everest region of eastern Nepal Himalaya was carried out using laser ablation-multi collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) at the University of Arizona, Tucson, USA. The analysis of zircons from sample 07EVT3 forms a discordia with upper and lower intercepts at 478±25 and 21.5±4.1 Ma with concordant ages of 488.5±9.2 and 20.9±0.9 Ma for cores and rims, respectively. Similarly, the analysis of zircons from sample U1206 forms a discordia with upper and lower intercepts at 515±20 and 34.8±2.7 Ma, and provides concordant ages of 463.9±10.9 and 24.6±0.6 Ma for cores and rims, respectively. No inherited zircon grains with older ages were found indicating that almost all these zircons must have formed along with the leucotomies during the ca. 500 Ma metamorphism of the protoliths. The high U/Th ratio, i.e. average 11.0 for zircons from sample 07EVT3 and 253.6 for sample U1206 also support a metamorphic origin of the zircons. The occurrences of zircons in the ca. 500Ma leucosomes in the HHCS strongly points that rocks in the Himalayan area had undergone to a high-grade metamorphism during the late Pan-African time. We call this metamorphism as the Proto himalayan metamorphism. More studies along this line will help to better understand and constrain the Pan-African orogenic history of the Proto-Himalayan Orogen within the Peri-Gondwana Orogenicterrains.

Provenance of the early to mid-Paleozoic sediments in the northern Alxa area: Implications for tectonic evolution of the southwestern Central Asian Orogenic Belt

The continental fragments in Northwest China are key to revealing the tectonic and crustal evolution of the Central Asian Orogenic Belt (CAOB). However, their tectonic correlation, affinity and implications have not been well defined. The early to mid-Paleozoic sediments in the northern Alxa area can help to understand this question. These sediments were deposited in a deep to shallow marine environment during a regression. The southeast paleocurrent attributes their provenance to the northwest. Detrital zircons from the collected sandstones record peak ages of approximately 1726 Ma, 1462 Ma, 915 Ma and 438 Ma. The zircon εHf(t) values are negative to positive at 1726 Ma, 915 Ma and 438 Ma, but only positive at 1462 Ma. The detrital zircon U–Pb ages and Hf isotopes suggest the provenance to be the blocks in Central Tianshan and Southern Beishan or their analogs, rather than the Tarim Craton. The source blocks show no tectonic affinity to the Tarim Craton but might be accreted to it in the Neoproterozoic Rodinia. The provenance analyses show tectonic correlation among the northern Alxa, Tianshan and Beishan orogenic belts. The Late Devonian molasse deposits, geochemical shifting to continental margins and suddenly increased early Paleozoic zircons indicate an arc-continent collision. The discovery of more indicators for continental fragments advocates a multiterrane model and dominant crustal reworking/contamination for the tectonocrustal evolution of the CAOB at least during the early to mid-Paleozoic.

Trans-Siberian Permian rivers: A key to understanding Arctic sedimentary provenance

Permian strata of northern Siberia contain a rich record of the late Paleozoic history of Siberia and surrounding fold and thrust belts (FTB). More than 850 uranium–lead (U–Pb) detrital zircon ages collected from the Permian strata provide vital information about sediment source areas and history of the sedimentary basins. The detrital zircon populations obtained from the Permian clastics of northern Siberia are characterized by large percentages of late Paleozoic and early Paleozoic zircons, whose ages can be correlated with magmatic events known from the Ural-Mongolian Orogen. Our data suggest that Permian clastics of northern Siberia were mainly sourced from orogens developed along the western and southwestern margins of the Siberian Craton (in present-day coordinates), with an additional sediment contribution from the reworked sedimentary cover and basement of Siberia. The contribution from Siberian sources is distinguished in the Precambrian part of the detrital zircon populations by wide distribution of ca. 1700–2000Ma and 2500–2750Ma zircons with an almost total lack of zircons ranging in age from 800 to 1700Ma. We propose that a major fluvial system, which we here term the “Paleo-Khatanga”, was the main sediment transport pathway along the western and northern margins of Siberia during the Permian. From a regional overview of detrital zircon populations in Permian deposits across the Arctic realm, we propose that the New Siberian Islands, Alexander and Farewell terranes were sourced from the western framework of the Ural-Mongolian Orogen and were located along the northern margin of Baltica during the late Paleozoic. The Arctic–Alaska–Chukotka Terrane on the other hand does not have Uralian signatures in the detrital zircon populations of the Permian sediments, and can be reconstructed adjacent to the northern margin of Laurentia. Our new data presented here help to better define the enigma of Arctic paleogeography during the Paleozoic.

Insights from heavy minerals and zircon U–Pb ages into the middle Miocene–Pliocene provenance evolution of the Yinggehai Basin, northwestern South China Sea

The well-preserved Cenozoic sedimentary record in the Yinggehai Basin, South China Sea, is suitable to explore the tectonic and climatic evolution of SE Asia. Red River, a large-scale fluvial system in this region, was previously regarded as the major sediment source for the basin. Here we combine heavy mineral analysis and detrital zircon U–Pb dating to shed new light on the middle Miocene–Pliocene provenance evolution at a basin scale. The results clearly reveal potential source areas additional to the Red River. Sediments have been delivered to the proximal areas from Hainan Island, as indicated by the high zircon content and the Yanshanian U–Pb ages in the southern segment of the Yingdong Slope. A provenance from Central Vietnam is explicitly discerned in the upper Miocene of the Central Depression, where sediments are characterized by few metamorphic heavy minerals and the U–Pb age pattern peaking at around 250Ma and 440Ma. Coeval large-scale relative sea-level fall and rapid exhumation along the Vietnamese margin together may have facilitated this long-distance sediment transport. Provenance of sediments from the Red River seems to change over time. Song Lo River, on the north side of the main stream, probably flowed from the NE and carried Neoproterozoic–early Paleozoic zircons to the Yinggehai Basin during the middle Miocene. Since the late Miocene, rocks along the Red River Fault Zone have become the dominant source. Subsequently, widespread metamorphic minerals in the Central Depression of the Yinggehai Basin, combined with the strong river incision and high offshore sedimentation rates, indicate an increased sediment supply from the Red River in the Pliocene.

Formation Age of the Qinling Complex and the early Paleozoic Tectonic Event

The Qinling orogenic belt (QOB) located between the North China Craton (NCC) and the South China Craton (SCC) is composed of the Northern Qinling Belt (NQB) and the Southern Qinling Belt (SQB). This study presents new geochemical data, zircon U-Pb ages and Hf isotopes from two rocks from the Qinling complex in the NQB. LA-ICP-MS zircon U-Pb dating results suggest that the Qinling complex was formed in early Neoproterozoic and experienced the early Paleozoic metamorphism. High εHf(t) values of 9.0-12.0 for the early Paleozoic zircons indicated that there is mantle-derived magma intruding into the Qinling complex in the early Paleozoic.

Early Paleozoic crustal anatexis in the intraplate Wuyi–Yunkai orogen, South China

Early Paleozoic amphibolite- to granulite-facies metamorphism, crustal anatexis and coeval magmatism are extensively developed in the Wuyi–Yunkai intraplate orogen in the South China block. However, the exact timing of granulite-facies partial melting and its link with orogenesis have not been well constrained. In this study, the charnockites, gneissic migmatites and Al-rich gneisses (Grt–Sil–Bt gneiss and Bt–Pl gneiss) from the Gaozhou Complex of the Yunkai uplift in the Cathaysia block were selected for the analysis of whole-rock major elements and zircon U–Pb dating, trace elements and Lu–Hf isotopes. The Gaozhou Complex experienced early Paleozoic regional high-temperature (up to 850°C), low- to medium-pressure (4–7kbar) metamorphism accompanied by crustal anatexis. The melts were produced through the dehydration of mica, such as biotite+quartz+plagioclase=orthopyroxene+K-feldspar+melt and biotite+quartz+plagioclase+sillimanite=garnet+K-feldspar+melt in the charnockites, and muscovite+quartz+plagioclase=sillimanite+K-feldspar+melt in the Grt–Sil–Bt gneisses. The charnockites, gneissic migmatites and gneisses are felsic with SiO2>64% and peraluminous with A/CNK>1.0, reflecting protoliths with affinities to sedimentary rocks. Zircons from these rocks partly show clear core–rim structure and yield concordant ages mainly around 440–425Ma, with minor groups at 2.8–2.4Ga, 1.5–1.25Ga, 1.2–0.9Ga, 850–540Ma and 460–450Ma. The 440–425Ma grains are euhedral, oscillatorily-zoned and have steep slopes from the LREE to the HREE with a positive Ce anomaly and clear negative Eu anomaly, suggesting they (re-) crystallized in the melts. These early Paleozoic zircons have negative εHf (t) (−34.1 to −1.5) and much older TCRUST (3.6–1.5Ga), demonstrating they were formed by re-melting of old crustal materials (>1.5Ga). The zircons with ages of 2.8–2.4Ga, 1.6–1.2Ga and 1.2–0.9Ga have relatively high εHf (t) values (up to +10.2–+15.2). The 850–540Ma zircons show variable εHf (t) values of +9.0 to −24.0 with TDM (depleted mantle Hf model ages)=2.2–1.0Ga and TCRUST (crustal Hf model ages)=3.1–1.1Ga. Combined with the published data, we suggest that the Cathaysia block contains Archean materials as old as 3.6Ga and has had a complex evolution, including the addition of juvenile materials at ca 2.7Ga, 1.6–1.2Ga and 1.2–0.9Ga. Reworking of old crustal components dominated at ca 850–750Ma, 750–540Ma, 460–450Ma and more intensively at ca 440–425Ma. Synthesizing the obtained results, we argue that the Yunkai charnockites, gneissic migmatites and Bt–Pl gneisses were formed due to the early Paleozoic high-T crustal anatexis, which may have been triggered by crustal shortening and thickening during the intraplate Wuyi–Yunkai orogeny in the South China block.

Detrital zircons reveal no Jurassic plateau in the eastern North China Craton

U–Pb–Hf isotopic analyses have been carried out on detrital zircons from Late Permian–Jurassic strata in the Western Shandong–Bohai Bay (WSBB) basins with aims of constraining the paleogeography and evolution of the eastern North China Craton (NCC). Four major groups of U–Pb ages (namely, 3.0–2.3Ga, 2.2–1.4Ga, 1250–430Ma and 410–150Ma) are recognized for zircons from the fine-grained sandstones. The post-Paleoproterozoic zircons of the Late Permian sample show an age cluster of 344–255Ma with εHf(t) values of −18 to −8, being similar to those extracted from Late Paleozoic igneous rocks from the Yinshan–Yanshan Orogenic Belt (YYOB) on the northern margin of the NCC. However, the Devonian–Jurassic zircons (390–150Ma) from the Jurassic sediments have εHf(t) values from −45 to +14, very similar to the mixture of Phanerozoic zircons from the Xing–Meng Orogenic Belt (XMOB) and the YYOB, but significantly different from those of the Liaodong Peninsula, Jiaodong Peninsula and the Western Shandong Uplift. In addition, Cambrian–Silurian zircons (535–430Ma) of the Jurassic samples have εHf(t) values from −27 to +7, resembling the Early Paleozoic zircons extracted from the Northern Qinling Orogen (NQO). The U–Pb age spectra and Hf isotope of Devonian–Jurassic zircons as well as bulk Nd isotopes suggest that the central eastern NCC received some juvenile materials from the XMOB, the YYOB and the NQO during the Jurassic. This indicates widespread prototype basins and a low elevation during the Jurassic, arguing against the presence of a paleo-plateau in the eastern NCC at that time. The lack of evidence predicted by lithospheric delamination (e.g., large-scale elevation or doming after Late Triassic) makes the delamination unlikely to be a viable mechanism of lithospheric thinning of the NCC. The subsidence rather than elevation of the eastern NCC after Late Triassic might be related to thermo-chemical erosion of the lithosphere by underlying convective mantle in a back-arc setting.

Discovery of the Early Paleozoic Boin Sum‐Ordor Sum Island Arc in the Hadamiao Gold Ore District, Inner Mongolia and its Significance to the Evolution of the Paleo‐Asian Ocean

AbstractEarly Paleozoic granodiorite has been identified on the northern margin of the North China craton in the east section of the central‐Asian orogenic belt, which was previously known as early Indosinian in age. By using the LA‐ICP‐MS method, the obtained zircon U‐Pb age is 445.6±2.7 Ma, which represents the crystallization age of the granodiorite. The granodiorite near the east of the large‐sized Bilihe gold deposit is of the tholeiite series with low potassium. It is quasi‐aluminous I‐type granite, enriched in sodium (Na2O/K2O=7.29–9.77) and magnesium (Mg#=0.51–0.67). The ΣREE value is relatively low, obvious differentiation is shown between LREE and HREE and within LREE, and the Eu anomaly is low and negative (δEu=0.74–0.91). In the primitive‐mantle normalized spider diagrams of trace elements, the granodiorite is relatively rich in LREE and LILE (Ba, Sr, Th), and strongly depleted in HFSE (Nb, Ta, Ti and P), which shows features of subduction zone components (SZC). In the discrimination diagrams of tectonic settings of granite for Rb vs. (Nb+Y), Rb vs. (Ya+Ta), La/Nb vs. Ba/Nb and Th/Nb vs. Ba/Nb, the granodiorite exhibits typical features of island arc granite. The normalized values of K and Rb are extremely low, while the values of Sr and Eu are very high, which are similar to those of island arc magma that has undergone metasomatism of fluid from the oceanic crust. The granodiorite is relatively depleted in εHf(t) (5.1–7.1) and low in εHf(t) model ages (1089–921 Ma). In the εHf(t) vs. age (T) diagram, the distribution area of the granodiorite is accordant with the field of the Xing'anling‐Mongolia orogenic belt, which indicates that the magmatic sources are mainly the mixture of partial melting of wedged mantle subjected to metasomatism of fluid from the oceanic crust and young substance from the crust The granodiorite is similar to the felsic arc magma in the Damao Banner, Bate Obon, Boin Sum and Ordor Sum regions, and they altogether constitute an early Paleozoic accretionary island arc magmatic belt on the northern margin of the North China craton. A number of early Paleozoic zircons trapped in late Paleozoic intrusions in the Hadamiao and Bilihe regions and the discovery of the early Paleozoic island arc magmatic belt near the east of the Bilihe gold deposit suggest that the late Paleozoic volcanic‐intrusive rocks have a basement of early Paleozoic arc accretionary complexes. This is just the evident of the multiphase subduction and accretion model of the Paleo‐Asian Ocean (PAO). Paleozoic structures and magmas on the northern margin of the North China craton are shown from south to north as the late Paleozoic Andes‐type arc magmatic belt in the Inner Mongolia plateau, the Chifeng‐Bayan Obo fault and the late and early Paleozoic arc magmatic belt, which shows that after the early Paleozoic arc‐continent collisional orogeny and at the stage of the late Paleozoic accretionary orogeny, the PAO plate was likely to continuously pulsate and underthrust beneath the early Paleozoic island arc accretionary complex belt and its front, i.e. the North China craton. During the early Paleozoic collisional orogeny, the PAO plate might not experience large‐scale breakup or delamination. The characteristics of the early Paleozoic island arc accretionary complex basement have a significant control on late Paleozoic diagenesis and metallization in the Hadamiao and Bilihe gold concentrated areas.

U–Pb ages and trace elements of detrital zircons from Early Cretaceous sedimentary rocks in the Jiaolai Basin, north margin of the Sulu UHP terrane: Provenances and tectonic implications

The Dabie–Sulu orogen in east-central China is the largest UHP belt in the world. Many studies have dealt with detrital minerals from sedimentary basins surrounding the Dabie belt in order to constrain the tectonic unroofing of this terrane. On the other hand, still few are the works focused on detritals from the basins associated with the Sulu belt. The Jiaolai basin, adjacent to the Sulu belt, is made of Mesozoic sedimentary rocks. Two sandstone samples collected from the Early Cretaceous Laiyang Group in the northern and southern margins of the Jiaolai basin were selected for zircon U–Pb dating and trace element analysis. The zircons show main U–Pb age clusters at ca. 2500–2400, 2000–1700, 850–700, and 330–130Ma, with a minor peak at ca. 1100Ma and a few Archean ages. Most zircons show texture features reflecting a magmatic origin, whereas several late Paleoproterozoic and Triassic zircons show homogeneous CL images and low Th/U ratios, indicating a metamorphic origin. The Neoproterozoic ages are consistent with the protolith ages of the metamorphic rocks in the Sulu terrane, implying that the Sulu tarrane may be a major source for this component. Whereas most Neoproterozoic zircons are euhedral to subhedral or angular in shape and are not surrounded by overgrowths, this implies that low-grade metamorphic Neoproterozoic metaigneous rocks ocurring along the northern margin of the Sulu terrane or metasediments overlying the HP–UHP rocks in the Sulu terrane might provide source materials to these detrital zircons. The late and early Paleoproterozoic age peaks are consistent with the thermal events occurred in the Jiaobei terrane, slightly younger than those in the Yangtze Block. These suggest that the Jiaobei terrane was a potential source for the Paleoproterozoic to Archean detrital zircon components. Only two early Paleozoic zircon grains were found in the studied samples, indicating the early Paleozoic arc did not extend into the Sulu terrane. According to the distribution of different kinds of rock adjacent to the Sulu terrane, the Early Cretaceous detrital zircons may be potentially derived from Cretaceous plutons from the Sulu belt. Eight detrital zircons including six metamorphic grians and two metamorphic overgrowth rims yield the Triassic ages, which might be derived from HP–UHP rocks from the Sulu terrane. A metamorphic overgrowth rim yields a metamorphic age of 246±3Ma, probably recording the timing of the prograde metamorphism of the Sulu terrane. One metamorphic grain yields an age of 212±2Ma, which is interpreted to record a retrograde metamorphic event. Based on the REE patterns, the remaining six Triassic analyses can be subdivided into two groups. Four of them record a weighted mean age of 230±6Ma and show nearly flat HREE patterns and slight negative or positive Eu anomalies. The last two grains are enriched HREE; considering their ages and the REE patterns, it is suggested that they may originate from other diverse UHP rocks. The Triassic metamorphic zircons were detected in the Laiyang Group, indicating that the Sulu UHP rocks were exposed to the surface before the Early Cretaceous.

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.

Detrital zircon provenance of Upper Ordovician and Silurian strata in the northeastern Yangtze Block: Response to orogenesis in South China

Upper Ordovician to Silurian strata along the northeastern margin of the Yangtze Block, South China Craton, were deposited in a syn-orogenic basin related to the Early Paleozoic Kwangsian Orogeny in the adjoining Cathaysia Block. U–Pb age data for 450 detrital zircons from six sandstones samples range in age from Archean to the early Paleozoic. All samples have a dominant age peak between 0.8 and 0.9Ga and subordinate peaks around 2.5Ga and 1.8Ga, with the youngest samples also containing zircons between 0.47 and 0.43Ga. The detrital zircon age spectrum is indicative of derivation from the southeast with Precambrian grains derived from the basement of Cathaysia Block and the Early Neoproterozoic Jiang-Shao suture, and Early Paleozoic zircons derived from igneous activity associated with the Kwangsian Orogeny. The restriction of Paleozoic detritus to the latter phases of the Kwangsian Orogeny (which started by 460Ma) suggests progressive exhumation of the Cathaysia Block, perhaps due to thrusting over the Yangtze Block, with the latter remaining a site of active sedimentation during orogenesis.