Zircon Lu-Hf Isotope Research Articles

Recycling of Paleo-oceanic crust: Geochemical evidence from Early Paleozoic mafic igneous rocks in the Tongbai orogen, Central China

Crustal subduction generally develops from oceanic to continental subduction in collisional orogens, with the disappearance of previously subducted paleo-oceanic crust. However, it is not straightforward to trace the fate of subducted paleo-oceanic crust due to modification by subsequent continental collision. In this study, we present a combined study of secondary ion mass spectrometry (SIMS) zircon UPb ages and O isotopes, laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) zircon LuHf isotopes, whole-rock major-trace elements and SrNd isotopes of Early Paleozoic mafic igneous rocks in the Tongbai orogen, central China. These geochemical data are interpreted and modelled in terms of crust-mantle interaction in a subduction channel, in order to account for geochemical transfer from the subducting crust to the mantle wedge. The results provide insight not only into paleo-oceanic crust recycling but also into the nature of orogenic lithospheric mantle. SIMS zircon UPb dating of the mafic igneous rocks yields Early Paleozoic ages of 436 ± 4 to 449 ± 4 Ma for magma crystallization. These mafic rocks have arc-type trace element distribution patterns, with enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE) but depletion in high field strength elements (HFSE) relative to rare earth elements (REE) and LILE. They have depleted whole-rock SrNd isotopic compositions, with initial 87Sr/86Sr ratios of 0.7037 to 0.7047 and positive εNd(t) values of 2.7 to 5.0. The mafic igneous rocks also display positive zircon εHf(t) values of 8.9 to 14.8 and variable δ18O values of 4.4 ± 0.3 to 5.9 ± 0.3‰. These geochemical features suggest derivation from fertile mantle sources enriched in LILE and LREE but depleted in radiogenic isotopes. The mantle sources are suggested to be part of the orogenic lithospheric mantle, which was generated by metasomatic reaction of the overlying mantle wedge with previously subducted Erlangping oceanic crust-derived fluids. Some samples have high Ba/Th, Th/Nb and (La/Yb)N ratios, suggesting that the metasomatic agents include both basaltic oceanic crust-derived aqueous solutions and sediment-derived hydrous felsic melts. Model calculations confirm that the geochemical composition of the Tongbai mafic igneous rocks can be explained by reaction of depleted mid-oceanic ridge basalt (MORB) mantle peridotite with 1–10% of subducted Erlangping oceanic crust-derived aqueous solutions plus 0.05–0.1% of sediment-derived hydrous melts. This melt-peridotite reaction would generate a pyroxenite-rich lithology in the mantle source. During the tectonic transition in the Ordovician to Silurian, partial melting of such mantle sources gave rise to mafic magmatism due to back-arc extension. Thus, the Early Paleozoic mafic igneous rocks in the Tongbai orogen record the recycling of earlier subducted paleo-oceanic crust and the nature of the orogenic lithospheric mantle in the collisional orogen.

The late-Paleoproterozoic I- and A-type granites in Lüliang Complex, North China Craton: New evidence on post-collisional extension of Trans-North China Orogen

The late-Paleoproterozoic granitoids from Lüliang Complex can provide pivotal constraints on the amalgamation process between Eastern and Western blocks of North China Craton along the Trans-North China Orogen. LA-ICP-MS zircon dating gives emplacement ages of 1854 ± 20 Ma for the Huijiazhuang granite, 1830 ± 21 Ma for the Xiyupi granite vein and 1760 ± 20 Ma for the Dacaoping porphyritic granite, respectively. The Huijiazhuang granite and Xiyupi granite dyke have variable SiO2 (66.71–74.31 wt%), high K2O (5.09–6.35 wt%), low P2O5 (0.02–0.16 wt%), Al2O3 (13.92–15.31 wt%), right inclined REE patterns with medium negative Eu anomalies, enrichment in LILE, depletion in HFSE, especially Nb, Ta, consisting to high-K I-type granite in a post-collisional setting. The Sr/Y (7.36–59.95), εNd(t) (−5.7 to −4.1) with TDM (2381 Ma to 2570 Ma) from whole rock Sm-Nd isotope and εHf(t) (−9.6 to 2.3) with TCDM (2360 Ma to 3070 Ma) from zircon Lu-Hf isotope suggest that they are produced by partial melting of slightly thickened Neoarchean-Paleoproterozoic basement materials (including both meta-sedimentary and meta-igneous rocks). The Dacaoping porphyritic granites are characterized by high SiO2 (70.83–74.30 wt%), K2O (4.84–5.60 wt%), FeOT/(FeOT + MgO) (0.86–0.92), “seagull-type” REE pattern with strong negative Eu anomaly (δEu=0.16–0.35) and higher 10000∗Ga/Al (2.99–3.36), HFSE (Zr + Nb + Ce + Y = 378–583 ppm), showing an affinity of A2-type granite. They have low Sr/Y (1.17–8.62), εNd(t) (-6.1 to -6.4) with TDM (2690 Ma to 2776 Ma) from whole rock Sm-Nd isotope and εHf(t) (-7.9 to -5.2) with TCDM (2775–2938 Ma) from zircon Lu-Hf isotope, indicating a result from the melting of thinned Neoarchean calc-alkaline intermediate basement. Taking into account the temporal-spatial distributions of late-Paleoproterozoic rocks in the Trans-North China Orogen, it suggests a post-collisional extension occurred during 1.89–1.76 Ga and the crustis thinnedvisibly since 1.82 Ga.

Reconstruction of the Cryogenian palaeogeography in the Yangtze Domain: constraints from detrital age patterns

AbstractDetrital zircons are often used to constrain the maximum sedimentary age of strata and sedimentary provenance. This study aimed at reconstructing the Cryogenian palaeogeography of the Yangtze Domain based on U–Pb ages and Lu–Hf isotopic signatures of detrital zircons from sandstones in the southeastern part of the Yangtze Domain. U–Pb ages of the youngest detrital zircon grains from the Niuguping, Gucheng and Datangpo formations yielded average ages of 712±24 Ma, 679.2±6.2 Ma and 665.1±7.4 Ma, respectively, which are close to the depositional ages of their respective formations. An integrated study of detrital zircon Lu–Hf isotopes and U–Pb ages from three samples revealed six main peak ages in the samples from the Anhua section atc. 680 Ma,c. 780 Ma,c. 820 Ma,c. 940 Ma,c. 2000 Ma andc. 2500 Ma. The characteristics of the U–Pb ages and Hf isotopes indicate a link between the north and southeast margins of the Yangtze Domain as early asc. 680 Ma, and the provenance of the coeval sedimentary sequences in the SE Yangtze Domain was the South Qinling Block on the northern margin of the Yangtze Domain. The provenance analysis on thec. 680 Ma detritus composing upper Neoproterozoic strata in the Yangtze Domain revealed that the detritus was transported southward from South Qinling to the southeast margin of the Yangtze Domain through the Exi Strait, but was hindered by the Jiangnan Orogenic Belt.

Geochemistry and zircon U–Pb–Hf isotopes of the 780 Ma I-type granites in the western Yangtze Block: petrogenesis and crustal evolution

ABSTRACTNeoproterozoic I-type granites could provide vital insights into the crust–mantle interaction and the crustal evolution along the western Yangtze Block, South China. This paper presents new zircon U–Pb ages, bulk-rock geochemistry, and in situ zircon Lu–Hf isotope on the Dalu I-type granites from the southwestern Yangtze Block. Zircon U–Pb dating show the crystallization ages of 781.1 ± 2.8 Ma for granodiorites and 779.8 ± 2.0 Ma for granites, respectively. The Dalu granodiorites are Na-rich, calc-alkaline, metaluminous to slightly peraluminous (A/CNK = 0.94–1.08). Zircons from granodiorite have positive εHf(t) values (+2.16 to +7.39) with crustal model ages of 1.21–1.54 Ga, indicating juvenile mafic lower crust source. The Dalu granites are high-K calc-alkaline, peraluminous rocks. They have variable zircon εHf(t) values (−4.65 to +5.80) with crustal model ages of 1.31–1.97 Ga, suggesting that they were derived from the mature metasediment-derived melts by the mixing of newly formed mafic lower crust-derived melts. The geochemical variations in Dalu pluton is dominated not only by the different source rocks but also by the different melting temperatures. Combining with the geochemistry and isotopic compositions of I-type granitoids and tectonic setting in the western Yangtze Block, we propose that the Dalu I-type granodiorites–granites associations are the magmatic response from different crustal levels, which were induced by the heat anomaly due to the asthenosphere upwelling in the subduction-related setting.

The Fangmayu Alaskan-type ultramafic intrusion: Implications for Paleoproterozoic assembly of the North China Craton

Alaskan-type ultramafic intrusions constitute a rare suite of rocks formed in subduction-related settings and provide important insights into mantle source and geodynamic processes associated with convergent plate margins. The North China Craton (NCC) witnessed subduction-accretion-collision events in the Paleoproterozoic prior to the final cratonization, and preserve important imprints of magmatic and metasomatic processes associated with oceanic plate subduction along the margins of the amalgamated crustal blocks and within the collisional orogens. Here we investigate a suite of serpentinized dunite, serpentinite, olivine orthopyroxenite, and anthophyllite glimmerite from the Fangmayu ultramafic complex along the eastern margin of the Trans-North China Orogen (TNCO) adjacent to the Eastern Block of the NCC. We present petrology, mineral chemistry, zircon U-Pb geochronology, REE and Lu-Hf isotopes, and whole rock geochemistry including REE and PGE data with a view to investigate the magmatic and metasomatic processes in this ancient subduction zone. The lithological distribution in the Fangmayu intrusion shows concentric zoning with dunite in the core, mantled by peridotite and pyroxenite, similar to that of Alaskan-type intrusions. Mineral chemistry including spinel composition shows distinct characteristics of stratiform chromite associated with Alaskan-type ultramafic intrusions formed in an arc-related subduction environment. Phase diagram computations show that the olivine (XMg = 0.92–0.93) and orthopyroxene (XMg = 0.9–0.91) in the olivine orthopyroxenite formed at high temperature conditions (∼1200 °C), and the antigorite (XMg = 0.92–0.98) chemistry shows that serpentinization occurred at much lower temperature (∼570 °C). Zircon U-Pb data from the ultramafic suite define two distinct groups of ages: 2.3 to 2.0 Ga and ca. 1.84 Ga corresponding to magma crystallization within suprasubduction zone mantle associated with subduction, and metamorphism during continental collision and final cratonization of the NCC. The REE patterns of zircons distinguish dominant population of magmatic grains and a minor group of metasomatic grains. Zircon Lu-Hf isotope data exhibit both positive and negative εHf(t) values in the range of −8.5 to 4.4 with TDM of 2434–2714 Ma, suggesting both enriched and depleted components in the magma source. Geochemical data including PGE characteristics suggest hydrous melting of depleted mantle wedge under high temperatures and fluid pressure in a subduction-related setting. Our study on the Paleoproterozoic Alaskan-type intrusion offers insights into arc-continent and continent-continent collision within a long-lived subduction system in the North China Craton.

Granite zircon U-Pb geochronology and geochemistry and the geological significance of the Saibo copper deposit in the western Tianshan Mountains, Xinjiang Province, China

The discovery of the Saibo copper deposit was a significant breakthrough in prospecting in the western Tianshan Mountains, Xinjiang Province. This deposit has great significance for studying the transboundary metallogenic belt because the deposit is associated with granitoids. Zircon dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) yield 206Pb/238U ages of 385.9 ± 1.3 Ma and 387.2 ± 1.4 Ma for the granodiorite and granite porphyries from the deposit, respectively, indicating that the granitoids are the products of Middle Devonian magmatism. In terms of their geochemistry, these porphyries have high SiO2 contents (between 62.60% and 67.47%) and low TiO2 contents (between 0.32% and 0.52%), with aluminum saturation indexes (ASI) between 0.76 and 0.90; these characteristics indicate a metaluminous medium-potassium (K) calc-alkaline I-type granite that is enriched in large-ion lithophile elements such as K and Sr, as well as in incompatible elements such as Th and U and light rare earth elements (LREE); is relatively depleted in high-field strength elements such as Na, Ta, P, and Ti; and lacks an obvious Eu anomaly. The zircon Lu-Hf isotope ratios are relatively high, with 176Hf/177Hf values varying between 0.28253 and 0.28272 and εHf (t) that varies between −0.4 and +6.5 (mostly positive). These features demonstrate that the granites were the products of co-magmatic evolution originating from the depleted mantle and the partially melting of juvenile crustal material, which occurred due to the North Tianshan Ocean subduction towards the southern Yili block that led to magma ascent from the depleted mantle.

Geochemistry and geochronology of the Qingshanjiao granites: Implications for the genesis of the Dongguashan copper (gold) ore deposit in the Tongling ore district, Eastern China

The Dongguashan copper (gold) ore deposit, which is located in the central region of the Middle–Lower Yangtze Cu–Fe–Au–Mo metallogenic belt, Eastern China, is one of the largest stratabound skarn copper (gold) deposits in the Tongling ore district, Anhui Province. The Qingshanjiao quartz monzodiorite is associated with the copper (gold) mineralization in the Dongguashan mining district. Vein-like and disseminated sulfide mineralization are developed within the Qingshanjiao pluton, with the thicknesses of the orebodies increasing closer to the pluton. The LA–ICP–MS zircon U–Pb analysis of the Qingshanjiao quartz monzodiorite yielded a weighted mean 206Pb/238U age of 136.7 ± 2.3 Ma (MSWD = 0.37, n = 10), which is approximately consistent with the previously published molybdenite-related copper (gold) mineralization Re–Os model ages of ca. 140–137 Ma. Based on whole-rock major and trace element data, as well as zircon Lu–Hf isotope data, the Qingshanjiao quartz monzodiorite is a high-K calc-alkaline, metaluminous I-type granite, which is characterized by the relative enrichment of LREE, Cs, K and Th, relative depletion of HREE, Nb, P, Ti and Ta, and εHf(t) values of magmatic zircons ranging from −1.7 to −31.7.Based on these results, combined with those of previous studies, we suggest that the Qingshanjiao quartz monzodiorite may be a mixture of mantle-derived basaltic magma and crust-derived granitic magma and that the Dongguashan copper (gold) ore deposit formed during the tectonic transition from compression to extension ca. 140 Ma.

Precambrian Hongqiyingzi Complex at the northern margin of the North China Craton: Its zircon U-Pb-Hf systematics, geochemistry and constraints on crustal evolution

The Precambrian Hongqiyingzi Complex (HQC) in the middle segment of the northern margin of the North China Craton (NCC) is a crucial magmatic intrusive complex offering insights into the early evolutionary history of the northern margin of the NCC. The HQC, exposed from Congli to Longhua towns in the northern Hebei Province, is mainly composed of Neoarchean quartz dioritic-tonalitic-granodioritic (DTG) gneisses and Paleoproterozoic granodiorite-monzogranite-syenogranite (GMS) intrusions. SHRIMP and LA-ICP-MS zircon dating results show that the DTG gneisses formed at 2546–2532 Ma, while the GMS intrusions were emplaced between 1870 and 1819 Ma. LA-MC-ICP-MS zircon Lu-Hf isotope analyses indicate that the Neoarchean DTG magmas were mainly derived from partial melting of juvenile crust, but the Paleoproterozoic GMS magmas originated from partial melting of the metamorphic basalts and greywackes from Neoarchean to Paleoproterozoic volcanic or related sedimentary materials.Lithological assemblages, chronological and geochemical data, petrogensis and geodynamic settings of the Neoarchean DTG and Paleoproterozoic GMS magmatism show that the HQC is most likely at the northernmost part of the Trans-North China orogen of the NCC. The Precambrian HQC thus recorded Neoarchean subduction-related arc magmatism and Paleoproterozoic post-collisional magmatism that were associated with subduction and collision at the northern margin of the NCC. These Precambrian geological units were intensively overprinted by Late Paleozoic calc-alkaline magmatism, which may be caused by southward subduction and collision of the Central Asian Orogenic Belt (CAOB) with the NCC.

Paleozoic granitic magmatism and tectonic evolution of the South Altun block, NW China: Constraints from zircon U-Pb dating and Lu-Hf isotope geochemistry

The South Altun orogenic belt (SAOB), consisting of the South Altun block (SAB) and the South Altun continental block (SACB), is one of several important orogenic belts in NW China. Numerous granite bodies are widely distributed in the SAB. However, the petrogenesis and tectonic environment of these granites, and their relationships to those of the SACB, Central Altun Continental block (CACB), North Altun block (NAB), Qilian block (QLB), and North Qaidam block (NQB) remain unclear. In this investigation, we selected the SAB granites for detailed study, and explore the petrogenesis employing bulk-rock geochemistry, zircon U-Pb dating, and Hf isotopic analysis. Zircon U–Pb LA-ICP-MS dating of the granites from the SAB identified seven spatially distinct Paleozoic plutonic suites: (a) Yigan—352–343 Ma; (b) Baiganhu—448–444 Ma; (c) west Mangya—444–435 Ma; (d) Aketishan—265 Ma; (e) Chaishuigou—406 Ma; (f) Changchungou—469 Ma; and (g) north Mangya—462 Ma. Based on previous research combined with our new U-Pb dating and bulk-rock geochemical investigations in the SAB, we identdified six distinct episodes of granitoid emplacement: episodes 1 and 2, quartz diorite + granodiorite + monzogranite with I-type affinities, and ages of 503–497 Ma and 483–458 Ma, respectively; episode 3, granodiorite + monzogranite + syenogranite with I- and S-type affinities, and an age of 456–432 Ma; episode 4, monzogranite + syenogranite + alkali feldspar granite with A-type affinities, and an age of 424–385 Ma; episode 5, granodiorite + monzogranite with S-type affinities, and an age of 352–338 Ma; and episode 6, quartz diorite + monzogranite + syenogranite with I-type affinities, and an age of 265–264 Ma. Zircon Lu-Hf isotope analyses from various episodes show that εHf (t) values are positive in most cases, but negative for a small number of inherited (xenocrystic) zircons. Source rocks were mainly juvenile crust, evidently mixed with minor ancient continental material. Based on our new results integrated with regional geological data, we conclude that episodes 1 and 2 granitic magma generations were related to the subduction of oceanic crust, episode 3 to post-collisional partial melting, episode 4 to the isostatic adjustment of orogenic blocks after plate suturing, episode 5 to petrotectonic thickening of the Altun crust, and episode 6 to Altun fault transcurrent slip attending Kunlun Paleo Tethys subduction.

New evidence for an old idea: Geochronological constraints for a paired metamorphic belt in the central European Variscides

New geochronological data reveal a prolonged tectonothermal evolution of the Variscan Odenwald-Spessart basement, being part of the Mid-German Crystalline Zone in central Europe. We report the results from (i) secondary ion mass spectrometry (SIMS) U-Pb dating of zircon, rutile and monazite, (ii) SIMS zircon oxygen isotope analyses, (iii) laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) zircon Lu-Hf isotope analyses and, (iv) LA-ICPMS zircon and rutile trace element data for a suite of metamorphic rocks (five amphibolite- and eclogite-facies mafic meta-igneous rocks and one granulite-facies paragneiss). The protoliths of the mafic rocks formed from juvenile as well as depleted mantle sources in distinct tectonic environments at different times. Magmatism took place at a divergent oceanic margin (possibly in a back-arc setting) at 460 Ma, in an intraoceanic basin at ca. 445 Ma and at a continental margin at 329 Ma. Regardless of lithology, zircon in eclogite, amphibolite and high-temperature paragneiss provide almost identical Carboniferous ages of 333.7 ± 4.1 Ma (eclogite), 329.1 ± 1.8 to 328.4 ± 8.9 Ma (amphibolite), and 334.0 ± 2.0 Ma (paragneiss), respectively. Rutile yielded ages of 328.6 ± 4.7 and 321.4 ± 7.0 Ma in eclogite and amphibolite, and monazite in high-temperature paragneiss grew at 330.1 ± 2.4 Ma (all ages are quoted at the 2σ level). The data constrain coeval high-pressure eclogite- and high-temperature granulite-facies metamorphism of the Odenwald-Spessart basement at ca. 330 Ma. Amphibolite-facies conditions were attained shortly afterwards. The lower plate eclogite formed in a fossil subduction zone and the upper plate high-temperature, low-pressure rocks are the remains of an eroded Carboniferous magmatic arc. The close proximity of tectonically juxtaposed units of such radically different metamorphic conditions and thermal gradients is characteristic for a paired metamorphic belt sensu Miyashiro (1961). Thus, the Odenwald-Spessart basement represents the first recognised paired metamorphic belt in the European Variscides.

Using the magmatic record to constrain the growth of continental crust—The Eoarchean zircon Hf record of Greenland

Southern West Greenland contains some of the best-studied and best-preserved magmatic Eoarchean rocks on Earth, and these provide an excellent vantage point from which to view long-standing questions regarding the growth of the earliest continental crust. In order to address the questions surrounding early crustal growth and complementary mantle depletion, we present Laser Ablation Split Stream (LASS) analyses of the U–Pb and Hf isotope compositions of zircon from eleven samples of the least-altered meta-igneous rocks from the Itsaq (Amîtsoq) Gneisses of the Isukasia and Nuuk regions of southern West Greenland. This analytical technique allows a less ambiguous approach to determining the age and Hf isotope composition of complicated zircon. Results corroborate previous findings that Eoarchean zircon from the Itsaq Gneiss (∼3.85 Ga to ∼3.63 Ga) were derived from a broadly chondritic source. In contrast to the Sm–Nd whole rock isotope record for southern West Greenland, the zircon Lu–Hf isotope record provides no evidence for early mantle depletion, nor does it suggest the presence of crust older than ∼3.85 Ga in Greenland.Utilizing LASS U–Pb and Hf data from the Greenland zircons studied here, we demonstrate the importance of focusing on the magmatic (rather than detrital) zircon record to more confidently understand early crustal growth and mantle depletion. We compare the Greenland Hf isotope data with other Eoarchean magmatic complexes such as the Acasta Gneiss Complex, Nuvvuagittuq greenstone belt, and the gneissic complexes of southern Africa, and all lack zircons with suprachondritic Hf isotope compositions. In total, these data suggest only a very modest volume of crust was produced during (or survived from) the Hadean and earliest Eoarchean. There remains no record of planet-scale early Earth mantle depletion in the Hf isotope record prior to 3.8 Ga.

Formation age and geodynamic setting of the Neoproterozoic Shalong iron formation in the Central Tianshan, NW China: Constraints from zircon U–Pb dating, geochemistry, and Hf–Nd isotopes of the host rocks

The recently discovered Shalong iron deposit in the Central Tianshan with a reserve of 14 Mt of iron at 25–30 wt.% Fe shows the typical iron formation geological characteristics: The host rocks are mainly metamorphosed volcanic rocks including quartz hornblende schist, mica quartz schist, and plagioclase amphibolite; the iron orebodies are stratiform and bedded, indicative of strata‐controlled deposits; metallic minerals are dominated by magnetite with haematite and ilmenite in minor quantities, whereas gangue minerals are quartz, amphibole, chloritoid, and plagioclase; and ore textures are banded and laminated. Here, we present LA‐ICP‐MS zircon U–Pb ages, whole‐rock geochemistry, Sm–Nd isotope, and zircon Lu–Hf isotope analyses on the host rocks in order to constrain the timing and geodynamic setting of the deposit. The geochemical characteristics, Sm–Nd isotope, and zircon Lu–Hf isotope compositions of the host rocks indicate that their protoliths were likely basic and felsic volcanic rocks. The bimodal kind rock types, the juvenile Nd–Hf isotopic characters, and the within‐plate trace element geochemical features of the host rocks together indicate that these rocks formed in a rift‐like extensional setting. Zircon U–Pb dating of the host rock interlayer suggests that the Shalong iron formation was formed in the Neoproterozoic (ca. 760 Ma). Combined with geological characteristics, close association with meta‐volcanic rocks, absence of glacial deposits, and within‐plate geochemical and juvenile isotopic signatures of the host rocks, the Shalong iron deposit is interpreted to be an Algoma‐type Neoproterozoic iron formation. The formation of this deposit can be linked to rift‐like volcanic activities related to the breakup of the Rodinia supercontinent. Our results in conjunction with previous studies suggest that the Central Tianshan should be related to the breakup of Rodinia, as indicated by the Neoproterozoic rift‐related igneous events of the Central Tianshan.

Late Neoarchean to early Paleoproterozoic tectonic evolution of the southern North China Craton: Evidence from geochemistry, zircon geochronology and Hf isotopes of felsic gneisses from the Taihua complex

The Archean-Paleoproterozoic Taihua Complex, extending from east to west along the southern margin of the North China Craton (NCC), is an ideal window to understand the tectonic evolution of the early Earth. Here we present new data on petrology, zircon geochronology, whole-rock geochemistry and isotopes of TTGs, granitic gneisses and felsic leucosomes of migmatites from the Taihua complex in the Xiaoqinling area. Zircon LA-ICP-MS analyses of rocks yield the formation ages of 2564–2503 Ma for TTGs, 2481–2476 Ma for felsic leucosomes and 2359–2334 Ma for granitic gneisses, respectively. The zircon Lu-Hf isotopes suggest that crustal growth occurred in the late Neoarchean and crustal reworking occurred in the end of Neoarchean and the early Paleoproterozoic. The TTG gneisses are characterized by high Na2O/K2O, La/Yb, Sr/Y and low Nb/Ta ratios, and they were likely generated by partial melting of subducted juvenile oceanic crust with garnet or amphibole in residuals, a mechanism similar to the slab melting model. Both the felsic leucosomes and granitic gneisses have high SiO2 contents and various Hf isotopic compositions, and they probably were formed in an extensional setting, attributing to partial melting as well as mixing of the preexisting TTG suite.Statistically, we report a major transitional phase in the tectonic milieu of the southern NCC from compression to extension during the late Neoarchean (ca. 2.57–2.42 Ga). The compressional tectonics can be attributed to amalgamation of micro-continental blocks during the late Neoarchean (ca. 2.57–2.5 Ga) as the leading period of crustal growth and associated multistage TTG magmatism. In contrast, the extensional phase occurred during the end of Neoarchean (ca. 2.5–2.42 Ga) that may represent the end of cratonic stabilization period and formation of large amounts of K-rich granitic rocks, widespread high-grade metamorphism and migmatites. Additionally, the formation of a large amount of crust-derived granites and mafic dykes during the early Paleoproterozoic in southern NCC reflect another stage (ca. 2.36–2.24 Ga) of crustal extension, which represents an episode of initial worldwide rifting events probably linking to the great oxygen event (GOE). Therefore, the present study proposes a new profile on multi-stage crustal growth/reworking and craton stabilization during Neoarchean-Paleoproterozoic period along the southern NCC, and provides useful insights on complex and heterogeneous evolutionary processes of early Earth.

Oldest lamproites from Peninsular India track the onset of Paleoproterozoic plume-induced rifting and the birth of Large Igneous Province

Potassic and ultrapotassic magmatism from deep lithospheric sources in intra-cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of Large Igneous Provinces (LIPs) triggered by mantle plumes. Here we report for the first time, precise zircon U–Pb age data from a suite of lamproites in the Bastar Craton of central India that mark the onset of Paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major LIP events during the Precambrian evolution of the Indian shield. The lamproites from the Nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile, apatite and zircon. The rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite. Geochemical features of the lamproites correlate with their counterparts in Peninsular India and other similar suites elsewhere in the world related to rift settings, and also indicate OIB-like magma source. The associated syenite shows subduction-related features, possibly generated in a post-collisional setting. Magmatic zircon grains with high Th/U ratios in the syenite from the Nuapada lamproite form a coherent group with an upper intercept age of 2473±8Ma representing the timing of emplacement of the magma. Zircon grains in three lamproite samples yield four distinct age groups at ca. 2.4Ga, 2.2Ga, 2.0Ga and 0.8Ga. The 2.4Ga group corresponds to xenocrysts entrained from the syenite whereas the 2.2Ga group is considered to represent the timing of emplacement of the lamproites. The ca. 2.0Ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern Bastar and the adjacent Dharwar Cratons. A few young zircon grains in the syenite and lamproites show a range of early to middle Neoproterozoic ages from 879 to 651Ma corresponding to younger thermal event(s) as also represented by granitic veins cutting across these rocks and extensive silicification. Zircon Lu–Hf isotope data suggest magma derivation from a refertilized Paleo-Mesoarchean sub-continental lithospheric mantle, or OIB-type sources. The differences in Hf-isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale. A combination of the features from geochemical and zircon Hf isotope data is consistent with asthenosphere-lithosphere interaction during the lamproite magma evolution.The timing of lamproite emplacement in central India correlates with the global 2.2Ga record of LIPs. We link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction-accretion history prior to the Neoarchean cratonization, as well as the thermal blanket effect of the Earth's oldest supercontinent. Pulsating plumes and continued rifting generated voluminous dyke swarms across the Bastar and Dharwar Cratons, forming part of a major global rifting and LIP event.

Petrogenesis and thermal overprint of S-type granites in Helanshan region, North China Craton: Constraints on the 1.90 Ga khondalites decompression melting and 1.32 Ga tectono-thermal event

Widespread Paleoproterozoic S-type granites and khondalites (high-grade sillimanite-garnet gneisses) are exposed in the Khondalite Belt of the North China Craton (NCC). Porphyritic biotite granites in the Helanshan region from the western Khondalite Belt exhibit a gradual contact relationship with the neighboring khondalites. In order to constrain the petrogenesis of these granites and their genetic relationship with the khondalites, detailed geochronological data, as well as geochemical and whole-rock Sm-Nd and zircon Lu-Hf isotope compositions of these granites are reported. LA-ICP-MS zircon U-Pb dating on magmatic zircon cores yields an emplacement age of 1902±22Ma, whereas metamorphic rims define a metamorphic age of 1356±57Ma. The unpolished surfaces of zircon crystals selected based on the presence of rims visible in cathodoluminescence were further analyzed by SIMS depth profiling, which gave a more precise metamorphic age of 1317±18Ma. The Helanshan granites display typical S-type geochemical characteristics, e.g., high A/CNK (1.16–1.29) and K2O (5.09–5.86wt%) contents, but low FeOt/MgO (2.39–4.88) and P2O5 (0.15–0.23wt%) contents. Similar trace and rare earth element patterns, and consistent zircon Hf model ages (2366–2483Ma) and whole rock Nd model ages (2407–2499Ma) between the porphyritic biotite granites and the khondalites, suggest that they were derived from partial melting of khondalites. The geochemical character of the porphyritic biotite granites, including significant negative Eu anomalies, high Rb/Ba and Rb/Sr ratios, and variable HREE contents and (La/Yb)N ratios, suggest that they are probably related to the post-peak decompression stage that was characterized by biotite breakdown and the progressive replacement of garnet with the presence of K-feldspar and plagioclase in the residues. Homogeneous zircon εHf(t) values (mostly from −0.5 to +1.7), combined with low bulk-rock Fe2O3T content and CaO/Na2O ratios, preclude the contribution from mafic magma. Following the continental collision, the emplacement of the porphyritic biotite granites at ca.1.90Ga provides the latest limit on the timing of post-peak decompression metamorphism of the khondalites, and their formation supports a post-collisional mantle upwelling model to account for the 1.92–1.90Ga regional metamorphic/magmatic events. On the other hand, the metamorphic zircon rims indicate that S-type granites were overprinted by a 1.32Ga tectono-thermal event, which was probably related to the breakup of the Columbia supercontinent.

Geochemistry, U-Pb dating, and Lu-Hf isotopes of zircon and monazite of porphyritic granites within the Jiao-Liao-Ji orogenic belt: Implications for petrogenesis and tectonic setting

Abundant porphyritic granites, including Grt-bearing and Bt-bearing porphyritic granites, and flesh-red porphyritic granites, as various scale batholiths are widely distributed within the Jiao-Liao-Ji belt (JLJB), which extends for a distance of at least 1000km, rather than being limited to sporadic outcrops in southern Liaoning and Jilin as stated in previous studies. On the basis of morphology, CL and BSE zoning patterns, and mineral inclusions of dated zircon and monazite grains from samples of various porphyritic granites, the grains exhibit evident magmatic zones with distinct cores and rims and preserve felsic mineral inclusions of Qtz+Kfs+Pl+Qtz±Ap in both domains. The magmatic zircon cores and rims from 18 dated samples yielded two distinct weighted mean age groups, from 1872±9 to 1866±7Ma and 1851±14 to 1842±10Ma, with age peaks at 1869±1.7 and 1848±2.4Ma, respectively. Similarly, the magmatic cores and rims of monazites from 10 dated samples also showed two distinct weighted mean age groups, from 1870±3 to 1864±2Ma and 1851±6 to 1842±12Ma, with age peaks at 1868±0.8 and 1847±1.2Ma, respectively. The numerous U-Pb age data of both zircons and monazites revealed that the JLJB experienced a major episode of granitic magmatism in the Paleoproterozoic with initial emplacement timing of melts at ∼1.87Ga and crystallisation end timing of melts at ∼1.84Ga as represented by the magmatic cores and rims of the zircons and monazites, respectively. A combined study of whole-rock geochemistry and zircon Lu-Hf isotopic analyses revealed that the three types of porphyritic rocks are enriched in HREE, Zr, Nb, Ga, and Y and are depleted in V, Cr, and Ni, and that most have high TFeO/MgO ratios and Zr-saturation temperatures of ∼850°C, which is suggestive of an affinity with A-type granite. Moreover, the dominant εHf(t) values of the magmatic zircons range from −4.8 to +3.3, which is consistent with those of the 2.2–2.1Ga calc-alkaline meta-granites in the JLJB. Considering the high contents of garnet, Al-rich paragneiss enclaves, and ∼1.92Ga inherited metamorphic zircons in the granites, these porphyritic rocks were most likely derived from the partial melting of the 2.2–2.1Ga calc-alkaline meta-granites with abundant involvement of Al-rich pelitic granulites from the basement of the JLJB. As the result of a newly combined study of traditional geothermobarometers and phase equilibria modelling together with geochronological U-Pb dating, a precise clockwise P-T-t path with a subsequent near isothermal decompression process has been well determined in the HP-MP granulite facies metamorphic rocks in the JLJB. Thus, the following sequence of events can be inferred. Abundant ∼2.2–2.1Ga granitic rocks and voluminous Paleoproterozoic sedimentary rocks were subducted to lower crustal depths and underwent a peak HP-MP granulite facies metamorphism at 1950–1900Ma. These granulite facies rocks were exhumed to middle crustal levels and experienced a post-peak MP-LP granulite facies metamorphism at 1875–1840Ma. The retrograde rocks continued to be exhumed to shallow crustal levels at 1830–1800Ma and were finally overprinted by late amphibolite facies retrogression. The numerous magmatic zircons and monazites from the various porphyritic granites record a distinct Paleoproterozoic granitic magmatic event with two evident age peaks of ∼1.87Ga and ∼1.84Ga, which are completely consistent with the post-peak MP-LP granulite facies metamorphism (1875–1840Ma), representing an anorogenic magmatic association formed in an extensional setting possibly resulting from mantle upwelling and lithospheric thinning and resulting in the violent partial melting of ∼2.2–2.1Ga meta-granites along with abundant Al-rich pelitic granulites. Considering these data in combination with previous whole-rock geochemistry and age data, it can be stated that similar porphyritic granites are not only limited to the entire JLJB but are also widely distributed in North and South Korea. Thus, it can be concluded that the ∼1.87–1.84Ga porphyritic granites, together with massive rapakivi granites, Kfs-megacrysts, and porphyritic monzogranites, as products of an anorogenic granitic magmatic event, may have widely formed in both the JLJB and Korean Peninsula in an extensional and thinning tectonic setting.

Late Neoarchean–Paleoproterozoic arc-continent accretion along the Khondalite Belt, Western Block, North China Craton: Insights from granitoid rocks of the Daqingshan–Wulashan area

Late Neoarchean-early Paleoproterozoic granitoid rocks are widely exposed in the Daqingshan–Wulashan area in the central segment of the Khondalite Belt (KB), Western Block, North China Craton (NCC), and are characterized by widespread evidence of ductile deformation and anatexis. To improve our understanding of the formation and evolution of the KB, in this study we analyzed zircon U–Pb ages, zircon Lu–Hf isotopes, and whole-rock geochemistry of the granitoid rocks. LA–ICP–MS U–Pb analysis of zircons from eight representative granitoid samples indicates the granitoid rocks were emplaced at ca 2.45 and ca 2.50Ga, and underwent multi-stage metamorphism at ca 1.90–1.95, 2.45, and 2.50Ga. Zircon Lu–Hf isotopic analysis shows that the granitoids have positive zircon εHf(t) values with an average of +4.36, and two-stage depleted mantle zircon Hf model ages (TDM2) clustering around 2.7–3.0Ga, indicative of a juvenile crustal source that formed at ca 2.7–3.0Ga. Furthermore, whole-rock geochemical analysis of 34 granitoid samples reveal them to be magnesian, low- to high-K, calcic to calc-alkalic, and metaluminous to weakly peraluminous (alumina saturation index (ASI)=0.74–1.17). They are characterized by high total rare-earth-element (REE) contents (57.45–346.96ppm), enrichment in light REE, and depletion in heavy REE with (La/Yb)n ratios of 8.33–224.16. They have weak Eu anomalies (Eu/Eu∗=0.37–2.53, average=1.08), high Sr contents (>300ppm), and relatively low Y and Yb concentrations (average=10.55 and 0.96ppm, respectively). Primitive-mantle-normalized trace-element diagrams show that the granitoid samples are depleted in high-field-strength elements (Nb, Ta, U and Ti) and enriched in large-ion lithophile elements (Ba, K, Rb and Sr). In general, the samples have geochemical characteristics consistent with cordilleran I-type granitoids, which form in subduction-related magmatic arcs. Therefore, our results, together with the occurrence of synchronous mafic rocks and other available geological data, indicate the KB contains multiple magmatic arcs and underwent long-term deposition and multi-phase metamorphism, analogous to Phanerozoic accretionary orogens such as the Cordilleran orogen. Consequently, we infer that the KB underwent long-term arc-continent accretion along the southern margin of the Yinshan Block during the late Neoarchean–Paleoproterozoic, and late-stage continent–continent collision between the Yinshan and Ordos blocks at ca 1.90–1.95Ga.

Early crustal evolution of the eastern Yangtze Block: Evidence from detrital zircon U-Pb ages and Hf isotopic composition of the Neoproterozoic Huashan Group in the Dahongshan area

The Yangtze Block is separated into the eastern Yangtze Block (EYB) and western Yangtze Block (WYB) by the Chongqing–Huaying line (CHL). An integrated study of detrital zircon Lu-Hf isotopes and U-Pb ages from two sandstones in the Huashan Group together with previous studies reveals six major tectonothermal events in the EYB occurring at about 2.87Ga, 2.67Ga, 2.5Ga, 2.0Ga, 1.84Ga and 0.8Ga. Combined with paleogeographic map, this study reveals distinct detrital zircon U-Pb ages and Hf isotopic characteristics in the western EYB and eastern EYB. The former has most zircon U-Pb ages grouped at about 2.0Ga, 2.67Ga and 2.87Ga with sporadic 2.5Ga ages. The ∼2.5Ga zircons show negative to slightly positive εHf(t) values. However, the latter has significant ages grouped at ∼2.0Ga and ∼2.5Ga with negligible 2.67Ga and older zircon ages. The ∼2.5Ga zircons show negative to high positive εHf(t) values. The Early Neoarchean (2.7–2.6Ga) was a significant period for production of mature continental crust in the western EYB and the majority of crustal materials were extracted from the depleted mantle until then. Zircon Hf isotopic compositions indicate that the Late Neoarchean to Early Paleoproterozoic event (∼2.5Ga) involved both reworking of old crust and juvenile crust growth. With previous studies of sedimentary facies, lithochemical compositions, zircon morphology and zircon Hf isotopes, it is proposed that there are unexposed ∼2.5Ga basement rocks in the EYB. During the 2.2–1.8Ga, subduction processes, collisional and post-collisional events were recorded in the north and west of the EYB, which can be correlated to the assembly and breakup of the supercontinent Columbia. Two changes in εHf(t) value at ∼840Ma and ∼790Ma have been found from detrital zircons in the northern margin of the EYB, which probably represent arc–continent collision and continent–continent collision events, respectively. This long-term subduction process occurring at 1100–790Ma in the EYB appeals for a peripheral position for the Yangtze Block in the supercontinent Rodinia.

Petrogenesis and tectonic implications of the charnockites in the Yishui Terrane, North China Craton

A combined study of zircon U-Pb ages, Lu-Hf isotopes and whole-rock geochemistry was carried out for representative charnockites from the Yishui terrane in the Western Shandong Province, NCC. The results demonstrate that the charnockites in the Yishui terrane are of igneous origin rather than derivation from remelting or metamorphism of supracrustal rocks. Zircon U-Pb dating for the charnockites in the Yishui terrane indicates protolith emplacement around 2.52–2.56Ga and synchronous metamorphism around 2.50–2.53Ga. Zircon Lu-Hf isotopes analyses show that the charnockites have positive εHf(t) values with an average +4.03, and depleted mantle two-stage zircon Hf model ages (TDM2) mainly cluster around 2.7–3.0Ga, indicative of a source of juvenile crust formed around 2.7–3.0Ga. Furthermore, the charnockites with <70% wt% SiO2 tend to be magnesian calcic to calc-alkalic and metaluminous, only a small population of the charnockites with >70wt% SiO2 are ferroan alkali-calcic and weakly peraluminous, which are consistent with geochemical features of Cordilleran-type granitoids, suggesting a deeply eroded magmatic arc derived from remelting of juvenile crust mainly formed around 2.7–3.0Ga. Taken the comprehensives of available whole-rock geochemical and Zircon Lu-Hf isotopic data of the charnockites, synchronous emplacement and metamorphism, high-temperature setting of charnockites, granulite-facies metamorphism of anticlockwise P-T path in the Yishui terrane as well as the whole NCC, we conclude that the combined geodynamics of mantle plume and oceanic crust subduction might contribute to the formation of the charnockites in the Yishui terrane as well as similar late Archean charnockites in other areas of the NCC, further implying extensive occurrences of modern-style plate tectonic accretions in late Archean in the NCC.

A reworked ∼3.45 Ga continental microblock of the North China Craton: Constraints from zircon U-Pb-Lu-Hf isotopic systematics of the Archean Beitai-Waitoushan migmatite-syenogranite complex

The Archean Beitai-Waitoushan migmatite-syenogranite complex (BWMC) is located in the northeast of the Anshan-Benxi continent block (ABCB) where has ∼3.8Ga rocks outcropped in the northeastern North China Craton (NCC). The BWMC consists chiefly of weakly migmatized tonalitic-trondhjemitic gneisses, migmatites with various volumes of potassium-rich granitoid veins from either syenogranite magma or anatexis of tonalitic- trondhjemitic gneisses, monzo- and syenogranitic intrusive rocks. LA-ICP-MS and SHRIMP zircon U-Th-Pb isotopic analyses reveal that the migmatized tonalitic-trondhjemitic gneisses were formed at 3454–3484Ma, and were the partial sources of the syenogranitic rocks and entire protolith of the migmatites. The dominant monzo- and syenogranitic magmas were emplaced at 2500–2540Ma and generally contain inherited Paleoarchean zircon grains with apparent 207Pb/206Pb ages of >3300Ma. An amphibolite sample in the form of boudin in the migmatized tonalitic-trondhjemitic gneisses formed at 3414Ma. These Paleoarchean rock samples and the inherited Paleoarchean zircons from the Neoarchean migmatites, monzo- and syenogranite samples indicate that a ∼3.45Ga continent microblock existed prior to the ∼2.50Ga migmatization and syenogranitic magmatism.When integrated with previous zircon Lu-Hf isotopic data from the study area, our new LA-ICP-MS zircon Lu-Hf isotope analyses for dated zircon spots from six dated samples reveal that the magmatic precursors of the ∼3.45Ga samples and the ancient inherited zircons from the Neoarchean migmatites and intrusive granitoid rocks were primarily derived from ∼3.45Ga partial melting of juvenile crustal materials from the depleted mantle, and either the mantle or more ancient continent crustal materials with CHUR-like Lu-Hf isotopic systematics. However, some of the Neoarchean monzo- and syenogranitoid rocks and the granitoid veins in the migmatites exhibit hybrid Lu-Hf isotopic features derived from both ancient ∼3.45Ga continental and Neoarchean juvenile crustal materials, including partial mixing between the Neoarchean granitoid magma and plastic Paleoarchean gneiss relicts.