Hf Crustal Model Ages Research Articles

Cretaceous magmatic arc in Hainan and the peri-South China Sea as evidenced by geochemical fingerprinting of granitoids in the region

Mesozoic magmatic rocks occur widely in the South China Block and are generally interpreted as the manifestations of the subduction of the Paleo-Pacific oceanic lithosphere beneath Asia. Subduction-driven magmatism in southeast (SE) China continued from the Late Permian through the Late Cretaceous with an inferred lull between 125 Ma and 115 Ma that is known in the literature as the Cretaceous “magmatic quiescence”. We report in-situ zircon U–Pb ages, Hf–O and whole-rock Sr–Nd isotopes, and whole-rock geochemistry of Cretaceous granitoids on Hainan Island and discuss their magmatic evolution within the framework of the Late Mesozoic geodynamics of SE China. We recognize two main stages of the emplacement of Cretaceous granitoids on Hainan, first around 120 Ma and then around 100–95 Ma, displaying high-K calc-alkaline, I-type geochemical affinities. Granites in both age groups are enriched in LILE and LREE, but depleted in Nb, Ta, Ba, Sr, and Eu. The 120 Ma granites have zircon εHf(t) values of –2.6 to 2.3 corresponding to Hf crustal model ages, ranging from 0.79 Ga to 1.03 Ga, and δ18O values ranging from 6.9‰ to 7.7‰. Zircons from 100–95 Ma granites have εHf(t) values of –4.2 to 1.1 corresponding to Hf crustal model ages of 1.08 Ga to 1.42 Ga, and δ18O values ranging from 6.7‰ to 8.4‰. Increasing εHf(t) values of the Cretaceous Hainan granites with younger crystallization ages indicate addition of more juvenile components and reworking of crustal material into their melt evolution. The εNd(t) values of the 120 Ma and 100–95 Ma granitoids range between –4.1 to –0.4 and –7.7 to –4.0, respectively. The calculated two–stage model age of the 100–95 Ma granitoids clusters between 1.25 Ga and 1.53 Ga. These isotopic data suggest that magmas of the Cretaceous granitoids were produced by partial melting of Mesoproterozoic metabasaltic rocks, which make up much of the crystalline basement of the southern Cathaysia block. The geochemical and isotopic characteristics of the Cretaceous granitoids on Hainan resemble those of magmatic arcs in the Circum–Pacific orogenic belts and identical to those of nearly coeval granitoid intrusions in the continental fragments within the South China Sea basin. We interpret these Cretaceous granitoids in the Peri–South China Sea region as the remnants of a once contiguous Late Mesozoic magmatic arc system that bounded the southern margin of the entire continental Southeast Asia. Our findings do not support the existence of an episode of magmatic quiescence in the geological record of SE China during the Aptian.

A uniform basement: Implications for the tectonics of Beishan Orogenic Belt in the southern Central Asian Orogenic Belt

The orogen is a significant window for studying the history and architecture of Earth; its architecture involves many significant issues. Currently, research on the architecture of orogenic belts mainly focuses on the process of orogeny, and few studies focus on the tectonics before the orogeny, which somewhat constrains orogen evolution. The nature of the basement(s) of microcontinents in the Beishan Orogenic Belt (BOB) in the middle Central Asian Orogenic Belt (CAOB) has been debated for a long time, which causes confusion about the tectonics of the BOB. This study conducted field surveys, geochronology, geochemistry, and Hf isotope analysis on the major microcontinents of BOB. The age information of ca. 1.4 Ga and the Paleoproterozoic-Archean with small scale were found in the northern BOB. The northern BOB (NBOB) and southern BOB (SBOB) (separated by the Hongliuhe-Niujuanzi-Xichangjing ophiolitic mélange belt) have experienced similar magmatic thermal events at ca. 1.4 Ga and ca. 0.9 Ga, which are revealed by the analogical tectonic setting, formation ages, and Hf isotopic features. The Precambrian basements of the NBOB and SBOB are analogous in terms of rock assemblages, detrital zircon ages, magmatic rock ages, εHf(t) of Precambrian rocks, and Hf crustal model ages TDMC of Paleozoic igneous rocks, which imply that they shared similar history and provenance and might originate from a uniform basement. The basement has no close tectonic affinity to the adjacent cratons or blocks, except the Baltica Craton and Laurentia Craton. And it might have been involved in the amalgamation of the Columbia Supercontinent and be situated on the periphery of the Rodinia Supercontinent, and then fragmented when the Rodinia Supercontinent rifted apart.

The key role of volatile‐rich magma in the formation of porphyry molybdenum deposits: A case study of the Chalukou deposit, China

Volatile element abundance is a crucial factor triggering mineralization and controlling the enrichment of molybdenum in porphyry deposits. The Chalukou deposit is the largest porphyry Mo deposit in NE China, with an average grade of 0.087% Mo. In this contribution, we present petrology, bulk geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes, and apatite geochemistry for the Chalukou deposit. The intrusive rocks include pre‐mineralization monzogranite, syn‐mineralization quartz porphyry, fine‐grained porphyry and granite porphyry, and post‐mineralization monzogranite and feldspar porphyry. These granitoids are metaluminous to peraluminous, and belong to alkali‐calcic to calc‐alkalic series. Zircon εHf(t) values of granitoids range from +0.2 to +5.7 with corresponding Hf crustal model ages of 805–1170 Ma, indicating a Mesoproterozoic juvenile crustal source modified by mantle‐derived magma. They are characterized by logf(O2) of −16.1 to −9.4, with an average of −12.5, ΔFMQ of +0.8 to +7.9, with an average of +4.5, showing a relatively high oxidation state for the syn‐mineralization magma. The apatites in quartz porphyry have the highest F contents, ranging from 3.61 to 4.62 wt%. At Chalukou, F‐rich magma is conducive to the convection of magma and promotes the efficient separation of differentiation magma, making the magmatic‐hydrothermal fluid circulate many times, eventually resulting in the accumulation of ore‐forming materials on the top of the magma chamber and gradually aggravating mineral enrichment processes.

Mantle magmatism, metamorphism and anatexis: evidence from geochemistry and zircon U–Pb-Hf isotopes of Paleoproterozoic S-type granites, Khondalite Belt of the North China Craton

ABSTRACT S-type granites constitute an important component of the Paleoproterozoic Khondalite Belt in the North China Craton. Here we present results from petrography, geochemistry and isotope geochronology on the porphyritic garnet-bearing syenogranite and garnet-bearing monzogranite samples in the Jining-Liangcheng area. The geochemical characteristics of these samples indicate formation through partial anatexis of the khondalites, with heat and material input from mantle-derived magma. Geochemical similarities between the porphyritic garnet-bearing syenogranite, garnet-bearing monzogranite, and metapelitic gneiss suggest their broad affinity. Sensitive high-resolution ion microprobe zircon U–Pb dating revealed that the S-type granites formed at ca. 1.92–1.90 Ga and were subsequently metamorphosed at ca. 1.85 Ga. The ca. 1.92–1.91 Ga porphyritic garnet-bearing syenogranite shows zircon εHf(t) values of −1.94–+3.38 with two-stage Hf crustal model ages (TDM2) ages of ca. 2.42–2.59 Ga. The 1.91–1.90-Ga garnet-bearing monzogranites show zircon εHf(t) values ranging from −4.36 to +0.38, with TDM2 ranging from ca. 2.57 to ca. 2.82 Ga. The geochemical isotopic compositions suggest that the porphyritic garnet-bearing syenogranite and garnet-bearing monzogranite originated from the partial melting of pre-existing crust of heterogeneous compositions with the addition of mantle-derived material. On the basis of our results, combined with geological data on the Paleoproterozoic structural evolution of the Khondalite Belt, we assume that the timing of the metamorphism and anatexis in the Jining–Liangcheng area is correlated with a regional metamorphism and mantle-derived magmatism.

Provenance and tectonic setting of the Sumdo Formation in the Lhasa Terrane, Tibet: Implications for early subduction evolution of the Sumdo Paleo–Tethys Ocean

The tectonic setting of the Tangjia–Sumdo metamorphic belt, which separates the North Lhasa Block (NLB) and South Lhasa Block (SLB), remains controversial. Moreover, the sedimentary evolution of the Tangjia–Sumdo metamorphic belt has been little studied, particularly during the early subduction evolution of the Sumdo Paleo-Tethys Ocean (SPTO). Here we present petrological, geochemical, and zircon U-Pb geochronological data on the clastic rocks and metabasaltic interlayers collected from the Sumdo Formation in the Sumdo area. The Sumdo Formation consists of metamorphosed sandstone, graywacke, phyllite, and interlayered metabasalts. Detrital zircon U-Pb dating of the metasandstone and quartz schist identified a youngest zircon age group of 389–316 Ma, which have negative εHf(t) values (−20.5 to −1.5) and old Hf crustal model ages (TCDM = 1450–2654 Ma). The zircon trace element features and Hf isotopic compositions show that the sedimentary detritus was sourced from the NLB, which indicates that this terrane experienced Late Devonian–early Carboniferous magmatism. The ages of the youngest detrital zircons (YC2σ age of 324 ± 13 Ma) indicate that the Sumdo Formation formed mainly during the late Carboniferous–early Permian. Combined with geochemical data of the metabasalts and other regional geological evidence, we conclude that the Sumdo Formation formed in an initial forearc basin. The Sumdo Formation was likely deposited along an active continental margin according to the in–situ suture model, where northward subduction of the Sumdo Paleo–Tethys oceanic lithosphere occurred beneath the NLB. As such, the Sumdo Formation provides a sedimentary record of the early subduction evolution of the SPTO.

Early Cretaceous A‐type Granites in the Dandong Area, NE China and its Geodynamical Implications

AbstractA‐type granites, as an important petrologic sign to build up environmental recognition, were mainly formed in extensional tectonic settings. A biotite syenogranite from the Fenghuangshan pluton in Dandong, Liaoning Province gave SHRIMP zircon U‐Pb ages of 122.5 ± 1.6 Ma, 124.9 ± 1.7 Ma and 126.9 ± 1.1 Ma. The monzogranites have SHRIMP zircon U‐Pb ages of 118.2 ± 1.6 Ma, 128.1 ± 1.7 Ma and 131.6 ± 1.9 Ma, giving an emplacement age for the pluton in the Early Cretaceous. SiO2 is 65.48–74.49 wt%, whereas that of K2O is 4.16–6.44 wt%, and that of Na2O is 2.99–4.70 wt%. They also contain 13.24–15.76 wt% of Al2O3, with an A/CNK ratio of 0.92–1.10, averaging 1.02. The alkalinity rate (AR) ranges from 2.68 to 5.12, and this range is within the AR of peraluminous type rocks. The granites of Fenghuangshan pluton are characterized by high contents of Na and K and low contents of Ca (thermophile element) and Mg, which are features of A‐type granites. The (Na2O + K2O) – Fe2O3∗ × 5 – (CaO + MgO) × 5 discrimination diagram also shows that Fenghuangshan pluton is an A2‐type granite. The above granite has zircon ∊Hf(t) values ranging from –17.06 to –9.09, with single‐stage Hf model ages (TDM) of 1141 Ma to 1498 Ma and two‐stage Hf crustal model ages (TDMC) of 1762 Ma to 2263 Ma. A comprehensive analysis suggests that the Fenghuangshan pluton might have been formed from the lithospheric‐plate sliding during the late stages of evolution of hot rift structures and might have been closely associated with the tectonic settings of Mesozoic Eurasia and the ancient Pacific Plate.

Crustal architecture studies in the Iranian Cadomian arc: Insights into source, timing and metallogeny

The Jalal Abad magmatic rocks, situated at the southern edge of the Saghand-Bafgh-Zarand district, include a thick pile of Cadomian extrusive and pyroclastic units intruded by younger granitoid stocks. New zircon U–Pb ages show eruptions at ∼552 Ma, followed by emplacement of granodiorite at ∼537 Ma. The Jalal Abad magmatic rocks have typical high-K and shoshonitic signatures, and are characterized by enrichment in large-ion lithophile elements (LILEs) and depletion in high-field-strength elements (HFSE). Zircon ɛHf(t) from the Jalal Abad magmatic rocks ranges from +3.9 to −3.9 for volcanic rocks and −1.2 to +8.1 for granodiorite. Zircon δ18O values for the Jalal Abad are variable from +5.1 to +8.8‰, progressively higher than those of mantle-derived melts. The whole-rock ɛNd(t) values range between −7.7 to −7.4 for granodiorite, −4.6 to −3 for volcanic rocks and −6.2 to −8.2 for ignimbrites/tuff. The whole-rock Nd and zircon Hf crustal model ages (TDMC) for the Jalal Abad magmatic rocks range between 0.8 and 2.3 Ga. All of the Jalal Abad magmatic rocks have quite similar trace element patterns, and slightly different whole-rock Nd and zircon Hf isotopic composition, indicating the involvement of the thick continental crust during the formation of these rocks. Modeling of zircon Hf–O data, bulk-rock trace elements, and Sr–Nd isotopes suggest the magmas were generated by interaction of mantle–derived melts with thick continental crust through assimilation/fractional crystallization (AFC) processes. However, crustal architecture studies in the Iranian Cadomian arcs show that AFC processes were more important during the Mesoarchean–Early Neoproterozoic (3000–1000 Ma), whereas juvenile magmas became increasingly important to the Cadomian (600–500 Ma) magmatism. Early Cambrian intrusive magmas seemingly intruded sedimentary sequences in the study region and provided magmatic constituents and a heat source for hydrothermal processes and mineralization.

Petrogenesis of the Late Triassic Biluoxueshan granitic pluton, SW China: Implications for the tectonic evolution of the Paleo-Tethys Sanjiang Orogen

The Sanjiang Orogen is important for us to better understand the tectonic evolution of the Paleo-Tethys Ocean. However, the petrogenesis and tectonic setting of the Late Triassic igneous rocks in the central part of the orogen are poorly understood. In this study, we present new whole-rock elemental and isotopic compositions for the Biluoxueshan Pluton, which consists of quartz diorite, granodiorite, and alkali-feldspar granite. Zircon U-Pb dating yields crystallisation ages of 231 ± 1 Ma for the quartz diorite, 227 ± 1 Ma for the granodiorite, and 227 ± 2, 224 ± 2, 222 ± 1, and 217 ± 3 Ma for alkali-feldspar granites, indicating a prolonged emplacement of the pluton. Quartz diorites are metaluminous, high-potassium calc-alkaline, and magnesian in composition. Granodiorites are characterized by peraluminous composition and the existence of normative-corundum, resembling S-type granite. They have negative zircon εHf(t) values (−13 to −10.8) and old Hf crustal model ages (2060–1920 Ma), indicating a Paleoproterozoic crustal source. Alkali-feldspar granites are metaluminous to weakly peraluminous, have higher SiO2 content, FeOT/MgO ratio and differentiation index (DI) than other samples, and pronouncedly negative Eu anomalies, which are characteristics of highly fractionated granites. They have narrow εHf(t) values of −2.7 to +2.6 with corresponding Hf crustal model ages of 1410–1060 Ma, indicating a Mesoproterozoic juvenile crustal source modified by mantle-derived magma. By combining previous and the new data, we proposed a new tectonic evolution model of a Late Triassic northward scissor-like post-collisional extension during ca. 235–223 Ma in the Changning-Menglian Suture Zone.

Late Paleoproterozoic post-collisional bimodal magmatism in the North China Craton: Insights from the Miyun gabbro-granite suite

Following the final cratonization of the North China Craton (NCC) through the assembly of major crustal blocks, the craton witnessed post-collisional magmatism during late Paleoproterozoic with the formation of diverse types of magmatic suites in the western and eastern margins of the Trans-North China Orogen (TNCO). Here, we investigate the anorogenic granitoid and associated gabbro from the Miyun complex located at the eastern margin of the TNCO. We present petrology, geochemistry, and zircon U-Pb, and Lu-Hf data on these rocks. The granite pluton is composed of a rapakivi phase with almost totally digested mafic magmatic enclaves, whereas the granite phase hosts gabbroic enclaves. The granitoids show high SiO2 content (71.28 to 78.83 wt%), with peraluminous A2 type affinity and within plate (rift-related) features. The magmatic zircon grains from the granite yielded 207Pb/206Pb weighted mean age of 1696 Ma. A similar crystallization age of 1683 Ma for the gabbro indicates coeval bimodal magmatism. Both rocks carry zircon xenocrysts with older ages that are consistent with the magmatic and metamorphic events recorded from the basement rocks. The εHf(t) values of the zircon grains from the granitoid are markedly negative (−7.9 to −5.0) with two-stage Hf crustal model ages (TC DM) ranging from 2688 Ma to 2855 Ma, indicating the involvement of Mesoarchean to Neoarchean crustal components in the magma source. In contrast, the zircon grains from gabbro show both positive and negative εHf(t) values, suggesting magma derivation from depleted mantle sources with minor juvenile crustal component. We envisage that lower crustal melting induced by mantle-derived mafic magmas during post-collisional rifting generated felsic magmas, into which the mafic magma was injected, resulting in magma mixing and mingling. In conjunction with the information from post-collisional magmatic suites in the adjacent locations including gabbro-anorthosite complex, and similar aged magmatic complexes within the TNCO, we propose a major post-collisional magmatic event in the NCC which involved extensive mantle upwelling and lower crustal melting.

Geochemical and geochronological constraints on the genesis of Pliocene post-collisional granite porphyry and shoshonite in Quanshuigou, western Kunlun Mountains, NW Qinghai–Tibet Plateau

ABSTRACT Post-collisional K-rich magmatic rocks of the Qinghai–Tibet Plateau provide important information for understanding the continental collision and uplift of this plateau during the Cenozoic. However, the source of these K-rich rocks is still debated, and limited investigations have been conducted in the western Kunlun Mountains (WKM) in the northwestern margin of the plateau. In this paper, we present geochemical, geochronological, and Sr–Nd–Hf isotope data for Quanshuigou post-collisional K-rich igneous rocks from the WKM. Geochronological results show that these rocks were emplaced during two stages: (1) ca. 5.3 Ma, as an intrusive suite of granite porphyries; and (2) ca. 4.8 Ma, as a suite of shoshonites. These rocks are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), and depleted in heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs). Compositions of the granite porphyries classify these rocks as high-K calc-alkaline peraluminous A-type granites. Combining the negative zircon ε Hf(t) values (−6.9 to −1.1) with Hf crustal model ages (TDM2) of 1.16–1.53 Ga and negative ε Nd(t) values (−5.31 to −4.96) with two-stage Nd model ages (TDM2) of 1.22–1.46 Ga, these signatures suggest that the granite porphyries most probably originated from partial melting of thickened lower crust with limited input of mantle-derived magmas. In contrast, the shoshonites have low SiO2 contents (50.84–53.94 wt.%), relatively high Mg# values (50–57), and εNd (t) values ranging from −6.18 to −5.34, with single-stage Nd model ages (TDM1) of 0.97–1.02 Ga. Our analyses show that the parental magma of the shoshonites probably formed by partial melting of EMII-type lithospheric mantle, with the addition of subducted and recycled oceanic sediments. Hence, we conclude that these granite porphyries and shoshonites formed in a post-collisional, extension-related geodynamic setting and that the melting was probably triggered by motion on the Altyn Tagh strike-slip fault system.

Petrogenesis of Archean TTGs and potassic granites in the southern Yangtze Block: Constraints on the early formation of the Yangtze Block

The southern Yangtze is underlain by Mesoarchean igneous rocks that were emplaced in two pulses, including trondhjemites at ca. 3092–3071 Ma followed by potassic granites at 2920 Ma. These represent the oldest TTG suites identified in the southern Yangtze and the oldest potassic granites in the entire Yangtze Block. Hf isotopic analysis reveals εHf(t) values of −2.49–7.49 and Hf crustal model ages (TDMC) of 3601–3000 Ma for zircons from the trondhjemites, whereas those from the potassic granites show εHf(t) values of −1.79–4.18 and TDMC ages of 3453–3043 Ma. The trondhjemites have high SiO2, Mg# and low Al2O3 and K2O/Na2O, and are highly evolved with low Ni, Cr and Co. The trondhjemites are characterized by low Sr/Y, Eu/Gd and (La/Yb)N, and high Y and HREE, typical of high-HREE and low-pressure TTGs. Their geochemical and isotopic compositions indicate that they are derived from melting of juvenile mafic crust with little contribution from older crustal materials, consistent with a plagioclase-bearing basaltic source. The multielement patterns of potassic granites are similar to that of the trondhjemites, albeit with lower HREE and Y contents. Their high K2O values, strongly fractionated REE patterns and low Y contents indicate the presence of garnet and/or amphibole as residual phases in the source region, which indicates they formed at higher pressure than the trondhjemites. The isotopic and geochemical data imply that the formation of the potassic granites could be related to reworking of older TTGs. The increasing K2O/Na2O of the 3092–3071 Ma trondhjemites to potassic 2920 Ma granites corresponds with stabilization, maturation and thickening of the Archean continental crust in the southern Yangtze. The geochemical data of the TTGs in the Kunming region show important differences from that of contemporaneous TTGs from the Kongling Complex, suggesting that southern Yangtze is composed by an independent old nucleus, which is exotic to the northern Yangtze. A synthesis of petrogenesis, geochronology, geochemistry and isotope data of Archean granites of the Yangtze Block provides important insights into the architecture of its Archean crust. We propose that the Yangtze Block can be subdivided into discrete northwestern, northeastern and southern domains, but which are all affected by late Paleoproterozoic tectonothermal events, suggesting that they had been assembled together by then to form the united Yangtze Block.

Major lithologies of the high-grade Zhoutan terrane within the Cathaysia Block and their tectonic implications for the Neoproterozoic - Paleozoic South China

Pre-Devonian crystalline basement of the Cathaysia Block was united through the Wuyi-Yunkai orogeny. The uplifted orogenic core is dominantly composed of Paleozoic high-grade terranes occurring in a northeast-southwest trending belt. The Zhoutan terrane in the middle part of this belt is one of the key terranes to reveal the tectonic architecture of the South China Block. However, how to correlate it with other high-grade terranes, what kind of rock records are preserved in this terrane and their tectonic implications for the Wuyi-Yunkai orogen are still unresolved. This paper carries out an integrated study on the petrology, zircon U--Pb geochronology, geochemistry and zircon Lu--Hf isotopic compositions of the main rock types in the Zhoutan terrane, with a purpose of better understanding the Wuyi-Yunkai orogeny. Mafic granulite (noritic) of high-T and low-P conditions occurs as lenses within the Zhoutan Formation. The zircon U--Pb geochronological data give magmatic and metamorphic ages of 460–450 Ma and ~ 430 Ma, respectively. Neoproterozoic and Paleoproterozoic (1.89 Ga) xenocrysts also occur. Meta-pelites of the Zhoutan Formation experienced high T/P amphibolite facies metamorphism, and ages of their detrital zircons are dominantly Neoproterozoic (810–820 Ma) with some subordinate Paleo- to Mesoproterozoic and Archean signatures. Amphibole gneiss layers of this formation give a Paleozoic metamorphic age of ~450 Ma, consistent with the high-P amphibolite facies metamorphism of the neighboring Longyou terrane. Fine-grained garnet mica-schist of the Wanyuan Formation consists of greenschist to amphibolite facies mineral assemblage and detrital zircons of these meta-sediments display both Neoproterozoic and early Precambrian ages at ~770 Ma, ~820 Ma, ~850 Ma, ~1.84 Ga and 2.48 Ga. Metamorphosed calc-silicates of the Wanyuan Formation show similar detrital zircon age peaks of 624 Ma, 780–790 Ma, ~810 Ma, 840–850 Ma, 1.8–1.98 Ga and ~ 2.48 Ga, and a Paleozoic metamorphic age of ~447 Ma. The Cizhu pluton is a composite granitoid body intruding the Zhoutan and Wanyuan formations, with emplacement ages ranging at least from 485 Ma to 446 Ma. εHf(t) values of zircons from the mafic granulite range from −10.9 to +8.5, indicating its protolith derived from enriched mantle sources with or without crustal contaminations. The Cizhu magmatic event is a crustal reworking event as indicated by the coherently negative zircon εHf(t) values and ancient Hf crustal model ages of 1530–1830 Ma. Zircon εHf(t) values of the metamorphosed calc-silicates show large variations, ranging from −21.2 to +11, consistent with its complex provenances. The deposition of the sedimentary rocks of the Zhoutan and Wanyuan formations is consistent with the development of the Neoproterozoic-Paleozoic Nanhua Rift. The development of continental margin sequences like the Zhoutan and Wanyuan formations, the evolution of the Paleozoic metamorphism from early higher P/T metamorphic stage to later lower P/T stage, as well as the generation of the Paleozoic mafic-ultramafic rocks and the intermediate Cizhu pluton, are best explained by collision to post-collision settings. We, therefore, conclude that the Zhuotan terrane (as well as other high-grade terranes) witnessed a whole geological cycle, from early rifting to the closure of a rifted basin (Nanhua Basin), and the final lithospheric delamination following the rejoining of continental blocks flanking the rift.

Petrogenesis and tectonic setting of Early Paleozoic granites and high-Mg diorites in the Northern Qilian Orogen, China

The Northern Qilian Orogenic Belt (N-QOB) was formed by oceanic subduction and collision between the Alashan and Central Qilian Belt in the Early Paleozoic. New zircon U–Pb ages, Hf isotopic and whole-rock elemental data of the intrusive rocks in the central N-QOB have been conducted to constrain the tectonic evolution of N-QOB. Zircon dating results revealed that the Ladonggou, Suyougou granitic plutons and Xichagou dioritic pluton were emplaced at 505 ± 3 Ma, 471 ± 3 M and 425 ± 3 Ma, respectively. The Ladonggou monzogranite displays depletion of Nb, Ta, Ti, P and negative εHf(t) values (−6.5 to −0.3), and old Hf crustal model ages (1.5–1.9 Ga), suggesting generation from melting of ancient crust above subducted North Qilian oceanic slab. The Suyougou granite possesses geochemistry of I-type granite. The relative enrichment of LILEs, depletion of HFSEs and negative Eu anomalies, as well as prominent Hf isotope heterogeneities and old Hf crustal model ages (2.1–2.5 Ga) suggest a magma source of ancient crust mixed with minor mantle-derived melts in a subduction-related setting. Diorites from the Xichagou plutonare characterized by high Mg# values, enrichments in Cr, Ni, Y, Yb and high Sr/Y ratios, and convincing subduction-related features, suggesting generation from partial melting of subducted sediments mixed with mantle components. Taking all these geochemistry and geochronology together with the regional geology, we interpreted the Ladonggou monzogranite, Suyougou granite and Xichagou diorite were related to the long-term northward subduction of North Qilian oceanic lithosphere during ca. 505 and 425 Ma.

Integrated U–Pb, Lu–Hf and (U–Th)/He analysis of zircon from the Banxi Sb deposit and its implications for the low-temperature mineralization in South China

Low-temperature Sb (Au–Hg) deposits in South China account for more than 50% of the world’s Sb reserves, however, their genesis remains controversial. Here we report the first study that integrates U–Pb and Lu–Hf analysis by LA-(MC)-ICPMS and conventional (U–Th)/He analysis, all applied to single zircon crystals, in an attempt to constrain the origin and timing of world-class Sb (Au–Hg) deposits in Banxi (South China). Zircon separated from a quartz-stibnite ore and an altered country rock samples revealed similar U–Pb age spectra defining two major populations – Paleoproterozoic (~1900–2500 ​Ma) and Neoproterozoic (~770 ​Ma), which are characterized by variable εHf(t) values (–10.7 to 9.1 and –16.5 to 11.2, respectively) and Hf crustal model ages (TDMC) (2.48 to 3.24 ​Ga and 0.97 to 2.71 ​Ga, respectively). The U–Pb age and Hf isotopic features of the zircons are consistent with the Banxi Group in the region, indicating that the zircons involved in the low-temperature hydrothermal system were originally from the Banxi Group country rocks. Thirty-three mineralization-related zircon crystals yielded a mean (U–Th)/He age of 123.8 ​± ​3.8 ​Ma, which is interpreted to represent the timing of the latest low-temperature mineralization stage of the Banxi Sb deposit. The combined U–Pb, Lu–Hf and (U–Th)/He data suggest that Precambrian basement rocks were the major contributors to the low-temperature mineralization, and that Early Cretaceous (130–120 ​Ma) could be the most important ore-forming epoch for the Sb deposits in South China. This study also demonstrates the analytical feasibility of integrated U–Pb - Lu–Hf - (U–Th)/He “triple-dating”, all applied to single zircon crystals. This approach reveals the full evolution of zircon, from its origin of the magmatic source, through its crystallization and low-temperature cooling. Although this study demonstrates the usefulness of this integrated approach in dating low-temperature mineralization, it has great potential for zircon provenance and other studies that may benefit from the large amount of information that can be extracted from single zircon crystals.

Neoproterozoic felsic magmatism in southern Kerala, India: The building blocks of Gondwana

The assembly of Gondwana supercontinent involved multiple stages of continent convergence during the Neoproterozoic including arc magmatism and final collisional metamorphism. Peninsular India occupies a key position in the Gondwana supercontinent assembly where widespread Neoproterozoic magmatic records are preserved. Here, we investigate representative felsic magmatic intrusions from the Achankovil Suture Zone that marks the boundary between the Madurai and Trivandrum crustal blocks. We present petrological, geochemical, and zircon U‐Pb and Lu‐Hf data from the Chengannur (CH) and Pathanapuram (PT) plutons. Petrographic studies on syenogranites from the CH pluton indicate I‐type features, and feldspar thermometry shows ultrahigh temperatures (~1,000°C) corresponding to similar temperatures reported for the surrounding metamorphic rocks. Geochemically, the PT suite displays island arc affinity, whereas the CH suite shows adakitic, oxidized A‐2 type features. In tectonic discrimination plots, the CH samples correspond to volcanic arc granite, whereas the PT samples traverse syn‐collisional granite and volcanic arc granite zones, indicating a transitional feature. Trace element relationships suggest magma fractionation dominantly controlled by plagioclase, K‐feldspar, amphibole, and biotite. Magmatic zircon grains from the CH rocks show upper intercept ages in the range of 783 to 819 Ma and lower intercept ages in the range of 519 to 545 Ma, with cumulative age peaks at 766 and 529 Ma. The combined age population of monzogabbro, granodiorite, and granite from the PT pluton shows distinct peaks at 1,021, 950, and 537 Ma. Zircon grains from the CH pluton show dominantly negative εHf (t) values in the range of −5.8 to −13.4 and yield Hf depleted model age (TDM) ranging from 1,541 to 1857 Ma and Hf crustal model ages ( ) of 2,029 to 2510 Ma. In contrast, zircon grains from the PT pluton show dominantly positive εHf (t) values (2.9 to 9.8) with depleted model ages (TDM) in the range of 1,145 to 1434 Ma and Hf crustal model ages ( ) in 1,164 to1,686 Ma. The zircon U‐Pb and Lu‐Hf data clearly indicate that the timing of magmatism and magma sources is different for the two plutons, although both witnessed a common metamorphic event during late Neoproterozoic–Cambrian. The PT pluton was emplaced during the early Neoproterozoic with magma source involving mostly juvenile or depleted mantle components, as also attested to by the geochemical signature of arc affinity. In contrast, the CH pluton formed later during mid‐Neoproterozoic with magma from deeper source and dominated by recycled Paleoproterozoic material, which possibly involved depleted mantle components, both associated with an earlier subduction regime. The results reported in our study correlate with those from the arc magmatic rocks in the southern part of the Madurai Block as well as from the crustal blocks in the adjacent terrane of Sri Lanka. The extensive Neoproterozoic arc magmatism in a subduction‐related setting involving both juvenile additions and recycled older components represents the building blocks of Gondwana.

Sedimentary Evolution and Provenance of the late Permian‐middle Triassic Raggyorcaka Deposits in North Qiangtang (Tibet, Western China): Evidence for a Forearc Basin of the Longmu Co‐Shuanghu Tethys Ocean

AbstractThe tectonic origin of the >500‐km‐long E‐W trending Central Qiangtang metamorphic belt (CQMB), which separates the North Qiangtang block (NQB) and South Qiangtang block (SQB), remains controversial. Moreover, the coeval geological evolution of the southern NQB has been poorly investigated, particularly its tectonic relationship with the CQMB. Here we present stratigraphic, sedimentary, and provenance analyses of the late Permian‐middle Triassic depositional succession at Raggyorcaka in the southern NQB and test two radically different hypotheses for origin of the CQMB. A complete marine transgression‐regression sequence with two‐sided provenance characterizes the late Permian‐Triassic sedimentary rocks in the southern NQB. Sandstone petrological analyses reveal a prominent provenance transition to an active volcanic source beginning in the late Changhsingian. Detrital zircon U‐Pb geochronological results of the transgression subsequence show a concentrated youngest zircon group of 236–288 Ma (peak at ~248.1 Ma), with negative εHf(t) values (−25.3 to −0.2) and large Hf crustal model ages (T ; 1,311–2,887 Ma). These new findings show that the Raggyorcaka sequence was most likely deposited in an active continental margin. Combined with other evidence, we further infer that the Carboniferous‐Triassic successions of the southern NQB were most likely deposited in a forearc basin under the in situ suture model, that is, the northward subduction of the Longmu Co‐Shuanghu Tethys Ocean beneath the NQB. Moreover, the detrital zircon age distribution of the southern NQB suggests that the NQB probably drifted from the Gondwana supercontinent in the early Paleozoic and became adjacent to peri‐Cathaysian blocks no later than the Carboniferous.

Late Mesozoic intraplate rhyolitic volcanism in the North China Craton: Far-field effect of the westward subduction of the Paleo-Pacific Plate

AbstractThe Late Mesozoic was characterized by extensive volcanism, crustal extension, lithospheric thinning, and craton destruction in the North China Craton (NCC). Here we investigate the petrology, whole-rock geochemistry, zircon U-Pb geochronology, and Lu-Hf isotope of rhyolitic rocks from the Chicheng region of China along the northern margin of the NCC to constrain their petrogenesis, magma evolution, and associated geodynamic processes. The newly obtained zircon U-Pb age data constrain the eruption age of rhyolitic rocks at ca. 144–114 Ma during the Early Cretaceous with multiple magmatic pulses at ca. 141, ca. 137, and ca. 130 Ma as defined by the age peaks. Zircon Hf isotopic data show markedly negative εHf(t) values of –23.0 to –11.8, and corresponding Hf crustal model ages (TDMC) are in the range of ca. 2650 to 1944 Ma, suggesting magma derivation through melting of Paleoproterozoic crustal materials with minor input of reworked Neoarchean components. Geochemically, the rhyolitic rocks correspond to A-type granites, with a mixed arc- and subduction-related signature, although generated in an extensional intraplate setting through partial melting of the mafic lower crust and upper crustal fractional crystallization. We correlate the late Mesozoic intraplate volcanism to the westward subduction of the Paleo-Pacific Plate and its far-field effect. Lithospheric extension and slab rollback of the Paleo-Pacific Plate are considered as the main triggers for the multiple eruptions. The late Mesozoic volcanism in the study area and adjacent regions also broadly coincide with the tectonic transition from the Paleozoic Paleo-Asian to Mesozoic Paleo-Pacific subduction realm with concomitant compressional to extensional tectonic regime.

Late Mesozoic magmatism in the East Qinling Orogen, China and its tectonic implications

The Qinling Orogen in Central China records the history of a complex geological evolution and tectonic transition from compression to extension during the Late Mesozoic, with concomitant voluminous granitoids formation. In this study, we present results from petrological, geochemical, zircon U-Pb-Lu-Hf isotopic studies on the Lengshui felsic dykes from Luanchuan region in the East Qinling Orogen. We also compile published geochronological, geochemical, and Hf isotopic data from Luanchuan region and present zircon Hf isotopic contour maps. The newly obtained age data yield two group of ages at ∼145 Ma and 140 Ma for two granite porphyries from the Lengshui felsic dykes, with the ∼145 Ma interpreted as response to the peak of magmatism in the region, and the ∼140 Ma as the timing of formation of the felsic dykes. The corresponding Hf isotopic data of the granite porphyries display negative εHf(t) values of –16.67 to –4.61, and Hf crustal model ages (TDMC) of 2255–1490 Ma, indicating magma sourced from the melting of Paleo- to Mesoproterozoic crustal materials. The compiled age data display two major magmatic pulses at 160–130 Ma and 111–108 Ma with magmatic quiescence in between, and the zircon Hf isotopic data display εHf(t) values ranging from –41.9 to 2.1 and TDMC values of 3387–1033 Ma, suggesting mixed crustal and mantle-derived components in the magma source, and correspond to multiple tectonic events during the Late Mesozoic. The Luanchuan granitoids are identified as I-type granites and most of these are highly fractionated granites, involving magma mixing and mingling and crystal fractionation. The tectonic setting in the region transformed from the Late Jurassic syn-collision setting to Early Cretaceous within-plate setting, with E–W extension in the Early Cretaceous. This extension is correlated with the N–S trending post-collisional extension between the North China Craton and Yangtze Craton as well as the E–W trending back-arc extension triggered by the westward Paleo-Pacific Plate subduction, eventually leading to lithospheric thinning, asthenospheric upwelling, mafic magma underplating, and crustal melting in the East Qinling Orogen.

Late Neoarchean synchronous TTG gneisses and potassic granitoids in southwestern Liaoning Province, North China Craton: Zircon U-Pb-Hf isotopes, geochemistry and tectonic implications

Abundant late Neoarchean granitoids occur in southwestern Liaoning Province, part of the Eastern Ancient Terrane of the North China Craton. These rocks include intermediate gneiss, TTG gneisses and potassic granitoids, and we report on the geochemistry and zircon SHRIMP ages as well as Hf-in-zircon isotopes of these granitoids in order to determine their petrogenesis. Field relationships suggest that most of these granitoids experienced widespread metamorphism and deformation, associated with anatexis at some localities. The intermediate gneisses, TTG gneisses and potassic granitoids were all emplaced at the end of the Neoarchean (2.50–2.53 Ga), and CL images document widespread recrystallization in the zircons. The intermediate and TTG gneisses yielded similar Hf isotopic systematics (εHf(t) = −3.73 to +6.42) as the associated potassic granitoids (εHf(t) = −2.44 to +7.80), and both rock types yielded mean Hf crustal model ages of 2.8–2.9 Ga. Combined with the geochemistry, we propose that the formation of the intermediate and TTG gneisses was related to partial melting of mafic rocks at different depth, whereas the potassic granitoids have variable petrogenesis. The nearly coeval TTG gneisses and potassic granitoids and their widespread metamorphism, deformation and zircon recrystallization suggest that a large-scale heat source must have been present at or near the base of the crust in southwestern Liaoning Province at the end of the Neoarchean. We propose that collision and post-collisional extension is the most likely tectonic environment for generation of the above granitoids, and the formation of widespread potassic granitoids played an important role in the maturation of continental crust in the North China Craton.

Zircon U–Pb, Lu–Hf and O isotopes from the 3414 Ma Strelley Pool Formation, East Pilbara Terrane, and the Palaeoarchaean emergence of a cryptic cratonic core

The detrital zircon record yields important information on crustal evolution that may be missing from extant magmatic rocks. The Palaeoarchaean to Neoarchaean East Pilbara Terrane (EPT), Western Australia, is the ancient core of the Pilbara Craton, and the archetypal granite-greenstone terrane. Magmatic zircon U–Pb crystallization ages from the EPT record crustal magmatism spanning 3.53–3.22 Ga. However, detrital zircons with ages as old as 3.65 Ga have been identified in EPT supracrustal sequences, which may provide key insights into the EPT’s early Archaean history. The Strelley Pool Formation (SPF), one of the earliest EPT siliciclastic sedimentary successions, is a critical unit in the field of Precambrian palaeobiology, containing multiple lines of evidence for some of Earth’s earliest life forms. The SPF was deposited on a continental shelf in a shallow water environment, upon perhaps the oldest preserved terrestrial erosion surface on Earth; it thus provides a record of a newly-emergent Palaeoarchaean continent. We report U–Pb, Lu–Hf and O isotope data from a suite of detrital zircon crystals sourced from the type locality of the SPF. Two hundred and five U–Pb detrital zircon analyses were undertaken via SIMS and LA–ICPMS. Four analyses define a young age peak of 3414 ± 34 Ma (2σ), which we interpret as a maximum depositional age. Zircon Hf isotope analyses yield εHfi of −3.5 to +5.2, clustering around chondritic values, with two-stage Hf crustal model ages of 3.9–3.5 Ga. Zircon O isotopes give a range in δ18O values from mantle-like (5.3‰) to more elevated (∼6.4‰). Taken together, the Hf and O isotope record, from new and published detrital and magmatic zircon crystals, implies a juvenile (mafic) source for evolved rocks of the EPT until ca. 3.3 Ga, after which time it experienced a period dominated by reworking of existing crust, possibly reflective of a change in geodynamics. The relationship between the cryptic core of the EPT, which is perhaps as old as 3.8–3.7 Ga, and the extant magmatic rocks that comprise the exposed Palaeoarchaean granite domes, remains uncertain.