Geochronology and Hf–Fe isotopic geochemistry of the Phanerozoic mafic–ultramafic intrusions in the Damiao area,northern North China Craton: Implications for lithospheric destruction

Timing and source of several Fe-mineralized mafic-ultramaficintrusions in the Damiao area are investigated here by coupling new geochronological and Hf–Fe isotopic data with previous results. Although regarded as a Late Paleoproterozoic assemblage previously, two ～140 Ma intrusions are recognized by zircon U–Pb dating, indicating emplacement of these intrusions from Middle Devonian to Early Cretaceous times. Both Hf and Fe isotopic features lead to the conclusion that distinct mantle components contributed to their magma generation. As the first magmatic phase, the ～395 Ma intrusions were mainly derived from the slightly-enriched SCLM that was prevalent during the Paleozoic. However, asthenospheric material was strongly involved in the formation of the ～215 Ma Gaositai intrusion. Therefore, the initiation of lithospheric destruction in the northern NCC is inferred to have occurred in Late Triassic time, triggered by post-orogenic extension following the ～250 Ma collision between the Siberian Craton and the NCC. The ～140 Ma intrusions originated from a significantly-enriched mantle component probably resided in the predominant slightly-enriched SCLM. This mantle source would have melted in the Late Mesozoic, when the thin lithosphere enabled enhanced heat transfer from the asthenosphere. In summary, these distinct mantle sources of mafic–ultramafic magmatism provide a record of mantle heterogeneity and the gradual upward migration of the lithosphere–asthenosphere boundary during lithospheric destruction.     

He–Ar isotope geochemistry of iron and gold deposits reveals heterogeneous lithospheric destruction in the North China Craton

The North China Craton (NCC) provides a classic example for extensive destruction of the cratonic lithosphere. The Mesozoic magmatism which contributed to the decratonization of the NCC was also accompanied by the formation of a variety of mineral deposits. In order to gain further insights into the cratonic destruction process, typical iron and gold deposits are investigated here. Helium–argon isotopic data on pyrite, from typical skarn iron deposits of the Beiminghe and Fushan in the Han-Xing district of the central NCC, and the Linglong and Canzhuang gold deposits in the Jiaodong district in the eastern NCC, are presented in this paper. The ³He/⁴He, ⁴⁰Ar/³⁶Ar and ⁴⁰Ar/⁴He ratios show generally uniform patterns within the individual deposits and reveal a complex evolutionary history of the ore-forming fluids with varying degree of crust–mantle interaction. The ore-forming fluids associated with the gold mineralization at the Jiaodong mine have higher content of fluids of mantle origin with mantle helium ranging from 1.24% to 18.02% (average 6.73%; N = 18). In contrast, the ore-forming fluids related to the iron ore deposits contain less mantle contribution with mantle helium ranging from 0.12% to 4.96% (average 1.29%; N = 10). Our results suggest complex and heterogeneous crust–mantle processes associated with the magmatism and metallogeny, where the lithosphere of the eastern NCC was subjected to more extensive thinning and destruction as compared with that in the western part, consistent with the observations from geophysical studies in the region. Our study demonstrates that fluids associated with the Mesozoic metallogenic processes in the NCC provide useful insights into the geodynamics of destruction and refertilization of the cratonic lithosphere.     

Petrogenesis of the Mesozoic intrusive complexes from the southern Taihang Orogen,North China Craton: elemental and Sr–Nd–Pb isotopic constraints

A geochemical and isotopic study was carried out for three Mesozoic intrusive suites (the Xishu, Wuan and Hongshan suites) from the North China Craton (NCC) to understand their genesis and geodynamic implications. The Xishu and Wuan suites are gabbroic to monzonitic in composition. They share many common geochemical features like high Mg# and minor to positive Eu anomalies in REE patterns. Initial Nd–Sr isotopic compositions for Xishu suite are _Nd(135 Ma)=–12.3 to –16.9 and mostly I_Sr = 0.7056–0.7071; whereas those for Wuan suite are slightly different. Pb isotopic ratios for Xishu suite are (²⁰⁶Pb/²⁰⁴Pb)_i = 16.92–17.3, (²⁰⁷Pb/²⁰⁴Pb)_i=15.32–15.42, (²⁰⁸Pb/²⁰⁴Pb)_i=37.16–37.63, which are slightly higher than for Wuan suite. The Xishu–Wuan complexes are considered to originate from partial melting of an EM1-type mantle source, followed by significant contamination of lower crustal components. The Hongshan suite (mainly syenite and granite) shows distinctly higher _Nd(135 Ma) values (–8 to –11) and slightly higher Pb isotopic ratios than the Xishu–Wuan suites. It was formed via fractionation of a separate parental magma that also originated from the EM1-type mantle source, with incorporation of a small amount of lower crustal components. Partial melting of the mantle sources took place in a back-arc extensional regime that is related to the subduction of the paleo-Pacific slab beneath the NCC.     

Geochronology, petrology and geochemistry of the Nanlinshan and Banpo mafic–ultramafic intrusions: implications for subduction initiation in the eastern Paleo-Tethys

The Nanlinshan and Banpo mafic–ultramafic intrusions belong to the prominent Yunxian-Jinghong magmatic belt in the western part of the Simao Block, one of several Gondwana-derived continental fragments assembled by the closure of multiple Tethyan oceans. Different petrogenic models including ophiolites, MORB-type cumulates and Alaskan-type complexes have been proposed for these intrusions. In order to better constrain possible origins, we have undertaken an integrated geochronological, petrological and geochemical study of both intrusions. Precise CA-ID-TIMS zircon U–Pb dating indicates that the Nanlinshan and Banpo intrusions have similar ages of ~298 and 295?Ma, respectively, confirming that they are the oldest intrusive rocks in the Yunxian-Jinghong magmatic belt. A comparison between whole rock compositions and the compositions of major silicate minerals, including trace elements in clinopyroxene, reveals that (1) the ultramafic rocks of these intrusions are crystal cumulates of a relatively primitive magma, (2) the associated gabbroic and dioritic rocks are the products of more fractionated liquids, and (3) the parental magmas of these rocks were all depleted in some high field strength trace elements including Nb, Zr and Hf. Both intrusions are also characterized by elevated ε_Nd values between +3.4 and +6.6. The positive ε_Nd values coupled with negative Nb and Zr–Hf anomalies are consistent with the interpretation that these two intrusions are the products of subduction-related basaltic magmatism. The results from this study suggest that subduction of the Paleo-Tethys Ocean along the western margin of the Simao Block initiated as early as ~298?Ma and that the Simao Block and the Northern Qiangtang Block of the Tibet Plateau are separate Gondwana-derived continental fragments instead of a single fragment as previously reported.     

Constraints on the paleogeographic evolution of the North China Craton during the Late Triassic–Jurassic

This paper reports U–Pb–Hf isotopes of detrital zircons from Late Triassic–Jurassic sediments in the Ordos, Ningwu, and Jiyuan basins in the western-central North China Craton (NCC), with the aim of constraining the paleogeographic evolution of the NCC during the Late Triassic–Jurassic. The early Late Triassic samples have three groups of detrital zircons (238–363 Ma, 1.5–2.1 Ga, and 2.2–2.6 Ga), while the latest Late Triassic and Jurassic samples contain four groups of detrital zircons (154–397 Ma, 414–511 Ma, 1.6–2.0 Ga, and 2.2–2.6 Ga). The Precambrian zircons in the Late Triassic–Jurassic samples were sourced from the basement rocks and pre-Late Triassic sediments in the NCC. But the initial source for the 238–363 Ma zircons in the early Late Triassic samples is the Yinshan–Yanshan Orogenic Belt (YYOB), consistent with their negative zircon ε_Hf(t) values (−24 to −2). For the latest Late Triassic and Jurassic samples, the initial source for the 414–511 Ma zircons with ε_Hf(t) values of −18 to +9 is the Northern Qinling Orogen (NQO), and that for the 154–397 Ma zircons with ε_Hf(t) values of −25 to +12 is the YYOB and the southeastern Central Asian Orogenic Belt (CAOB). In combination with previous data of late Paleozoic–Early Triassic sediments in the western-central NCC and Permian–Jurassic sediments in the eastern NCC, this study reveals two shifts in detrital source from the late Paleozoic to Jurassic. In the Late Permian–Early Triassic, the western-central NCC received detritus from the YYOB, southeastern CAOB and NQO. However, in the early Late Triassic, detritus from the CAOB and NQO were sparse in basins located in the western-central NCC, especially in the Yan’an area of the Ordos Basin. We interpret such a shift of detrital source as result of the uplift of the eastern NCC in the Late Triassic. In the latest Late Triassic–Jurassic, the southeastern CAOB and the NQO restarted to be source regions for basins in the western-central NCC, as well as for basins in the eastern NCC. The second shift in detrital source suggests elevation of the orogens surrounding the NCC and subsidence of the eastern NCC in the Jurassic, arguing against the presence of a paleo-plateau in the eastern NCC at that time. It would be subsidence rather than elevation of the eastern NCC in the Jurassic, due to roll-back of the subducted paleo-Pacific plate and consequent upwelling of asthenospheric mantle.     

Evidences from zircon U-Pb geochronology,whole -rock geochemistry and Hf isotope of Early Cretaceous magmatic rocks in Baishan area,southern Jilin Province: Constraints on destruction of the North China CratonSCIEI北大核心CSCD

This paper reports new geochemical data including zircon U-Pb ages with Hf isotopic data, whole -rock major and trace isotopic compositions for the Early Cretaceous magmatic rocks in the northeastern North China Craton ( NCC), with the purpose of constraining its petrogenesis and tectonic setting. It also provides a basis for further discussion on the formation and evolution of the lithosphere in the northeastern NCC during the Late Mesozoic. Zircons in the Xinglin granite porphyry, Hongtuya andesitic crystal tuff and Jiangyuan rhyolitic breccia-bearing crystal-lithic tuff all show magmatic origin. Zircon U-Pb dating yield age are 130 +/- 1Ma, 128 +/- 1Ma and 120 +/- 1Ma, respectively. The Xinglin granite porphyry and the Hongtuya andesitic crystal tuff have high content of SiO2, Al2O3 Sr, high Na2O/K2O, Sr/Y and ( La/Yb)(N) ratios. In addition, they exhibit low Y and Yb. They are enriched in LILE ( e. g., Ba, Th and U), depleted in HFSE ( e. g., Nb, Ti and P) with weak negative Eu anomalies (delta Eu =0. 82 similar to 0. 94), showing they are typical of adakitic rocks. The Xinglin granite porphyry has high content of total -alkali, low content of TiO2, characterized by peraluminous-weakly peraluminous granite A/CNK = 1. 06 similar to 1. 14, the zircon saturated temperature values of 798 similar to 815 degrees C and a distribution pattern of LREE enrichment with incline to the right, which indicates it is I -type granite. The zircon ( t) values in the Xinglin granite porphyry ranged 17. 96 0. 19, and the two -stage model ages yield t(DM2) = 1197 similar to 2313Ma, which imply that the Xinglin granite porphyry is derived from partial melting of the thickened mafic lower crust of Paleoproterozoic to Mesoproterozoic. The zircon epsilon(Hf)( t) values in the Hongtuya andesitic crystal tuff ranged 3. 37 similar to 5. 47, and the two -stage model ages yield t(DM2) = 830 similar to 967Ma, indicating that the Hongtuya andesitic crystal tuff is a metasomatism product of the Neoproterozoic delaminated eclogite lower crust partial melting and mantle peridotite. Combined with the epsilon(Hf)( t) values in the Jiangyuan rhyolitic breccia-bearing crystal-lithic tuff ranged 2. 69 1. 00, and the two -stage model ages yield t(DM2) = 1115 similar to 1349Ma, we conclude that the epsilon(Hf)( t) values of magmatic rocks are heterogeneous in the southern Jilin Province, and the magmatic source area is characterized by multi -component origin, including both ancient crust and juvenile crust. We supposed that there were two accretion evolution events in the continental crust of the northeastern NCC during Proterozoic. Comprehensive studies have shown that subduction and slab roll -back of the Paleo-Pacific plate ( Izanagi) led to the thickened the northeastern NCC being in an extensional tectonic setting during the Early Cretaceous, and the destruction of the northeastern NCC by delamination occurred spatially from west to east. The partial melting of delaminated lower continental crust resulted in a wide distribution of adakitic rocks.     

Geochronology, Geochemistry and Sr-Nd-Hf Isotopes of Early–Middle Triassic Adakitic Plutons in Central-eastern Jilin Province, NE China: Constraints on the Non-synchronous Closure of Paleo-Asian Ocean

The Changchun–Yanji suture zone (CYSZ) in NE China is considered as the suture between the North China Craton (NCC) and Central Asian Orogenic Belt (CAOB). The geochronology, geochemistry and Sr-Nd-Hf isotopes of Early–Middle Triassic adakitic plutions from the CYSZ, are presented in this paper to discuss their petrogenesis and tectonic setting, as well as to constrain the timing and style of the Paleo-Asian Ocean''s final closure. In Early Triassic, the Dayushan pluton (ca. 250 Ma) from western CYSZ has negative εNd(t) values, bidirectional provenances (NCC and CAOB) of εHf(t), which are formed in a collision tectonic setting. In contrast, in eastern CYSZ, the early Triassic samples in Liangshan (ca. 242 Ma) were high Mg# values, positive εNd(t), single provenances (CAOB) of εHf(t) resulting from a subduction setting. In the Middle Triassic, the A-type granites in western CYSZ are found in previous studies representing a post-collisional extensional environment, whereas syn-collisional Lianyanfeng granites (ca. 237 Ma) in eastern CYSZ with low ISr and large scale εNd(t) and εHf(t) values from bidirectional provenances (NCC and CAOB), represent a collisional setting. The Paleo-Asian Ocean''s occurred in a scissor-like fashion along the CYSZ during the Triassic period.     

Field geology,geochronology and geochemistry of mafic–ultramafic rocks from Alxa,China: Implications for Late Permian accretionary tectonics in the southern Altaids

The time of termination of orogenesis for the southern Altaids has been controversial. Systematic investigations of field geology, geochronology and geochemistry on newly discriminated mafic–ultramafic rocks from northern Alxa in the southern Altaids were conducted to address the termination problem. The mafic–ultramafic rocks are located in the Bijiertai, Honggueryulin, and Qinggele areas, stretching from west to east for about 100 km. All rocks occur high-grade gneisses as tectonic lenses that are composed of peridotite, pyroxenite, gabbro, and serpentinite, most of which have undergone pronounced alteration, i.e., serpentinization and chloritization. Geochemically, the rocks are characterized by uniform compositional trends, i.e., with low SiO₂-contents (42.51–52.21 wt.%) and alkalinity (Na₂O + K₂O) (0.01–5.45 wt.%, mostly less than 0.8 wt.%), and enrichments in MgO (7.37–43.36 wt.%), with Mg# = 52.75–91.87. As the rocks have been strongly altered and have a wide range of loss-on-ignition (LOI: 0.44–14.07 wt.%) values, they may have been subjected to considerable alteration by either seawater or metamorphic fluids. The REE and trace element patterns show a relatively fractionated trend with LILE enrichment and HFSE depletion, similar to that of T-MORB between N-MORB and E-MORB, indicating that the parental melt resulted from the partial melting of oceanic lithospheric mantle overprinted by fluid alteration of island-arc origin. The ultramafic rocks are relics derived from the magma after a large degree of partial melting of oceanic lithospheric mantle with superposed island arc processes under the influence of mid-ocean-ridge magmatism. LA-ICP MS U–Pb zircon ages of gabbros from three spots are 274 ± 3 Ma (MSWD = 0.35), 306 ± 3 Ma (MSWD = 0.49), 262 ± 5 Ma (MSWD = 1.2), respectively, representing the formation ages of the mafic–ultramafic rocks. Therefore, considering other previously published data, we suggest that the mafic–ultramafic rocks were products of south-dipping subduction, most probably with a slab window caused by ridge subduction, of the Paleo-Asian Ocean plate beneath the Alxa block in the Late Carboniferous to Late Permian before the Ocean completely closed. This sheds light on the controversial tectonic history of the southern Altaids and supports the concept that the termination of orogenesis was in the end-Permian to Triassic.     

Mesozoic magmatism and metallogenesis associated with the destruction of the North China Craton: Evidence from U–Pb geochronology and stable isotope geochemistry of the Mujicun porphyry Cu–Mo deposit

The North China Craton (NCC) provides a classic example of lithospheric destruction and refertilization. The timing and duration of magmatism and related metallogenesis associated with the destruction process are pivotal to understanding the geodynamic controls. In this study, we present zircon U–Pb and Hf data, Re–Os ages, and He, Ar, Pb and S isotope data from the Mujicun porphyry Cu–Mo deposit in the northern Taihang Mountains within the Central Orogenic Belt of the NCC. We constrain the timing of magmatism as 144.1 ± 1.2 Ma from zircon U–Pb data on the diorite porphyry that hosts Cu–Mo mineralization. Another U–Pb age of 139.7 ± 1.4 Ma was obtained from an epidote skarn that is located in the contact zone between the porphyry and its wall rocks. These data and five Re–Os molybdenite ages that range from 142.7 ± 2.0 Ma to 138.5 ± 1.9 Ma suggest that magmatism and mineralization occurred in about five million year duration from ~ 143 Ma to ~ 138 Ma. The He, Ar, Pb and, Hf data suggest that magmatism involved recycled Neoarchean lower crustal components, with input of heat and volatiles from an upwelling mantle. The Mujicun porphyry and associated mineralization provide a typical example for magmatism and metallogeny associated with lithospheric thinning in the NCC.     

Petrogenesis and tectonic setting of volcanic rocks in the Xiaoshan and Waifangshan areas along the southern margin of the North China Craton: Constraints from bulk-rock geochemistry and Sr–Nd isotopic composition

As part of the Xiong'er volcanic belt along the southern margin of the North China Craton, volcanic rocks in the Xiaoshan and Waifangshan areas have a compositional range from the basaltic andesite, andesite, dacite to rhyolite, which display consistent variation trends in terms of their major and trace elements and Sr–Nd isotopic compositions. The variable Yb contents with nearly constant La/Yb and Tb/Yb ratios of volcanic rocks in two areas suggest that the fractional crystallization may have played an important role in the differentiation from the basaltic andesite, through andesite and dacite, to rhyolite. The volcanic rocks in these two areas are characterized by the LILE and LREE enrichments and negative HFSE anomalies, implying hydrous melting of a mantle wedge in a subduction zone. Variable Sr/Nd ratios of the basaltic andesite and andesite are interpreted as a result of the fluid addition from a subducting slab. Non-radiogenic Nd isotopic compositions as well as high Zr/Y and Nb/Y ratios suggest that the volcanic rocks in these areas were derived from an enriched mantle source. On the other hand, the volcanic rocks of the basaltic andesite and andesite possess markedly higher Fe–Ti and HFSE concentrations than those of typical intra-oceanic arcs, implying that the mantle source from which the volcanic rocks were derived was metasomatised by siliceous melts during the Archean to Paleoproterozoic subduction/collision in the Trans-North China Orogen. These data suggest that in the Paleo-Mesoproterozoic, the southern margin of the North China Craton was most likely an Andean-type continental arc in which slab dehydration not only induced the melting of a pre-existing metasomatised mantle source, but also released LILE-enriched fluids into the mantle source, masking the inherent HFSE-enriched characteristics of the volcanic rocks along the southern margin of the craton. The results of this study indicate that the North China Craton, like many other continental components (e.g. North America, Greenland, Baltica, Amazonia, Australia, etc.) of the supercontinent Columbia (Nuna), also underwent a subduction-related outgrowth along its southern margin during the Paleo-Mesoproterozoic time.     

Triassic volcanism along the eastern margin of the Xing'an Massif,NE China: Constraints on the spatial–temporal extent of the Mongol–Okhotsk tectonic regime

We present new zircon U–Pb–Hf and whole-rock geochemical data for volcanic rocks along the eastern margin of the Xing'an Massif of NE China in order to further our understanding of the history of subduction towards the SE and the spatial extent of the Mongol–Okhotsk tectonic regime. Zircon U–Pb dating indicates that the Triassic volcanism in the Xing'an Massif occurred in two stages during the Middle (ca. 242 Ma) and Late (ca. 223–228 Ma) Triassic. Middle Triassic basaltic andesites in the Heihe area have an affinity to arc-type volcanic rocks. The zircon ε_Hf(t) values (+ 8.5 to + 12.7) suggest that the primary magma was generated by the partial melting of a relatively depleted mantle wedge that had been metasomatized by subduction-related fluids. The Late Triassic andesites in the Handaqi area exhibit geochemical affinities to high-Mg adakitic andesites. Their zircon ε_Hf(t) values (+ 11.5 to + 14.5) and T_DM2 ages (313–484 Ma) indicate that their primary magma was derived from the partial melting of a young subducted oceanic crust, followed by interaction with melts derived from mantle peridotite. The Late Triassic basaltic andesites, andesites, and dacites in the Zhalantun–Moguqi area have features similar to those of igneous rocks formed in subduction zones. Their zircon ε_Hf(t) values (+ 8.4 to + 15.4) and T_DM1 ages (260–542 Ma) indicate that their primary magma was derived from the partial melting of a depleted mantle wedge that had been metasomatized by subduction-related fluids. These data suggest that the Triassic volcanic rocks of the Xing'an Massif formed in an active continental margin setting associated with the southward subduction of the Mongol–Okhotsk oceanic plate towards the SE. We conclude that the Mongol–Okhotsk tectonic regime extended at least as far as the eastern margin of the Xing'an Massif, and that the tectonism spanned the period from the late Permian to early Early-Cretaceous.     

Age and significance of voluminous mafic–ultramafic magmatic events in the Murchison Domain,Yilgarn Craton

Mafic–ultramafic rocks in structurally dismembered layered intrusions comprise approximately 40% by volume of greenstones in the Murchison Domain of the Youanmi Terrane, Yilgarn Craton. Mafic–ultramafic rocks in the Murchison Domain may be divided into five components: (i) the ～2810 Ma Meeline Suite, which includes the large Windimurra Igneous Complex; (ii) the 2800 ± 6 Ma Boodanoo Suite, which includes the Narndee Igneous Complex; (iii) the 2792 ± 5 Ma Little Gap Suite; (iv) the ～2750 Ma Gnanagooragoo Igneous Complex; and (v) the 2735–2710 Ma Yalgowra Suite of layered gabbroic sills. The intrusions are typically layered, tabular bodies of gabbroic rock with ultramafic basal units which, in places, are more than 6 km thick and up to 2500 km² in areal extent. However, these are minimum dimensions as the intrusions have been dismembered by younger deformation. In the Windimurra and Narndee Igneous Complexes, discordant features and geochemical fractionation trends indicate multiple pulses of magma. These pulses produced several megacyclic units, each ～200 m thick. The suites are anhydrous except for the Boodanoo Suite, which contains a large volume of hornblende gabbro. They also host significant vanadium mineralisation, and at least minor Ni–Cu–PGE mineralisation. Collectively, the areal distribution, thickness and volume of mafic–ultramafic magma in these complexes is similar to that in the 2.06 Ga Bushveld Igneous Complex, and represents a major addition of mantle-derived magma to Murchison Domain crust over a 100 Ma period. All suites are demonstrably contemporaneous with packages of high-Mg tholeiitic lavas and/or felsic volcanic rocks in greenstone belts. The distribution, ages and compositions of the earlier mafic–ultramafic rocks are most consistent with genesis in a mantle plume setting.     

Re–Os isotope and platinum-group element geochemistry of the Pobei Ni–Cu sulfide-bearing mafic–ultramafic complex in the northeastern part of the Tarim Craton

A number of mafic–ultramafic intrusions that host Ni–Cu sulfide mineralization occur in the northeastern Tarim Craton and the eastern Tianshan Orogenic Belt (NW China). The sulfide-mineralized Pobei mafic–ultramafic complex is located in the northeastern part of the Tarim Craton. The complex is composed of gabbro and olivine gabbro, cut by dunite, wehrlite, and melatroctolite of the Poyi and Poshi intrusions. Disseminated Ni–Cu sulfide mineralization is present towards the base of the ultramafic bodies. The sulfide mineralization is typically low grade (<0.5 wt.% Ni and <2 wt.% S) with low platinum-group element (PGE) concentrations (<24.5 ppb Pt and <69 ppb Pd); the abundance of Cu in 100 % sulfide is 1–8 wt.%, and Ni abundance in 100 % sulfide is typically >4 wt.%. Samples from the Pobei complex have εNd (at 280 Ma) values up to +8.1, consistent with the derivation of the magma from an asthenospheric mantle source. Fo 89.5 mol.% olivine from the ultramafic bodies is consistent with a primitive parental magma. Sulfide-bearing dunite and wehrlite have high Cu/Pd ratios ranging from 24,000 to 218,000, indicating a magma that evolved under conditions of sulfide saturation. The grades of Ni, Cu, and PGE in 100 % sulfide show a strong positive correlation. A model for these variations is proposed where the mantle source of the Pobei magma retained ~0.033 wt.% sulfide during the production of a PGE-depleted parental magma. The parental magma migrated from the mantle to the crust and underwent further S saturation to generate the observed mineralization along with its high Cu/Pd ratio at an R-factor varying from 100 to 1,200. The mineralization at Poshi and Poyi has very high γOs (at 280 Ma) values (+30 to +292) that are negatively correlated with the abundance of Os in 100 % sulfide (5.81–271 ppb) and positively correlated with the Re/Os ratios; this indicates that sulfide saturation was triggered by the assimilation of crustal sulfide with both high γOs and Re/Os ratios. When compared to other Permian mafic–ultramafic intrusions with sulfide mineralization in the East Tianshan, the Poyi and Poshi ultramafic bodies were formed from more primitive magmas, and this helps to explain why the sulfide mineralization has high Ni tenor.     

Zircon U–Pb–Hf isotopes and geochemistry analyses of the Huyu igneous rocks in northwestern Beijing,China: possible new evidence for the initial destruction of the North China Craton

The timing and extent of cratonic destruction are crucial to understanding the crustal evolution of the North China Craton (NCC). Zircon U–Pb–Hf isotope data and the whole-rock major and trace element characteristics of the Huyu igneous rocks in northwestern Beijing, China, provide possible new evidence for the initial destruction of the NCC. The igneous rocks occur as several sills and dikes, including lamprophyre, monzonite porphyry, and aplite. The lamprophyres have high Mg^# and K₂O contents. The monzonite porphyries have high Mg^#, high K₂O contents, and negative ε_Hf(t) values with zircon U–Pb ages of 225.5–227.7 Ma. These two types of rocks are both enriched in large ion lithosphere elements (LILEs) and light rare earth elements (LREEs) but are depleted in high field strength elements (HFSEs) and high rare earth elements (HREEs) and have almost no Eu anomalies and relatively high total rare earth element (ΣREE) contents. In contrast, the aplites exhibit high silica and K₂O contents, low MgO contents, and more negative ε_Hf(t) values with a zircon U–Pb age of 206.2 Ma. The aplites are also enriched in LILEs and LREEs but are depleted in HFSEs and HREEs, with strongly negative Eu, Ti, P, La, Ce, and Sr anomalies and relatively low ΣREE contents. These results indicate that the lamprophyres and monzonite porphyries represent a continuous cogenetic magma evolution series after melt derived from an enriched metasomatized lithospheric mantle experienced crust assimilation and fractional crystallization. The aplites were produced by the fractional crystallization of low-Mg parental magma derived from melting of the ancient Archaean crust. The occurrence of the Huyu intrusive rocks with many other plutons of similar ages on the northern margin of the NCC suggests that the northern NCC entered an intraplate extensional tectonic environment in the Late Triassic.     

Geochemical constraints on the origin of the Permian Baimazhai mafic–ultramafic intrusion,SW China

The ∼260 Ma Baimazhai mafic–ultramafic intrusion is considered to be part of the Emeishan large igneous province and consists of orthopyroxenite surrounded by websterite and gabbro. The intrusion is variably mineralized with a massive sulfide ore body (∼20 vol.%) in the core of the intrusion. Silicate rocks have Ni/Cu ratios ranging from 0.3 to 46 with majority less than 7 and are rich in LREE relative to HREE and show Nb and Ta anomalies in primitive mantle-normalized trace element patterns, with low Nb/Th (1.0–4.5) and Nb/La (0.3–1.0) ratios. Their ɛ Nd(t) values range from −3.3 to −8.4. Uniform Pd/Pt (0.7–3.5) and Cu/Pd (100,000–400,000) ratios throughout the intrusion indicate that all the sulfides in the rocks were formed in a single sulfide-saturation event. Modeling suggests that the Baimazhai rocks were formed when an Mg-rich magma became crustally contaminated in a deep-seated staging chamber. Crustal contamination (up to ∼35%) drove the magma to S-saturation and forced orthopyroxene (Opx) onto the liquidus. The crystal-bearing magma forced out of the staging chamber was migrated by flow differentiation and consequently, the denser sulfide melt and the Opx crystals became centrally disposed in the flowing magma to form the Baimazhai intrusion.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Tectonic nature of the NE Asian continental margin during the Late Jurassic–Early Cretaceous: constraints from the geochronology and geochemistry of igneous rocks in the NE North China Craton

ABSTRACT

This paper presents geochronological, geochemical, and zircon Hf–O isotope data for late Mesozoic intrusive rocks from the northeastern North China Craton (NCC), with the aim of constraining the late Mesozoic tectonic nature of the NE Asian continental margin. U–Pb zircon data indicate that the Late Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Jurassic (161 ? 156 Ma) and Early Cretaceous (125 ? 120 Ma). Late Jurassic magmatism consists mainly of monzogranites. These monzogranites display high Sr/Y ratios and the tetrad effect in their REE, respectively, and have negative ε_Hf(t) values (?22.6 to ?15.8). The former indicates that the primary magma was generated by partial melting of thickened NCC lower crust, the latter suggests that the monzogranites were crystallized from highly fractionated magma, with the primary magma derived from partial melting of lower continental crust. Combined with the spatial distribution and rock associations of the Late Jurassic granitoids, we conclude that the Late Jurassic magmatism in the eastern NCC formed in a compressional environment related to oblique subduction of the Paleo-Pacific Plate beneath the Eurasia. The Early Cretaceous magmatism consists mainly of granitoids and quartz diorites. The quartz diorites formed by mixing of melts derived from the mantle and lower crust. The coeval granitoids are classified as high-K calc-alkaline and metaluminous to weakly peraluminous series. Some of the granitoids are similar to A-type granites. The granitoid ε_Hf(t) values and T_DM2 range from ?14.3 to ?1.4 and 2089 to 1274 Ma, respectively. These values indicate that their primary magma was derived from partial melting of lower crustal material of the NCC, but with a contribution of mantle-derived material. We therefore conclude that Early Cretaceous magmatism in the northeastern NCC occurred in an extensional environment related to westward subduction of the Paleo-Pacific Plate beneath Eurasia.     

Geochronology of Early Cretaceous copper mineralization at the NE China–North Korea border

ABSTRACT

North Korea is host to world-class metallic mineral deposits, such as the Komdok Cu–Pb–Zn polymetallic mineral belt, but little is known about the resource. To better understand the genesis of the Cu mineralization around the China–North Korea border, we determined the U–Pb, Re-Os, and Rb–Sr ages of three deposits in the area. Sulfide samples from the Hyesan Cu deposit produced Rb–Sr isochron ages of 127.4 ± 4.5 Ma. The Wanbaoyuan Cu deposit yielded a molybdenite Re–Os isochron age of 127.5 ± 3.2 Ma, and a granodiorite sample from the Linjiang Cu deposit gave a zircon U–Pb age of 129.5 ± 0.8 Ma. Combined with geochronological data from previous studies, these new ages suggest that the Cu mineralization occurred mainly during the Cretaceous, and the rollback of the Paleo-Pacific Plate was responsible for the Cu mineralization in NE China–North Korea border.     

Geochronology,Mineralogy, and Geochemistry of the Tonsteins from the Permo–Carboniferous Benxi Formation,Ordos Basin,North China Craton

Tonstein layers are found worldwide in the Permo–Carboniferous coal-bearing strata. This study investigates the geochronology, mineralogy, and geochemistry of four tonstein samples from the Permo–Carboniferous Benxi Formation, Ordos Basin, North China Craton(NCC). The typical features of the studied tonsteins include thin beds, lateral continuity, angular quartz grains, and euhedral zircons with similar U-Pb ages, indicating a significant pyroclastic origin. In addition, the tonstein samples hav...