Jiaobei Terrane Research Articles

Magnetic Susceptibility Reveals Differential Retrogression in Meta-Mafic Enclave Consistent with Metamorphic P–T Estimation and Petrography

Magnetic susceptibility is widely applied in geology, but its use in the study of metamorphic rocks has been limited due to the complex nature of metamorphism. In this study, analyzing a partially retrogressed mafic enclave within Archean TTG gneiss from the Jiaobei Terrane, North China craton, we incorporate magnetic susceptibility with conventional metamorphic (petrographic and major element) proxies in order to investigate profiles of metamorphic retrogression. The magnetic susceptibility results show more complete retrogression in the direction parallel to the tectonic fabric and partial retrogression perpendicular to it. This geophysical observation, which is broadly consistent with the petrological observations and P–T estimates, suggests that the availability of fluids and perhaps even non-lithostatic pressure play roles in the preservation of such differential retrogression. This study thus introduces magnetic susceptibility as a novel proxy in this context, revealing its utility in rapidly and quantitatively identifying variable retrogression gradients consistent with, but with more precision than, measured metamorphic pressures.

Heterogeneity of the late Mesozoic lithospheric mantle beneath the Jiaodong Peninsula, eastern North China Craton: a synthesis from geochemistry and Sr-Nd-Pb isotopes of mafic dykes

ABSTRACT The Late Mesozoic lithospheric mantle evolution of the Jiaodong Peninsula is crucial for understanding the destruction of the eastern North China Craton (NCC) and large-scale gold mineralization, but it still remains highly controversial. Here, we comprehensively compiled published Late Mesozoic mafic dyke magmatism data from the Jiaodong Peninsula to provide key constraints on the nature and evolution of the lithospheric mantle. Mafic dykes are widely emplaced in the Jiaodong Peninsula and have been divided into two groups (Jiaobei terrane and Sulu orogenic belt); they mainly comprise lamprophyre, dolerite, and gabbro. The ages of the mafic dykes in the Jiaobei terrane are predominantly between 120 and 125 Ma, and those of the Sulu orogenic belt are between 110 and 120 Ma. The Jiaobei and Sulu mafic dykes both have high contents of Mg and compatible elements (Cr, Ni), as well as low SiO2 content; they are characterized by arc-like mafic magma, including enrichment in Large Ion Lithophile Elements and Light Rare Earth Elements, depletion in High Field Strength Elements, high (87Sr/86Sr)i, and low εNd(t), implying a metasomatized lithospheric mantle source. However, the Jiaobei mafic dykes have relatively higher (87Sr/86Sr)i, lower εNd(t), and a larger range of (206Pb/204Pb)i, (208Pb/204Pb)i, and (207Pb/204Pb)i compared with the Sulu mafic dykes. The Jiaobei and Sulu mafic dykes exhibit Ba/Rb ratios of 1.29‒64.39 (average 29.3) and 6.61‒108.28 (average 33.1), respectively, indicating the presence of hornblende in the melts. The high Fe/Mn (>60) and Zn/Fe (>12) ratios of Jiaobei and Sulu mafic dykes indicate the mixed mantle source of peridotite and pyroxenite. But the content of pyroxenite in the mantle source of Jiaobei terrane is higher with wider range of Fe/Mn and Zn/Fe ratios. These features indicate the heterogeneity of the mantle sources of the mafic dykes in the Jiaobei and Sulu regions. It is suggested that both regions originated from the partial melting of hornblende-bearing peridotite, with the addition of more pyroxenite to the mantle source of the Jiaobei terrane compared to Sulu orogenic belt. The mafic dykes have the low Nb/Zr (Jiaobei: 0.024–0.229; Sulu: 0.030–0.166) and Th/Zr ratios (Jiaobei: 0.017–0.081; Sulu: 0.010–0.068), and the high Rb/Y (Jiaobei: 0.347–12.162; Sulu: 0.224–9.600) and low Nb/Y ratios (Jiaobei: 0.202–1.486; Sulu: 0.140–1.322). It implies that the mantle source area in both regions was metasomatized by subducted slab-derived fluids. The increase in (La/Yb)N and decrease in Hf/Sm implies carbonate metasomatism in both regions. In addition, some Jiaobei and Sulu mafic dykes have high Ti/Eu ratios, implying that the silicate metasomatism occurred in the mantle source of both regions. Based on the regional evolution, the lithospheric mantle source in the two regions beneath Jiaodong Peninsula experienced carbonated fluid metasomatism resulting from the subduction of the Palaeo-Asian Ocean plate beneath the northern NCC (ca. ~250 Ma), silicate melt-related metasomatism from subduction of the Yangtze Craton plate beneath the southern NCC (ca. 240‒220 Ma), and oceanic slab-derived fluid metasomatism from the subducted Palaeo-Pacific plate (at 180‒110 Ma). It is believed that the mantle source of Jiaobei terrane had undergone stronger carbonated fluid metasomatism and silicate melt-related metasomatism, compared to Sulu orogenic belt. Moreover, the continental fluid-related metasomatism only occurred in the Sulu orogenic belt. During the Late Mesozoic, the eastern NCC experienced large-scale lithospheric thinning, leading to upwelling of the asthenospheric mantle. The mafic dykes in Jiaobei and Sulu, show different geochemical features, were derived from partial melting of the metasomatized lithospheric mantle through upwelling of the asthenospheric mantle.

Mesoarchean–Neoarchean coupled crust–mantle differentiation followed by gravity-driven lithospheric delamination and subduction initiation in the North China Craton

The geodynamic regime that formed Archean silicic continental crust is unclear. The episodic Archean TTGs (tonalite–trondhjemite–granodiorite rocks) and associated granitoids, with emplacement ages of ca. 2.9, 2.7, and 2.5 Ga, occurred in the Jiaobei Terrane, North China Craton (NCC), provide a continuous record of the formation of the Mesoarchean–Neoarchean silicic continental crust. To investigate the crust–mantle differentiation, crustal reworking and recycling, and geodynamic regime associated with formation of the Mesoarchean–Neoarchean silicic continental crust, we undertook zircon U–Pb dating and Hf–O isotope, and whole-rock major and trace element analysis of Archean TTGs and associated granitoids. The episodic Archean TTGs and juvenile crust coexisted spatially–temporally in the Jiaobei Terrane, indicating Mesoarchean-Neoarchean synchronous differentiation of crust and mantle. In addition, the ca. 2.9 and 2.7 Ga TTGs have an identical Mesoarchean juvenile crustal source and similar mantle-like zircon δ18O values, whereas the ca. 2.5 Ga TTGs were derived mainly from younger Neoarchean juvenile crust, indicating removal and replacement of the Mesoarchean juvenile lower crust. Some ca. 2.5 Ga TTGs, granitic gneisses, and sanukitoids have markedly higher zircon δ18O values compared with mantle δ18O values, which are indicative of Neoarchean supracrustal recycling. Consequently, we can constrain the geodynamic processes responsible for the formation of the Mesoarchean–Neoarchean silicic continental crust in the Jiaobei Terrane, NCC. Episodic hot upwelling mantle (or plume)–lithosphere interactions at ca. 2.9, 2.7, and 2.5 Ga resulted in coupled crust–mantle differentiation, which produced the TTGs, juvenile crust, and dense lower crustal restites. Subsequently, lithospheric delamination triggered by gravitational instability occurred followed by continental uplift, subduction of altered oceanic crust, and upwelling of asthenosphere and mantle-derived mafic melts. This resulted in extensive anatexis and metamorphism with anticlockwise P–T paths in the middle to lower crust at ca. 2.5 Ga. Furthermore, following the large-scale melting and cooling of the mantle, a thick, stable, cratonic lithosphere had likely developed by the end of the Neoarchean. The geodynamic processes during the Mesoarchean–Neoarchean were diverse, and episodic hot upwelling mantle (or plume)–lithosphere interactions could have been responsible for the formation of Archean silicic continental crust in the Jiaobei Terrane, NCC.

Inherited zircons in Early Cretaceous dyke: Implication of growth and reworking of continental crust in the Jiaodong Peninsula

Inherited zircons from Early Cretaceous dykes across the Jiaodong Peninsula provide a means of exploring magmatic episodes. Negative Eu anomalies, high Th and U contents, and high U/Yb ratios confirmed a zircon source of ancient continental crust. Differences in mineralogy, chronology, geochemistry, and Hf isotopes showed that these inherited zircons were not brought in by the Triassic Yangtze Craton collision. Zircons within 2938–2800 Ma confirmed that the ancient crust in the Jiaobei Terrane originated from the Mesoarchean crustal growth. This crustal growth continued until the Early Paleoproterozoic and was accompanied by crustal transformation activities in the later period. After the collision of the Jiao–Liao–Ji Belt, the Jiaodong Peninsula entered a typical craton period until it was reactivated at the end of the Neoproterozoic, which was characterised by the Archean crustal transformation. During the Palaeozoic, smooth crustal thickness change with limited addition of oceanic crust material indicated the Qinling–Dabie–Sulu Orogenic Belt as a distal island arc system that slowed the impact of Paleo-Tethys subduction. There was no record of positive-εHf(t) zircons in the Jiaodong Peninsula during the Mesozoic, but the crust thickened rapidly. This confirmed that the Paleo-Pacific Plate may have directly subducted beneath the lithospheric mantle and had little contact with the lower crust. This subduction pattern released little hydrous fluid but much heat, which prompted the remodelling of the lower crust in the Mesozoic. Furthermore, the large-scale lithospheric thinning event around 120 Ma was identified as a result of the delamination of the lithospheric mantle together with lower crust.

Roles and perspectives of A- and I-type magmas in rare earth element and gold mineralization

A- and I-type magmas are commonly associated with rare earth element (REE) and gold (Au) mineralization. However, the behavior and solubility of the REEs and gold within the A- and I-type magmas and their synchronous magmatism remain unclear. This study focused on the synchronous Early Cretaceous A- and I-type magmatism that formed alkaline and granodioritic complexes within the Luxi and Jiaobei terranes of the central-eastern North China Block, terranes that contain the third largest known REE deposit in China and the third largest gold province in the world. Our integrated whole-rock geochemical and Nd isotopic data and zircon Hf-O isotopic data provide new insights into the petrogenesis of these contemporaneous A- and I-type magmas and their role in the generation of the REE and gold mineralization in this area. The alkaline magmas that formed the intrusions in the Luxi terrane had A- and I-type affinities, were oxidized, were fluorine-, sulfur-, and copper-rich, were H2O-poor, and were generated by low-pressure partial melting of a source region containing enriched lithospheric mantle material and minor amounts of Paleoproterozoic A-type granitic crust. In comparison, the granodioritic magmas within the Jiaobei terrane had I-type affinities, were relatively reduced, were sulfur-rich, contained low concentrations of Cu, were hydrous, and were formed by high-pressure partial melting of a source region containing enriched mantle material and large volumes of Archean to Paleoproterozoic crustal material. The A- and I-type magmas within the Luxi terrane also have higher high field strength element (HFSE; e.g., Th, Nb, Ta) and total light rare earth element (ΣLREE) concentrations as well as higher ΣLREE/total heavy rare earth element (ΣHREE) ratios than the I-type magmas enriched in large ion lithophile elements (LILEs; e.g., Ba, Sr) in the Jiaobei terrane. These characteristics suggest that the diversity of REE and gold mineralization was the result of interaction between the lithospheric mantle and hybrid sediment-derived melts and aqueous fluids under rutile-bearing eclogite-facies (>2.0 GPa) conditions within the Luxi terrane and with aqueous fluids under amphibolite- to eclogite-facies (>1.5 GPa) conditions within the Jiaobei terrane. Our study strongly suggests that the interaction between the lithospheric mantle and sediment-derived melts, the presence of coexisting REE- and fluorine-rich magmas, and low-pressure partial melting were all crucial factors in the formation of A-type intrusion-related REE deposits, whereas high-pressure partial melting and contemporaneous sulfur and chalcophile element enrichment were critical processes in the formation of I-type intrusions prospective for gold mineralization.

Initiation of Mesoarchean nascent subduction zone in the North China Craton

Exploring the nature of Archean plate tectonics is crucial for understanding the geodynamic evolution of early Earth. While previous studies have focused on (ultra-)mafic metavolcanic and tonalite−trondhjemite−granodiorite (TTG) rocks, the crust-mantle interactions of Archean intermediate magmatism have received much less attention. Mesoarchean (ca. 2936−2855 Ma) dioritic and tonalitic-trondhjemitic magmatism occurred in the Jiaobei terrane, North China Craton. While low-silica (65.67−68.82 wt%) TTG magmatism persisted throughout the entire magmatic period, both the high-silica (69.79−74.54 wt%) TTG and biotite dioritic (MgO of 1.52−2.45 wt%) magmatism were transient (ca. 2922−2901 Ma). They were mainly sourced from metabasaltic crust, though the biotite dioritic and low-silica TTG rocks show variable mantle input. In comparison, the hornblende dioritic magmatism (MgO of 2.07−5.00 wt%) occurred later (ca. 2912−2865 Ma) and was derived from melt-metasomatized mantle sources. Spatially, the magmatism became younger from northeast to southwest. Combined with increasing crustal melting pressures after ca. 2920 Ma and mildly elevated zircon δ18O (up to +6.8‰) of TTG rocks, a Mesoarchean nascent subduction zone is proposed for the Jiaobei terrane that is featured by the recycling of supracrustal basaltic rocks to thickened lower crust (forming high-pressure and high-δ18O TTG) and subsequent melt-related mantle metasomatism (forming relatively high-Mg hornblende dioritic rocks). The recycled supracrustal materials may have lubricated the basal part of the thickened crust and then triggered the opening of a nascent mantle wedge. Further compilation of data from global Archean dioritic and TTG rocks reveals chemical discontinuities at ca. 3.6−3.5 Ga and after ca. 3.0 Ga; these periods are marked by the occurrence of both high-Mg (median MgO >3 wt%) dioritic magmatism and high-(La/Yb)N (median >30) and high-δ18O (median >5.9‰) TTG magmatism. These data, along with independent geological evidence, suggest that the nascent subduction processes may have initiated locally at ca. 3.6−3.5 Ga but globally after ca. 3.0 Ga.

Petrogenesis of Early Cretaceous High Ba-Sr Granitoids in the Jiaodong Peninsula, East China: Insights into Regional Tectonic Transition

Element geochemistry, Sr and Nd isotope, and LA-ICP-MS zircon U-Pb isotope data have been obtained for the granitoids of Dazesan pluton in the Jiaodong Peninsula, East China, and their intermediate microgranular dark enclaves so as to reveal their petrogenesis and tectonic implications. These granitoids have high SiO2 (68.25–71.56 wt.%), K2O (3.44–5.50 wt.%), total alkalis (K2O + Na2O = 7.29–9.00 wt.%), Sr (451–638 ppm), Ba (1157–2842 ppm) and light rare earth elements (LREEs) (131.57–210.08), with strong depletion both in heavy rare earth element (HREE) and high field strength element (HFSE) concentrations as well as unclearly Eu anomalies, showing typical signatures of high Ba-Sr granitoids. They possess high (La/Yb)N (32–50) and Sr/Y (50–79) values and low MgO (0.76–1.11 wt.%), Cr (9.9–19.6 ppm) and Ni (4.51–7.04 ppm) concentrations. All the above geochemical compositions are similar to those of late Early Cretaceous granitoids, in combination with zircon LA-ICP-MS U-Pb ages of 119.6 ± 1.3 to 120 ± 1 Ma for these granitoids obtained in this study, indicating c. 120 Ma probably represents the lower limit of ages when late Early Cretaceous granitoids emplaced in the Jiaodong Peninsula. The microgranular dark enclaves, forming a linear trend with their host granitoids on the oxide against SiO2 plots, display higher MgO contents of 3.05–4.39 wt.% at lower SiO2 concentrations of 54.25–56.84 wt.% and possess a zircon LA-ICP-MS U-Pb age of 119 ± 2 Ma, identical to those of these granitoids, indicating the acid magma and intermediate magma were coeval. Furthermore, dark enclaves and their host granitoids have indistinguishable (87Sr/86Sr)i values of 0.709523–0.70972 and 0.709361–0.709858, respectively, and plot within a two-liquid immiscible field on the Greig pseudoternary phase diagram. In addition, they have markedly parallel REE patterns, with the dark enclaves having much greater REE and HFSE abundances than those of their host granitoids. Therefore, it is suggested that liquid immiscibility is a viable model to explain the chemical compositional variations between the Dazeshan granitoids and their dark enclaves. Based on the element geochemistry, geochronology and Sr- and Nd-isotope of the Dazeshan granitoids and their dark enclaves, it is envisaged the crust-derived acid melts due to partial melting of ancient continental lower crust in the Jiaodong Peninsula (mainly Neoarchean-Palaeoproterozoic basement in the Jiaobei terrane) containing a subduction-related material, resulting from the addition of the enriched subcontinental lithospheric mantle-derived melts, assimilated the lithospheric mantle-derived basic melts and formed the homogeneous magma chamber at the crust base, then split into two immiscible liquids, with one granitic liquid producing the Dazeshan granitoids and the other intermediate one forming the dark enclave during its ascent. Combined with previous studies, the identification of a lithospheric mantle-derived material in the Dazeshan granitoids suggests a catastrophic lithospheric thinning at c. 120 Ma, reflecting an abrupt change in the direction of Palaeo-Pacific plate subducting and the corresponding regional tectonic transition from E–W extension to NW–SE extension.

Relationship between the crystallization of graphite and metamorphism of graphite-bearing granulite in Rizhuang, Jiaobei Terrane

Relationship between the crystallization of graphite and metamorphism of graphite-bearing granulite in Rizhuang, Jiaobei Terrane

High-pressure/ultrahigh-temperature mafic and felsic granulites associated with magnetite deposits from the Jiaobei terrane, Jiao-Liao-Ji Belt, North China Craton

Garnet-bearing mafic and felsic granulites associated with magnetite deposits that have undergone high-pressure (HP) and ultrahigh-temperature (UHT) metamorphism occur in the Yangjiazhai area of the Jiaobei terrane within the Jiao-Liao-Ji Belt, North China Craton. In mafic granulite, the early prograde assemblage (M1) is preserved as inclusions in the core of garnet. Matrix minerals and the garnet mantle define the peak metamorphic assemblage (M2). Near-isothermal decompression (M3) is recorded by the garnet rim and symplectitic minerals. The final cooling process is defined by the late growth of amphibole (M4). Abundant magnetite occurring in some mafic granulite samples may be inherited from the protolith. The felsic granulite records the peak metamorphic stage (M2) defined by the matrix minerals and the garnet mantle, and the retrograde stage defined by the symplectite and the garnet rim (M3). P-T estimations using pseudosection techniques and two-feldspar thermometry yield ∼8–9.8 kbar/710–828 °C for the prograde stage M1, ∼14.5–15 kbar/1040–1073 °C for the peak P-T stage M2, 9.1–10 kbar/965–1015 °C for the post-peak stage M3 and 6.6–9.4 kbar/820–853 °C for the cooling stage M4 as recorded by the mafic granulite. P-T conditions of ∼14–16.5 kbar/985–1077 °C for the peak P-T stage M2 and ∼7.8–9 kbar/889–902 °C for the post-peak stage M3 were derived from the felsic granulite. Thus a clockwise trajectory can be defined by constraining peak-metamorphic high-pressure/ultrahigh-temperature (HP-UHT) conditions. Zircon U-Pb dating and REE characteristics show a contrasting information. Oscillatory zoned zircon domains yield an age of ∼2150 Ma with a steep HREE characteristic, which is interpreted to indicate a magmatic origin of the mafic granulite. The peak HP-UHT stage obtained from metamorphic zircon domains in felsic and mafic granulites is constrained by an age of ∼1950–1900 Ma, which possibly corresponds to a collisional event shortly after subduction. The decompression occurred at ∼1880 Ma following the subsequent cooling at ∼1820 Ma indicating a rapid exhumation of the HP-UHT granulite followed by slow cooling.

The Formation of the Jiaodong Gold Province

AbstractGold deposits in Jiaodong, termed Jiaodong‐type, are tectonically located in the southeastern margin of the North China Craton. Their major features are reviewed in this paper to highlight the differences between Jiaodong deposits and other genetic types of gold deposits. The mineralization was synchronized with asthenosphere upwelling indicated by syn‐ore OIB‐like mafic dike and large‐scale crustal thinning suggested by decrease of Sr/Y from pre‐ore to syn‐ore granites. Asthenosphere upwelling induced by the roll‐back of Paleo‐Pacific Plate drove partial melting of lithospheric mantle and devolatilization, which induced the release of the ore‐forming fluids. In concomitant with magmatic records, mineralization migrated from the western Jiaobei terrane (133–127 Ma) to the eastern Sulu orogenic belt (114–108 Ma), corresponding to the eastward roll‐back of Paleo‐Pacific Plate. Gold mineralization in Jiaodong formed in the transitions of ductile to brittle deformation, rapid to slow crustal uplift, and regional compression to extension. In the regional‐scale, the gold deposits in the Jiaobei terrane are mostly situated at intersections between NE‐trending faults and EW‐trending basement faults, and gold orebodies dominantly controlled by the lithologic contacts between Precambrian metamorphic rocks and Mesozoic granites. The mineralization was dominated by the disseminated‐veinlet ores related to quartz–sericite alteration in strong cataclasite‐breccia zone, with subsidiary thick quartz‐sulfide veins developed in secondary fault zones. The ore‐forming fluids belong to a H2O–CO2–NaCl±CH4system and show minor variations in salinity among different types of ore. Structure‐fluid feedback involving fluid‐rock reaction and hydrofracturing triggered the fluid phase separation and resultant gold deposition. The Jiaodong gold deposits are distinct from orogenic and intrusion‐related gold deposits in terms of tectonic setting, origin of ore‐forming fluids, and mechanism of gold deposition.

Timing of Paleozoic Metamorphism in the Jiaobei Terrane, East China: Evidence from Apatite U-Pb Age and Trace Element Composition

The northward subduction of the Paleo-Tethys oceanic crust in the Paleozoic to Mesozoic is critical for the tectonic evolution of the Qinling-Tongbai-Hong’an-Dabie-Sulu-Imjingang-Gyeonggi orogenic belt. However, the Paleozoic geological fingerprint of the Paleo-Tethys oceanic crust subduction in the Dabie-Sulu orogenic belt remains obscure. In the present study, apatite from the Muniushan monzogranite in the Houkuang area was analyzed to constrain the age of metamorphism in the Jiaobei Terrane and is regarded as the response to the Paleo-Tethys oceanic crust subduction in the Early Permian. Muniushan apatite with obvious negative Eu anomaly is enriched in LREE and depleted in HREE. The chondrite-normalized REE patterns of apatite correspond with I-type granitoids and mafic igneous rocks, implying a magmatic origin. Igneous apatite grains have reset compositional zonation in the cathodoluminescence image. Apatites plotted on a support vector machine apatite classification biplot and Eu/Y-Ce discrimination diagram shows a tendency from the region of “mafic igneous rocks and I-type granitoids” to “low and middle metamorphic”. This evidence consistently suggests that the Muniushan apatite suffered metamorphism at a later stage. The twenty-six apatite grains from the Muniushan monzogranite yield a metamorphic age of 297 ± 8 Ma (by LA-ICP-MS U-Pb), which is different from the Muniushan zircon SHRIMP U-Pb results of 2110 ± 4 Ma, indicating the metamorphism occurred in the Early Permian and reset the U-Pb system of apatite. The Early Permian metamorphism that occurred in the Jiaobei Terrane is synchronous to the subduction of the Paleo-Tethys oceanic crust and is the response to the Paleo-Tethys oceanic crust subduction.

Deep exploration of Jiaodong type gold deposit, taking Shanhou gold deposit, southern part of Zhaoping fault as an example

Crustal response induced by the subduction of Paleo-Pacific Plate, is crucial to study the metallogenic law and prediction of Jiaodong type gold deposit. Gold deposits are preferentially hosted in the lithospheric-scale second-order faults, which provide migration channels, mineralization corridors, and the physicochemical conditions. Super-large gold deposits in northwestern Jiaobei Terrane are generally controlled by regional linear faults, such as Sansandao, Jiaojia, Zhaoping and Qixia faults. However, Zhaoping fault is exposed sporadically (in Xiadian and Jiangjiayao gold deposits) beneath a thick cover of Quaternary basalts, which indicating that limited information can be obtained by traditional geological survey. In this study, high-precision geophysical surveys such as gravity and controlled source audio frequency magnetotellurics (CSAMT) are conducted in the Shanhou gold deposit, which hosted in southern part of Zhaoping fault. Three integrated geophysical profiles results further identified the spatial distribution of second-order oblique-slip faults of Zhaoping fault and established the relationships between brittle deformation and mineralization. The spatial variability of stratum (high density 2.82 g/cm3 and intermediate to high specific resistivity 4000 Ω m), brittle-slip faults (intermediate density 2.73 g/cm3 and low specific resistivity 200 Ω m) and magmatite (low density 2.57 g/cm3 high specific resistivity 8000 Ω m) are identified by two inversion techniques, including the man-machine interactive inversion technology and nonlinear conjugate gradient technology. In addition, the geophysical inversion pseudo sections delicately portray a smooth-out waveform low specific resistivity anomaly, which strongly couples with the spatial ore-hosted locations and enrichment places. The gold mineralized alteration zones generally dips to southeast and the angle changing from 45° to 30°, which are strong coupling with the large-scale acid magmatic intrusion and extensional tectonics occurred in the late Mesozoic. Finally, according to the deep prospecting prediction, a gold ore body with 10 m in thickness was revealed by drilling below the depth of 1,015 m, which is hosting in the brittle deformation of Zhaoping fracture zone.

Petrogenesis of Mo-associated Mesozoic granitoids on the Jiaodong Peninsula: Implications for crustal architecture and Mo mineralization along the Dabie–Sulu Orogen

Recent studies have demonstrated a linkage between the crustal architecture and the location of magmatic–hydrothermal Cu deposits in collisional orogens. However, if and how the crustal architecture controls the distribution of magmatic–hydrothermal Mo deposits in collisional orogens is unclear. Here, we present zircon U–Pb dating, geochemical and Sr–Nd–Hf–O isotopic data for granitoids associated with Mesozoic Mo mineralization on the Jiaodong Peninsula which exhibits substantial endowment differences to the Dabie Orogen. Geochronology data show that the Mo-associated granitoids occurred at ca. 160 Ma and 117 Ma. The Jurassic Mo-associated monzogranite was derived from melting of the thickened North China Block lower crust in a subduction-related setting. The Early Cretaceous Mo-associated granodiorite and granite were originated from a modified North China Block thorough crust–mantle interactions, induced by rollback of the Paleo-Pacific Plate. Our results complemented by published data indicate a crustal architecture characterized by South China Block gneisses overlying North China Block lower crust in the Sulu Orogen and wedging into the North China Block in the Jiaobei Terrane. By comparing the Mo–associated granitoids in Dabie Orogen and Jiaodong Peninsula, we conclude that magma source differences controlled by crustal architectures lead to Mo endowment diversities along the Dabie–Sulu Orogen.

Geochemistry and Isotopic Characteristics of Apatite and Zircon From Late Jurassic Granites in the Jiaobei Terrane, East China: Implications for Petrogenesis and Geodynamic Setting

The North China Craton (NCC) was stable for more than 2.0 Gyr before a Jurassic–Cretaceous large-scale lithospheric thinning event, but the geodynamic setting during the early phases (Late Jurassic) of NCC reworking remains controversial. We present new petrological and whole-rock geochemical data, zircon and apatite geochemistry, U–Pb ages, O isotopic data, and Sr–Nd isotopic data for two phases of Late Jurassic granite (Linglong and Luanjiahe) from the Jiaobei terrane, southeastern NCC. LA-ICP-MS zircon U-Pb dating suggests that the Linglong granite formed about 6 Myr earlier than Luanjiahe granite (158 Ma vs 152 Ma), after the inception of the paleo-Pacific plate subduction. High zircon U/Yb ratios, high δ18O values [7.89 ± 0.10‰ to 7.67 ± 0.14‰ (2σ)], and inherited zircon age spectra, as well as high apatite F/Cl ratios and Sr–Nd isotopic compositions, suggest that the Linglong and Luanjiahe granites formed by partial melting of ancient thickened lower continental crust of the NCC and Yangtze Craton. Magma evolution modelling based on Rb and Rb/Nb data suggests a similar decoupled assimilation-fractional crystallization process for the generation of Linglong and Luanjiahe granite but with different assimilation degrees. The water contents of parental magma evaluated by using whole-rock Ba, Sr and apatite F, Cl data indicate that the Linglong granite was formed in a relatively water-rich environment than Luanjiahe. This is consistent with the presence of amphibole and minor negative Eu anomalies in the Linglong granite, as water input can promote amphibole fractionation and suppresses plagioclase crystallization. Considering the similar magma sources but distinct water contents of the granites, and the oblique Paleo-Pacific plate subduction setting in the Late Jurassic, the fluids were likely released from the ocean plate beneath a stacked thickened crust. Since the earliest mafic dikes (OIB-type) in the NCC are coeval with the Luanjiahe granite, we suggest that the lower water contents of the Luanjiahe granite were associated with roll-back that resulted in an increasing distance from slab to continental crust. Such a tectonic transition from subduction compression (158 Ma) to initial extension (152 Ma) in the Late Jurassic perhaps possibly marks the beginning of the reworking of the NCC.

Correlating metamorphic mineral assemblages with metamorphic ages in rocks recording multiple tectonothermal events: A case study of the Jiaobei terrane, eastern North China Craton

Interpretations of high-grade terranes recording more than one episode of metamorphism can often be problematic due to the difficulties in assigning the metamorphic conditions to the time of metamorphism. The Jiaobei terrane as a typical Precambrian metamorphic terrane in the North China Craton (NCC) records multiple high-grade metamorphic events. Resolving the timing and features of each metamorphic event can cast light on the above issue and also play a key role in understanding the geological evolution of the Jiaobei terrane and the NCC. This study reports paired U-Pb dating with in-situ trace elements and oxygen isotope compositions of metamorphic zircons in meta-mafic rocks from the Qixia area of Jiaobei terrane. The zircons develop core-rim structures with both of them exhibiting metamorphic features. Zircon rims, although widely developed, are mostly too thin for in-situ age dating. LA-ICPMS as well as SIMS zircon U-Pb analysis of zircon cores yielded metamorphic ages of ∼ 2500 Ma, whereas the rims yielded 207Pb/206Pb ages of 1915–1717 Ma. The rare earth elements (REE) patterns and δ18O values measured in the Paleoproterozoic metamorphic zircon rims are distinct from those measured in the Archean cores. Distinct features of the cores and rims imply that the garnet-bearing (high-pressure) mineral assemblages were formed during late Paleoproterozoic metamorphic event and absent during the Neoarchean event. These new geochronological data further confirm that the Jiaobei terrane records both the late Neoarchean metamorphism and the late Paleoproterozoic tectonic thermal event. Also, our study argues for the existence of global subduction network geological records in the NCC during Paleoproterozoic, rather than during Neoarchean. The influence of the overprinted late Paleoproterozoic metamorphism should be fully considered when estimating P-T conditions of the earlier tectonothermal event (Neoarchean metamorphism).

Petrogenesis of Early Cretaceous granitoids and mafic enclaves from the Jiaodong Peninsula, eastern China: Implications for crust-mantle interaction, tectonic evolution and gold mineralization

Early Cretaceous granitic plutons in the Jiaobei Terrane, Eastern China, contain abundant mafic enclaves (MMEs), which are important to understand the tectonic settings and genesis of gold mineralization in the Jiaodong Peninsula. Here, we combine petrology, geochronology, and isotopic geochemistry for MMEs and host granitoids to constrain their tectonic evolution and understand the genesis of coeval gold mineralization in the Jiaodong Peninsula during the Early Cretaceous. Zircon U-Pb dating reveals two magmatic events: (1) the earlier magmatic event (130–126 Ma), represented by Congjia MME (CJ-MMEs) and host granodiorite, and (2) the later magmatic event (121–116 Ma), including Gushan MME (GS-MMEs) and host granite. Field relationship, disequilibrium textures, and elemental and Sr-Nd-Hf isotopic compositions indicate that MMEs and host granitoids formed through mixing/mingling of mafic and felsic magmas. However, significant differences between CJ-MMEs and GS-MMEs indicate that the former has adakitic affinity and was produced by mixing of magmas from lithospheric mantle and mafic lower crust in deep hot zone, whereas the latter has arc-magmatic affinity, suggesting enriched lithospheric mantle source. Higher SiO2 and lower MgO contents in the host granitoids indicate that they were originated from reworking ancient NCC lower crust. Our results reveal crustal growth during the earlier magmatic event, followed by rapid crustal/lithospheric thinning in the later magmatic event, all triggered by ongoing rollback of subducting Paleo-pacific plate. These results combined with complex assemblages of sulfides and volatiles in GS-MMEs indicate that the lithospheric thinning, the rise of enriched lithospheric mantle-derived melts to shallow crustal levels, and crustal-mantle interactions around ∼ 120 ± 3 Ma, are the main factors for massive gold precipitation in the Jiaodong Peninsula.

Petrogenesis and implications of ∼2.1 Ga Jingqishan granites in the Jiaobei Terrane, North China Craton

Widely distributed 2.2–2.1 Ga A-type granites in the North China Craton (NCC) have not only a significant role in unveiling the regional Palaeoproterozoic tectonic evolution but also crucial implications for the spatial and temporal evolution of A-type granite. This paper presents zircon U-Pb dating, geochemistry and Nd and Hf isotopes of Jingqishan Palaeoproterozoic gneissic granites from the Jiao-Liao-Ji Belt (JLJB) of the eastern NCC. The Jingqishan granites are mainly monzogranites. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb analyses of three samples yield concordant ages of 2124 ± 7 Ma, 2089 ± 11 Ma and 2088 ± 10 Ma. The Jingqishan granites are ferroan, calc-alkalic to alkali-calcic, and metaluminous-peraluminous. The high Ga/Al ratios, Zr + Nb + Y + Ce contents and Zr saturation temperatures (861 °C on average) of these granites are consistent with the features of A-type granite. The granites have εNd(t) values of −5.7 to −0.8 with two-stage Nd model ages of 2.99–2.63 Ga and zircon εHf(t) values of −7.3 to −2.9 with two-stage Hf model ages (TDM2(Hf)) of 2.94–2.61 Ga. These TDM2(Hf) ages are similar to those of ∼ 2.5 Ga Jiaobei Tonalite-Trondhjemite-Granodiorite (TTG) gneisses. Based on petrology, geochemistry and isotopic characteristics, we infer that the Jingqishan A-type granites are mainly partial melts of the Jiaobei 2.5 Ga TTGs. Combining our data with those published for 2.2–2.1 Ga JLJB granites and extensive data, we discover that both 2.1 Ga and 2.18 Ga A-type granites of the JLJB have A2-type granite characteristics and formed in a back-arc basin but were generated from the partial melting of different sources at two magmatic stages. Most 2.2–2.1 Ga A-type granites of the NCC belong to A2-type that sourced from late Achaean crustal rocks in an extensional setting.

Zircon U-Pb dating, Hf isotope characteristics of Late Jurassic granites in eastern Jiaodong Peninsula and their constraints on metallogenetic tectonic setting of gold deposit

胶东地区是目前我国最重要的金矿产地，已累积探明黄金储量接近5000t。金矿在胶东地区分布非常不均，主要集中在胶北地体，而胶东东部地区金矿产出较少。晚侏罗世的玲珑花岗岩是胶北金矿区最重要的赋矿围岩之一。虽然胶东东部同样有晚侏罗世花岗岩发育，但赋存金矿较少，因此前人对东部这些花岗岩体的研究相对较少。本文选取胶东东部的文登岩体和垛崮山岩体进行了锆石U-Pb定年和Hf同位素分析，同时收集整理了胶北地体的玲珑岩体数据，通过开展胶东东部及西北部同一时期岩体的差异性研究，为该区金成矿作用的研究提供重要线索。分析结果显示，文登岩体和垛崮山岩体的形成时代为晚侏罗世（~160Ma），与玲珑岩体时代一致。三个岩体均含有较多的三叠纪（~230Ma）和新元古代（~780Ma）的继承锆石，表明晚侏罗世花岗岩的岩浆源区主要为经历了超高压变质作用的扬子板块。不同的是，玲珑岩体中有更多的华北板块物源的年龄记录（~1400Ma、~1700Ma、~2500Ma），垛崮山岩体中这些年龄的继承锆石少于玲珑岩体，而文登岩体更少。文登岩体、垛崮山岩体的新生岩浆锆石ε_Hf（t）值范围分别为-30.7~-20.3和-27.5~-17.9，玲珑岩体的新生岩浆锆石ε_Hf（t）值的变化范围更广，在-29.3~-9.3之间，而且呈现出从文登岩体到垛崮山岩体到玲珑岩体，ε_Hf（160Ma）值逐渐增高的现象。其原因可能是扬子板块与华北板块碰撞后，幔源岩浆底侵并诱发加厚的地壳发生部分熔融，形成花岗岩。在此过程中胶北地体深部受到幔源物质的影响，从而对金及成矿相关元素产生一定的预富集作用，而同时期胶东东部地区未受到明显的地幔物质影响，可能是该区金矿产出较少的原因之一。;Jiaodong Peninsula is the most important gold producing province in China, with an explored reserve of nearly 5000t gold. However, the gold deposits are very unevenly distributed in this area, e.g., most in Jiaobei terrane but less in eastern Jiaodong Peninsula. Late Jurassic Linglong pluton is one of the important ore-hosting rocks in Jiaobei terrane. Although Late Jurassic granites also exist in eastern Jiaodong Peninsula, gold deposits are much less abundant in them. Thus, relatively few studies were focused on these granite plutons in the eastern Jiaodong Peninsula. Here, we carried out zircon U-Pb dating and Hf isotopic analysis on the Wendeng and Duogushan plutons in eastern Jiaodong Peninsula to compare them with those of the Linglong pluton in Jiaobei terrane to seek the differences of the gold mineralization in the Late Jurassic granites between these two areas. Our results show that the Wendeng and Duogushan plutons were formed at Late Jurassic (~160Ma), which is consistent with those of the Linglong pluton. The inherited zircons from the three plutons are all dominated by Triassic (~230Ma) and Neoproterozoic (~780Ma) ages, indicating their magmatic source mainly derived from crustal materials of Yangtze Craton, which had undergone ultrahigh-pressure metamorphism in Triassic. The difference among them is the number of inherited zircons relating to North China Craton (~1400Ma,~1700Ma,~2500Ma), which are most abundant in Linglong pluton, less in Duogushan pluton, and least in Wendeng pluton. Magmatic zircons from the two plutons in eastern Jiaodong Peninsula have variably negative ε_Hf(160Ma) values, from -30.7 to -20.3 for Wendeng pluton, and from -27.5 to -17.9 for Duotgushan pluton. Contrastively, the range of ε_Hf(160Ma) values of Linglong pluton is significantly wider, i.e., from -29.3 to -9.3. Moreover, the ε_Hf(160Ma) values also increase gradually from the Wendeng pluton to the Duogushan pluton, and then to the Linglong pluton. The possible interpretation of this trend is that after the collision of the Yangtze Craton and North China Craton in Triassic, the underplating of mantle material induced partial melting of the thickened crust as early as Late Jurassic. Meanwhile, the Jiaobei terrane was influenced by mantle materials, which promoted the pre-enrichment of gold. In contrast, the eastern Jiaodong Peninsula was lack of involvement of mantle material in Late Jurassic, which might be one of the reasons for fewer gold deposits in the area.

Early Cretaceous uplift of the Jiaobei Terrane: Evidence from the detrital zircon and sediment compositions of sandstones in the Jiaodong Peninsula, China

In this study, we conducted sandstone petrography analyses and determined detrital zircon U–Pb ages and Hf isotopes for sandstones collected at different stratigraphic levels of the lowest strata of the Laiyang Group. All results nearly point to an evolutionary trend for the source regions of the strata. The detrital zircon U–Pb results reveal multiple age groups at 140–123 Ma, 810–700 Ma, and 2,500–1,750 Ma, but variable age proportions for two sandstones (19LY‐01Z and ‐05Z) collected at lowermost and middle levels of strata, respectively, but only one unimodal age mode at ca. 1,850 Ma for the uppermost sandstone 19LY‐09Z. Provenance analysis illustrates that the lower strata likely include two source regions, including the Jiaobei Terrane and the Sulu orogen, whereas the upper strata appeared to have one dominant source region (i.e., Jiaobei Terrane). Framework modes of sandstones display that lower samples contain more metamorphic lithic fragments, which corresponds to the recycled orogenic field in the Q‐F‐L diagram, while middle‐upper samples are enriched in feldspars but deficient in lithics and plot in the basement uplift field of the Q‐F‐L diagram. This compositional variation reflects an evolution of the source regions from the Sulu Orogen to the Jiaobei Terrane, completely consistent with the observation of an increase in the amount of detrital zircons sourced from the Jiaobei Terrane, but decreasing detrital zircons from the Sulu Orogen in an upward order. This shift in the provenance of sediments reflects two tectonic events including exhumation of the Sulu Orogen to the surface before sedimentation of the Laiyang Group, and a rapid uplift of the Jiaobei Terrane after ca. 125 Ma following removal of lithospheric mantle.

Late Neoarchean crustal growth under paired continental arc-back arc system in the North China Craton

The late Archean (~3.0–2.5 Ga) was a key period of continental growth globally, which is widely considered to reflect the onset of vigorous plate tectonic activity, although related continental growth modes remain contentious. Here we investigate a suite of late Neoarchean metavolcanic rocks from the southwest Qixia area of the Jiaobei terrane in the North China Craton. The rocks in this suite include amphibolites, clinopyroxene amphibolites, and hornblende plagioclase gneisses. We present zircon U-Pb isotopic data which indicate that the protoliths of these rocks formed during ~2549–2511 Ma.The (clinopyroxene) amphibolites correspond to meta-basaltic rocks, with some containing high modal content of titanite. These rocks show moderate to high FeOT (8.96–13.62 wt.%) and TiO2 (0.59–1.59 wt.%), flat to less fractionated REE patterns, and mildly negative Th, Nb, and Ta anomalies, resembling those of Fe-tholeiites. In addition, they display positive zircon ƐHf(t) values (+2.6 to +8.7), and are devoid of crustal contamination or fractional crystallization. Combined with the low Nb/Yb (mostly < 1.60) and (Hf/Sm)N (mostly < 0.95), low to moderate Th/Yb (0.08–0.54), and low V/Sc (5.53–9.19) ratios, these basaltic rocks are interpreted to have been derived from a relatively reduced and depleted mantle source that was mildly metasomatized by hydrous fluids. The hornblende plagioclase gneisses are meta-andesitic rocks, and occur interlayered with the basaltic rocks. They are transitional between tholeiitic and calc-alkaline rock series, and show fractionated REE patterns with evidently negative Th, Nb, and Ta anomalies. The depleted zircon ƐHf(t) values (+2.4 to +8.4) and quantitative chemical modeling suggest that the andesitic rocks were most likely generated by injection and mixing of juvenile felsic magmas with the tholeiitic basaltic magmas.In general, the chemical features and genesis of late Neoarchean meta-basaltic rocks in our study area resemble those of Mariana back-arc basin basalts. Combined with regional geological data, it is proposed that the Jiaobei terrane witnessed late Neoarchean crustal growth under a paired continental arc-back arc setting. On a regional context, we propose two distinct geodynamic mode of late Neoarchean continental growth across North China Craton (particularly the Eastern Block), i.e., (1) arc-continent accretion along northwestern part of the Eastern Block; and (2) paired continental arc-back arc system surrounding the ~3.8–2.7 Ga continental nuclei to the southeast.