Geochronology, geochemistry, and tectonic significance of Permian intrusive rocks from the Shaolanghe region, northern margin of the North China Craton

In situ zircon U–Pb ages and Hf isotopic data, whole‐rock major and trace element contents, and Sr–Nd isotopic compositions are reported for Permian intrusive rocks at Shaolanghe in Eastern Inner Mongolia in order to explore the magmatic origin and tectonic significance of these rocks for the evolution of the northern margin of the North China Craton. Three intrusive rocks, quartz diorite, Xishuiquan granite, and Xinglong granite, yield zircon U–Pb ages of 285.9 ± 3.1, 274.2 ± 2.9, and 260.0 ± 8.4 Ma, respectively. The quartz diorite and Xishuiquan granite belong to the high‐K calc‐alkaline series, enriched in large ion lithophile elements (e.g., Rb) and depleted in high field strength elements (e.g., Nb and Ti). They are defined as I‐type granites. The quartz diorite has initial 87Sr/86Sr ratios of 0.7049–0.7051, εNd(t) values of −10.0 to −11.4, and εHf(t) values of −15.2 to −9.9. The εHf(t) values of the Xishuiquan granite (−4.8 to 4.0) vary in discrete segments, whereas the εNd(t) values (−12.9 to −13.3) are consistent with those of the quartz diorites (−10.0 to −11.4). A magma mixing model is proposed for the formation of the quartz diorites of the Shaolanghe region, and the Xishuiquan granite was likely derived from partial melting of the Paleoproterozoic crust with involvement of mantle components. Geochemical analyses show that the tectonic setting of the northern margin of the North China Craton during the late Palaeozoic was an Andes‐type active continental margin associated with subduction of the Paleo‐Asian Ocean plate.

Plagioclase crystallisation in a granodioritic melt and its petrogenetic implications for the origin of the A‐type granite in East Junggar, NW China

Crystallisation experiments were performed on a natural I‐type granodiorite from East Junggar of Xinjiang, NW China, at 1.0 and 1.5 GPa in the temperature range between 700 and 875 °C and for various water contents to investigate the crystallisation behaviour of plagioclase in granodioritic melts. Experimental results indicate that the optimal conditions for plagioclase to crystallise in this granodioritic melt are approximately 875 °C, 1.0 GPa, and ~10 wt% water content. All the experimental feldspars have ternary composition because of the high pressure in this study, with Or contents increasing while An contents decreasing with the increase of pressure. They consist of Or‐rich plagioclase at 1.0 GPa, passing to An‐rich alkali feldspars at 1.5 GPa. The ternary feldspar plays a role in keeping the total amount of alkali in the residual melt relatively constant. After plagioclase‐dominant crystallisation, the residual melt shows characteristics similar to the A‐type granites from East Junggar, implying that the fractional crystallisation of the I‐type granodioritic melt at high pressure may be one of the important processes generating the A‐type magmas in East Junggar. Mass balance calculation and trace element modelling show that the fractionally crystallised phase assemblage and proportion could be plagioclase (40.2 wt%) + orthopyroxene (6.3 wt%) + hornblende (6.3 wt%). The experimentally determined plagioclase crystal growth rates range from 1.17 × 10−8 to 2.70 × 10−8 mm/s. By comparing the crystal growth rate with the crystal size in natural rocks, the timescale of the crystallisation and differentiation of the I‐type granodioritic magma that is parental to the A‐type granitic magma in East Junggar was estimated to be several hundred years, in excellent agreement with the result from a simple numerical model.

Timing of formation of the Keketale Pb–Zn deposit, Xinjiang, Northwest China, Central Asian Orogenic Belt: Implications for the metallogeny of the South Altay Orogenic Belt

The Keketale is the largest Pb–Zn deposit in the volcano‐sedimentary Maizi Basin of the South Altay Orogenic Belt (AOB), Northwest China. The stratabound orebodies are hosted in a suite of meta‐sedimentary rocks intercalated with volcanic rocks of the Lower Devonian Kangbutiebao Formation. The massive and banded ores representing the main mineralization stage are relatively well‐preserved in the ore district. This paper reports systematic geochronological results including the zircon laser ablation–multiple collector–inductively coupled plasma–mass spectrometry (LA‐MC‐ICP‐MS) U–Pb analyses on two meta‐felsic volcanic rocks from the Kangbutiebao Formation and Rb–Sr isotope dating on seven sphalerite samples from the main mineralization stage, together with some sulphur isotopic data to constrain the mineralization age and the genesis of the deposit. Rb–Sr isotope dating yield an isochron age of 398.2 ± 3.3 Ma generally synchronous with the zircon (LA‐MC‐ICP‐MS) U–Pb analyses of a meta‐rhyolite and a meta‐dacite from the strata (410.5 ± 1.3 Ma and 394.8 ± 1.9 Ma, respectively). The δ34S values of seven pyrite samples in the main massive and banded ores vary from −12.4‰ to −6.2‰, indicating that the main ore‐forming sulphur of the deposit was derived from bacterial reduction of seawater sulphate. By integrating the field, chronological, and isotopic evidences, we conclude that the Keketale Pb–Zn deposit is a VMS‐type deposit. Combining our results with the isotopic geochronology in the South AOB, we argue that the South AOB has undergone three mineralization episodes: the syndepositional mineralization (412–387 Ma), the subvolcanic hydrothermal‐related mineralization (382–379 Ma), and the epigenetic mineralization that is genetically linked to regional metamorphism and deformation (260–204 Ma). The Keketale Pb–Zn deposit is a product of the Devonian seafloor hydrothermal exhalation system in the South AOB.

Discovery of Mesoproterozoic kimberlite from Dörbed Banner, Inner Mongolia and its tectonic significance

Porphyritic olivine kimberlitic breccia, discovered in the Dörbed Banner of Inner Mongolia, Western China, is referred to as Longtou Shan Kimberlite in our study. This kimberlite occurs as a pipe in the Halahuogete Formation of Bayan Obo Group. Zircon U–Pb ages of Longtou Shan Kimberlite reveals a Mesoproterozoic age of ~1,552 Ma, constraining the deposition age of Halahuogete Formation to the Mesoproterozoic. Compared with Mesoproterozoic kimberlite of the ancient landmass, it can be inferred that the North China Craton is a member of the Ur ancient continent of the Columbia supercontinent. Furthermore, according to the tectonic background of the Bayan Obo Group, we raise this possibility that “Bayan Obo Aulacogen” should be renamed the “Bayan Obo Continental Rift.”

Petrogenesis and tectonic setting of the Shiduolong skarn Pb–Zn deposit in the East Kunlun Orogenic Belt: Constraints from whole‐rock geochemical, zircon U–Pb and Hf isotope analyses

The Shiduolong Pb–Zn deposit, located in the East Kunlun Orogenic Belt, is a medium‐scale skarn deposit (0.4 Mt metal reserves with a grade of 1.46% Pb and 4.38% Zn). The mineralization occurs along the contact zone between Carboniferous marbles and Triassic quartz diorite and granodiorite. Zircon LA‐ICP‐MS dating indicates that the Shiduolong quartz diorite is coeval with the granodiorite (245 Ma). Whole‐rock geochemical analysis shows that both phases are high‐K calc‐alkaline metaluminous (A/CNK < 1) I‐type granites with similar rare earth (REE) element contents and (La/Yb)N values, indicating that they formed via crystal fractionation from a common parental magma. However, the granodiorite has higher SiO2 contents, lower total Fe2O3, TiO2, MgO, Sr, and Ba contents, and more negative Eu anomalies than the quartz diorites, suggesting that the granodiorite experienced stronger fractional crystallization during magmatic evolution. The zircon εHf(t) values of the quartz diorite range from −3.3 to 1.6. The two‐stage model ages (TDM2) vary from 1,175 to 1,487 Ma. Hf isotope data indicate that the magma of the quartz diorite was mainly derived from partial melting of Mesoproterozoic lower crustal materials with contributions from mantle‐derived magmas. Combined with the regional tectonic and magmatic activities, we propose that the Shiduolong Pb–Zn deposit might have formed during the hydrothermal event associated with the release of magmatic water from the granodiorite‐quartz diorite intrusions, which were generated by the subduction of the Paleo‐Tethys oceanic slab in the Early Triassic.

Fluid inclusion and isotope geochemistry of the Atebayue Sb deposit, South Tianshan Orogen, Kyrgyzstan

The Atebayue Sb deposit is hosted in the Silurian clastics in the South Tianshan Orogen in Kyrgyzstan. The Sb ores appear as veins/veinlets and disseminations, with stibnite being the main ore mineral. Gangue minerals comprise quartz, calcite, and clay minerals. The quartz at Atebayue only contains aqueous fluid inclusions with low homogenization temperature (215–336 °C) and salinity (3.4–6.9 wt.% NaCl equiv.), supporting an epizonogenic hydrothermal origin. The minimum trapping pressures estimated from the NaCl─H2O inclusions are 9–14 MPa, suggesting that the Sb mineralization mainly occurred at a depth of 0.9–1.4 km. Sulphur isotopes (δ34S = −0.4 to 6.2‰) suggest that the host rocks within the Silurian system to be a significant source of ore metals. The ores contain average 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.112, 15.547, and 38.064, respectively, and 2‐stage model ages of 337–381 Ma, indicating the ores were likely sourced from the Paleozoic strata. Integrating the data obtained from the studies including ore geology, fluid inclusion, and S─Pb isotope geochemistry, we conclude that that the Atebayue Sb deposit is best classified as epizonogenic type formed by the Tarim–Kazakhstan continent–continent collision.

Early Carboniferous tectonic evolution of the northern Heihe–Nenjiang–Hegenshan suture zone, NE China: Constraints from the mylonitized Nenjiang rhyolites and the Moguqi gabbros

The Heihe–Nenjiang–Hegenshan suture zone has long been accepted as the major tectonic boundary between the Xing’an and Songliao blocks and extends through the Great Xing’an Range in NE China, but its location of the northern segment between the Moguqi and Nenjiang areas and its timing remain unclear. We address these issues by presenting zircon LA‐ICP‐MS U–Pb ages, Lu‐Hf isotopes, bulk‐rock major, and trace elemental data for mylonitized rhyolites collected from the Moergenhe Formation in the Nenjiang area and for gabbros of the Moguqi area, respectively. The mylonitized rhyolites, which display an arc‐related geochemical affinity with enrichment in Th and U, and depletion of Nb, Ta, and Ti, and gently right‐tilted rare earth element (REE) patterns (light REE [LREE]/heavy REE [HREE] =4.53–7.60), as well as the εHf (t) values (+6.4 to +11.8) of analyzed zircons, indicate an origin by partial melting of potentially young lower continental crust of a subducting slab. The zircon LA‐ICP‐MS U–Pb data show the formation age of the mylonitized rhyolites is 352.4 Ma. The analyzed gabbros with an emplacement age of 352.6 Ma have high concentrations of Th and U, slightly enriched LREE patterns and relative low LREE/HREE ratios (4.3 to 4.6). These features, together with their high positive εHf (t) values (+7.7 to +15.2), suggest that they were likely derived from the partial melting of a depleted mantle source that was metasomatized by subduction‐related fluids. Combined with the geochemical features of the coeval igneous rocks from the northern Great Xing’an Range, these results reveal that the existence of an early Carboniferous NE‐trending magmatic arc (ca. 350–330 Ma), extending along the west of the Heihe–Nenjiang–Hegenshan suture zone, gives more constraints on the amalgamation of the Xing’an and Songliao blocks along the Nenjiang–Moguqi areas and indicates that the amalgamation should have terminated by at least the end of the early Carboniferous.

Structural, stratigraphic, and petrological clues for a Cretaceous–Paleogene abortive rift in the southern Adria domain (southern Apennines, Italy)

This study provides new structural, stratigraphic, and geochemical data and a literature review of the Cretaceous–Paleogene stratigraphy, biostratigraphy, tectonics, and magmatism in the southern Apennines belt, Italy, with the aim to demonstrate the occurrence of an Albian to Eocene abortive rifting stage in the southern Adria domain. During this time, the tectono‐stratigraphic evolution of the Adria domain is characterized by episodes of coeval uplift and drowning. Different sectors of the Apennine and Apulian platforms were so characterized by changes in the paleoenvironments, leading to different stratigraphic records (from shallow‐water to slope and basin), as well as the development of thick bauxitic levels. Contemporaneously, a large amount of calciclastic sediments supply from the emerging sectors was deposited in the basins surrounding the carbonate platforms (i.e., Ligurian and Lagonegro–Molise basins). The Albian–Eocene interval was also characterized by the occurrence of anorogenic magmatism and synsedimentary extensional faulting that, along with the changed sedimentary facies distribution, points out for a crustal‐scale extensional tectonics. We suggest that such tectonics is the result of a rifting episode, characterized by limited anorogenic magmatism, starting in the Albian and reaching its climax in the uppermost Cretaceous–Eocene times. In this scenario, the extensional tectonics recorded in the Adria domain was the product during an event of a single abortive rift system, which extended toward the south, from the southern margin of the Ligurian Ocean to the Hyblean (Sicily), Pelagian (Tunisia), and Sirte Basin Province Rift (Libya).

The controlling factors of modern facies distributions in a half‐graben lacustrine rift basin: A case study from Hulun Lake, Northeastern China

Hulun Lake is located in Northeast China and is a well‐exposed modern lacustrine rift basin. In this study, recent fieldwork has demonstrated that it was mainly filled by alluvial fan and fan delta deposits along the western escarpment, which were controlled by the Eerguna Fault Zones. However, it was filled by river‐deltaic and eolian deposits along the eastern slope. The distributions of the depositional systems were found to be controlled by their positions within the basin. The western escarpment was determined to have influenced the distributions of the alluvial fan and fan delta deposits. In contrast, the river‐deltaic and eolian deposits were controlled by the sediment supply, paleogeomorphology, and wind forces. The asymmetric geometry of the basin was determined to have resulted in different facies associations. First, a region of maximum sediment thickness and high‐gradient escarpment was found to be located near a normal fault foot (Eerguna Fault). Second, a region of a shallower and low‐gradient slope was located near the margin of a river‐lake transition. The depositional characteristics obtained from the prospecting trench indicated that the coarse deposits on the western side were mainly derived from unexpected flooding, gravity, and episodic flooding in an ascending order. In contrast, the fine deposits on the eastern side were mainly sourced from a meandering river. A clear understanding of controlling factors on facies associations can potentially reveal the sedimentary process and evolution of the depositional systems, as well as provide an important methodology for the prediction of facies in other sedimentary basins with similar characteristics.

The uppermost Carboniferous (Gzhelian)–Lower Permian (Asselian–Sakmarian) stratigraphy and smaller foraminifers of the Ozbak‐Kuh region (Tabas Block, east central Iran)

The uppermost Carboniferous (Gzhelian)–Lower Permian (Asselian to Sakmarian) Anarak Group of the Zaladou section in central Iran is more than 180‐m thick and includes thick units of shale, calcareous sandstone, fusulinid limestone, sandy limestone, and dolomite. The Zaladou and Tigh‐e‐Madanu formations of this group were dated as Gzhelian to Sakmarian. A review of the smaller foraminifers of the Zaladou section is presented. Five foraminiferal subzones grouped in three biozones are proposed in this work: The first assemblage zone (I) is Gzhelian; the second zone (II) corresponds to the Gzhelian–Asselian boundary interval, and the third biozone (III) is Asselian in age. Biozone I is subdivided informally into two subzones: the Hemigordius spirilliniformis‐Bradyina cf. samarica subzone IA (probably early Gzhelian in age) and the Raphconilia modificata and Globivalvulina spp. subzone IB (middle to late Gzhelian); biozone II is the Nodosinelloides spp. zone; biozone III is subdivided informally into two subzones: IIIA with Pseudoacutella partoazari‐Bradyina lucida and IIIB with Planoendothyra persica n. sp.‐Rectogordius sp. The studied assemblages are correlated with those from the Carnic Alps (Austria–Italy), East European Platform of Russia, the Urals (Russia), Darvas (Uzbekistan), the northern and central Pamirs (Tajikistan), northern Iran (Alborz), northern Afghanistan, and other classical regions of the Tethyan realm. The genera Raphconilia and Planoendothyra are revised, and Planoendothyra persica n. sp. is described.