Proto-Tethys magmatic evolution along northern Gondwana: Insights from Late Silurian–Middle Devonian A-type magmatism, East Kunlun Orogen, Northern Tibetan Plateau, China

The East Kunlun Orogen records the geological evolutions of the Neoproterozoic – Early Paleozoic Proto-Tethyan Ocean and Late Paleozoic–Mesozoic Paleo-Tethys Ocean along northern Gondwana. However, the late-stage evolution of the Proto-Tethyan Ocean and the configuration of peri-Gondwana microcontinents during the Silurian – Devonian is under debate. Here we report new geochronological and geochemical data of A-type granites from the western Wulonggou and the eastern Gouli areas in the East Kunlun Orogen to deepen our understanding of these problems. Zircon LA-ICP-MS UPb data reveal that the Danshuigou monzogranite and Shenshuitan syenogranite from the western Wulonggou area were emplaced simultaneously at 418 ± 3 Ma, while the Niantang syenogranite from the eastern Gouli area was emplaced at 403 ± 2 Ma. All these rocks display high-K calcic-alkalic to shoshonitic and metaluminous to slight peraluminous signatures, with relatively low CaO, Al2O3, MgO and Sr, and high FeOt/MgO, Ga/Al, Zr, and Nb, indicating their A-type affinity. Their moderate whole-rock εNd(t) (−5.3 to −0.6) and zircon εHf(t) (−6.3–6.4) are different from those of depleted mantle and old basement rocks, but similar to those of the Ordovician–Silurian granitoids in the East Kunlun Orogen. These chemical signatures, together with the anhydrous, low-pressure and high-temperature characteristics of the magmas, indicate that partial melting of the Ordovician–Silurian granitoids generated these A-type granites. Regionally, these A-type granites and previously reported A-type granites in the East Kunlun Orogen compose a Late Silurian – Middle Devonian A-type granite belt. This belt, together with the regionally coeval molasse formation and mafic-ultramafic rocks, indicate a post-collisional extensional regime for the East Kunlun Orogen during the Late Silurian – Middle Devonian. Given that extensive contemporaneous post-collision-related magmatic rocks have also been revealed in the neighboring West Kunlun, Altyn, Qilian and Qinling blocks/terranes, we contend that the Neoproterozoic – Early Paleozoic Proto-Tethyan Ocean that separated these blocks/terranes from Gondwana had closed by the Late Silurian – Middle Devonian, which]resulted in the re-welding of the above blocks/terranes to northern Gondwana or Gondwana-derived microcontinents

Multiple episodes of gold mineralization in the East Kunlun Orogen, western Central Orogenic Belt, China: Constraints from Re-Os sulfide geochronology

The Gouli goldfield (>110 t Au), located in the East Kunlun Orogen, western Central Orogenic Belt of China, is one of the most important goldfields in this area. In the last decade, a number of orogenic gold deposits (e.g., Guoluolongwa and Annage) have been shown to be hosted by rock units of different lithology and ages. Rhenium-osmium (Re-Os) geochronology of sulfides from gold-bearing veins was performed to define the chronologic relationships between gold mineralization present in the metamorphic rocks (Proterozoic and Silurian) of the East Kunlun Orogen. Sulfides (pyrite and chalcopyrite) from pyrite-quartz vein and polymetallic sulfides-quartz vein in the Guoluolongwa gold deposit yield Re-Os isochron dates of 374 ± 15 Ma (MSWD = 4.6; initial 187Os/188Os ratio (Osi) = 0.06 ± 0.22) and 354 ± 7 Ma (MSWD = 0.18; Osi = 0.13 ± 0.01), respectively. Similar ages are also revealed by the pyrite mineral separates from the Annage gold deposit (383 ± 8 Ma and 349 ± 6 Ma). These ages are interpreted to record the timings of the formation of the two vein types in these deposits, which are nominally separated by ~20 Ma. The new Re-Os ages presented here identify the first two Late Paleozoic (Devonian and Early Carboniferous) gold-mineralizing events in the East Kunlun Orogen and thus indicate at least two mineralization epochs in this area given ages (Late Triassic) of other gold systems and field observations. Considering the geological background and temporal distribution of gold deposits in adjacent areas (western Qinling and Qaidam-Qilian), we suggest that gold deposits in the western Central Orogenic Belt were formed in collisional/post-collisional settings being controlled by common tectonic-magmatic activities related to the evolution of both the Prototethys Ocean (Proterozoic – Paleozoic) and Paleotethys Ocean (Paleozoic – Early Cenozoic). Further, the initial Os (Osi) obtained from the Re-Os isochron suggest that for the two vein types in the Guoluolongwa gold deposit the Os and by inference the ore metal (Au) were derived from a mantle-like source (Osi values = ~0.12–0.13), which should be related to the contemporaneous mantle-like magmatism. In contrast, the pyrite-quartz vein in the Annage gold deposit possesses a significantly radiogenic Osi value (3.65 ± 0.51). Given the similar timing of mineralization between the Guoluolongwa and Annage deposits, it is considered that the ore metal likely has a similar origin, i.e., a mantle-like source, however at Annage the hydrothermal fluid interacted with the Proterozoic metamorphic host rocks and leached radiogenic Os that masks any evidence of a mantle-like source

Origin of Quartz Diorite and Mafic Enclaves in the Delong Gold-Copper Deposit and Evaluation of the Gold-Copper Mineralization Potential

The Triassic Paleo-Tethyan magmatic belt in the East Kunlun Orogen (EKO) hosts a small number of porphyry-skarn deposits. The controls of these deposits, especially those in the eastern EKO, are poorly understood. In this contribution, we report new petrological, zircon U-Th-Pb-Hf isotopic, whole-rock elemental with Sr-Nd isotopic, and mineral chemistry data of the Delong quartz diorite and mafic enclaves to constrain their petrogenesis and metal fertility. The quartz diorite and mafic enclaves are emplaced in the Late Triassic (ca. 234 Ma). They are medium-K, metaluminous, enriched in large-ion lithophile elements (e.g., Rb, Ba, Th) and light rare earth elements (e.g., La, Ce, Nd), and relatively depleted in high field strength elements (e.g., Nb, Ta, Ti, P) and heavy rare earth elements (e.g., Gd, Er, Tm, Yb). The quartz diorite show similar (87Sr/86Sr)i (0.712584~0.713172) and more depleted εNd(t) (−6.4~−5.7) and εHf(t) (−2.3~+2.6) to those of mafic enclaves ((87Sr/86Sr)i = 0.712463~0.713093; εNd(t) = −6.4~−6.0; εHf(t) = −9.4~−4.8). Geochemical compositions of zircon, amphibole, and biotite yield high water content (5.3 wt.%~6.9 wt.% and 6.1 wt.%~7.3 wt.% based on amphibole, respectively) and high redox state for both the quartz diorite and mafic enclaves. These data, together with petrography, indicate the Delong intrusion was formed by mingling of magmas from enriched mantle and lower continental crust with juvenile materials. The oxidized and water-rich features of these magmas denote they have potential for porphyry Cu (±Au ± Mo) deposits, as do some Triassic magmatic rocks in the eastern EKO that show similar geochemical and petrographic characteristics with the Delong intrusion

Generation and structural modification of the giant Kengdenongshe VMS-type Au-Ag-Pb-Zn polymetallic deposit in the East Kunlun Orogen, East Tethys: constraints from geology, fluid inclusions, noble gas and stable isotopes

The Kengdenongshe giant Au-Ag-Pb-Zn polymetallic deposit is located in the East Kunlun Orogen (EKO). It contains about 42.2 t of Au, 608.6 t of Ag and 1.05 Mt of Pb and Zn with an average grade of Au 2.31 g/t, Ag 19.29 g/t and Pb + Zn 3.49 wt% (Pb: 1.23 wt%, Zn: 2.26 wt%). The NWW-trending ore bodies are predominantly hosted in Late Permian to Triassic rhyolitic tuff, which formed during Late Permian back-arc extension to Triassic arc-continental collision. The ore bodies are subdivided into Pb-Zn rich ore bodies on the top with high grades of Pb and Zn and low grades of Au and Ag, and Au-Ag rich ore bodies below with high grades of Au and Ag and low grades of Pb and Zn. The Pb-Zn rich ore bodies occur as vein, stockwork, and in breccia, and comprise quartz, pyrite, galena, sphalerite, and small amounts of chalcopyrite. The Au-Ag rich ore bodies consist of auriferous barite-sulfide-oxide veins and contain barite, pyrite (early strawberry and oolitic pyrite and later eu- to subhedral pyrite), galena, sphalerite, chalcopyrite, tetrahedrite and covellite. Gold is present as electrum, kustelite and native gold and silver is present as polybasite, pearceite, kongsbergite, and as minor native silver in microfractures in sulfides. The hydrothermal alteration minerals include, from bottom to top, quartz + barite + calcite around the Au-Ag rich orebodies, quartz + chlorite + epidote around the Pb-Zn rich orebodies, and quartz + K-feldspar within the tuff. Fluid inclusions from both the Pb-Zn rich and the Au-Ag rich orebodies consist of two phases (V–L-type) fluid inclusions of which the vapor phase has a size of 10–40 vol%. Fluid inclusions microthermometry reveal homogenization temperatures of fluid inclusions in Pb-Zn rich and Au-Ag rich ore bodies of 128–230 °C and 110–320 °C, with corresponding salinities of 0.7–9.9 and 0.2–18.3 wt% NaCl equivalent, respectively. H-O-S-Pb stable isotope and He-Ar noble gas isotope data indicate a mixed magmatic water-seawater source for both the Pb-Zn and Au-Ag rich ore bodies, and an additional meteoric water component for the Au-Ag rich ore bodies. The Pb-Zn and Au-Ag rich ore bodies share the same sulfur and lead sources, i.e. sulfur is derived from crustal magma and seawater/marine sulfate, and the lead originated from a mixed magmatic-ancient crustal sedimentary source. Collectively, the regional geology, mineralogy, alteration, and geochemistry indicate that the Kengdenongshe Au-Ag-Pb-Zn polymetallic deposit can be characterized as a VMS-type (volcanic-associated massive sulfide) deposit. Formation of the ore-hosting rhyolite tuff and mineralization are associated with Late Permian to Triassic marine volcanic exhalation. Middle to Late Triassic basin closure and arc-continent collision modified the deposit and resulted in the location inversion of the Pb-Zn and Au-Ag rich orebodies

Multiple sources of the Early Mesozoic Gouli batholith, Eastern Kunlun Orogenic Belt, northern Tibetan Plateau: Linking continental crustal growth with oceanic subduction

Orogenic belts have been among the most important locations to investigate the growth of continental crust (CC). The Eastern Kunlun Orogenic Belt (EKOB), which contains widespread Permian–Triassic granitoids, is volumetrically comparable to the Cenozoic Gangdese magmatic belt in the Tibetan Plateau and is an ideal region to investigate the mechanism of the Paleozoic–Mesozoic CC growth in this region. The Gouli batholith at the eastern end of the EKOB consists of the synchronous Xiangride granodiorite, Asiha quartz diorite (ca. 242 Ma) and adamellite. The granodiorite and quartz diorite, both of which contain magmatic enclaves, show medium–high K, calc-alkalic and metaluminous signatures and have similar rare earth element and trace element patterns to those of bulk CC. Besides, the Xiangride granodiorite displays distinct adakitic signatures (average Sr/Y of 47). The Sr-Nd isotopic values for the different types of rocks are roughly similar ((87Sr/86Sr)i = 0.708167–0.713553, εNd(t) = − 6.8 to − 5.3), while Hf isotopes are distinguishable, with εHf(t)granodiorite = 0.3 to 5.1 and εHf(t)diorite = − 1.6 to 0.7. These geochemical and petrographic signatures suggest that the granodiorite originated from the partial melting of subducting oceanic crust and terrigenous sediments, and the quartz diorite and enclaves formed via the mixing of slab-derived magma and enriched mantle-derived melt. Further comprehensive analyses of the spatial and temporal distribution of regional magmatic rocks, metamorphism and sedimentary facies reveal that the Gouli batholith and most of the Permian–Triassic granitoids in the EKOB formed during the subduction of the Paleo-Tethys Ocean instead of subsequent syn-collision setting. Thus, we contend that the Permian–Triassic CC growth of the EKOB occurred in a slab subduction setting and that both oceanic slab and subcontinental mantle significantly contributed to this process

Multi-stage crustal melting from Late Permian back-arc extension through Middle Triassic continental collision to Late Triassic post-collisional extension in the East Kunlun Orogen

The East Kunlun Orogen is an important part of the East Tethys region and has received significant attention with regards to the evolution of the Tethys Ocean. This contribution presents geochronological,whole-rockmajor and trace element geochemical, and Sr-Nd-Hf isotopic data of magmatic rocks within the Kengdenongshe polymetallic deposit in the eastern part of the East Kunlun Orogen. Here, we report zircon U\\Pb ages of ca. 257 Ma and ca. 211 Ma for granite porphyry intrusions, and ca. 240Ma for the rhyolitic tuff. These rocks are characterized by high SiO₂, variable Al₂O₃ and K₂O, lowNa2O, MgO and CaO contents, and high A/CNK ratios,which is typical of S-type granitic rocks. They exhibit large-ion lithophile element enrichment, depletion of high field strength elements, have low (La/Yb)N ratios, and negative εNd anomalies. They also display variable (⁸⁷Sr/⁸⁶Sr)i ratios (0.709981 to 0.720907), negative εNd (t) values (−8.7 to −5.5), and a wide (enriched) zircon εHf (t) range (−10.1 to −0.8). The geochemical and isotope data indicate magma derivation through dehydration melting of heterogeneous crustal sources including clay-poor meta-sedimentary rocks and amphibolite, which are both parts of the East Kunlun Orogen basement. These results provide evidence for the evolution of the Paleo-Tethys Ocean in the East Kunlun Orogen including Late Permian (266–255 Ma) back-arc extension, Late Permian to Middle Triassic (255–240 Ma) subduction, Middle Triassic (240–225 Ma) continental collision, and Late Triassic (b 225 Ma) post-collisional extension. This study further suggests that the 257 Ma and 211 Ma granite porphyries are related to the asthenosphere upwelling in a back-arc basin and post-collision extensional setting, respectively. The 240 Ma rhyolitic tuff is linked to anatexis associated with crustal thickening during continental collision

Noble gases in pyrites from the Guocheng-Liaoshang gold belt in the Jiaodong province: evidence for a mantle source of gold

The recent mineral exploration programme (2009–2014) in the Jiaodong gold province identified the new Guocheng-Liaoshang gold metallogenic belt which contains reserves of 92 tonnes (t) Au. In the main deposits the ore is fault-hosted in massive sulfides that make up to 25 to 95 vol%. The He-Ar isotope compositions of ore-forming fluids from 20 pyrite samples from the five main deposits are reported here. 3He/4He range between 0.41 and 2.39 Ra, 40Ar/36Ar are 367 to 2112 and 40Ar⁎/4He are 0.40–3.78. The data require four gas sources; a dominant mantle-derived component plus sub-ordinate crustal radiogenic, meteoric and basin brine components. The mantle end-member has 3He/4He (3.32–4.00 Ra). This is lower than most estimates for sub-continental lithospheric mantle (SCLM: 6–7 Ra), implying that it was probably refertilized by subduction-related fluid metasomatism. This is consistent with He-Ar isotopes reported for SCLM xenoliths from basalts in the Shandong Province. Within the mineralisation province, the mine Au reserve is positively correlated with the proportion of mantle-derived He in the ore-forming fluids. This implies that the fluids, and by inference the gold, was largely derived from mantle melts during lithospheric extension. Given the conspicuous association of gold ore deposits with mantle-derived magma in the Jiaodong Peninsula, we envisage that our genetic model can be applied, to some extent, to evaluate the potential of some mineral exploration targets