Geochemistry and zircon U–Pb–Hf isotopes of the granitoids of Qianjinchang pluton in the Xi Ujimqi, Inner Mongolia: Implications for petrogenesis and geodynamic setting

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We present new zircon U–Pb ages, geochemical data on the Late Palaeozoic volcanic rocks of the Suji and Dahongshan formations, which are exposed in the Plate Marginal Orogenic Belt along the northern margin of the North China Craton. Our aim is to constrain the petrogenesis, tectonic setting of volcanic rocks, and to address the late stage tectonic evolution of the Paleo‐Asian Ocean. Lithologically, the Suji and Dahongshan formations present the main rock association with basaltic andesite, andesite, dacite, rhyolite, and tuff. New zircon U–Pb dating results suggest that the volcanic rocks formed during 280–261 Ma and 277–267 Ma, respectively. Geochemically, these volcanic rocks belong to the low‐K tholeiitic to high‐K calc‐alkaline series and are characterized by highly enriched light rare earth elements, K, Rb, Ba; depleted Nb, Ta, Ti; and highly negative Eu anomalies, very similar to that of the continental arc magmatism. These data, together with geological field investigations, suggest that the Early Permian volcanic rocks from Suji and Dahongshan formations were related to southward flat subduction of the Paleo‐Asian Ocean beneath the northern margin of the North China Craton. Therefore, these volcanic rocks were interpreted as Andean‐style continental margin arc magmatism. This also indicates that the final collision between the North China Craton and the Siberian Craton did not occur until the Early Permian.

Section: Introductionmentioning

confidence: 99%

Geochronology, petrogenesis, and tectonic implications of the Early Permian volcanic rocks in the northern margin of the North China Craton

Zhou

et al. 2018

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“…Most of the dated zircon grains were transparent and colourless under the optical microscope. Some appeared dark rim, however, possibly due to high U contents (G. S. Wang et al, ). Zircon grains chosen for this study were euhedral, subhedral, and stubby prismatic in shape and ~30–200 μm long.…”

Section: Resultsmentioning

confidence: 99%

Geochronology and geochemistry of the Late Devonian–Early Carboniferous volcanic rocks in Aksu River area, western end of the East Kunlun Orogen

Liu

et al. 2019

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We present LA‐ICP‐MS zircon U–Pb dating, geochemical data for the Late Devonian–Early Carboniferous volcanic rocks in the Aksu River area, western end of the East Kunlun Orogen, with an aim to constrain the ages, petrogenesis, and tectonic setting of volcanic rocks and to comprehend the Late Devonian–Early Carboniferous tectonic evolution of the north branch of the Paleo‐Tethys Ocean. The Late Devonian–Early Carboniferous volcanic rocks are mostly composed of andesite and rhyolite. The new U–Pb ages show that the volcanic rocks formed in the Late Devonian–Early Carboniferous with ages of ca. 364–343 Ma. The volcanic rocks are classified as calc‐alkaline series. All of the volcanic rocks are characterized by enrichment in large‐ion lithophile elements (e.g., Rb, Ba, U, Sr, and K) and light rare earth elements and depletion in some high‐field‐strength elements (e.g., Nb, Ta, P, and Ti). The andesite samples have relatively high La/Nb (1.66–3.63) but low La/Ba (0.05–0.23) ratios, indicating the mantle source could be depleted mantle, and it had been metasomatized before partial melting. The rhyolite samples have low Nb/Ta and Zr/Hf ratios and Cr, Ni, and Co contents, which indicate that the material source was mainly crust derived and has experienced fractional crystallization process. Combined with our zircon U–Pb dating, geochemical data and geological field investigation, the tectonic setting of the Late Devonian–Early Carboniferous volcanic rocks is possibly related to the subduction process. Furthermore, the Paleo‐Tethys oceanic crust between the Bayan Har and East Kunlun‐Qaidam terrane northward subducted beneath the East Kunlun‐Qaidam terrane in the Late Devonian–Early Carboniferous, and the north branch of the Paleo‐Tethys Ocean between the Bayan Har and East Kunlun‐Qaidam terrane opening event should be earlier than this time (~364 Ma).

“…The pressure condition and the nature of the magma source can be roughly deduced by the geochemical composition (e.g., Inger & Harris, ; Wang et al, ). It is evident from Figure b that the compositions of the samples are comparable with melts produced at low pressures (<5 kb), suggesting that their precursor magma was derived from a shallow crustal level (Patiño Douce, ).…”

Section: Discussionmentioning

confidence: 99%

Petrogenesis and tectonic significance of the late Devonian‐early Carboniferous Jianxiashan pluton in the western domain of the eastern Kunlun Orogen, northern Tibetan Plateau

Jiao

Liu

et al. 2020

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The Eastern Kunlun arc activities were interrupted by repeated continent–continent collision followed by ocean opening along the older suture zones previous created in the Neoproterozoic. The first report of the later Devonian‐early Carboniferous arc magmatism has played a vital role in constraining the evolution of the Eastern Kunlun Orogen. We undertook zircon U–Pb dating, Hf isotopic compositions, whole‐rock geochemical and Nd–Sr isotopic analyses of the Jianxiashan pluton in the western end of the Eastern Kunlun Range. The pluton is composed of tonalite, granodiorite, and monzogranites. Our new data suggest that the pluton formed during the late Devonian‐early Carboniferous with ages of 339–358 Ma. These rocks have high A/CNK = 1.06–1.30, with 1.11–3.80% of normative corundum and are characterized by negative Eu anomalies and strong depletion in Ba, Nb, and Sr elements. The zircon Hf isotopic analyses give predominantly negative εHf(t) values (−9.25 to −2.80), whereas the values of inherited zircons are various from −25.84 to +8.80. The U–Pb age and Hf isotopic data of these inherited zircons are similar to the widespread meta‐sediments of Kuhai Group basement. The peraluminous granitoids have negative εNd(t) values (−7.1 to −5.1) and relatively high initial 87Sr/86Sr ratios (0.71009). These isotopic compositions suggest that the Kuhai Group could possibly be the source rocks of these peraluminous granitoids. We suggest the tonalite and granodiorite are I‐S transition type, whereas the monzogranite is highly fractionated S‐type formed in a back‐arc extensional tectonic setting, which was possibly related to the northern subduction of the Paleo‐Kunlun oceanic lithosphere.