Paleo-Asian Oceanic Plate Research Articles

U-Pb geochronology of hydrothermal zircon from the Mesoproterozoic Gaoyuzhuang Formation on the northern margin of the North China Block and its geological implications

This paper reports LA-ICP-MS zircon U-Pb ages and REE compositions on detrital zircons (Type 1) and hydrothermal zircons (Type 2) from low-metasedimentary rocks in the Mesoproterozoic Gaoyuzhuang Formation, Pingquan area, Hebei Province that provide important constraints on the tectonic evolution along the northern margin of the North China Block. The detrital zircons are characterized by an oscillatory magmatic core, surrounded by a narrow structureless rim in CL images. They yield 207Pb/206Pb ages ranging from 1703 to 2543 Ma with two age peaks at 2473 and 1794 Ma, which is consistent with the Neoarchean and Paleoproterozoic tectono-thermal events recorded in the NCB basement, indicating that the source of the detritus was locally derived. By contrast, the hydrothermal ones are euhedral, sector zoning or internally structureless. They have relatively higher U and Th contents and Th/U ratios (U=139–2918 ppm, Th=35–1327 ppm, Th/U (average) =0.78 vs. U=15–1044 ppm, Th=8–341 ppm, Th/U (average) =0.57 for detrital zircons). Moreover, they are also enriched in REEs relative to detrital zircons and show a lower positive Ce anomaly (ΣREE = 659–2418 ppm vs. 231–611 ppm for detrital zircon; Ce/Ce*=2–13 vs. 33–174 for detrital zircons), similar to known hydrothermal zircons derived from many locations. These characteristics, combined with our field petrographic observations, indicate that the hydrothermal zircons possibly formed from a low temperature aqueous fluid. Twelve concordant or near-concordant analyses on hydrothermal zircons yield weighted mean 206Pb/238U ages of 325–327 Ma, which provide unambiguous evidence that the northern NCB underwent late Paleozoic low temperature hydrothermal modification. This timing of this hydrothermal event is compatible with that of the late Paleozoic magmatic and metamorphic-deformational events occurred on the northern margin of the NCB, it appears likely that the hydrothermal activity resulted from southward subduction of the Paleo-Asian Oceanic plate underneath the NCB during late Paleozoic.

Crust–mantle interaction in the central North China Craton during the Mesozoic: Evidence from zircon U–Pb chronology, Hf isotope and geochemistry of syenitic–monzonitic intrusions from Shanxi province

In-situ zircon U–Pb ages, Hf isotopic compositions and whole rock geochemical and Sr–Nd isotopic compositions are presented for three Mesozoic syenitic–monzonitic intrusions from Shanxi province, central North China Craton. Zircons from these intrusions all show core–rim structures in that the oscillatory rims recorded their intrusive ages, whereas the cores are interpreted as xenocrysts. The U–Pb age data reveal that the northernmost Dishuiyan monzonite was emplaced at 241Ma, while the Huyanshan and Erfengshan syenitic–monzonitic complexes were emplaced at 130Ma and 128–134Ma, respectively. The Dishuiyan monzonite is petrologically and geochemically uniform, it shows LREE enrichment and HFSE depletion and exhibits enriched Sr and Nd isotopic compositions with (87Sr/86Sr)i=0.7065 and εNd(t)=−8.3–−7.9. The zircon rims in the Dishuiyan monzonite show highly varied Hf isotopic compositions with εHf(t)=−27.8–−6.4. The varied Hf isotopic compositions and enriched Sr–Nd isotopic compositions, together with the ubiquitous xenocrystic zircon cores, suggest the Dishuiyan monzonite was produced by the mixing of melts from enriched lithospheric mantle and lower crust. The monzonite and syenite from the Huyanshan complexes exhibit different geochemical features. The εNd(t) values of syenite, which are higher than those of monzonite resemble the enriched lithospheric mantle, and together with the absence of zircon in the syenite, we propose that it was originated by partial melting of enriched lithospheric mantle. Monzonites from Huyanshan and Erfengshan share similar petrological and geochemical characteristics, being enriched in LREE and depleted in HFSE, and they show low εNd(t) values between −18.2 and −13.9. Similar to zircon rims in the Dishuiyan monzonite, those in the Huyanshan and Erfengshan monzonites also exhibit highly varied Hf isotopic compositions. The consistent ages between the xenocrystic zircons in monzonites and the lower crustal basement rocks of the NCC reveal a significant contribution from the lower crust in the formation of the monzonites. We propose that the monzonites from Huyanshan and Erfengshan were formed through hybridization of enriched lithospheric mantle-derived and lower crust-derived magmas. The Mesozoic syenitic–monzonitic intrusions in Shanxi province were produced under extensional environments which linked to different geodynamic settings. The Triassic Dishuiyan monzonite is a product of post-collisional lithospheric extension related to the subduction of the paleo-Asian oceanic plate under the NCC and subsequent slab break-off in the north, while the Cretaceous Huyanshan and Erfengshan syenite–monzonite was produced under a back-arc extensional regime linked to the subduction of the paleo-Pacific slab beneath East Asia.

Permian bimodal volcanism in the Zhangguangcai Range of eastern Heilongjiang Province, NE China: Zircon U–Pb–Hf isotopes and geochemical evidence

In this paper, we report on zircon U–Pb dating, Hf isotopes, major and trace elements, and Sr–Nd isotope data, with the aim of constraining the petrogenesis and regional tectonic evolution of late Paleozoic volcanic rocks in the Zhangguangcai Range of eastern Heilongjiang Province, NE China. Located in the eastern segment of the Central Asian Orogenic Belt (CAOB), between the Siberian and North China cratons, the late Paleozoic volcanic rocks in the Zhangguangcai Range are composed mainly of basalt, basaltic andesite, rhyolite, and minor dacite. The results of LA–ICP–MS zircon U–Pb dating for two basaltic rocks, three rhyolites, and one dacite indicate that they formed in the early Permian (ca. 292 Ma). The mafic rocks have SiO 2 = 50.13–53.80 wt.%, K 2O = 0.98–2.28 wt.%, Mg# = 0.51–0.71, Cr = 144–541 ppm, Ni = 74–260 ppm, ( 87Sr/ 86Sr) i = 0.7044, and ε Nd ( t) = +4.28, whereas the felsic rocks have SiO 2 = 69.12–77.98 wt.%, K 2O = 3.09–5.33 wt.%, Mg# = 0.17–0.36, ( 87Sr/ 86Sr) i = 0.7032, and ε Nd ( t) = +4.32. These data are typical of bimodal volcanism. The mafic volcanic rocks are characterized by a strong enrichment in large ion lithophile elements (LILEs) such as Rb, Ba, Sr, and Pb, depletion in high field-strength elements (HFSEs) such as Nb, Ta, and Ti, depletion in heavy rare-earth elements (HREEs), and weak negative Eu anomalies (Eu/Eu * = 0.88–0.94). On the other hand, the felsic rocks show a strong depletion in Nb, Ta, Sr, P, and Ti, enrichment in Th, U, and K, and relatively large negative Eu anomalies (Eu/Eu * = 0.28–0.95). Taken together, these data suggest that the mafic magma was derived from the partial melting of a depleted lithospheric mantle, modified by subducted slab-derived fluids, and that the felsic magma originated by partial melting of newly accreted crust. The early Permian bimodal volcanic rocks, together with the coeval A-type granites, indicate an extensional environment, similar to a back-arc basin. Such a setting was possibly related to subduction of the Paleo-Asian oceanic plate beneath the Jiamusi and Songnen–Zhangguangcai Range massifs.

U–Pb and Hf isotope analyses of detrital zircons from Late Paleozoic sediments: Insights into interactions of the North China Craton with surrounding plates

U–Pb dating and Hf isotope analyses were performed on detrital zircons from the Upper Permian sandstones in the Ordos and Jiyuan basins, with aims of defining the sediment provenance, and by inference, to determine the influence of the surrounding plates on the evolution of the North China Craton (NCC). Detrital Zircons from these two basins fall into three major groups based on their U–Pb ages: Phanerozoic, Paleoproterozoic, and Neoarchean. The youngest grain from every sample is only slightly younger than the real depositional age of strata. The Phanerozoic zircons from the Jiyuan basin (244–390 Ma) show ε Hf ( t) ranging from −30.3 to −1.3, suggesting a provenance from the Inner Mongolia Paleo-uplift (245–376 Ma, ε Hf ( t) = −18.9 to −1.7). A bi-modal distribution of ages and ε Hf ( t) is noted for detrital zircons from the Ordos basin; one resembles that of the Jiyuan basin, the other is characterized by Early Paleozoic ages and relatively high ε Hf ( t) values (−10.9 to 7.7). A hybrid source is thus inferred for the Ordos sediments; the Northern Qinling Orogen (428–478 Ma, ε Hf ( t) = −10.9–7.7) must have served as a source in addition to the Inner Mongolia Paleo-uplift source. This interpretation is consistent with the fact that the Northern Qinling Orogen was an active margin during the Early Paleozoic and suggests that the western part of the Northern Qinling Orogen was elevated relative to the center of the craton during the Late Paleozoic. It is likely that the Early Paleozoic arc-trench in the northern part of the Dabie Orogen was under-thrusted below the NCC due to the subduction of the Yangtze plate during the Triassic. The Inner Mongolia Paleo-uplift was strongly uplifted by subduction of the Paleo-Asian Ocean Plate underneath the northern NCC and functioned as a sediment source for the inner craton during the Late Paleozoic. These results reveal a heterogeneous pattern of destruction of the North China Craton, with its northern margin starting to be activated no later than Late Paleozoic.

Late Paleozoic to Early Mesozoic mafic–ultramafic complexes from the northern North China Block: Constraints on the composition and evolution of the lithospheric mantle

The Late Paleozoic to Early Mesozoic mafic–ultramafic complexes from the northern North China Block (NCB) are used to constrain the isotopic composition and evolution of mantle reservoirs during different tectonic stages prior to the initiation of lithosphere destruction in the Late Mesozoic. Zircon U–Pb ages show that emplacement of the mafic–ultramafic complexes occurred in at least three stages: Middle Devonian (ca. 395 Ma), Late Carboniferous–Early Permian (308–276 Ma) and Triassic (250–220 Ma). Most of the Middle Devonian complexes display low initial 87Sr/ 86Sr ratios of 0.70467–0.70492, weak to moderate negative ε Nd( t) values from − 6.3 to − 1.5 and weakly negative to weakly positive zircon ε Hf( t) values from − 11.5 to 5.5, indicating that the parent magma was derived from slightly enriched lithospheric mantle. The Late Carboniferous–Early Permian complexes are characterized by low initial 87Sr/ 86Sr ratios of 0.70521–0.70604, significant negative ε Nd( t) values from − 14.1 to − 9.3 and zircon ε Hf( t) values from − 17.0 to − 10.5, and were probably derived from metasomatized lithospheric mantle. The Early Triassic complexes exhibit initial 87Sr/ 86Sr ratios of 0.70656–0.70825 and significant negative ε Nd( t) values from − 17.1 to − 8.2, indicating their derivation from enriched lithospheric mantle. However, the Late Triassic mafic–ultramafic complexes display weakly negative to weakly positive ε Nd( t) values of − 4.4 to 0.5 and zircon ε Hf( t) values from − 2.9 to 1.7, indicating that magma sources likely resulted from mixing of depleted asthenospheric mantle and enriched lithospheric mantle. Zircon ages, geochemistry and Sr–Nd–Hf isotopic studies suggest that the lithospheric mantle beneath the northern NCB had a slightly enriched signature during the Middle Devonian, but it became significantly enriched during the Late Carboniferous to Early Permian due to metasomatism of lithospheric mantle during the southward subduction of the Paleo-Asian oceanic plate. After final closure of the Paleo-Asian Ocean and amalgamation of the Mongolian arc terranes with the northern NCB in the latest Permian to earliest Triassic, enriched lithospheric mantle still existed beneath the northern NCB during the Early Triassic. However, in the Late Triassic involvement of asthenospheric mantle became significant, owing to strong upwelling of asthenospheric mantle and post-collisional lithospheric delamination in the Early–Late Triassic. These results suggest that the cratonic lithospheric mantle beneath the northern NCB underwent multiple stages of modification prior to its destruction and thinning. Initiation of lithospheric destruction and thinning in the northern NCB likely occurred during the Early–Late Triassic, which is much earlier than in other parts of the NCB, where it occurred in the Late Mesozoic. It appears likely that lithospheric destruction and thinning of the NCB initially started at the northern and eastern margins of the craton as a result of post-collisional lithospheric delamination, and then spread to the interior of the craton.

Contrasting Late Carboniferous and Late Permian-Middle Triassic intrusive suites from the northern margin of the North China craton: Geochronology, petrogenesis, and tectonic implications

Two contrasting intrusive suites have been identified from the northern margin of the North China craton: a Late Carboniferous dioritegranodiorite suite mainly made up of quartz diorite, diorite, granodiorite, tonalite, and hornblende gabbro, and a Late Permian–Middle Triassic suite of granitoid intrusions consisting of monzogranite, syenogranite, and quartz monzonite. Plutons from the Late Carboniferous suite exhibit variable SiO2 contents and calc-alkaline or high-K calc-alkaline, metaluminous geochemical features. Most have low negative whole-rock ϵNd(T) values (where T is the crystallization age) of −17.1 to −11.5 and zircon ϵHf(T) values of −38.3 to −11.2, indicating that they were derived mainly from anatectic melting of the ancient lower crust with some involvement of mantle materials. However, an older pluton in the suite exhibits higher ϵNd(T) values of −11.5 to −9.9, Nd model ages of 1.82–1.64 Ga, lower initial 87Sr/86Sr ratios of 0.7046–0.7048, and it contains some zircon grains that are characterized by high negative to positive zircon ϵHf(T) values of −8.7 to 1.2, indicating strong involvement of juvenile materials derived from the lithospheric mantle. The Late Carboniferous plutons are interpreted as subduction-related and to have been emplaced in an Andean-style continental-margin arc during the southward subduction of the paleo–Asian oceanic plate beneath the North China craton. Rocks from the Late Permian–Middle Triassic intrusive suite display geochemical signatures ranging from highly fractionated I-type to A-type. They exhibit higher zircon ϵHf(T) values of −14.9 to −6.7, whole-rock ϵNd(T) values of −10.6 to −8.8, and younger Hf and Nd model ages than most of the Late Carboniferous plutons, indicating that they could have been produced by extreme fractional crystallization of hybrid magmas resulted from mixing of coeval mantle- and crust-derived melts. They are interpreted as postcollisional/postorogenic granitoids linked to lithospheric extension and asthenosphere upwelling due to slab break-off and subsequent sinking after final collision and suturing of the Mongolian arc terranes with the North China craton. These two contrasting intrusive suites suggest that the final closure of the paleo–Asian Ocean and collision between the Mongolian arc terranes and the North China craton occurred during the Late Permian, and these events were followed by postcollisional/postorogenic extension, large-volume magmatism, and significant continental growth. No significant syncollisional crustal thickening, high-pressure metamorphism, or S-type granitoid magmatism occurred during the collision process.

Vendian Paleoasian Ocean: New Paleomagnetic Results from Daribi and Khantaishiri Ophiolites (Western Mongolia)

Following the breakup of Rodinia and the opening of the Paleo-Asian ocean the relative positions of geological units (now in Mongolia) remain uncertain, and in consequence relevant paleogeographic reconstructions are poorly construed. In this paper, we apply an integrated approach to the reconstruction of the Paleo-Asian ocean using preserved ophiolites and ocean plate stratigraphy (OPS) in the Mongolian Lake and Altay zones in western Mongolia, which surround the Precambrian Central Mongolian Microcontinent (CMM) in the center of Central Asia.The Lake Zone of Mongolia contains many sediments of Ocean Plate Stratigraphy (OPS) and their underlying basalt-dominated ophiolites, which occur in three main zones along the western margin of the Precambrian crystalline basement of the CMM. The ophiolites in all zones have similar isotopic ages of ca. 570 Ma. The sections of OPS, together with serpentinite mélanges and other volcanogenic-sedimentary assemblages, have been thrust in nappe sheets over the Zavkhan block of the CMM.In the Neoproterozoic microcontinents derived from Rodinia drifted towards Siberia, and a passive margin developed on the Zavkhan block on the eastern margin of the Paleo-Asian ocean. In mid-upper Neoproterozoic times the eastern side of the Paleo-Asian oceanic plate was thrust over the CMM, and in the early Cambrian the Khasagt and Tas Khairkhan ophiolites were obducted and a mid-ocean ridge (?) reached the CMM, preventing further obduction. In the Neoproterozoic the western margin of the Paleo-Asian ocean was subducted under the Rodinia-derived microcontinent and evolved into an active continental margin. In mid-Cambrian–early Ordovician times thick turbidites were deposited in the Altay. Marine sediments, which had accumulated in the Devonian to Carboniferous in the Paleo-Asian ocean are preserved in a remnant ocean in the Lake Zone. Locally in the Devonian, terrigenous – volcanogenic sequences were deposited in the Ulgey extensional superimposed basin, and later in Meso-Cenozoic time (?) some ophiolitic and OPS fragments (Tsagaan Nuur, Ulaankhus and Bodonch) were exposed along fault escarpments that were possibly re-activated during transpression related to the India-Eurasia collision.Our analysis of the Neoproterozoic–Middle Paleozoic tectonic development of western Mongolia leads to a new holistic model for the evolution of the western Altaids, according to which the ophiolites and OPS formed in the Mongolian Lake and Altay zones between two microcontinents within a new tectonic framework of the western Altaids.