U–Pb ages and Hf–O isotopes of zircons from Late Paleozoic mafic–ultramafic units in the southern Central Asian Orogenic Belt: Tectonic implications and evidence for an Early-Permian mantle plume (original) (raw)
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The Jiaodong Terrane of the Eastern Shandong Complex in the Eastern Block of the North China Craton (NCC) consists predominantly of Archean granitoid gneisses with minor supracrustal rock enclaves or lenses. This study presents new zircon LA-ICP-MS U–Pb and Lu–Hf isotopic data for these lithologies, which help to better understand the Archean crustal evolution of the Eastern Block of the NCC. Magmatic zircon U–Pb data reveal that zircons in the supracrustal rocks and granitoid gneisses were generated by multi-stage events at ~ 2.9 Ga, ~ 2.7 Ga and ~ 2.5 Ga. Metamorphic zircon U–Pb data obtained for these rocks show distinct metamorphic ages at ~ 2.50 and ~ 1.9–1.8 Ga, suggesting that the Jiaodong Terrane experienced a regional metamorphic event at the end of the Neoarchean and encountered reworking by a tectonothermal event that was associated with the formation of the Paleoproterozoic Jiao–Liao–Ji Belt. Magmatic zircons have variable εHf(t) values from − 5.5 to + 7.7 with model ages of 3.92–2.57 Ga, of which most εHf(t) values are positive with a predominant peak of model ages at 3.4–3.1 Ga and a subordinate peak at 2.8–2.7 Ga. These Hf features reveal major juvenile crustal growth stages with significant additions of older crustal materials at 3.4–3.1 Ga and 2.8–2.7 Ga, and a crustal reworking event with minor juvenile additions at ~ 2.5 Ga in the Jiaodong Terrane.
Precambrian Research, 2012
The Tarim Block is an important geologic unit in the reconstruction of the tectonic evolution of the Central Asian Orogenic Belt and the Precambrian Columbia and Rodinia supercontinents. In order to examine the evolution and crustal generation of the Tarim Block, we performed detrital zircon U-Pb dating and in situ Hf isotopic analysis of Devonian sandstones of the Baluntai area in Central Tianshan, which is part of the Tarim Block. Most analyzed zircon grains show oscillatory zoning and have Th/U ratios >0.4, suggesting that they were mainly derived from igneous rocks. A total of about 400 detrital zircon analyses yielded five age populations, namely, early Paleoproterozoic (peak at 2470 Ma), middle Paleoproterozoic (peak at 1858 Ma), early Mesoproterozoic (peak at 1541 Ma), early Neoproterozoic (peak at 952 Ma), and late Neoproterozoic (820-750 Ma). These peak ages are remarkably consistent with the polyphase tectonothermal events that occurred in the Tarim Block. The peak at 2470 Ma indicates the presence of late Neoarchean to early Paleoproterozoic magmatism in the Tarim Block. The two peaks at 1858 Ma and 952 Ma coincide with the two periods of assembly of the Columbia and Rodinia supercontinents. This further suggests that the Tarim Block was part of these two supercontinents. In fact, the age peak of 1541 Ma correlates with the breakup of Columbia, and the age range of 820-750 Ma is interpreted to represent the time of the breakup of Rodinia. The zircon Hf model ages suggest three major stages of crustal evolution at 1.0-1.4 Ga, 1.8-3.3 Ga, and 3.4-3.8 Ga. The zircons exhibit a huge range of ɛ Hf (t) values from −33 to +51, suggesting that they were derived from highly diverse protoliths. However, since most detrital zircons show negative ɛ Hf (t) values, the protoliths of the Baluntai sandstones of Central Tianshan probably comprise rocks of Archean to Proterozoic crust. Owing to the similar Precambrian basement, lithology and age spectra between Central Tianshan and Tarim, it is argued that Central Tianshan belonged to the Tarim Block in the Precambrian time. Furthermore, euhedral zircons with high Th/U ratios (>0.4) yielded a prominent peak of 447 Ma. This can be correlated with an early Paleozoic arc development in Central Tianshan.
Precambrian Research, 2008
The North China Craton is one of the few places in the world where >3.8 Ga crustal material exists, since zircons of this age have been found in the Baijiafen and Dongshan gneisses from Anshan in northeastern China. However, it has been questioned whether any 3.8 Ga rock exists in the area, since various younger zircons exist within single rock samples, and zircons with age of ∼3.8 Ga are few and can be interpreted as inherited in origin. A study of zircons using combined cathodoluminescence imaging and SHRIMP U-Pb dating indicates that the Baijiafen and Dongshan gneisses record several stages of granitic magmatism. The oldest magmatic event is recorded by a zircon with an age of 3887 ± 5 Ma, with a subsequent magmatic event at 3.8 Ga (3808 ± 24, 3798 ± 30, 3802 ± 11 and 3799 ± 6 Ma), confirming the existence of 3.8 Ga materials in the area. The next magmatic event took place at ∼3.6-3.7 Ga. However, all samples contain younger zircons with ages of 3.1-3.3 Ga, although they contain a few zircon grains with ages of ∼3.6-3.8 Ga. The 3.1-3.3 Ga zircons show typical igneous oscillatory zoning and do not show any evidence that were produced by metamorphism, indicating that these samples were emplaced at 3.3 and 3.1 Ga, respectively and the zircons with older ages are interpreted as inherited in origin. The exposure of 3.8 Ga rock is therefore much smaller than previously thought. In situ zircon Hf isotopic analyses indicate that these granitic rocks were derived from juvenile crust with age peaks of crustal growth at ∼3.4, 3.6 and 3.9 Ga, there is no evidence for existence of crustal material older than 4.0 Ga.
Journal of Earth Science, 2019
The Sulu Orogen preserves the Neoproterozoic tectonic-magmatic events, corresponding to the breaking up of the Rodinia supercontinent. The ages and petrogenesis of meta-igneous rocks in the Liansandao area in the northern Sulu Orogen are not well-constrained. This study reports zircon U-Pb ages and Hf isotopes of these rocks from the Liansandao area. Three meta-igneous rock samples give similar weighted mean 206 Pb/ 238 U ages of 744±11, 767±12, and 762±15 Ma, respectively, indicating the Neoprotero-zoic crystallization ages. These rocks formed coevally with the Wulian and Yangkou intrusions that located along the Yantai-Qingdao-Wulian fault zone. The Neoproterozoic ages indicate that the meta-igneous rocks from the Liansandao area have affinity to the Yangtze Block. The three samples have ε Hf (t) values of-7.2-10.5,-6.0-17.5, and-6.8-12.0, respectively. These negative ε Hf (t) values indicate a primarily crustal source. However, the widely various ε Hf (t) values that are higher than the continental crust, suggesting magma mixing between mantle-derived materials and the continental crust or source heterogeneity. Combined with the Hf model ages and geochemical characteristics, the monzodiorite (sample LSD-2) is most likely to be mantle-derived magma then interacted with ancient continental crust, and the granitic pro-tolith (samples LSD-1 and LSD-3) in the Liansandao area might derive from the re-melting of a Paleopro-terozoic continental crust at ~750 Ma, resulting from the upwelling and underplating of mantle-derived magma formed in an extensional setting due to the break-up of the Rodinia supercontinent.
Geological Magazine, 2014
Cretaceous granites are widespread in the North Dabie orogen, Central China, but their emplacement sequence and mechanism are poorly known. The Tiantangzhai Complex in the North Dabie Complex is the largest Cretaceous granitic suite consisting of six individual intrusions. In this study, zircon U-Pb ages are used to constrain the crystallization and protolith ages of these intrusions. The Shigujian granite is a syn-tectonic intrusion with an age of 141 Ma. This granite was emplaced under a compressional regime. Oscillatory rims of zircons have yielded two peaks at 137 ± 1 Ma and 125 ± 1 Ma. The 137 ± 1 Ma peak represents the beginning of orogenic extension and tectonic collapse, whereas the 125 ± 1 Ma peak represents widespread granitic magmatism. Zircon cores have yielded concordant ages between 812 and 804 Ma, which indicate a crystallization age for the protolith. The Tiantangzhai granites show relatively high Sr contents and high La/Yb and Sr/Y ratios. The Shigujian granite has positive Eu anomalies resulting from partial melting of a plagioclaserich source in an over-thickened crust. Correspondingly, in situ Lu-Hf analyses from zircons yield high negative ε Hf (t) values from −24.8 to −26.6, with two-stage Hf model ages from 2748 ± 34 to 2864 ± 40 Ma, suggesting that the magmas were dominantly derived from partial melting of middle to lower crustal rocks. The Dabie orogen underwent pervasive NW-SE extension at the beginning of the early Cretaceous associated with subduction of the Palaeo-Pacific plate beneath eastern China.
Journal of Asian Earth Sciences, 2010
a b s t r a c t 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 show e Hf (t) ranging from À30.3 to À1.3, suggesting a provenance from the Inner Mongolia Paleo-uplift (245-376 Ma, e Hf (t) = À18.9 to À1.7). A bi-modal distribution of ages and e 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 e Hf (t) values (À10.9 to 7.7). A hybrid source is thus inferred for the Ordos sediments; the Northern Qinling Orogen (428-478 Ma, e Hf (t) = À10.9-7.7) 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.
Precambrian Research, 2012
We report here the first integrated U-Pb dating and hafnium-oxygen isotope analyses of detrital zircon grains from sedimentary and volcaniclastic rocks in the Neoproterozoic Nanhua Basin, central South China. These data provide vital information on the depositional cycles of the Cryogenian strata and their bearings on the breakup of the Rodinia supercontinent, and the characteristics of Precambrian crustal growth in the South China Block and neighboring continents. Zircon SIMS U-Pb ages indicate that the Qingshuijiang Formation was deposited at 772 ± 5 Ma and the Fanzhao Formation was deposited between 800 and 770 Ma. The onset time of the Sturtian (Jiangkou) glaciation is constrained to be no older than 730 Ma. Together with compilations of all available high precision zircon U-Pb data on tuff beds in the Nanhua Basin, our work demonstrates that the Cryogenian deposition in South China began at about 850 Ma and had three depositional cycles at ca. 850-820 Ma, 820-720 Ma and 720-635 Ma. Hf isotope analyses and U-Pb dating, combined with existing O isotope analyses, of detrital zircon have revealed three striking features for grains with 1.0-0.7 Ga ages: (1) about 22% of total analysed grains have Hf isotope compositions that plot between the new continental crust and depleted mantle growth curves;
Gondwana Research, 2011
Late Paleozoic magmatic rocks (including basic dykes, basaltic andesite, rhyolite, keratophyre and syeniteporphyry with minor tuff) are widespread in the western margin of the East Junggar terrane. In-situ zircon U-Pb dating and Hf isotope analyses were carried out for these magmatic rocks from the Baijiangou and Zhangpenggou localities of East Junggar, integrating with geochemical data, to investigate their tectonic evolution as well as crustal accretionary process of this region in the Late Paleozoic. Inherited zircons from basic dykes range in age from 435 Ma to 300 Ma. The Zhangpenggou rhyolite and keratophyre have typical arc-like geochemical signatures and were formed in the Early Carboniferous (332 Ma and 336 Ma, respectively), suggesting they are products of subduction-related magmatism. The Baijiangou rhyolites were formed in the Late Carboniferous (315 Ma and 323 Ma) and their formation ages are similar to those of the syenite-porphyries (307 Ma and 312 Ma). The Hf model ages and the formation ages of zircons from these magmatic rocks are alike, with positive ε Hf (t) values vary from + 0.7 to + 16.6, implying that voluminous growth of juvenile crust happened in the East Junggar terrane during the Late Paleozoic. The absence of Precambrian inherited zircons in basic dykes indicates the lack of Precambrian basement beneath the East Junggar terrane. Taking geochronological studies on regional ophiolites into account, the East Junggar terrane is considered as a Devonian-Carboniferous oceanic island arc which has been continuously accreted to the southern active margin of the Siberian Craton since the Early Carboniferous.