Geochemical zonation across a Neoproterozoic orogenic belt: Isotopic evidence from granitoids and metasedimentary rocks of the Jiangnan orogen, China (original) (raw)
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Precambrian Research, 2018
Neoproterozoic amalgamation and timing of collision between the Yangtze and Cathaysia sub-blocks along the Jiangnan Orogen in South China remain disputed. With a view to constrain the crustal evolution in this major orogen, here we presents new results from petrology, geochemistry, zircon U-Pb chronology and Lu-Hf isotopes, on a suite of meta-sedimentary rocks from the Shuangqiaoshan Group and tuffaceous rock from the Liantuo Formation in the Jiuling terrane of central Jiangnan Orogen. Magmatic zircon grains in meta-sedimentary and sedimentary samples from the bottom to top part of the lower and upper Shuangqiaoshan groups constraints the deposition during 863-820 Ma and 797-780 Ma, respectively. The unconformities were formed during 820-797 Ma, reflecting the final amalgamation of Yangtze with Cathaysia sub-blocks along the central Jiangnan Orogen. Our data also
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
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.
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.
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;
Precambrian Research, 2015
Middle Neoproterozoic sedimentary rocks are widespread in the South China Block, especially around the periphery of the Yangtze Block. They are separated into the Sibao and Danzhou groups (and their equivalents) by a "mid-Neoproterozoic angular unconformity" in the south margin of the Yangtze Block. This unconformity, previously interpreted as the evidence of continental collision between the Yangtze and Cathaysia blocks, is crucial for understanding the early-middle Neoproterozoic tectonic regime in the South China Block. We report integrated in situ U-Pb, Hf and O isotopes analyses of detrital zircon grains from sandstones across this unconformity, and use these data to decipher their sedimentary provenances and shed new light on the basin evolution and the tectonic significance of this mid-Neoproterozoic unconformity.
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.
Gondwana Research, 2011
This paper reports some new results from U-Pb geochronological, Hf isotopic and REE geochemical studies of detrital zircons in the Ordovician sandstones from South Jiangxi within Cathaysia. 426 groups of U-Pb age determinations define five major age populations: 2560-2380 Ma (a peak of 2460 Ma), 1930-1520 Ma (a peak of 1700 Ma), 1300-900 Ma (a major peak at 970 Ma and two subordinate peaks at 1250 Ma and 1130 Ma), 850-730 Ma (a prominent peak of 780 Ma) and 670-530 Ma (a major peak at 540 Ma and a subordinate peak at 650 Ma). We also report zircon U-Pb concordia age of 3.96 Ga, which is the oldest age so far obtained from Cathaysia. The age peak at 2460 Ma correlates with similar ages reported for Neoarchean global continental growth. The 1930-1520 Ma population broadly overlaps with the time of amalgamation and disruption of the Columbia supercontinent. The major age peak at 970 Ma and two secondary peaks at 1250 Ma and 1130 Ma reflect multiple tectonothermal events associated with the assembly of Rodinia. Similar ages are widely reported from the South China Craton (SCC). Our study reveals that the 850-730 Ma population is consistent with the breakup period of Rodinia, suggesting that the SCC within Rodinia began to break up since 850 Ma. Geologically, the evidence for this breakup event is widespread and presented by Neoproterozoic granites, bimodal igneous rocks, basic dyke swarms and formation of continental rift type basins. Our study also reveals a 670-530 Ma population that correlates well with the assembly of Gondwana during end Neoproterozoic. However, direct geological evidence for this event has not yet been found within the studied area. Furthermore, the Hf isotopic model age data suggest two major stages of crustal evolution within Cathaysia. The first is the event dated at 1.6-2.8 Ga and the second one at 3.5-3.9 Ga. The zircons show a large range of εHf(t) values from + 8.64 to − 30.54, suggesting that they have different origins with a similar age of crystallization. The fact that most detrital zircons show negative εHf(t) values suggests the ancient provenances of Cathaysia were dominated by reworked crustal materials.