Coupled Precambrian crustal evolution and supercontinent cycles: Insights from in-situ U-Pb, O- and Hf-isotopes in detrital zircon, NW india
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Oxygen and hafnium isotopic compositions, measured *in-situ* on U-Pb dated zircon grains from Paleoproterozoic to early Cambrian successions in NW India have implication for regional crustal evolution and supercontinent cycles. Analyzed zircon grains have high Th/U ratios (\>0.1), display strongly fractionated REE patterns, metamorphic overprint, and evidence of interaction with low temperature fluids. Their positive Ce and negative Eu anomalies preclude any Pb loss after zircon crystallization. The U-Pb age spectra (concordance between 90 and 110%) indicate prominent peaks at 2.6 to 2.4 Ga, 1.9 to 1.7 Ga, 1.6 to 1.5 Ga, 1.2 to 1.0 Ga and 0.9 to 0.7 Ga that coincide with the assembly and breakup of Precambrian supercontinents. The Hf model ages of zircon grains with mantle like δ^18^O values reveal continuous generation of the continental crust from 3.3 to 1.3 Ga in NW India with major episodes during 3.3 to 2.7 Ga and 1.7 to 1.5 Ga. These ages correspond well with the 3.4 to 2.9 Ga and 2.2 to 1.6 Ga age peaks recognized in detrital zircon populations from eastern Australia and North America, underlining the significance of these time brackets in continental crust generation during the global continental evolution. Magmatic episodes at 1.9 to 1.7, 1.2 to 1.0 and 0.9 to 0.7 Ga are considered to represent crustal reworking rather than juvenile addition and the former two phases correspond with periods of supercontinent assembly. However, a progressive depletion in ^18^O from supra-mantle to mantle values in the 1.7 to 1.5 Ga zircons, coupled with their mantle-like ε~Hf(t)~ values, indicate at least some juvenile input. Moreover, the 1344 to 1120 Ma zircon grains with low δ^18^O (3.7--1.5‰) but high ε~Hf(t)~ (+8.1− +1.9 with one exception of −2.5) values signify rapid reworking of mantle derived materials in an extensional setting during this period. The 0.9 to 0.7 Ga peak, corresponding to the fragmentation of Rodinia supercontinent, documents crustal reworking that is in contradiction to the generally considered juvenile crustal addition in extensional setting associated with supercontinent breakup.Keywords:
Supercontinent
Rodinia
Rodinia
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The middle Mesoproterozoic is a crucial time period for understanding the Precambrian tectonic evolutionary history of the northern Yangtze Block and its relationship with the supercontinent Columbia. The Dagushi Group (Gp) is one of the Mesoproterozoic strata rarely found at the northern margin of the Yangtze Block. U–Pb geochronology and Lu–Hf isotopic analyses of detrital zircons were analyzed for three metamorphic quartz sandstone samples collected from the Luohanling and Dangpuling formations of the Dagushi Gp. These metasandstones yielded major zircon populations at ~2.65 Ga and ~1.60 Ga, respectively. The ~1.60 Ga ages first discovered yield a narrow range of ɛHf(t) values from −1.8 to +1.8, which lie above the old crust evolutionary line of the Yangtze Block, suggesting the addition of mantle material. Trace element data indicate that ~1.60 Ga detrital zircons share a basic provenance, whereby they have low Hf/Th and high Nb/Yb ratios. Zircon discrimination diagrams suggest that the ~1.60 Ga detrital zircon source rocks formed in an intra-plate rifting environment. Dagushi Gp provenance studies indicate that the ~1.60 Ga detrital zircon was most likely sourced from the interior Yangtze Block. Thus, we suggest that the late Paleoproterozoic to early Mesoproterozoic continental break-up occurred at the northern margin of the Yangtze Block.
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Rodinia
Passive margin
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Continental Margin
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The Kuluketage block is the best area for Precambrian geology in north western China, because it contains the most complete Precambrian lithology units. Thus, the study of this ancient basement can improve the understanding of the Precambrian evolution of the Tarim Craton. In this study, we report LA-ICPMS zircon U-Pb ages and Hf isotopes of detrital zircons from a magnetite quartzite from the Shayiti Formation of the Xingditage Group. The 65 zircon ages and Hf isotopes obtained are used not only to constrain the maximum depositional ages of the Shayiti Formation but also to obtain the information about the evolution of regional tectonic-magmatic activities in the Paleoproterozoic of the Kuluketage block. According to the youngest concord 207Pb/206Pb zircon age of 1851 ± 36 Ma in magnetite quartzites and the 1.47 Ga of the diabase sills which intrude into the Shayiti Formation, the most probable depositional age of the Shayiti Formation is between 1.47 Ga and 1.85 Ga. The detrital zircon dates are mainly clustered at 1806 Ma to 1889 Ma, 1898 Ma to 1981 Ma, and 1988 Ma to 2054 Ma, with the most prominent age peak appearing at around 1900 Ma and the subordinate peak age at around 1960 Ma. The magmatic features of Cathodoluminescence (CL) images indicate that two large magmatic tectonic-magmatic activities occurred in this district. The metamorphic rims of magmatic zircons and some baddeleyites also show regional metamorphism in the Paleoproterozoic, which may be related to the amalgamation of the Columbia supercontinent. We obtained two sets of concordant U-Pb ages older than 2.5 Ga, and several sets of two-stage Hf model ages older than 3.0 Ga. Combined with previous data in the literature, we suggest that Meso- to Neo-Archean basement rocks existed in the Kuluketage block, but were strongly reformed by tectonics, magmatism, and metamorphism in the Paleoproterozoic.
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Supercontinent
Laurentia
Protolith
Rodinia
Geochronology
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Baltica
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Rodinia
Supercontinent
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Rodinia
Supercontinent
Felsic
Continental arc
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Abstract The Mesoproterozoic Baoban Group is the oldest basement in Hainan Island and has played an important role in Columbia (Nuna) supercontinent reconstructions. The Mesoproterozoic granitic intrusions in the Baoban Group are the most widely‐exposed Precambrian magmatic rocks and are the key to understanding the tectonic settings of Hainan Island and its relationship with the South China Block and the Columbia supercontinent. New LA‐ICP‐MS zircon U‐Pb dating on three mylonitic granite samples from the Tuwaishan and Baoban areas yield ages ranging from 1447 Ma to 1437 Ma, representing the absolute timing of the emplacement of the granitic intrusions. Combined with previously published geochronological data for rocks from the Baoban Group and regional mafic intrusions, it is concluded that the Baoban Group formed at 1460–1430 Ma, coeval with the emplacement of the granitic and mafic intrusions. New in‐situ zircon Lu‐Hf isotope analyses for the three mylonitic granite samples yielded positive ∊ Hf ( t ) values, ranging from +0.49 to +8.27, with model ages ( ) ranging from 2181 Ma to 1687 Ma, suggesting that the granitic intrusions originated from a mixed source of Paleoproterozoic crust with juvenile crust. New zircon trace element data show characteristics of high Th/U values of 0.24–1.50, steep slopes from LREE to HREE and negative Pr, Eu anomalies with positive Ce, Sm anomalies, representing typical magmatic zircons formed in continental crust. Compared with available magmatic and detrital zircon ages from Precambrian rocks in the Cathaysia Block, Yangtze Block and western Laurentia, it is inferred that Hainan Island was separated from both the Cathaysia Block and the Yangtze Block, instead being connected with western Laurentia in the Columbia supercontinent. Considering the decreasing tendency of basin deposition time along the western margin of Laurentia, it is proposed that Hainan Island was located to the north or northwest of the Belt‐Purcell Supergroup, along the western margin of Laurentia, during the breakup of the Columbia supercontinent.
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Abstract The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang–Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U–Pb chronology, and Hf isotope approaches. We obtained the following conclusions: (1) Yaganbuyang granitoids mainly consist of two‐mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc–alkaline or high‐K calc–alkaline granite types. Zircon U–Pb data yielded ages of 939±7.1 Ma for granodiorite and ∼954 Ma for granitoids, respectively. (2) The ε Hf ( t ) values of two–mica granite and granodiorite are in the range of –3.93 to +5.30 and –8.64 to +5.19, respectively. The Hf model ages ( T DM2 ) of two‐mica granite and granodiorite range from 1.59–.05 Ga and 1.62–2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenile crust. (3) Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic.
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Rodinia
Petrogenesis
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Abstract Detrital zircons are frequently used for crustal evolutionary studies as they sample vast regions of the continental crust. In the present study, we utilise newly compiled U-Pb detrital zircon data from the Indian subcontinent as well as a compilation of previously reported global data along with Hf isotopes of modern and ancient sediments in order to understand crustal evolution in the Indian subcontinent. The detrital zircon U-Pb age data from the Indian subcontinent show peaks (at 2400–2700, 1600–1900, 850–1200, and 450–550 Ma) that correlate with the formation of major known supercontinents. In addition, two other peaks at 3200–3400 Ma and <100 Ma do not correspond to periods of supercontinent formation. The former peak may represent uneven geographic sample density due to enhanced erosion and exhumation of Archean sources. The distinctly younger (<100 Ma) detrital zircon age peak may represent zircon preservation due to the Himalayan orogeny. The zircon Hf model ages from the Indian subcontinent suggest that the Precambrian crust was the major source of continental crust with younger ages. The conspicuous shift to positive εHf (t) at ca. 3600 Ma from detrital zircons of the Indian subcontinent may underscore a change in geodynamic processes, while the highly negative values post ~3200 Ma may be associated with the crustal reworking. A wavelet analysis of detrital zircons from the Indian and global databases reveals a prominent cyclicity of ~800 Myr and ∼350 Myr plausibly representing the supercontinent cycle and its half cycle. An incongruence in power between global and Indian εHf (t) could be due to the local subcontinental geologic processes during the Paleo- to Mesoarchean.
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Hadean
Rodinia
Indian subcontinent
Orogeny
Stromatolite
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