Precambrian Research最新文献

{"title":"Decoding Calymmian juvenile mafic magmatism in the Ribeira Belt, Brazil: Evidence for a long-lived arc system along the margin of Columbia","authors":"Frederico M. Faleiros ,&nbsp;Bruno V. Ribeiro ,&nbsp;Anny J. Forero-Ortega ,&nbsp;Ginaldo A.C. Campanha ,&nbsp;Peter A. Cawood","doi":"10.1016/j.precamres.2024.107588","DOIUrl":"10.1016/j.precamres.2024.107588","url":null,"abstract":"<div><div>The combined São Francisco-Congo Craton, now preserved in South America and Africa, existed from 2050 Ma to 130 Ma, is an important Archean-Paleoproterozoic block for reconstructions of the Proterozoic supercontinents Columbia (Nuna) and Rodinia. Both counterparts contain Calymmian-Stenian rock assemblages along their western margins and as inliers in Neoproterozoic-Cambrian marginal belts. New U–Pb–Hf–Nd isotopic and geochemical data of Calymmian metamafic rocks from the southern Ribeira Belt (Brazil) are integrated with data from the Brasília, Dom Feliciano and Kaoko Belts (Brazil, Uruguay and Namibia) and Angola Shield (Angola and Namibia) to unravel the Mesoproterozoic evolution of the cratonic block. Metamafic rocks from South America present variable geochemical and Hf–Nd isotopic signatures, suggesting contrasting tectonic settings. Rocks with crystallization ages of 1570–1540 Ma and 1500–1450 Ma show signatures of juvenile magmas derived from supra-subduction zone metasomatized mantle sources. Rocks formed at 1310–1280 Ma are dominated by signatures of intracontinental mafic magmatism. The Angola Shield presents voluminous granitoid rocks with crustal and juvenile signatures emplaced within 1530–1360 Ma, recently inferred as related with a convergent margin setting. There are also records of regional high-grade metamorphism and deformation involving a prograde stage at 1530–1510 Ma, peak conditions of 950–1000 °C and 9–10 kbar at ca. 1490 Ma, and a late stage at ca. 1450 Ma, suggesting a protracted orogenic metamorphic event. In a regional context, the available data supports a long-lived convergent margin setting along the present-day western margin of the São Francisco-Congo Craton. In a global perspective, this belt requires an extensive and long-lived (120–210 million years) Calymmian-Stenian ocean subducting beneath an active margin comprising stages of oceanic island arc–back-arc environments between 1570–1450 Ma that evolved to a continental arc on the margin of Columbia between 1450 and 1360 Ma. Regional metamorphism and deformation at 1340–1320 Ma support the existence of a collisional event related with ocean closure, while metamafic rocks of 1310–1280 Ma record lithospheric extension in a continental rifting setting.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142552494","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleoproterozoic ultrahigh-temperature metamorphism and anatexis of the pelitic granulites in the Kongling terrane, South China","authors":"Shaoji Yang ,&nbsp;Yanru Song ,&nbsp;Haijin Xu ,&nbsp;Qingsen Han ,&nbsp;Songbai Peng","doi":"10.1016/j.precamres.2024.107591","DOIUrl":"10.1016/j.precamres.2024.107591","url":null,"abstract":"<div><div>Crustal anatexis and ultrahigh-temperature (UHT) metamorphism provide crucial insights into metamorphic evolution and tectonic process at the convergent plate margins. Pelitic granulites in the Kongling terrane record both Paleoproterozoic UHT metamorphism and anatexis, providing an ideal window to reveal the model of plate tectonic during early earth. The pelitic granulites from the Kongling terrane are mostly composed of the coarse-grained unfoliated granulite and the fine-grained foliated or migmatized granulite. The unfoliated granulite preserves a peak granulite-facies metamorphic mineral assemblage of coarse-grained garnet + sillimanite + plagioclase + K-feldspar + biotite + quartz + rutile. The foliated granulite, displaying banded structure of melanosome and leucosome, is composed of fine-grained garnet + biotite + plagioclase + quartz + rutile/ilmenite + felsic melt. The coarse-grained garnets have core-mantle-rim structures. The clean cores are rich in grossular contents and contain oriented needle-like rutile exsolution. Ti-in-garnet thermometer on the garnet cores reveals temperatures ranging from 837 to 1030 °C with a mean ± 1σ uncertainty of 943 ± 12 °C, which are consistent with ternary feldspar temperature (940 °C), suggesting a UHT granulite-facies metamorphism. The garnet ‘dirty’ mantles and rims are almandine-pyrope solutions with inclusions of felsic melt, biotite and ilmenite. Zircon grains have two groups: most of them are anatectic grains, and few of them exhibit granulite-facies core with anatectic rim. The granulite-facies zircons yield ∼2.05 Ga ²⁰⁷Pb/²⁰⁶Pb ages for peak UHT metamorphism, and the anatectic zircons give ∼2.0 Ga ²⁰⁷Pb/²⁰⁶Pb ages for anatexis. Ti-in-zircon thermometer on the anatectic zircons yields temperatures ranging from 595 to 828 °C (692 ± 4 °C), which are consistent with temperatures of the low-temperature perthite grains (670–740 °C, 705 ± 7 °C) but are lower than Ti-in-garnet temperatures of the peritectic garnets (820–916 °C, 855 ± 4 °C), suggesting a process from anatexis to melt crystallization. These results suggest that the pelitic granulites underwent crustal UHT metamorphism and subsequent anatexis during Paleoproterozoic. Together with the contemporaneous low-temperature and high-pressure metapelites from the Shuiyuesi mélange belt in the Kongling terrane, our study suggests the presence of a paired metamorphic belt at a convergent plate margin during the Paleoproterozoic orogeny.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142552493","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mesoproterozoic (∼1.4 Ga) magmatism in northern Alxa, China: Implications for tectonic affinity of microcontinents in the southern Central Asian Orogenic Belt","authors":"Xing-Jun Shi ,&nbsp;Tao Wang ,&nbsp;Heng Zhang ,&nbsp;Chen-Guang Zhang ,&nbsp;Jin-Li Pang ,&nbsp;Lei Zhang ,&nbsp;Jian-Jun Zhang","doi":"10.1016/j.precamres.2024.107611","DOIUrl":"10.1016/j.precamres.2024.107611","url":null,"abstract":"<div><div>The origin and paleogeographic reconstruction of Precambrian microcontinents in the Central Asian Orogenic Belt (CAOB) are crucial for understanding continental crustal evolution, mechanisms of accretionary orogeny, and assemblage and breakup of the supercontinent during the Earth’s early history. The existence and basement nature of the South Gobi microcontinent within the central segment of the southern CAOB remain controversial. This study represents the first work to unveil the presence of Mesoproterozoic (∼1.4 Ga) intrusive rocks in the Zhusileng-Hangwula tectonic zone that is the central segment of the southern CAOB, and is distributed along the border areas between China and Mongolia. It offers pivotal evidence for the existence of the South Gobi microcontinent.</div><div>Three alkali feldspar granite<del>s</del> samples collected from the Zhusileng-Hangwula tectonic zone yielded crystallization ages ranging from 1371 ± 17 Ma to 1420 ± 29 Ma, while detrital zircons from a two-mica quartz schist xenolith yielded similar ²⁰⁶Pb/²³⁸U ages clustered around ∼1.4 Ga. The ∼1.4 Ga zircons display depleted Hf isotopic signatures (εHf(t) = 3.2–6.0) and relatively young two-stage Hf model ages (1.9–1.7 Ga), suggesting rapid reworking of juvenile mantle-derived materials. These findings indicate that the Zhusileng-Hangwula tectonic zone constitutes a microcontinental fragment with Mesoproterozoic basement, rather than a Paleozoic accretionary complex as previously postulated. Combining the contemporaneous magmatism data from the microcontinents in the southern CAOB, the 1.48–1.32 Ga arc-related magmatism exhibits a coherent trend of geochemical evolution, potentially indicating a geodynamic transition from a convergent to an extensional environment. Moreover, the temporal, tectonic evolution, and petrological similarities imply a tectonic affinity between these microcontinents and Fennoscandia, and they may have originated from an accretionary belt along the edge of Nuna during the Mesoproterozoic.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142573170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Paleoproterozoic amphibolite to ultrahigh temperature granulite facies metamorphism of the Rangnim massif in the Northern Korean Peninsula and tectonic implications","authors":"Lei Zhao ,&nbsp;Rucheng Zhang ,&nbsp;Yi Zou ,&nbsp;Won Jong Choe ,&nbsp;JongHyok Yang ,&nbsp;JongNam Kim ,&nbsp;Yanbin Zhang ,&nbsp;Mingguo Zhai","doi":"10.1016/j.precamres.2024.107606","DOIUrl":"10.1016/j.precamres.2024.107606","url":null,"abstract":"<div><div>Three Paleoproterozoic orogenic/mobile belts were suggested for the North China Craton (NCC), which were further suggested to represent global networks of narrow plate boundaries and argue for the operation of plate tectonics during the Paleoproterozoic. However, recent studies raised serious challenges to such advocates in that the seemingly belt-like occurrences of the Paleoproterozoic high-grade terranes are related to Phanerozoic tectonic processes. The basement components and metamorphic features of the Rangnim Massif in North Korea can provide critical evidence for a thorough understanding of the tectonic implications of these high-grade terranes, because it was assumed to be an Archean microcontinent that accreted to the NCC during the Paleoproterozoic through one of the three orogenic bents. This massif was assumed to be linked to the NCC through the Jiao-Liao-Ji orogenic belt in the traditional tectonic models. In this paper, we present both new study results and a summarization of previously published data on the Rangnim Massif. The Paleoproterozoic metamorphic rocks collected from the Rangnim Massif show amphibolite to UHT granulite facies metamorphism at ∼ 1.90 Ga, with peak metamorphic conditions reaching up to 940 – 980 ℃ at 7 – 9 kbar. The Paleoproterozoic metamorphism, the widespread Paleoproterozoic sedimentary and magmatic rocks of this massif, are identical with those of the Paleoproterozoic “orogenic belts” of the NCC. Therefore, the Jiao-Liao-Ji “orogenic belt” is extendable to the Rangnim Massif, or even to the whole Korean Peninsula. The newly established spatial occurrences and the metamorphic features of these metamorphic rocks of the eastern NCC are different from those of plate margin orogenic belts. Therefore, the exact geological implications should be reconsidered and that these high-grade terranes might represent the NCC’s uplifted Paleoproterozoic lower crustal components.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142573168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Late Paleoproterozoic within-plate mafic magmatism in the western Yangtze Block, South China Craton: Implications for the initial break-up of the Columbia supercontinent","authors":"Luyu Huang ,&nbsp;Jing Zhao ,&nbsp;Youliang Chen ,&nbsp;Xiaoping Long ,&nbsp;Jingsi Zhang ,&nbsp;Qiaoping Guo","doi":"10.1016/j.precamres.2024.107609","DOIUrl":"10.1016/j.precamres.2024.107609","url":null,"abstract":"<div><div>The Paleoproterozoic was an important period for the tectonic-magmatism evolution of the Yangtze Block, which coincided with the assembly and break-up of the global Columbia (also known as Nuna) supercontinent. However, an essential issue, when the Yangtze Block initiated rifting from the supercontinent, remains controversial. This paper presents new zircon chronology, Lu-Hf isotopic data, and whole-rock geochemical analyses of the Bajiaojing and Xiaoqingshan meta-diabases in the western Yangtze Block to address this issue. The magmatic zircons from the Bajiaojing and Xiaoqingshan meta-diabases yielded U-Pb ages of 1675 ± 38 Ma and 1719 ± 10 Ma, representing an episode of mafic magmatism during the Late Paleoproterozoic. Moreover, the abundances and elemental ratios of high-field-strength elements (HFSEs, e.g., Y, Ta, Th, and Hf) in both meta-diabases are very similar to those of within-plate and mantle plume magmas. This implies that these Late Paleoproterozoic mafic rocks were likely derived from a mantle plume source in a continental within-plate extensional setting. Their magmatic source was relatively heterogeneous in isotopic and geochemical compositions, as inferred from significant differences in ε_Hf(t) values and certain HFSE ratios (e.g., Nb/Yb, Ta/Yb, Th/Yb, Nb/Y, and Zr/Y) among samples. Such source heterogeneity might be attributed to interactions between the mantle plume and the overlying lithosphere. Combined with published ε_Hf(t) values of detrital zircons and whole-rock ε_Nd(t) values of (meta-)magmatic rocks, we speculate that the Yangtze Block experienced a tectonic transition from plate convergence to continental extension at ∼ 1.7 Ga. This means that the block began to rift from the Columbia supercontinent as early as 1.7 Ga. The Yangtze Block then evolved progressively as an isolated fragment until it was amalgamated into the Rodinia supercontinent.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142573171","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Detrital zircon geochronology and whole-rock geochemistry of the 1.8–1.7 Ga Xiong’er volcanic-sedimentary succession in the southern North China craton and their implications for basin evolution","authors":"Fengbo Sun ,&nbsp;Yuting Wu ,&nbsp;Taiping Zhao ,&nbsp;Deshun Zheng ,&nbsp;Peng Peng","doi":"10.1016/j.precamres.2024.107608","DOIUrl":"10.1016/j.precamres.2024.107608","url":null,"abstract":"<div><div>The Xiong’er volcanic-sedimentary succession in the southern North China Craton (NCC) documents crucial data regarding the geological evolution of the supercontinent Columbia (Nuna). Previous researches largely focused on the volcanic rocks in the Xiong’er succession, while the paleo-tectonic significance of its sedimentary rocks has not been explored. LA-ICP-MS detrital zircon U-Pb dating and whole-rock geochemistry of the interlayered sedimentary units within the succession are conducted to ascertain the provenance and tectonic driver of the basin infill. New chronological constraint suggests the deposition of the succession persisted until ca. 1710 Ma, temporally aligned with the initial deposition of the overlying Ruyang Group. Normalized rare earth elements (REE) and classification diagrams indicate derivation predominantly from felsic sources with supplementary input from mafic sources. Detrital zircon U-Pb ages indicate a major 2.5 Ga provenance from the proximal latest Archean and Paleoproterozoic metamorphic complexes and a subordinate ca. 2.3 ∼ 1.8 Ga provenance from adjacent regions. Notably, an elevated ca. 1.8 ∼ 1.7 Ga detrital zircon peak in the uppermost section of the succession implies contributions from coeval granites and volcanogenic rocks. Integrating these observations with the stratigraphic progression, the Xiong’er succession is interpreted as a magma-rich <em>syn</em>-rift basin infill and we hypothesize the existence of a “breakup unconformity” separating the <em>syn</em>-rift Xiong’er Group from the overlying post-rift Ruyang Group.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142552495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sapphirine + quartz assemblage from the Irumide Belt, northern Malawi: Implications for Mesoproterozoic ultrahigh-temperature metamorphism related to Rodinia assembly","authors":"So Wakabayashi ,&nbsp;Kabang’u Grace Sakuwaha ,&nbsp;Toshiaki Tsunogae ,&nbsp;M. Santosh ,&nbsp;Mzee Wandembo Nyirongo","doi":"10.1016/j.precamres.2024.107607","DOIUrl":"10.1016/j.precamres.2024.107607","url":null,"abstract":"<div><div>The Irumide Belt <em>sensu lato</em> situated between the Bangweulu Block to the northwest and the Neoproterozoic Mozambique–Zambezi Belt to the southeast is a Mesoproterozoic orogenic belt that developed probably during the amalgamation of the supercontinent Rodinia. In this study, we present new petrological, geothermobarometric, and geochronological data of pelitic granulites and related rocks from the Jenda area in northern Malawi, and evaluate the timing and pressure–temperature (<em>P</em>–<em>T</em>) conditions of high-grade metamorphism. To the best of our knowledge, we are the first to report the occurrence of sapphirine + quartz association in pelitic granulite from the Irumide Belt <em>sl</em>. which provides a robust evidence of peak ultrahigh-temperature (UHT) metamorphism. The sapphirine occurs as poikiloblastic grains with rounded quartz inclusions in the absence of any retrograde minerals. The mineral phase equilibrium modeling constrains the peak UHT conditions of the pelitic granulites as 950–1000 °C and 7–8.5 kbar for sapphirine-bearing and ∼6 kbar and &gt; 950 °C for sapphirine-free samples. These conditions are consistent with the results of ternary-feldspar geothermometry (900–1000 °C at 8 kbar). From the stability of rutile, we estimate a prograde pressure of &gt;9 kbar, and the occurrence of retrograde cordierite and biotite suggests that the rocks went through <em>P</em>–<em>T</em> conditions of ∼6–7 kbar/∼775–825 °C, indicating a clockwise <em>P</em>–<em>T</em> path and defining high-pressure and UHT conditions. In-situ monazite Th–U–Pb_total geochronology of the sapphirine-bearing rock yielded a weighted-mean age of 1022 ± 10 Ma which is considered to mark the timing of peak metamorphism. Sapphirine-free granulites also gave consistent ages of 1049 ± 13 Ma and 1048 ± 10 Ma, which are also comparable with published ages. We thus infer that the Irumide Belt <em>sl</em>. underwent regional high-pressure to UHT metamorphism at ca. 1.05 to 1.02 Ga possibly related to the main collisional event of the Bangweulu Block with an unknown craton or magmatic arc during the assembly of Rodinia supercontinent.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578419","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Precambrian Earth: Co-evolution of life and geodynamics","authors":"Frances Westall ,&nbsp;Shuhai Xiao","doi":"10.1016/j.precamres.2024.107589","DOIUrl":"10.1016/j.precamres.2024.107589","url":null,"abstract":"<div><div>The Precambrian covers 80% of the history the Earth. In this timespan, the Earth developed from an anaerobic planet to the oxygenic planet dominated by Wilson-style plate tectonics that we know today. Concomitant with geological evolution, life emerged and evolved, gradually colonising all known aqueous habitats. Until the Palaeoarchaean, life was largely dominated by its geological environment. However, as of the Mesoarchaean, when there were major changes in geodynamics leading to continental erosion and runoff of essential nutrients, the effects of life started to impinge on the geological environment. The interaction of life and Earth was and is reciprocal, hence the term biogeodynamics. In this review, we trace the evolution of geology and life in parallel, thus highlighting the gradual buildup of the importance of life on terrestrial processes, and the importance of changes in the geological environment on the evolution of life. We do not attempt to make an exhaustive review of all the occurrences of life in the Precambrian but use selected examples to illustrate key events and changes. We conclude by addressing certain aspects of the evolution of life that require more in-depth study and show how the finding of extra-terrestrial life would advance our understanding of life on Earth.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142578418","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Widespread ca. 800 Ma granitoids in the southern Dabie Orogen: Petrogenesis and implications for Neoproterozoic accretion-type orogeny in the northern Yangtze Block","authors":"Chao Chen ,&nbsp;Zhenbing She ,&nbsp;Changqian Ma ,&nbsp;Jinling Yuan ,&nbsp;Lingyao Kong ,&nbsp;Di Wang ,&nbsp;Jiang Zhu ,&nbsp;Chuan Fan ,&nbsp;Pan Guo ,&nbsp;Hao Deng ,&nbsp;Roger Mason","doi":"10.1016/j.precamres.2024.107610","DOIUrl":"10.1016/j.precamres.2024.107610","url":null,"abstract":"<div><div>Large-scale Neoproterozoic granitoids occur widely in the Dabie Orogen of the northern Yangtze Block and provide significant clues to understanding the geological evolution of the Block within the Rodinia supercontinent. We present evidence for a prominent episode of granitoid intrusion at ca. 800 Ma in the southern Dabie Orogen (SDO), verified by new zircon LA-ICP-MS ages from four separate granitoid intrusions ranging from 807 Ma to 795 Ma in age. The granitoids are dominated by monzogranite and granodiorite with bulk-rock A/CNK and zircon <em>δ</em>¹⁸O values of 0.90–1.10 and 5.03–6.45‰, respectively, corresponding to I-type affinity. This is also supported by negative correlations of SiO₂ vs. P₂O₅ and Sr vs. P₂O<strong>₅</strong>, and positive correlations of SiO₂ vs. A/CNK, Rb vs. Y and Rb vs. Th. Low zircon ε_Hf(t) values (−15.03 to −3.84) and relatively old two-stage Hf model ages (mainly between 1900 and 2200 Ma) for these granitoids are consistent with primary derivation of magma from partial melting of Paleoproterozoic metabasites. Relatively low Ga/Al ratios, Zr contents, and zircon saturation temperatures and consistently negative zircon ε_Hf(t) and bulk-rock ε_Nd(t) values are distinct from those of 780–720 Ma A-type granites in the Dabie Orogen that formed in a rift setting. We propose that the ca. 800 Ma granitoids in the SDO were products of variable degrees of partial melting of ancient mafic crust, promoted by heating of the upwelled asthenosphere due to oceanic slab breakoff in an accretion-type orogeny. Our observations suggest that the formation of the unified Yangtze Block was achieved by diachronous assembly of multiple micro-blocks during the Neoproterozoic, consistent with a peripheral location of the Yangtze Block in the Rodinia supercontinent.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142573169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Syn-rift volcanism (ca. 670 Ma) in the lower Windermere Supergroup, southern Canadian Cordillera: New constraints on the syn- to post-rift transition for northwestern Laurentia","authors":"Thomas Hadlari ,&nbsp;N.M. Rayner ,&nbsp;T.P. Poulton ,&nbsp;R.W.C. Arnott","doi":"10.1016/j.precamres.2024.107604","DOIUrl":"10.1016/j.precamres.2024.107604","url":null,"abstract":"<div><div>The southern Canadian Cordillera is considered the type area for the Windermere Supergroup, where it had long been assumed that the <em>syn</em>-rift basaltic lavas of the Irene Formation were co-genetic with the ca. 720 Ma Franklin LIP. Accordingly, the inferred age of the Irene volcanics is variously cited for either the breakup of Rodinia or for the base of Cryogenian strata in the southern Canadian Cordillera, and yet they have not been directly dated until now. Reported here are geochronological data from a volcanic sample of the Irene Formation yielding a U-Pb SHRIMP zircon age of 669.6 ± 6.7 Ma, which is significantly younger than the presumptive age. The Irene Formation is overlain by basin floor turbidite facies that correlate with the Horsethief Creek Group, which represent some of the oldest post-rift deposits in the study area and are interpreted as the earliest indication of a passive continental margin setting for northwestern Laurentia. The dated sample was collected from the upper portion of the Irene Formation and so the transition from <em>syn</em>-rift to post-rift is younger than ca. 670 Ma, which is estimated at approximately 660–650 Ma. Additionally, these new age data place the associated diamictites at the end of the Sturtian glaciation.</div></div>","PeriodicalId":49674,"journal":{"name":"Precambrian Research","volume":null,"pages":null},"PeriodicalIF":3.2,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142561091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}