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The increase in initial Hf isotopes identified in early Mesoarchean detrital zircon is commonly interpreted as a reflection of the geodynamic transition from stagnant‐lid to mobile‐lid tectonics. However, given the lack of petrogenetic context, interpreting detrital zircon may lead to spurious conclusions. In this contribution, we use zircon U‐Pb‐Hf‐O isotopic and bulk rock compositions of newly identified 3.05–2.9 Ga granitoids from the SW Yangtze Block to posit petrogenesis within an isotopically juvenile magmatic system. A statistical analysis of these data with a global igneous zircon Lu‐Hf isotopic compilation reveals an increase in average initial radiogenic Hf isotopes during the Paleoarchean to Mesoarchean transition. We posit that the Earth's continental crust underwent a global rejuvenation across the Paleo‐Mesoarchean transition. This rejuvenation can be explained by an independently observed increase in mantle temperatures resulting from mantle thermal evolution and does not require a change in tectonic style. Plain Language Summary: In this study, we explore the Earth's continental crust evolution before 3.0 billion years ago, a period characterized by limited preserved ancient rocks. We focus on zircon from igneous rocks, which provides a more reliable petrogenetic record than detrital zircon. Our study challenges the widely observed increase in detrital zircon initial Hf isotopes during the Paleo‐to Mesoarchean transition, often interpreted as a shift in tectonic regimes. We present new data from 3.05 to 2.9 billion‐year‐old granitoids in the Yangtze Block, suggesting isotopically juvenile magmatic activity. Statistical analysis of a global database of igneous zircon Hf isotopes reveals a state‐shift increase in εHf(t) across the Paleo‐to Mesoarchean transition, indicating global crustal rejuvenation at that time. Contrary to prevailing theories, we propose that this rejuvenation can be attributed to elevated mantle temperatures, challenging the notion of a significant geodynamic change during this period. Our findings emphasize the need to consider mantle thermal evolution in understanding continental crust growth on early Earth. Key Points: 3.05 and 2.9 Ga granitoids derived from juvenile crust are identified in the SW Yangtze BlockGlobal crust rejuvenation occurred across the Paleo‐to Mesoarchean transitionThis period of rejuvenation resulted from the effects of peak mantle temperatures [ABSTRACT FROM AUTHOR]

The start of the Paleoproterozoic supercontinent cycle is typically taken as the initiation of orogenesis at ca. 2.1 Ga leading to the assembly of Earth's first supercontinent, Columbia. However, the dearth of ca. 2.5–2.2 Ga geological records makes it difficult to deduce tectonic factors during the onset of the Paleoproterozoic supercontinent cycle. The petrogenesis of tonalite–trondhjemite–granodiorite (TTG) provides useful proxies for tracing prevailing geodynamic regimes of early continental evolution. However, marked decreases of TTG and other magmatism occurred across the Archean–Paleoproterozoic transition and have previously precluded forming testable hypotheses. Early Paleoproterozoic TTGs have been identified in the North China Craton (NCC) and other cratons, which may represent the last major pulse of TTGs globally. Here we present low δ18O and δ30Si ca. 2.3 Ga TTGs from the NCC, together with thermodynamic modeling and compilation of stable O and Si isotopes for TTGs globally through time. The ca. 2.3 Ga TTGs were derived from the partial melting of Archean basaltic crust and give lighter average zircon δ18O (3.15 ± 0.35‰) and whole‐rock δ30Si values (−0.17 ± 0.08‰) than most Archean TTGs. Considering coeval mafic‐felsic igneous rocks, and lithospheric thinning since ca. 2.5 Ga based on estimated crustal thickness through the Neoarchean–Paleoproterozoic, we posit the onset of an intraplate rifting consistent with the anomalous low‐δ18O magmatism. Continental rifting of Archean cratons/supercratons plausibly hints at the formation of rifts driving subduction initiation as the veritable onset of the Paleoproterozoic supercontinent cycle. Plain Language Summary: The Earth's first supercontinent, Paleoproterozoic–Mesoproterozoic Columbia, likely began to form during ca. 2.1 Ga (billion years ago) orogenesis. However, the limited record of ca. 2.5–2.2 Ga magmatism makes it difficult to establish how exactly the Paleoproterozoic supercontinent cycle commenced. The tonalite–trondhjemite–granodiorite (TTG) series of felsic rocks forms the backbone of Archean cratons and can provide key constraints on the Earth's early tectonic evolution. Some early Paleoproterozoic TTGs occur in North China and other cratons, which may represent the last major TTG event globally, presenting the possibility to fulfill this role. Here we carry out zircon O and bulk‐rock Si isotopic analyses and thermodynamic modeling for these ca. 2.3 Ga TTGs, together with Si‐O‐Hf data compilation of TTGs globally through time. These ca. 2.3 Ga TTGs show lighter zircon O and bulk‐rock Si isotopes than those of Archean TTGs. They might be formed within‐plate, associated with lithospheric thinning and mantle‐crust remelting to form mafic‐felsic magmatism. We propose an intraplate rift setting for this early ca. 2.3 Ga magmatism, which drove the mobilism that led to the subsequent 2.1–1.8 Ga orogenesis and should be posited as the real start of the Paleoproterozoic supercontinent cycle. Key Points: Ca. 2.3 Ga tonalite–trondhjemite–granodiorite (TTG) in the North China Craton (NCC) shows the affinity of low‐pressure (LP) TTGs and contains low zircon δ18O and bulk‐rock δ30Si valuesCa. 2.3 Ga low δ18O and δ30Si TTG and coeval low‐δ18O magmatism herald the initiation of an intraplate rift settingSuch intraplate rifting hints at the formation of rifts driving subduction as the real onset of the Paleoproterozoic supercontinent cycle [ABSTRACT FROM AUTHOR]

Since the Archean, secular change in orogenic style is demonstrated through evolution of metamorphic conditions and geochemical proxies. Linked to orogenic style is the amount of crustal thickening and elevation, whereas orogenic vigor is related to the supercontinent cycle. An array of Proterozoic orogens spanned the assembly of supercontinents Columbia and Rodinia, but the vigor of orogenesis is debated, with proposals for both Mesoproterozoic quiescence and climax. We show mid‐Proterozoic orogenesis occurred globally and was broadly continuous; furthermore, orogens exhibit elevated metamorphic thermobaric ratios with large volumes of high‐temperature felsic magmatic rocks. These features reflect higher mantle heat flux leading to increased mid‐crustal flow and lower elevation. In this context, proposals that geochemical proxies for crustal thickness record orogenic quiescence are inconsistent with the geological record. Alternatively, secular change in crustal thickness is attributed to orogenic style, namely the prevalence of hot, thin, and low orogens in the mid‐Proterozoic. Plain Language Summary: Orogenesis is the process whereby tectonic plates converge and mountain systems are created. In the case of the Andes and Himalayas, orogenesis resulted in significant thickening of the continental crust. Recent attempts to provide geochemical proxies for crustal thickness have allowed geologists to track the thickness of the crust through geologic time. One period of time in particular between 1850 and ∼850 million years ago—the mid‐Proterozoic—was characterized as having relatively thin crust. Some have argued this is evidence for a period of "orogenic quiescence." However, the geologic record is rife with ancient orogenic belts during this time as evidenced by the metamorphic and igneous rock records. In particular, the metamorphic rocks display higher than normal temperature/pressure ratios indicating unusually hot crust. We propose that the thin crust at this time is a product of high temperatures resulting in greater crustal flow and therefore lower mountain ranges. Key Points: The mid‐Proterozoic was characterized by unusually hot orogenesisElevated orogenic temperatures limited crustal thickening and promoted crustal flow and hinterland extensionSecular change in orogenic process explains independent estimates of variation in Proterozoic crustal thickness [ABSTRACT FROM AUTHOR]

Strongly peraluminous granites (SPGs) form through the partial melting of metasedimentary rocks and therefore represent archives of the influence of assimilation of sedimentary rocks on the petrology and chemistry of igneous rocks. With the aim of understanding how variations in sedimentary rock characteristics across the Archean–Proterozoic transition might have influenced the igneous rock record, we compiled and compared whole-rock chemistry, mineral chemistry, and isotope data from Archean and Paleo- to Mesoproterozoic SPGs. This time period was chosen as the Archean–Proterozoic transition broadly coincides with the stabilization of continents, the rise of subaerial weathering, and the Great Oxidation Event (GOE), all of which left an imprint on the sedimentary rock record. Our compilation of SPGs is founded on a detailed literature review of the regional geology, geochronology, and inferred origins of the SPGs, which suggest derivation from metasedimentary source material. Although Archean and Proterozoic SPGs are similar in terms of mineralogy or major-element composition owing to their compositions as near-minimum melts in the peraluminous haplogranite system, we discuss several features of their mineral and whole-rock chemistry. First, we review a previous analysis of Archean and Proterozoic SPGs biotite and whole-rock compositions indicating that Archean SPGs, on average, are more reduced than Proterozoic SPGs. This observation suggests that Proterozoic SPGs were derived from metasedimentary sources that on average had more oxidized bulk redox states relative to their Archean counterparts, which could reflect an increase in atmospheric O2 levels and more oxidized sedimentary source rocks after the GOE. Second, based on an analysis of Al2O3/TiO2 whole-rock ratios and zircon saturation temperatures, we conclude that Archean and Proterozoic SPGs formed through partial melting of metasedimentary rocks over a similar range of melting temperatures, with both 'high-' and 'low-'temperature SPGs being observed across all ages. This observation suggests that the thermo-tectonic processes resulting in the heating and melting of metasedimentary rocks (e.g. crustal thickening or underplating of mafic magmas) occurred during generation of both the Archean and Proterozoic SPGs. Third, bulk-rock CaO/Na2O, Rb/Sr, and Rb/Ba ratios indicate that Archean and Proterozoic SPGs were derived from partial melting of both clay-rich (i.e. pelites) and clay-poor (i.e. greywackes) source regions that are locality specific, but not defined by age. This observation, although based on a relatively limited dataset, indicates that the source regions of Archean and Proterozoic SPGs were similar in terms of sediment maturity (i.e. clay component). Last, existing oxygen isotope data for quartz, zircon, and whole-rocks from Proterozoic SPGs show higher values than those of Archean SPGs, suggesting that bulk sedimentary 18O/16O ratios increased across the Archean–Proterozoic boundary. The existing geochemical datasets for Archean and Proterozoic SPGs, however, are limited in size and further work on these rocks is required. Future work must include detailed field studies, petrology, geochronology, and constraints on sedimentary source ages to fully interpret the chemistry of this uniquely useful suite of granites. [ABSTRACT FROM AUTHOR]

The 4·0–3·6 Ma Don Manuel igneous complex (DMIC), central Chile, provides a window into igneous processes involved in magma genesis associated with porphyry-style copper mineralization. This study uses petrographic, petrological, geochemical and isotopic data to examine the evolution of magmas from the mid- to lower-crustal source region to shallow emplacement. The data provide evidence for progressive oxidation of magma during differentiation and ascent, fractionation of Cl from S through degassing, and the late-stage, near-solidus removal of Cl from the system. Magmas of basaltic andesite to rhyolite composition were produced by polybaric differentiation of hydrous parental mafic magmas. Variations in crustal differentiation depths led to variable suppression of plagioclase saturation that is recorded in distinctive strontium versus anorthite evolution patterns. Hydrous, derivative magmas generated over a wide range of pressures were episodically emplaced into the shallow crust at depths between 3·5 and 5 km. Intermediate porphyry dikes closely associated with copper mineralization contain diverse crystal cargoes indicating significant magma mixing. These crystal cargoes represent samples of crystal mush entrained from different depths, as well as crystals originating in different magmas and crystals grown in situ from hybridized magmas. Mafic enclaves containing plagioclase and amphibole compositions that match those of the basaltic andesites occur within biotite tonalite, testifying to magma mingling during ascent. Sulfur and chlorine contents of apatite within the different DMIC units record variable degassing and decoupling of volatile components with sulfur showing variations of three orders of magnitude compared with one order of magnitude for chlorine. The hypabyssal nature of the DMIC affords a detailed, integrated record of magmatic differentiation processes occurring within trans-crustal magmatic systems of the sort thought to characterize many crustal arc settings and play a fundamental role in driving porphyry-style copper mineralization. [ABSTRACT FROM AUTHOR]

A global U-Pb and δ18O zircon database shows temporal changes in the magmatic record related to changes in the degree of crustal reworking. The δ18O composition of bulk sediment remains relatively constant through geologic time, with a mean value of 14.9‰. In contrast, the δ18O values in magmatic zircons vary from relatively low values averaging ~6‰ in the Archean to increasingly higher and scattered values defining a series of peaks and troughs in post-Archean data. The degree of crustal reworking increases at times of supercontinent assembly. Therefore we attribute the pattern of post-Archean δ18O values recorded by magmatic zircons to a significant increase in the incorporation of high δ18O sediment in response to enhanced crustal thickening and reworking associated with the onset of collisional tectonics, especially during formation of supercontinents. [ABSTRACT FROM AUTHOR]

• 2.25 Ga A 2 -type granites are identified in the SW Yangtze Block. • The Paleo-Mesoproterozoic A 2 -type granites yield a secular increase in δ18O. • Diverse high-δ18O materials contribute to this secular increase. The elevation of δ18O in zircon through Earth history has been previously identified as being coeval with the assembly of post-Archean supercontinents. This was interpreted to result from the increasing incorporation of high-δ18O sediments into magmas due to enhanced crustal thickening and reworking during supercontinent assembly. However, little attention has been paid to the variations of δ18O in igneous rocks during the extensional phases of the supercontinent cycle. Given the scarcity of early Paleoproterozoic granites due to the ca. 2.3–2.2 Ga tectono-magmatic lull, we first report a suite of ca. 2.25 Ga granites from the SW Yangtze Block by providing zircon U-Pb-Hf-O isotopes, whole-rock geochemical, and Sm-Nd isotopic analyses to constrain their petrogenesis. The results demonstrate that they are A 2 -type granite and originated from the partial melting of Meso-Neoarchean igneous crust in a post-collision extensional setting. Integrating these data with a global compilation of Paleo-Mesoproterozoic A 2 -type granites allows us to further explore secular changes in elemental and isotopic compositions of these granite types. The A 2 -type granites in this study exhibit mantle-like zircon δ18O values, in accord with those from the compiled pre-1.85 Ga A 2 -type granites. Additionally, the data show a secular increase in zircon δ18O for the compiled Paleo-Mesoproterozoic A 2 -type granites. Similar increasing trends are also observed in various compositional proxies that imply the increasing addition of mafic igneous rocks into magma sources that are likely associated with the back-arc extensional settings of the Great Proterozoic Accretionary Orogen (GPAO). Considering that the compiled post-1.8 Ga A 2 -type granites have depleted Nd-Hf isotopes, we posit that they were mainly derived from mafic rocks with arc-like geochemical compositions. In this context, the secular increase in zircon δ18O for the post-1.8 Ga A 2 -type granites might reflect the increasing assimilation of altered oceanic crust into the back-arc and inboard magmatic systems of retreating accretionary orogens. In contrast, the compiled ca. 1.85 Ga A 2 -type granites possess non-radiogenic Hf and elevated O isotopes, indicative of the incorporation of ancient sediments in their magma sources. We suggest that they are most likely generated in a post-collision extensional setting associated with the very early stages of assembly of the Columbia/Nuna supercontinent. [ABSTRACT FROM AUTHOR]

We use a filtered database that tracks the composition of hydrated mantle with time using arc-type basalts, including an unknown amount of plume-type mantle in the Archean. A factor of 2–10 geochemical variability, both between and within sample sites, characterizes arc-type basalts and especially so >3.5 Ga and < 2.0 Ga. Based on which geographic sites are available for sampling, this variability is probably due to an anomalously high proportion of enriched components in some arc-type mantle sources. The proportion of an enriched component in magma sources is related to the ratio of continental to oceanic arc sites in the database, and thus is at least in part controlled by tectonic setting sample biases. We suggest that online geochemical databases of mafic igneous rocks should not be used to track secular changes in mantle composition or temperature unless they have been carefully filtered for tectonic setting, alteration/metamorphism, reliable ages, rock type, and major element composition. If the relatively few geographic sites are representative, large variations in incompatible element distributions in arc-type basalts suggest poorly mixed mantle before 3.5 Ga. However, the uniformity of incompatible element distributions from 3.5 to 2.6 Ga supports the existence of well-mixed mantle sources during this time. Long-term changes in major and compatible element contents of arc-type basalt mantle sources from 3.5 to 1.0 Ga are consistent with decreasing mantle temperature and degree of melting during this time. Although enriched mantle sources for arc-type basalts appear in the Neoarchean, they do not become widespread until after 2.0 Ga. From 2.0 to 1.0 Ga, enriched mantle contributions are relatively high but variable, probably in response to some combination of increased enriched mantle in the magma sources, sampling biases from relatively few sites with an anomalously high proportion of enriched mantle, and recycling of oceanic and continental lithosphere into the mantle in response to global propagation of subduction. Superimposed on long-term geochemical trends are five geographically widespread geochemical anomalies (deviations of greater than ±2σ from a smoothed Gaussian curve) in incompatible element distributions (2.55, 2.15, 1.75, 0.65 and 0.25 Ga) and an additional anomaly at 3.6–3.3 Ga in some compatible elements. All five incompatible element anomalies occur near age peaks in the U/Pb zircon age record (at 2.5, 2.15, 1.85, 0.60, and 0.25 Ga in both detrital and igneous zircons) and the 2.55, 2.15 and 1.75 Ga anomalies are very close to peaks in Re/Os model ages for mantle ultramafic rocks. The simplest explanation for the incompatible element anomalies is episodic enrichment of mantle sources of arc-type basalts, perhaps related to widespread mantle events (overturn or/and mantle plume) that brought enriched components into subduction-related sources of arc-type basalts. [Display omitted] • Unless filtered, online databases should not be used to track mantle composition. • Hydrated mantle is poorly mixed before 3.5 Ga and well mixed at 3.5–2.6 Ga. • From 2 to 1 Ga, arc type basalts show an increase in the proportion of enriched mantle. • Major geochemical anomalies in arc-type basalts correlate with zircon age peaks. [ABSTRACT FROM AUTHOR]

• Diancangshan-Ailaoshan (DCS-ALS) trondhjemites and granites formed at ca. 771–762 Ma. • The trondhjemites were produced by water-fluxed melting of the juvenile mafic lower continental arc crust (with addition of ancient Yangtze basement). • The granites were produced by dehydration melting of juvenile felsic middle crust. • The Neoproterozoic magmatisms in the DCS-ALS fold belt represent the southwestern extension of the Panxi-Hannan arc. The Neoproterozoic magmatic and tectonic history of the South China Craton (SCC) is critical for the reconstruction of Rodinia break-up and subsequent Gondwana assembly. Nonetheless, the tectonic attribution of the Neoproterozoic igneous rocks in the southwestern Yangtze is contentious, and the mechanism for crustal anatexis remains unclear. Here, we report mineralogical, whole-rock geochemical and Sr-Nd isotope data, and zircon U-Pb-Hf-O isotope data from the newly found Neoproterozoic trondhjemites and granites in the Diancangshan-Ailaoshan (DCS-ALS) fold belt along the southwestern Yangtze. Both the trondhjemites (ca. 771–762 Ma) and granites (ca. 767 Ma) have high SiO 2 and low MgO contents. The trondhjemites have relatively high CaO, Na 2 O and Sr contents, but low K 2 O contents and Rb/Sr ratios, and show positive to slightly negative Eu anomalies and heavy rare earth elements (HREEs) depletions, resulting in high Sr/Y and La/Yb ratios. In contrast, the granites have lower CaO, Na 2 O, and Sr contents, but higher K 2 O and Rb/Sr, and display negative Eu anomalies and flat HREEs patterns. The trondhjemites have negative εNd(t) (-4.12 to −3.85), positive to negative εHf(t) (-2.50 to + 5.28) and low δ18O (4.37 ‰–7.27 ‰) values. In comparison, the granites have positive εNd(t) (0.09 to 0.26), εHf(t) (+1.24 to + 9.86) and higher δ18O (6.50 ‰–7.24 ‰) values. The distinct elemental and isotopic compositions between the trondhjemite and granite samples reflect two different types of crustal anataxis within different crustal levels. The trondhjemites were formed by water-fluxed melting of the juvenile mafic lower continental arc crust (with addition of ancient Yangtze basement). The granites were derived from dehydration melting of juvenile felsic middle crust. Our results imply that the trondhjemites and granites were formed in a continental arc setting. The melting processes revealed here should be applicable to decipher the widespread Neoproterozoic crustal melting along the southwestern Yangtze, which was most likely fluid-controlled via subduction-induced asthenosphere upwelling. Combined with available regional geological data, we suggest that a long-lived Neoproterozoic (∼880–730 Ma) subduction zone may have extended from the Panxi-Hanna region in the northern/western Yangtze Block to the DCS-ALS fold belt in the southwestern Yangtze. Thus, the SCC may have located on the northwestern margin of Rodinia. [ABSTRACT FROM AUTHOR]