Continental Growth Research Articles

Continental growth during Devono-Carboniferous switching accretionary tectonics: the Katebasu granitoid stock, Central Tianshan, NW China

Continental growth during Devono-Carboniferous switching accretionary tectonics: the Katebasu granitoid stock, Central Tianshan, NW China

Crustal deformation of intermontane basins beneath Central Tien Shan revealed by full-wave ambient noise tomography

The Tien Shan is one of the highest, youngest, and most active orogenic belts at the southwestern margin of Central Asia. The topography of the Central Tien Shan is characterized by nearly parallel orogenic belts with interposing intermontane basins, providing an ideal site to investigate the formation and modification of the intermontane basins. Here we construct a high-resolution crustal velocity model of the Central Tien Shan using full-wave ambient noise tomography based on high-quality Rayleigh wave empirical Green's functions at periods of 5–50 s extracted from the dense seismic array during 1997–2000. Our new model reveals two high-velocity crustal anomalies beneath the Naryn Basin and Issyk-Kul Basin, respectively, and widespread low-velocity anomalies in the middle to lower crust beneath the mountain belts. We propose that the high-velocity crustal features of the Naryn Basin and Issyk-Kul Basin may be the remnant structures from the Palaeozoic collision. Widespread low-velocity anomalies reflect mantle upwelling and partial melting due to the Kazakh and Tarim lithosphere underthrusting, which have been consequently modifying the overlying crustal structures. High-resolution tomographic results reveal significant crustal heterogeneities beneath the Central Tien Shan, which shed new light on the continental growth mechanism and the crustal deformation of intermontane basins.

Evaluating preservation bias in the continental growth record against the monazite archive

Abstract Most recent models of continental growth are based on large global compilations of detrital zircon ages, which preserve a distinctly episodic record of crust formation over billion-year timescales. However, it remains unclear whether this uneven distribution of zircon ages reflects a true episodicity in the generation of continental crust through time or is an artifact of the selective preservation of crust isolated in the interior of collisional orogens. We address this issue by analyzing a new global compilation of monazite ages (n >100,000), which is comparable in size, temporal resolution, and spatial distribution to the zircon continental growth record and unambiguously records collisional orogenesis. We demonstrate that the global monazite and zircon age distributions are strongly correlated throughout most of Earth history, implying a link between collisional orogenesis and the preserved record of continental growth. Our findings support the interpretation that the continental crust provides a preservational, rather than generational, archive of crustal growth.

Highly refractory dunite formation at Gibbs Island and Bruce Bank, and its role in the evolution of the circum-Antarctic continent

ABSTRACT The continental margin is of profound importance as it records continental growth by accretion of orogenic magmas and following continental rifting. A high degree of mantle melting due to hydrous fluid input is expected to simultaneously stimulate continental growth and lower the intrinsic density of the mantle than more fertile mantle, which in turn isolates the continental lithosphere from the convective mantle. The mantle peridotites from Gibbs Island (South Shetland Islands) and Bruce Bank in the Drake Passage provide us an insight into the tectonic history in the circum-Antarctic region. To elucidate the continental growth of Antarctica, we present geochemical data of eight dunites from Gibbs Island and one dunite from Bruce Bank, including Re–Os isotope and highly siderophile element compositions. The dunites are severely affected by serpentinization as evidenced by antigorite + brucite or lizardite (loss on ignition = LOI ranging from 3 to 34 wt.%) but contain primary euhedral to subhedral chromites with or without spherical inclusions. The chromites rarely form lens-shaped aggregates. A dunite from Gibbs Island contains fresh olivine grains filling a fracture in the chromite with low LOI (3 wt.%), indicating a deserpentinization origin from a precursor serpentinized dunite. The dunites show highly depleted bulk-rock major element compositions (Mg/Si = 1.4–1.6 and Al/Si = 0.004–0.01 for Gibbs Island dunites, Mg/Si = 0.66 and Al/Si = 0.008 for Bruce Bank dunite), overlapping a compositional field defined by forearc peridotites. The positive correlation in Re/Ir–LOI space corroborates Re input during the later serpentinization process. The 187Os/188Os ratios of the dunites range from 0.11907 to 0.14493. Phanerozoic Re-depletion (melt depletion) ages of ca. 535–129 Ma are recorded in the Gibbs Island dunites, except for one with a Mesoproterozoic Re-depletion age of ca. 1.2 Ga. Since there exists serpentinization-related perturbation of Re, the ages provide minimum time estimates for melt depletion events. The early Paleozoic melt depletion is inferred to have occurred at a very early stage of Antarctic Peninsula formation in response to plate convergence along the margin of Gondwana, whereas the Mesoproterozoic Re-depletion age reflects convecting mantle heterogeneity unrelated to any nearby crust-forming events. The petrographic characteristics of the chromites and highly depleted nature of the dunites are attributed to melt–peridotite reaction in a subduction zone setting. A feasible interpretation for the dunite formation is that the mantle had experienced two stages of melting with the final stage occurring along the Gondwana continental margin in the subduction zone setting. Resultant highly refractory lithospheric mantle was later displaced and dispersed during the Gondwana breakup. Widespread existence of the dunite may be attributed to multi-stage melt depletion along the continental margin.

Phenocryst zonation records magma mixing in generation of the Neoproterozoic adakitic dacite porphyries from the Kongling area, Yangtze Craton

Adakites and adakitic rocks are pivotal in understanding the formation and evolution of the early continental crust. However, there remain controversies about the origin of these rocks. This paper reports petrological, mineralogical and geochemical data for the newly identified Neoproterozoic (ca. 819 Ma) adakitic dacite porphyries in the Kongling area, Yangtze Craton, with the aim of constraining their petrogenesis and elucidating the role of magmatic processes in generating the adakitic melts. The dacite porphyries are characterized by high SiO2 (62.2–64.8 wt%), Mg# (52–60), Sr/Y and (La/Yb)N ratios, as well as depleted Nd-isotope compositions (ƐNd (819 Ma) = 0.1–1.6), geochemically comparable to high-Mg# adakitic rocks. Core-rim zoned amphibole and plagioclase phenocrysts are common. Overall, the amphibole cores show lower MgO, FeO, Sr, but higher Al2O3 concentrations than the rims. Similarly, the plagioclase cores exhibit lower An [Ca/(Ca + Na + K), atomic ratios] but more enriched 87Sr/86Sr(i) than the rims. Geochemical modeling demonstrates that the melts in equilibrium with the amphibole cores have high SiO2, low MgO, CaO, Fe2O3T and TiO2 as well as flat REE patterns and low Sr/Y ratios. Such felsic melts were likely generated by low-degree dehydration melting of the Paleo- to Meso-proterozoic amphibolites of the Kongling Complex. On the contrary, the melts in equilibrium with the amphibole rims possess lower SiO2 and higher MgO with elevated (La/Yb)N and Sr/Y ratios, suggesting involvement of more mafic melt components. In combination with regional geology, we propose that this mafic endmember possibly formed through fractional crystallization of original subduction-related basaltic magmas that are geochemically equivalent to the Neoproterozoic Panxi-Hannan arc-type basaltic rocks. Mass-balance calculation further reveals that the Kongling dacite porphyries could form by mixing of the above two geochemically distinct endmembers in ratios of ca.50: 50. Importantly, the adakitic signature of these rocks (i.e., high Sr/Y and (La/Yb)N ratios) was inherited from the fractionated arc-type mafic melts, highlighting the significant role of magma mixing in generating the adakitic melts. We propose that this mechanism may have been much more common than as previously thought and contributes significantly to continental growth and evolution.

Crustal reworking and growth during India–Asia continental collision: Insights from early Cenozoic granitoids in the central Lhasa Terrane, Tibet

Studying granitoids can provide important knowledge on the composition of continental crust and the geodynamic processes of continental growth. Nevertheless, the mechanisms of granitoids formation during continental collision remain uncertain. In this paper, we present new zircon U–Pb–Hf isotope and whole‐rock Sr–Nd isotope compositions, and major‐ and trace‐element data for granitoids from the Chacangka area of the central Lhasa Terrane, southern Tibet. The Chacangka quartz monzonites crystallized at ca. 61 Ma, whereas the monzonites and granites were emplaced at ca. 51 Ma. The quartz monzonites are peraluminous and have high 87Sr/86Sri ratios (0.7129–0.7131), and their low εNd(t) (−7.65 to −7.10) and zircon εHf(t) (−9.3 to −7.5) values are more depleted than those of ancient crustal basement beneath the central Lhasa Terrane, which suggests that they originated from a mixed source of juvenile and ancient lower crust. Compared with the quartz monzonites, the monzonites have much higher contents of MgO (2.34–3.62 wt%) and values of Mg# (42.3–46.3) and zircon εHf(t) (−6.9 to 1.9) and show more depleted Sr–Nd isotopes, indicating that more juvenile materials were involved in their source. The granites have Sr–Nd isotope compositions that are similar to those of the coeval monzonites but have higher SiO2 contents, lower CaO and MgO contents, and lower values of Mg#, suggesting that they were differentiates of the monzonites. The elemental and isotopic compositions of the Chacangka granitoids exhibit a marked transformation from 61 to 51 Ma, probably indicating breakoff of the Neo‐Tethyan oceanic slab. The Neo‐Tethyan slab breakoff not only induced the upwelling of deep material and eruption of magma but also caused re‐melting and destruction of ancient crustal basement of the central Lhasa Terrane.

Episodic growth of felsic continents in the past 3.7 Ga.

Continents form the most accessible parts of Earth, but their complex compositions make their origin difficult to investigate. A novel approach based on a comprehensive compilation of samarium-neodymium isotopic compositions of detrital sedimentary rocks is here used to unravel continental growth through time. This record reveals that continents were as felsic as today in the past 3.7 Ga (billion years) and that their growth was not continuous but episodic. Reworking of preexisting crust was a ubiquitous process during most of Earth history, but at least six periods of continental growth can be identified every 500 to 700 Ma (million years) in the past 3.7 Ga. This recurrence could be accounted for by changes in tectonic plate velocities favoring periods of rapid subduction and enhanced production of juvenile felsic crust.

Discovery of a hidden Triassic Arc in the Southern South China Sea: Evidence for the breakaway of a ribbon continent with implications for the evolution of the Western Pacific margin

AbstractPaleo‐Pacific subduction generated a prolonged active continental margin along the coast of the South China Block (SCB). A Triassic magmatic gap was argued to have occurred and was ascribed to flat‐slab subduction of an oceanic plateau. We study for the first time a >330‐m‐long core of typical arc volcanics dated at ca. 218 Ma from the Meiji Atoll in the southern South China Sea (SCS). Paleomagnetism suggests 4.1°± 1.5° of post‐eruption southward drift. These observations clearly support the existence of a Triassic arc in the SCB and imply that part of the arc later split off and drifted southward during the opening of the SCS in the Oligocene. Our results better constrain the lateral extent of the proposed flat‐slab subduction along the margin of the SCB. Moreover, we provide direct evidence of how the breakaway of ribbon continents operated in active continental margins, a recurrent scenario that has been invoked for Phanerozoic tectonics and continental growth throughout Asia.

Some New Concepts in the Plate Tectonics Paradigm Fifty Years after Its Inception

AbstractWe have gained significant insights into the dynamic evolution of the earth, causes of geohazards, processes of continental growth, feedback mechanisms between tectonics, topography and cli...

U-Pb provenance fingerprints of metavolcanic-sedimentary successions of the Mineiro belt: Proxies for the continuity of plate tectonics through the Paleoproterozoic

We document new U-Pb detrital zircon LA-MC-ICP-MS data for seven metavolcanic-sedimentary successions and metasedimentary sequences and reassess additional dates of five siliciclastic samples toward their tectonic significance in the context of the Mineiro belt, Southern São Francisco Craton. This belt represents a crustal segment of the 2.47–2.00 Ga Minas Orogen, classically known by its Siderian and Rhyacian juvenile rocks with important implications in the Earth's geodynamics. The new and compiled detrital provenance constraints unravel the long-lived magmatic and sedimentary history of the studied basins, lasting ca. 230–220 Myr. The maximum depositional dates around 2.1 Ga reflect the renewed sediment budget with the subsequent metamorphic episode ca. 2.0 Ga. Most of the unmixed relative probability diagrams are consistent with sourcing from the Siderian and Rhyacian arcs of the Mineiro belt, determining a detrital provenance change in time and space for the precursor basins. Alternative potential sources could be the youngest rocks of the Mantiqueira and Juiz de Fora terranes that constitute the other segments of the Minas Orogen, given the age match. The overall detrital fingerprints determine the study basins resumed mainly in Rhyacian fore-arc and/or back-arc settings, i.e., akin to a subduction-related system that evolved to a collisional (foreland) environment. Few samples show fingerprints of primary extensional settings, determined by major Archean detrital populations sourced from areas outside the Mineiro belt beside the Paleoproterozoic detritus. The working model considers the collage between the Mineiro belt and the ancient foreland around 2.10 Ga and eventual interaction with other crustal segments of the Minas Orogen, generating the ca. 2.0 Ga metamorphism over the metasedimentary samples. The more complete isotopic repository in detrital and igneous zircon grains for the studied supracrustal successions and the associated rocks allows new insights into the Rhyacian–Orosirian dynamics of the Minas orogeny. In a broader perspective, the juvenile nature of the Mineiro belt reinforces the paradigm of uninterrupted continental growth during the Paleoproterozoic Earth.

Episodic construction of the early Andean Cordillera unravelled by zircon petrochronology

The subduction of oceanic plates beneath continental lithosphere is responsible for continental growth and recycling of oceanic crust, promoting the formation of Cordilleran arcs. However, the processes that control the evolution of these Cordilleran orogenic belts, particularly during their early stages of formation, have not been fully investigated. Here we use a multi-proxy geochemical approach, based on zircon petrochronology and whole-rock analyses, to assess the early evolution of the Andes, one of the most remarkable continental arcs in the world. Our results show that magmatism in the early Andean Cordillera occurred over a period of ~120 million years with six distinct plutonic episodes between 215 and 94 Ma. Each episode is the result of a complex interplay between mantle, crust, slab and sediment contributions that can be traced using zircon chemistry. Overall, the magmatism evolved in response to changes in the tectonic configuration, from transtensional/extensional conditions (215–145 Ma) to a transtensional regime (138–94 Ma). We conclude that an external (tectonic) forcing model with mantle-derived inputs is responsible for the episodic plutonism in this extensional continental arc. This study highlights the use of zircon petrochronology in assessing the multimillion-year crustal scale evolution of Cordilleran arcs.

Ocean Plate Stratigraphy of a long-lived Precambrian subduction-accretion system: The Wutai Complex, North China Craton

Ocean Plate Stratigraphy (OPS) is the travelogue of the oceanic lithosphere from its birth at the Mid Ocean Ridge to its demise at the subduction zone in convergent plate margins. Here we present an OPS succession preserved onland in the Wutai Complex of the North China Craton (NCC), representing a prolonged subduction-accretion-collision system and continental growth during the Neoarchean-Paleoproterozoic. The OPS succession in Wutai includes metabasalts and banded iron formation representing the pelagic sequences together with intercalated metacarbonates. Phyllite, greenschist, and mica schist represent the hemipelagic sequence. Quartzite and conglomerate correspond to the turbidite sequence, with a progressive southward accretion towards a magmatic arc in the north. We present results from petrological, geochemical, zircon U-Pb, REE, and Lu-Hf studies from representative rocks in the OPS sequence of the Wutai Complex. The trace elements including the rare-earth element (REE) data of the metabasalt show transitional features between normal mid-ocean ridge basalt (N-MORB) and enriched mid-ocean ridge basalt (E-MORB). The REY (lanthanide elements and Y) data of the banded iron formation (BIF), greenschists, and phyllite suggest the interaction of high-temperature hydrothermal fluids and seawater. Magmatic zircon grains from the quartzite show 206Pb/207Pb upper intercept age of 2443 ± 21 Ma, whereas zircon grains in the phyllite show upper intercept age of 2494 ± 32 Ma, with minor xenocrysts with older ages of 2726 ± 46 Ma and 2672 ± 48 Ma. Zircon grains in the metaconglomerate show upper intercept age of 2569 ± 32 Ma. Those from the siliceous and intercalated bands in the BIF yield upper intercept ages of 2583 ± 34 Ma and 2524 ± 49 Ma. The zircon Lu-Hf data on zircon grains from the BIF, phyllite, quartzite, and metaconglomerate all show positive εHf(t) values (+1.3 to +7.4) in the range of depleted mantle to new crust, suggesting Neoarchean intra oceanic arc subduction. Combined with the zircon U-Pb and Hf isotopic data previously reported from the Wutai Complex, we infer the following four tectonic evolution stages: ca. 2800 Ma subduction initiation, ca. 2750–2300 Ma arc-accretionary complex, ca. 2300–2100 Ma back-arc rifting, and ca.1900–1750 Ma arc-continent collision. The metavolcanics and part of the metasedimentary rock assemblages in the Wutai Complex represent a deformed and dismembered OPS sequence generated through northward subduction and closure of the Wutai Ocean.

Jurassic Arc: Reconstructing the Lost World of eastern Gondwana

AbstractThe tectonic setting of the Australian sector of the eastern Gondwanan margin during the Jurassic and Cretaceous is enigmatic. Whether this involved convergent tectonism and a long-lived continental magmatic arc or rift-related extension unrelated to subduction is debated. The paucity of Australian Jurassic–Cretaceous igneous outcrops makes resolving these competing models difficult. We used the detrital zircon record of the Jurassic–Cretaceous Great Australian Superbasin (GAS) as a proxy for igneous activity. We attribute the persistent magmatism recorded in GAS sedimentary fill throughout the Mesozoic to ca. 95 Ma to continuation of the established Paleozoic continental arc system. The detrital zircon record signals short (~10 m.y.) pulses of elevated Jurassic and Cretaceous magmatic activity and strongly positive εHf values, indicating juvenile crust or mantle-derived magmatism. Margin reconstruction indicates sustained continental growth at rates of at least ~55 km3 km–1 m.y.–1, mainly to the tract now represented by submerged northern Zealandia, due to the retreat of this arc system. We posit that arc retreat was a key factor in rapid crust generation and preservation, and that continental sedimentary systems globally may host cryptic records of juvenile crustal addition that must be considered in estimating crustal growth rates along convergent plate margins.

Neoproterozoic tectonics of the Jiangnan orogen: The magmatic record of continental growth by arc and slab-failure magmatism from 1000 to 780 Ma

The Neoproterozoic NE-striking Jiangnan orogen in the South China Block (SCB) separates the Cathaysia microcontinent on the southeast from the Yangtze craton in the northwest. The origin and evolution of the Jiangnan orogen is unresolved, with individual models explaining part of the history, such as various magmatic, deformational, metamorphic, and sedimentary events including extensional, contractional, and transpressional modes. Here, we present detailed geochronological and Nd-Hf isotopic data for Neoproterozoic mafic and felsic intrusions in the Jiangnan orogen and identify three episodes of Neoproterozoic magmatism. The first stage ranging from ~1013–942 Ma is preserved predominantly in the eastern segment of the orogen, including a series of mafic rocks with ages of ~1010–952 Ma, contrasting with weak magmatic activity in the western segment with a peak at ~997 Ma. The second stage ranges from ~906 Ma to ~820 Ma, with intensive and extensive bimodal magmatism occurring in the eastern and western parts. The last stage mainly occurred in the western Jiangnan orogen in the period from ~800 to 780 Ma, associated with drastic mafic magmatism and weakly bimodal volcanic activities. The bimodal volcanism in the eastern segment exhibits a striking weak trend after ~823 Ma, distinctly different from the western segment where the magmatism lasted until ~785 Ma, indicating its syn- to post-collisional in nature. The pre-800 Ma magmatic rocks in western Jiangnan orogen have a dominant negative Nd isotopic signature but exhibit a significant positive trend after 800 Ma, different from those in east, which have a decreasing trend. Both parts display a roughly decoupled Nd-Hf isotopic character presented by a dominant positive pattern in Hf isotopes of the Neoproterozoic intrusive rocks, indicating a significant addition of previous slab-derived components or accretionary wedges in the pre-800 Ma magma evolution, and more depleted materials involved in the source in the later stages. Oceanic subduction under the northwestern Cathaysia Block occurred around ~1.0 Ga, slightly earlier than the subduction to the southeastern Yangtze. A gradual tectonic transition from post-orogenic extension to intracontinental rifting dominated the tectonics in Jiangnan orogen in the middle-late Neoproterozoic, followed by slab failure after ~790 Ma. Arc magmatism was the dominant source of crustal growth before 820 Ma in the SCB, but was exceeded in volume by later slab failure magmatism after ~790 Ma.

Late Paleozoic adakitic magmatism in the Zogdor Cu occurrences, southern Mongolia, and their tectonic implications: New SHRIMP zircon age dating, Lu-Hf isotope systematics and geochemical constraints

The Zogdor Cu occurrences are located in the Gurvansayhan island arc terrane of southern Mongolia, which corresponds to the southern part of the Central Asian Orogenic Belt (CAOB). The major porphyry type copper–gold (molybdenum) mineralized belt including Oyu Tolgoi, Tsagaan Suvarga, Shuteen, and Kharmagtai deposits are located in this terrane and were known to have formed during 372–324 Ma. The Zogdor Cu occurrences are found within this porphyry Cu-Au mineralized belt and are limitedly distributed in granitoids including granodiorite and monzogranite. In this study, we present new SHRIMP zircon U-Pb geochronology, LA-MC-ICPMS zircon Lu-Hf isotopes, and geochemical data for the granitoids in the Zogdor Cu occurrences and provide a new tectonic model including igneous activities and Cu mineralization in southern Mongolia. The emplacement ages of granodiorite and monzogranite are 329.1–326.4 Ma, and 329.9–326.1 Ma, respectively. All zircons have positive εHf values corresponding to two-stage model ages (T2DM) ranging from 581 to 331 Ma, possibly demonstrating that late Neoproterozoic to middle Carboniferous juvenile continental crust growth was derived from a depleted mantle source. Both granitoids are characterized by high Al2O3 and Sr, and low Y and Yb contents, as well as high Sr/Y and (La/Yb)N ratios, which are typical geochemical characteristics of adakites. The trace elements are characterized by an enrichment in the large ion lithophile elements (e.g., Cs, Rb, Ba, and Sr) and a depletion in the high field strength elements (e.g., Nb, P, and Ti), indicating that these granitoids intruded in subduction tectonic settings. In conclusion with data from previous studies, the intermittent igneous activities during the Cambrian to Ordovician (519–482 Ma), middle Devonian (374–363 Ma), middle to late Carboniferous (353–304 Ma), and early Permian (298–286 Ma) took place in the southern Mongolia and porphyry copper mineralizations seem to be closely related the middle Devonian and middle Carboniferous adakitic or adakite-like magmatism. The Lu-Hf isotopic results for these associated granitoids including previous Rb-Sr and Sm-Nd isotopic studies imply that the Neoproterozoic to middle Carboniferous juvenile continental growth derived from a depleted mantle source. The middle Devonian and middle Carboniferous magmatic activities triggered by the subduction of the Paleo-Asian Oceanic plate and formed the porphyry copper deposits in the southern Mongolia.

Anduo Late Cretaceous high-K calc-alkaline and shoshonitic volcanic rocks in central Tibet, western China: Relamination of the subducted Meso-Tethyan oceanic plateau

The Mesozoic Meso-Tethyan oceanic plateaus could have played important roles in both Tibetan continental marginal orogenesis and Tethyan oceanic evolution. However, little has been known whether fragments of these tremendous oceanic highs underplated beneath the active southern Qiangtang margin and impinged on the later magmatic and/or tectonic evolution. The Anduo volcanic rocks of this study in the southern Qiangtang, erupted at 79.6 ± 0.8 Ma, comprise predominantly high-K trachyte and trachyandesite, including 5 adakites with high Sr and low Y and Yb contents and high La/Yb normalized to chondrite ratios (> 20). These high-K calc-alkaline and shoshonitic rocks, classified according to immobile trace elements, have enriched isotope compositions with (87Sr/86Sr)i = 0.7073–0.7079, εNd(t) = −1.78 to −3.90 and zircon εHf(t) = −1.3 to 1.4. Geochemical modeling reveals that the Late Cretaceous Anduo high-silica adakites were most likely derived from the melting of the mixed material of 80–90% of the subducted Meso-Tethyan oceanic plateau metabasalt with 10–20% of the subducted sediments. Variable negative Eu and Sr anomalies, relatively large range of Mg#, increases of the εNd(t) values with increasing Mg# and decreasing SiO2, and increases of (87Sr/86Sr)i with decreasing Mg# and increasing SiO2 between adakites and non-adakites indicate the latter might have derived from lithospheric mantle assimilation and mineral fractional crystallization of the adakite parent magmas. It is thus concluded that the Meso-Tethyan oceanic plateaus could not only directly lead to the initial uplift of the Tibetan plateau through obduction and accretion onto the continental margin, but also contributed to the continental growth through relamination of the subducted oceanic plateaus.

Post-collisional mafic magmatism: Insights into orogenic collapse and mantle modification from North Qaidam collisional belt, NW China

Post-collisional magmatism contains important clues for understanding processes of orogenic belts, potentially including unrooting and collapse. Here we report new geochronological and geochemical data for a suite of post-collisional mafic dykes in the North Qaidam ultrahigh-pressure metamorphic (UHPM) belt. Two groups of magmatic rocks can be distinguished: (1) Middle Devonian (392–375 Ma) basic-intermediate dykes; (2) Upper Devonian (~360 Ma) ultrabasic dykes. Whole-rock geochemistry and zircon Hf isotopes reveal that the intermediate-basic dykes are derived from a lithospheric mantle source, whereas the ultrabasic dykes are melting of asthenosphere mantle. We suggest that such mantle-derived mafic magmatism is the critical indicator for the start of post-collisional magmatism and orogen unrooting and collapse. We propose a geodynamic model explaining the activities of the lithospheric and asthenospheric mantle during the post-collisional stage, which reveals a ~ 35 million year unrooting process, from slow lithospheric mantle erosion between ~395–375 Ma, to final collapse by lithosphere delamination and asthenosphere upwelling at ~360 Ma. Addition of juvenile mantle materials to the crust by the post-collisional mafic magmatism suggests that the post-collisional stage is an important period for continental growth in Earth's history.

Crustal melting vs. fractionation of basaltic magmas: Part 1, granites and paradigms

Granitoids are a major component of the continental crust. They play a pivotal role in its evolution, either by adding new material (continental growth), or by reworking older continental crust. These two roles correspond to two main ways of forming granitic magmas, either by partial melting of pre-existing crustal rocks yielding granitic melts directly, or by fractionation of mantle-derived mafic to intermediate magmas. Both models represent endmembers, or paradigms that have shaped the way the geological community envisions granitoids, their occurrence, features, formation and meaning for crustal evolution and differentiation of the whole planet.In this paper, we expose the two competing paradigms and their implications. We explore the evidence on which each model is based, and how each school of thought articulates a comprehensive view of granitic magmatism based on field geological, petrological, geochemical (including isotopes) and physical constraints; and how, in turn, each view shapes the thinking on crustal growth and evolution, and the interpretation of proxies such as age and Hf isotopic patterns in detrital zircon databases. We emphasize that both schools of thought build a different, but internally consistent view based on a large body of evidence, and we propose that each of them is, or has been, relevant to some portions of the Earth. Thus, the key question is not so much “which” model applies, but “where, when and to which extent”.

Untapping FOCAC higher education scholarships for Africa's human capital development: lessons from haigui

The future development of Africa hinges on the development of its human capital. Higher education is one of the critical resources that will help unlock Africa's potential. China has been a significant partner in the continent's growth. African Heads of State have lauded China's development model and have developed policies to emulate what they consider the most suitable model for a developing nation. Twenty years since the birth of the Forum on China–Africa Cooperation (FOCAC), the value of higher education cooperation between Africa and China remains untapped by the private and public sectors. Under FOCAC, China has made provisions to support Africa in human development through various programs, including education. China has invited African scholars to Chinese universities to earn higher education degrees, as well as learn the Chinese language and study China's programs for alleviating poverty. After graduation, students are required to return to their home countries and contribute to the development of their national economies. This paper reviews the usefulness of international education cooperation for human capital development in the Africa–China context. The study examines China's experience with haigui and identifies lessons for Africa. The paper argues that a more intentional, incentive-driven, and standalone action plan for higher education could help both sides with national branding and enhance future policy and industry development. The results will have a far-reaching, sustainable, and strategic impact on regional integration, industrial development, and diplomatic relations.

Continental crust growth during the evolution of accretionary orogens: insights from the early Paleozoic granitoids in the Western Kunlun orogen, Northwest China

Accretionary orogens are the primary sites for continental growth, but the rate and amount of crust generation throughout its evolution are poorly constrained. In this contribution, our new results about the genesis of two intermediate-felsic plutons are combined with a compiled granitoid dataset to evaluate the amount and rate of crustal growth throughout the evolution of the Western Kunlun orogen, which is a typical accretionary orogen associated with the consumption of the Proto-Tethys during the early Paleozoic. The ca.446 Ma Sanshili pluton was formed through interactions between metasomatized mantle wedge-derived oxidized magmas and the lower arc crust, as indicated by high whole-rock Mg#, high Ce4+/Ce3+ ratios (308–861) of ca.446 Ma zircons, and the existence of inherited zircons with ages of 546–472 Ma. The Yirba dioritic to granodioritic pluton was emplaced at 474 ± 3 Ma. Samples from the Yirba pluton are characterized by high K2O content, higher Mg# (40–49) than pure crustal melts, slightly higher Y + Nb concentrations, and high Th/Nb ratios, and slightly enriched to depleted Hf–Nd isotopes. Combined with the presence of the 502–531 Ma inherited zircons, the Yirba pluton is suggested to from through differentiation of the metasomatized lithospheric mantle derived-magmas beneath the juvenile intra-oceanic arc in combination with crustal reworking during regional extensions. The Yirba pluton, together with contemporary A1-type granites, thus marks an extension event at ca. 475 Ma in the Western Kunlun orogen. The compiled dataset reveals three magmatic flare-ups at 530–500 Ma, 480–470 Ma, and 445–430 Ma, corresponding to two slab rollback events and the slab break-off after the final closure of the Proto-Tethys. The three episodes of more intensive magmatism are associated with more radiogenic Hf–Nd isotopes and increased Nb/La and Nb/Y ratios, indicating more contributions from intraplate-like sources during lithospheric extensions. Meanwhile, element ratios (La/Yb, Sm/Yb, and Sr/Y) that are sensitive to crustal thickness are also elevated. These phenomena are consistent with rapid juvenile crust generation during extensional stages of accretionary orogens. Our study has also shown that the rate of new crust production is quite uniform for different extensional events. The crustal generation rate during slab break-off is much higher than that during slab rollback, although the proportions of juvenile inputs in granitoids formed during slab rollback are relatively higher. This may reflect extra inputs from partial melting of oceanic slabs and subducting sediments like those in continental collision zones and/or rapid asthenospheric upwelling coupled with enhanced crust reworking during slab break-off.