Crustal Growth Rates Research Articles

Constraints on the growth and evolution of continental crust in the NE Cathaysia Block: insights from detrital zircon U–Pb ages and Hf–O isotopic analyses in Tingjiang sediments

Fluvial detrital zircons provide crucial insights into crustal evolution in the early Precambrian. We used U–Pb geochronology and the Hf–O isotopic compositions of detrital zircons from the Tingjiang River to determine the provenance and continental crustal evolution of the NE Cathaysia Block. The zircon U–Pb ages show seven major populations at 177–105, 262–200 and 520–376 Ma, with striking peaks at c. 422, 775–606, 1457–836, 2042–1710 and 2661–2300 Ma, corresponding to documented tectono-thermal events in the South China Block. Episodic magmatism was the response to the formation and break-up of the Columbia and Rodinia supercontinents. The episode at 422 Ma matches with the ages of widespread early Paleozoic intraplate orogenic events in the South China Block. The isotopic signatures of Hf and O in the detrital zircons indicate that the majority of the Precambrian zircons likely originated from remelted ancient continental crust, with contributions from juvenile mantle-derived magmas. The Phanerozoic zircons, by contrast, were formed through the partial melting of recycled crustal material. Analysis of crustal growth rates, based on the two-stage Hf model ages, suggests a significant presence of juvenile crustal growth during the Paleoproterozoic era. Specifically, it is estimated that c. 40 and 90% of the present crust within the NE Cathaysia Block was formed at c. 2.3 and 1.6 Ga, respectively.

Evaluation of plume-induced continental crust growth rate in early Earth: Insight from integrated petrological-thermo-mechanical modeling

The origin of Earth’s felsic continental crust remains a mystery. The generation of felsic continental crust requires a two-stage partial melting from original mantle sources. There are two hypotheses for the continental crust generation in the early Earth. One is the subduction-related magmatism, e.g., island arcs, which produces intermediate to felsic magma that constitutes the early buoyant continental crust. The other is the magmatism induced by the mantle plume that creates thick basaltic crust and finally the continental crust. However, there is controversy about the origin of plate tectonics, which is an obstacle for simply applying the subduction-induced model in the early Earth. On the other hand, the efficiency of mantle plume-induced continental crust growth remains unknown. In this study, we develop a new numerical model, integrating the petrological-thermo-mechanical model with melt migration and crystallization, to evaluate the efficiency of continental crust production by mantle plumes in Earth’s history. Our results indicate that mantle plumes are considerably more effective for continental crust generation in the hot early Earth than that in the present Earth. The contribution of plume-induced continental crust growth may be greatly promoted by the possible high frequency of mantle plume generation in the early Earth than the present.

Geochronology and Sr-Nd-Pb-Hf-O isotopes of Neoproterozoic orthogneisses in the Jiamusi Block, NE China: Implications for tectonic origin and secular crustal evolution

There is a considerable debate as to when and how the continental crust has evolved to its present state. Existing studies of crustal evolution have focused on large cratons, whereas microcontinents within accretionary orogenic belts have been conspicuously neglected. The controversial definition of tectonic origins and lack of Precambrian basement rocks of microcontinents, lead to an equivocal issue of their secular crustal evolution processes. Here we present zircon U-Pb ages and Hf-O isotopes, as well as whole-rock elemental and Sr-Nd-Pb-Hf isotopic data for the newly discovered Neoproterozoic orthogneisses from the Jiamusi Block of NE China in the easternmost Central Asian Orogenic Belt (CAOB). LA-ICP-MS U-Pb dating of zircons from the orthogneisses recorded two episodes of magmatism at 896–886 Ma and 752–726 Ma. Combined with zircon Hf-O isotopes and REE patterns, the peak of the late Pan-African metamorphism is proved to occur at 566–565 Ma, demonstrating the linkage between the Jiamusi Block and the Kuunga-Pinjarra interior orogen of East Gondwana. In conjunction with compiled zircon U-Pb-Hf isotopic data of Neoproterozoic-Mesozoic granitoids, a new crustal evolution model has been established for the Jiamusi Block, which defines a continuous rather than an episodic crustal growth pattern during the Neoarchean to Neoproterozoic, as well as four stages of crustal reworking at 940–880 Ma, 780–660 Ma, 560–460 Ma, and 340–240 Ma. The enhanced and reduced rates of crustal growth during the progressive period are related to the assembly-breakup and collision phases of supercontinent cycles, respectively. Our study along with previous researches on eastern CAOB not only highlights that the Phanerozoic accretionary orogen underwent diverse forms of crustal growth with most of the continental crust formed during the Precambrian, but also provides an example to show the heterogeneity of the lower continent and the complexity of global secular crustal evolution.

Enhanced arc magmatic productivity of the Western Pacific island arcs deduced from gravity-derived arc crustal growth rates

Island arcs are postulated as the juvenile components that contribute to the growth of continental crust. Growth rates of arc crusts were previously computed using crustal thicknesses derived from seismic data. Consequently, crustal growth rates of oceanic island arcs are also constrained by the limited seismic data availability. This work presents the first comparison of gravity-derived magmatic growth rates of Western Pacific oceanic island arcs. We used the statistical correlation between Bouguer anomalies and seismic-derived crustal thicknesses to generate an empirical formula. The new empirical formula was utilized to estimate the crustal thicknesses of oceanic island arcs using Bouguer anomalies from the EGM2008 global gravity model. The resulting crustal thicknesses were employed to compute the magmatic growth rates of western Pacific island arcs and the Philippine island arc system. The latest magmatic growth rate estimates show that the magmatic productivity of Western Pacific island arcs, which are directly associated with Pacific Plate subduction, is significantly higher (28–60 km3/km/m.y). The growth rate of the Pacific island arcs is higher compared to the magmatic growth rate computed for the other oceanic island arcs (12–25 km3/km/m.y), which are derived from the subduction of other oceanic lithospheres (i.e., the Philippine Sea Plate; Caribbean Sea Plate; and Eurasia-South China Sea slabs). This is attributed to the variation in the ages of the subducting plates. The Pacific Plate, being older, is associated with higher degrees of serpentinization and sediment cover, which introduce more volatiles inducing more robust partial melting of the mantle wedge.

A Positive Feedback Between Crustal Thickness and Melt Extraction for the Origin of the Martian Dichotomy.

A North/South difference in crustal thickness is likely at the origin of the Martian dichotomy in topography. Recent crustal thickness maps were obtained by inversion of topography and gravity data seismically anchored at the InSight station. On average, the Martian crust is 51-71km thick with a southern crust thicker by 18-28km than the northern one. The origin of this crustal dichotomy is still debated although the hypothesis of a large impact is at present very popular. Here, we propose a new mechanism for the formation of this dichotomy that involves a positive feedback between crustal growth and mantle melting. As the crust is enriched in heat-producing elements, the lid of a one-plate planet is hotter and thinner where the crust is thicker, inducing a larger amount of partial melt below the lid and hence a larger rate of melt extraction and crustal growth. We first demonstrate analytically that larger wavelength perturbations, that is, hemispherical perturbations, grow faster because smaller wavelengths are more attenuated by thermal diffusion. We then use a parameterized thermal evolution model with a well-mixed mantle topped by two different lids characterized by their thermal structures and thicknesses to study the growth of the crust in the two hemispheres. Our results demonstrate that this positive feedback can generate a significant crustal dichotomy.

Did the Neoproterozoic Revolution Extend to the Deep Mantle?

Did the Neoproterozoic Revolution Extend to the Deep Mantle?

A linked evolution for granite-greenstone terranes of the Pilbara Craton from Nd and Hf isotopes, with implications for Archean continental growth

Granite-greenstone terranes, such as in the Pilbara Craton (Western Australia), record the growth and stabilisation of Archean (>2.5 Ga) continental crust. Yet, uncertainty surrounds the formation of the silica-rich portions of these terranes, important for preservation of continental lithosphere, specifically whether this involved reprocessing of older continental nuclei over hundreds of millions of years, or rapid differentiation of juvenile mantle additions, as preserved in the greenstone belt volcanic sequences. In part, the uncertainty reflects difficulties with establishing the isotope evolution of the early Archean mantle, critical for ascertaining the time gap between the extraction of new crust and granitic emplacement in Archean cratons. To investigate the formation of silica-rich Archean crust, we report Hf and Nd isotope data for 46 mafic–ultramafic samples and zircon Hf isotope data for 83 felsic igneous rocks from the Pilbara Craton, selected to be representative of the major magmatic episodes from 3.56 to 2.72 Ga. The strikingly similar secular isotope trends defined by mafic and felsic rocks reveal a linkage between mantle and crustal processes throughout the history of the craton. From 3.56 Ga to 3.12 Ga, craton evolution was dominated by the transformation of juvenile mantle derived inputs into felsic igneous rocks on short timescales, thus recording sustained continental growth over 400 million years. Incorporation of older crust by felsic magmas was minor during this interval. Evolution toward sub-chondritic Nd and Hf after collision of the East and West Pilbara terranes at 3.1 Ga signals greater involvement of pre-existing crust in magma generation, possibly by recycling of crustal material into mantle source regions or by enhanced reworking of older, thickened cratonic lithosphere. Mafic–ultramafic rocks provide no evidence for anomalous or strongly depleted mantle domains in the Paleoarchean. Rather, the flat zircon εHf–time array indicates extraction of continental materials from mildly super-chondritic mantle from ca. 3.6 to 3.12 Ga and attests to a distinctive style of crust production that operated in the Archean. This study highlights the importance of comparing the mantle and crustal isotope records in order to reconstruct the crustal growth rates in ancient terranes.

Along-strike island-arc crustal growth rate estimation: case study of the Izu–Bonin–Mariana subduction system

SUMMARYThe island-arc crustal growth rate (IACGR) is the island-arc magma production volume per 1 km width along the arc strike within one million years, and its variations are highly related to slab dehydration and mantle wedge melting. A novel method that includes Earth density modelling, gravity forward and inversion, and arc crustal growth thickness integration is designed to estimate the IACGR. This method can not only estimate the IACGR along the entire arc length but also assess the crustal growth of both remnant and active arcs. Therefore, the estimation result has high coverage and low uncertainty. Here, the Izu–Bonin–Mariana (IBM) subduction zone is taken as a case study region. The estimated time-averaged IACGR along the IBM arc changes between 16 and 59 km3 km−1 Myr−1, with a mean value of 40 km3 km−1 Myr−1, and this result matches the findings of previous studies well. The uncertainties due to crustal thickness inversion are relatively larger than those from flow line reconstruction. The rate results of the Mariana part have lower uncertainties than those of the Izu–Bonin parts since the arc boundaries can be delineated more accurately. The IACGR of the region where a plateau approaches the trench tends to be overestimated because the collision of the plateau with the island arc thickens the island arc crust and bias the uniform pre-existing crustal thickness assumption.

U-Pb geochronology of the Silurian-Devonian Bega Batholith, south-eastern Australia: Insights into the origin and development of I-type granites

Earth’s continental crust is primarily composed of buoyant, felsic igneous (granitic) material that has been extracted from the mantle along convergent plate margins. Establishing the timescales of subduction-related granite batholith assembly is key to understanding the processes of magma generation, segregation, and transport that define the dynamics and rates of crustal growth. The ‘Cordilleran’ Bega Batholith is the largest I-type granite batholith in the Lachlan Fold Belt (LFB) of south-eastern Australia. The product of accretionary orogenesis along the Terra Australis Orogen, it has been extensively characterised by isotopic and geochemical studies yet lacks a robust geochronological framework. We present new ID-TIMS and SHRIMP U-Pb zircon ages for twenty-two plutonic rocks of the Bega Batholith. This geochronological survey indicates a prolonged duration for I-type magmatism, with crystallisation ages ranging from ca. 420 Ma in the west, to 385 Ma in the eastern Bega Batholith. These I-type granites collectively occupy ∼90,000 km3 and were emplaced over a period of ∼20–35 Ma, corresponding to a magma production rate of ∼8–15 km3/Ma km−1, considerably lower than that of S-type granites of the region and other subduction-related granite terranes globally. Fundamentally, the temporal overlap between the Bega I-type granites and S- and A-type granites also argues against a hiatus between each phase of granite magmatism in the LFB, suggesting a continuum between the granite types and derivation from common source components. This new geochronological data provides the first comprehensive compilation of U-Pb ages from across the Bega Batholith, establishing initial constraints on the development and evolution of I-type magmatism in south-eastern Australia. Our results demonstrate that I-type granite petrogenesis is linked with crustal growth processes, requiring the modification of global crustal growth curves during the Phanerozoic to account for new continental crust generated within I-type granite terranes of the Paleo-Pacific Gondwanan margin.

A crustal growth model for the eastern Central Asian Orogenic Belt: Constraints from granitoids in the Songnen Massif and Duobaoshan terrane

The crustal growth and reworking processes of accretionary orogen such as the Central Asian Orogenic Belt (CAOB) have been a controversial issue. Here, we present in situ zircon U–Pb and Lu–Hf isotopic data for granitoids from a microcontinent (the Songnen Massif) and an arc terrane (the Duobaoshan arc terrane), which generally represent two main crustal components in the eastern CAOB to establish a crustal growth model for an accretionary orogen and to trace the influence of the assembly and breakup of supercontinents on crustal evolution in an accretionary orogen. Neoproterozoic–Mesozoic granitoids distributed in the Songnen Massif show a step-like crustal growth pattern over time with three major periods of development: Paleoproterozoic crustal growth at 2.2–1.8 Ga, Mesoproterozoic growth at 1.6–1.0 Ga, and a third pulse of growth at 0.85–0.6 Ga, along with two short pauses at 1.8–1.6 Ga and 1.0–0.85 Ga. The assembly and collision phases of supercontinents corresponded to the enhanced and degressive crustal growth rates of the Songnen Massif, respectively, suggesting that the supercontinent cycles are responsible for the episodic crustal growth pattern in the region. Crustal reworking of the Songnen Massif occurred during 1000–180 Ma, with a fluctuation at 800–600 Ma, which provided a major contribution to the isotopic heterogeneity of lower continental crust. Isotopic compositions of granitoids from the Duobaoshan arc terrane located between the Xing'an and Songnen massifs, together with those of granitoids from other microcontinents, suggest that most of the continental crust beneath the microcontinents in the eastern CAOB generated during the Precambrian, whereas a significant amount of lateral crustal accretion occurred in continental arc settings during orogenies and amalgamation of microcontinents during the Phanerozoic.

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.

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.

PHILCRUST3.0: New constraints in crustal growth rate computations for the Philippine arc

A revised crustal thickness map for the Philippine island arc, PHILCRUST3.0, has been generated using new gravity data from the EGM2008. The gravity-derived crustal thickness is compared with crustal thickness estimates obtained using the Sr/Y ratios. PHILCRUST3.0 shows that crustal thickness in the Philippines varies from 13 to 33 km. The Philippine arc appears to be at its thinnest in areas underlain by ophiolites and young magmatic arcs. The resulting crustal thickness values are used to revisit the growth rates of the Philippine arc from magmatic and amagmatic contributions. Arc magmatism contributes more significantly to the growth of Philippine crust with rates from specific volcanoes varying from 5 to 35 km3/km/m.y. Despite being relatively young, magmatism associated with the volcanoes of the East Philippine Arc displayed a higher growth rate (32 km3/km/m.y.) compared to volcanoes belonging to older magmatic arcs in the archipelago. This is attributed to the more hydrated oceanic lithosphere subducting beneath the Philippine Trench. PHILCRUST3.0 provides the most complete crustal thickness map of the Philippines to date. This will enable the computation of crustal growth rate in areas within the Philippines where point gravity or geochemical data is not available.

Hidden Eoarchean crust in the southwestern Central Asian Orogenic Belt

U-Pb and Hf-isotope analyses of zircon xenocrysts from drilling-sampled Carboniferous volcanic rocks suggest the presence of unexposed Eoarchean crust beneath the Junggar Basin (NW China), southwestern Central Asian Orogenic Belt (CAOB). The oldest zircon population with U-Pb ages of 3.8 Ga shows chondritic εHf(t) of −0.7 to +0.7, and Hf model ages of 3900–3952 Ma (TDM) and 3973–4062 Ma (Tcrust). Three slightly younger populations at 3.7, 3.62 and 3.45 Ga have εHf(t) of −5.7 to +2.4, TDM of 3.6–3.9 Ga and Tcrust of 3.7–4.1 Ga. The youngest xenocrysts yield U-Pb ages of 2.55 Ga with εHf(t) values of +3.7 to +8.0. Crustal mineral inclusions and the trace-element compositions of all these zircons show that they probably crystallized from granitic magmas. The observation of deeply hidden Archean crust significantly older than the exposed Phanerozoic upper crust suggests that the juvenile origin in CAOB may be overestimated, and the study of crustal growth rates through time for young orogens will require revision. By comparing the Hf isotopic signatures of ancient zircons (>3.4 Ga) worldwide, we infer that there may have been a great change in early crustal evolution at the Hadean–Archean transition (~3.9 Ga), possibly linked to the Late Heavy Bombardment (LHB).

Near/far side asymmetry in the tidally heated Moon

Using viscoelastic mass spring model simulations to track heat distribution inside a tidally perturbed body, we measure the near/far side asymmetry of heating in the crust of a spin synchronous Moon in eccentric orbit about the Earth. With the young Moon within ≲8 Earth radii of the Earth, we find that tidal heating per unit area in a lunar crustal shell is asymmetric due to the octupole order moment in the Earth's tidal field and is 10 to 20% higher on its near side than on its far side. Tidal heating reduces the crustal basal heat flux and the rate of magma ocean crystallization. Assuming that the local crustal growth rate depends on the local basal heat flux and the distribution of tidal heating in latitude and longitude, a heat conductivity model illustrates that a moderately asymmetric and growing lunar crust could maintain its near/far side thickness asymmetry but only while the Moon is near the Earth.

Improving confidence in ferromanganese crust age models: A composite geochemical approach

Accurate age models for marine ferromanganese (Fe-Mn) crusts are essential to understand paleoceanographic changes and variations in local environmental factors affecting crust growth rate and their lateral continuity. However, no absolute method exists for dating these deposits beyond the age of 10 Myr, which requires the combination of a number of approaches. Here, we present a composite age model for a 15 cm thick Fe-Mn crust sample obtained by unique core drilling using a remotely operated vehicle at a water depth of 1130 m, on the summit of Tropic Seamount, in the north-east Atlantic. The age model is based on cross-validation of laser-ablation U-Pb dating, Co-chronometry and Os isotopes. These enable robust calibration of the age-depth model using the Bayesian statistical modelling of Markov Chain Monte Carlo (MCMC) simulations. The results show that this Fe-Mn crust commenced growth in the Late Cretaceous between 73 and 77 Ma, and grew at a rate between 1 and 24 mm/Myr, averaging 4 mm/Myr. The phosphatised carbonate substrate, capping Tropic Seamount and underlying most of the Fe-Mn crusts, yields a U-Pb age of 84 ± 4 Myr, and provides the upper age limit for the model. Less radiogenic excursions of 188Os/187Os in the vertical profile through the crust permit the identification of key inflection points in the Os isotope seawater curve at the Eocene-Oligocene and Cretaceous-Paleogene transitions. Growth rates estimated from the empirical Co-chronometer are combined with the age envelope defined by the Os data and used to validate the MCMC simulations. The model identifies five hiatuses that occurred during the Pliocene (2.5 ± 1.9–5.3 ± 1.7 Ma), Early Miocene (16 ± 1–27 ± 2 Ma), Oligocene (29 ± 2–32 ± 1 Ma), Eocene (41 ± 2–52 ± 0.6 Ma), and the Late Paleocene (55 ± 1–59 ± 1.4 Ma). A major phosphatisation event affecting the Fe-Mn core can be dated to the Late Eocene (38 ± 1.2 Ma), which coincides with a recorded change in the global oceanic system, from warm and sluggish circulation to cold and vigorous thermohaline-driven meridional overturn at the onset of Antarctic glaciation.

Step-like growth of the continental crust in South China: evidence from detrital zircons in Yangtze River sediments

Detrital zircons from nine river sand samples from the upper, middle and lower streams of the Yangtze River (the world's third largest river) and its two largest tributaries, the Han and Jialing rivers have been analyzed for U–Pb–Lu–Hf–O isotope compositions. Zircons from the upper Yangtze River cluster in age groups at 0–100, 200–300, 400–500, 700–1000, 1800–1900 and 2300–2500 Ma, with a marked peak at 41 Ma diagnostic of magmatism on the Tibetan Plateau. Zircons from the middle and lower Yangtze River and its tributaries exhibit broadly similar age groups at 100–300, 400–500, 700–900, 1800–2000 and 2300–2700 Ma, except for the lack of Cenozoic ages.The Yangtze River catchment is covered by thick Phanerozoic sedimentary rocks and so Archean-aged zircons are likely to be under-represented in modern river sands. We therefore applied the approach of Dhuime et al. (2012) to calculate a crustal growth curve for South China, and the resultant curve has two inflections. The older inflection at ~2.8 Ga is slightly younger than that of Dhuime et al. (2012), suggesting the onset of plate tectonics in the Yangtze Craton. The younger inflection at ~1.8 Ga appears to mark the onset of another period of relatively high crustal growth rate in South China. This period of increased crustal growth rate in the Mesoproterozoic is coeval with the breakup of the supercontinent Columbia, suggesting that the Mesoproterozoic crustal growth in South China may be related to supercontinent dispersal.Comparison with global crustal growth curves based on detrital zircons highlights the distinct step-like pattern of crustal growth in South China. This emphasizes the potential of comparing regional with global crustal growth curves, and the changes in the rates of crustal growth in South China appear to have been controlled by changes in regional geodynamics. The maximum δ18O values in the zircons analyzed increase markedly at the end of the Archaean, and these increases therefore accompany the estimated increases in atmospheric oxygen at that time. It is therefore suggested the atmospheric O2 levels were associated with increased crustal weathering, the development of more elevated δ18O sediments and their increasing incorporation in the generation of crustally derived magmas from ca. 2.5 Ga.

The Tectonics of the Altaids: Crustal Growth During the Construction of the Continental Lithosphere of Central Asia Between ∼750 and ∼130 Ma Ago

The largest mountain belt in Central Asia (∼9 million km2) is called the Altaids. It was assembled between ∼750 and ∼130 Ma ago around the western and southern margins of the Siberian Craton, partly on an older collisional system (the “Urbaykalides”). Geological, geophysical, and geochemical data—mostly high-resolution U-Pb ages—document the growth of only three arc systems in Central and Northwest Asia during this time period, an interval throughout which there were no major arc or continental collisions in the area. While the Altaids were being constructed as a Turkic-type orogen, continental crust grew in them by 1/3 of the global total. The Altaids thus added some 3 million km2 to the continental crust over a period of 0.6 billion years, typical of Phanerozoic crustal growth rates.

Interaction between mantle-derived magma and lower arc crust: quantitative reactive melt flow modelling using STyx

Abstract The magmatic processes occurring in the lowermost arc crust play a major role in the evolution of mantle-wedge-derived melt. Geological evidence indicates that mantle-derived magmas and in-situ products of lower crust partial melting are reacting in a pervasive melt system and are eventually extracted towards higher levels of the crust. Resolving the relative contribution of mantle-derived magma and partial melting products of pre-existing crust is essential to: (1) quantify crustal growth rate; (2) better understand the compositional range of arc magmatic series; and (3) constrain the chemical differentiation of the lower crust. In this study, we present STyx, a new modelling tool, coupling melt and heat flow with petrology to explore the dynamics of storage, transfer and hybridization of melts in complex liquid/rock systems. We perform three models representing a magmatic event affecting an amphibolitic lower arc crust in order to quantify the relative contribution between partial melting of the pre-existing crust and fractional crystallization from mantle-derived hydrous-magma. Our models demonstrate that most of the differentiated arc crust is juvenile, deriving from the differentiation of mantle melts, and that pre-existing crust does not significantly contribute to the total thickness of magmatic products.

Old Continental Crust Underlying Juvenile Oceanic Arc: Evidence From Northern Arabian‐Nubian Shield, Egypt

AbstractThe Neoproterozoic Arabian‐Nubian Shield (ANS) is the best preserved and the largest exposed Neoproterozoic juvenile crust on Earth. While the lithology and early Sr and Nd isotopic data demonstrate that the ANS crust is overwhelmingly juvenile, pre‐ANS old zircon crystals have been increasingly recognized in the ANS igneous and sedimentary rocks, casting doubt on the “juvenility” of the ANS crust. In order to understand the origin of the old continental materials in the ANS and its roles in generation of juvenile oceanic arcs, we carry out for the first time an integrated in situ analysis of zircon U‐Pb age and Hf‐O isotopes for greywacke and felsic volcanic cobble samples from the Atud Formation in the Eastern Desert of northwestern part of the ANS. Our data indicate that the Atud Formation was deposited between ca. 720 and 700 Ma, concurrent with the production of oceanic arcs in the ANS. The Atud greywacke was derived from the erosion of a proximal arc terrane that contains numerous old continental crust materials. We identify for the first time a 755‐Ma felsic volcanic cobble from the Atud Formation that is derived from old continental materials during juvenile crust production, suggesting presence of an old continental crust substrate that underlies the ANS. Our work demonstrates that reworking of old continental crust played important roles in generation of oceanic arcs in the northwestern ANS that is likely much less juvenile than previously thought. Thus, the crustal growth rates calculated based on estimates of temporal island arc development need to be revised.