ORCID Profile
0000-0003-4264-3701
Current Organisations
Queen's University
,
Curtin University
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Publisher: Springer Science and Business Media LLC
Date: 20-04-2021
Publisher: Elsevier BV
Date: 05-2012
Publisher: Tektonika
Date: 27-03-2023
DOI: 10.55575/TEKTONIKA2023.1.1.32
Abstract: Higher than average thermobaric ratios (temperature ressure) of metamorphic rocks and abundant ‘dry’ ferroan magmatism including massif anorthosite suites are two enigmatic features of the mid-Proterozoic (1.85–0.85 Ga) that have unclear origins. It has been proposed that elevated mantle temperatures due to insulation under the Columbia supercontinent, and/or to plate slowdown, combined with thin lithosphere, led to high continental geothermal gradients, high-temperature metamorphism, and an increase in dry, ferroan magmatism. Geodynamic modelling predicts that continental subduction zones at mid-Proterozoic mantle potential temperatures (80–150 °C hotter than at present) would exhibit key differences to the Phanerozoic, critically, extensive slab rollback combined with greater volumes of decompression melting of the asthenosphere would lead to wide regions of back-arc magmatism. We posit that these hot, wide continental back-arcs can effectively explain the abundance of ferroan magmatism, anorthosite suites, and high T/P metamorphism. Our model negates the need for extra mantle heating from supercontinental insulation or plate slowdown and shows that the tectonic regime of the mid-Proterozoic was a transitional phase between those of the Archean (likely comprising peel-back tectonics and episodic subduction) and the Phanerozoic (comprising deep continental subduction), and which could have resulted solely from secular cooling of the mantle.
Publisher: Elsevier BV
Date: 05-2019
Publisher: Elsevier BV
Date: 04-2008
Publisher: American Journal of Science (AJS)
Date: 06-2011
DOI: 10.2475/06.2011.03
Publisher: Elsevier BV
Date: 07-2016
Publisher: Elsevier BV
Date: 06-2021
Publisher: Wiley
Date: 23-06-2020
DOI: 10.1002/GJ.3899
Publisher: Association of Environmental and Engineering Geologists
Date: 08-2008
Publisher: Elsevier BV
Date: 08-2014
Publisher: Elsevier BV
Date: 07-2019
Publisher: Elsevier BV
Date: 05-2011
Publisher: Geological Society of London
Date: 21-07-2022
DOI: 10.1144/JGS2022-050
Abstract: When disturbed, dynamic emergent systems, such as tectonics on Earth, may transition from one stable state to another if the perturbation is sufficiently large. Here, we identify such state shifts through examination of statistically significant change points in the time series of metamorphic pressure–temperature and cooling rate data. Change points occur in the mid-Paleoproterozoic, the Mesoproterozoic, the early and late Paleozoic and the Cenozoic. To compare the timing of change points with mantle geodynamics, we interrogate the time series of calculated mantle potential temperature, which yields a statistically significant drop of °C in the mid-Paleoproterozoic, indicating a change in the mechanism of mantle cooling. We interpret changes in the mid-Paleoproterozoic to relate to the global emergence of stable subduction, orogenesis associated with the formation of the Nuna megacontinent, and slab breakoff, consistent with the operation of a distinctive style of Proterozoic plate tectonics. By contrast, changes from the dawn of the Cambrian onward may relate to the large volume of sediments supplied to trenches following multiple Cryogenian and Paleozoic glaciations. Sediments acted as a lubricant, allowing deeper subduction, transport of lower continental plates to mantle depths and faster metamorphic cooling rates, features characteristic of modern plate tectonics. Supplementary material: A dataset of metamorphic cooling rates is available at 0.6084/m9.figshare.c.5943418
Publisher: American Association for the Advancement of Science (AAAS)
Date: 30-06-2023
Abstract: Identifying the oldest evidence for the recycling of hydrated crust into magma on Earth is important because it is most effectively achieved by subduction. However, given the sparse geological record of early Earth, the timing of first supracrustal recycling is controversial. Silicon and oxygen isotopes have been used as indicators of crustal evolution on Archean igneous rocks and minerals to trace supracrustal recycling but with variable results. We present Si-O isotopes of Earth’s oldest rocks [4.0 billion years ago (Ga)] from the Acasta Gneiss Complex, northwest Canada, obtained using multiple techniques applied to zircon, quartz, and whole rock s les. Undisturbed zircon is considered the most reliable recorder of primary Si signatures. By combining reliable Si isotope data from the Acasta s les with filtered data from Archean rocks globally, we observe that widespread evidence for a heavy Si signature is recorded since 3.8 Ga, marking the earliest record of surface silicon recycling.
Publisher: Elsevier BV
Date: 07-2012
Publisher: GeoScienceWorld
Date: 16-11-2016
DOI: 10.1130/L479.1
Publisher: Geological Society of America
Date: 18-04-2014
DOI: 10.1130/B30884.1
Publisher: American Geophysical Union (AGU)
Date: 02-2012
DOI: 10.1029/2010TC002853
Publisher: Elsevier BV
Date: 03-2019
Publisher: Springer Science and Business Media LLC
Date: 02-11-2022
DOI: 10.1038/S41467-022-34343-0
Abstract: Earth’s earliest continental crust is dominated by tonalite–trondhjemite–granodiorite (TTG) suites, making these rocks key to unlocking the global geodynamic regime operating during the Archaean (4.0–2.5 billion years ago [Ga]). The tectonic setting of TTG magmatism is controversial, with hypotheses arguing both for and against subduction. Here we conduct petrological modeling over a range of pressure–temperature conditions relevant to the Archaean geothermal gradient. Using an average enriched Archaean basaltic source composition, we predict Ba concentrations in TTG suites, which is difficult to increase after magma generated in the source. The results indicate only low geothermal gradients corresponding to hot subduction zones produce Ba-rich TTG, thus Ba represents a proxy for the onset of subduction. We then identify statistically significant increases in the Ba contents of TTG suites worldwide as recording the diachronous onset of subduction from regional at 4 Ga to globally complete sometime after 2.7 Ga.
Publisher: American Geophysical Union (AGU)
Date: 18-08-2021
DOI: 10.1029/2021GL093312
Abstract: 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.
Publisher: American Geophysical Union (AGU)
Date: 10-05-2022
DOI: 10.1029/2022GL098541
Abstract: Sediment relamination in subduction zones is posited to be important for the compositional evolution, physical structure and material recycling of the Earth. Despite support from numerical experimental modeling and geophysical observation, magmatic evidence for relamination is rare and difficult to identify in ancient and modern convergent systems. Here we report newly identified ca.32–27 Ma adakite‐like granites with high δ 18 O values (up to 10.38‰) from the Ailaoshan‐Red River (ASRR) shear zone in western Yunnan (SE Tibet). Their geochronological and compositional data strongly exhibits significant contributions from Permian‐Eocene sedimentary rocks in the lower crust (30–45 km). Our study provides further evidence that the lower crust may be partially composed of more felsic lithologies likely originating from rapid supracrustal material recycling via diapiric relamination of (meta)sedimentary material during Cenozoic‐age continental subduction. The ASRR adakite‐like granites thus represent clear magmatic evidence for sediment relamination in a subduction system.
Publisher: Elsevier BV
Date: 11-2016
Publisher: Springer Science and Business Media LLC
Date: 29-08-2022
Publisher: California Digital Library (CDL)
Date: 31-01-2022
DOI: 10.31223/X55P64
Abstract: Forearc basins preserve the geologic record relating strictly to arc magmatism. The provenance of forearc sediment can be used to differentiate periods of crustal growth, accretion, and destruction, enhanced magmatism, advancing and retreating subduction slabs, delamination, etc. All these tectonic events systems predict differing degrees of sedimentary reworking of the older forearc units. Additionally, Hf isotopes of zircon can be used to evaluate the degree of continental reworking that occurs in the arc system. In this paper, we evaluate the changes in a long-lived subduction system using detrital zircon U-Pb and Hf data from forearc units in northern Honshu, Japan that span in age from the Silurian Period to the present from the forearc provenance of the Japanese subduction system. Our data demonstrate a series of dominant age peaks (430 ± 20, 360 ± 10, 270 ± 20, 184 ± 12, 112 ± 22, and 7 ± 7 Ma) and a progressive loss of the older zircon populations. Zircon Hf data reveal three discrete shifts that correspond to differing degrees of isotopic enrichment and correlate with changes in the dominant zircon age peaks. Additionally, each temporal isotopic shift is associated with isolation of the older sedimentary packages wherein no detrital zircon from the previous stages are observed in subsequent stages. We propose these shifts provide evidence for rapid shifts in arc tectonics including: magmatic flare-ups, producing the dominant peaks protracted tectonic erosion progressively removing older sources of zircons reveals a late Carboniferous event triggering the complete removal of the Precambrian crust and the Cretaceous melting of the entire Permian arc crust, likely related with the subduction of the mid-oceanic ridge separating the Izanagi and Pacific plates.
Publisher: American Geophysical Union (AGU)
Date: 02-02-2019
DOI: 10.1029/2018GL080579
Abstract: Exhumation of plutonic systems is driven by a range of mechanisms including isostatic, tectonic, and erosional processes. Variable rates of plutonic exhumation in active subduction systems may be driven by idiosyncrasies of regional geology or by first‐order tectonic features. We report new age, isotope, and low‐temperature thermochronology constraints of granitoids from the Hida Mountains of central Japan that constrain the highest rates and magnitude of plutonic rock exhumation within the Japan and one of the highest worldwide. This extreme exhumation is centered on the apex of a lithospheric scale anticlinorium associated with the subduction of the Izu‐Bonin oceanic arc. The spatial and temporal relationship between the exhumation of these Pleistocene plutons and the subducting/accreting Izu‐Bonin oceanic arc links the plate‐scale geodynamics and regional exhumation patterns. Identifying thermochronological anomalies within magmatic arcs provides an opportunity to identify ancient asperities previously subducted and responsible for rapid exhumation rates within ancient subduction systems.
Publisher: Elsevier BV
Date: 05-2022
Publisher: Wiley
Date: 15-05-2018
DOI: 10.1111/TER.12338
Publisher: Elsevier BV
Date: 2022
Publisher: Elsevier BV
Date: 09-2010
Publisher: Elsevier BV
Date: 10-2014
Publisher: Elsevier BV
Date: 11-2017
Publisher: Geological Society of America
Date: 21-03-2014
DOI: 10.1130/G35363.1
Publisher: Elsevier BV
Date: 06-2016
Publisher: Geological Society of America
Date: 06-06-2013
DOI: 10.1130/G34520.1
Publisher: Geological Society of London
Date: 07-11-2014
DOI: 10.1144/SP389.14
Publisher: Elsevier BV
Date: 05-2015
Publisher: Elsevier BV
Date: 10-2016
Publisher: American Geophysical Union (AGU)
Date: 18-11-2021
DOI: 10.1029/2021GL096049
Abstract: Subaerial continental crust plays a fundamental role in modulating the composition of the ocean, atmosphere, and biosphere, but the timing and rate of continental emergence above sea level remain unclear. Here, we use the zircon oxygen isotopic compositions of early Paleoproterozoic metasediment‐derived granitoids from the southwestern Yangtze Block to constrain the rapidity of continental emergence. Statistical analyses of compiled igneous and detrital zircon oxygen isotopic database show a rapid increase in zircon δ 18 O at ∼2.36 Ga. We suggest that this isotopic shift is best explained by a significant increase of continental freeboard between ∼2.43 and ∼2.36 Ga due to the increasing strength of the continental lithosphere since the late Archean, concomitantly yielding a high‐δ 18 O sedimentary reservoir. Subsequent melting of these high‐δ 18 O sediments in a variety of tectonic regimes results in high zircon δ 18 O.
Publisher: Geological Society of London
Date: 18-05-2024
Abstract: The metamorphic conditions of the Natal Metamorphic Province (NMP) have been the focus of previous studies to assist with Rodinia reconstructions but there are limited constraints on the age of metamorphism. We use a combination of modern techniques to provide new constraints on the conditions and timing of metamorphism in the two southernmost terranes: the Mzumbe and Margate. Metamorphism reached granulite facies, 780–834°C at 3.9–7.8 kbar in the Mzumbe Terrane and 850–892°C at 5.7–6.1 kbar in the Margate Terrane. The new pressure and temperature constraints are supportive of isobaric cooling in the Margate Terrane as previously proposed. Peak metamorphism of the two terranes is shown to have occurred c. 40 myr apart, which contrasts strongly with previous assumptions of coeval metamorphism. While the age of peak metamorphism of the Margate Terrane (1032.7 ± 4.7 Ma) coincides with the tectonism and magmatism associated with the emplacement of the Oribi Gorge Suite ( c. 1050–1030 Ma), the age of metamorphism of the Mzumbe Terrane (987.4 ± 8.1 Ma) occurs c. 30–40 myr after tectonism is previously thought to have finished. We propose that models of advective cooling during transcurrent shearing can explain the metamorphic conditions and timing of the NMP.
Publisher: Springer Science and Business Media LLC
Date: 29-01-2018
Publisher: Elsevier BV
Date: 08-2015
Publisher: Elsevier BV
Date: 05-2023
Publisher: Springer Science and Business Media LLC
Date: 14-10-2021
DOI: 10.1038/S41467-021-26322-8
Abstract: How serpentinites in the forearc mantle and subducted lithosphere become involved in enriching the subarc mantle source of arc magmas is controversial. Here we report molybdenum isotopes for primitive submarine lavas and serpentinites from active volcanoes and serpentinite mud volcanoes in the Mariana arc. These data, in combination with radiogenic isotopes and elemental ratios, allow development of a model whereby shallow, partially serpentinized and subducted forearc mantle transfers fluid and melt from the subducted slab into the subarc mantle. These entrained forearc mantle fragments are further metasomatized by slab fluids/melts derived from the dehydration of serpentinites in the subducted lithospheric slab. Multistage breakdown of serpentinites in the subduction channel ultimately releases fluids/melts that trigger Mariana volcanic front volcanism. Serpentinites dragged down from the forearc mantle are likely exhausted at km depth, after which slab-derived serpentinites are responsible for generating slab melts.
Publisher: Elsevier BV
Date: 05-2016
Publisher: American Geophysical Union (AGU)
Date: 28-04-2019
DOI: 10.1029/2019GL082313
Abstract: Deducing mechanisms for advance and retreat of magmatic arcs is fundamental to understanding accretionary tectonics and the evolution of continents. However, first‐order explanations of large spatial and long temporal changes in magmatic arcs remain elusive. We present isotopic evidence that Cordilleran magmatic arc systems were controlled by spherical harmonic degree‐2 mantle convection and characterized by two antipodal upwellings bisected by a meridional downwelling. Once established, the meridional “subduction girdle” drives hemispheric slab rollback and remains the locus of Cordilleran oceanic arcs. Continual westward migration of the North and South American continents led to arc advancement and consumption of back‐arc basins, culminating in arc‐continent collisions and reversals of subduction polarity. Continental arcs initiated diachronously as North and South America arrived at the subduction girdle and oceanic arcs were accreted. Systematic patterns in radiogenic isotopes along the Cordilleran system support that slab dynamics are controlled, to first order, by long‐wavelength mantle convection.
Publisher: Research Square Platform LLC
Date: 08-12-2021
DOI: 10.21203/RS.3.RS-986686/V1
Abstract: Diamonds are erupted at Earth’s surface in volatile-rich magmas called kimberlites 1,2,3 . These enigmatic magmas, originating from depths exceeding 150 kilometres in Earth’s mantle 1 , occur in stable cratons and in pulses broadly synchronous with supercontinent cyclicity 4 . Whether their mobilization is driven by mantle plumes 5 or mechanical weakening of cratonic lithosphere 4,6 remains unclear. Here we show that most kimberlites spanning the past billion years erupted approximately 25 million years after the onset of continental fragmentation, suggesting an association with rifting processes. Our dynamic models show that physically steep lithosphere-asthenosphere boundaries formed during terminal rifting (necking) generate convective instabilities in the asthenosphere that slowly migrate many hundreds of kilometres inboard of the rift, causing destabilization of cratonic mantle keel tens of kilometres thick. Displaced lithosphere is replaced by hot, upwelling asthenosphere in the return flow, causing partial melting of carbonated mantle and variable assimilation of lithospheric material. The resulting small-volume kimberlite magmas ascend rapidly and adiabatically, exsolving amounts of carbon dioxide (CO 2 ) that are consistent with independent constraints 7 . Our model reconciles diagnostic kimberlite features including association with cratons and geochemical characteristics that implicate a common asthenospheric mantle source contaminated by cratonic lithosphere 8 . Together, these results provide a quantitative and mechanistic link between kimberlite episodicity and supercontinent cycles via progressive disruption of cratonic keels.
Publisher: Springer Science and Business Media LLC
Date: 26-07-2023
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Christopher Spencer.