ORCID Profile
0000-0002-6959-0462
Current Organisation
University of Oxford
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Publisher: Wiley
Date: 12-08-2016
DOI: 10.1111/JMG.12212
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: 04-2019
DOI: 10.1029/2018GC008079
Publisher: Wiley
Date: 24-11-2016
DOI: 10.1111/JMG.12227
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: Geological Society of London
Date: 07-07-2023
DOI: 10.1144/JGS2023-004
Abstract: Ophiolitic peridotites in Myanmar (Burma) occur along three major tectonic zones: the Kaleymyo–Nagaland suture along the Indo-Burman Ranges, the Jade Mines belt and the Tagaung–Mytkyina belt. These belts all show harzburgite–lherzolite–dunite peridotites, but the Hpakan-Taw Maw region (Jade Mines belt) also hosts jadeitites, including pure jadeite, mawsitsit (Cr-rich jadeite) kosmochlore (Cr-rich clinopyroxene) and albitite. Jadeitites with high Na and Al contents require either very unusual Al-rich, Si-poor protoliths or extensive fluid metasomatism, or both. The Hpakan jadeitites formed by Na-, Al- (and Si-) metasomatic alteration of pyroxenite–wehrlite intrusions into harzburgite–dunite from widespread fluid alteration. The fluids could have been derived from a mid-Jurassic intermediate pressure subduction event during ophiolite formation and emplacement. In the Lake Indawgyi area, normal ophiolitic peridotites, including harzburgite and dunite with pyroxenite veins, have not been jadeitized. Gabbros related to the Jade Mines ophiolite gave a U–Pb zircon age of 169.71 ± 1.3 Ma (MSWD 2.2), a similar timing to the Myitkyina ophiolite (173 Ma) to the east, suggesting that the ophiolite belts were originally continuous. The jade ‘boulders’ in the Uru conglomerate beds at Hpakan have also resulted from normal in situ serpentinization weathering processes, followed by limited fluvial mass transport processes along the Uru River. Supplementary material: U–Pb zircon data are available at 0.6084/m9.figshare.c.6655269
Publisher: Elsevier BV
Date: 06-2017
Publisher: Springer Science and Business Media LLC
Date: 14-12-2016
DOI: 10.1038/NGEO2605
Publisher: Wiley
Date: 31-08-2016
DOI: 10.1111/JMG.12211
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Richard Palin.