New Caledonia Ophiolite is crosscut by coarse to medium grained pyroxenites and hornblende gabbros/diorites dykes intruded between 55.5Ma and 50Ma (U-Pb zircon and 40Ar/39Ar hornblende), while finer-grained dolerites of tholeiitic affinity are younger (50-47 Ma). Production of hornblende-gabbros/diorites was modelled by moderate degree (20-40%) of partial melting of the HT amphibolites of the metamorphic sole. End-member compositions, hornblendites and anorthosites, resulted from solid-state phase segregation of crystal mushes within tectonically active magmatic conduits. Cascade reactions of slab melts with mantle wedge peridotites successively formed clinoenstatite-boninite magmas, which fed gabbronorite cumulate lenses at the mantle-crust transition, in turn clinoenstatite-boninite melts reacted with peridotites to form websterites. The youngest magmas of tholeiitic affinity, appeared about 6 Ma after subduction inception when the cooler subducting slab plunged more steeply. Incipient slab retreat allowed corner flow, triggering low pressure hydrous melting of the uplifted asthenosphere . The early stages of forearc magmatism were closely associated with transcurrent shear zones, which recorded oblique subduction inception. The lower Eocene tectonic and magmatic features of the New Caledonia ophiolite witness the existence of a north- or northeast-dipping hot (forced) subduction zone in the Southwest Pacific, which appears notably distinct from the slightly younger west-dipping Izu-Bonin-Marianna cold (spontaneous) subduction system.

New geochemical and age constraints (40Ar/39Ar and U-Pb) on forearc intrusive rocks from New Caledonia Ophiolite (SW Pacific): diversity of melts generated at hot subduction inception [New geochemical and age constraints (⁴⁰Ar/³⁹Ar and U-Pb) on forearc intrusive rocks from New Caledonia Ophiolite (SW Pacific): diversity of melts generated at hot subduction inception] / D. Cluzel, A. Montanini, A. Secchiari, E. Ferrari, M. Heizler, F. Jourdan, S. Meffre, R. Zhou, C. Teyssier. - In: JOURNAL OF THE GEOLOGICAL SOCIETY. - ISSN 0016-7649. - 181:1(2024), pp. jgs2023-145.1-jgs2023-145.18. [10.1144/jgs2023-145]

New geochemical and age constraints (40Ar/39Ar and U-Pb) on forearc intrusive rocks from New Caledonia Ophiolite (SW Pacific): diversity of melts generated at hot subduction inception [New geochemical and age constraints (⁴⁰Ar/³⁹Ar and U-Pb) on forearc intrusive rocks from New Caledonia Ophiolite (SW Pacific): diversity of melts generated at hot subduction inception]

A. Secchiari;
2024

Abstract

New Caledonia Ophiolite is crosscut by coarse to medium grained pyroxenites and hornblende gabbros/diorites dykes intruded between 55.5Ma and 50Ma (U-Pb zircon and 40Ar/39Ar hornblende), while finer-grained dolerites of tholeiitic affinity are younger (50-47 Ma). Production of hornblende-gabbros/diorites was modelled by moderate degree (20-40%) of partial melting of the HT amphibolites of the metamorphic sole. End-member compositions, hornblendites and anorthosites, resulted from solid-state phase segregation of crystal mushes within tectonically active magmatic conduits. Cascade reactions of slab melts with mantle wedge peridotites successively formed clinoenstatite-boninite magmas, which fed gabbronorite cumulate lenses at the mantle-crust transition, in turn clinoenstatite-boninite melts reacted with peridotites to form websterites. The youngest magmas of tholeiitic affinity, appeared about 6 Ma after subduction inception when the cooler subducting slab plunged more steeply. Incipient slab retreat allowed corner flow, triggering low pressure hydrous melting of the uplifted asthenosphere . The early stages of forearc magmatism were closely associated with transcurrent shear zones, which recorded oblique subduction inception. The lower Eocene tectonic and magmatic features of the New Caledonia ophiolite witness the existence of a north- or northeast-dipping hot (forced) subduction zone in the Southwest Pacific, which appears notably distinct from the slightly younger west-dipping Izu-Bonin-Marianna cold (spontaneous) subduction system.
New Caledonia Ophiolite; forearc magmatism; subduction inception; mantle shear zones, 40Ar/39Ar; U-Pb zircon;
Settore GEO/07 - Petrologia e Petrografia
Settore GEO/08 - Geochimica e Vulcanologia
2024
dic-2023
https://www.lyellcollection.org/doi/10.1144/jgs2023-145
Article (author)
File in questo prodotto:
File Dimensione Formato  
cluzel-et-al-2023-new-geochemical-and-age-constraints-(40ar-39ar-and-u-pb)-on-forearc-intrusive-rocks-from-new.pdf

embargo fino al 01/01/2025

Tipologia: Post-print, accepted manuscript ecc. (versione accettata dall'editore)
Dimensione 3.9 MB
Formato Adobe PDF
3.9 MB Adobe PDF   Visualizza/Apri   Richiedi una copia
jgs2023-145.pdf

accesso riservato

Tipologia: Publisher's version/PDF
Dimensione 5.14 MB
Formato Adobe PDF
5.14 MB Adobe PDF   Visualizza/Apri   Richiedi una copia
Pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/1022670
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 1
  • ???jsp.display-item.citation.isi??? 1
social impact