Subduction initiation terranes exposed at the front of a 2 Ma volcanically-active subduction zone

Patriat, M.; Falloon, Trevor J.; Danyushevsky, Leonid V.; Collot, Julien; Jean, M. M.; Hoernle, Kaj; Hauff, Folkmar; Maas, Roland; Woodhead, Jon; Feig, Sandrin T.

doi:10.1016/j.epsl.2018.12.011

Cited by 53 publications

(35 citation statements)

References 55 publications

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“…However, flat-lying ophiolites (e.g. Mirdita), the IBM arc basement and the recently recognised Matthew and Hunter protoarc show significant variations in upper-crustal architecture with distance from the trench (Dilek et al, 2008;Hickey-Vargas et al, 2018;Patriat et al, 2019). The upper crustal unit proportions documented herein are therefore not necessarily representative of an entire proto-arc crustal swath, but rather represent the best estimate currently available.…”

Section: Proportions Of the Upper-crustal Unitsmentioning

confidence: 77%

A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

Belgrano¹,

Diamond²,

Vogt³

et al. 2019

Preprint

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Abstract. Recent studies have revealed genetic similarities between Tethyan ophiolites and oceanic proto-arc sequences formed above nascent subduction zones. The Semail ophiolite (Oman–U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction-initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in submarine fore-arcs. In contrast, the Semail ophiolite, in which the 3–5 km thick upper-crustal succession is exposed in an oblique cross-section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the protoarc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulphide (VMS) deposits that they host, we have re-mapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses and geophysical interpretations with pre-existing geological maps. By linking the major element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in in a new map showing 2100 km2 of upper-crustal bedrock. Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes) through to axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley) and finally boninites (Boninitic Alley). Geotimes (Phase 1) axial dykes and lavas make up ~55 vol% of the Semail upper crust, whereas post-axial (Phase 2) lavas constitute the remaining ~ 45 vol % and ubiquitously cover the underlying axial crust. The Semail boninites occur as discontinuous accumulations up to 2 km thick at the top of the sequence and constitute ~ 15 vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.

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Section: Proportions Of the Upper-crustal Unitsmentioning

confidence: 77%

A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

Belgrano¹,

Diamond²,

Vogt³

et al. 2019

Preprint

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“…In this primarily horizontally and externally forced case, it takes approximately 5 Myr for the Pacific plate to begin moving beneath the Philippine plate, but once it does so, subduction progresses at a similar speed to the vertically and internally driven case. This style of subduction initiation is likely occurring at the Puysegur ridge south of New Zealand 27 or in the Matthew and Hunter subduction system in the southwest Pacific 28 : much smaller systems in which initiation is more likely governed by external, horizontal forces.…”

Section: Resultsmentioning

confidence: 99%

Rapid subduction initiation and magmatism in the Western Pacific driven by internal vertical forces

et al. 2020

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Plate tectonics requires the formation of plate boundaries. Particularly important is the enigmatic initiation of subduction: the sliding of one plate below the other, and the primary driver of plate tectonics. A continuous, in situ record of subduction initiation was recovered by the International Ocean Discovery Program Expedition 352, which drilled a segment of the fore-arc of the Izu-Bonin-Mariana subduction system, revealing a distinct magmatic progression with a rapid timescale (approximately 1 million years). Here, using numerical models, we demonstrate that these observations cannot be produced by previously proposed horizontal external forcing. Instead a geodynamic evolution that is dominated by internal, vertical forces produces both the temporal and spatial distribution of magmatic products, and progresses to self-sustained subduction. Such a primarily internally driven initiation event is necessarily whole-plate scale and the rock sequence generated (also found along the Tethyan margin) may be considered as a smoking gun for this type of event.

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“…The youngest, and not fully evolved, is now believed to be the much smaller-scale, 2 Ma M&H (Matthews and Hunter) subduction initiation terrane at the southern edge (Figs. S2E-S2F [footnote 1]) of the Vanuatu arc (Sigurdsson et al, 1993;Patriat et al, 2019). As demonstrated and explained more fully in Figures S1A-S1F, subduction initiation was followed by creation of oceanic crust by a seafloor spreading event in which compositions evolved from tholeiitic basalt (forearc basalt) to low-Si boninite (Reagan et al, 2010(Reagan et al, , 2017.…”

Section: Boninites From Oceanic Subduction Initiation Terranes (Izu-bmentioning

confidence: 92%

Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

2019

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Boninites are rare, high-Si, high-Mg, low-Ti lavas that have considerable tectonic significance, especially for recognizing and interpreting episodes of subduction initiation in the geologic record. Formal identification and classification of boninites may be carried out using MgO-SiO2 and MgO-TiO2 diagrams to find compositions that satisfy modified International Union of Geological Sciences (IUGS) criteria of Si8 > 52 and Ti8 < 0.5, where Si8 and Ti8 refer to concentrations of the oxides at 8 wt% MgO. However, screening of highly metasomatized rocks and accurate classification require precautions, including normalization to a 100% volatile-free basis. The MgO-SiO2 diagram can also be used for subdivision into low-Si boninites (Si8 < 57) and high-Si boninites (Si8 > 57). Satisfying one but not both of the boninite criteria are rocks with Si8 > 52 but Ti8 ≥ 0.5 (siliceous high-magnesium basalts) and rocks with Si8 ≤ 52 but Ti8 < 0.5 (low-Ti basalts). We tested the classification methodologies using ∼100 low-Ti lava suites dating from the present-day back to the Eoarchean. We conclude that, of those classifying as “boninite series,” Izu-Bonin-Mariana arc–type subduction initiation terranes provide the dominant setting only back as far as ca. 2 Ga, which marks the maximum age of extensive clinopyroxene-undersaturated melting and eruption of high-Si boninites. From 2 to 3 Ga, most boninites formed in intraplate settings by melting of refertilized, depleted cratonic roots. Prior to 3 Ga, hot, depleted mantle plumes provided the main boninite sources. Nonetheless, arc-basin boninites, though rare, do extend back to 3.8 Ga, and, together with the inherited subduction component in intracratonic boninites, they provide evidence for some form of subduction during the Archean.

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Subduction initiation terranes exposed at the front of a 2 Ma volcanically-active subduction zone

Cited by 53 publications

References 55 publications

A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

A revised map of volcanic units in the Oman ophiolite: insights into the architecture of an oceanic proto-arc volcanic sequence

Rapid subduction initiation and magmatism in the Western Pacific driven by internal vertical forces

Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

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