Limited recycling of crustal osmium in forearc mantle during slab dehydration

AbstractHow 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 >200 km depth, after which slab-derived serpentinites are responsible for generating slab melts.

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Subduction-Induced Fractionated Highly Siderophile Element Patterns in Forearc Mantle

Minerals ◽

10.3390/min9060339 ◽

2019 ◽

Vol 9 (6) ◽

pp. 339 ◽

Cited By ~ 3

Author(s):

Yang Xu ◽

Chuan-Zhou Liu

Keyword(s):

New Caledonia ◽

Melt Extraction ◽

Highly Siderophile Elements ◽

Group I ◽

Mantle Peridotites ◽

Tectonic Settings ◽

Siderophile Elements ◽

Fe Alloys ◽

Slab Dehydration ◽

Forearc Mantle

Compositions of highly siderophile elements (HSEs) in forearc mantle have been little studied and effects of slab dehydration on their abundances in forearc mantle remains unclear. This study reports two different kinds of HSE patterns for peridotites from a New Caledonia forearc ophiolite. The Group-I samples show relatively flat patterns of Ir-group-platinum-group elements (IPGEs) and enrichment of Pt over Pd. Such patterns imply that interstitial sulfides were significantly removed through melt extraction, whereas sulfides enclosed within silicates were mostly unaffected. Meanwhile, Pt-Fe alloys were generated, resulting in suprachondritic Pt/Pd ratios. In contrast, the Group-II samples display convex HSE patterns and are depleted in all HSEs except for Ru, yielding strongly positive Ru anomalies. This indicates that both enclosed and interstitial sulfides were substantially consumed, whereas chromite was generated to stabilize Ru. Compared to abyssal peridotites, subduction-related peridotites commonly have stronger fractionation in the HSEs. Therefore, the HSE data of mantle peridotites are potentially able to discriminate the tectonic settings of ophiolites.

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Limited Recycling of Crustal Osmium in Forearc Mantle During Slab Dehydration

Acta Geologica Sinica - English Edition ◽

10.1111/1755-6724.14160 ◽

2019 ◽

Vol 93 (S2) ◽

pp. 17-17

Author(s):

Chuanzhou LIU ◽

Yang XU ◽

Fuyuan WU

Keyword(s):

Slab Dehydration ◽

Forearc Mantle

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Geneses of Two Contrasting Antigorite Crystal Preferred Orientations and Their Implications for Seismic Anisotropy in the Forearc Mantle

Journal of Geophysical Research Solid Earth ◽

10.1029/2020jb019354 ◽

2020 ◽

Vol 125 (9) ◽

Cited By ~ 1

Author(s):

Wenlong Liu ◽

Junfeng Zhang ◽

Yi Cao ◽

Zhenmin Jin

Keyword(s):

Seismic Anisotropy ◽

Forearc Mantle

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Postseismic geodetic signature of cold forearc mantle in subduction zones

Nature Geoscience ◽

10.1038/s41561-020-00679-9 ◽

2021 ◽

Vol 14 (2) ◽

pp. 104-109

Author(s):

Haipeng Luo ◽

Kelin Wang

Keyword(s):

Subduction Zones ◽

Forearc Mantle

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Testing the effects of basic numerical implementations of water migration on models of subduction dynamics

Solid Earth ◽

10.5194/se-5-537-2014 ◽

2014 ◽

Vol 5 (1) ◽

pp. 537-555 ◽

Cited By ~ 8

Author(s):

M. E. T. Quinquis ◽

S. J. H. Buiter

Keyword(s):

Upper Mantle ◽

Water Distribution ◽

Mantle Wedge ◽

Bound Water ◽

Free Water ◽

Water Velocity ◽

Water Migration ◽

Creep Flow ◽

Dehydration Reactions ◽

Slab Dehydration

Abstract. Subduction of oceanic lithosphere brings water into the Earth's upper mantle. Previous numerical studies have shown how slab dehydration and mantle hydration can impact the dynamics of a subduction system by allowing a more vigorous mantle flow and promoting localisation of deformation in the lithosphere and mantle. The depths at which dehydration reactions occur in the hydrated portions of the slab are well constrained in these models by thermodynamic calculations. However, computational models use different numerical schemes to simulate the migration of free water. We aim to show the influence of the numerical scheme of free water migration on the dynamics of the upper mantle and more specifically the mantle wedge. We investigate the following three simple migration schemes with a finite-element model: (1) element-wise vertical migration of free water, occurring independent of the flow of the solid phase; (2) an imposed vertical free water velocity; and (3) a Darcy velocity, where the free water velocity is a function of the pressure gradient caused by the difference in density between water and the surrounding rocks. In addition, the flow of the solid material field also moves the free water in the imposed vertical velocity and Darcy schemes. We first test the influence of the water migration scheme using a simple model that simulates the sinking of a cold, hydrated cylinder into a dry, warm mantle. We find that the free water migration scheme has only a limited impact on the water distribution after 1 Myr in these models. We next investigate slab dehydration and mantle hydration with a thermomechanical subduction model that includes brittle behaviour and viscous water-dependent creep flow laws. Our models demonstrate that the bound water distribution is not greatly influenced by the water migration scheme whereas the free water distribution is. We find that a bound water-dependent creep flow law results in a broader area of hydration in the mantle wedge, which feeds back to the dynamics of the system by the associated weakening. This finding underlines the importance of using dynamic time evolution models to investigate the effects of (de)hydration. We also show that hydrated material can be transported down to the base of the upper mantle at 670 km. Although (de)hydration processes influence subduction dynamics, we find that the exact numerical implementation of free water migration is not important in the basic schemes we investigated. A simple implementation of water migration could be sufficient for a first-order impression of the effects of water for studies that focus on large-scale features of subduction dynamics.

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