Does Fracture Zone Subduction Increase Sediment Flux and Mantle Melting in Subduction Zones? Trace Element Evidence from Aleutian Arc Basalt

2013 ◽  
pp. 285-291 ◽  
Author(s):  
Bradley S. Singer ◽  
William P. Leeman ◽  
Matthew F. Thirlwall ◽  
Nicholas W. Rogers
Keyword(s):  
Trace Element ◽  
Fracture Zone ◽  
Subduction Zones ◽  
Sediment Flux ◽  
Mantle Melting ◽  
Aleutian Arc

scholarly journals The role of sulphur on the melting of Ca-poor sediment and on trace element transfer in subduction zones: an experimental investigation

2021 ◽  
Author(s):  
Anne-Aziliz Pelleter ◽  
Gaëlle Prouteau ◽  
Bruno Scaillet
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Subduction Zones ◽  
Sediment Flux ◽  
Arc Magmas ◽  
Trace Element Contents ◽  
The Stability ◽  
Element Transfer ◽  
High Sediment

Abstract We performed phase equilibrium experiments on a natural Ca-poor pelite at 3 GPa, 750-1000 °C, under moderately oxidizing conditions, simulating the partial melting of such lithologies in subduction zones. Experiments investigated the effect of sulphur addition on phase equilibria and compositions, with S contents of up to ∼ 2.2 wt. %. Run products were characterized for their major and trace element contents, in order to shed light on the role of sulphur on the trace element patterns of melts produced by partial melting of oceanic Ca-poor sediments. Results show that sulphur addition leads to the replacement of phengite by biotite along with the progressive consumption of garnet, which is replaced by an orthopyroxene-kyanite assemblage at the highest sulphur content investigated. All Fe-Mg silicate phases produced with sulphur, including melt, have higher MgO/(MgO+FeO) ratios (relative to S-free/poor conditions), owing to Fe being primarily locked up by sulphide in the investigated redox range. Secular infiltration of the mantle wedge by such MgO and K2O-rich melts may have contributed to the Mg and K-rich character of the modern continental crust. Addition of sulphur does not affect significantly the stability of the main accessory phases controlling the behaviour of trace elements (monazite, rutile and zircon), although our results suggest that monazite solubility is sensitive to S content at the conditions investigated. The low temperature (∼ 800 °C) S-bearing and Ca-poor sediment sourced slab melts show Th and La abundances, Th/La systematics and HFSE signatures in agreement with the characteristics of sediment-rich arc magmas. Because high S contents diminish phengite and garnet stabilities, S-rich and Ca-poor sediment sourced slab melts have higher contents of Rb, B, Li (to a lesser extent), and HREE. The highest ratios of La/Yb are observed in sulphur-poor runs (with a high proportion of garnet, which retains HREE) and beyond the monazite out curve (which retains LREE). Sulphides appear to be relatively Pb-poor and impart high Pb/Ce ratio to coexisting melts, even at high S content. Overall, our results show that Phanerozoic arc magmas from high sediment flux margins owe their geochemical signature to the subduction of terrigenous, sometimes S-rich, sediments. In contrast, subduction of such lithologies during Archean appears unlikely or unrecorded.

Boninites as windows into trace element mobility in subduction zones

2010 ◽  
Vol 74 (2) ◽  
pp. 684-704 ◽  
Author(s):  
Stephan König ◽  
Carsten Münker ◽  
Stephan Schuth ◽  
Ambre Luguet ◽  
J. Elis Hoffmann ◽  
...  
Keyword(s):  
Trace Element ◽  
Subduction Zones ◽  
Element Mobility ◽  
Trace Element Mobility

scholarly journals The Fluid Mobilities of K and Zr in Subduction Zones: Thermodynamic Constraints

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 394
Author(s):  
Richen Zhong ◽  
Min Zhang ◽  
Chang Yu ◽  
Hao Cui
Keyword(s):  
Trace Element ◽  
Subduction Zones ◽  
Critical Role ◽  
High Field Strength ◽  
Trace Element Pattern ◽  
Arc Magmas ◽  
Thermodynamic Simulations ◽  
Element Pattern ◽  
Element Transfer ◽  
Complex Ion

A subduction zone plays a critical role in forging continental crust via formation of arc magmas, which are characteristically enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs). This trace element pattern results from the different mobilities of LILEs and HFSEs during slab-to-wedge mass transfer, but the mechanisms of trace element transfer from subducting crusts are not fully understood. In this study, thermodynamic simulations are carried out to evaluate the mobilities of K and Zr, as representative cases of LILE and HFSE, respectively, in slab fluids. The fluids buffered by basaltic eclogite can dissolve > 0.1 molal of K at sub-arc depths (~3 to 5.5 GPa). However, only minor amounts of K can be liberated by direct devolatilization of altered oceanic basalt, because sub-arc dehydration mainly takes place at temperatures < 600 °C (talc-out), wherein the fluid solubility of K is very limited (<0.01 molal). Therefore, serpentinite-derived fluids are required to flush K from the eclogite. The solubility of K can be enhanced by the addition of NaCl to the fluid, because fluid Na+ can unlock phengite-bonded K via a complex ion exchange. Finally, it is further confirmed that Zr and other HFSEs are immobile in slab fluids.

scholarly journals Aleutian island arc magma production rates and mechanisms

2019 ◽  
Author(s):  
Yongliang Bai ◽  
Diya Zhang ◽  
Dongdong Dong ◽  
Shiguo Wu ◽  
Zhenjie Wang
Keyword(s):  
High Temperature ◽  
Production Rate ◽  
Island Arc ◽  
Mantle Melting ◽  
Fracture Zones ◽  
Seismic Profiles ◽  
Production Rates ◽  
Aleutian Arc ◽  
Slab Dehydration ◽  
Arc Magma

Abstract. The variation in island arc magma production rates and their influencing mechanisms are of great significance since island arc magma is considered a main source of continental crust growth. The island arc magma directly originates from the molten mantle wedge, and the mantle melting is driven by fluids or melts from the subducted slab. Slab dehydration flux mainly depends on the slab thermal structures, and subducted slab melting requires a sufficiently high temperature. For the Aleutian subduction system, the subducted Pacific Plate has diverse thermal structures due to the existing fracture zones, ridges and slab window, so it is an ideal region for arc magma production rate research. However, the previous estimations are based on seismic profiles that only provide magma production rates at specific regions of the Aleutian arc, and these results are controversial. Here, we design a magma production rate estimation method based on gravity inversion constrained by deep seismic profiles. The first overview map of magma production rates along the Aleutian arc strike demonstrates that the magma production rates have the same trend as the slab dips, and the peaks correspond to the subduction of the fracture zones and ridges. The potential mechanisms for these correlations are as follows: (1) Slab water flux at subarc depths increases with increasing slab dip. More fluid flux would induce more mantle melting, and so the arc magma production rates are increased. (2) Water-rich serpentine is formed by hydrothermal alteration on or near the surface of the subducted slab when there are fracture zones. Serpentine decomposition at a depth of 80–120 km releases fluids in addition to the fluids released during normal slab dehydration. Therefore, more fluids induce more mantle melting and correspond a larger magma production rate. (3) The slab located in the Emperor Seamounts has a relatively high temperature and is also weak, so its melting is easier. Similarly, more slab melt means more mantle melt and a higher island arc magma production rate.

Seismic imaging evidence that forearc underplating built the accretionary rock record of coastal North and South America

2019 ◽  
Vol 158 (1) ◽  
pp. 104-117 ◽  
Author(s):  
David W. Scholl
Keyword(s):  
South America ◽  
Subduction Zones ◽  
Seismic Imaging ◽  
Southern Chile ◽  
Late Palaeozoic ◽  
Aleutian Arc ◽  
Seaward Edge ◽  
Metamorphic Facies ◽  
North And South America ◽  
North And South

AbstractThe submerged forearcs of Pacific subduction zones of North and South America are underlain by a coastally exposed basement of late Palaeozoic to early Tertiary age. Basement is either an igneous massif of an accreted intra-oceanic arc or oceanic plateau (e.g. Cascadia(?), Colombia), an in situ formed arc massif (e.g. Aleutian Arc) or an exhumed accretionary complex of low and high P/T metamorphic facies of late Palaeozoic (e.g. southern Chile, Patagonia) and Mesozoic age (e.g. Alaska). Seismic studies at Pacific forearcs image frontal prisms of trench sediment accreted to the seaward edge of forearc basement. Frontal prisms tend to be narrow (10–40 km), weakly consolidated and volumetrically small (∼35–40 km3/km of trench). In contrast, deep seismic imaging of submerged forearcs commonly reveals large volumes (∼2000 km3/km of trench) of underplated material accreted at subsurface depths of ∼10–30 km to the base of forearc basement. Underplates have been imaged below the southern Chile, Ecuador–Colombia, north Cascade, Alaska, and possibly the eastern Aleutian forearcs. Deep underplates have also been observed below the Japan and New Zealand forearcs. Seismic imaging of northern and eastern Pacific forearcs supports the conclusion drawn from field and laboratory studies that exposed low and high P/T accretionary complexes accumulated in the subsurface at depths of 10–30 km. It seems significant that imaged underplated bodies are characteristic of modern well-sedimented subduction zones. It also seems likely that large Pacific-rim underplates store a significant fraction of sediment subducted in Cenozoic time.

Lawsonite geochemistry and stability - implication for trace element and water cycles in subduction zones

2014 ◽  
Vol 32 (5) ◽  
pp. 455-478 ◽  
Author(s):  
L. A. J. Martin ◽  
J. Hermann ◽  
L. Gauthiez-Putallaz ◽  
D. L. Whitney ◽  
A. Vitale Brovarone ◽  
...  
Keyword(s):  
Trace Element ◽  
Subduction Zones ◽  
Water Cycles

Generation of Calc-Alkaline Magmas During Crystallization at High Oxygen Fugacity: An Experimental and Petrologic Study of Tephras from Buldir Volcano, Western Aleutian Arc, Alaska, USA

2020 ◽  
Author(s):  
L E Waters ◽  
E Cottrell ◽  
M L Coombs ◽  
K A Kelley
Keyword(s):  
Oxygen Fugacity ◽  
Subduction Zones ◽  
Volcanic Rocks ◽  
High Oxygen ◽  
Calc Alkaline ◽  
Edge Structure ◽  
Liquidus Phase ◽  
High Oxygen Fugacity ◽  
Alkaline Volcanism ◽  
Aleutian Arc

Abstract Despite agreement that calc-alkaline volcanism occurs at subduction zones and is responsible for the genesis of continental landmasses, there is no consensus on the source of the Fe-depleted signature hallmark to calc-alkaline volcanism. In this study, we utilize mafic tephras collected from Buldir Volcano to address the genesis of strongly calc-alkaline volcanic rocks (those with a low Tholeiitic Index; ≤0.7) in a segment of the western Aleutian Arc to determine if the eruptions are plausibly part of a liquid line of descent, if they are mixtures of crustal melts and parental magmas, or if they are mixtures of melts of the mantle and the subducting slab. We conducted a series of H2O-saturated phase equilibrium experiments (1175–1000 °C; 100 MPa) in a rapid-quench cold-seal (MHC) apparatus on the most primitive natural lava from Buldir (9.34 wt% MgO) at oxidizing conditions near the Re-ReO2 buffer. We confirmed that all experiments equilibrated 0.3 ± 0.23 log units above the Re-ReO2 buffer (ΔQFM ∼ +2.8) using X-ray Absorption Near Edge Structure (XANES) spectroscopy. Chromite is the liquidus phase, followed by olivine, then plagioclase, then clinopyroxene, and finally hornblende. Once clinopyroxene saturates, spinel composition shifts to magnetite. We compared our experimental results to the major element geochemistry and petrology of six tephras (51.9–54.8 wt% SiO2) from Buldir collected during the 2015 field season of the GeoPRISMS shared platform. Tephras contain olivine + plagioclase + clinopyroxene + spinel ± hornblende; plagioclase comprises most of the crystalline volume, followed by either olivine or hornblende. Spinel is ubiquitous; with Cr- rich spinel inclusions in olivine and hornblende, and magnetite in the groundmass. Variations in phenocryst assemblages and compositions between samples can be attributed to differences in pre-eruptive temperatures, where hotter samples are devoid of hornblende, and contain Fo-rich olivine and plagioclase with lower An-contents, owing to the position of the mineral-in curves at fluid-saturated conditions. Experimental glasses match the depletion in FeOT observed in the tephra whole rock compositions. The continuous depletion in FeOT is attributable to saturation of spinel as a liquidus phase (initially as chromite) and continuous crystallization through the experimental series (changing to magnetite at colder temperatures). In contrast to the natural samples, the experiments show enrichment in TiO2 with decreasing MgO, suggesting that differentiation did not occur at 100 MPa on Buldir. The TiO2 depletion in volcanic rocks from Buldir can be accounted for if hornblende crystallization occurs close to the liquidus of a parental magma; a condition that is met at higher pressures and hydrous conditions. The emerging picture for Buldir Island is that (1) oxidizing conditions are required to drive the observed depletions in FeOT via crystallization of spinel, and (2) elevated H2O contents and high pressures are required to saturate hornblende close to the liquidus to reproduce the entire suite of major elements. Our study provides a mechanism to generate the calc-alkaline trends observed at Buldir without requiring mixing of slab and mantle melts. We conclude that calc-alkaline volcanic rocks with extremely low Tholeiitic Indices (0.7), like those from Buldir, cannot be generated in absence of high oxygen fugacity, even at high pressure and/or elevated water pressures.

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