Trace element modeling of aqueous fluid - peridotite interaction in the mantle wedge of subduction zones

1998 ◽  
Vol 132 (4) ◽  
pp. 390-404 ◽  
Author(s):  
John Ayers
Keyword(s):  
Trace Element ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Aqueous Fluid ◽  
Element Modeling

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 Miocene and Pliocene Silicic Coromandel Volcanic Zone Tephras from ODP Site 1124-C: Petrogenetic Applications and Temporal Evolution

2021 ◽  
Author(s):  
◽  
Matthew Thomas Stevens
Keyword(s):  
Trace Element ◽  
Mantle Wedge ◽  
Major Element ◽  
Volcanic Glass ◽  
Fractional Crystallisation ◽  
Volcanic Zone ◽  
Arc Magmas ◽  
Glass Shard ◽  
Tephra Layers ◽  
Glass Shards

<p>The Coromandel Volcanic Zone (CVZ) was the longest-lived area of volcanism in New Zealand hosting the commencement of large explosive rhyolitic and ignimbrite forming eruptions. The NW trending Coromandel Peninsula is the subaerial remnant of the Miocene-Pliocene CVZ, which is regarded as a tectonic precursor to the Taupo Volcanic Zone (TVZ), currently the most dynamic and voluminous rhyolitic volcanic centre on Earth. This study presents new single glass shard major and trace element geochemical analyses for 72 high-silica volcanic tephra layers recovered from well-dated deep-sea sediments of the SW Pacific Ocean by the Ocean Drilling Program (ODP) Leg 181. ODP Site 1124, ~720 km south and east from the CVZ, penetrated sediments of the Rekohu Drift yielding an unprecedented record of major explosive volcanic eruptions owing to the favourable location and preservation characteristics at this site. This record extends onshore eruptive sequences of CVZ explosive volcanism that are obscured by poor exposure, alteration, and erosion and burial by younger volcanic deposits. Tephra layers recovered from Site 1124 are well-dated through a combination of biostratigraphic and palaeomagnetic methods allowing the temporal geochemical evolution of the CVZ to be reconstructed in relation to changes in the petrogenesis of CVZ arc magmas from ~ 10 to 2 Ma. This thesis establishes major and trace element geochemical "fingerprints" for all Site 1124-C tephras using well-established (wavelength dispersive electron probe microanalysis) and new (laser ablation inductively coupled plasma mass spectrometry) in situ single glass shard microanalytical techniques. Trace element analysis of Site 1124-C glass shards (as small as 20 um) demonstrate that trace element signatures offer a more specific, unequivocal characterisation for distinguishing (and potentially correlating) between tephras with nearly identical major element compositions. The Site 1124-C core contains 72 unaltered Miocene-Pliocene volcanic glass-shard-bearing laminae > 1 cm thick that correspond to 83 or 84 geochemical eruptive units. Revised eruptive frequencies based on the number of geochemical eruptive units identified represent at least one eruption every 99 kyr for the late Miocene and one per 74 kyr for the Pliocene. The frequency of tephra deposition throughout the history of the CVZ has not been constant, rather reflecting pulses of major explosive eruptions resulting in closely clustered groups of tephra separated by periods of reduced activity, relative volcanic quiescence or non-tephra deposition. As more regular activity became prevalent in the Pliocene, it was accompanied by more silicic magma compositions. Rhyolitic volcanic glass shards are characterised by predominantly calc-alkaline and minor high-K enriched major element compositions. Major element compositional variability of the tephras deposited between 10 Ma and 2 Ma reveals magma batches with pre-eruptive compositional gradients implying a broad control by fractional crystallisation. Trace element characterisation of glass shards reveals the role of magmatic processes that are not readily apparent in the relatively homogeneous major element compositions. Multi-element diagrams show prominent negative Sr and Ti anomalies against primitive mantle likely caused by various degrees of plagioclase and titanomagnetite fractional crystallisation in shallow magma chambers. Relative Nb depletion, characteristic of arc volcanism, is moderate in CVZ tephras. HFSEs (e.g. Nb, Zr, Ti) and HREEs (e.g. Yb, Lu) remain immobile during slab fluid flux suggesting they are derived from the mantle wedge. LILE (e.g. Rb, Cs, Ba, Sr) and LREE (e.g. La, Ce) enrichments are consistent with slab fluid contribution. B/La and Li/Y ratios can be used as a proxy for the flux of subducting material to the mantle wedge, they suggest there is a strong influence from this component in the generation of CVZ arc magmas, potentially inducing melting. CVZ tephra show long-term coherent variability in trace element geochemistry. Post ~ 4 Ma tephras display a more consistent, less variable, chemical fingerprint that persists up to and across the CVZ/TVZ transition at ~ 2 Ma. Initiation of TVZ volcanism may have occurred earlier than is presently considered, or CVZ to TVZ volcanism may have occurred without significant changes in magma generation processes.</p>

scholarly journals Supplemental Material: Petrogenesis of Ordovician granitoids in Western Kunlun, NW Tibetan Plateau: Insights into the evolution of the Proto-Tethys Ocean

2020 ◽  
Author(s):  
Peng Wang ◽  
Guochun Zhao ◽  
et al.
Keyword(s):  
Tibetan Plateau ◽  
Trace Element ◽  
Partition Coefficients ◽  
Hf Isotope ◽  
Igneous Rocks ◽  
Pb Isotope ◽  
Element Modeling ◽  
Western Kunlun ◽  
Tethys Ocean ◽  
Ordovician Granitoids

Table S1: Zircon U-Pb ages of igneous rocks in the Western Kunlun orogenic belt; Table S2: Results of whole-rock major- (wt%) and trace-element (ppm) data from the three intrusions; Table S3: Zircon U-Pb age of the three intrusions; Table S4: Zircon Hf isotope compositions of the three intrusions; Table S5: Whole-rock Sr-Nd-Pb isotope compositions of the three intrusions; Table S6: Representative analyses of feldspar, amphibole, and pyroxene from the Aqiang and Yutian intrusions; Table S7: Bulk partition coefficients used for trace-element modeling in Figure 14; Figure S1: CL images of zircons showing internal textures and ages of 206Pb/238U (Ma).

Phase equilibrium and trace-element modeling of the partial melting of basaltic rocks under low pressure: Implications for plagiogranite generation

2021 ◽  
Author(s):  
Xiao-Fei Xu ◽  
Long-Long Gou ◽  
Xiao-Ping Long ◽  
Yu-Hang Zhao ◽  
Feng Zhou
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Low Pressure ◽  
Bulk Rock ◽  
Hydrous Mineral ◽  
Rock Composition ◽  
Bulk Rock Composition ◽  
Element Modeling ◽  
Anhydrous Mineral ◽  
Ree Patterns

Abstract Phase equilibria and trace-element modeling using two previously reported basaltic bulk-rock compositions (samples D11 and 104-16), were carried out in this study, in order to better understand mechanism of low-pressure (LP) partial melting of mafic rocks and associated melt compositions. The T–MH2O pseudosections for both samples at three pressures (i.e. 0.5, 1.0 and 2.0 kbar) display that the H2O-stability field gradually increased with decreasing pressure within the T–MH2O range of 600–1100 °C and 0–12 mol.%. The H2O contents of 10, 5.0, and 0.5 mol.% were selected on the basis of the T–MH2O pseudosections to calculate P–T pseudosections over a P–T window of 0.1–3 kbar and 600–1100 °C, so that the reactions of both the H2O-fluxed and -absent meltings at LP conditions can be investigated. The solidus displays a negative or near-vertical P–T slope, and occurs between 710 and 900 °C at pressure between 0.1 and 3.0 kbar. LP melting of metabasites is attributed to the reactions of the hydrous mineral (hornblende and/or biotite) melting and anhydrous mineral (plagioclase, orthopyroxene, and augite) melting. The hydrous mineral melting is gradually replaced by anhydrous mineral melting as pressure decreasing, as the stability of hornblende decreases with falling pressure. With increasing temperature at a given pressure, the modeled melt compositions are expressed as progressions of the granite-granodiorite-gabbroic diorite fields for sample D11and granite-quartz monzonite-monzonite-gabbroic diorite fields for sample 104-16 on the total alkali–silica diagram. The modeled melts produced through the H2O-fluxed melting display higher Al2O3, CaO, MgO, and lower SiO2 and K2O than those formed by H2O-absent melting at the same P–T conditions. Furthermore, the modeled melts formed by H2O-absent melting, become richer in Al2O3, CaO, MgO, FeO, Na2O, but poorer in SiO2 and K2O as increasing water content. The results of trace-element modeling suggests that the nearly flat REE patterns of modeled bulk-rock composition are inherited by all the modeled melts, and the negative Eu anomalies and Sr depletion of the modeled melts gradually decrease as melting degree increases. Combined with the geochemical characteristics of natural oceanic plagiogranites, which have low K2O contents and flat or slightly LREE-depleted REE patterns, our results imply that a bulk-rock composition with low K2O (&lt;0.17 wt.%) and slightly LREEs depletion is the most likely protolith composition (e.g. basalt D11) for plagiogranites, and the compositions of modeled melts formed by LP H2O-absent partial melting of the basalt D11 at relatively high temperatures (1000–1025 °C) are coincident with those of 1256D tonalites.

scholarly journals Saline aqueous fluid circulation in mantle wedge inferred from olivine wetting properties

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Yongsheng Huang ◽  
Takayuki Nakatani ◽  
Michihiko Nakamura ◽  
Catherine McCammon
Keyword(s):  
Fluid Transport ◽  
Mantle Wedge ◽  
Aqueous Fluid ◽  
High Electrical Conductivity ◽  
Interconnected Network ◽  
Fluid Circulation ◽  
Wetting Properties ◽  
Mantle Fluid ◽  
Conductivity Anomalies ◽  
Electrical Conductors

AbstractRecently, high electrical conductors have been detected beneath some fore-arcs and are believed to store voluminous slab-derived fluids. This implies that the for-arc mantle wedge is permeable for aqueous fluids. Here, we precisely determine the dihedral (wetting) angle in an olivine–NaCl–H2O system at fore-arc mantle conditions to assess the effect of salinity of subduction-zone fluids on the fluid connectivity. We find that NaCl significantly decreases the dihedral angle to below 60° in all investigated conditions at concentrations above 5 wt% and, importantly, even at 1 wt% at 2 GPa. Our results show that slab-released fluid forms an interconnected network at relatively shallow depths of ~80 km and can partly reach the fore-arc crust without causing wet-melting and serpentinization of the mantle. Fluid transport through this permeable window of mantle wedge accounts for the location of the high electrical conductivity anomalies detected in fore-arc regions.

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