scholarly journals An experimental study of the partitioning of trace elements between rutile and silicate melt as a function of oxygen fugacity

2014 ◽  
Vol 86 (4) ◽  
pp. 1609-1629 ◽  
Author(s):  
GUILHERME MALLMANN ◽  
RAÚL O.C. FONSECA ◽  
ADOLFO B. SILVA
Keyword(s):  
Oxygen Fugacity ◽  
Silicate Melt ◽  
Accessory Mineral ◽  
High Field Strength ◽  
Arc Magmas ◽  
Melt Polymerization ◽  
Incompatible Elements ◽  
Order Of Magnitude ◽  
Melt Composition ◽  
Partitioning Behavior

Subduction zone or arc magmas are known to display a characteristic depletion of High Field Strength Elements (HFSE) relative to other similarly incompatible elements, which can be attributed to the presence of the accessory mineral rutile (TiO2) in the residual slab. Here we show that the partitioning behavior of vanadium between rutile and silicate melt varies from incompatible (∼0.1) to compatible (∼18) as a function of oxygen fugacity. We also confirm that the HFSE are compatible in rutile, with D(Ta)> D(Nb)>> (D(Hf)>/∼ D(Zr), but that the level of compatibility is strongly dependent on melt composition, with partition coefficients increasing about one order of magnitude with increasing melt polymerization (or decreasing basicity). Our partitioning results also indicate that residual rutile may fractionate U from Th due to the contrasting (over 2 orders of magnitude) partitioning between these two elements. We confirm that, in addition to the HFSE, Cr, Cu, Zn and W are compatible in rutile at all oxygen fugacity conditions.

Partitioning of V and 19 other trace elements between rutile and silicate melt as a function of oxygen fugacity and melt composition: Implications for subduction zones

2020 ◽  
Vol 105 (2) ◽  
pp. 244-254 ◽  
Author(s):  
Megan Holycross ◽  
Elizabeth Cottrell
Keyword(s):  
Trace Elements ◽  
Subduction Zones ◽  
Silicate Melt ◽  
High Field Strength ◽  
Trace Element Partitioning ◽  
Element Partitioning ◽  
Oxygen Buffer ◽  
Melt Composition ◽  
Refractory Slab ◽  
Partitioning Behavior

Abstract Vanadium is a multivalent element that can speciate as V2+, V3+, V4+, and V5+ over a range of geologically relevant oxygen fugacities (fO2). The abundance of V in planetary materials can be exploited as a proxy for fO2 when its partitioning behavior is known. The mineral rutile (TiO2) is an important carrier of the high field strength elements Nb and Ta in the solid Earth, but it can also incorporate substantial quantities of vanadium (up to ~2000 ppm; e.g., Zack et al. 2002). However, little work has been done to systematically investigate how the partitioning of V in rutile-bearing systems changes as a function of both fO2 and composition. We measured the partitioning of V and 19 other trace elements (Sc, Cr, Y, Zr, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu, Hf, and Ta) between rutile and three silicate melt compositions equilibrated at 1 atm pressure, 1300 °C and fO2 values from two log units below the quartz-fayalite-magnetite oxygen buffer (QFM-2) to air (QFM+6.5). Rutile/melt partition coefficients (DVrt/melt) change dynamically over an eight-log unit range of fO2 and are greatest at fO2 = QFM-2 in all compositions. Vanadium solubility in rutile declines continuously as fO2 increases from QFM-2 and approaches unity in air. Trace-element partitioning between rutile and melt is also correlated with melt composition, with the greatest values of Drt/melt measured in the most polymerized melt systems containing the least TiO2. We do not find any circumstances where V becomes incompatible in rutile. Our results indicate that rutile is a considerable sink for V at terrestrial fO2 values and will contribute to the retention of V in refractory slab residues in subduction zones. In agreement with previous work, we find that DTart/melt>DNbrt/melt under all conditions investigated, suggesting that rutile fractionation does not lead to low Nb/Ta ratios in Earth's continental crust.

scholarly journals The effect of melt composition and oxygen fugacity on manganese partitioning between apatite and silicate melt

2019 ◽  
Vol 506 ◽  
pp. 162-174 ◽  
Author(s):  
T.N. Stokes ◽  
G.D. Bromiley ◽  
N.J. Potts ◽  
K.E. Saunders ◽  
A.J. Miles
Keyword(s):  
Oxygen Fugacity ◽  
Silicate Melt ◽  
Melt Composition

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.

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