Thallium elemental behavior and stable isotope fractionation during magmatic processes

Abstract

Please cite this article as: Prytulak, J., Brett, A., Webb, M., Plank, T., Rehkämper, M., Savage, P.S., Woodhead, J., Thallium elemental behavior and stable isotope fractionation during magmatic processes, Chemical Geology (2016), doi: 10.1016/j.chemgeo. 2016.11.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT AbstractStable thallium (Tl) isotopes are an extremely sensitive tracer for the addition of small amounts of sediments or materials altered at low temperatures to the source(s) of mantle-derived melts. The ability of Tl to trace such materials is due to the large concentration contrast between the mantle (Tl < 2ng/g) and possible exotic inputs (Tl ~100ng/g to >g/g), which also often display fractionated Tl isotope compositions.However, the magnitude of Tl isotope fractionation induced by igneous processes alone has not been systematically assessed. Here, two suites of co-genetic magmas, spanning a large range of differentiation, from Hekla, Iceland, and Anatahan, in the Mariana arc, are used to assess the behavior of thallium and its stable isotope variations during magmatic processes. Thallium behaves as a near-perfectly incompatible lithophile element throughout magmatic evolution, mirroring elements such as Rb, Cs, and K. Lavas from Hekla have restricted Cs/Tl ratios and stable Tl isotope compositions, which overlap with mantle estimates. Lavas from subductionrelated Anatahan volcano also have a restricted range in Tl isotope composition, which overlaps with Hekla and MORB, demonstrating that fractional crystallisation and partial melting does not fractionate stable Tl isotopes. Subduction environments display variable Cs/Tl, indicating that the subduction process commonly fractionates these two elements. The immunity of thallium stable isotopes to fractionation by magmatic processes coupled with its extreme sensitivity for tracing pelagic sediments, FeMn crusts and low temperature altered oceanic crust highlight its value in elucidating the nature of mantle sources of both oceanic basalts and arc lavas.Critically, meaningful interpretation of thallium isotope compositions need not be restricted to primitive lavas.

Thallium Mass Fraction and Stable Isotope Ratios of Sixteen Geological Reference Materials

“…Of these, BCR-2 has the most widely reported e 205 Tl SRM997 and can be considered isotopically homogeneous with respect to Tl isotope ratio. The values we obtain for BCR-2 and BHVO-2 are in excellent accord with Prytulak et al (2013Prytulak et al ( , 2017 and Coggon et al (2014) and are indistinguishable from values obtained by Baker et al (2009).…”

“…The values we obtain for BCR‐2 and BHVO‐2 are in excellent accord with Prytulak et al . (, ) and Coggon et al . () and are indistinguishable from values obtained by Baker et al .…”

“…, Prytulak et al . ). Applications include investigations of extraterrestrial materials (Nielsen et al .…”

Assessing Thallium Elemental Systematics and Isotope Ratio Variations in Porphyry Ore Systems: A Case Study of the Bingham Canyon District

“…Thallium (Tl) is a volatile, highly incompatible trace metal, which displays both lithophile and chalcophile affinities [28][29][30][31]. Where sulfides are absent, Tl behaves like the large-ion lithophile (LIL) elements K, Rb, and Cs, due to their similar ionic radii (K + : 1.33 Å; Tl + : 1.49 Å; Rb + : 1.49 Å; Cs + : 1.65 Å; e.g., [32,33]), and preferentially partitions into K-bearing phases, such as biotite (K D = 8.6) and K-feldspar (K D = 3.67) [34]. Although some experimental studies have predicted that sulfides might contain high abundances of Tl [35], only a minority (14 of 38) of natural sulfides analysed in a recent study [36] contained Tl abundances above the detection limit (0.2 µg/g).…”

“…(standard deviation) analytical reproducibility, which is conservatively estimated to be ±0.5 epsilon units [31,42]. Magmatic processes do not appear to cause significant Tl isotope fractionations [33], allowing Tl isotopes to be applied, for example, as useful tracers of different sediment types in variably evolved arc lavas [43][44][45][46]. In general, stable isotope fractionations strongly increase in magnitude with decreasing temperature (e.g., [47]).…”