Elemental Systematics in MORB Glasses From the Mid‐Atlantic Ridge

Abstract

In this study, a data set of 60 elements in 319 mid‐oceanic ridge basalt (MORB) glasses representing 144 chemically distinct lava flows from the Mid‐Atlantic Ridge was acquired by laser ablation inductively coupled plasma mass spectrometry. Our new data are comparable in terms of the number of elements analyzed to several recent MORB data sets, albeit limited in geographic coverage to the North Mid‐Atlantic Ridge. This extensive data set was used to examine the elemental systematics of depleted (D)‐, normal (N)‐, and enriched (E)‐MORBs. We show that elemental ratios sensitive to fluid transport in subduction zones (e.g., Th/U, Nb/U, Ba/Th, and Ba/La) are constant and similar to their primitive mantle values in N‐ and E‐MORBs, but depleted in accordance with their compatibility in D‐MORBs. The absence of evidence for subduction zone processing indicates the need to reassess the relation between MORB enrichment and recycled materials. Additionally, we reexamined the ratios of chalcophile and siderophile elements to lithophile elements of comparable compatibility, which are important in assessing planetary accretion, core formation, crust‐mantle differentiation, and hydrothermal ore formation processes. MORBs show significant negative anomalies of As, Tl, Pb, and Bi, but not of Sb, relative to lithophile elements of similar compatibility, which cannot be accounted for by melt depletion alone. The depletions of As, Tl, Pb, and Bi in MORB are complementary to significant enrichments observed in the continental crust, indicating that they have been transferred to the continental crust via fluid mobility in arcs or obduction of seafloor hydrothermal ores.

Ge/Si Partitioning in Igneous Systems: Constraints From Laser Ablation ICP‐MS Measurements on Natural Samples

“…Ge and Si data from mid‐ocean ridge basalts (MORBs; Jenner & O'Neill, ; Yang et al, ) show that Ge/Si correlates negatively with MgO content (Figure a). To understand the evolution of Ge/Si in MORB during crystallization, we modeled fractional crystallization using thermodynamic programs (Asimow & Ghiorso, ; Ghiorso & Sack, ).…”

“…(a) Ge/Si versus MgO in mid‐ocean ridge basalt (MORB; Jenner & O'Neill, ; Yang et al, ). Open squares represent modeled fractional crystallization liquid lines of descent (Asimow & Ghiorso, ; Ghiorso & Sack, ) with Ge/Si exchange coefficients determined in this study.…”

“…We used pMELTS (Ghiorso et al, 2002) to calculate the major element composition of primary MORB, starting with a fertile mantle composition (Palme & O'Neill, 2014) having a Ge/Si ratio of R s 0 = 5.45 × 10 −6 (McDonough & Sun, 1995;Palme & O'Neill, 2014). We assumed isentropic Neill, 2012;Yang et al, 2018). Open squares represent modeled fractional crystallization liquid lines of descent (Asimow & Ghiorso, 1998;Ghiorso & Sack, 1995) with Ge/Si exchange coefficients determined in this study.…”

Unique achondrite Northwest Africa 11042: Exploring the melting and breakup of the L chondrite parent body

“…Peaks analyzed, interference corrections, and standardization followed Yang et al. (, ). Major elements were determined on the same spots using methods described in Humayun et al.…”

“…), and for trace elements, it varies as a function of the concentration from 2% to 10%, except for elements near the detection limit (Yang et al. ).…”