Origin of geochemical mantle components: Role of spreading ridges and thermal evolution of mantle

Abstract

We explore the element redistribution at mid-ocean ridges (MOR) using a numerical model to evaluate the role of decompression melting of the mantle in Earth's geochemical cycle, with focus on the formation of the depleted mantle component. Our model uses a trace element mass balance based on an internally consistent thermodynamic-petrologic computation to explain the composition of MOR basalt (MORB) and residual peridotite. Model results for MORB-like basalts from 3.5 to 0 Ga indicate a high mantle potential temperature (T p ) of 1650-15008C during 3.5-1.5 Ga before decreasing gradually to 13008C today. The source mantle composition changed from primitive (PM) to depleted as T p decreased, but this source mantle is variable with an early depleted reservoir (EDR) mantle periodically present. We examine a twostage Sr-Nd-Hf-Pb isotopic evolution of mantle residues from melting of PM or EDR at MORs. At high-T p (3.5-1.5 Ga), the MOR process formed extremely depleted DMM. This coincided with formation of the majority of the continental crust, the subcontinental lithospheric mantle, and the enriched mantle components formed at subduction zones and now found in OIB. During cooler mantle conditions (1.5-0 Ga), the MOR process formed most of the modern ocean basin DMM. Changes in the mode of mantle convection from vigorous deep mantle recharge before 1.5 Ga to less vigorous afterward is suggested to explain the thermochemical mantle evolution.

Recycled selenium in hot spot–influenced lavas records ocean-atmosphere oxygenation

“… *Average δ 82 Se (±95% CI, N = 27) and Sr-Nd isotopic ratios (±95% CI, N = 66) of PAR glasses [( 21 , 46 ) and references therein]; δ 34 S (±1 s ) from ( 46 ). †δ 82 Se (±95% CI, N = 31) is estimated using all the depleted MORBs from the MAR and PAR; δ 34 S (±1 s ) and Sr-Nd isotopic ratios from ( 15 , 27 , 48 ). …”

“…See the Supplementary Materials and Methods for the sample literature data. † 82 Se (±95% CI, N = 31) is estimated using all the depleted MORBs from the MAR and PAR;  34 S (±1s) and Sr-Nd isotopic ratios from(15,27,48).…”

Origin of the basal lherzolite of the Muslim Bagh Ophiolite, Pakistan, deduced from the trace element characteristics of clinopyroxene

“…Primitive mantle‐normalized trace‐element patterns for modelled clinopyroxene (grey lines) and the Muslim Bagh basal lherzolite (AM‐33 and B‐6). The influx composition (black line) in the influx‐induced open‐system melting models (b, c) was the composition of a slab‐derived fluid composition estimated from Japanese arc magma (Kimura, Gill, van Keken, Kawabata, & Skora, 2017). Details of the model were given in the text.…”

“…The primitive mantle values are from McDonough and Sun (1995). The influx composition in the influx‐induced open‐system melting models (not shown in this diagram) was the composition of a slab‐derived fluid estimated from Japanese arc magma (Kimura et al, 2017)…”

Effect of Serpentinite Dehydration in Subducting Slabs on Isotopic Diversity in Recycled Oceanic Crust and Its Role in Isotopic Heterogeneity of the Mantle

“…Stracke et al (2005) subsequently modified the definition of FOZO to a range of 206 Pb/ 204 Pb compositions that includes but extends beyond the high 206 Pb/ 204 Pb end of the MORB array. More recent studies have proposed the existence of a deep reservoir of intermediate isotopic composition, formed early in Earth's history, called the early depleted reservoir (EDR), situated near PREMA (Boyet & Carlson, 2005, 2006Jackson et al, 2010;Kimura et al, 2017). Although recent studies using the short-lived 146 Sm-142 Nd radiometric system have obviated the need for EDR (Bouvier & Boyet, 2016;Burkhardt et al, 2016), others using geochemical models or the short-lived 182 Hf-182 W radiometric system have suggested that such a reservoir is preserved in the mantle (Kimura et al, 2017;Rizo et al, 2016).…”