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Title: ReversePetrogen : A Multiphase Dry Reverse Fractional Crystallization‐Mantle Melting Thermobarometer Applied to 13,589 Mid‐Ocean Ridge Basalt Glasses
Abstract

We present a new algorithm,ReversePetrogen (RevPet), to infer mantle melting conditions (pressure, temperature, source composition) using evolved basalts that have experienced multiphase fractional crystallization.RevPetmeasures and minimizes the compositional distance between experimentally predicted phase saturation boundaries and an erupted basalt and the more primitive liquids that return it to a primary melt. We useRevPetto investigate mantle melting conditions at mid‐ocean ridges (MORs) using a global data set of 13,589 basaltic glasses. We find that their average apparent mantle potential temperature (TP*) is 1322°C ± 56°C with melting pressures of 13.0 ± 5 kbars. Inferring the true initial (pre‐melted)TPfromTP* requires knowing the style and degree of melting of the input basalts. If MORB glasses were entirely produced by near‐fractional melting of a homogenous source, they would record the cooling of the mantle during melting from an initialTP = ∼1380°C (ΔTP = 0°C) down toTP = ∼1270°C. If, instead, they were all fully pooled near‐fractional melts of the same source, they would record variations in ambient MORTPfrom ∼1300°C to 1450°C (ΔTP = 150°C). However, because MOR basalts are thought to be both near‐fractional and variably pooled melts of variable sources, MORTPmust be intermediate between these two extremes. Our best estimate, consistent with MOR crustal thickness, is that ambient MORTPis homogenous (∼1350°C–1400°C) except near hotspots whereTPreaches ∼1600°C. Some primitive glasses found near slow‐spreading ridges and back‐arcs record very low temperatures (TP* < 1250°C) and pressures of melting (<10 kbar) and reflect mantle cooling during melting and melt equilibration in the mantle lithosphere.

 
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NSF-PAR ID:
10445362
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Journal of Geophysical Research: Solid Earth
Volume:
126
Issue:
8
ISSN:
2169-9313
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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