Temperatures and cooling rates recorded in REE in coexisting pyroxenes in ophiolitic and abyssal peridotites

Abstract

Mantle peridotites from ophiolites are commonly interpreted as having mid-ocean ridge (MOR) or supra-subduction zone (SSZ) affinity. Recently, an REE-in-two-pyroxene thermometer was developed (Liang et al., 2013) that has higher closure temperatures (designated as TREE) than major element based two-pyroxene thermometers for mafic and ultramafic rocks that experienced cooling. The REE-in-two-pyroxene thermometer has the potential to extract meaningful cooling rates from ophiolitic peridotites and thus shed new light on the thermal history of the different tectonic regimes. We calculated TREE for available literature data from abyssal peridotites, subcontinental (SC) peridotites, and ophiolites around the world (Alps, Coast Range, Corsica, New Caledonia, Oman, Othris, Puerto Rico, Russia, and Turkey), and augmented the data with new measurements for peridotites from the Trinity and Josephine ophiolites and the Mariana trench. TREE are compared to major element based thermometers, including the two-pyroxene thermometer of Brey and Köhler (1990) (TBKN). Samples with SC affinity have TREE and TBKN in good agreement. Samples with MOR and SSZ affinity have near-solidus TREE but TBKN hundreds of degrees lower. Closure temperatures for REE and Fe–Mg in pyroxenes were calculated to compare cooling rates among abyssal peridotites, MOR ophiolites, and SSZ ophiolites. Abyssal peridotites appear to cool more rapidly than peridotites from most ophiolites. On average, SSZ ophiolites have lower closure temperatures than abyssal peridotites and many ophiolites with MOR affinity. We propose that these lower temperatures can be attributed to the residence time in the cooling oceanic lithosphere prior to obduction. MOR ophiolites define a continuum spanning cooling rates from SSZ ophiolites to abyssal peridotites. Consistent high closure temperatures for abyssal peridotites and the Oman and Corsica ophiolites suggests hydrothermal circulation and/or rapid cooling events (e.g., normal faulting, unroofing) control the late thermal histories of peridotites from transform faults and slow and fast spreading centers with or without a crustal section.