Phosphorus zonation as a record of olivine crystallization history

Abstract

Rapid diffusion of divalent cations through olivine at magmatic temperatures can result in relaxation of their zoning profiles and a loss of information regarding early crystallization history. Recent studies [1-3] show that zoning of P (and often associated Al and Cr) is ubiquitous in igneous olivines from a range of rock types, even in crystals homogenized with respect to divalent cations. We present results of 1-atm controlled cooling rate experiments (5-15°C/hr; QFM) that crystallized olivine from a natural Hawaiian basalt to which olivine was added (liquidus = 1287°C) and a P-free but otherwise compositionally identical synthetic analog. Experiments were either initially superheated to 1300°C for 3 h (leading to destruction of olivine nuclei) or held at subliquidus conditions for 3 h (1280°C; resulting in ~5% olivine nuclei), followed by linear cooling, and then quenching at 1150°C.

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