The origin of the high-K latites from Camp Creek,Arizona: constraints from experiments with variable fO2 and a_{{\text{H}}_{\text{2}} {\text{O}}}期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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The origin of the high-K latites from Camp Creek,Arizona: constraints from experiments with variable fO2 and a_{{\text{H}}_{\text{2}} {\text{O}}}

Authors:	Sonia Esperança John R Holloway

Institution:	(1) Department of Geology, Arizona State University, 85287 Tempe, AZ, USA;(2) Present address: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., 20015 Washington, D.C., USA

Abstract:	Near-liquidus melting experiments were performed on a high-K latite at fO₂'s ranging from iron-wustite-graphite (IWG) to nickel-nickel oxide (NNO) in the presence of a C-O-H fluid phase. Clinopyroxene is a liquidus phase under all conditions. At IWG $(a_{{\text{H}}_{\text{2}} {\text{O}}} = 0.17)$ , the liquidus at 10 kb is about 1,150° C but is depressed to 1,025° C at NNO and $a_{{\text{H}}_{\text{2}} {\text{O}}} = 1$ . Phlogopite and apatite are near-liquidus phases, with apatite crystallizing first at pressures below 10 kb. Phlogopite is a liquidus phase only at NNO and high $a_{{\text{H}}_{\text{2}} {\text{O}}}$ . Under all conditions the high-K latites show a large crystallization interval with phlogopite becoming the dominant crystalline phase with decreasing temperature. Increasing fO₂ affects phlogopite crystallization but the liquidus temperature is essentially a function of $a_{{\text{H}}_{\text{2}} {\text{O}}}$ . The chemical compositions of the near-liquidus phases support formation of the high-K latites under oxidizing conditions (NNO or higher) and high $a_{{\text{H}}_{\text{2}} {\text{O}}}$ . It is concluded from the temperature of the H₂O-saturated liquidus at 10 kb, the groundmass: crystal ratio and presence of chilled latite margins around some xenoliths that the Camp Creek high-K latite magma passed thru the lower crust at temperatures of 1,000° C or more.

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