Metamorphic petrology of the northeast Front Range, Colorado: the Pingree Park area.

被引：0

作者：

Nesse, W.D. ^{[1
]}

机构：

[1] Dept. of Earth Sciences, Univ. of N Colorado, Greeley, CO 80639, USA., United States

来源：

| 1984年 / 95期

关键词：

Mica - Sodium compounds;

D O I：

暂无

中图分类号：

P57 [矿物学];

学科分类号：

070901 ;

摘要：

This area is underlain by Precambrian pelitic and semipelitic gneiss and schist that were metamorphosed approx 1700 m.y. ago, forming a distinct zonal pattern of minerals indicating an increase in metamorphic grade to the W and S. Three isograds have been identified. The andalusite-sillimanite isograd is defined by the first appearance of sillimanite from andalusite in the prograde direction. The K-feldspar-sillimanite isograd represents the reaction (K,Na)muscovite + quartz rt arrow (K,Na)microcline + sillimanite + H2O. The migmatite-in isograd is defined by the first occurrence of migmatitic rocks in the prograde direction marking the inception of partial melting. Based on the composition of the minerals and comparison with experimental data, the conditions of metamorphism at the K-feldspar-sillimanite isograd are estimated to have been PH2O approx Ptotal = 3-4 kbar, T 650 + or - 30oC, fO2 approx 10-12 to 10-15 bars and fHF approx 0.25 to 1 bar. The geothermal gradient at the peak of metamorphism was approx 60oC/km.-L.di H.

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