Formation of anorthosite-Gabbro rhythmic phase layering: an example at North Arm Mountain, Bay of Isands ophiolite
Journal of Petrology
By: S.C. Komor and D. Elthon
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Abstract
Rhythmically layered anorthosite and gabbro are exposed in a 4-10-m thick interval at the base of the layered gabbro unit on North Arm Mountain, one of four massifs that compose the Bay of Islands ophiolite, Newfoundland. The rhythmically layered interval is sandwiched between thick layers of adcumulate to orthocumulate uniform gabbro. Calculated fractional crystallization paths and correlated cryptic variation patterns suggest that uniform and rhythmically layered gabbros represent 20-30% in situ crystallization of two distinct magma batches, one more evolved and the other more primitive. When the more primitive magma entered the crystallization site of the NA300-301 gabbros, it is estimated to have been ~40??C hotter than the resident evolved magma, and may have been chilled by contact with a magma chamber margin composed of uniform gabbro. In this model, chilling caused the liquid to become supercooled with respect to plagioclase nucleation temperatures, resulting in crystallization of gabbro deficient in plagioclase relative to equilibrium cotectic proportions. Subtraction of a plagioclase-poor melagabbro enriched the liquid in normative plagioclase, which in turn led to crystallization of an anorthosite layer. -from Authors
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Formation of anorthosite-Gabbro rhythmic phase layering: an example at North Arm Mountain, Bay of Isands ophiolite |
| Series title | Journal of Petrology |
| Volume | 31 |
| Issue | 1 |
| Year Published | 1990 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Journal of Petrology |
| First page | 1 |
| Last page | 50 |
| Google Analytic Metrics | Metrics page |