Petrology of gabbroic xenoliths in 1960 Kilauea basalt:
crystalline remnants of prior (1955) magmatism |
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| Authors: | R V Fodor R B Moore |
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| Institution: | (1) Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695 USA, US;(2) U.S. Geological Survey, MS 903, Denver, CO 80225 USA, US |
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| Abstract: | The 1960 Kapoho lavas of Kilauea’s east rift zone contain 1–10 cm xenoliths of olivine gabbro, olivine gabbro-norite, and
gabbro norite. Textures are poikilitic (ol+sp+cpx in pl) and intergranular (cpx+pl±ol±opx). Poikilitic xenoliths, which we
interpret as cumulates, have the most primitive mineral compositions, Fo82.5, cpx Mg# 86.5, and An80.5. Many granular xenoliths (ol and noritic gabbro) contain abundant vesicular glass that gives them intersertal, hyaloophitic,
and overall ‘open’ textures to suggest that they represent ‘mush’ and ‘crust’ of a magma crystallization environment. Their
phase compositions are more evolved (Fo80–70, cpx Mg# 82–75, and An73–63) than those of the poikilitic xenoliths. Associated glass is basaltic, but evolved (MgO 5 wt%; TiO2 3.7–5.8 wt%). The gabbroic xenolith mineral compositions fit existing fractional crystallization models that relate the origins
of various Kilauea lavas to one another. FeO/MgO crystal–liquid partitioning is consistent with the poikilitic ol-gabbro assemblage
forming as a crystallization product from Kilauea summit magma with ∼8 wt% MgO that was parental to evolved lavas on the east
rift zone. For example, least squares calculations link summit magmas to early 1955 rift-zone lavas (∼5 wt% MgO) through ∼28–34%
crystallization of the ol+sp+cpx+pl that comprise the poikilitic ol-gabbros. The other ol-gabbro assemblages and the olivine
gabbro-norite assemblages crystallized from evolved liquids, such as represented by the early 1955 and late 1955 lavas (∼6.5
wt% MgO) of the east rift zone. The eruption of 1960 Kapoho magmas, then, scoured the rift-zone reservoir system to entrain
portions of cumulate and solidification zones that had coated reservoir margins during crystallization of prior east rift-zone
magmas.
Received: January 7, 1993/Accepted: November 23, 1993 |
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| Keywords: | : basalt – gabbro – xenolith – Kilauea – basalt crystallization – basalt phases – cumulate |
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