Abstract
Reactive liquid flow is a common
process in layered intrusions and more generally in episodically
refilled magma chambers. Interaction between newly injected melt and
cumulates, or crystal mushes, perturbs the liquid line of descent of the
melt and modifies mineral chemistry and texture. We present insights
into the effects of assimilation of mafic cumulate rocks (gabbro,
troctolite) by cogenetic Mg-rich basalt liquid using one-atmosphere,
controlled fO2 phase
equilibrium experiments on picritic parental liquid to the Rum layered
intrusion, Scotland. For picrite-only experiments at fO2 = QFM, Cr-spinel (Cr# = Cr/[Cr + Al + Fe3+] = 0.43; Fe# = Fe2+/[Mg + Fe2+] = 0.32) saturates at 1320 °C, olivine (Fo88) at ~1290 °C, plagioclase (An77)
at 1200 °C, and clinopyroxene (Mg#: 0.81) at 1180 °C. In melting
experiments on picrite + gabbro mixtures, plagioclase (1230 °C, An80)
and clinopyroxene (1200 °C, Mg#: 0.85) saturation temperature and mode
are increased significantly. Cr-spinel in these experiments has a
distinctive, low Fe#. In melting experiments on picrite + troctolite
mixtures, plagioclase (An86) saturates at 1240 °C and
clinopyroxene (Mg#: 0.81) at 1170 °C. Al-rich spinel crystallizes at
high temperature (>1220 °C) and becomes more Cr-rich upon cooling,
reaching the highest Cr# = 0.47 at 1180 °C (0.54 at QFM-1.2). The
experimental results confirm that plagioclase and clinopyroxene
stability plays a major role in determining the composition of
coexisting spinel. Comparing our experimental results to the Rum Eastern
Layered Intrusion, we propose a model for the precipitation of spinel
from picrite–troctolite hybrid melt that is compatible with the observed
olivine, plagioclase, and clinopyroxene chemistry.
Original language | English |
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Article number | 12 |
Number of pages | 27 |
Journal | Contributions to Mineralogy and Petrology |
Volume | 170 |
Issue number | 2 |
Early online date | 25 Jul 2015 |
DOIs | |
Publication status | Published - 29 Aug 2015 |
Keywords
- 1atm experimental petrology
- Cr-spinel
- Gabbro melting
- Picrite
- Reactive liquid flow
- Rum layered intrusion
- Troctolite melting