Ce. Manning et al., RAPID HIGH-TEMPERATURE METAMORPHISM OF EAST PACIFIC RISE GABBROS FROMHESS DEEP, Earth and planetary science letters, 144(1-2), 1996, pp. 123-132
Metamorphosed oceanic gabbros provide a record of the cooling history
of the lower crust near mid-ocean ridges, but the temperature range, r
ate, and location of subsolidus events are poorly known. We combine ho
rnblende-plagioclase thermometry, statistical analysis, and thermal mo
dels to estimate precisely the temperature, time, distance from axis,
and duration of metamorphism in East pacific Rise gabbros from Hess De
ep, ODP Hole 894G. Metamorphic hornblende and plagioclase, which forme
d during microfracturing and sea water penetration, equilibrated at a
mean temperature of 716+/-8 degrees C (90% confidence level). Comparis
on of the properties of the observed temperature distribution with tho
se of model events indicates that metamorphism spanned less than or eq
ual to 60 degrees C. When combined with thermal models of fast-spreadi
ng centers, this implies that metamorphism was rapid (less than or equ
al to 6000 yr) and occurred 1-4 km off axis. Application of this appro
ach to other gabbros will allow comparison of spatial and temporal cha
racteristics of deformation and fluid flow in the lower oceanic crust
as a function of ridge setting.