Summary: Amphibolite and blueschist­greenschist facies metamorphism,
Blue Mountain inlier, eastern Jamaica
RICHARD N. ABBOTT Jr 1* and BETSY R. BANDY 2
1
Department of Geology, Appalachian State University, Boone, NC, USA
2
Department of Geography and Geology, University of the West Indies, Mona, Kingston, Jamaica
Cretaceous (possibly older) metamorphic rock occurs mainly in the Blue Mountain inlier in eastern Jamaica. Fault-bounded
blocks reveal two styles of metamorphism, Westphalia Schist (upper amphibolite facies) and Mt. Hibernia Schist (blueschist
(BS)­greenschist (GS) facies). Both Westphalia Schist and Mt. Hibernia Schist preserve detailed records of retrograde P­T
paths. The paths are independent, but consistent with different parts of the type-Sanbagawa metamorphic facies series in Japan.
For each path, phase relationships and estimated P­T conditions support a two-stage P­T history involving residence at depth,
followed by rapid uplift and cooling. Conditions of residence vary depending on the level in a tectonic block. For the critical
mineral reaction (isograd) in Westphalia Schist, conditions were P $7.5 kbars, T $6008C (upper amphibolite facies). Retrograde
conditions in Hibernia Schist were P ¼ 2.6­3.0 kbars, T ¼ 219­2378C for a(H2O) ¼ 0.8­1.0 (GS facies). Mt. Hibernia Schist
may represent a volume of rock that was separated and uplifted at an early time from an otherwise protracted P­T path of the sort
that produced the Westphalia Schist. Reset K­Ar ages for hornblende and biotite indicate only that retrograde metamorphism of
Westphalia Schist took place prior to 76.5 Ma (pre-Campanian). Uplift may have commenced with an Albian­Aptian ($112 Ma)
orogenic event. Copyright # 2008 John Wiley & Sons, Ltd.
Received 28 June 2007; accepted 8 May 2008

Source: Abbott Jr., Richard N. - Department of Geology, Appalachian State University

Collections: Geosciences