Amphibolite and blueschist–greenschist facies metamorphism, Blue Mountain inlier, eastern Jamaica

Abstract

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 P-T 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 P-T conditions support a two-stage P-T 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 2.6-3.0 kbars, T ¼ 219-2378C for a(H 2 O) ¼ 0.8-1.0 (GS facies). Mt. Hibernia Schist may represent a volume of rock that was separated and uplifted at an early time from an otherwise protracted P-T path of the sort that produced the Westphalia Schist. Reset K-Ar 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 Albian-Aptian ($112 Ma) orogenic event.

Protolith provenance and thermotectonic history of metamorphic rocks in eastern Jamaica: Evolution of a transform plate boundary

“…Minor constituents include marble, partially serpentinized peridotite, and riebeckite-bearing metachert (Draper, 1987). Metamorphic mineral assemblages in the mafi c rocks involve combinations of glaucophane, pumpellyite, and epidote, coexisting with actinolite, chlorite, albite, and quartz, consistent with blueschist facies metamorphism (Draper, 1986;Willner et al, 1995;Abbott et al, 2003;Abbott and Bandy, 2008). Peak metamorphic conditions for the Mt.…”

“…Peak metamorphic conditions for the Westphalia Schist are unknown. Retrograde conditions have been estimated at ~600 °C at ~8 kbar and ~530 °C at ~6.5 kbar (Abbott et al, 1996;Abbott and Bandy, 2008), consistent with upper amphibolite facies conditions. The only constraint on the timing of this metamorphism is a single K-Ar hornblende age of 78 Ma and two K-Ar biotite ages of 50 Ma and 54 Ma (Lewis et al, 1973, corrected).…”

“…(4) Several isolated, fault-bounded bodies of relatively high-grade metamorphic rock that occur near the southwestern margin of the inlier and immediately outside the inlier (Draper, 1986;Abbott et al, 1996Abbott et al, , 2003Abbott and Bandy, 2008). These include the Westphalia Schist and Mt.…”

“…Hibernia Schist. The conditions of metamorphism within these rocks are well constrained (Willner et al, 1995;Abbott et al, 1996Abbott et al, , 2003Abbott and Bandy, 2008), but little is known of the protoliths or the timing of this metamorphism. Whole-rock geochemical studies are helpful in determining the tectonic settings of the protoliths and provide important constraints on processes occurring along the northern margin of the Caribbean plate.…”

Some speculations on the Paleogene and Neogene tectonics of Jamaica

“…There are even high pressure-low temperature subduction zone metamorphic rocks (of Early? Cretaceous age) in the Blue Mountain area of eastern Jamaica (Draper 1986(Draper , 1987Abbott and Bandy 2008).…”