MG-AL-RICH ADIRONDACK GRENVILLE ULTRAMAFICS: ANYTHING SIMILAR IN SOUTHERN APPALACHIANS?

Most small Adirondack ultramafic bodies associated with anorthosite massifs are relatively Mg-rich, possibly remobilized cumulate bodies (including cross-cutting pyroxenite dikes) with minor interstitial plagioclase as the main Al-bearing phase.

Three southeastern Adirondack Mg-rich ultramafics have distinctly higher Al-content and lack plagioclase. Earliest Al-phase is spinel; others are pyrope, diaspore after spinel, corundum, and sapphirine. The Moon Mountain body comprises forsterite+bronzite+tschermakite+spinel+ phlogopite, with later(?) pyrope, corundum, sapphirine, and kornerupine. The Kelm Pond body comprises high-Al clinopyroxene (with spinel exsolution)+forsterite+ phlogopite+spinel+hornblende and has been mostly serpentinized. The Whitehall body (Whitney, 2002), apparently completely retrogressed, comprises actinolite+phlogopite+serpentine+talc+chlorite+diaspore. The Moon Mountain and Kelm Pond occur as lenses within anorthosite sills. The Whitehall lens is in gneiss. Spinel, rather than plagioclase, as the primary aluminous phase suggests crystallization at lower crustal – upper mantle depths. These Mg-Al-rich ultramafics are interpreted to be slices from the crust-mantle boundary, brought up by anorthositic magmas into the middle crust.

In the southern Appalachians, small ultramafic lenses occur within the Montpelier anorthosite, but are not as aluminous as these Adirondack bodies. Has anyone found Al-rich Grenville ultramafics in the southern Appalachians?