34 Tectonics and Petrology

Friday, 24 March 2006
1:30 PM - 5:30 PM

DISMEMBERED OPHIOLITES OF THE BLUE RIDGE BELT: WHERE ARE THE PERIDOTITES AND PLUTONIC COMPLEXES

Paper number: 34-11
Program: Technical Sessions
Time: 4:30 PM – 4:50 PM

Authors

Abstract

Ophiolites thought to form in ultraslow, slow, and fast spreading centers all contain various proportions and types of mafic and ultramafic rocks. Alpine (ophiolitic?) ultramafic rocks in the the Blue Ridge Belt of North Carolina and northern Georgia are predominantly (Ca- and Al-poor) metadunites and Ca- and Al-bearing amphibole-chlorite-talc schists. Metaharzburgite, minor metaorthopyroxenite, and rare clinopyroxene-bearing rocks occur locally. Some schists are metamafic rocks, but metabasalt and metagabbro are predominantly represented by hornblende schist and gneiss structurally associated with the ultramafic rocks. The metamorphic hydration of dunites and mafic rocks locally yields Ca- and Al-bearing schists, but the reconstructed structural package of Blue Ridge rocks matches none of the model ophiolites formed at spreading centers, nor do the ultramafic bodies match the common peridotite body types. Plutonic complexes are largely absent.

The peridotite- and plutonic complex-deficient ophiolites either represent a new type of primary ophiolite complex or complexes formed through some combination of metamorphism, metasomatism, and structural fragmentation. Blue Ridge rocks experienced a deep-seated (high pressure) and structurally complex history compared to most well studied ophiolites. The absence of metaperidotites in the Blue Ridge tectonic assemblage may be related to selective removal of the peridotites during deep seated tectonism or preferential conversion of peridotite to amphibole-chlorite-talc schists. The absence of plutonic complexes, however, argues for structural dismemberment. Any identification of ophiolite types in the Blue Ridge Belt must rely on available characteristics, plus analysis of the rarely preserved Ca-bearing metaperidotites.