Metamorphism of the Murphy belt, Marble Hill, GA
- Georgia State Univ., Atlanta, GA (United States). Geology Dept.
Rocks of the Murphy belt consist of marble and metamorphosed mafic and highly aluminous pelitic rocks. The aluminous rocks contain sillimanite + kyanite + staurolite + garnet (gt) + muscovite + biotite + plagioclase + quartz [+-] tourmaline. Staurolite and kyanite are relict and closely intergrown. Garnet occurs as two generations, gt 1 and gt 2. Gt 1 and the biotite schistosity are coeval. Sillimanite needles and large porphyroblasts of muscovite (0.5--2.0 cm), formed from kyanite-staurolite aggregates coevally with gt 2, and both contain inclusions of relict kyanite and staurolite. Both are younger than the primary biotite schistosity and grew at sillimanite-muscovite grade. Muscovite porphyroblasts are partially recrystallized, leaving mica fish with thin trails of fine-grained muscovite. Kyanite [+-] staurolite are partially to completely recrystallized to spindle shaped aggregates and fine-grained muscovite. Some fine muscovite mantles the earlier phases and defined the new foliation. No sillimanite occurs in the recrystallized muscovite. This extreme grain size reduction occurred during medium-T retrograde metamorphism and converted many rocks into button schists or phyllonites. The above indicate extreme internal deformation following the metamorphic peak, during which primary sedimentary structures were destroyed. Also, competent mafic lithologies were dismembered into pods and discontinuous layers. Lithologic boundaries are no longer sedimentary, but tectonic. The association of aluminous schists and mafic rocks suggests deep-marine deposition, probably along a convergent margin. Conversely, the association is inconsistent with shallow deposition along a stable passive margin. The marble probably represents discontinuous reefs associated with the volcanic arc.
- OSTI ID:
- 6119366
- Report Number(s):
- CONF-9304188-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:4; Conference: 42. annual Geological Society of America (GSA) Southeastern Section meeting, Tallahassee, FL (United States), 1-2 Apr 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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