Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)

Paper No. 2
Presentation Time: 1:55 PM


ROOT, Polly, WINTSCH, Robert P., SCHIEBER, Juergen and GROWDON, Martha, Department of Geological Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47405,

Folded rocks of the Moretown member of the Missisquoi Formation, located in the Green Mountains of Vermont, are conspicuously pinstriped and defined by alternating layers of chlorite+muscovite+biotite+epidote+quartz and quartz+feldspar+biotite domains, each 1.5-0.5 mm thick. Contacts between the micaceous and quartzofeldspathic domains appear to alternate between sharp and gradational boundaries on opposing sides of the micaceous domains. Large biotites, approximately 230 microns long, are oriented parallel to the sharp contacts and progressively decrease in grain size into the micaceous layer and away from these sharp contacts. This grain size decrease is accompanied by the occurrence of 10-micron epidote grains. Biotite flakes found within the quartzofeldspathic domain are oriented parallel to the domain boundaries, and, together with these domains, form a penetrative Sn fabric. This Sn fabric is folded by open to tight North-plunging folds. Backscatter electron imaging reveals an incipient Sn+1 biotite fabric, defined by biotite flakes up to 100 microns long, that truncates all minerals in both domains. This new fabric is most prominent at the fold hinges, and, therefore, likely axial planar to these folds. The concentration of biotite in this Sn+1 fabric shows that this axial planar fabric was probably developed by pressure solution/precipitation processes. In contrast, Sn fabrics may be largely inherited from primary S0 bedding.