FOLDS PRODUCED BY GRAVITY SPREADING OF A BANDED RHYOLITE LAVA FLOW

Recumbent folds near the top of the Minyon Falls banded rhyolite flow, in northeastern New South Wales, Australia, indicate lateral radial extension of lava as it flowed from the vent under the influence of gravity. These structures occur near the vent of the flow and differ from the upright folds commonly observed near the tops of lava flows. Farther from the vent, the fold patterns indicate lateral radial shortening and shearing as the spread of lava was impeded. Interpretation of the folds leads to a kinematic model of coaxial flow near the vent grading to simple shear and sub-simple shear away from the vent.