HR: 0800h
AN: T11A-0334    [Abstracts]
TI: Clinker formation in basaltic lava flows
AU: Van Wyk de Vrie, B
EM: B.vanwyk@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, 5 rue Kessler, Clermont Ferrand, 63038, France
AU: * Loock, S
EM: S.Loock@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, 5 rue Kessler, Clermont Ferrand, 63038, France
AU: Henot, J
EM: JM.Henot@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, 5 rue Kessler, Clermont Ferrand, 63038, France
AB: Basaltic lava flows are classified according their surface morphology. They can be either aa, displaying a rough clinkery surface or pahoehoe, displaying a smooth clinkerless surface. These two surface types differ also in their emplacement and rheology, and can be differentiated in a shear-strain rate vs. apparent viscosity diagram (Hon & al., 2003). To understand clinker formation, one way is to see how a pahoehoe lava converts to an aa through shear-viscosity changes. Two possibilities occur: 1) the viscosity can increase (e.g. by levee formation) and clinkers will be formed by torque on the flow edges, or 2) the shear-strain will increase (lava influx increasing, topographic obstacles, slope change) and clinker will be formed by crust-breakage. These two clinker formatting processes are called magmatic fragmentation. Clinker will be formed on the summit and to the edges of the flow and they will appear at the base of its according the caterpillar motion usually associated with flows. However, in the Chaîne des Puys (French), basal clinker appears without top clinker (i.e. a pahoehoe lava flow with basal clinker) and thus another explanation is needed to explain them. Clinker samples were collected in different emplacement contexts and different part of flows. The SEM analysis of these samples and comparisons with ash samples from the literature show classical magmatic fragmentation textures (stepped fractures, non- synchronic fractures) in three aa lava flows. However, in one pahoehoe flow there are typical phreatomagmatic textures (blocky shapes, adhering fine particles). There are also shearing structures, such as microfaults in an intermediate flow. Thus, there are at least three different ways to form clinker: 1) classically by fragmentation at the flow base and the edges; 2) by phreatomagmatism at the base flow; 3) by shearing at the flow base and the edges. Basal shearing structures include fault gauges and welded clasts, indicating possible shear heating at the base of some flows. Heated water in breccia may also aid to lubricate the base, aiding flow advancement by slippage.
DE: 1832 Groundwater transport
DE: 5104 Fracture and flow
DE: 5112 Microstructure
DE: 8030 Microstructures
DE: 8429 Lava rheology and morphology
SC: Tectonophysics [T]
MN: 2007 Fall Meeting