Presentation on theme: "R. A. De Hon 2011 GSA Annual Meeting CRATER MORPHOLOGIES IN MONOGENETIC VOLCANIC FIELDS OF WESTERN NEW MEXICO."— Presentation transcript:
R. A. De Hon 2011 GSA Annual Meeting CRATER MORPHOLOGIES IN MONOGENETIC VOLCANIC FIELDS OF WESTERN NEW MEXICO
THE SIGNIFICANCE OF MAARS ON EARTH AND MARS R. A. De Hon 2011 GSA ANNUAL MEETING Rebranded
THIS PRESENTATION As original title states… Morphology of landforms in three monogenic volcanic fields in western New Mexico Specifically, the morphology of… Maar craters Tuff cones Cinder cones Located in …New Mexico: Red Hill-Quemado Volcanic Field Bandera Volcanic Field Mt. Taylor-Mesa Chivato Volcanic Field
WITH SPECIAL ATTENTION TO MAAR CRATERS Maar craters are formed when magma encounters groundwater. The resultant steam explosion excavates a bowl-shaped pit surrounded by a tuff ring that resembles a meteorite crater. The term maar comes from a Franconian dialect for lake derived from the Latin “mare” (sea). In the type locality—the Efiel Region of Germany— the craters extend below the water table and are occupied by lakes. Maar craters range in size from a few hundred meters to several kilometers in diameter. Their eruptive history consists of repeated venting over a period of weeks or months.
CREDITS – PREVIOUS WORKERS Jayne C. Aubele Larry S. Crumpler A. W. Laughlin P. W. Lipman C. Maxwell And many others
WHY DO WE CARE? Early ejecta in maar craters contain accidentals from underlying strata. Occasionally the ejecta incudes mantle xenoliths. Maare on Mars may be unique sites to obtain deep crustal samples. Mantle xenolith Kilbourne Hole, NM
ULTIMATE OBJECTIVES Volcanic morphometry with attention to explosive craters and transitional forms Early ejecta as sampling of subjacent rock materials Magma, vapor, country rock interactions and final crater morphology Application to Mars volcanic craters and possibility of maar craters as crustal sampling sites
Base surge and Air Fall— Reworked shallow sublacent material Vent Opening Breccia— Most of the subcrater xenoliths are found here.
PRISTINE Tuff Ring Maar Cinder cone VOLCANIC CENTRAL VENT VARIATIONS 1 km All profiles to same scale. Variation in size is chiefly due to the duration of eruptions and volume of material ejected. Constituents of the eruption changes as eruption progresses… Lava Scoraceous cinders Epiclastic tuff Early xenolith-rich breccia
VENT MORPHOLOGY A FUNCTION OF Composition of magma and volatile content of magma Depth of magma and groundwater interaction Volatiles in country rock Connate water Groundwater Ground ice Continuing activity Pyroclastic Lava Resistance of country rock Slumping during eruptive phase Degradation following eruption
Renewed activity Pristine Degraded Cone filling maar Tuff Ring Breached crater Cone-in-maarMaarRimless depression Explosion crater?Cinder cone Scoria Mound VOLCANIC CENTRAL VENT VARIATIONS 1 km All profiles to same scale.
SO, THE POINT IS… Earliest maar ejecta provide a sampling of substrate materials. Those materials may be preserved in a variety for subsequent structures. Some day, in future exploration of Mars, maare will be important sites to visit and sample.