EOLIAN DEPOSITS OF PYROCLASTIC VOLCANIC DEBRIS IN METEOR CRATER

Barringer Meteorite Crater, more commonly known as Meteor Crater, was excavated by an impacting iron asteroid ~50 ka. It is Earth’s best preserved impact crater. Nonetheless, some erosion has affected the crater walls, and sediments have accumulated on the crater floor. Recently, an eolian deposit was discovered along the southwest crater wall beneath a layer of colluvium. It contains sediments derived from the local target material, as well as unexpected pyroclastic vesicular volcanic ash and cinder debris. Here we (1) report petrologic analyses of the pyroclastic debris and (2) explore possible sources for the volcanic material. Samples were examined under an optical petrographic microscope to characterize the internal textures and particle sizes. Two samples were selected for further compositional analyses of mineral phases. Major and minor element analyses were conducted using a Cameca SX-100 Electron Microprobe (EMP) at NASA Johnson Space Center (JSC), with five wave-dispersive spectrometers. Samples contained Mg-rich olivine (Fo_80.5-74.9), Ca-rich plagioclase (An_72.0-55.3Ab_42.8-27.4Or_2.0-1.0) and Ca-rich clinopyroxene (Wo_44.3-43.8En_44.7-36.8Fs_19.0-11.5), and are classified as either basalt or andesitic basalt. Two potential source vents occur in the region, Sunset Crater and Merriam Crater. Both basaltic cinder cones have similar mineral compositions and are <60 km from Meteor Crater. Sunset Crater is younger than Meteor Crater, so its ash could have been deposited directly into the crater. Merriam, on the other hand, is older, which would require the reworking and secondary transport of ash to Meteor Crater after it formed.