Paper No. 3
Presentation Time: 8:00 AM-6:00 PM
GEOLOGIC HISTORY OF APOLLINARIS PATERA, MARS
FARRELL, Alexandra K.1, LANG, N.P.
2, PRABHAT, K.C.
1, DEFAZIO, Elizabeth
1, KELLEY, R.J.
3 and SCHNEIDER, Richard
1, (1)Department of Geology, Mercyhurst College, 501 E. 38th Street, Erie, PA 16546, (2)Department of Geology, Mercyhurst University, Erie, PA 16546, (3)Geography-Geology, Illinois State University, 1612 1/2 Beech st, Normal, IL 61761, afarre87@mercyhurst.edu
Apollinaris Patera (AP; 8.5°S, 174°E) is a singular, isolated volcano located along the boundary between Mars’ northern lowlands and the southern highlands. AP has an E-W diameter of 160 km with slopes of ~3° at the base that steepen to ~5° near the summit. Morphologically, AP is divisible into an inner and outer summit caldera, two fan-shaped units that originate from the summit, and homogeneous, undifferentiated flank materials that comprise much of the volcanic edifice. The outer caldera is ~80 km in diameter and is denoted by concentric graben that are locally overlain by texturally rough, easily erodible deposits that we interpret as pyroclastic in origin. The inner caldera cuts into the outer caldera and is ~50 km in diameter; in contrast to the outer caldera, the inner caldera consists of texturally smooth, mechanically strong material that we interpret as representing one effusive deposit. The flank materials and fan-shaped deposits are incised by numerous channels suggesting that much of the volcano is composed weak, friable materials that are similar to the outer caldera (i.e., pyroclastic deposits) that have locally undergone some slumping. In turn, a ~2000 m high basal scarp bounds much of the edifice, which is overlain by both fan-shaped units.
Based on superposition, cross-cutting, and topographic relationships, we interpret AP’s geologic history as follows: 1) Multiple episodes of explosive activity that resulted in the emplacement of much of the homogeneous, undifferentiated flank materials; this activity likely included formation of the outer caldera. Because of the homogeneous nature of much of the flank materials, it is indeterminable as to exactly how many eruptive episodes occurred. 2) A period of repose during which time the basal scarp formed. 3) Renewed explosive activity that resulted in the emplacement of the two fan-shaped deposits. 4) A period of effusive activity that included formation of the inner caldera; this likely represents the end of volcanism at AP. 5) Erosion of the volcanic edifice through channel formation (via water?) and local mass-wasting. The duration of each phase of activity at AP is unknown, but may be constrained by acquiring crater model ages of each of the volcano’s deposits.
