Site 07 :Apollinaris Patera

MC-23 SE

Viking Orbiter Images : 635A55-57, 596A36

Geologic Setting :

Apollinaris Patera is a shield volcano located just north of the highland-lowland border, and southeast of Elysium Mons; it consists of several members including deposits dissected by channels.

A dome-shaped volcano nearly 200 km across, Apollinaris Patera rises about 5 km above the martian datum ; crater counts and stratigraphic relations suggest a middle Hesperian age for its younger flow. The volcano shows a large, complex summit caldeira 75 km across consisting of at least three coalescing collapse depressions.

Unlike most volcanoes on Mars, Apollinaris Patera does not lie along large fault zones like those in the Tharsis region, nor is it associated with regional alignments such as the volcanic chain extending between Amphitrites and Tyrrhena Patera and possibly on Elysium Mons and Hecates Tholus. Possibly Apollinaris is associated with faulting along the highland-lowland boundary that has been obscured by a cover of younger materials.

Geology Significance :

Apollinaris Patera and the surrounding region is of particular interest for geologists because of the different active episodes pointed out by the succession of lava flows. Volcanic (probably basaltic) eruptions at Apollinaris probably started very early in Hesperian or possibly in Late Noachian and continued intermittently throughout the Hesperian period. The initial effusive lava flows that formed the lower part of the dome were followed by more explosive eruptions of pyroclastic rocks and lavas to build the upper, steeper part of the structure. Depletion of the magma chamber by these eruptions or by withdrawal of the magma produced roof collapse and a large caldera. The last eruption from Apollinaris filled the caldera floor and overflowed from a narrow notch in the south wall of the crater.

Thus, to explore the region of Apollinaris Patera will provide important informations on the past volcanic activity on this region of Mars, and its different phases.

Interaction between volcano and ground-ice is also visible in this region. Throughout the growth of the volcano, magmatic heating heating by dikes and other conduits, as well as by lava flows, melted ground ice within the regolith. The resulting desintegration and collapse of the terrain continued into the Late Hesperian and formed cluster of chaotic hills and mesas. Floods from Ma'adim Vallis, a large channel south of the map area, contributed to the breakup of surface rocks.

A rover mission in this martian region could provide imagery from the walls of the remnant mesas and hills and show the stratigraphy. In addition, outcrops of the Amazonian Madusae Fossae Formation, Hesperian lava flows, and channel material, and Noachian rocks may be readily accessible to a roving vehicle traversing the relatively smooth surface of the flood-plain material.

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