Basaltic Magma-Water Interaction on Earth: Recognition Criteria To Aid Planetary Mapping on Mars (Invited)
Abstract
The interaction of basaltic magma with frozen/liquid water or wet sediment is a very common process on Earth, resulting in a wide array of explosively and non-explosively generated products at the micron to kilometre scale. A variety of products and edifices on Mars have also been interpreted as having formed by such interaction, but with the exception of rootless cones, such interpretations are rarely unequivocal. This talk focuses on terrestrial process recognition criteria at a scale, orientation (vertical) and erosion level that is relevant to Mars geological mapping. In this context, we emphasise intrusions with peperite margins and wide hydrothermal haloes, steep margins of ice-contact lava flows, subaerial-subaqueous lava delta transitions, lava domains with distinctive water-cooled jointing, edifices that are dominated by slumped and rotated beds, and the presence of surrounding fluvial deposits and erosion. The most common products of magma-water interaction on Earth are subaqueously emplaced lava flows, which are dominated by pillow lavas. Though pillows are not easy to distinguish from subaerial pahoehoe toes at the resolution of most remote imagery, they are commonly associated with distinctively jointed lava domains, which are usually on a larger scale, including areas of water-cooled jointing (curvicolumnar, blocky etc), lava-filled tubes, which often display radial jointing, and steep talus deposits of joint-block breccia. Subaqueous basaltic lavas emplaced in an ice-confined environment may also display near-vertical ice-contact margins, draped by curtains of elongate pillows or cavities formed from melting of included ice-blocks. Subaerial lava flows that transition into water also develop large-scale foreset-bedding close to the angle of repose, which should be easily visible, at least in oblique imagery. As the majority of the Martian surface is more deeply eroded than most areas of terrestrial basaltic volcanism, it is important to discuss intrusive processes in wet environments on Earth, where intrusions commonly mingle with surrounding unconsolidated clastic deposits, generating peperite. Such domains are typically on the metre to 100s metres scale and may be associated with wide (<25m) surrounding haloes of hydrothermal alteration. Basaltic peperite is often intimately associated with coherent domains, including dikes with pillowed margins, pillowed stringers, and irregular domains of water-cooled lava. Basaltic magma emplaced into ice-cemented deposits can also generate distinctive clastic dikes with coherent margins of chilled lava. Basaltic lavas emplaced in shallow (<500m) water may be draped with a variety of explosively-generated vitriclastic deposits and their reworked equivalents. A distinctive feature of these deposits that is relevant to planetary mappers, is that they are very susceptible to collapse, during or shortly after emplacement, generating rotated beds with bedding angles greater than the angle of repose and slump structures. In ice-confined environments the deposits may also be reworked as meltwater flood deposits in erosion channels
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.V51G..03S
- Keywords:
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- 5480 PLANETARY SCIENCES: SOLID SURFACE PLANETS Volcanism;
- 6225 PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS Mars;
- 8427 VOLCANOLOGY Subaqueous volcanism