5 Deposition and Diagenesis of Volcaniclastic Sediments on Earth and Mars

Tuesday, 23 May 2017
8:30 AM - 11:50 AM
Room 325B

CHARACTERISTICS OF BASALTIC SEDIMENTS DEPOSITED IN A VARIETY OF GEOLOGIC ENVIRONMENTS ON HAWAII

Paper number: 5-2
Program: Theme Sessions
Time: 8:35 AM – 8:55 AM

Authors

Abstract

Terrestrial sediments are often classified by the amount of quartz that is present. Analyses of the shapes and textures of the quartz grains can also provide important diagnostic information about the geologic processes responsible for transporting the sediments as well as provenance and diagenesis. However, the surface of Mars is composed exclusively of basalt, which does not contain quartz. Instead, basaltic sediments consist of lithic and vitric fragments, olivine, pyroxene, feldspars, and other heavy minerals such as magnetite. To better understand the characteristics of basaltic sediments and how they mature as a function of transport process, we have analyzed a variety of deposits collected from different environments, including ephermal streams, playas, aeolian dunes, and glacial till.

The chemical stability of terrestrial felsic sediments can be arranged in a sequential order that essentially reflects Bowen’s Reaction Series. For example, olivine is the most labile whereas quartz, tourmaline and zircon are the most stable. For basaltic sediments, we propose applying the mineral paragenesis table derived by Wright and Okamura (1977) by sampling the Makaopuhi lava lake in Hawaii over time. Their table 15 presents the following minerals that crystalized at progressively decreasing temperatures:

Olivine (Fo80-85)

Augite

Plagioclase

Ilmenite

Olivine (Fo55)

Pigeonite

Magnetite

Apatite

The more stable minerals crystalize at lower temperatures. Vitric fragments, which are a common constituent in basaltic sediments, would be the most labile, while lithic fragments would be the most stable. Lithic fragments of basalt share many of the same properties of quartz crystals. Quartz has a hardness of 7, a specific gravity of 2.6, and fractures conchoidally. Basalt has a hardness of 6, a specific gravity of 2.8-3.0, and also fracture conchoidally. However, quartz is anisotropic and basalt is isotropic. We will show examples as to how this difference influences the grain shape and surface texture of basaltic sediments.

Geological Society of America Abstracts with Programs. Vol. 49, No. 4

doi: 10.1130/abs/2017CD-292423

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