Constraints on the Thickness of the Ionian Lithosphere

Details Constraints on the Thickness of the Ionian Lithosphere Constraints on the Thickness of the Ionian Lithosphere

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p72b0502j&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #P72B-0502

Physics

5475 Tectonics (8149), 8010 Fractures And Faults, 8120 Dynamics Of Lithosphere And Mantle: General

Scientific paper

The surface of Io primarily consists of isolated mountains and paterae (i.e., volcanic depressions) scattered over vast, smooth plains with occasional scarps. Though Io is the most volcanically active body in the solar system, the jagged morphology of its mountains and their lack of summit calderas suggest that they are not volcanoes [1,2,3]. Instead it is hypothesized that most mountains are thrust sheets uplifted primarily by subsidence-related stresses [4,5] and secondarily by thermal expansion [5]. If this hypothesis is correct, the geometries of thrust faults and the depth to which they penetrate should be important factors in controlling mountain dimensions. On average, ionian mountains are observed to be 158 km x 80 km x 6.3 km [7] and estimated to contain ~32,500 km3 of material [5]. Using these values, previous work has constrained the thickness of Io's lithosphere to >13 km by equating the volume of material needed to accommodate global subsidence and thermal expansion (two values dependent on lithospheric thickness) with the volume taken up by mountains and predicted rock compression [5]. Individual thrust faults on Io may have either linear or listric profiles, and individual mountains may be uplifted along any number of faults. Because the magnitude of the horizontal compressive stress in Io's lithosphere is zero at the surface and increases with depth, it is likely that ionian mountains are uplifted along leading imbricate thrust complexes (i.e., stacks of thrust sheets in which the most slip occurs along the frontal fault) that fully transect the lithosphere [6]. Assuming that ionian mountains are uplifted along such thrust complexes and that individual faults within the complexes have constant dips of 25°, we find that mountains consistent with the observed dimensions are formed for a lithosphere ~20 km thick. We also find that, if our assumptions are realistic, Io's elastic lithosphere must be <40 km thick. Our continuing research is aimed at placing a more rigid upper limit on the thickness of the ionian lithosphere by investigating the effect of listric fault profiles. References: [1] Schaber (1982) in The Satellites of Jupiter, pp. 556-597. [2] Nash et al. (1986) in Satellites, pp. 629-688. [3] McEwen et al. (1989) in NASA Spec. Pub. SP-464, pp. 11-47. [4] Schenk and Bulmer (1998) Science 279, 1514-1517. [5] Jaeger et al., (in review) JGR. [6] Jaeger et al. (2002) LPSC XXXIII, abstract 1741. [7] Schenk et al. (2001) JGR 106, 33210-33222.

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