The Lassell massif-A silicic lunar volcano

J. W. Ashley, Mark Robinson, J. D. Stopar, T. D. Glotch, B. Ray Hawke, C. H. van der Bogert, H. Hiesinger, S. J. Lawrence, B. L. Jolliff, B. T. Greenhagen, T. A. Giguere, D. A. Paige

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Abstract

Lunar surface volcanic processes are dominated by mare-producing basaltic extrusions. However, spectral anomalies, landform morphology, and granitic or rhyolitic components found in the Apollo sample suites indicate limited occurrences of non-mare, geochemically evolved (Si-enriched) volcanic deposits. Recent thermal infrared spectroscopy, high-resolution imagery, and topographic data from the Lunar Reconnaissance Orbiter (LRO) show that most of the historic "red spots" and other, less well-known locations on the Moon, are indeed silica rich (relative to basalt). Here we present a geologic investigation of the Lassell massif (14.65°S, 350.96°E) near the center of Alphonsus A basin in Mare Nubium, where high-silica thermal emission signals correspond with morphological indications of viscous (possibly also explosive) extrusion, and small-scale, low-reflectance deposits occur in a variety of stratigraphic relationships. Multiple layers with stair-step lobate forms suggest different eruption events or pulsing within a single eruption. Absolute model ages derived from crater size-frequency distributions (CSFDs) indicate that the northern parts of the massif were emplaced at ~4 Ga, before the surrounding mare. However, CSFDs also indicate the possibility of more recent resurfacing events. The complex resurfacing history might be explained by either continuous resurfacing due to mass wasting and/or the emplacement of pyroclastics. Relatively low-reflectance deposits are visible at meter-scale resolutions (below detection limits for compositional analysis) at multiple locations across the massif, suggestive of pyroclastic activity, a quenched flow surface, or late-stage mafic materials. Compositional evidence from 7-band UV/VIS spectral data at the kilometer-scale and morphologic evidence for possible caldera collapse and/or explosive venting support the interpretation of a complex volcanic history for the Lassell massif.

Original languageEnglish (US)
Pages (from-to)248-261
Number of pages14
JournalIcarus
Volume273
DOIs
StatePublished - Jul 15 2016

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Keywords

  • Image processing
  • Infrared observations
  • Moon, interior
  • Moon, surface
  • Volcanism

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Ashley, J. W., Robinson, M., Stopar, J. D., Glotch, T. D., Hawke, B. R., van der Bogert, C. H., Hiesinger, H., Lawrence, S. J., Jolliff, B. L., Greenhagen, B. T., Giguere, T. A., & Paige, D. A. (2016). The Lassell massif-A silicic lunar volcano. Icarus, 273, 248-261. https://doi.org/10.1016/j.icarus.2015.12.036