Non-mare silicic volcanism on the lunar farside at Compton–Belkovich

Journal name:
Nature Geoscience
Volume:
4,
Pages:
566–571
Year published:
DOI:
doi:10.1038/ngeo1212
Received
Accepted
Published online

Abstract

Non-basaltic volcanism is rare on the Moon. The best known examples occur on the lunar nearside in the compositionally evolved Procellarum KREEP terrane. However, there is an isolated thorium-rich area—the Compton–Belkovich thorium anomaly—on the lunar farside for which the origin is enigmatic. Here we use images from the Lunar Reconnaissance Orbiter Cameras, digital terrain models and spectral data from the Diviner lunar radiometer to assess the morphology and composition of this region. We identify a central feature, 25 by 35km across, that is characterized by elevated topography and relatively high reflectance. The topography includes a series of domes that range from less than 1km to more than 6km across, some with steeply sloping sides. We interpret these as volcanic domes formed from viscous lava. We also observe arcuate to irregular circular depressions, which we suggest result from collapse associated with volcanism. We find that the volcanic feature is also enriched in silica or alkali-feldspar, indicative of compositionally evolved, rhyolitic volcanic materials. We suggest that the Compton–Belkovich thorium anomaly represents a rare occurrence of non-basaltic volcanism on the lunar farside. We conclude that compositionally evolved volcanism did occur far removed from the Procellarum KREEP terrane.

At a glance

Figures

  1. Compton-Belkovich thorium anomaly.
    Figure 1: Compton–Belkovich thorium anomaly.

    The location of the CBTA is northeast of Humboldtianum basin and just beyond the Moon’s eastern limb (LP–GRS 0.5°, ~15km resolution Th data1, 2 as deconvolved by Lawrence et al. 3, overlain on WAC 400m per pixel base). The highest measured Th intensity corresponds to a concentration at this resolution of ~10ppm at the centre of the Th hotspot.

  2. Geomorphology of the CBF.
    Figure 2: Geomorphology of the CBF.

    a, Portion of WAC image showing high-reflectance terrain. Dashed outline denotes the topographically elevated area (Fig. 3). b, NAC mosaic showing the central region of the CBF and location of features discussed in text. Arrows indicate arcuate escarpments; double arrow locates the elongate rock body referred to in the text and Fig. 4 as ‘middle dome.’ Numbers 1 and 2 locate corresponding areas on parts b and c, 1, 2, and 3 correspond to irregular depressions (see text). c, Digital terrain model of the area noted in part a. d, Arcuate escarpment along the western side of the central depression. e, Small dome.

  3. Topography of the CBF.
    Figure 3: Topography of the CBF.

    a, WAC DTM (200m per pixel, draped over WAC orthophoto, 100m per pixel). b, Elevation profiles for sections a–a′ and b–b′ generated from the WAC DTM.

  4. Domes in the CBF.
    Figure 4: Domes in the CBF.

    Positive relief features in the CBF inferred to be volcanic in origin.

  5. Compositions of the CBTA and surrounding region.
    Figure 5: Compositions of the CBTA and surrounding region.

    LP–GRS Th versus FeO for the region 80°–120°E and 50°–65° N. Low altitude, 2° binned data1, 2, 8. Vectors point to compositions of relevant lunar rock types6, 12, 13, 14, 15, 17. The LP–GRS data in the Compton–Belkovich region are consistent with granite (rhyolite) or a mixture of granite and alkali anorthosite, norite and/or gabbro with well-mixed feldspathic highlands and basalt derived from nearby mare surfaces via impact processes.

  6. Mineralogical information from LRO Diviner.
    Figure 6: Mineralogical information from LRO Diviner.

    Spectral data from Diviner showing the Christiansen feature position (7.1–8.6μm; refs 22, 23) overlain on an LRO WAC image. The red line represents the outline of the highly reflective area. The CF modelled data shown here as being more polymerized (blue) correspond more closely to the highly reflective terrain than to the topographically elevated area.

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Author information

Affiliations

  1. Department of Earth and Planetary Sciences and the McDonnell Center for the Space Sciences, Washington University, One Brookings Drive, St Louis, Missouri 63130, USA

    • Bradley L. Jolliff
  2. Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA

    • Sandra A. Wiseman
  3. School of Earth and Space Exploration, Box 871404, Arizona State University, Tempe, Arizona 85287, USA

    • Samuel J. Lawrence,
    • Thanh N. Tran,
    • Mark S. Robinson &
    • Hiroyuki Sato
  4. Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii 96822, USA

    • B. Ray Hawke
  5. German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstr. 2, D-12489 Berlin, Germany

    • Frank Scholten &
    • Jürgen Oberst
  6. Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Muenster, Germany

    • Harald Hiesinger &
    • Carolyn H. van der Bogert
  7. Jet Propulsion Laboratory, 4800 Oak Grove Drive, M/S 183-301, Pasadena, California 91109, USA

    • Benjamin T. Greenhagen
  8. Department of Geosciences, Stony Brook University, Stony Brook, New York 11794, USA

    • Timothy D. Glotch
  9. Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA

    • David A. Paige

Contributions

B.L.J. drafted the initial manuscript. S.A.W. processed WAC images and DTMs, and assisted with NAC image processing. S.J.L. worked with B.L.J. on the topic of lunar red spots and volcanic domes. M.S.R is the principal investigator of the LRO Cameras, was responsible for development and operation of the camera system, and contributed to scientific interpretations. F.S. and J.O. of DLR derived and provided the WAC DTM. T.N.T. processed and provided the NAC DTMs and first characterized the ‘big dome.’ S.J.L., M.S.R., B.R.H., H.H., and C.H.v.d.B. provided input on geological relationships and contributed to writing the paper. H.S. provided data for reflectance analysis. B.T.G. and D.A.P. provided the Diviner data, T.D.G. contributed to interpretation of the CF, and D.A.P. is the principal investigator of the Diviner lunar radiometer. All of the authors contributed to assessment and discussion of the results.

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The authors declare no competing financial interests.

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