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STUDY OF A LUNAR CONE NEAR FLAMSTEED P

By Raffaello Lena, Maria Teresa Bregante and Charles Kapral

GLR GROUP

1) Introduction

On the Moon there are different cone morphologies due to differences in eruption style which, in turn, is determined by magma volume, extrusion rate, eruption energy and other factors [1]. Because of this, lunar cones come in many shapes and sizes [2]. The most common are: circular (Osiris in Mare Serenitatis) , breached cones with a short sinuous rille disappearing into the mare (Isis in Mare Serenitatis), or cones that are elongated and aligned along a rille (two cones near Milichius— as described in a previous paper,there are no signs of dark pyroclastic deposits (LPD) nearthese two Milichius cones, suggesting thattheywere formed from the surface eruptions of a lateral dike [2]).

The International Lunar Cone Survey (LCS) started on April 2004 is a joint effort of the American Lunar Society (ALS), the Geologic Lunar Research group (GLR), and independent observers [3]. Since the ALS/GLR project is a long-term study, this and any report of specific lunar cones should not be viewed as a final work. Observations and notes of lunar cones will continue to be accepted and included in our catalogue. As part of the LCS project, a small cone was identified close to Flamsteed P utilizing the Lunar Orbiter frame LO-IV-143-H3 (Figures 1 and 2). The position was determined using the LAC #75 (Table 1).For earth-based observers, this is a difficult feature.However, in the Consolidated Lunar Atlas frames E 24, 25, and 26 the cone appearsas a mound.

Here we report the description of another lunar cone with elongate shape, this one located at 42.60º W,4.80º S ( Xi – 0.675, Eta -0.084) near Flamsteed P.

2)Digital images

The cone near Flamsteed P is not described in the file report of the US Geological Survey [4] (In this file report the authors reported measurements for 18 lunar volcanoes, including five lunar cones. The measurements of these lunar volcanoes (diameters, height, depth of the summit crater) were computed from Lunar Topographic Orthophotomosaics, Lunar Orbiter imagery and Apollo images).Schultz, in his book "Moon Morphology",states that "the volcanic coneshave a relief comparable to that of the domes forming the Flamsteed ring" [5].However, a close analysis of figures 1 and 2 does not show any domes in the Flamsteed ring.

FIG.1

3) Geological considerations and discussion

The dome is located in Oceanus Procellarum, the largest expanse of Mare on the moon not controlled by a single circular multi-ringed basin [6, 7].Procellarum contains ghost craters such as the Flamsteed ring, suggesting that the mare is relatively shallow.As can be seen on the Lunar Orbiterframe, there are different basalts in the Flamsteed P structure.The regional mare units with highest415/750 nm values are found within the eastern portion of the Flamsteed P ring. These basalts, blue in the Clementine color ratio image, represent some of the latest stages of mare volcanism [8, 9]. They have been mapped as being Eratosthenianin age, while the surrounding units are likely Imbrian [6].The northern half of the ejecta blanket of crater Flamsteed (Eratosthenianin age) has been partially buried by lava flows encroaching from the north.


FIG.2

The present structure appears to be a lunar cone, in that it is elongated with a high-sloped rim (Figure 2). The cone is located in an Imbrian mare unit (Im) [5] reddish in Clementine color ratio data (Figure 3). There are no signs of dark pyroclastic deposits.Even Gaddis, using the multispectral Clementine imagery, did not identify lunar pyroclastic deposits in this region [10, 11]. Therefore, the conewas probably not built by explosive eruptions, but by overflows of lava that either erupted slowly or were quite viscous.


FIG.3

Table 1

References:

[1] C.A. Wood; “Monogenetic Volcanoes of the Terrestrial Planets”, Proc. Lunar Planet. Sci. Conf. 10 th 1979.

[2] R. Viegas, R. Lena, M.T. Bregante ;“ Two Cones Near Milichius”, Selenology, 2005, vol.24, n.2, pp 13-16.

[3] R. Lena; “Farside Lunar Dome Survey and Nearside Lunar Cone Survey”, Selenology, 2004, Vol 23, No 2, pp 17-20.

[4] Pike and Clow; “Revised Classification of Terrestrial Volcanoes and Catalogue of Topographic Dimensions, With new Results of Edifice Volume”, US Geological Survey Open-File Report 81-1038, 1981.

[5]P.H. Schultz, "Moon Morphology",University of Texas Press, Copyright 1972.

[6] D. E. Wilhelms and John F. MacCauley; “Geologic Map of the Near Side of the Moon”, USGS, Flagstaff, AZ , 1971.

[7] D.E. Wilhelms; “Geologic History of the Moon”, USGS Prof. Paper- 1348, 1987

[8] D. E. Melendrez , J. R. Johnson, S. M. Larson, R. B. Singer ; “Remote sensing of potential lunar resources-high spatial resolution mapping of spectral reflectance ratios and implications of nearside mare TiO2 content”, J. of Geophysical Research, vol99, pp 5601-5619, 1994.

[9] H. Heisinger, J.W. Head III, U. Wolf, R. Jaumann; “Ages and stratigraphy of mare basalts in Oceanus Procellarum, Mare Nubium, Mare Cognitum and Mare Insularum”, J. of Geophysical Research, vol 108, 7, pp 1-27, 2003.

[10] L. Gaddis; “Lunar Pyroclastic Volcanism Database.” July, 2002 http://wwwflag.wr.usgs.gov/USGSFlag/Space/LunPyro/lunpyroWebDb.html

[11] L. Gaddis et al.; “Compositional Analysis of lunar pyroclastic deposits”, Icarus, Vol 161, 2003.

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