Morphology and development of pahoehoe flow-lobe tumuli and associated features from a monogenetic basaltic volcanic field, Bahariya Depression, Western Desert, Egypt

Khalaf, Ezz El Din Abdel Hakim; Hammed, Mohamed

doi:10.1016/j.jafrearsci.2015.10.010

Cited by 10 publications

(8 citation statements)

References 59 publications

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“…We cannot rule out a tectonic compressional ridge as a possible explanation for this feature. The formation of elongate, ridge‐like tumuli or tumuli alignment over a well‐established lava tube has been documented by many authors (e.g., Bernardi et al, 2015; Cashman & Kauahikaua, 1997; Chitwood, 1994; Duncan et al, 2004; Glaze et al, 2005; Kauahikaua et al, 1998; Keszthelyi & Pieri, 1993; Khalaf & Hammed, 2016; Orr et al, 2015; Pasquarè et al, 2008).…”

Section: Discussionmentioning

confidence: 91%

Ring‐Moat Dome Structures (RMDSs) in the Lunar Maria: Statistical, Compositional, and Morphological Characterization and Assessment of Theories of Origin

et al. 2020

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Ring‐moat dome structures (RMDSs) are positive morphologic features found clustered across many mare regions on the Moon, of which only a few isolated examples have been previously reported. Our continuing survey has expanded the known locations of the RMDSs from ~2,600 to over 8,000, indicating that RMDSs are more common geological features than previously thought. This work presents a detailed geomorphological analysis of 532 RMDSs identified in several mare basins. The combination of detailed elemental mapping, morphological and morphometric analyses, spatial distribution relationships with other geologic structures, and comparison with terrestrial analogs lead us to conclude that (1) RMDSs represent low circular mounds with diameters of a few hundred meters (average about 200 m) and a mean height of 3.5 m. The mounds are surrounded by moats ranging from tens to over 100 m in width and up to several meters in depth; (2) there is a wide variation of titanium abundances, although RMDSs are more commonly found in mare regions of moderate‐to‐high titanium content (>3 wt% TiO2); (3) RMDSs are found to occur on or around fractures, graben, and volcanic edifices (small shields and cones); (4) a spatial association between RMDSs and Irregular Mare Patches (see Braden et al., 2014, https://doi.org/10.1038/ngeo2252) is observed, suggesting that both may form from related lava flows; (5) comparisons between RMDSs and lava inflationary structures on Earth support an inflation‐related extrusive nature and a genetic relationship with host lava flow processes; and (6) RMDS embayment relationships with craters of different degradation ages superposed on the host mare, and regolith development models, produces conflicting age relationships and divide theories of RMDS origin into two categories, (1) synchronous with the emplacement and cooling of the host lava flows ~3–4 Ga and (2) emplaced substantially after the host mare lava unit, in the period ~0–3 Ga. We outline the evidence supporting this age conundrum and implications for the different theories of origin and describe future research avenues to help resolve these outstanding questions.

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Section: Discussionmentioning

confidence: 91%

Ring‐Moat Dome Structures (RMDSs) in the Lunar Maria: Statistical, Compositional, and Morphological Characterization and Assessment of Theories of Origin

et al. 2020

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“…Inflation will be greater where flows are thicker, causing differential stresses and a non-random spatial distribution of fractures through which extrusions can take place. Furthermore, field experience of the patterns of inflation of compound pahoehoe flow systems on Earth shows that the interiors of the flows are clearly not laterally homogeneous, and that preferred, and meandering, pathways develop within them (Vye-Brown et al, 2013;Khalaf and Hammed, 2016;Rader et al, 2017). The same is likely to be true of inflating flows on the Moon.…”

Section: Crack Formationmentioning

confidence: 99%

A theoretical model for the formation of Ring Moat Dome Structures: Products of second boiling in lunar basaltic lava flows

Wilson

Head

Zhang

2019

Journal of Volcanology and Geothermal Research

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Newly documented Ring Moat Dome Structures (RMDSs), low mounds typically several hundred meters across with a median height of ~3.5 m and surrounded by moats, occur in the lunar maria. They appear to have formed synchronously with the surrounding mare basalt deposits. It has been hypothesized that they formed on the surfaces of lava flows by the extrusion of magmatic foams generated in the flow interiors as the last stage of the eruption and flow emplacement process. We develop a theoretical model for the emplacement and cooling of mare basalts in which the molten cores of cooling flows are inflated during the late stages of eruptions by injection of additional hot lava containing dissolved volatiles. Crystallization of this lava causes second boiling (an increase in vapor pressure to the point of supersaturation due to crystallization of the melt), generating copious quantities of vesicles (magmatic foam layers) at the top and bottom of the central core of the flow. Flow inflation of many meters is predicted to accompany the formation of the foam layers, flexing the cooled upper crustal layer, and forming fractures that permit extrusions of the magmatic foams onto the surface to form domes, with subsidence of the subjacent and surrounding surface forming the moats. By modelling the evolution of the internal flow structure we predict the properties of RMDSs and the conditions in which they are most likely to form. We outline several tests of this hypothesis. 1. Introduction: The volcanic origin of the lunar maria has been known confidently for more than fifty years (see reviews in Head, 1976; Hiesinger and Head, 2006; Spudis, 2016), but new very high-resolution image and altimetry data from the Lunar Reconnaissance Orbiter (LRO) have continued to reveal surprises, including the widespread occurrence of features originally detected by Schultz (1976) and Schultz et al. (1976), and now called Ring Moat Dome Structures (RMDSs) (Zhang et al., 2017). More than two thousand of these features were recently documented in numerous maria (Figure 1) (Zhang et al., 2017). Theories proposed for their origin, summarized in Zhang et al. (2017), include emplacement of domes of more viscous magma, extrusions into impact craters billions of years after mare emplacement, squeeze-ups or hornitos formed synchronously with lava flow emplacement, and extrusion of magmatic foams (i.e., lavas with greater than ~70% vesicularity, Mangan and Cashman, 1996) that developed below a cooling lava flow surface. The availability of LRO imaging (Robinson et al., 2010) and topographic (Smith et al., 2010) data, together with a better understanding of the ways in which magma is transferred from the lunar mantle to the surface (Wilson and Head, 2017a; Head and Wilson, 2017), and improvements in the analysis of patterns of gas release from lunar magmas (Rutherford et al., 2017; Wilson and Head, 2018a) have prompted recognition of the importance of the formation and extrusion of magmatic foams in shaping lunar volcanic features (Qiao et al., 2017, 2018a...

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“…Within the BD, there are numerous inselbergs of Cenomanian units capped with (a) ferricrite crusts similar to those of the Black Desert (El Aref et al, 1991;El Aref et al, 2017), (b) karstified Campanian and Eocene carbonates (El Heiz, El Hefuf, and Naqb Fms, and Knoman Chalks) such as those of Gebel Tobog, El Dist, El Maghrapha, Gebel Hammad, El Hefuf, and Fugget El Harra (Figure 2A) (El Aref et al, 2017), or (c) units of Oligo-Miocene basaltic intrusions and extruded magmatic volcanic units (Figure 3) (Meneisy, 1990;Bosworth et al, 2015;Khalaf and Hammed, 2016).…”

Section: Stratigraphymentioning

confidence: 99%

“…Remnant fields of effusive basaltic deposits and shallow intrusions are well preserved and exposed within the footwall block of the Mid Bahariya fault and form the hills (also called Gabal) of El Mandisha, El Mayesra, El Agoz, El Marssos, and El Hefuf (Figure 2A) (Khalaf and Hammed, 2016). These occurrences are mainly represented by basaltic units enriched in olivine and may change to dolerite with holocrystalline mediumgrained groundmass in the intrusive varieties (El Qaluabi, 1974;Medani, 1995).…”

Section: Volcanism and Shallow Intrusionsmentioning

confidence: 99%

Concentric Structures and Hydrothermal Venting in the Western Desert, Egypt

et al. 2019

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Morphology and development of pahoehoe flow-lobe tumuli and associated features from a monogenetic basaltic volcanic field, Bahariya Depression, Western Desert, Egypt

Cited by 10 publications

References 59 publications

Ring‐Moat Dome Structures (RMDSs) in the Lunar Maria: Statistical, Compositional, and Morphological Characterization and Assessment of Theories of Origin

Ring‐Moat Dome Structures (RMDSs) in the Lunar Maria: Statistical, Compositional, and Morphological Characterization and Assessment of Theories of Origin

A theoretical model for the formation of Ring Moat Dome Structures: Products of second boiling in lunar basaltic lava flows

Concentric Structures and Hydrothermal Venting in the Western Desert, Egypt

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