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Abstract: It is widely accepted that lunar volcanism started before the emplacement of the mare fills ( b.p.) and lasted for probably more than 3.0Ga. While the early volcanic activity is relatively easy to understand from a thermal point of view, the late stages of volcanism are harder to explain, because a relatively small body like the Earth''s Moon is expected to cool rapidly and any molten layer in the interior should solidify rather quickly. We present several thermal evolution models, in which we varied the boundary conditions at the model surface in order to evaluate the influence on the extent and lifetime of a molten layer in the lunar interior. To investigate the influence of a top insulating layer we used a fully three-dimensional spherical shell convection code for the modelling of the lunar thermal history. In all our models, a partial melt zone formed nearly immediately after the simulation started (early in lunar history), consistent with the identification of lunar cryptomare and early mare basalt volcanism on the Moon. Due to the characteristic thickening of the Moon''s lithosphere the melt zone solidified from above. This suggests that the source regions of volcanic rock material proceeded to increasing depth with time. The rapid growth of a massive lithosphere kept the Moon''s interior warm and prevented the melt zone from fast freezing. The lifetimes of the melt zones derived from our models are consistent with basalt ages obtained from crater chronology. We conclude that an insulating megaregolith layer is sufficient to prevent the interior from fast cooling, allowing for the thermal regime necessary for the production and eruption of young lava flows in Oceanus Procellarum. [Copyright &y& Elsevier]

We examine compositional variations of volcanic units in the Imbrium basin using spectral observations from the Moon Mineralogy Mapper (M³) instrument on board the Chandrayaan-1 spacecraft. The spectral range of M³ reflectance measurements from 400 to 3000 nm is well-suited to study distinctive absorption bands near 1000 and 2000 nm resulting from mafic minerals in lunar basaltic flows. Eighty-three units with various mineralogical compositions were identified, and spectroscopic analyses were used to map variations in olivine and pyroxene content within basalts emplaced in the Imbrium basin. The results exhibit a more precise mapping of basaltic flow units with M³ data based on their better spatial and spectral range in comparison to previous available datasets. Nevertheless, there is a general correlation between units mapped in this work and previous studies. Moreover, the results tend to indicate an increase in olivine abundances in the stratigraphically younger high-Ti basalts compared to the older low-Ti basalts. Therefore, on the basis of M³ data, we refine previous spectral maps that have been used, for example, to determine first order homogenous units for crater size-frequency distribution measurements. [ABSTRACT FROM AUTHOR]

Abstract: Syrtis Major Planum is a volcanic plain dominated by lava flows. High resolution stereo camera (HRSC) images of the northern Syrtis Major region display erosional features such as grooves, teardrop-shaped islands and valleys. These landforms are characteristics of outflow channels seen on Mars, therefore implying that a flood event took place in this region. The flow of 100km long and a few kilometer wide followed the local slopes in most locations. Maximum flood discharges estimated from images and topography vary from about 0.3×106 to 8×106 m3/s, and therefore are in the range of terrestrial mega-floods in the Scablands or Lake Bonneville. In North Syrtis Major, the relationships with surrounding lava flows and the timing of the flood coeval to Syrtis Major volcanic activity suggest that it could be related to the subsurface water discharge mobilized by the volcanic activity. The proximity of Noachian age basement rocks 20km away from the flood and below lava flows might have played a role in its formation and water presence. [Copyright &y& Elsevier]