It has been thought that the lunar highland crust was formed by the crystallization and floatation of plagioclase from a global magma ocean, although the actual generation mechanisms are still debated. The composition of the lunar highland crust is therefore important for understanding the formation of such a magma ocean and the subsequent evolution of the Moon. The Multiband Imager on the Selenological and Engineering Explorer (SELENE) has a high spatial resolution of optimized spectral coverage, which should allow a clear view of the composition of the lunar crust. Here we report the global distribution of rocks of high plagioclase abundance (approaching 100 vol.%), using an unambiguous plagioclase absorption band recorded by the SELENE Multiband Imager. If the upper crust indeed consists of nearly 100 vol.% plagioclase, this is significantly higher than previous estimates of 82-92 vol.% (refs 2, 6, 7), providing a valuable constraint on models of lunar magma ocean evolution.

A new inverse technique is presented here to separate stresses from heterogeneous fault-slip data without a priori information on the stresses nor on the classification of faults according to the stresses. Four parameters are determined by the inversion: one for the shape of stress ellipsoid and three for the direction of stress axes. Accordingly, the inversion is equivalent to the projection of fault-slip data to a point in four-dimensional parameter space. The data are divided into k-element subsets to which inverse technique is applied, where k = 4 or 5 is the optimal choice for the stability of solutions and for the reduction of computation. Significant solutions are identified as the clusters in the parameter space. The technique is demonstrated first by simulated fault-slip data. And, as an example, field data obtained from Miocene fore-arc sediments in western Japan were processed by the method.

Observations of the subsurface geology of the Moon help advance our understanding of lunar origin and evolution. Radar sounding from the Kaguya spacecraft has revealed subsurface layers at an apparent depth of several hundred meters in nearside maria. Comparison with the surface geology in the Serenitatis basin implies that the prominent echoes are probably from buried regolith layers accumulated during the depositional hiatus of mare basalts. The stratification indicates a tectonic quiescence between 3.55 and 2.84 billion years ago; mare ridges were formed subsequently. The basalts that accumulated during this quiet period have a total thickness of only a few hundred meters. These observations suggest that mascon loading did not produce the tectonics in Serenitatis after 3.55 billion years ago. Global cooling probably dominated the tectonics after 2.84 billion years ago.

We determined model ages of mare deposits on the farside of the Moon on the basis of the crater frequency distributions in 10-meter-resolution images obtained by the Terrain Camera on SELENE (Selenological and Engineering Explorer) (Kaguya). Most mare volcanism that formed mare deposits on the lunar farside ceased at approximately 3.0 billion years ago, suggesting that mare volcanism on the Moon was markedly reduced globally during this period. However, several mare deposits at various locations on the lunar farside also show a much younger age, clustering at approximately 2.5 billion years ago. These young ages indicate that mare volcanism on the lunar farside lasted longer than was previously considered and may have occurred episodically.

Although life‐times of major continental rifts are tens of millions of years, intra‐arc rifting in Miocene NE Japan lasted for only about 3 m.y. before back arc spreading began. The rate of initial subsidence was over 1 km/m.y., much faster than that in major continental rifts. Thus this intra‐arc rift evolved 10 times as fast as major intracontinental rifts. The large temperature dependence of lithosphere rheology and the hot thermal regime of island arc lithosphere account for the rapid rifting. Less than 1 m.y. before the rifting‐spreading transition, the inner NE Japan arc subsided from shallow marine depths to middle or lower bathyal depths (1.0–2.5 km). The average total basement subsidence was 2–3 km during the rifting. The rapid submergence occurred during one third of the duration of rifting but accounts for two thirds of the total subsidence during rifting. Namely, the initial subsidence rate accelerated toward the time of breakup of the arc crust. At the same time, the region along the present Pacific coast remained only shallow marine or terrestrial throughout, presumably influenced by global eustacy.

The clustering and classification of fracture orientations are important in rock mechanics and in brittle tectonics, the latter of which includes the paleostress analysis of extension fractures hosting dikes or mineral veins. Here, we present an unsupervised clustering method for the orientations of extension fractures using mixed Bingham distributions. The method not only detects the elliptical clusters and girdles made by the poles to such planar features, but also determines the appropriate number of those groups by means of Bayesian information criterion (BIC) without a priori information. The method was tested with artificial data sets, and successfully detected the assumed groups, when the clusters had little overlaps. However, clusters with the common maximum concentration orientation and large aspect ratios were distinguished, provided that their minimum concentration orientations were separated by a large angle. Our method separated two stress states from natural data from a Miocene dike swarm in SW Japan. The method also evaluated the probabilities of the stresses to form each of the dike.

Plio-Pleistocene epithermal quartz veins in southern Kyushu, Japan, include gold deposits. The coherent trend of the ore veins suggests tectonic control for their formation. However, the stress regime during the formation has been controversial. To solve this problem, we improved existing methods for inferring paleostresses from vein orientations. It was assumed that veins making a cluster were formed intermittently from thermal fluids with various pressures. The present method determines stress ratio and stress axes with 95% confidence regions. The method was applied to mid Pliocene quartz veins cropping out at Hashima, southwestern Kyushu. We obtained a normal faulting regime of stress with the trend of sigma3 at 167 • ± 10 • and the stress ratio at 0.20 +0.13/−0.09. The low stress ratio and the lack of slickenlines and slickenfibers on vein walls suggest that the host rock was subject to a small differential stress, i.e., a weak tectonic stress, when the veins were formed.

The inside of Shackleton Crater at the lunar south pole is permanently shadowed; it has been inferred to hold water-ice deposits. The Terrain Camera (TC), a 10-meter-resolution stereo camera onboard the Selenological and Engineering Explorer (SELENE) spacecraft, succeeded in imaging the inside of the crater, which was faintly lit by sunlight scattered from the upper inner wall near the rim. The estimated temperature of the crater floor, based on the crater shape model derived from the TC data, is less than approximately 90 kelvin, cold enough to hold water-ice. However, at the TC's spatial resolution, the derived albedo indicates that exposed relatively pure water-ice deposits are not on the crater floor. Water-ice may be disseminated and mixed with soil over a small percentage of the area or may not exist at all.