I. Rolfe (ed.) Statistical methods in geology R. F. Cheeney Echinoid palaeobiology A. Smith Geomorphology in arid regions D. O. Doehring (ed.) Petroleum geology F. K. North Environmental change and tropical geomorphology I.
The Hokusai (H05) quadrangle is in Mercury's northern mid-latitudes (0-90°E, 22.5-65°N) and covers almost 5 million km 2 , or 6.5%, of the planet's surface. We have used data from the MESSENGER spacecraft to make the first geological map of H05. Linework was digitized at 1:400,000-scale for final presentation at 1:3,000,000-scale, mainly using a ∼166 m/pixel monochrome basemap. Three major photogeologic units of regional extent were mapped: intercrater, intermediate, and smooth plains. Materials of craters ≥ 20 km in diameter were classified according to their degradation state. Two classification schemes were employed in parallel, one with three classes and the other with five classes, for compatibility with existing MESSENGER-era quadrangle maps and the first global geologic map. This map will provide science context and targets for the ESA-JAXA BepiColombo mission to Mercury.
SUMMARYCommonly used variation diagrams do not convincingly distinguish strongly alkaline, alkaline and calc-alkaline rocks over the full range of silica contents, especially for more acid varieties. In particular, the Rittmann Suite Index, a, becomes invalid once SiO2 exceeds about 70%.
The deformed, low-grade, metasedimentary-volcanic schist belts of NW Nigeria, and the voluminous granitoid plutons which invaded them, are expressions of late Proterozoic-early Phanerozoic activity in the terrain separating the W African and Congo cratons. Recent interpretations of Nigerian geotectonic evolution have invoked two generations of schist belt, one a product of Kibaran (
c
. 1100 Ma) ensialic processes, the other due to Pan-African (700–450 Ma) marginal basin development. The detailed histories of the Anka Belt (Pan-African), Maru Belt (Kibaran) and Birnin Gwari Belt (unknown age), and the plutons emplaced in them, are documented here on the basis of new field, chemical and isotopic data.* Each belt represents a dominantly quiet-water sedimentary environment but volumetrically minor lithologies reveal important differences between the belts. The volcanic rocks and early minor intrusions have strong affinities with those of destructive plate margins. The schist belts were deformed congruently and simply before
c
. 750 Ma, following the development of flat-lying, possibly thrust-related structures in the Maru and Birnin Gwari Belts. Subsequent plutonism, beginning
c
. 750 Ma ago, has the calcalkaline, I-type characteristics of subduction zones but younger plutons have mildly peralkaline compositions due to thickening crust.
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