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We present a model for microcontinent formation that is based on the structure of the Tamayo trough in the Gulf of California, Mexico. Potential field modeling of a transect through the Tamayo trough and Tamayo Bank suggests that the crust of the Tamayo trough is oceanic, and that the Tamayo Bank is a detached continental fragment. The oceanic crust that separates the Tamayo Bank from the mainland of Mexico is thin (5 km), so oceanic spreading was probably magma starved before it ceased. Such a thin crust has also been described on the Aegir Ridge in the North Atlantic, which became extinct after the Jan Mayen microcontinent separated from Greenland. In our model for the origin of microcontinents, the locus of plate spreading jumps to the weakened continental margin when the spreading ridge becomes amagmatic and the force required for continued extension at the ridge increases. A microcontinent is formed when the ridge jumps into a continental margin, and an asymmetric ocean basin or microplate is formed when the ridge jumps within oceanic crust.

Periodic assessment of released common bean cultivars is essential to screen genotypes that offer superior intercropping advantage to farmers when grown in association with maize. Thus, comparative performance of improved genotypes representing commonly used growth habit and market classes were investigated under sole and intercropping system at Halaba special district, Southern Ethiopia. Treatments consisted of a factorial combination of seven common bean genotypes and two cropping systems, which were arranged in a split plot design replicated three times. Cropping system and genotype were assigned as main and sub plot factors, respectively. Cropping system by genotype interaction was significant for bean grain yield and two of the yield components causing moderate changes in ranking. Relative yield reduction due to association with maize varied from 26% for genotype Sari-1 (Type II)

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