Evidence for late Middle Proterozoic extension in the Precambrian basement beneath the Permian basin

Article Abstract:

The Pecos mafic intrusive suite in the basement of the Permian basin of west Texas and eastern New Mexico is composed of a series of at least four interconnected layered mafic intrusions. The suite, one of the largest intrusions in the world, covers an area of 9200 square km. Combined seismic reflection, gravity, and magnetic measurements provide a characteristic geophysical profile. a geophysical profile The intrusion is a result of rifting due to collision of rocks in the foreland of the Grenville orogeny which resulted in a sill with a dikelike structure beneath.

Natural history, Geology, Stratigraphic, Stratigraphy, Proterozoic Eon, Intrusions (Geology), Permian Basin

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Paleoclimatic and tectonic control on the accumulation of North American cratonic sediment

Article Abstract:

J. Berry and B. Wilkinson's work on North American cratons, especially the additional knowledge on the extraction of sediment-volume and lithofacies data and the distribution of these data in terms of paleoaltitudes, is commended. However, the adoption of Alexander Ronov's tectonic philosophy is rejected on the basis of its focus on the evolution of hydrosphere chemistry and sediment composition, rather than on tectonic geography. It is also recommended that the use of graphical inversion is discontinued in favor of allowing geologic time to move forward.

Geology, Structural, Structural geology

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Segmentation, fragmentation and jostling of cratonic basement in and near Aspo, southeast Sweden

Article Abstract:

The underground escavations of the island of Aspo reveals the segmentation, fragmentation and jostling of cratonic basement over a period of time. In the lower crust, the rock mass segmented and fragmented along ductile shear zones, and was jostled by the continuous reactivation of the brittle fracture zones. The first strains were ductile and penetrative in nature and later strains were found in the boundaries of unstrained blocks. Fracture zones with wide range of orientations involved more jostling.

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