Browsing by Subject "Igneous"
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Item Petrography and Petrology of Big Aguja Sill, Northwest Davis Mountains, Jeff Davis and Reeves Counties, Texas(Texas Tech University, 1972-05) Evans, Kathryn CThe Big Aguja Sill is located in the northeast Davis Mountains in Jeff Davis County, Texas. The purpose of investigating this unit is to delineate the horizontal extent of the Big Aguja Sill, to determine if the unit was intrusive, to determine its relationship to the Huelster and Washington Tank Formations and to determine its relationship to the Star Mountain Rhyolite. Field work indicates that the Big Aguja Sill, if continuous and exposed, would have covered 100 square miles. The Big Aguja Sill was intruded as a finely crystalline, soda-rich, peralkaline traechyle porphyry along the contact of the Huelster and Washington Tank Formations. The Big Aguja Sill and the Star Mountain Rhyolite shared a common origin and possibly a common vent. Field work, petrographic and chemical analyses indicate that the Big Aguja Sill is a massive, homogeneous unit. The predominant phenocrysts are anorthoclase, but sanidine and mafic phenocrysts also occur. Most phenocrysts show resorption and exsolution. The ground mass is composed of feldspar with minor amounts of mafic minerals, glass and opaques. Quartz grains are small and rare. Pilotaxitic texture is the most striking textural aspect.Item The petrology of certain igneous rocks of eastern New Mexico(Texas Tech University, 1932-08) McCullough, Edward AllenNot availableItem Variations in zircon crop measurements due to weathering of igneous rocks(Texas Tech University, 1968-06) Allen, Ron RZircon is one of the most widespread heavy accessory minerals in all rock types of all ages. Recent investigators have used statistical parameters of zircon crystal measurements to draw a variety of petrologic conclusions. Experiments have shown that igneous rocks from the same outcrop liberate similar zircon crops. Length and breadth measurements were made for 13 paired samples. Each paired set consisted of a fresh rock and an altered rock from the same exposure. The altered rocks liberate a zircon crop which is more numerous, larger in maximum size, mean size, and size range, and have larger elongation ratios. The absence of longer crystals in the fresh sample is due to breakage during grinding. Future investigations drawing conclusions and correlations from such measurements must take this source of error into consideration.