Late Cenozoic basaltic magmatism in the Salton Trough: Implications for tectonic development
Charles T. Herzig, David C. Jacobs, 1991. "Late Cenozoic basaltic magmatism in the Salton Trough: Implications for tectonic development", The Diversity of Mineral and Energy Resources of Southern California, Michael A. McKibben
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The geochemistry of late Cenozoic basalts within the Salton Trough of southern California suggests that crustal extension has occurred in two very different tectonic settings. Initial extension of thick continental crust occurred during the Oligocene-Miocene, leading to the alkalic basalts now located along the trough margins. Following an ~10 Ma hiatus in igneous activity, tholeiitic basalts have been emplaced during the past 4 Ma along the trough axis as oceanic spreading centers of the East Pacific Rise – Gulf of California transtensional system exploited the previously extended and thinned crust of the North American continent. The correlation of basaltic xenoliths in the Quaternary rhyolite of Salton Buttes with oceanic rocks in the Gulf of California is strengthened in this study by new radiometric ages, and geochemical and isotopic data. In addition, a new U-Pb age of <100,000 years for zircons from a granophyre xenolith in the rhyolite of Salton Buttes does not support the presence of pre-Tertiary, crystalline materials within this spreading center.
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The Kramer borate deposit is located in the northwestern Mojave Desert, about 90 air miles northeast of Los Angeles and 3 miles north of the town of Boron (figure 1). The deposit derives its name from the mining district in which it lies. The Kramer deposit, presently being mined from the Boron open pit, has been a world-class source of sodium borates since mine startup in 1926 and continues to be the largest source of borates in the world.
The Kramer ore body is a roughly lenticular sedimentary sequence of borax (Na2B4O7 • 10H2O) and kernite (Na2B4O7 • 4H2O) containing interbedded claystone. This central crystalline facies is successively enveloped by facies consisting of ulexite (Na,CaB5O9 • 8H2O) -bearing claystone, colemanite (Ca2B6O11 • 5H2O) -bearing claystone, and barren claystone. Studies indicate the Kramer borates were deposited in a small structural, nonmarine basin, associated with thermal (volcanic) spring activity during Miocene time.
The Kramer deposit does not crop out. It was discovered accidentally in 1213 by Dr. John Suckow, a homesteader, who struck colemanite while drilling a water well (figure 2). Exploratory drilling and shaft sinking after World War I by Pacific Coast Borax Company, the predecessor of U.S. Borax, led to the discovery of borax and kernite in 1925. In 1926 PCB went into large-scale, underground sodium borate mining in the Baker mine, located nearly 2 miles east of Suckow's discovery well. The company soon closed all its calcium borate operations near Ryan in Death Valley in favor of the more easily processed sodium borates at Boron.
U.S. Borax ships mostly bulk, refined sodium borate products and boric acid to both domestic and world markets from Boron. Principal uses for these products are in the manufacturing of glass and fiberglass, herbicides, ceramics, soaps and detergents, fluxes, fertilizers, and fire retardants.