W. E. Brooks 1986 <div id="15570416" class="article-section-wrapper js-article-section js-content-section " data-section-parent-id="0"><p>Metasomatized Tertiary lavas with anomalously high K₂O and low Na₂O content are distributed within the northwest-trending Miocene extensional terrane of southwestern Arizona. These rocks are common near core-complex–related detachment faults at Picacho Peak and the Harcuvar Mountains and in listric-faulted terrane at the Vulture Mountains. In addition to systematic changes in K₂O and Na₂O, the rocks have been enriched in Zr and depleted in MgO.</p><p>Secondary, introduced minerals include orthoclase, quartz, and calcite. Fine-grained, euhedral orthoclase (var. adularia), from 2 to 10 µm, is the dominant potassium mineral.</p><p>Metasomatic changes at Picacho Peak are spatially associated with a major detachment fault. Thus, it is interpreted that detachment provided a conduit for hydrothermal fluids that altered the initial chemical composition of the Tertiary volcanics by potassium metasomatism and charged the upper-plate rocks with mineralizing fluids that carried Zr and Ba, along with Au, Ag, and Cu, during detachment 17–18 Ma.</p></div> application/pdf 10.1130/0091-7613(1986)14<339:DOAHKV>2.0.CO;2 en Geological Society of America Distribution of anomalously high K2O volcanic rocks in Arizona: metasomatism at the Picacho Peak detachment fault article