Untangling differentiation in arc lavas: constraints from unusual minor and trace element variations at Salak Volcano, Indonesia

Volcanic rocks from Salak Volcano in West Java display intriguing minor and trace element geochemical variations with silica. TiO2 and P2O5 contents, Y, HFSE and REE concentrations are abnormally rich in the Central Vent Group (CVG) lavas (e.g. Y = 32–69 ppm; Yb, 3–6.5 ppm) and display striking positive correlations with SiO2. This contrasts with rocks erupted at side vents (SVG) on the eastern and western flanks of Salak and with rock suites of most other Javan volcanoes where these elements remain relatively constant with increasing SiO2. Modelling of major and trace element data indicate that low pressure fractional crystallisation exerts strong control on the composition of CVG lavas. HFSE and HREE data are inconsistent with magma mixing, and can be explained by incompatible behaviour during fractionation of plagioclase, clinopyroxene and Fe-Ti oxide ± orthopyroxene and olivine. The observed variations in K/Rb and Ba/Th ratios and correlation of 87Sr/86Sr with indices of differentiation necessitate assimilation of a low K/Rb, low Ba/Th, Sr-rich contaminant with 87Sr/86Sr of ~ 0.7048 during fractional crystallisation. For the eastern flank SVG, deep fractionation of a phase in which HFSE and HREE are compatible (e.g. amphibole) is implicated. By extension, this is also suggested to occur beneath the majority of Javan volcanoes. Radiogenic isotope ratios (Sr-Hf-Nd) of Salak lavas are similar to other Javan lavas. SVG rocks erupted from the eastern flank vent have significantly more primitive Hf-Nd isotope ratios than other Salak volcanic rocks and may represent the least contaminated (by arc crust or subduction input) Salak lavas

Geologic Map of the Northeastern Vulture Mountains and Vicinity, Central Arizona

This report presents 1:24,000-scale geologic mapping of the eastern Vulture Mountains and vicinity. This mapping, along with concurrent mapping of the Wickenburg Mountains and western Hieroglyphic Mountains (Stimac and others, 1987). was completed between January and April 1987 and was jointly funded by the u.s. Geological Survey and Arizona Bureau of Geology and Mineral Technology as part of the cost-sharing Cooperative Geologic Mapping Program (COGEOMAP). These areas were mapped because they were previously unmapped in detail, and were suspected to contain a highly faulted and potentially mineralized assemblage of Proterozoic crystalline rocks, Cretaceous granite, and middle Tertiary volcanic and sedimentary rocks. The Vulture Mountains represent an important link between previously studied middle Tertiary rocks and structures in the Big Horn Mountains (Capps and others, 1985; Stimac and others, 1987) and central Vulture Mountains (Rehrig and others, 1980) to the southwest and Hieroglyphic Mountains to the east (Capps and others, 1986). Together, the geologic studies in these mountain ranges provide a transect from the highly distended Basin and Range Province to -the edge of the Transition Zone.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]

Preliminary Geologic Maps of the Eastern Big Horn and Belmont Mountains, West-Central Arizona

This report presents preliminary 1:24,000-scale geologic maps of the eastern Big Horn and Belmont Mountains in west-central Arizona. The mapping, completed between January and April 1985, was jointly funded by the U.S. Geological Survey and the Arizona Bureau of Geology and Mineral Technology as part of the cost-sharing, Cooperative Geologic Mapping Program (COGEOMAP). The aim of COGEOMAP is to produce high-quality geologic maps for areas that have been inadequately mapped. The Big Horn and Belmont Mountains were chosen because neither range had been previously mapped, except in broad reconnaissance for previous State geologic maps, and because both ranges have substantial mineralization and exploration activity. One report and two map sheets, 1:24,000 map scale.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]

Geologic map of the Wickenburg, Southern Buckhorn, and Northwestern Hieroglyphic Mountains, central Arizona

This report describes the geology of the Red Picacho quadrangle and parts of the Wickenburg, Garfias Mountain, and Wittman quadrangles. The map area comprises metamorphic-plutonic basement unconformably overlain by Tertiary volcanic and sedimentary rocks. Geologic map of the Wickenburg, Southern Buckhorn, and Northwestern Hieroglyphic Mountains, central Arizona Scale 1:24,000, with report.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]

Geologic Map of the Southern Hieroglyphic Mountains, Central Arizona

This reconnaissance geologic map covers both the Baldy Mountain and the Hieroglyphic Mountains SW 7.5 minute quadrangles of central Arizona. The geologic mapping was done between January and June, 1986 and November and December, 1987. This mapping was jointly funded by the U. S. Geological Survey and the Arizona Bureau of Geology and Mineral Technology as part of the cost-sharing, Cooperative Geologic Mapping Program (COGEOMAP). The aim of COGEOMAP is to produce high-quality geologic maps for areas that have been inadequately mapped and that have high mineral resource or natural potential. This mapping was done on 1:24,000-scale topographic maps and on 1:24,000-scale color aerial pholographs provided by Raymond A. Brady, U. S. Bureau of Land Management, Phoenix. The reader is referred to a previous report on the northeastern Hieroglyphic Mountains (Capps, R.C., and others, 1986) for a more detailed discussion of the geology of the region. Additional descriptions of the area are contained in Ward (1977). Rock-unit names in this report are from Stimac and others (1987) and Capps and others (1986) as modified from Ward (1977).Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]

Detailed geologic map and cross sections of the Big Horn and Belmont Mountains, West-central Arizona

The principal geologic feature of the Big Hom and Belmont Mountains is a complexly faulted and tilted series of mostly Miocene volcanic rock that record a period of Middle Tertiary magmatism and extension. These volcanic rocks vary widely in composition, but basaltic and rhyolitic rocks are most abundant (Figure 1). Intrusive equivalents of these volcanics exposed in the Belmont Mountains are dominantly granitic. Despite the large volume of rhyolite erupted, small, coalescing flow and dome complexes were formed in preference to large-volume ash-flow tuffs, and no collapse calderas were formed. These rocks lie in the upper plate ofthe regional Whipple-Buckskin-Bullard detachment fault [Rehrig and Reynolds, 1980], at its southeastern tip [Richard et aI, 1990a]. A regional boundary between major tilts domains in Tertiary strata follows an irregular course from northwest to southeast through the range [Rehrig et aI., 1980]. Northeast of this boundary, strata dip to the northeast, and southwest of the boundary, Tertiary strata dip to the southwest. Pre-Tertiary rocks are exposed in several parts of the range. These rocks consist of a Laramide-age (71-63 Ma)hornblende-biotite granodiorite, informally referred to as the Big Hom granodiorite, which intrudes a complex of Proterozoic igneous and metamorphic rocks. Metamorphic grade in the Proterozoic rocks increases from southeast to northwest, and associated igneous rocks become more abundant to the northwest. In the southeast the Proterozoic rocks consist of highly deformed, greenschist facies, mafic and pelitic schist. These grade to heterogeneous mafic-tointermediate- composition gneiss to the northwest. Report with geologic map and cross sections of the Big Horn and Belmont Mountains, west-central Arizona. Scale 1:50,000.Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]