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Typical notecard size3/22/2023 ![]() Though more variable and less distinctive than RP, the similarities among the HSR rocks (dikes, lavas, tuffs) and the leucogranite also suggest a direct SLP-HRV connection. The HSR dikes emanate from leucogranite that forms the upper part of the middle SLP though differing in texture, the fine- to medium-grained leucogranite is compositionally almost identical to the HSR dikes and volcanic rocks. Phenocryst-poor high-silica rhyolite (HSR) dikes in the upper SLP and roof that are cut by RP dikes are very similar in mineralogy, texture, and composition to HSR lavas and tuffs that dominate the silicic HRV. The RP connection provides strong evidence for direct connection between SLP and HRV.Ī second highly plausible connection between SLP and HRV is strengthened by the RP correlation. RP is also very similar in composition, mineralogy, and texture (except for its aphanitic groundmass) to the coarse low-silica granite that dominates the middle SLP. In all environments in which it is exposed, RP is extensively mingled with mafic magma. This terminal lava also includes basaltic trachyandesite and mechanical mixtures of basaltic trachyandesite and RP. RP dikes emanate from the middle SLP and crosscut the upper SLP and the pluton's roof (Proterozoic basement and lower HRV) small plugs intrude the upper part of the silicic HRV, and identical RP lava is part of a composite lava flow that is the last silicic material erupted in the HRV sequence. This lithology is phenocryst-rich (40–50%), with large quartz, alkali feldspar, plagioclase, as well as biotite, amphibole, titanite, apatite, Fe-Ti oxides, zircon, and chevkinite. ![]() ![]() New results reveal that the youngest silicic rocks exposed in both the middle SLP and the silicic HRV are distinctive rhyolite porphyries (RP) that are essentially identical in texture, mineral assemblage, and elemental compositions. Throughout the system's history, subordinate mafic magma accompanied the more silicic magmas. Over the final ∼0.2 million years of the evolution of the system, silicic magma (70–78 wt% SiO 2) constructed the youngest part of the pluton (middle SLP granite) and the coeval volcanic sequence (silicic HRV: rhyolite lavas and tuffs). For most of this period the system produced primarily intermediate rocks: dominantly quartz monzonite in the lower and upper SLP and trachyandesite-trachydacite lavas of the HRV (∼58–70 wt% SiO 2). We summarize herein three decades of published and unpublished research on this system, emphasizing new work on its final silicic products that verifies direct connections between SLP and HRV and provides insights about storage, extraction, transport, and eruption processes in the waning stages of the system.Ĭircumstantial evidence strongly suggests that volcanic and plutonic SLP-HRV products were directly linked for one million years (∼17–16 Ma). The Searchlight pluton (SLP) and coeval Highland Range volcanic sequence (HRV) have been suggested to represent intruded and erupted counterparts, and the 15 km tilted crustal section in which they are exposed has been presented as an illustration of the anatomy of a large, upper crustal, intermediate to silicic magmatic system.
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