VOLCANIC-PLUTONIC CONNECTIONS IN THE CENTRAL DEATH VALLEY VOLCANIC FIELD MAGMATIC SYSTEM, CALIFORNIA

The Black Mountains in the central Death Valley transtensional rhombochasm preserve exposures of coeval plutons, hypabyssal intrusions, and volcanic rocks of the Central Death Valley Volcanic Field (CDVVF). Structural juxtaposition of upper plate volcanic deposits with lower plate intrusions calls into question whether these rocks are part of the same magmatic system or derive from separate magmatic systems. We address this by integrating geologic mapping, geochronology and whole rock and mineral chemistry. The largest intrusion, the Willow Spring pluton (WSP), is approximately 30 km in exposed length and 2-3 km or more in apparent exposed thickness and spans a broad compositional range from gabbroic (48 wt. % SiO₂) to granodioritic (65 wt. % SiO₂). New LA-ICP-MS zircon U-Pb dating of seven WSP samples indicates protracted magmatism spanning at least 4 m.y. from ca. 12 Ma to 8 Ma with the youngest ages occurring at the northern extent of the mapped pluton, indicating a northward migration of magmatism through time. Age constraints also support pulsed emplacement that correlates with eruption of mapped volcanic units delineated by erosional unconformities. Two distinct rhyolitic ignimbrite eruptions, the ca. 10.8 Ma Rhodes Tuff and the ca. 10.0 Ma tuff of Resting Spring Pass, contain mafic enclaves with microdioritic textures and compositions similar to that of the WSP. These enclaves contain abundant amphibole with compositions consistent with pressures above 400 MPa, suggesting crystallization in the middle to lower crust (≥15 km). These compositions are similar to amphibole compositions in two of the lower WSP samples in the southern Black Mountains. Al-in-amphibole barometry in the more evolved WSP and coeval hypabyssal plutons indicate pressures from 150-225 MPa, corresponding to depths of 5-8 km. Whole rock and mineral compositions indicate that these rocks are expressions of the same long-lived, polybaric magmatic plumbing system correlative with the highest magma flux rates observed in the CDVVF.