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| Cima volcanic field | |
|---|---|
| Name | Cima volcanic field |
| Photo caption | Lava flows and cinder cones near Cima Dome |
| Location | Mojave Desert, San Bernardino County, California, United States |
| Elevation | 1,500–1,800 m |
| Type | monogenetic volcanic field |
| Age | Pleistocene–Holocene |
| Last eruption | Holocene (disputed) |
Cima volcanic field is a Pleistocene to Holocene monogenetic volcanic field in the Mojave Desert of southern California, United States. The field contains dozens of cinder cones, extensive basaltic lava flows and associated volcanic landforms distributed across and around Cima Dome, near the Mojave National Preserve and the Cima Road. Its eruptions have produced relatively fluid low-viscosity lavas that record interactions between regional Basin and Range Province extension, the San Andreas Fault system and crustal magmatic processes.
The volcanic field lies within San Bernardino County, California, northeast of Barstow, California and southeast of Ivanpah Valley. The area is bounded by Mojave Desert playas, the Providence Mountains and the Kelso Dunes. The field occupies an ecotone between lower-elevation Joshua Tree National Park environs and higher-elevation Mojave National Preserve terrain. Geologically it overlies Precambrian basement rocks, Mesozoic plutons of the Sierra Nevada batholith and Cenozoic sedimentary cover; basaltic volcanism erupted through brittle crust influenced by nearby faults such as the Garlock Fault and the Eastern California Shear Zone.
The field comprises numerous monogenetic edifices including scoria and cinder cones, spatter cones, shield-like cones and pahoehoe and ʻaʻā lava flows. Many cones exhibit classic Strombolian morphology with well-preserved craters, radial lava channels and leveed margins. Notable morphological elements include flow lobes that descend Cima Dome slopes, flow-front compression ridges, lava tubes and basaltic pavements that coalesce into lava fields tens of square kilometers in extent. Surface textures record transition from pahoehoe near vents to ʻaʻā on steeper slopes, while tephra rings and tuff deposits show phreatomagmatic signatures where magma encountered groundwater or sedimentary aquifers exposed along paleovalleys.
Eruptive activity is dominantly Pleistocene with some vents yielding ages extending into the latest Pleistocene and possible Holocene. Radiometric dating using argon–argon dating and potassium–argon dating on basalt flows gives a range of ages commonly between ~1.5 million and ~15 thousand years before present, with clusters around 400–800 thousand years and younger pulses near 30–10 thousand years. Paleomagnetic studies, stratigraphic relationships with regional glacial and alluvial deposits, and tephrochronology have been used to refine the chronology. Reports of very young, possibly historical eruptions are unconfirmed; archaeological surface contexts and radiocarbon dating of associated charcoal help constrain the youngest eruptive episodes.
Lavas are dominantly alkaline to transitional basalts, including olivine- and plagioclase-bearing basalts, basanites and tephrites with minor phonotephrite compositions. Mineral assemblages typically include olivine, clinopyroxene, plagioclase and spinel. Geochemical signatures show enrichment in incompatible elements (e.g., light rare earth elements) relative to mid-ocean ridge basalts, indicating modest degrees of partial melting of an enriched mantle source. Trace-element ratios and isotopic compositions such as strontium, neodymium and lead isotopes have been used to distinguish mantle metasomatism versus crustal contamination; overall trends favor melts derived from a heterogeneous lithospheric mantle modified by small-degree melts and limited interaction with continental crustal material.
The field formed within the broad extensional and transtensional regime of the southern Basin and Range Province and the western margin of the Colorado Plateau transition, influenced by the right-lateral San Andreas Fault system and the Eastern California Shear Zone. Regional stress promotes decompression melting in the shallow mantle and enables ascent of small-volume magmas along fractures and faults. Geophysical surveys including seismic tomography, gravity anomalies and magnetotelluric studies indicate portions of the mantle beneath the field are thermally and chemically anomalous, with possible contributions from mantle upwelling related to lithospheric thinning and edge-driven convection near the continental margin.
Indigenous peoples, including groups associated with the Chemehuevi and Mojave cultural regions, occupied lands around the volcanic field and likely used obsidian and volcanic glass from regional volcanic sources for toolmaking and trade networks with Southern Paiute and Yuman speaking peoples. Euro-American exploration, railroad expansion and prospecting in the 19th and 20th centuries mapped the region more extensively. Scientific investigation accelerated in the 20th century with geologic mapping by the United States Geological Survey and academic studies by researchers at institutions such as the University of California, Los Angeles and the California Institute of Technology. Ongoing work includes detailed mapping, geochronology, geochemical analysis and geophysical imaging to resolve vent ages, eruption rates and hazards.
The volcanic landscape hosts characteristic Mojave Desert biota including Joshua tree woodlands, creosote bush scrub, yucca, endemic lichens and a diversity of reptiles, small mammals and avifauna. Soils derived from basalt produce unique microhabitats supporting specialized plant communities and rare species that are the focus of conservation within the Mojave National Preserve and adjacent protected lands. Land management agencies such as the National Park Service and Bureau of Land Management coordinate efforts to balance recreation, cultural resource protection and scientific study while mitigating impacts from off-road vehicle use and invasive species.
Category:Volcanic fields of California Category:Geology of San Bernardino County, California