Composite Devonian island-arc batholith in the northern Sierra Nevada,California
Hanson, Richard E; Saleeby, Jason B; Schweickert, Richard A (1988) Composite Devonian island-arc batholith in the northern Sierra Nevada,California. Geological Society of America Bulletin, vol.100, no.3, pp.446-457, Mar1988
| Authors | Hanson, Richard E; Saleeby, Jason B; Schweickert, Richard A |
|---|---|
| Year | 1988 |
| Title | Composite Devonian island-arc batholith in the northern Sierra Nevada,California |
| Source | Geological Society of America Bulletin, vol.100, no.3, pp.446-457, Mar1988 |
| ISSN | 0016-7606 |
| GeoRef | 1988-019492 |
| Keywords | absolute age; batholiths; Bowman Lake Batholith; California; dates;Devonian; emplacement; genesis; geochronology; granites;granodiorites; Grizzly Formation; hybridization; hypabyssal rocks;igneous rocks; intrusions; island arcs; magmas; nesosilicates; NevadaCounty California; Northern California; orthosilicates; Paleozoic;Plumas County California; plutonic rocks; Shoo Fly Complex; SierraButtes Formation; Sierra County California; Sierra Nevada; silicates;U/Pb; United States; volcanic rocks; zircon; zircon group |
| DOI | 10.1130/0016-7606(1988)100<0446:CDIABI>2.3.CO;2 |
Abstract
The Bowman Lake batholith intrudes the pre-Upper Devonian Shoo FlyComplex in the northern Sierra Nevada. The eastern margin of thebatholith extends to within 1.5 km of the base of a thick sequence ofPaleozoic island-arc rocks that rests unconformably on the Shoo FlyComplex. Hypabyssal silicic intrusions associated with the batholithpenetrate the Upper Devonian Sierra Buttes Formation, the lowestvolcanic unit of the arc sequence, but do not extend to higherstratigraphic levels. The intrusions in the Sierra Buttes Formationpossess marginal peperites and show other evidence of their injectioninto wet, unconsolidated sediments. On the basis of these fieldrelations, the batholith is interpreted to represent a subvolcanicmagma chamber emplaced concurrently with deposition of Sierra Buttesarc rocks.The batholith is composite and consists of trondhjemite,granodiorite, biotite granite, and hornblende tonalite, formed fromdiscrete batches of magma injected into a common plutonic chamber.Mingling of tonalitic and trondhjemitic magmas produced abundantrounded inclusions of tonalite dispersed within trondhjemite and ledto hybridization of the two magmas by fine-scale intermixing.Zirconsfrom the trondhjemitic, granodioritic, and granitic phases of thebatholith and an associated Sierra Buttes rhyolite sill show complexU-Pb isotopic systematics. A multistage history is suggested,involving the incorporation of earliest Paleozoic and/or Proterozoiczircons during magma generation or ascent in Devonian time and one ormore stages of disturbance in Mesozoic-Cenozoic(?) time. Considerationof these different discordance mechanisms results in a model U-Pbigneous age for the batholith of 364 to 385 Ma (Middle to LateDevonian); on the basis of the field relations, a Late Devonian agefor the batholith is adopted. Zircon characteristics and isotopicsystematics suggest that petrogenesis of the granite involved mixingof trondhjemitic and/or granodioritic magmas with partial melt from aseparate, large-ion-lithophile-enriched source.