STRUCTURE, CONSTRUCTION, AND EMPLACEMENT OF THE NORTHERN PART OF THE CRETACEOUS SONORA PASS INTRUSIVE SUITE, CENTRAL SIERRA NEVADA BATHOLITH, CALIFORNIA

2016 ◽  
Author(s):  
Kevin P. Loeb ◽  
◽  
Robert B. Miller
Keyword(s):  
Sierra Nevada ◽  
Sierra Nevada Batholith ◽  
Intrusive Suite

High-precision geochronology requires that ultrafast mantle-derived magmatic fluxes built the transcrustal Bear Valley Intrusive Suite, Sierra Nevada, California, USA

Geology ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 106-110
Author(s):  
Benjamin Z. Klein ◽  
Oliver Jagoutz ◽  
Jahandar Ramezani
Keyword(s):  
Sierra Nevada ◽  
Thermal Ionization Mass Spectrometry ◽  
Ionization Mass ◽  
Crustal Material ◽  
Crustal Assimilation ◽  
Sierra Nevada Batholith ◽  
Magma System ◽  
Intrusive Suite ◽  
Hf Isotopic Composition ◽  
Lower Crustal

Abstract The Bear Valley Intrusive Suite (BVIS), located in the southernmost Sierra Nevada Batholith (SNB; California, USA) exposes a transcrustal magma system consisting of lower-crustal gabbros and volumetrically extensive middle- and upper-crustal tonalites. New chemical abrasion–isotope dilution–thermal ionization mass spectrometry U-Pb geochronology shows that the bulk of this ca. 100 Ma magmatic system crystallized in 1.39 ± 0.06 m.y. and was constructed with ultrahigh magmatic fluxes (∼250 km3/km/m.y.). This magmatic flux is roughly a factor of three greater than estimates for the SNB-wide flux during the Late Cretaceous flare-up, showing that individual magmatic systems can be constructed at extremely rapid rates. Further, the Hf isotopic composition of the BVIS (εHfi ∼–2 to +4) only allows for limited (∼25%) crustal assimilation. Our results show that the high magmatic fluxes recorded in the BVIS were dominantly derived from the mantle, and that “flare-up”–like local magmatic fluxes can be produced without extraordinary assimilation of crustal material.

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