Physical Sciences and Mathematics Commons^™

The Role Of Carbonate Factories And Sea Water Chemistry On Basin-Wide Ramp To High-Relief Carbonate Platform Evolution: Triassic, Nanpanjiang Basin, South China, Daniel J. Lehrmann, Leanne M. Stepchinski, Hannah E. Wolf, Liangzi Li, Xiaowei Li, Marcello Minzoni, Meiyi Yu, Jonathan L. Payne

Geosciences Faculty Research

The end-Permian extinction and its aftermath altered carbonate factories globally for millions of years, but its impact on platform geometries remains poorly understood. Here, the evolution in architecture and composition of two exceptionally exposed platforms in the Nanpanjiang Basin are constrained and compared with geochemical proxies to evaluate controls on platform geometries. Geochemical proxies indicate elevated siliciclastic and nutrient fluxes in the basal Triassic, at the Induan—Olenekian boundary and in the uppermost Olenekian. Cerium/Ce* shifts from high Ce/Ce* values and a lack of Ce anomaly indicating anoxia during the Lower Triassic to a negative Ce anomaly indicating oxygenation in the …

Leveraging Detrital Zircon Geochemistry To Study Deep Arc Processes: Ree-Rich Magmas Mobilized By Jurassic Rifting Of The Sierra Nevada Arc, D. Clemens-Knott, Kathleen Degraaff Surpless, A. P. Barth, J. L. Wooden

Geosciences Faculty Research

Anomalous trace element compositions of Middle to Late Jurassic detrital zircon separated from Sierra Nevada forearc and intra-arc strata reveal processes of differentiation occurring within the deep arc lithosphere. REE-Sc-Nb-Ti-Hf-U-Th covariations define three populations of atypically REE-rich grains that we interpret as crystallizing from (1) differentiates produced by olivine+clinopyroxene+plagioclase+garnet±ilmenite fractionation; (2) mixing between mafic arc magmas and partial melts of Proterozoic Mojave province crust; and (3) compositionally transient, low Gd/Yb magmas generated by hornblende resorption during decompression. We interpret a fourth population of Middle Jurassic to Early Cretaceous zircons having REE contents similar to “typical” arc zircon but with atypically …

A Survey Of Sierra Nevada Magmatism Using Great Valley Detrital Zircon Trace-Element Geochemistry: View From The Forearc, Kathleen D. Surpless, D. Clemens-Knott, A. P. Barth, M. Gevedon

Geosciences Faculty Research

The well-characterized Sierra Nevada magmatic arc offers an unparalleled opportunity to improve our understanding of continental arc magmatism, but present bedrock exposure provides an incomplete record that is dominated by Cretaceous plutons, making it challenging to decipher details of older magmatism and the dynamic interplay between plutonism and volcanism. Moreover, the forearc detrital record includes abundant zircon formed during apparent magmatic lulls, suggesting that understanding the long-term history of arc magmatism requires integrating plutonic, volcanic, and detrital records. We present trace-element geochemistry of detrital zircon grains from the Great Valley forearc basin to survey Sierra Nevadan arc magmatism through Mesozoic …

Hornbrook Formation, Oregon And California: A Sedimentary Record Of The Late Cretaceous Sierran Magmatic Flare-Up Event, Kathleen D. Surpless

Geosciences Faculty Research

Early Late Cretaceous time was characterized by a major magmatic flare-up event in the Sierra Nevada batholith and early phases of magmatism in the Idaho batholith, but the sedimentary record of this voluminous magmatism in the U.S. Cordillera is considerably less conspicuous. New detrital zircon U-Pb ages from the Hornbrook Formation in southern Oregon and northern California reveal a significant and sustained influx of 100–85 Ma detrital zircons into the broader Hornbrook region beginning ca. 90 Ma. Detrital zircon ages and hafnium isotopic compositions, combined with whole-rock geochemistry, suggest that sediment was largely derived from the Sierra Nevada, requiring uplift …

Intrusive History And Petrogenesis Of The Ash Mountain Complex, Sierra Nevada Batholith, California (Usa), Julie E. Holland, Benjamin E. Surpless, Diane R. Smith, S. L. Loewy, J. S. Lackey

Geosciences Faculty Research

The Ash Mountain Complex (AMC) in the western Sierra Nevada batholith (SNB; California, USA) is an exposure of six compositionally diverse intrusive lithologies with clear crosscutting relationships that permit a focused investigation of magma source characteristics and the relative roles of petrogenetic processes on the evolution of the system. We use new field observations, zircon U-Pb dates, major and trace element data, and Sr-Nd-Pb isotopic data to develop a model that can be applied to similar SNB intrusive suites. Stage 1 units, emplaced ca. 105 Ma, consist of two gabbros, a gabbrodiorite, and a granite. Stage 2 and stage 3 …

Petrology And Geochemistry Of Late-Stage Intrusions Of The A-Type, Mid-Proterozoic Pikes Peak Batholith (Central Colorado, Usa): Implications For Petrogenetic Models, Diane R. Smith, J. Noblett, R. A. Wobus, D. Unruh, J Douglass, R. Beane, C. Davis, S. Goldman, G. Kay, B. Gustavson, B. Saltoun, J. Stewart

Geosciences Faculty Research

The ~1.08 Ga anorogenic, A-type Pikes Peak batholith (Front Range, central Colorado) is dominated by coarse-grained, biotite ± amphibole syenogranites and minor monzogranites, collectively referred to as Pikes Peak granite (PPG). The batholith is also host to numerous small, late-stage plutons that have been subdivided into two groups (e.g. Wobus, 1976. Studies in Colorado Field Geology, Colorado School of Mines Professional Contributions, Colorado): (1) a sodic series (SiO₂ = ~44–78 wt%; K/Na = 0.32–1.36) composed of gabbro, diabase, syenite/quartz syenite and fayalite and sodic amphibole granite; and (2) a potassic series (SiO₂ = ~70–77 wt%; K/Na = 0.95–2.05), …

A Review Of The Pikes Peak Batholith, Front Range, Central Colorado: A "Type Example" Of A-Type Granitic Magmatism, Diane R. Smith, J. Noblett, R. A. Wobus, D. Unruh, K. R. Chamberlain

Geosciences Faculty Research

The N 1.08-Ga Pikes Peak composite batholith of central Colorado is a type example of an Atype granitic system. From the 1970s through the 1990s, details of the field relations, mineralogy, major and trace element compositions, and isotopic geochemistry of Pikes Peak rocks were documented, and they reveal the existence of two chemical groups, a potassic and a sodic series. The potassic series (~64-78 wt % SiO₂) includes the Pikes Peak Granite, which is mostly coarse-grained biotite f hornblende syenogranite and minor monzogranite that dominates the batholith. The potassic series also includes fine- to medium-grained biotite granite found …

Petrogenesis Of Mid-Proterozoic Granitic Magmas: Examples From Central And West Texas, Diane R. Smith, C. Barnes, W. Shannon, R. Roback, E. James

Geosciences Faculty Research

Circa 1.1 Ga granitic magmatism in Texas was manifested as two compositional groups: (1) the 1.12 Ga Red Bluff granitic suite in west Texas; and (2) 1.12-1.07 Ga granites of the Llano uplift of central Texas. Both suites share some characteristics typical of 'anorogenic' granites (e.g. potassium- and iron-rich bulk compositions, Fe-rich hydrous silicates, emplacement conditions involving low oxygen fugacities and water contents) and exhibit similar isotopic characteristics. However, rock associations, mineral chemistries, and trace element compositions of the two suites are distinct and no single petrogenetic model for the two suites is possible.

The Red Bluff granitic suite includes …