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Contents
The application deadline (1 May 2012) has now passed.
Cosponsored by
GSA MGPV Division
GSA Mineralogy, Geochemistry, Petrology, and Volcanology (MGPV) Division

AGU VGP Section
AGU Volcanology, Geochemistry, and Petrology Section

TecTask
Support provided by TecTask
for international students from developing countries

Field Forum


Formation of the Sierra Nevada Batholith: Magmatic and Tectonic Processes and Their Tempos

1–8 September 2012 • Sierra Nevada, California

Conveners:
Scott R. Paterson
Department of Earth Sciences, University of Southern California, Los Angeles, California 90089-0740, USA,
Jade Star Lackey
Pomona College, Claremont, California 91711, USA
Vali Memeti
Department of Earth Sciences, University of Southern California, Los Angeles, California 90089-0740, USA
Robert B. Miller and Jonathan S. Miller
Department of Geology, San José State University, San José, California 95192-0102, USA
Roland Mundil
Berkeley Geochronology Center, Berkeley, California 94709, USA
Keith D. Putirka
Department of Earth and Environmental Sciences, California State University, Fresno, California 93740, USA

Overview

Central Tuolumne Panorama
View of central Sierra Nevada batholith, looking south from May Lake area in Yosemite National Park. Yosemite Intrusive Suite (day 4) to the right, Tuolumne Intrusive Complex (day 5) in center, and metavolcanic rocks (day 6) in far distance in left-center. Click on photo for larger image.

The evolution of continental margin orogens and magmatic arcs involve non–steady-state processes of subduction, orogeny, magmatism, exhumation, and erosion/redeposition. Recent studies have begun to examine the tempo of cyclic volumetric addition rates to arcs of plutonic and volcanic materials, driven by feedbacks between these processes both at the scale of arcs and single magmatic or volcanic systems. A full evaluation of these arc tempos requires the development and syntheses of large databases with high-precision temporal control. One arc, where a number of research groups have been actively developing and synthesizing high-precision databases, is the Sierra Nevada, California. This Field Forum will bring researchers together to share and discuss various data sets while examining components of the Mesozoic arc. Our goal is to foster cross-disciplinary discussions, leading to a better understanding of the components of batholith formation; the tectonic controls on the tempo of arc development; and the significance of important new field, geochronologic, and geochemical databases.


Schlieren-bounded troughs
Schlieren-bounded troughs with large k-feldspar megacrysts both in the schlieren layers and in k-feldspar rich clusters in the Sawmill Canyon area, eastern Tuolumne Intrusive Complex (day 6). Also note magmatic folds and faults of schlieren and late leucogranite dikes. Click on photo for larger image.
Magma mingling
Magma mingling in the Guadalupe Igneous Complex (day 2). Click on photo for larger image.

Field Excursions

The field program will focus on a west to east transect through the central Sierra Nevada to examine both volcanic and plutonic components of the Mesozoic arc, regional tectonics, and the characteristics of the underlying basement units. Specific targets will include the following:

  1. Ca. 151 Ma Guadalupe Igneous complex, a tilted plutonic section that exposes from top to bottom a volcanic section, granophyres, a mingled granite to dioritic section, a large sequence of high Mg, layered gabbros, and a potential underlying, vertically sheeted feeder zone.
  2. The ca. 124–105 Ma, ~80 × 40 km, tonalitic-granodioritic Fine Gold intrusive complex. This incrementally constructed complex intrudes across a fundamental basement suture (Foothills suture) between oceanic and displaced passive margin basement in the Sierras and thus allows us to examine issues of incremental chamber construction, magma-wall rock interactions, and the isotopic and geochemical systematics across a major basement suture.
  3. Plutons west of the Tuolumne batholith: The ca. 102–100 Ma Yosemite Valley Intrusive Suite (El Capitan/Mt. Hoffman granodiorite, Taft Granite, and isolated mafic bodies), and ca. 98–95 Ma Yosemite Creek–Sentinel plutons. New mapping, structural analysis, and a growing database of geochemistry (elemental and isotopic whole rock, minerals) and U/Pb geochronology, suggest that these plutons grew via numerous increments that produced superficially very different plutons with differing scales of heterogeneity. The new data should allow us to speculate on why/how the resulting differences arose.
  4. The 95–85 Ma Tuolumne intrusive complex, an ~1100 km2, incrementally constructed, internally zoned complex that has been extensively studied over the past 10 yr by a number of research groups. New data sets abound, including (a) extensive 1:10,000 scale mapping, (b) detailed structural studies and strain analyses, (c) whole rock and single mineral element geochemistry and a range of isotopic studies, (d) high-precision CA-TIMS U/Pb zircon and 40Ar-39Ar geochronology, and (e) thermobarometry of plutons and host rocks. Models for the construction of this intrusive complex and interpretation of these data sets remain controversial and our focus will be on the presentation of new data sets and discussion of the proposed growth models.
  5. A nearly vertically tilted section through the Triassic to Cretaceous volcanic sequence that was constructed above the Mesozoic plutons and is now exposed in the Saddlebag pendant located along the eastern margin of the Tuolumne intrusive complex. New results will also be presented from studies of this volcanic section to the north (Virginia Canyon area) and south (Ritter Range pendant).
  6. There are also a number of new arc-scale data sets being developed and synthesized, including (a) new mapping in a number of pendants and plutons, (b) extensive structural data, (c) strain analyses in both the central and southern Sierras, (d) CA-TIMS and LA-ICPMS ages of plutons and volcanic rocks plus LA-ICPMS detrital zircon ages from metasedimentary and volcaniclastic units, (e) geochemical and isotopic (Sri, eNd, Pb, O, Hf) analyses and regional syntheses, and (f) syntheses attempting to combine all of the above with regional tectonics. Where appropriate, we will present these new syntheses with the goal of discussing tempos at various scales.

Preliminary Agenda

Sat., 1 SeptemberMeet at San Francisco International Airport and drive to Oakhurst, California, welcoming meal and overview presentation.
Sun., 2 SeptemberField trip to Guadalupe Igneous complex, evening discussions.
Mon., 3 SeptemberField trip to Fine Gold intrusive complex, evening discussions.
Tues., 4 SeptemberField trip across Yosemite Valley Intrusive Suite, travel to Mammoth, evening discussions.
Wed., 5 SeptemberField trip to Tuolumne batholith, evening discussions.
Thurs., 6 SeptemberField trip to Triassic–Cretaceous volcanic arc section, evening discussions.
Fri., 7 SeptemberReturn trip to Oakhurst, regional overview, and summary discussions.
Sat., 8 SeptemberDepature: Return to San Francisco International Airport by 1 p.m.

Transportation

GSA requires all participants to take group transportation while on the Field Forum. Personal vehicles are not permitted and are not covered by GSA insurance. We encourage participants who drive to the Field Forum to leave personal vehicles in Oakhurst, California. Vans will be available to pick up (Sept. 1 before 2 p.m.) and return (Sept. 8 by 1 p.m.) participants to the San Francisco International Airport. The daily field excursions will involve road stops and short (≤3 km) hikes at high elevations.


Costs

Registration fees for students and recent postdoctoral researchers at U.S. institutions will be partially subsidized through NSF funds. The cost of the field forum will be $1,200/person and will include (1) all travel throughout the field forum once participants arrive at either the San Francisco airport or the Best Western in Oakhurst, California*, (2) all double occupancy lodging for a total of 4 nights at the Best Western in Oakhurst and 3 nights at Mammoth Mountain Inn in Mammoth, (4) and meals except for two dinners**.

*We are not responsible for any participant’s airfare, or their method of transportation prior to arriving at San Francisco airport or Best Western in Oakhurst so please arrange your travel plans with this in mind.
**All meals are covered (breakfast, lunch, and dinner) for the duration of the program, except for two dinners, one in Oakhurst and one in Mammoth. The participants will be given one unplanned night in each of the two towns for leisure time off from the program.

Applications and Registration

Application deadline: 1 May 2012

There will be a maximum of 54 participants. Participants will have to commit to attending the full 7 days of the conference. To apply, please submit a vitae and short statement including any potential presentation (posters only), requests for registration subsidy (students and early postdocs only), and any other information pertinent to the Field Forum to Scott Paterson, . Please feel free to contact Paterson with any questions that arise.

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