Arizona Geological Society


Upcoming events

    • 04 Jun 2019
    • 6:30 PM - 8:30 PM
    • Borderlands Brewing, 119 East Toole Avenue, Tucson AZ 85701

    Sponsored by:  TBA

    Meet and Greet, A Networking Event
    June 4, 2019

    Members of the Arizona Geological Society as well as members of the public, who are interested in Arizona's geology, are invited to attend this event.  Come out and have a good time, drink some beer, eat some snacks, and "talk rocks".

    Additional information to be announced soon.


    • 08 Jun 2019
    • 7:00 AM - 3:00 PM
    • Gas Station?Parking Lot NE Corner of Tanque Verde and Mt Lemmon Highway

    Spring Field Trip - Petrologic and Structural Evidence for Flat Subduction Tectonics in Santa Catalina Mountains

    Windy Point looking SSE toward Santa Rita Mountains with an outcrop of Wilderness Granite in foreground. 

    Field Trip Leader:  Stan Keith, MagmaChem and Jan Rasmussen, Consultant

    Field Trip Description - AGS Members and their guests are invited to participate in the AGS 2019 Spring Field Trip to Mount Lemmon along the Catalina Highway. 

    Tour Date/Time -  Saturday. June 8, 2019, 7:00 AM.  The official trip will end at 3:00 PM. You are welcome to stay longer to enjoy the cool mountain air and stay for the weekend. Accommodations are limited to camping and perhaps a few air-b-n-b rentals, and good eating and drinks at the Iron Door restaurant at the ski lift.

    Carpooling - For safety reasons, Carpooling is strongly encouraged (4 passengers per vehicle if possible), since parking space along the Highway is limited.  Attendees should meet at the gas station/parking lot, located on the northeast corner of Tanque Verde and Mount Lemmon Highway at 7:00 AM.

    Registration Fees - Members - $35, Non-member -$40, Students - $15

    Registation Fees include a Field Trip Gruide Book, lunch, beverages and snacks.

    Meals -We will provide sandwiches and soft drinks and water. There will be a lunch stop at the famous garnet schleiren locality south of Summerhaven.

    Level of Difficulty - The level of difficulty for the trip is normal. Temperatures are expected to be in pleasant warm ranging from 70 to 85 degrees F..   Elevation is 3,600 to 8,000 feet).   Sunscreen lotion and a good hat to protect the head from too much UV are strongly recommended.  Eye protection is required, to protect yourself not only from your own hammering away on rocks, but also to shield you from rock chips flying of the adjacent geologist's pick.  Hand protection is also encouraged (work gloves).

    Field Trip Stops - All of the stops will be essentially road cuts or places where people only have to walk 50 yards on easy trails.

    White Biotite Eocene Wilderness Granite (~55 Ma) intruding darker Precambrian Oracle Granite (~1440 Ma) exhibiting synkinematic deformation at Babad Do'ag Overlook

    Stop 1: Babad Do’ag overlook at picnic area at base of mountain to examine the light-colored, biotite granite phase of the lower part of the Wilderness two-mica (biotite-muscovite) granite sill complex (now well dated at 55 Ma) that intrudes into the dark-colored, sheared Proterozoic Oracle Granite (1440 Ma). We will also discuss the influence of hydrous magmato-hydrothermal effects on the peraluminous sills as shown on zircons.

    Windy Point looking East with outcrop of Wilderness Granite in foreground.

    Stop 2: Windy Point to examine the two-mica granite in the main range Wilderness sill to examine “fish flash” showing the southwest-directed tectonic flow in the Windy Point shear zone. The zircon characteristics differ between the main range two mica granite sill (melt products of 1440 Ma crust) and the fore range biotite granite sills (older xenocrystic zircons that are in part melt products of older crust).

    Stop 3: Bear Wallow to see folded Apache Group and southwest-directed thrust tectonics in the Bear Wallow thrust. The co-eval relationship between the two-mica granite emplacement (45-48 Ma) and the Bear Wallow thrust will be discussed. 

    Spessartine Garnet Schleiren cross cut by a small pegmatite dike at Marshall Gulch south of Summerhaven.

    Stop 4: Garnet schleiren south of Summerhaven to see garnet bands in the Lemmon Rock Leucogranite, the youngest sill (up to 40 Ma) in the Wilderness granite sill complex, indicating left slip in an east-west shear zone that occurred during the emplacement of the multi-phased aplo-pegmatite dike. The garnet geobarometry indicates emplacement at depths of 13-18 km and the displacements indicate a NE-SW compressive tectonic regime.

    Petrologic and Tectonic Significance of the Wilderness Plutonic Suite: Products from a Massive Water Flood Event of Hydrous Crustal Melting Event During High-Speed Flat Subduction in the Latest Laramide by Stan Keith and Jan Rasmussen

    Abstract:  The main goal of the field trip is to demonstrate with field evidence the petrologic and tectonic connection of Wilderness suite peraluminous magmatism to flat subduction toward the northeast beneath the North American plate in the Eocene. The petrology of the peraluminous two-mica magmatism is linked to massive hydrous melting of Proterozoic to Mesozoic basement by water flood events resulting from dehydration of the flatly subducting slab. The peraluminous magmatism fractionated W-Be metallogeny that was inherited from pre-existing peraluminous crustal sources, such as the 1400-1450 Ma Oracle Granite. This observation precludes explaining the origin of the porphyry copper deposits by leaching from pre-existing rocks. The source for porphyry copper deposits is better explained by their associated metaluminous calc-alkalic magmatism from mafic sources in the layered upper mantle. The scale and volume of the peraluminous magmatism throughout Arizona dwarfs that of the porphyry copper event. A consistent SW-directed mylonitic fabric is present in many of the peraluminous sills and fits with a SW-directed thrust and the anvil shape of the intrusive sill complex.

    The entire suite of peraluminous magmatism occurs in the lower plate of a regional SW-directed thrust system that we previously named the Maricopa Thrust system (Keith and Wilt, 1986), which we suggested may have over 100 km of southwest-directed transport. In the context of Laramide flat subduction tectonics, we now interpret the Maricopa thrust as an intraplate subduction zone linked to the flatly subducted Orocopia Schist. The presence of Orocopia Schist has recently been mapped in the Plomosa Mountains (Strickland and others, 2017) and oceanic ultramafic harzburgite rocks were identified by Haxel and Jacobson (2013) at Cemetery Ridge. A regional plate of deformed mylonitic rocks that dips northeastward under the Colorado Plateau was documented in a seismic section in Reif and Robinson (1983). These new data and interpretations of older data emphasize the importance of flat subduction as the principle Cretaceous-Cenozoic tectonic episode. The field data (such as SW-directed mylonitization) is now more properly ascribed to the trench-directed tectonics induced by flat subduction.

    The Santa Catalina mylonites and their well-developed associated peraluminous magmatism provide one of the best field examples of flat subduction tectonics as it impacts the mid-crust. Hence, the main Cretaceous-Cenozoic event in Arizona and the rest of southwestern North America has more to do with compression, flat subduction, and associated deep, mid-crustal level, peraluminous magmatism than mid-Cenozoic crustal extension, which was a denudation effect of relative uplift of the mountain. In this regard, the term 'Metamorphic Core Complex' is a misnomer. This reconsideration of Catalina field geology may lead the way to a massive rethink of Cordilleran geology in the context of compressive flat subduction at the end of the Laramide orogeny and points to future research possibilities.

    Contact Info - If you have additional questions about the Spring Field Trip contact Stan Keith at (520) 668-4890 or

Past events

07 May 2019 Bootprints in Bear Country: Discovery History and Geology of the Malmyzh Cu-Au porphyry cluster, Khabarovsk krai, Russia by Mac Canby - Senior President Exploration for Freeport-McMoRan
02 Apr 2019 Florence Copper: Copper Recovery Using In-situ Technology By Dan Johnson BSc, MSc, PE – Vice-President | General Manager, Florence Copper Inc.
05 Mar 2019 Sarah Elizabeth Baxter presents "Treasures of Arizona's Sky Islands: Geology and Mineral Resources of Coronado National Forest
05 Feb 2019 Jeffrey E. Post presents The Hope Diamond and Smithsonian National Gem Collection
08 Jan 2019 John Dilles presents - Using the Zonation of Trace Metal Geochemistry and Hydrothermal Mineralogy for Porphyry Copper Mineral Exploration
04 Dec 2018 David (Duff) Gold presents - Deep-Seated Volcanism and the Genesis of Diamonds
06 Nov 2018 William Wilkinson Presents - The Good, The Bad and The Ugly: Three Decades of Exploration
02 Oct 2018 Ihor Kunasz Presents - The Geology and Economics of Lithium
04 Sep 2018 Jim Reed Presents - Applying Geological Exploration Methods Towards the Location of Clandestine Gravesites
07 Aug 2018 Rhodochrosite: Red Treasure of the Rockies - The Story of the Sweet Home Mine
03 Jul 2018 Alison Jones Presents - Rafting through 2 Billion Years of Geologic Time
05 Jun 2018 Gary Huckleberry Presents - The Geoarcheology of Ancient Water Control in the Southwest: Lessons from the Past
01 May 2018 William B. White presents The Science of Caves and Cave Contributions to Science
21 Apr 2018 Spring Field Trip - Jerome - An Early Proterozoic Volcanogenic Massive Sulfide Deposit
03 Apr 2018 Volker Spieth and Stanley Keith Present - Finding Gold in the Kupferschiefer
29 Mar 2018 Future Home of the University of Arizona Gem and Mineral Museum
06 Mar 2018 Joe Wilkins, Jr. Presents - Piedras Verdes and Cuatro Hermanos, Sonora, Mexico - A Tale of Two Porphyries
06 Feb 2018 Paul F. Hlava presents Causes of Color in Minerals and Gemstones
02 Jan 2018 Peter L. Ward presents Bringing Peace to the Climate Wars
05 Dec 2017 Joellen Russell presents The Ocean's Role in the Climate of the Anthropocene
07 Nov 2017 Eric Sundquist presents Geological Perspectives on Carbon Dioxide, the Carbon Cycle and Carbon Management
03 Oct 2017 Lily Jackson presents Andean River Sediments as a Window into the Tectonic History of Ecuador
05 Sep 2017 Vic Baker presents The Influence of the 18th Century Enlightenment on the Natural Sciences
22 Aug 2017 AGS Meet and Greet, A Networking Event
11 Jul 2017 Andrew Zaffos presents Global Tectonics and Marine Animal Diversity
06 Jun 2017 Dan Johnson presents Introduction to the Florence Copper Project and In-Situ Copper Recovery
02 May 2017 Robert Glennon presents America's Water Crisis and What To Do About It
22 Apr 2017 Spring Field Trip - The Laramide-age Chilito Porphyry Copper Deposit
04 Apr 2017 David London presents The Nature and Origins of Internal Zonation within Granitic Pegmatites
07 Mar 2017 Derek J. Thorkelson presents The Precambrian Tectonic Connection between Yukon and Arizona
07 Feb 2017 Daniel Hummer presents Mineral ecology and evolution: Using large datasets to tell the story of the co-evolution of Earth and life
03 Jan 2017 David A. Sawyer presents Dating Geologic Time in the Cretaceous: Integrating Biostratigraphy, Isotope Geochronology, and Astrochronology in Sedimentary Deposits of the Cretaceous Western Interior Seaway
06 Dec 2016 John W. Ewert presents USGS Responses to Some Volcanic Crises and Eruptions Around the World
01 Nov 2016 Alexander Schauss presents Minerals, Trace Elements and Human Health
22 Oct 2016 Fall Field Trip - The Peach Spring Tuff and the Silver Creek Caldera, Northwestern Arizona
04 Oct 2016 Hamish Martin Presents Geology of the Resolution Cu-Mo Deposit, Superior Arizona
06 Sep 2016 Keith R. Long Presents No Bonanza from Cheap Oil
02 Aug 2016 Lee Allison Presents The Future of State Geological Surveys: the Arizona Case Study
05 Jul 2016 Don Applebee Presents Genesis of the Chilito Porphyry Copper Deposit
07 Jun 2016 Robert Hildebrand Presents Collisions, Slab Failure Magmatism and the Development of Cordilleran Batholiths
03 May 2016 Peter Modreski will present "Pegmatites: Mineralogy, Gemstones, Economic Geology, and maybe not quite the same Giant-Crystal Rocks you always thought they were"
30 Apr 2016 Spring Field Trip - An Introduction to the Pinal Schist in Southeastern Arizona
05 Apr 2016 Jordon Bright Presents Looking for an Ocean in the Desert, the Enigmatic Bouse Formation
01 Mar 2016 Peter R. Johnson Presents Tectonics and Mineral Deposits of the Arabian-Nubian Shield
02 Feb 2016 Dr. Karen Wenrich Presents The Ga-Ge Rich Apex Mine, Utah - A Tsumeb, Namibia Analogue
05 Jan 2016 Sarah Baxter Presents Calc-silicate Alteration and Ore Characterization, ASARCO Mission Complex, Pima County, Arizona
01 Dec 2015 Peter Smith Presents The Latest News from Mars
14 Nov 2015 Fall Field Trip - Northern Plomosa Mountains and Bouse Formation in Blythe Basin
03 Nov 2015 Karen Kelley presents The Giant Concealed Pebble Cu-Au-Mo Porphyry Deposit, Southwest Alaska
06 Oct 2015 Caleb King presents Eocene Hydrothermal Systems and Contrasting Hydrothermal Alteration in the Battle Mountain District, Nevada
01 Sep 2015 Carl Bowser presents The Genesis of the Kramer Borax Deposit, Rogers Lake, Mojave Desert, CA:
04 Aug 2015 Dan Lynch presents Volcanoes in the Back Yard
07 Jul 2015 Erik Melchiorre presents The Complex Geological History Recorded by Arizona Placer Deposits:
02 Jun 2015 Jan C. Rasmussen Presents - Arizona Mineralization through Geologic Time
05 May 2015 Gordon Haxel Presents - Alpine peridotite in the desert - Arizona's Laramide subduction complex
02 May 2015 Spring Field Trip - Oak Creek - Mormon Lake Graben
18 Apr 2015 Third Annual Arizona Geological Society Doug Shakel Student Poster Event
03 Mar 2015 Apollo 17 Astronaut and Former Senator Harrison H. Schmitt presents A Geological Visit to a Valley on the Moon
03 Feb 2015 Don Yurewicz Presents Assessing Unconventional (Continuous) Hydrocarbon Resource Plays
06 Jan 2015 Arend Meijer presents: Sulfide-rich Proterozoic Mafic Rocks and Arizona Porphyry Copper Deposits - A Connection?
02 Dec 2014 Victor R. Baker: Megafloods on Earth, Mars, and Beyond
15 Nov 2014 Fall Field Trip - Debris Flows Shape the Sabino Canyon Landscape - look out below!
04 Nov 2014 Isabel F. Barton: Historical Development & Current State of Geological Research in the Central African Copperbelt
07 Oct 2014 Apollo 17 Astronaut and Former Senator Harrison H. Schmitt presents A Geological Visit to a Valley on the Moon
02 Sep 2014 Lewis Land presents Evaluation of Groundwater Residence Time in a Karstic Aquifer System
05 Aug 2014 Jamie Molaro presents Thermal Stress Weathering in the Inner Solar System
01 Jul 2014 Jim Leenhouts presents Surface-water/groundwater Interactions in Arizona
03 Jun 2014 Arend Meijer presents Pinal Schist of So. Arizona--A Paleoproterozoic Fore-Arc Complex
06 May 2014 John C. Lacy presents The Genesis of Mining Law
26 Apr 2014 Spring Field Trip - Geology of the Christmas Porphyry Copper Deposit
24 Apr 2014 Second Annual Arizona Geological Society Doug Shakel Student Poster Event
01 Apr 2014 Eric Seedorff presents, Structural Dismemberment of a Porphyry Molybdenum System, Spruce Mountain District, Northeastern Nevada
04 Mar 2014 John Dreier presents, Copper Deposits of the Coast Ranges of Chile; A trip through time, space, and ore deposit nomenclature
04 Feb 2014 Ralph Stegen presents The Morenci Porphyry Cu-Mo Deposit, Greenlee County, Arizona: A Geologic Summary with Emphasis on Hypogene and Supergene Mineralization
07 Jan 2014 Steve Castor presents, Mountain Pass and other North American Rare Earth Element Deposits
03 Dec 2013 Stephen Jackson, USGS, Looking forward from the past: Ecological impacts of climate change through the lens of history
05 Nov 2013 Malcolm Siegel, PhD, MPH, LJS Consulting, Inc and School of Medicine, University of New Mexico, Albuquerque, NM. 87047: Uranium Mining in the American Southwest: Can Medical Geologists Ask the Right Questions?
04 Oct 2013 Field Trip - H. Wilson Sundt Generating Station
01 Oct 2013 Mark Logsdon, Principal Geochemist, Geochimica, Inc.: What Does “Perpetual” Management and Treatment Mean? Toward a Framework for Determining an Appropriate Period-of-Performance for Management of Reactive, Sulfide-Bearing Mine Wastes
01 Oct 2013 Mark J. Logsdon, Geochimica, Inc., Does acid-rock drainage lead to waste-rock instability? Geological, hydrological, and geochemical framework for the Questa Mine
03 Sep 2013 Pete Reiners, UA, Geosciences Dept., Geochronology of secondary Fe & Mn oxides in bedrock
30 Aug 2013 Field Trip - University of Arizona Tree-Ring Research Laboratory
06 Aug 2013 Bill Stavast, Freeport-McMoRan Copper & Gold, The Safford Mine: What we have learned since production began
02 Jul 2013 Lukas Zurcher, USGS, presents: "Tectono-magmatic evolution of the Central Tethys Region"
04 Jun 2013 Steve Van Nort presents, "Gold Fever! The BRE-X/Busang Story
07 May 2013 Federal lands and mineral resources: Colorado Plateau uranium deposits and the Sonoran Desert Heritage
18 Apr 2013 First Annual Arizona Geological Society Doug Shakel Student Poster Event

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