Mary Leech profile picture

Mary Leech

Professor and School Associate Director
Petrology, geochemistry, geochronology, the tectonics of mountain building, and natural hazards
Phone: (415) 338-1144
Location: TH 521


B.S. Geology - San Jose State University

Ph.D. Geological and Environmental Sciences - Stanford University

My research involves field work that has taken me to mountain belts all over the globe - the Indian Himalaya, the Dabie-Sulu belt in eastern China, the Scandinavian Caledonides of Norway, the Urals Mountains in Russia and the Kokchetav massif in Kazakhstan. While each is unique, these mountain belts have one thing in common: ultrahigh-pressure eclogite-facies rocks. The eclogites form in subduction zone complexes in the suture zones of mountain belts (where two continents are essentially stitched together) and record a complete pressure-temperature-time history from comprising the edge of a continent, to subduction into the upper mantle and then the return path back to the surface. An ever-increasing number of these subduction zone complexes contain evidence that eclogites were subducted to depths in the upper mantle where pressures are great enough to form microscopic diamond (>100 km or >70 miles) thus making them ultrahigh-pressure rocks. Study of these subduction zone complexes involves investigation into not only the petrology and geochemistry of these rocks but also large-scale processes of continental collision and subduction, crust-mantle interactions and the tectonics of mountain building.

My research has required a variety of analytical techniques, in which undergraduate and graduate students have already been involved: radiometric dating (U-Pb dating of zircon on an ion microprobe [SHRIMP] using cathodoluminescence imaging, and apatite fission-track dating); establishing mineral chemistry using an electron microprobe; investigating the graphite-diamond transition using x-ray diffraction, raman and infrared spectroscopy, and scanning and transmission electron microscopy; and stable isotope analyses of carbon, oxygen, and nitrogen using infrared CO2 and in-situ UV laser ablation mass spectrometry and on an elemental analyzer.

Published peer-reviewed papers:

Adirondack Highlands & the Grenville orogen
The graphite-diamond transition & diamond preservation in UHP rocks
The Himalaya and southern Tibetan plateau 
The Dabie-Sulu orogen in Eastern China
The Ural Mountains, Russia 
Eclogitization & the  role of fluids in brittle-ductile processes, Norway
  • Leech, M.L. and Shulman, D.J., in revision, Fluid-controlled metamorphism of eclogitic pseudotachylite-bearing shear zones, Flakstadøy, northern Norway.
  • Leech, M.L. and **Shulman, D.J., 2014, Fluid-controlled eclogitization of pseudotachylyte-bearing shear zones, Flakstadøy, Norway, Goldschmidt conference abstract, 22f-302.
  • Leech, M.L. and **Shulman, D.J., 2012, Fluid-controlled metamorphism of eclogitic pseudotachylite-bearing shear zones, Flakstadøy, northern Norway, Eos Trans., Am. Geophys. Union, Fall Meeting Supplement, Abstract MR51A-03.
  • *Dutra, S.M., **Shulman, D.J., and Leech, M.L., 2010, Thermobarometry of eclogites-facies shear zones in the Lofoten Islands, Norway, Geol. Soc. Am. Abstr. Prog., 42,  p. 100.
  • Leech, M.L., **Shulman, D., and *Dutra, S., 2009, Pseudotachylite in eclogite-facies shear zones from the Lofoten Islands, northern Norway, Eos Trans., Am. Geophys. Union, Fall Meeting Supplement, Abstract V43C-2265.
  • **Shulman, D., Leech, M.L., and *Dutra, S., 2009, Eclogite-facies pseudotachylite in deep crustal rocks exposed in northern Norway, Geol. Soc. Am. Abstr. Prog., 41, p. 485.
  • *Polito, C. and Leech, M.L., 2006, Petrology and new U-Pb SHRIMP dating for eclogues of the Lofoten Islands, Flakstadøy and Vestvagøy, northern Norway, Eos Transactions AGU, 87, Fall Meeting Supplement, Abstract V31A-0571.
Cordilleran gneiss domes
Other publications - Education-related

(**graduate student and *undergraduate student co-authors)

My current research projects include ca. 1 Ga ultrahigh-temperature metamorphism and migmatization in the Adirondack Highlands, New York; ca. 53 Ma ultrahigh-pressure subduction zone metamorphism in the India-Asia collision zone, and Miocene granite intrusion and mid-crustal channel flow processes in kyanite-bearing Greater Himalaya Sequence rocks, India; and the interplay between britle and ductile deformational processes in pseudotachylyte-bearing eclogite-facies shear zones in the Lofoten Islands, Norway.

External grants

  1. U.S. Geological Survey EDMAP program (2020-2021) part of the National Cooperative Geologic Mapping Program, “Geologic mapping of the Ledge Mountain migmatites, Rock Lake 7.5’ quadrangle, Adirondack Highlands, New York” (extended 1 year because of Covid-19 restrictions on research/travel), PI

  2. NSF Tectonics program (2013-2014) EAR 1406054, “Microstructural Analysis and EBSD Applications in Earth Sciences” (workshop using David Mainprice's MTEX/MATLAB), PI

  3. NSF Instrumentation & Facilities (2010-2013) EAR 0949176, Upgrade of Electron Microscopy Facility to Increase Geoscience Functionality at San Francisco State University, PI

  4. NSF Continental Dynamics (2010-2011) EAR 0965796, “Conference Support for the 25th International Himalaya-Karakoram-Tibet (HKT) Workshop” and “Future directions for NSF-sponsored geoscience research in the Himalaya/Tibet”, PI

  5. NSF CAREER — Tectonics, Petrology & Geochemistry, and Education and Human Resources (2009-2014) EAR 0847721, Petrogenetic affinity of Miocene granites to test the mid-crustal channel flow model in the Himalaya (two no-cost extensions to 2016), PI

  6. NSF Major Research Instrumentation (2008-2011) CHE 0821619, Acquisition of a FE-SEM to enhance research and student training in Biology, Chemistry, Geosciences, Physics, and Engineering at San Francisco State University, Co-PI

  7. NSF-AAAS Women's International Science Collaboration grant (2003-2004) Collaborative research on the petrotectonic evolution of the ultrahigh-pressure Tso Morari Crystallines, western Himalaya, India, PI

  8. NSF Continental Dynamics (2001-2005) EAR 0003355, Subduction and exhumation of ultrahigh-pressure rocks: Field and drilling studies in eastern China, ~20% of proposal effort

  9. University of California President's Postdoctoral Fellowship Program (2001-2003) The impact of eclogite formation on the dynamics of continental collision

  10. NSF Office of International Science and Engineering (1999-2001) OISE 9901573, Mountain building in the Urals and the nature of ultrahigh-pressure metamorphism, PI

Current students

Graduate students

  • Laura Horsley (M.S. exp. 5/2022) U-Pb SHRIMP dating and phase equilibria modeling of Ledge Mountain migmatites, Adirondack Highlands, New York
  • Zachary Smirnov (M.S. exp. 5/2023) Thermodynamic modeling of ultrahigh-temperature granulites in the Ledge Mountain region, Adirondack Highlands, New York

Undergraduate students

  • Victoria "Tori" Hicks (B.S. exp. 2023)
  • Grayson Kohary (B.S. exp. 2023)
  • Kaitlyn "Kei" Mowry (B.S. exp. 2023)

Former students

Graduate students

  • Mike Davis (M.S. exp. 5/2021) Petrotectonic evolution of Ledge Mountain migmatites with phase equilibria modeling and melt reintegration, Adirondack Highlands, New York (Now a Research Assistant at the U.S. Geological Survey, Menlo Park)
  • Brandon Swanson (M.S. 2018) Pressure-temprature conditions of Kyanite-bearing Migmatites at Ledge Mountain, Central Adirondack Highlands (Now a Hydrologist at Nevada Gold Mines, Elko, NV)
  • Katherine "Katie" Sullivan (M.S. 2017) Correlation of erupted plutonic clasts and volcanic deposits from Newberry volcano, Oregon (Now a contractor for the US Geological Survey, Menlo Park, CA)
  • Jackson Reeder (M.S. 2017) U-Th-Pb geochronology and trace element chemistry of zircon from Ledge Mountain, central Adirondack Highlands, New York (Now a Geologist at Amec Foster Wheeler, Oakland, CA)
  • Rui Liu (M.S. 2016) Regional tectonic evolution of the Pioneer core complex, south-central Idaho (Now a Geologist at StructureSolver LLC, Houston, Texas)
  • Andy Nieblas (M.S. 2016) Pressure-temperature-time-deformation history of the Lahul valley, NW Indian Himalaya (Now a Senior Staff Geologist at LGC Geotechnical, Inc., San Clemente, CA)
  • Ozum Basta (M.S. 2015) The tectonometamorphic evolution of the Greater Himalayan Sequence along the Zanskar shear zone, NW Himalaya (Now a Reservoir Geologist at Turkish Petroleum, Ankara, Turkey)
  • Emma Beck (M.S. 2014) P-T-t-d history of mylonites from the Zanskar shear zone, NW India (Now an MBA Candidate at Harvard Business School)
  • Forrest Horton (M.S. 2011) Geochronology and zircon geochemistry of Greater Himalaya leucogranites in Zanskar, NW India (Completed his PhD in Geological Sciences at UC Santa Barbara in 2015. Now an Assistant Scientist at Woods Hole Oceanographic Institution)
  • Pariskeh Hosseini (M.S. 2011) EBSD analysis of partially-eclogitized rocks from the Marun-Keu Complex, Polar Urals, Russia (Now a PhD candidate at Queens College, City University of New York)
  • Deborah Shulman (M.S. 2011) Fluid controlled metamorphism of eclogitic pseudotachylite-bearing shear zones, Flakstadøy, northern Norway (Completed a PhD in Geology in 2016 at the University of Maine. Now an Event Coordinator, University of Maine)
  • Will Hassett (M.S. 2010) Geochemical signature of Himalayan gneiss domes: Implications for channel flow (Now a teacher with Teach for America)

Research facilities in the Department of Earth & Climate Sciences include:

• Mineral separation/sample preparation lab - Rock saws, thin sectioning equipment, grinder/polisher, vibratory polisher, jaw crusher, disk mill, shatterbox, slope Frantz magnetic separator, ovens, lap wheels, sieves and sieve shakers, rock storage

• Twenty Leica DM750P petrographic microscopes available for student use, and one trinocular Leica DM750P scope with a dedicated 18 megapixel DSLR camera with HD video recording (Canon EOS Rebel T3i) for taking photomicrographs or videos of thin sections.

• Leech’s personal lab has a Nikon E600POL polarizing microscope and a Nikon SMZ1500 reflected and transmitted light microscope with a polarizing, rotatable stage and base capable of pseudo-darkfield imaging. These two microscopes share a DSLR camera (a Canon EOS Rebel T3i) that can be used interchangeably between the two scopes. The Leech lab also houses a custom Xidax X-8 and an Alienware Aurora R12 "gaming" PC for thermodynamic modeling of complex rocks using Perple_X; these PCs are set up with convenient remote access capability.

Research centers and facilities in the College of Science & Engineering:

• Zeiss Ultra 55 Field emission scanning electron microscope with BSE, STEM detector, Oxford INCA EDS and EBSD, and a Gatan MiniCL. We use the SEM in conjunction with an XEI Evactron plasma cleaner and ibss Gentle Asher to maintain a clean sample chamber. Sample preparation equipment includes a Gatan Model 682 PECS + RIBE that is a coater/ion beam etcher, a Cressington 208HR sputter coater, a Cressington 208C carbon coater equipped with sample holders specifically for geological thin sections, and a critical point dryer. We use Channel5 software to process EBSD data.

• Bruker D8 ADVANCE powder x-ray diffractometer

• Raman spectrometer with a 532 nm laser and 50 mW power (in the Department of Physics & Astronomy), and a Horbia Raman system with two laser lines (532 and 788 nm) and a TERS microscope (in the School of Engineering).

• Various spectrometers, gas and liquid chromatographs, radiochemistry facilities and equipment, centrifuges, lasers, etc. (in the Department of Chemistry and Biochemistry)

• Scanning laser confocal microscope, fluorescence and epi-fluorescence microscopes, and a dissecting scope (in the Cell and Molecular Imaging Center, Department of Biology)

• The Atomic Force Microscopy Facility

• Gas chromatograph stable isotope analyzer, elemental analyzer, etc. (at the Romberg Tiburon Center for Environmental Studies)

• Glass shop and an electronics repair facility

 The Sierra Nevada Field Campus

Other facilities (in the Bay Area and at other U.S. institutions):

• We also regularly use lab facilities at other universities including collecting mineral composition data on the electron microprobe in the Microchemical Analysis Facility and performing U-Pb zircon geochronology & trace element geochemistry on the Stanford-USGS SHRIMP-RG lab at Stanford University. 

• We send samples to the Peter Hooper GeoAnalytical Lab at Washington State University for whole-rock major and trace element geochemical analyses.

• We have an established relationship with the Noble Gas Lab at the University of Vermont for 40Ar/39Ar geochronology and thermochronology.

• We have collected combined U-Th-Pb geochronologic data and Hf isotope ratios by Laser Ablation ICP Mass Spectrometry (ICP-MS) at the University of Arizona's LaserChron Center

Currently offered*

  • Global Tectonics (ERTH 795 – graduate level)
  • Mineralogy and Petrology I (ERTH 420 – required major course, Spring only)
  • Mineralogy and Petrology II (ERTH 520 – major elective, Fall only)
  • Our Dynamic Earth (ERTH 112 – GE & required major course)
  • Volcanology (ERTH 410 – major elective)

Offered in the past*

  • Geochemistry (ERTH 522)
  • Physical Geology (ERTH 210)
  • Science Partners in K-12 Education (ERTH 652)
  • Tectonic Geomorphology (ERTH 795)
  • The Violent Earth (ERTH 310)
  • Earthquakes and the San Andreas fault
  • Geology of the National Parks
  • California Rocks!