Paleomagnetic constraints on the emplacement and temperature of select volcaniclastic debris flows of the Pliocene Tuscan Formation in Northern California Presented by: Roy Hull Advisor: Dr. Rachel Teasdale California State University – Chico

Why this Research? We want to know more about the emplacement process of the debris flows Magmatic Meteoric and/or volcanic event Identify new characterization attributes for Tuscan Formation – correlation aid Validate that paleomagnetic techniques can be used on volcanic related debris flows

Similar Research Paleomagnetic techniques have been used in the past. ◦Pyroclastic flows i.e. Japan, Italy ◦Volcanic debris avalanche flows i.e. Mexico ◦Lava deposits worldwide Why not debris flows?

2008 Proof of concept ◦Big Chico Creek Ecological Reserve USGS CSU – Chico CSU – Sac

Proof of concept Upper Flow  Plots were widely scattered – Cold emplacement Medial Flow  Plots were inconclusive either way Base Flow  Type 3 vector that indicated a reheating to ˚C, but slightly scattered Possible brief interval between lower and upper units Emplaced around 3Ma Distance from source might be a factor (45Km)

Was the debris flow hot or cold when emplaced? ◦If hot, can the actual temperature of reheating be determined ◦If hot, can the genesis be interpreted, i.e. volcanic episode Can a geomagnetic reversal be detected? Can a depositional age be assigned to a specific debris flow? Research Questions

Geomagnetic Reversals Tuscan Debris flows were deposited during a time interval when numerous reversals occurred

Site Logistics Sample collection ◦Interbedded lava ◦Proximal, midway and distal from Mt Yana

?

Sample Processing Progressive Thermal Demagnetization ◦Heating and Cooling cycle Cryogenic Magnetometer (USGS – Menlo Park) ◦3 axis magnetic moment (x, y, z)  Total magnetic moment, H  Inclination, I (vertical component)  Declination, D (horizontal component)

Rocks do not age well ◦Lightening and Chemical ◦Viscous Remanent Magnetism  Minimum Temperatures Hematite > 300°C Magnetite > 190°C Titanomagnetite < 200°C

Progressive Thermal Demagnetization Points 0 – 3 younger magnetic Points 4 – 6 original magnetic

Type 1 ◦Vector  Similar inclination  Similar declination ◦Highest temperature  Unknown ◦What is this?  Lava

Type 2 Vector ◦Different vector directions between clasts  Widely scattered plots Example – Cold flow and conglomerates

Type 3 Vector ◦Two component vectors Why two? ◦Clasts reheated, but not enough to completely over-write older imprints Lower vector – Consistent direction Higher vector – Random direction

Current Analysis Proximal (small sample lots size)  Site 2: ◦ Lava flows are all normal polarity, NE declinations and different inclinations  Site 3: ◦ Very similar inclination and declination  Site 2 and 3 debris flows: ◦ “Somewhat scattered and general indication of normal polarity” Site 1 (Medial), 4 (Distal)  Not processed

What is left? More sample collection ◦Proximal sites ◦Find another medial site Trip(s) to Menlo Park ◦Sample processing and document results Write thesis

References Butler, Robert, “Paleomagnetism: Magnetic Domains to Geologic Terranes”, University of Portland, Electronic Edition, September 2004 Clement, B.M., Conner, C.B. and Graper, G, “Paleomagnetic estimate of the emplacement temperature of the long-runout Nevado de Colima volcanic debris avalanche deposit, Mexico”, Earth and Planetary Sciences Letters, 120, pp ,1993 Lydon, Philip, “Geology and Lahars of the Tuscan Formation, Northern California”, GSA Memoir 116, 1969 (Former Chico Prof) Dr. Duane Champion – USGS Volcano Hazards Team (Paleomagnetic Expert) Google Earth