Physics & Astrophysics Colloquium
Friday, December 6, 2013 4 PM - 5 PM
Physics & Astrophysics welcomes Will Gosnold for a colloquium titled "A link between coincident heat flow, gravity and erosional anomalies in the mid-continent of North America." The colloquium is at 4 p.m. Friday, Dec. 6, in 211 Witmer Hall. Come at 3:30 p.m. for coffee, cookies and conversation in 215 Witmer Hall.
An 80,000 km2 area of anomalously high heat flow (70 mW m-2 to 140 mW m-2) in the mid-continent coincides with a large negative isostatic gravity anomaly (-40 mgal), and the entire region has been uplifted and eroded by at least 400 m during the past several million years. Numerical models of the thermal structure of the crust from the surface to the Mohorovicic discontinuity were applied to test several hypotheses that link the heat flow, gravity and uplift of the area.
1) The heat flow anomaly is due to advective heat transport in a gravity-driven, confined aquifer system that formed when the Black Hills were uplifted during the Laramide Orogeny 50 Ma. The duration of the thermal anomaly has caused the lower crust to warm sufficiently to induce about 2 km of downward displacement of the gabbro-to-garnet granulite phase boundary. The reduced density in the lower crust causes the negative gravity anomaly and vertical stresses generated by the buoyancy of the lower crust caused isostatic uplift and subsequent erosion of the Upper Cretaceous and Tertiary strata. Numerical models of advective heat transport in the aquifer system provide a test of the heat flow element of this hypothesis. Analysis of the thickness of the crust using receiver functions from the transportable array in the Earthscope project provides a test of the gravity and uplift elements of this hypothesis.
2) Radioactive heat production in a large granitic pluton having a density lower than the enclosing crystalline basement generates both the heat flow and gravity anomalies. Radioactive heat production and rock density can be coupled by differentiation of the expressions for V and T as follows:
F= -∂V/∂r=-Gm ∂/∂r 1/r
q= -λ ∂T/∂r=-A'/4π ∂/∂r 1/r
Combining the expressions yields F/Gm=q4π/A^' converting A’ to volumetric heat production and the mass term to density yields q=FA/fπGρ. The size and depth extent of the gravity anomaly can be estimated using forward modeling methods. Thus, estimates for heat production can be obtained from the density estimates. Calculation of the thermal structure of the crust provides a test of this hypothesis.
Parking InformationUnless special parking arrangements have been stated above, off-campus guests for this event may use the pay-as-you-go option in the Parking Ramp (corner of 2nd Ave N and Columbia Road), the Visitor Lot (off Centennial Drive), or a Parking Meter. Parking in any other parking lot on-campus requires a parking pass which can be purchased directly through UND Parking Services, Twamley Hall Rm 204 (M, W-F 8:00 AM – 4:30 PM and Tu 9:00 AM – 4:30 PM).
Other Events on This Day
- Men's Swimming U.S. Winter National Champs (All Day)
- Men's Diving Mizzou Invite (All Day)
- Women's Swimming at U.S. Winter National Champs (All Day)
- Women's Diving at Mizzou Invite (All Day)
- Denim Day (All Day)
- Breakfast Chat Fridays (9 AM)
- St. Nicholas Celebration (11 AM)
- Local Author Day (11 AM)
- UND Art Collections Exhibition (12 PM)
- Healthy UND Monthly Meeting (12 PM)
- Crock Pot Cooking (12:30 PM)
- ZUMBA (2 PM)
- Women's Hockey at Clarkson (2 PM)
- Institutional Review Board Meeting (2 PM)
- (editor's pick)Student Showcase Recital (2 PM)
- Yoga Renewal (3:30 PM)
- Children's Chess Club @ GFPL (3:45 PM)
- Revolution (5 PM)
- Christmas in the Park (5:30 PM)
- Winter Wunderland (6 PM)
- Men's Hockey at Western Michigan (6:05 PM)