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SDAG Monthly Meeting
Wednesday, November 14, 2018

Location: Best Western Seven Seas
411 Hotel Circle South, San Diego, CA 92108

FROM INTERSTATE 5: If you are heading south on the I-5 take the I-8 east for 2.2 miles. Take the Hotel Circle E exit. Turn left on Hotel Circle. The Best Western will be on your right just before you cross under the freeway.
FROM INTERSTATE 8: Take the I-8 West to exit 4B for Hotel Circle W. Turn right onto Hotel Circle N which has you heading back east. Slight right onto Hotel Circle S. Best Western will be on your left just past the freeway bridge.
happy hour
5:30pm -
Social hour  

Menu: Pot Roast, Roast Pork, Red Potatoes, Salad, Mixed Veggies and Dessert
6:30pm -

Cost: $35.00 for non-members, $30.00 for members, $20.00 for students.
if pre-registered by the deadline, $5 extra if you did not make a reservation. Click the SDAG member checkbox on the reservation form if you are a member.

Reservations: Make your reservation online by clicking the button below no later than NOON, Monday, November 12
Late reservations/cancellations are preferred over walk-ins or no-shows. Fees payable at the meeting or pre-pay with PayPal.
As a new payment option, there will be a phone credit card reader at the meeting.

If you are a current SDAG member and are not getting e-mail announcements,
make sure the SDAG secretary has your correct e-mail address.

7:30pm - 8:30

Student Presentations:

Speaker: Christeanne Santos - Instability of Thermoremanence and the Problem of Paleointensity Estimation

Abstract: Information gathered from studies of Earth's magnetic field has been integral to advancing many aspects of the geosciences. As a vector quantity, both direction and intensity data can provide considerable insight into the complex processes of the earth, such as models of the dynamic liquid outer core and descriptions of Earth's intricate geological history. Even more relevant to us, the geomagnetic field can affect the functioning of the electrical grid and it also protects us by deflecting harmful radiation from the sun back into space. Directional information is relatively simple to retrieve and analyze, however, intensity estimation requires intricate methodology and broad assumptions. Magnetic minerals within a cooling unit of lava essentially act as a compass and align themselves with the ambient magnetic field of the Earth, gaining a thermal remanent magnetization (TRM). As the rock cools past a critical temperature, that TRM remains stable over geologically significant periods of time, thus providing a snapshot of the magnetic field in which it formed. Stepwise thermal laboratory experiments are favored among paleomagnetists for their robust approach to obtaining measures of this remanent magnetization. These types of experiments result in a simple linear problem to produce an accurate intensity estimate, however, only for samples that are considered "ideal." Complications arise in the theory and method when non-ideal, large-grain magnetic recorders are used, which make up a significant portion of the natural magnetic material sampled in the field for experimental use. These thermal experiments are founded on the ideas that the thermal magnetic history of a sample is entirely reproducible in the laboratory and that acquired remanent magnetization remains stable for long spans of time. Empirical observation from a previous study showed a violation of these fundamental ideas and that the theory does not hold true for non-ideal magnetic recorders. The samples showed growth in their magnetic moments and that their original plots were not able to be reproduced. As an experimental continuation, in this study we used natural samples from previous, unrelated experiments and followed the same experimental protocol of this previous study. We gave a known, laboratory-controlled total remanent magnetization to see if its given laboratory intensity could be accurately reproduced from a typical thermal experiment. These samples were also "aged" over a two-year period to test the assumption of magnetic stability over time. The reason for these changes is not explained by the theory. In the future, we will use sophisticated numerical models of the micromagnetic structures to explore solutions to this problem.


Speaker: Jennifer Maria-Benavides - Constraining the Nature of Electrum From Low-Sulfidation Epithermal Deposits in the Northern Nevada Rift

Abstract: Gold is a noble metal that has fueled mineral resource exploration in the Northern Great Basin and profoundly affected the national economy. The origin of the gold deposits has been at the center of basic and applied research, with the goal to develop refined exploration models. For the first time, I am able to unambiguously constrain the nature of electrum from a low-sulfidation epithermal deposit in the Northern Nevada Rift. In this study, the highly siderophile elements (HSE; Os, Ir, Ru, Rh, Pt, Pd, Re and Au) serve as an innovative tracing tool due to the inherent relationship between the HSE and Au that can be used to trace the origin of electrum directly. Coupled precise 187Os/188Os compositions and isotope dilution HSE abundance data are reported for electrum grains from the Fire Creek Mine, as well as for a suite of host rocks that encompass the bimodal basalt-rhyolite volcanism of northern Nevada. The mid-Miocene bimodal host-rocks have Os isotope compositions consistent with crustal contamination observed in the Columbia River Flood Basalt (CRFB) province. The host rocks are isotopically similar to the CRFB Wannapum, Grande Ronde, and Imnaha basalt formations. Highly siderophile element concentrations are heavily fractionated for the host rocks but are less fractionated for the electrum. Rhenium-Osmium isotope analysis of electrum yields a relatively unradiogenic initial 187Os/188Os of 0.1588, demonstrating a source distinct from the crust and that can only be of mantle origin. From this, I estimate that as much as 96% of the gold in the Fire Creek deposit is of mantle origin, in contrast to evidence for much larger crustal contributions from proxy measurements.

Upcoming SDAG meetings - 2018

December 19: Tom Deméré - San Diego Natural History Museum

Upcoming SDAG meetings - 2019

January 16: Matt Burgess, Ken Hudnut, and Diane and Monte Murbach – Kilauea Volcano - Green Dragon Tavern

February: TBD

Meetings are usually scheduled for the 3rd Wednesday evening of the month. Meeting information on this website is normally updated the second week of the month.

If you have any information, announcements, ads or suggestions for an upcoming newsletter, please submit it to Adam Avakian, (2018 SDAG Secretary). Any news regarding upcoming events that may be of interest to the Association or news of your business can be submitted. The submittal deadline for the next SDAG newsletter is the last Friday of the month.
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