SDAG Monthly Meeting
Wednesday, August 20, 2014
Catalina Room (southern end of MVCC)
Marina Village Conference Center
1936 Quivira Way
San Diego, CA 92109
FROM INTERSTATE 5: Take the SEA WORLD DRIVE exit. From SEA WORLD DRIVE,
take WEST MISSION BAY DRIVE on your right. When you see the large green sign that
says QUIVIRA ROAD, get in the farthest left of the two left turn lanes. Turn left, go one
very short block and turn left again. Drive about one half mile and MARINA VILLAGE will
be on your right.
FROM INTERSTATE 8:Take the WEST MISSION BAY DRIVE exit to the right. You will
be on INGRAHAM STREET for a short distance from which you will take the next exit
marked WEST MISSION BAY DRIVE on your right. When you see the large green sign
that says QUIVIRA ROAD, get in the farthest left of the two left turn lanes. Turn left, go
one very short block and turn left again. Drive about one half mile and MARINA VILLAGE will be on your right.
Cash Bar (aka the Walawender Tavern).
Menu: Hawaiian Buffet (Teriyaki Pork Ribs and Chicken, Vegetarian Stir Fry, etc). Beverage Station, Dessert. Cash Only Bar (aka the Walawender Tavern)
Cost: $30.00 for non-members, $25.00 for members, $15.00 for students and professors
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.
Make your reservation online by clicking the button below
no later than NOON, Monday, August 18th.
RESERVATIONS CANNOT BE ACCEPTED AFTER Monday at noon.
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 DO NOT MAKE A RESERVATION, WE CANNOT GUARANTEE YOU A MEAL.
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.
Speaker: Dr. Monte Marshall, Professor Emeritus, SDSU
"A Tale of Two Shields, The Canadian and Baltic Shields - Their Archean Rocks, Tectonic History, Beautiful Landscapes, and Melting Ice Sheets"
With increasingly good geochemical and paleomagnetic data and zircon age dating, our
understanding of the evolution of continents and supercontinents has greatly expanded in recent
decades. About 80 % of continental crust was created in the Precambrian, and every continent has
patches of Archean crust that are sutured together with crust that was created in Proterozoic
orogenies. Because they are cooler and have thicker lithospheric mantles than the younger crust,
these areas are stronger and less deformable and are called cratons. Any Phanerozoic sedimentary
rocks deposited on them are usually fairly flat lying. Regions of the cratons where the Precambrian
igneous and metamorphic rocks are exposed at the surface are called shields.
One of the largest and best exposed shields is the Canadian Shield. It extends from the famed
Northwest Passage down to the Great Lakes and from west of Hudson Bay to almost all of the
coastal/exposed areas of Greenland. Across the Atlantic lies another shield, the Baltic Shield. It is
exposed in northern Norway, Sweden, Finland, and in very northwestern Russia between St.
Petersburg and the Arctic Ocean. The Baltic Shield is no stranger to North America and the
Canadian Shield. It lay next to Greenland in the paleogeographic reconstruction of all three past
supercontinents - Pangea, Rodinia, and Nuna/Columbia. Greenland itself is really part of North
America. Based on the linear marine magnetic anomalies, the step-wise opening of the North Atlantic
during the breakup of Pangea was somewhat complicated. Greenland only rifted from Baffin Island
and Labrador during the interval 90 Ma--40 Ma. The Labrador Sea and Baffin Bay were created in
those 50 My. At 55 Ma some spreading between Greenland and Northern Europe began and by 40
Ma the current North Atlantic spreading center was firmly established.
The oldest rocks found so far in the Baltic Shield are 3.5-3.7 Ga granitic orthogneisses. The largest
and best preserved region of early Archean continental crust in the world is the Itsaq Gneiss
Complex in Greenland and contains rocks dated at 3.8-3.9 Ga. However, the oldest rocks on earth,
found to date, are the Acasta Gneiss found near Great Slave Lake in the Northwest Territory of
Canada and dated at 4.0 Ga. As you might expect, we have the Canadian Shield to thank for the
oldest rocks in the United States. Just before it dives under the Paleozoic sedimentary rocks in SW
Minnesota, the shield contains gneisses dated at 3.5 Ga! There are only 25 to 30 places in all the world's
shields that are known to contain Paleoarchean (3200-3600 Ma) or older rocks!
Finally, a few words about the beautiful blue-green ice that remains in the far north of the Canadian Shield area.
The ice cap that covers 98% of Greenland and reaches a thickness of two miles in its center contains about 10 percent of the earth's fresh water.
Antarctica has most of the rest. The velocity of the ice flowing out of some of the fjords has increased greatly in the last century.
Jacobshaven, on the southwest coast, is its most prolific iceberg producer - it probably produced the iceberg that sank the Titanic.
When we approached, so much ice was entering the sea that our icebreaker couldn't enter the harbor!
But Baffin Island, which was probably covered with ice a few thousand years ago, now has only a few isolated ice caps that feed small glaciers that flow down to the sea.
The Arctic is warming more quickly than the Antarctic and ironically the number of tourists (who, in part, want "to see the ice before it melts")
is also increasing rapidly! Ships burn a lot of fuel.
I have visited parts of these areas in recent years and will show you the landscape, largely fashioned by the recent Ice Age, and vegetative
cover - tundra in the far north and stunted forests (taiga) to the south. You will see polar bears and killer whales frolicking at the bow of our ice breaker.
And you will see what some of the oldest rocks in the world look like.
For the most part they are gneisses and their foliation is often flat-lying, but at times is contorted into folds whose wavelengths range from
centimeters to entire hill sides.
The dark rocks are often laced with bands of beautiful pink granite that has either been intruded as veins or formed in place as migmatites.
One of the most moving moments for me was when I stood on the western edge of Greenland's ice cap, now a hundred miles inland from the Labrador Sea,
and visualized how much ice had melted in just a few thousand years, and how much more the ice cap may continue to shrink in years to come!
Those of you who have read my recent articles or attended my recent talks, know that I have become interested in deep space and deep time in my declining years.
So, I've decided to write this biography in that vein!
I was born on a sunny Sunday morning in April, in Mercy Hospital, San Diego. But I had birth complications and the physicians had to use tongs to pull my head out first.
My mother told me that she cried when she saw my somewhat misshaped head laced with tong bruise marks!
I doubt that she realized that my birth trauma was partially due to the most important anatomical change in hominid evolution - the five-fold increase
in the size of our brains/skulls, since we split from chimpanzees about 7 million years ago!
Since that day, advances in biology, especially molecular biology and genetics, new fossil finds in Africa,
and much more accurate geochronology have opened amazing chapters in our evolution.
By 4 Ma a group of African apes, the Australopithecines (Remember Lucy?) began to use their hind limbs less for tree climbing and more for walking.
Around 3 Ma the first hominids of our genus appeared, Homo habilis. They were full-time bipedals, made primitive stone tools, and began losing much of their body hair.
There have been some 20 species of Homo and those extant at 1.5 Ma had learned the controlled use of fire, made more sophisticated stone tools,
and developed black skin since they no longer had much fur to protect them from the sun.
At about 200 ka, a species, Homo sapiens, appeared in the forests and grasslands of Africa that had an anatomy very similar to ours.
In fact, the study of mitochondrial DNA has shown that everyone on earth today is the descendant of one Homo sapiens woman, called the "mitochondrial Eve"!
Successive innovations in culture and lifestyle and a change in the climate of northern Africa led to waves of migration out of northeast
Africa and up into Europe and Asia at 60 ka. But the wonder doesn't end here!
Anthropologists had been finding the bones of other hominids mixed with those of our ancestors in caves in Europe and Asia.
In Europe it was Neanderthal man and in the Middle East it was the Denisovans. Since they were considered a different species,
and therefore mating should only produce at most a single generation of sterile hybrids, their disappearance shortly after 'we' arrived
was assumed to be their elimination/genocide by our 'superior' technology and intelligence.
More modern research and genetics suggests that our merging was more peaceful - AND that everyone on earth, except the sub-Saharan Africans,
have 1-5 % Neanderthal genes and as-yet-not-precisely quantified percentage of Denisovan genes!
The National Geographic/IBM have collected and analyzed the DNA of 500,000 people all over the world (including MM).
Wouldn't my mother be surprised to learn that her poor, bruised baby was two percent Neanderthal, about three percent Denisovan,
and that our early African ancestors spent some time in the Middle East, then pulled up stakes and moved to NW Europe, Ireland, and the British Isles
about 10 thousand years ago! And..., as they say, the rest is history :>) - Montek the Terrible
Upcoming SDAG meetings - 2014
September 17: Jill Krezoski - The Mineralogy of Mars
October: Field trip!
November 19: Vic Camp – Mid-Miocene Flood-Basalt Volcanism in the Columbia River Province, Mantle Upwelling and Basin and Range Extension.
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
Randy Wagner (2014 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.