Australian Sabbatical - 2002
Kent C. Condie, Professor of Geochemistry

My experience at Macquarie University was great. It has been many years since I actually analyzed samples myself. I was at GEMOC (National Key Centre for the Geochemical Evolution and Metallogeny of Continents) in the Department of Earth & Planetary Sciences, and while there I focused on two major research projects: 1) a study of the distribution of rare earth and high field strength elements (esp. Nb and Ta) in mantle and lower crustal xenoliths, and 2) a search for evidence of juvenile continental crust in the two age gaps on the continents, 1.6-.14 Ga and 2.4-2.2 Ga. My main reason for going GEMOC for my sabbatical was to use their new cutting-edge research equipment including their laser probe ICPMS units, with which one can analyze small (30 micron) spots on minerals for many trace elements as well as radiogenic isotopic ratios, with high degrees of precision. Perhaps the most important finding in the mantle xenolith study is that both the rare earths and high field strength elements are housed primarily in secondary (metasomatic?) phases in cracks and around grain boundaries. Less than 50% of these elements occur in primary mantle minerals (olivine, pyroxenes, spinel, garnet). This is important because these elements are typically used to model the magmatic history of the mantle xenoliths, assuming equilibrium between magma and residual minerals. Our findings, however, indicate that these elements were introduced later, probably in fluid phases.

Our work with zircons was also really exciting. Using a laser probe ICPMS, one can analyze for Pb, U, and Th isotopes and thus date single spots on the zircons. And then using the multicollector laser probe ICPMS, it is possible to determine Hf isotopic ratios in another spot near the spot used to date the mineral. From the combination of U/Pb isotopic age and Hf isotope results, it is possible to estimate the amount of juvenile component (coming directly from the mantle) in the source rocks of the zircons. Although our results are incomplete, because the multicollector unit malfunctioned during the last month of my stay, they indicate for at least one population of detrital zircons from NW Canada that the zircons with ages of 2.2-2.4 Ga are not from juvenile sources, but represent either older reworked crustal sources or mixed juvenile and older crust.

While here in Australia I travelled to Beijing in China to attend the Geological Society of America Penrose conference on Archean high and low grade rocks. Much of the time was spent on a field trip into the Hengshan and Wutai areas to observe high grade and low grade terranes of the North China Archean craton. The rocks and the weather were great, as were the Buddist temples we saw in the Wutai valley. However, as typical of Chinese field trips, the unexpected continually delayed us. On our return from Wutai area to Beijing, we came to a long line of trucks stopped—it turned out the road had been washed out and they trucks had been there for nearly two days! Fortunately, we got the buses turned around and headed back the long way. On this road we came to a washed out bridge and had to take another long detour; we didn’t get back to Peking University until nearly 2 AM.  After the meetings at the university, about 10 foreign geologists and 15 Chinese geologists visited the controversial Dongwanzi ophiolite, allegedly the oldest know ophiolite in the world (ophiolites are thought to represent ancient fragments of oceanic crust). This site had been described in a paper published in the American Science magazine and had also received attention in the Chinese media (we had reporters with us on the field trip). Again, because of typical travel problems, washed out roads, backed up traffic, road construction, bridge construction, etc., we did not see all of the evidence to support an ophiolite origin. However, what we saw was convincing (sheared harzburgites, podiform chromite) and the isotopic dating indicates an age of 2.5 billion years.

One incident at the site where the bridge over a river was closed is worth describing. The detour involved fording a river, which was possible if one went slowly (the bottom was hard). But our drivers, who typically know nothing about 4-wheel drive vehicles, sped through and one of the vans got water on the spark plugs, and stalled in the middle of the river. After what seemed an endless time, the vehicle was finally pulled out, only to burst into flames. Geologists were abandoning the vehicle rapidly through any and all openings. Bill Collins, an Australian scientist, went under the van and put the fire out, otherwise the whole van would have burned up. Now about 10 Chinese geologists had no place to ride. They managed to talk one of the locals into renting a much smaller van, and we proceeded onwards. On our return, the mayor to Zuhua met the group, let us use 3 new cars, and supervised the fording of the river. This might not seem unusual for the mayor of a small town to personally help, but Zuhua is a city of over half a million people!

The first time I visited China and Beijing was in the early 80s. The changes in the last 20 years are enormous. Beijing is beginning to look more like Hong Kong or Tokyo—skyscrapers going up all around, freeways criss-crossing the city, big shopping centers. There are many fewer bicycles today and many more cars. I heard that 5000 cars are entering the car pool in China every day! Construction on freeways and buildings goes on 24 hrs/day. Big hotels are everywhere, and tourist buses now frequent all of the interesting places around Beijing. Almost everyone has a cell phone and a TV. Commerce is booming. BUT: this rapid growth is essentially limited to the big cities. In going around the countryside on our field trips, I see no changes in the last 20 years, and in fact, the living conditions of the rural peasants have been the same for hundreds of years. Primitive housing, no plumbing, poor transportation, old putt-putt trucks, donkey-pulled wagons, hand thrashing of grains, lots of manual labor. All the money is going into the cities, and apparently none into the farming and peasant populations.