[continued from page 9] As if these and other innovations were not enough, the HPCAT staff is also exploring the use of a “virtual laboratory” to automatically align and control experiments. This system would also allow partners to use the facility from remote locations. Since the enclosures are closed during measurements because of the very high radiation levels anyway, and all activities are computer controlled, this possibility is an attractive way to save time and money required for travel.

What’s Next?

The three years it has taken to get to this point have been a long, hard haul with many unexpected challenges along the way. But, Häusermann says, the team is looking forward to beginning scientific experiments this October in the first experiment enclosure. And it is determined to start solving key scientific problems from day one. After this, it is expected that another enclosure will be brought into operation every three months until the full completion of the construction phase at the end of summer 2003.

Read all about it!

Finding My Way:

The Autobiography of an Optimist

Longtime Carnegie friend Evelyn Stefansson Nef recently published her autobiography, Finding My Way: The Autobiography of an Optimist. The daughter of Hungarian-Jewish immigrants, Nef has had an extraordinary life. She was virtually on her own as an adolescent in New York and became part of that city’s art community in the 1930s. She became a puppeteer with Bil Baird and then his wife. Later she worked as a researcher and writer for the Arctic explorer Vilhjalmur Stefansson, whom she married. After his death, she married John Nef, through whom she came to know some of the most famous artists of the day. In her late fifties, Nef changed her course again and became a psychotherapist—a profession she retired from at age 80. Her stories make a fascinating read.

Diamonds are Much More

Than Just Pretty Gemstones

Steven Shirey and David James, staff scientists at the Department of Terrestrial Magnetism (DTM), and their colleagues have found that diamonds, and the smaller minerals sometimes included in them, can reveal the details of how and when the oldest parts of our planet formed. Their results were published in the September 6 Science.

For their research, the scientists looked at evidence documented over the past two decades from 4,000 diamonds, and at data from seismic P-waves from the Kaapvaal-Zimbabwe Cratonin southern Africa. Their goal was to determine if the composition and age of the diamonds correlate to the geologic structure of their deep-seated source region. They found that there was a correlation, and that diamonds can reveal a lot about the evolution of the cratonic roots in the area.

Cratons contain the oldest rocks on the planet and provide the nucleus around which younger continental material assembles. They also hold much of the Earth's mineral wealth including diamonds, which typically form beneath the cratonic crust in rootlike structures called mantle keels. These keels extend to depths of more than 200 kilometers, where pressure is high enough for diamond formation. They date to the Archean period (3.9 to 2.5 billion years ago), are thought to be as old as the over-lying crust, and have long been a focus of Carnegie scientists, notably Joe Boyd and Richard Carlson. Diamonds in the Kaapvaal Craton are found in much younger volcanic eruptions of kimberlite—a volatile-rich magma that carries diamonds to the surface from deep within the cratonic mantle keel. The scientists looked at the trace element and isotopic composition of the diamonds, and the age and composition of mineral inclusions. Based on the seismic velocity of P-waves, they also constructed maps of the cratonic mantle keel. The resulting imagery of the deep structure showed the type of mantle above which diamond mines are located. “When the picture emerged, we wondered if regional patterns of diamond age and composition would fit the seismic structure. What we found was the first general framework for diamond formation that is applicable on a continental scale,” says Shirey.

Through detailed analysis, the researchers determined that diamond formation in the cratonic mantle keel occurred episodically rather than continuously—there were multiple generations of diamonds. Their examination suggested that the craton formed in at least two stages and was subsequently modified in a third stage. The cratonic nuclei were created first by a process of mantle melting, which was followed by an accretion process involving old oceanic lithosphere—the rigid layer of crust and mantle under the ocean basins. This latter stage helped stabilize the cratonic mantle keel. Subsequent tectonic and magnetic events added new diamonds whose inclusion compositions closely corresponded with changes in the composition of the cratonic mantle keel.

Support for this work came from the National Science Foundation (NSF), Continental Dynamics Program, the South African National Research Foundation (NRF), and the Diamond Trading Company (De Beers).