Rock of Ages
Where did the world’s highest mountains come from? Geologist Elizabeth Catlos takes a new view
When Elizabeth Catlos decided to become a geologist, she could barely tell one type of granite from another. Fortunately, she's a quick study. She had majored in chemistry at the University of California at San Diego, and when she enrolled in graduate school at UCLA, she threw herself into some of the most challenging work in her new field: Catlos volunteered to go on a three-month-long mapping expedition to the Tibetan Himalayas. In other expeditions to Nepal, she collected garnet-bearing rocks along a spectacular fault that snakes its way for 1,500 miles from Pakistan to Bhutan.
Now an associate professor at Oklahoma State University, Catlos, 35, vividly recalls those early trips in the late 1990s. The fault, a rugged corridor of fractured rock known to geologists as the Main Central Thrust, is all but obscured by jungle in many places. "I kept saying to myself, ‘I don't want to be here! There are leeches here!'" she recalls. But the garnets she and her colleagues collected were beautiful. "They looked like you could just pluck them out, polish them up and put them into a ring!"
Forged tens of miles beneath the surface of the earth, garnets are more than semiprecious gems; they are also exquisite recorders of geologic data. Through variations in their chemical composition, garnets preserve information about the extreme pressures and temperatures at which they crystallized. They also contain tiny grains of monazite, a rare earth mineral that lends itself to radioactive dating.
Back at UCLA, Catlos sliced the garnets and dated the monazites with an instrument called an ion microprobe. The data she recorded contradicted the prevailing picture of how the world's highest mountains were formed. The Himalayas, Catlos explains, trace their origin to a massive crumpling of the earth's crust that began around 55 million years ago when India, sailing north on a plume of semi-molten rock, slammed into Asia. Until recently, most geologists thought that this crumpling had occurred in a rather orderly fashion, starting in the north and then moving south along the sequence of faults that lie between the Greater Himalayas and the Indo-Gangetic Plain.
According to this picture, the Main Central Thrust, the oldest and highest of the faults, was most active around 20 million years ago. But Catlos' rock samples told her they had been buried as recently as one million years ago, suggesting that multiple episodes of earth-wrenching uplift must have shaken the Main Central Thrust during its supposed quiescence. Catlos thinks it may still be active today—posing a threat to the millions of people who live in this region.
Catlos' findings caused some tremors of their own, with aftershocks that continue to rattle geologists a decade later. Which doesn't surprise her friend and colleague Sorena Sorensen, a geologist at the Smithsonian's National Museum of Natural History. "After all," says Sorensen, "Liz basically rewrote the geological time frame for one of earth's major features, meaning that a lot of people's work got reexamined very quickly."
Not that controversy is likely to deter Catlos. UCLA geologist Mark Harrison, her thesis adviser, marvels at her "extraordinary tenacity," a trait that seems to run in the Catlos family. Her father, an engineer, and her mother, a pediatrician, had to struggle to establish themselves in the United States after fleeing Communist Czechoslovakia in 1966. And her late grandmother, also a doctor, started over at an age when many start winding down, says Catlos, who grew up in San Mateo, California. "She came here and, at the age of 54, she learned English, passed her medical boards and opened a dermatology practice."
Catlos is taking leave from Oklahoma State this year to do research at the University of Texas at Austin, where she wants to analyze the 200 or so rocks, most of them garnet-laden, that she and her collaborators recently brought back from the Menderes Massif in western Turkey. In contrast to the Himalayas, this rugged range was created by the rifting of the earth's continental plates, and its history is even less well understood. Catlos hopes she can help dispel some of the mystery or, as she puts it, "take the mountain-building process from the scale of minerals and translate it into as big a picture as possible." Let the chips fall where they may.
J. Madeleine Nash traveled to the Tibetan plateau for a story about glaciologist Lonnie Thompson in the July Smithsonian.