Taking mylonites' temperatures
Matthew J. Kohn and C.J. Northrup, Dept. of Geosciences, Boise State University, Boise, Idaho 83725, USA. Pages 47-50.
Ductile shear zones are the mid- to deep-crustal expressions of faults, yet understanding their deformation behavior has proved elusive. One key problem is determining the temperatures at which shear zones deform. Kohn and Northrup show that a novel new thermometer, the titanium content of quartz, recovers temperatures in ductile shear zones with unprecedented precision. This result, in turn, improves estimates of the mechanical behavior of the crust, particularly the viscosities and strain rates during deformation. Applications indicate that some commonly observed textures result not simply from temperature, but also from huge differences in strain rate (four orders of magnitude).
Australian desert dune fields initiated with Pliocene-Pleistocene global climatic shift
Toshiyuki Fujioka et al., Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia. Pages 51-54.
Using an innovative approach, burial dating using cosmogenic beryllium-10 and aluminium-26, Fujioka et al. reveal that Australian desert dune fields began to form one million years ago, when global ice age cycles changed their pace from 40 thousand years to 100 thousand years. This is the first paper to use cosmogenic nuclides
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Geological Society of America