May 2009 Geology media highlights

Boulder, CO, USA - Hot topics include (1) opposition to the idea that chevron-shaped dunes are indicative of mega-tsunamis; (2) discovery of a complex microbial community that extends the fossil record of cavity-dwelling life by more than 1.5 billion years; (3) documentation of nanoscale, respirable cristobalite fibers in volcanic ash from Chaiten volcano and the likely adverse health effects; (4) closing the gap between Earth's first animals and fossil and geochemical evidence; and (5) the largest trilobites ever found.

New evidence from seismic imaging for subduction during assembly of the North China craton
Tianyu Zheng et al., Seismological Laboratory (SKL-LE), Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. Pages 395-398.

The "frozen-in" information in the crust plays an important role in improving our understanding of cratonic formation and evolution, and of plate tectonics in the Precambrian. The Trans-North China orogen (TNCO) is a continental-to-continental collision belt generated by the assembly of the North China craton (NCC). The mechanism and modality of the collision are disputed. Here, Zheng et al. present a seismic image of the Western Block and the TNCO of the NCC-derived using receiver function analysis of the teleseismic records from a dense array. A low-velocity zone extending from the middle crust to the Moho is interpreted as a remnant of upper-middle crustal material associated with westward-dipping subduction beneath the Western Block of the NCC. Crustal uplifting and magmatic underplating resulting from subsequent tectonic events were responsible for modifying the remaining subduction architecture. The western boundary of the TNCO is located west of the boundary earlier identified by surface investigation. The results, combined with previous seismic imaging in the eastern NCC, provide insight into the amalgamation of the Eastern and Western Blocks and the subsequent tectonic deformation of the NCC.