Extreme persistence of cratonic lithosphere in the southwest Pacific: Paleoproterozoic Os isotopic signatures in Zealandia
Alex J. McCoy-West et al., Research School of Earth Sciences, Australian National University, Canberra, NSW 0200, Australia. Posted online 13 Dec. 2012; http://dx.doi.org/10.1130/G33626.1.
Pieces of the mantle in the form of xenoliths entrained in basaltic magmas provide a rare opportunity to directly study the composition and age structure of the largely inaccessible deep Earth. Osmium isotopic data from mantle xenoliths from around Zealandia, a largely submerged, continental fragment, provide new constraints on continent formation in the southwest Pacific. Alex McCoy-West and colleagues have discovered a large, coherent, chunk of early Proterozoic mantle (~1.9 billion years old) underlying New Zealand's South Island. This is a highly unexpected find because the basement crustal rocks in this region are only 200 million years old. This >1.7 billion years age difference is the largest temporal decoupling between the mantle lithosphere and overlying crust yet observed, suggesting that old cratonic mantle lithosphere may be responsible for the stabilization of new continental crust, even on the modern Earth. Additionally, the discovery of extensive ancient lithosphere within Zealandia provides new information on its origins and assembly history, with tectonic implications for the present-day development of the Australia-Pacific plate boundary cutting through New Zealand.
Direct observations of degassing-induced crystallization in basalts
L. Jane Applegarth et al. (Hugh Tuffen, corresponding), Lancaster Environment Centre, Lancaster University, Bailrigg, Lancaster LA1 4YQ, UK. Posted online 13 Dec. 20
|Contact: Kea Giles|
Geological Society of America