CO2- and LREE-rich mantle below eastern Australia: a REE and isotopic study of alkaline magmas and apatite-rich mantle xenoliths from the Southern Highlands Province,Australia |
| |
| Authors: | Martin A Menzies Suzanne Y Wass |
| |
| Institution: | 1. Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, Bucks. MK7 6AA England;2. School of Earth Sciences, Macquarie University, North Ryde, N.S.W. 2113 Australia |
| |
| Abstract: | Alkaline magmatism in the Southern Highlands Province, New South Wales, Australia is associated with continental rifting. Near-primary liquids have a wide range in Nd and Sr isotope composition that indicates gross isotopic and chemical heterogeneities in a mantle source region depleted in light rare earth elements (LREE) for much of Earth's history. The large-ion lithophile element and LREE-enriched nature of the primary lavas ((Ce)N = 95–182 and (Yb)N = 8.5–13.3) is consistent with an enriched mantle source region. This elemental enrichment may be accomplished by veining of the subcontinental mantle with volatile-rich phases like amphibole, apatite and carbonate which provide the volatile flux necessary to trigger anatexis.Degassing of mantle CO2 has led to migration of LREE-enriched fluids and local transformation of the lherzolitic mantle to pyroxenite veined by apatite ± kaersutite ± mica ± diopside. The mantle veining event may be related to upwelling of silica-undersaturated incompatible element-enriched magmas similar to the host magma of the Kiama xenoliths. In a relatively short period of time (100 m.y.), the Sr and Nd isotopes in essentially LREE-depleted mantle have evolved in response to low Sm/Nd and low Rb/Sr ratios, and now define a near-vertical vector on a isotope-isotope plot. From this rather unique signature we can infer that CO2- and LREE-rich, Rb-poor mantle is a potentially suitable mantle source region for the genesis of alkali-potassic volcanic rocks characterized by a narrow range in87Sr/86Sr ratio and a wide range in143Nd/144Nd ratio (e.g. Leucite Hills). |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
