TY - JOUR
T1 - CO2- and LREE-rich mantle below eastern Australia
T2 - a REE and isotopic study of alkaline magmas and apatite-rich mantle xenoliths from the Southern Highlands Province, Australia
AU - Menzies, Martin A.
AU - Wass, Suzanne Y.
PY - 1983
Y1 - 1983
N2 - 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 in 87Sr/86Sr ratio and a wide range in 143Nd/144Nd ratio (e.g. Leucite Hills).
AB - 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 in 87Sr/86Sr ratio and a wide range in 143Nd/144Nd ratio (e.g. Leucite Hills).
UR - http://www.scopus.com/inward/record.url?scp=0021052375&partnerID=8YFLogxK
U2 - 10.1016/0012-821X(83)90167-X
DO - 10.1016/0012-821X(83)90167-X
M3 - Article
AN - SCOPUS:0021052375
SN - 0012-821X
VL - 65
SP - 287
EP - 302
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 2
ER -