mantle; however, there is no evidence to suggest a high heat flux ..... Latitude,. Rock. Age spectra. Isochron longitude type. T otal gas. Increments. Number. K/Ca.
JOURNAL OF PETROLOGY
VOLUME 44
NUMBER 1
PAGES 55–91
2003
Petrogenesis of Cenozoic Basalts from Mongolia: Evidence for the Role of Asthenospheric versus Metasomatized Lithospheric Mantle Sources T. L. BARRY1∗, A. D. SAUNDERS1, P. D. KEMPTON2, B. F. WINDLEY1, M. S. PRINGLE3, D. DORJNAMJAA4 AND S. SAANDAR4 1
GEOLOGY DEPARTMENT, UNIVERSITY OF LEICESTER, UNIVERSITY ROAD, LEICESTER LE1 7RH, UK
2
NERC ISOTOPE GEOSCIENCES LABORATORY, KEYWORTH NG12 5GG, UK
3
SUERC/NSS AR FACILITY, SCOTTISH ENTERPRISE TECHNOLOGY PARK, EAST KILBRIDE G75 0QF, UK
4
CENTRE OF PALAEONTOLOGY, MONGOLIAN ACADEMY OF SCIENCES, ULAAN BAATAR—210613, PO BOX 863,
MONGOLIA
RECEIVED AUGUST 14, 2000; REVISED TYPESCRIPT ACCEPTED JULY 10, 2002
mantle; however, there is no evidence to suggest a high heat flux mantle plume. Volcanism is likely to occur where localized extensional conditions are favourable.
Diffuse Cenozoic volcanism in Mongolia forms part of a widespread tectono-magmatic province that extends from NE China to Lake Baikal, Siberia. Mafic lavas from the Gobi Altai, southern Mongolia (>33 Ma) and Hangai, central Mongolia (70 km. Three isotopic end-members can explain the heterogeneity: (1) is similar to bulk silicate Earth with 206 Pb/204Pb >>17·8 and is asthenospheric; (2) is EM1-like, characterized by low 206Pb/204Pb (>17·062), and may represent mobilized ancient lithospheric mantle; (3) also lithospheric, is characterized by low 143Nd/144Nd (>0·512292) and shows similarities to EM2, although decoupling of isotopic systems suggests a complex enrichment process. The timing of lithospheric enrichment is unconstrained, but may be related to Mesozoic magmatic events and/or melts mobilized during the Cenozoic responding to higher than ambient potential temperature mantle. Published geophysical studies suggest anomalous material at the base of the lithospheric
Cenozoic intraplate volcanism in Mongolia is diffuse and widespread but generally small in volume; individual volcanic provinces typically comprise
