ENRICHED ND-SR-PB ISOTOPIC SIGNATURES IN THE DOVYREN LAYERED INTRUSION (EASTERN SIBERIA, RUSSIA), EVIDENCE FOR SOURCE CONTAMINATION BY ANCIENT UPPER-CRUSTAL MATERIAL
Yv. Amelin et al., ENRICHED ND-SR-PB ISOTOPIC SIGNATURES IN THE DOVYREN LAYERED INTRUSION (EASTERN SIBERIA, RUSSIA), EVIDENCE FOR SOURCE CONTAMINATION BY ANCIENT UPPER-CRUSTAL MATERIAL, Chemical geology, 129(1-2), 1996, pp. 39-69
Major- and trace-element concentrations and Nd-, Sr- and Pb-isotopic r
atios are reported for the Dovyren layered mafic-ultramafic intrusion
in the northern Baikal region, eastern Siberia. Sm-Nd internal isochro
ns for an olivine gabbro from the layered series and a gabbronorite fr
om a sill at the bottom of the Dovyren intrusion yield ages of 673 +/-
22 and 707 +/- 40 Ma, respectively. Initial isotopic ratios: Sr-87/Sr
-86 (673) from 0.7101 to 0.7135, epsilon(Nd)(673 Ma) from -16.3 to -14
.1, Pb-206/Pb-204 from 16.80 to 17.14, Pb-207/Pb-204 from 15.477 to 15
.501 and Pb-208/Pb-204 from 37.17 to 37.59, are similar to those of la
te Archean-early Proterozoic upper continental crust, but do not appea
r to be a result of wallrock assimilation in the magma chamber. These
isotopic features, as well as high K, Rb and LREE and low Ti concentra
tions in the calculated composition of the Dovyren parental magma, may
be explained by subduction of sediments derived from upper continenta
l crust into depleted mantle and subsequent melting of the metasomatiz
ed peridotite.