Va. Makrygina et al., Andesite magmatism and its place in geological history of the Ol'khon area(Western Baikal region), GEOCHEM INT, 38(12), 2000, pp. 1161-1174
The geochemistry of biotite-amphibole schists and amphibolites of the Anga
Sequence and lower formation of the Ol'khon Group was studied. According to
relies of porphyritic textures and morphology of geological bodies, these
rocks were attributed to metavolcanics. The composition and geochemical fea
tures of these rocks, including REE distribution, Nb minimum, and Sr maximu
m, are similar to medium-potassium andesites of the calc-alkaline series of
mature island arcs formed on a relatively thick crust. The metaandesites a
re intruded by hypabyssal gabbroids of the Ozersk Complex and granodiorite-
granite massifs of the Khaidai Complex. The latter also belong to the calc-
alkaline series according to their geochemical features. The whole rock ass
ociation reflects a temporal evolution of island-are magmatism. The geochem
ical affinity of metavolcanic and metasedimentary rock associations of the
Anga Sequence acid lower formation of the Ol'khon Group allows us to consid
er both as tectonic plates of the same stratigraphic unit.