Comparison of the composition and geochemical features of bedrocks and solid runoff of big rivers in the Baikal catchment basin

Citation
Is. Lomonosov et al., Comparison of the composition and geochemical features of bedrocks and solid runoff of big rivers in the Baikal catchment basin, GEOL GEOFIZ, 42(1-2), 2001, pp. 278-297
Citations number
31
Categorie Soggetti
Earth Sciences
Journal title
GEOLOGIYA I GEOFIZIKA
ISSN journal
00167886 → ACNP
Volume
42
Issue
1-2
Year of publication
2001
Pages
278 - 297
Database
ISI
SICI code
0016-7886(2001)42:1-2<278:COTCAG>2.0.ZU;2-Q
Abstract
We have studied the relations of the composition of the solid runoff of riv ers in the Baikal basin with mineralogy and geochemistry of bedrocks of rec ognized feeding petrographic provinces - Primor'e, Khamar-Daban, and Barguz in. The latter are made up of ancient volcanoplutonic rocks of subalkalic a nd calc-alkalic compositions, mainly granitoids, deeply metamorphosed rocks of the Precambrian basement, and Meso-Cenozoic sediments. The basin of the Selenga River, supplying 70% of the runoff of all river drifts, is of part icular value. Chemical elements in solid runoff occur in mineral phases and their associa tions and also migrate in adsorbed state on organic and mineral suspensions and colloids. The major element concentrators are minerals of heavy (0.25- 0.05 mm) and fine-pelitic (0.001 mm) fractions. The concentrations of eleme nts in the solid runoff of the rivers are close to their Baikal clarkes, wh ereas the contents of ore elements (Mn, V, Cr, Co, Ni, Zn, Pb, and Sn) are 2-6 times lower than their clarkes in sedimentary rocks, which reflects the general geochemistry of bedrocks in the Baikal catchment basin. The heavy fractions of the solid runoff of rivets in the Primor'e province are dominated by amphiboles, pyroxenes, and minerals of epidote group, i. e ., minerals with elevated contents of Ag, Pb, Cu, Ni, and Mo, whereas in th e solid runoff of the Barguzin province the contents of these elements are minimum. The Khamar-Daban province abounds in ilmenite-magnetite, amphibole -pyroxene-epidote, and magnetite-ilmenite-garnet-epidote associations, acid the Barguzin province, in sphene-ilmenite association with rutile, titanon iobate, corundum, and other minerals. Such elements as Ce, Th, Y, Se, etc, have been found in the heavy fraction of the solid runoff of rivers in the Khamar-Daban province and are absent from the Primor'e province. The mineral and elemental compositions of the solid runoff of the Selenga R iver are governed by the wash-out from its vast water catchment area compos ed of compositionally different rocks. The runoff has elevated contents of Sr, B, and Zn and reduced contents of Mn. The specific features of the mineral composition and geochemistry of the so lid runoff of rivers in the Baikal catchment basin determined the compositi on of modern bottom sediments, which allows reconstruction of their geologi c history in the Holocene and prediction of the behavior of sedimentation d uring climatic changes.