Timing of Early Proterozoic collisional and extensional events in the granulite-gneiss-charnockite-granite complex, Lake Baikal, USSR: A U-Pb, Rb-Sr, and Sm-Nd isotopic study

Journal Article · Fri Nov 01 04:00:00 EST 1991 · Journal of Geology; (United States)

DOI:https://doi.org/10.1086/629556· OSTI ID:5616706

Aftalion, M ^[1]; Bibikova, E V ^[2]; Bowes, D R ^[3]; Hopwood, A M ^[4]; Perchuk, L L ^[5]

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1. Scottish Univ. Research and Reactor Centre, Glasgow (United Kingdom)
2. Vernadsky Inst. of Geochemistry and Analytical Chemistry, Moscow (USSR)
3. Univ. of Glasgow (United Kingdom)
4. Univ. of St. Andrews, Fife (United Kingdom)
5. Inst. of Experimental Mineralogy, Moscow (USSR)

In the Sharyzhalgay Complex of the Lake Baikal region in eastern Siberia Early Proterozoic collisional and extensional events were separated by ca. 100 m.yr. The earlier collisional event, associated with the development of granulites and gneisses as the result of high-grade dynamothermal metamorphism, took place close to 1965 {plus minus} 4 Ma. A {sup 207}Pb/{sup 204}Pb vs. {sup 206}Pb/{sup 204}Pb isochron for zircon from five size fractions and a six point Rb-Sr whole-rock errorchron give generally corresponding ages of 1956 {plus minus} 8 and 1963 {plus minus} 163 Ma, respectively. The later extensional event, associated with charnockitization due to the uprise of fluids and heat in a regime corresponding to the middle to upper crustal levels of a Basin and Range-type province, was initiated in the 1880-1860 Ma period. The event was continued with magmatic emplacement of granitic masses into the deep levels of caldera-like structures, possibly during the upper time range of lower concordia intercept ages of 1817 +30/{minus}32 and 1797 +40/{minus}44 Ma for two distinctly different zircon populations in a pyroxene-bearing granodiorite interpreted as an evolved (and contaminated) product of the mantle-derived magma that was the source of CO{sub 2} involved in the charnockitization. Upper intercept ages of 2784 +48/{minus}45 and 2775 +61/{minus}55 Ma indicate late Archean crust at depth as the source region of the incorporated zircon. T{sub DM} ages from Sm-Nd isotopic data show that the protolith of the lithologically layered supracrustal assemblage, subsequently polyphase deformed and polymetamorphosed in Early Proterozoic times, was also formed in Early Proterozoic (not Archean) times.

• OSTI ID: 5616706
• Journal Information: Journal of Geology; (United States), Journal Name: Journal of Geology; (United States) Vol. 99:6; ISSN JGEOA; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDE ISOTOPES
AGE ESTIMATION
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
ALPHA DECAY RADIOISOTOPES
ASIA
CONTINENTAL CRUST
DEVELOPED COUNTRIES
EARTH CRUST
EUROPE
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GNEISSES
GRANITES
GRANULITES
HEAVY NUCLEI
HOURS LIVING RADIOISOTOPES
IGNEOUS ROCKS
ISOMERIC TRANSITION ISOTOPES
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LAKE BAIKAL
LAKES
LEAD 204
LEAD 206
LEAD 207
LEAD ISOTOPES
MAGMA
METAMORPHIC ROCKS
METAMORPHISM
MILLISEC LIVING RADIOISOTOPES
MINERALS
NEODYMIUM ISOTOPES
NUCLEI
PLUTONIC ROCKS
PRECAMBRIAN ERA
RADIOISOTOPES
RARE EARTH ISOTOPES
ROCKS
RUBIDIUM ISOTOPES
SAMARIUM ISOTOPES
SECONDS LIVING RADIOISOTOPES
SIBERIA
SILICATE MINERALS
STABLE ISOTOPES
STRONTIUM ISOTOPES
SURFACE WATERS
TECTONICS
URANIUM ISOTOPES
USSR
YEARS LIVING RADIOISOTOPES
ZIRCON