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 00:00:00 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), Vol. 99:6; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

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