Lead mobilization during tectonic reactivation of the western Baltic Shield

Journal Article · Tue Jun 01 04:00:00 EDT 1993 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(93)90417-U· OSTI ID:6191693

Romer, R L ^[1]; Wright, J E ^[2]

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1. Rice Univ., Houston, TX (United States) Luleaa Univ. (Sweden)
2. Rice Univ., Houston, TX (United States)

Lead isotope data from sulfide deposits of the western part of the Baltic Shield define mixing lines in the [sup 206]Pb/[sup 204]Pb-[sup 207]Pb/[sup 204]Pb diagram. Lead from two types of sulfide deposits have been investigated: (1) Exhalative and volcanogenic deposits that are syngenetic with their host rocks; and (2) vein deposits. The syngenetic deposits locally show a very wide range of lead isotopic compositions that reflect a variable addition of highly radiogenic lead, while the vein deposits, although they have radiogenic lead isotopic compositions, exhibit only limited isotopic variations. In different provinces of the shield, both types of deposits fall on the same lead mixing array. The slope of the lead mixing lines varies as a function of the age of basement rocks and the age of the tectonic event which produced the lead mobilization and therefore relates the source rock age with the age of lead mobilization. Calculated mixing ages fall into several short time periods that correspond either to orogenic events or to major phases of continental rifting. The orogenic events are the ca 360--430 Ma Caledonian, ca 900--1100 Ma Sveconorwegian, and the ca 1800--1900 Ma Svecofennian orogenic cycles. The rifting events correspond to the formation of the ca 280 Ma Oslo rift and the Ordovician (ca 450 Ma) graben system in the area of the present Gulf of Bothnia. Each mixing age indicates that lead was mobilized, probably as a consequence of mild thermal disturbances, and that the crust was permeable to lead migration. The data show that the geographic distribution of sulfide deposits with highly radiogenic lead isotopic compositions coincides with old graben systems, orogenic belts, and orogenic forelands on the Baltic Shield. The ages of vein deposits and their geographic distribution demonstrate multiple tectonic reactivation of the interior of the Baltic Shield in response to orogenic events at its margin. 68 refs., 6 refs., 4 tabs.

• OSTI ID: 6191693
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 57:11; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540220* -- Environment
Terrestrial-- Chemicals Monitoring & Transport-- (1990-)
ALPHA DECAY RADIOISOTOPES
BALTIC SEA
CHEMICAL ANALYSIS
ELEMENTS
ENVIRONMENTAL TRANSPORT
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
HEAVY NUCLEI
HOURS LIVING RADIOISOTOPES
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LEAD
LEAD 204
LEAD 206
LEAD 207
LEAD ISOTOPES
MASS TRANSFER
METALS
MILLISEC LIVING RADIOISOTOPES
MINERAL CYCLING
MINERALS
NUCLEI
OROGENESIS
PLATE TECTONICS
QUANTITATIVE CHEMICAL ANALYSIS
RADIOISOTOPES
SEAS
SECONDS LIVING RADIOISOTOPES
STABLE ISOTOPES
SULFIDE MINERALS
SURFACE WATERS
TECTONICS
YEARS LIVING RADIOISOTOPES