Geological surveys showed that rhyolite and basalt strata with pillow structures typical for underwater volcanism form sheets over the Svecofennian basement. Original geochemical and isotope-geochemical data confirmed...Geological surveys showed that rhyolite and basalt strata with pillow structures typical for underwater volcanism form sheets over the Svecofennian basement. Original geochemical and isotope-geochemical data confirmed that the rhyolites were formed contemporaneously with the rapakivi granites of the Wiborg Massif（1 640 Ma）, and the basalts are similar to gabbro-anorthosites. Abnormally high content of K2O and relatively low content of Na2O in rhyolites and basalts are interpreted as a result of hydrothermal interaction of eruptive magmas with K-enriched hot seawater. The strata of siliceous metasedimentary rocks（microquartzites） within basaltic and rhyolitic lavas were formed in processes of chemogenic sedimentation and subsequent contact metamorphism during underwater volcanism. Microquartzites showed carbon vastly depleted of heavy isotope 13С. This is typical for rocks formed with participation of living substance. The Raman spectra of the remaining carbon-containing substance have graphite bands. In the microquartzites among basalts and rhyolites we found a community of structures with external and internal morphology similar to modern or fossilized marine microorganisms： spiral cyanobacterias, amoebas, diatoms, foraminifers, virus capsids, flagellates and multicellular organisms. It is assumed that these silificated and ferruginizated microfossils represent the Paleoproterozoic community of marine microorganisms.展开更多
基金supported in part by grant from International Science Foundation [ISF,NY,USA] N RI E000grants of Russian Foundation for Basic Research (RFBR) (Nos.95-05-15305,97-05-65446,and 3.15.865.2013)
文摘Geological surveys showed that rhyolite and basalt strata with pillow structures typical for underwater volcanism form sheets over the Svecofennian basement. Original geochemical and isotope-geochemical data confirmed that the rhyolites were formed contemporaneously with the rapakivi granites of the Wiborg Massif（1 640 Ma）, and the basalts are similar to gabbro-anorthosites. Abnormally high content of K2O and relatively low content of Na2O in rhyolites and basalts are interpreted as a result of hydrothermal interaction of eruptive magmas with K-enriched hot seawater. The strata of siliceous metasedimentary rocks（microquartzites） within basaltic and rhyolitic lavas were formed in processes of chemogenic sedimentation and subsequent contact metamorphism during underwater volcanism. Microquartzites showed carbon vastly depleted of heavy isotope 13С. This is typical for rocks formed with participation of living substance. The Raman spectra of the remaining carbon-containing substance have graphite bands. In the microquartzites among basalts and rhyolites we found a community of structures with external and internal morphology similar to modern or fossilized marine microorganisms： spiral cyanobacterias, amoebas, diatoms, foraminifers, virus capsids, flagellates and multicellular organisms. It is assumed that these silificated and ferruginizated microfossils represent the Paleoproterozoic community of marine microorganisms.
