Mineralogical and Rb-Sr Isotope Studies of Low-Temperature Diagenesis of Lower Cambrian Clays of the Baltic Paleobasin of North Estonia

2000 ◽  
Vol 48 (1) ◽  
pp. 95-105 ◽  
Author(s):  
Kalle Kirsimäe
Keyword(s):  
Low Temperature ◽  
Lower Cambrian ◽  
Sr Isotope ◽  
Isotope Studies ◽  
The Baltic

The Early Cambrian worm tube Onuphionella from California and Nevada

1988 ◽  
Vol 62 (2) ◽  
pp. 233-240 ◽  
Author(s):  
Philip W. Signor ◽  
Mark A. S. Mcmenamin
Keyword(s):  
New Species ◽  
North America ◽  
Lower Cambrian ◽  
Early Cambrian ◽  
Western North America ◽  
Baltic Region ◽  
Two New Species ◽  
Modern Genus ◽  
The Baltic ◽  
Middle Member

Two new species of worm tubes referable to the genus Onuphionella occur in Lower Cambrian strata in eastern California and western Nevada. Onuphionella durhami n. sp. is found in the Campito Formation (in pre-trilobite strata, in the Fallotaspis and, possibly, the Nevadella Zones) and O. claytonensis n. sp. occurs in the Middle Member of the Poleta Formation (Nevadella Zone). The unusual tubes are armored with an imbricated coat of mica flakes, reminiscent of the modern genus Owenia. The lowest occurrence of Onuphionella in western North America corresponds closely with the lowest occurrence of the genus in the Baltic region, indicating that correlations between the two regions are not greatly in error.

Lower Cambrian olenellid trilobites from the Baltic Faunal Province

1986 ◽  
Vol 108 (1) ◽  
pp. 39-56 ◽  
Author(s):  
Per Ahlberg ◽  
Jan Bergström ◽  
Jan Johansson
Keyword(s):  
Lower Cambrian ◽  
The Baltic

The Source of Ore-Forming Material in Barite-Fluorite Deposits, Southeast Sichuan in China: Sr Isotope Evidence

2013 ◽  
Vol 395-396 ◽  
pp. 187-190
Author(s):  
Hao Zou ◽  
Yi Fang ◽  
Zhan Zhang Xu
Keyword(s):  
Carbonate Rocks ◽  
Lower Cambrian ◽  
Initial Ratio ◽  
Sr Isotope ◽  
Mineralization Process ◽  
Ordovician Limestone ◽  
Metallogenic Belt ◽  
Isotope Evidence ◽  
Good Tracer

Barite-fluorite metallogenic belt of southeast Sichuan is one of the important metallogenic belt in China. The initial ratio of 87Sr/86Sr is the good tracer in study of diagenetic mineralization process and sources of ore-forming materials. The 87Sr/86Sr ratio of fluorite and barite from barite-fluorite deposits in southeast Sichuan is 0.708800~0.712999, and it similar to The 87Sr/86Sr ratio of Cambrian carbonate rocks and ordovician limestone, but expect the lower Cambrian Niutitang group stratum, the Ba content of other layers are generally low, Therefore, the Ca source of ore-forming materials should be multisource, mainly from Cambrian-Ordovician carbonate strata , and the main Ba source of layer should be the lower Cambrian Niutitang group stratum.

scholarly journals Rb-Sr age determination of the Kattsund-Koster dyke swarm in the Østfold-Marstrand belt of the Sveconorwegian Province, W Sweden - SE Norway

1988 ◽  
Vol 37 ◽  
pp. 51-61
Author(s):  
B. Hageskov ◽  
S Pedersen
Keyword(s):  
Shear Zone ◽  
Baltic Shield ◽  
Age Determination ◽  
Dyke Swarm ◽  
Sr Isotope ◽  
Se Norway ◽  
The Baltic ◽  
Isotope Analyses

The Kattsund-Koster dyke swarm in the Sveconorwegian Province of the Baltic shield is a dense swarm of evolved tholeiites derived from N-MORB type parental magmas selectively contaminated with K, Rb and Ba. In the Koster archipelago the NNE-SSW trending dyke swarm enters a ductile sinistral shear zone in the margin of which the dolerites are partially recrystallised metadolerites. In the highly deformed interior of the shear zone the dykes are completely recrystallised to amphibolites. Rb-Sr isotope analyses have been carried out on samples of the dolerites and the partially recrystallised metadolerites. A profile through one dolerite yields a whole rock age of 1421 ± 25 Ma with a (87Srl"6S)0 ratio of 0. 7028 ± 0.0002. Samples of the dolerites and partially recrystallised metadolerites lie close to the isochron. The age of 1421 Ma indicates that the dyke swarm is the oldest member of a 1420-1300(?) Ma old bimodal suite of tholeiites and potassic granites, which were injected into the crust under tensional conditions.

Rb–Sr isotope studies on Tinos Island (Cyclades, Greece): additional time constraints for metamorphism, extent of infiltration-controlled overprinting and deformational activity

1998 ◽  
Vol 135 (3) ◽  
pp. 369-382 ◽  
Author(s):  
MICHAEL BRÖCKER ◽  
LEANDER FRANZ
Keyword(s):  
High Pressure ◽  
Ductile Shear Zone ◽  
Sr Isotope ◽  
Additional Time ◽  
Variable Intensity ◽  
High Pressure Metamorphism ◽  
Fluid Infiltration ◽  
Intermediate Unit ◽  
Isotope Studies ◽  
Jurassic Ophiolites

This study presents new Rb–Sr age data concerning the metamorphic evolution of the Attic-Cycladic Crystalline Belt which represents a complex polymetamorphic terrane within the Alpidic orogenic belt of the Hellenides. Two major groups of tectonic units can be distinguished. Metamorphism in parts of the upper units is commonly considered as a Cretaceous event. In contrast, the group of lower units experienced Tertiary high-pressure metamorphism which was followed by a medium-pressure overprint. We focus on the island of Tinos where a representative spectrum of the rock units found in the Cyclades is exposed in three tectonic units: the Upper Unit, the Intermediate Unit and the Basal Unit. The complete range of tectono-metamorphic and magmatic events affecting the Attic-Cycladic Crystalline Belt is documented by numerous petrological and tectonic studies. Phyllites and phyllonites from the ophiolitic Upper Unit yielded Rb–Sr apparent ages (phengite–whole-rock) between c. 92 and 21 Ma. The older age differs from the Cretaceous dates reported for upper unit rocks elsewhere in the Cyclades. It is suggested that the sequence studied belongs to the Jurassic ophiolites of the Hellenides rather than to Cretaceous occurrences. The spread to younger ages is related to non-pervasive rejuvenation and resetting of the Rb–Sr system during tectonic juxtaposition of the Upper Unit over the Intermediate Unit. The youngest age obtained so far for a sample from the Upper Unit (21 Ma) is believed to approximate the timing of tectonic juxtaposition which probably occurred during a regional greenschist-facies episode producing a pervasive overprint in the structurally lower tectonic unit. The major phyllite/meta-gabbro/serpentinite sequence of the Upper Unit is interpreted as an emplacement-related ductile shear zone which experienced reworking under brittle conditions. In the Intermediate Unit, a gradient in Rb–Sr ages from top (c. 40 Ma) to the bottom (c. 22 Ma) was recognized, which is interpreted to represent greater effects of fluid infiltration and overprinting in the lower parts of this unit, possibly controlled by variable intensity of deformation which might be related to tectonic juxtaposition onto the Basal Unit. We suggest that synmetamorphic stacking of all three tectonic units took place during an Oligocene–Miocene greenschist event. Extensional deformation continued after tectonic stacking and after intrusion of the main granite, as is indicated by a Rb–Sr whole-rock isochron (15.1∓0.6 Ma) for a ductilely deformed garnet-bearing leucogranite from the marginal parts of the main undeformed pluton. Application of the Rb–Sr dating technique provided no unequivocal evidence that previously published Eocene K–Ar and 40Ar–39Ar dates for high-pressure phengites from the lower units are significantly contaminated with excess argon.

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