scholarly journals An attempt to determine the age of geological fractures by applying Rb-Sr mineral isochron dating to fracture-filling minerals

2007 ◽  
Vol 41 (3) ◽  
pp. 165-172 ◽  
Author(s):  
MARI T. ASAHARA ◽  
TSUYOSHI TANAKA
Keyword(s):  
Mineral Isochron

Geochemistry and age of Timiskaming alkali volcanics and the Otto syenite stock, Abitibi, Ontario

1990 ◽  
Vol 27 (10) ◽  
pp. 1304-1311 ◽  
Author(s):  
D. Ben Othman ◽  
N. T. Arndt ◽  
W. M. White ◽  
K. P. Jochum
Keyword(s):  
Volcanic Rocks ◽  
Lake Area ◽  
Incompatible Elements ◽  
Ion Probe ◽  
Mineral Isochron

Tephrites and trachytes of the Timiskaming volcanics from the Kirkland Lake area (Ontario) and syenites and a granite from the nearby Otto Stock are characterized by extreme enrichment of incompatible elements coupled with relative depletion of Nb, Ti, and to a lesser extent Zr and Y.The volcanic rocks have a whole-rock Sm–Nd isochron age of 2740 ± 117 Ma (2σ error), and minerals separated from the Otto Stock, a Sm–Nd age of 2544 ± 50 Ma. Conventional and ion probe U–Pb analyses of zircons from the Otto Stock yielded an upper intercept age of 2700 ± 19 Ma, whereas the more concordant ion probe analyses had a mean 207Pb/206Pb age of 2671 ± 8 Ma (2σ). The latter is interpreted as the age of emplacement of both the volcanics and the pluton, and the Sm–Nd mineral isochron age is thought to reflect a period of later disturbance, probably during regional metamorphism.A high initial εNd of 2.5 ± 1.5 for Kirkland Lake volcanics indicates long-term isotopic depletion of their source. This value is the same as that for volcanic rocks throughout the Abitibi belt and indicates that any chemically enriched material in the source cannot have been much older than the volcanics themselves. An environment remote from older continents is inferred.

Rb–Sr Geochronology of the Hida metamorphic belt, Japan

1970 ◽  
Vol 7 (6) ◽  
pp. 1383-1401 ◽  
Author(s):  
K. Shibata ◽  
T. Nozawa ◽  
R. K. Wanless
Keyword(s):  
Granitic Rocks ◽  
Metamorphic Event ◽  
Crystalline Schist ◽  
Metamorphic Rocks ◽  
Schist Belt ◽  
Metamorphic Belt ◽  
Early Mesozoic ◽  
Mineral Isochron ◽  
Middle Paleozoic ◽  
Later Phase

Rb–Sr whole-rock and mineral isochron ages have been determined for metamorphic and granitic rocks of the Hida metamorphic belt. The results indicate that an extensive metamorphic event together with plutonic activity took place within the belt during the latest Paleozoic – early Mesozoic period. The older ages of 220–250 m.y. represent an earlier phase of the metamorphism, whereas the younger ages of 170–180 m.y. represent a later phase. The Funatsu granitic rocks yielded a whole-rock isochron age of 176 m.y. with an initial 87Sr/86Sr ratio of 0.7056. This age is believed to indicate the time of original emplacement, and the rocks are considered to represent late-kinematic intrusion in the Hida belt.Some information on the middle Paleozoic metamorphism in the Hida Mountains was obtained from the isochron study. The whole-rock isochron age of 412 m.y. for the metamorphic rocks of the Fujibashi area may be considered, although not confirmed, to indicate the time of older metamorphism. The Omi Schist of the Circum–Hida crystalline schist belt, which belongs to the glaucophanitic type of metamorphism, gave a mineral isochron age of 350 m.y. thereby providing evidence of mid-Paleozoic metamorphism.The initial 87Sr/88Sr ratios for the whole-rock samples of the Hida metamorphic belt are found to be generally low, i.e. 0.705–0.708. This is especially so for the metamorphic rocks from the northern part of the belt where the lowest values were found.

First report of Pan-African Sm—Nd and Rb—Sr mineral isochron ages from regional charnockites of southern India

1995 ◽  
Vol 132 (3) ◽  
pp. 253-260 ◽  
Author(s):  
C. Unnikrishnan-Warrier ◽  
M. Santosh ◽  
M. Yoshida
Keyword(s):  
Sri Lanka ◽  
Shear Zone ◽  
East Antarctica ◽  
Southern India ◽  
Peninsular India ◽  
Pan African ◽  
Mineral Isochron ◽  
Nd Model Age ◽  
Tectonothermal Event ◽  
Good Agreement

AbstractMineral and whole-rock isotope data for a massive charnockite from Kottaram in the Nagercoil Block at the southern tip of Peninsular India yield Sm—Nd and Rb—Sr ages of 517 ± 26 Ma and 484 ± 15 Ma respectively. The Nd model age calculated for the charnockite is c. 2100 Ma. Our study reports the first Pan-African mineral isochron ages from regional charnockites of Peninsular India, which are in good agreement with the recently obtained ages of incipient charnockites in the adjacent blocks, as well as alkaline plutons within the same block. Our results indicate that the Pan-African tectonothermal event in the granulite blocks south of the Palghat—Cauvery shear zone was regional, with terrain-wide rejuvenation. These results correlate with similar Pan-African tectono-thermal events reported from Sri Lanka and East Antarctica, and have an important bearing on Gondwana reconstructions.

Absolute timing of Caledonian orogenic wedge assembly, Central Sweden, constrained by Rb–Sr multi-mineral isochron data

Lithos ◽  
2019 ◽  
Vol 344-345 ◽  
pp. 339-359 ◽  
Author(s):  
Hagen Bender ◽  
Johannes Glodny ◽  
Uwe Ring
Keyword(s):  
Orogenic Wedge ◽  
Mineral Isochron

Multimethod radiometric age for a bentonite near the top of the Baculites reesidei Zone of southwestern Saskatchewan (Campanian–Maastrichtian stage boundary?)

1993 ◽  
Vol 30 (4) ◽  
pp. 769-775 ◽  
Author(s):  
H. Baadsgaard ◽  
J. F. Lerbekmo ◽  
J. R. Wijbrans ◽  
C. C. Swisher III ◽  
M. Fanning
Keyword(s):  
Mineral Isochron

A 15 cm thick bentonite at the top of the Baculites reesidei Zone in Cruikshank Coulee north of Herbert in southwestern Saskatchewan yielded biotite, sanidine, plagioclase, and zircon. Rb–Sr analyses give a mineral isochron with an age of 72.5 ± 0.2 Ma (± 2σ). U–Pb analyses of zircon produced concordant 206Pb/238U and 207Pb/235U ages of 72.4 ± 0.4 Ma (± 2σ) and 72.6 ± 0.4 Ma (± 2σ), respectively. Laser 40Ar/39Ar dating of sanidine and biotite revealed ages of 72.5 ± 0.2 Ma (± SE) and 72.6 ± 0.2 Ma (± SE), respectively. If the Campanian–Maastrichtian stage boundary is near the top of the Baculites reesidei Zone, then the overall average age of 72.5 ± 0.4 Ma dates the stage boundary.

Evaluation of Rb–Sr Dating Methods Applied to the Matachewan, Abitibi, Mackenzie, and Sudbury Dike Swarms in Canada

1973 ◽  
Vol 10 (6) ◽  
pp. 900-919 ◽  
Author(s):  
T. M. Gates ◽  
P. M. Hurley
Keyword(s):  
Late Stage ◽  
Significant Loss ◽  
Normal Surface ◽  
Host Environment ◽  
Dike Swarm ◽  
Dating Methods ◽  
Mineral Isochron ◽  
Dike Swarms ◽  
Sr Method ◽  
Age Determinations

Re-evaluation of the age of Canadian dike swarms using Rb–Sr whole-rock data give the following results:[Formula: see text]Detailed studies of the Matachewan dike swarm show that in most cases Rb–Sr mineral isochron age values from individual samples are concordant with the Rb–Sr whole-rock age values for the dike swarm as a whole and are clearly greater than K–Ar age values on the same material. The fact that the mineral isochron ages and the whole-rock ages by the Rb–Sr method are similar suggests that there has been no significant thermal overprinting of these particular dikes since their emplacement and solidification or contamination by radiogenic 87Sr from the host environment. Furthermore, the general scatter and lack of significant grouping of the lower K–Ar values similarly suggests that there was no single period of thermal resetting of the K–Ar ratios. It is observed that the K–Ar age values are greater in samples containing mica, and are more scattered and lower in samples in which potassium is contained in late-stage or principal phases other than mica. Therefore, it seems likely that significant loss of argon may result at near or normal surface temperatures and that the rate of diffusion is dependent on the mineralogy of the sample. It is concluded that reasonably good age determinations can be made on diabase dike rocks of ancient age by the Rb–Sr whole-rock isochron method, if the mineral isochrons are concordant.

Sm–Nd and Rb–Sr dating of amphibolite from the Nellore–Khammam schist belt, SE India: constraints on the collision of the Eastern Ghats terrane and Dharwar–Bastar craton

2001 ◽  
Vol 138 (4) ◽  
pp. 495-498 ◽  
Author(s):  
T. OKUDAIRA ◽  
T. HAMAMOTO ◽  
B. HARI PRASAD ◽  
RAJNEESH KUMAR
Keyword(s):  
Eastern Ghats ◽  
Schist Belt ◽  
Bastar Craton ◽  
Pan African ◽  
Mineral Isochron ◽  
Peak Metamorphism ◽  
Thermal Overprint ◽  
Early Neoproterozoic

The Nellore–Khammam schist belt, SE India, is sandwiched in between the Proterozoic Eastern Ghats terrane and the Archaean Dharwar–Bastar craton. We report Sm–Nd and Rb–Sr mineral isochron ages of amphibolite from the schist belt. The Sm–Nd and Rb–Sr ages are 824±43 Ma and 481±16 Ma, respectively. The Sm–Nd age indicates the timing of peak metamorphism, whereas the Rb–Sr age indicates the Pan-African thermal overprint. The peak metamorphism was related to collision of the Eastern Ghats terrane with the Dharwar-Bastar craton, which occurred during early Neoproterozoic time.

Isotopic study of basaltic dikes in the Nain Plutonic Suite: evidence for enriched mantle sources

1993 ◽  
Vol 30 (6) ◽  
pp. 1141-1146 ◽  
Author(s):  
R. W. Carlson ◽  
R. A. Wiebe ◽  
R. I. Kalamarides
Keyword(s):  
Mantle Source ◽  
Incompatible Element ◽  
Isotopic Study ◽  
Major Element Composition ◽  
Enriched Mantle ◽  
Mantle Sources ◽  
Mineral Isochron ◽  
Lithospheric Mantle Source ◽  
Nain Plutonic Suite ◽  
Alkalic Basalts

Basaltic dikes cutting the Nain Plutonic Suite (NPS) of Labrador include two chemically distinct groups. One is a high-Fe tholeiitic to transitional alkalic composition similar to some of the magmas involved in the formation of the NPS. The other, distinguished by high phosphorus and incompatible element contents, is similar in major element composition to intraplate oceanic alkalic basalts. A Rb–Sr mineral isochron for one high-P2O5 sample defines an age of 1276 ± 23 Ma indicating that it is similar in age to, or only slightly younger than, the circa 1305 Ma anorthosites.Compositional and isotopic characteristics of the high- and low-P2O5 dikes show that the gross features of their initial isotopic characteristics (i.e., low 87Sr/86Sr, negative εNd, nonradiogenic Pb) probably derive from a distinct lithospheric mantle source with similar characteristics. To have developed these isotopic characteristics by the time of dike emplacement, their mantle source must have formed and separated from oceanic-type upper mantle well prior to Nain anorthosite genesis, possibly between 2.0 and 2.6 Ga.

Sign in / Sign up

Export Citation Format

Share Document