Sanidin k ar dating

Collectively, these rocks represent a late stage of Hercynian magmatism in the eastern Pontides.... Petrochemistry, 40Ar-39Ar geochronology ans Sr-Pb isotope geochemistry of the Tertiary volcanics in Eastern Pontide Southern Zone, NE Turkey: geodynamic evolution related to slab break-off and transtensional tectonics.The massive volcanic suite of Upper Cretaceous Elazığ Magmatic Complex, and Miocene basic volcanic rocks of crop out to the southern vicinity of Elazığ.However, all the chemical and isotopic (low Sr ratio and positive ( ) εNd values) data indicate that the source magma of these volcanic rocks was derived from a depleted garnet free magma (astenospheric mantle) and was modified once again by the post collosional geodynamical events and show interplate Zr and Th enrichment.Ar ages for rocks from the Valles caldera of New Mexico imply that resurgent uplift of the caldera floor occurred within 27 ± 27 k.y. Redondo Peak, part of the resurgent dome of the Valles caldera, was uplifted at least 1000 m above the surrounding caldera floor during resurgence.Both intrusions have high Si O2 (74–77 wt.%) contents and show high-K calc-alkaline and I- to S-type characteristics.Primitive mantle-normalized element diagrams display enrichment in K, Rb, Th, and U, and depletion in Ba, Nb, Ta, Sr, P, and Ti.This study demonstrates that the Sr isotope ratios generally display negative correlation with Nd isotopes; Sr isotope ratios were lowered in some samples by hydrothermal interaction or alteration. Mafic globular occurrences within the basaltic trachyandesitic dykes, the existence of ......

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These features imply crystal-melt fractionation of plagioclase and K-feldspar without significant involvement of garnet.Geochemical analyses show that the volcanic rocks are mainly high-K and calc-alkaline, and have high contents of large-ion lithophile elements and low contents of high-field strength elements, revealing that they evolved from parental magmas that were derived from an enriched subcontinental lithospheric mantle source.The chondrite-normalized rare earth element patterns of the rocks are concave upwards with La CN/Lu CN = 11.9–21.2 and Eu CN/Eu* = 0.84–0.92, implying significant fractional crystallization of hornblende during their evolution.They also contain low Ti, have negative Nb and Ta anomaly and low Sr ratios.Geochemical and isotopic data for the massive volcanic suite point out that these volcanic rocks were originated from an upper mantle source (lithospheric) which undergone fractional crystallisation and crustal contamination and enriched by these processes and metasomatized within a subduction zone.

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