Abstract
The Hoting gabbro, located in the northern part of Jämtland County, is one of the largest layered mafic intrusions in Sweden. The rounded, main part of the intrusion has the shape of a funnel, in which the magmatic layering is concentrically developed with steeply dipping outer layers, and flat layering in the central part. The modal composition is dominated by plagioclase, where most samples classify as leucogabbro. SIMS U–Pb zircon data give a concordia age of 1786±10 Ma (2σ), interpreted to date the emplacement of the Hoting gabbro, which thus took place contemporaneously with emplacement of the Revsund granitoid suite. The latter can be considered to belong to the main phase of the Transscandinavian Igneous Belt. A ‘Revsund age’ is also supported by some field relationships, indicating that melts of Revsund granite and gabbro coexisted. Three highly discordant analyses define the lower intercept of the regression line in the concordia diagram to an age of 453±19 Ma. This age corresponds in time with the Scandian period of Caledonian orogenic activity and is suggested to represent an episodic leaching of Pb from metamict zircon domains.
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