A non-collisional, accretionary Sveconorwegian orogen - Comment

In a stimulating contribution, Slagstad et al. (2013) propose to interpret the 500-km-wide Sveconorwegian orogen in Scandinavia as a non-collisional, accretionary orogen. They challenge the more widely held view that it is the product of a late Mesoproterozoic to early Neoproterozoic continent–continent collision, formed during welding of supercontinent Rodinia. We question the model proposed by Slagstad et al. (2013) as it fails to integrate the lithotectonic and tectonometamorphic framework of the entire orogen, in particular the present-day eastern parts where the principal records of high-pressure metamorphism and collisional tectonics have been retrieved

Precambrian gold mineralization at Djamgyr in the Kyrgyz Tien Shan : Tectonic and metallogenic implications

The Djamgyr gold deposit is located within the Neoproterozoic basement of the Middle Tien Shan terrane immediately west of the Talas-Fergana fault. The deposit comprises a system of auriferous quartz veins cross-cutting the Beshtor plagiogranite. The veins are surrounded by hydrothermal alteration aureoles and are oriented parallel to the Talas-Fergana fault. The Beshtor granite sampled in the vicinity of the deposit yielded a Neoproterozoic (Tonian) U-Pb zircon age of 815 ± 6 Ma, which is the first single grain zircon age of the Middle Tien Shan basement west of the Talas-Fergana fault. Ar-Ar dating of two muscovite fractions from the alteration aureoles of the auriferous quartz veins yielded ages of 804 ± 3 and 805 ± 3 Ma suggesting that the mineralization in the Djamgyr deposit occurred during the Neoproterozoic ca. 10 m.y. after emplacement of the Beshtor granite. The structural pattern of the auriferous quartz veins and the new geochronological data, combined with the results of previous structural studies, may tentatively constrain the age of pre-existing major fault possibly marking an inherited terrane boundary in the northern part of the present-day Talas-Fergana strike-slip fault. The discovery of Precambrian gold mineralization in the Middle Tien Shan suggests re-evaluation of the metallogenic potential of its Precambrian basement that occupies significant areas west and east of the Talas-Fergana fault