STENSJöSTRAND SUPRACRUSTALS: A HIGH-GRADE SUPRACRUSTAL BELT IN HALLAND, SOUTHWESTERN SWEDEN

Supracrustals are rare in the orthogneiss dominated Eastern Segment of the Sveconorwegian Orogen. The Stensjöstrand supracrustal belt has been mapped in detail in a strip 2.5 km long and 0.5 km wide along the coast north of Steninge, Halland Province SW Sweden. Reconnaissance mapping indicates that the belt continues at least two kilometers further north. The belt gives us an opportunity to study supracrustal rocks associated with the orthogneisses of the Eastern Segment and hence offers clues to the original tectonic environment. It consists of semipelitic metatexites (sill, kfs, plag, bt +/- grt, mus), mafic metatexites (hbl, grt, bt, plag, +/- opx, qtz, scap), and banded quartzofeldspathic gneisses (plag, kfs, qtz, bt +/- grt). Epidote-garnet rich calcsilicate lenses occur in linear arrays and swarms in the mafic metatexites and quartzofeldspathic gneisses suggesting that they formed through disruptions of calcareous layers. The lithologies of the Stensjöstrand supracrustal belts suggest that the protoliths were probably shales, shaley sandstones, sandstones and lava flows with minor amounts of calcareous sediments. The rocks of the Stensjöstrand belt have undergone at least two episodes of folding and migmitization. Mineral assemblages and chemistries record metamorphic conditions of ~ 750 ^oC and 8.5 kb. Calcareous enclaves are present in the diatexites of the Bårarp quarry 4 km to the east of Stensjöstrand suggesting that the calcsilicate rocks may be older than the protoliths of the diatexites and that the diatexite protoliths possibly were derived from a source area similar to the Stensjöstrand supracrustal belt. Reconnaissance ion-microprobe investigations of zircons from a granitic leucosome indicate igneous cores (~1.68 Ga) surrounded by secondary domains with ages of ~1.4 Ga , followed by thin younger rims and tips (~0.98 Ga) , the latter age corresponding to the Sveconorwegian. Detailed work to resolve the geochronology is planned for this winter.