Abstract The Changbaishan volcanic field located on the Gaima (Gaema, Gaiman) Plateau has witnessed plateau-forming eruptions along with the uplift of the Gaima Plateau. The Tianchi basaltic lava shield volcano was formed at the main peak of Changbaishan, with cone construction eruptions that formed a huge and steep trachytic composite cone on the gentle lava shield. At the peak of the Millennium Eruption (ME), the height of the eruption column reached 25 km and the bulk volume of tephra was about 120 km 3 . The ME eventually formed Tianchi caldera, after which several eruptions occurred, albeit of a much smaller scale. The magmas involved in the shield-forming eruptions are characterized by both alkalic series trachybasalt and basaltic trachyandesite and subalkalic tholeiite and basaltic andesite. In the cone-construction and ignimbrite-forming eruption stages, the magma is completely composed of alkalic series trachyte and comendite. The largest negative Eu anomalies observed in ME magmas indicate that plagioclase was strongly crystallized and differentiated.

Abstract Trachyandesitic to trachybasaltic lavas, interlayered siliciclastic sedimentary rocks and subaerial ignimbrites with a rhyolitic to trachydacitic composition lie unconformably above metamorphic rocks in west-central Sweden. These volcanic rocks erupted at 1711 + 7/−6 to 1691 ± 5 Ma and belong to a high-K, calc-alkaline to shoshonitic suite deposited in a continental arc setting. Positive ɛ Nd values and Nb/Yb ratios in the trachyandesitic to trachybasaltic rocks indicate an enriched mantle source. Coeval, 1710 ± 11 to 1681 ± 16 Ma plutonic and subvolcanic rocks are mainly granitic or quartz syenitic in composition. Subordinate components include quartz monzonite, quartz monzodiorite and monzogabbro or gabbro. ɛ Nd values in the range −1.0 to + 1.1 overlap with those in the inferred 1.9–1.8 Ga source rocks. All these rocks belong to the youngest phase of the lithodemic unit referred to as the Transscandinavian Igneous Belt. This magmatic province extends in a roughly NNW direction for at least 900 km, variably deformed and metamorphosed equivalents occurring inside and beneath younger orogenic belts to the south (Sveconorwegian) and north (Caledonian). The part of the province in west-central Sweden addressed here represents a far-field and shallow crustal component in this 1.7 Ga accretionary orogenic system.