The Songpan–Garze Orogenic Belt (northeastern Tibet Plateau) INTRODUCTION experienced polyphase deformation and metamorphism that is best The Songpan–Garze Orogenic Belt (SGOB) occupies developed in the Danba Domal Metamorphic Terrane (DDMT), the northeastern portion of the Tibet Plateau (Fig. 1a), in which three tectonometamorphic events can be identified. The first which comprises the tectonically distinct Tethyan– event (D1–M1) is characterized by prograde sericiteto kyanite-grade Himalayan domain between India and Eurasia and is Barrovian metamorphism during late Indosinian (>205–190 Ma) characterized by a polyphase continent–continent colcrustal thickening and shortening. A subsequent early Yanshanian lisional history (Dewey et al., 1988). The Tibet Plateau (>165 Ma) sillimaniteto migmatite-grade event (M2) developed has been the subject of a number of studies, which have during predominantly east–west compression (D2). A final greenfocused on the Himalayas themselves and on the major schist-facies event (M3) is best developed in shear zones of probable strike-slip faults within, or fault zones along, the margin Himalayan age. P–T conditions during M1 varied from >3–5 of the Tibet Plateau (e.g. Dirks et al., 1994; Roger et al., kbar and >410–530°C (biotite zone) to 5·3–8 kbar and 1995; Arne et al., 1997; Meng & Zhang, 1999). In 570–600°C (staurolite and kyanite zones), and during M2 from comparison, little work has focused on the interior of the 4·8–6·3 kbar and 640–680°C (sillimanite zone) to 5·8–6·2 SGOB. As the SGOB resulted from the closure of the kbar and 660–725°C (migmatite zone). Clockwise P–T–t segPalaeo-Tethys and subsequent continental collision and ments were inferred for the staurolite, kyanite and sillimanite zones. convergence associated with interaction between the TiMuscovite-dehydration melting during M2 was largely responsible bet, Indochina, South China and North China Blocks for the generation of migmatites and locally voluminous pegmatites. (Xu et al., 1992), the multiphase deformational and metaThe polyphase tectonometamorphic evolution of the eastern Tibet morphic evolution of the SGOB is critical for underPlateau, as documented in the Danba area, resulted from interactions standing the Mesozoic–Tertiary tectonometamorphic between the Indian, Tibet, and the South and North China Blocks. evolution of the Tibet Plateau. The eastern Tibet Plateau experienced limited uplift during the Metamorphic studies of the SGOB are hampered by its Mesozoic, followed by large-scale uplift and rapid cooling during generally low grade (lower greenschist facies). However, the Tertiary Himalayan Orogeny. poorly documented medium-pressure Barrovian-type metamorphic complexes as high as upper amphibolite grade occur locally, and are associated with basementcored structural domes (Mattauer et al., 1992). The best examples are the Danba Domal Metamorphic Terrane