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The migration of arc magmatism that is a fundamental aspect of plate tectonics may reflect the complex interaction between subduction zone processes and regional tectonics. Here we report new observations on volcanic migration from northwestern Sumatra, in the westernmost Sunda arc, characterized by an oblique convergent boundary between the Indo-Australian and Eurasian plates. Our study indicates that in northwestern Sumatra, volcanism ceased at 15–10 Ma on the southern coast and reignited to form a suite of active volcanoes that erupt exclusively to the north of the trench-parallel Sumatran fault. Younger volcanic rocks from the north are markedly more enriched in K2O and other highly incompatible elements, delineating a geochemical variation over space and time similar to that in Java and reflecting an increase in the Benioff zone depth. We relate this mid-Miocene volcanic migration in northwestern Sumatra to the far-field effect of propagating extrusion tectonics driven by the India-Eurasia collision. The extrusion caused regional deformation southward through Myanmar to northwestern Sumatra and thus transformed the oblique subduction into a dextral motion–governed plate boundary. This tectonic transformation, associated with opening of the Andaman Sea, is suggested to be responsible for the volcanic migration in northwestern Sumatra.

Sibumasu is inferred to have developed as a united terrane in East Gondwana, with West Sumatra linked to Cathaysia. New detrital zircon U‐Pb and Hf isotopic data from Sumatra, complemented by literature data, challenge the above views. The scarcity of early Neoproterozoic zircons in West Sumatra argues against a direct connection between West Sumatra and Cathaysia. Detrital zircons from East Sumatra exhibit age profiles similar to those of Lhasa, West Burma, and Western Australia, with detritus most probably sourced from Western Australia. By contrast, Sibusima (Sibumasu excluding East Sumatra) shows detrital zircon age patterns resembling those of the South Qiangtang and the Tethyan and High Himalaya terranes, whose detrital materials are most likely derived from northern India. Our observations require disaggregation of Sibumasu and a new configuration of northern East Gondwana in the early Paleozoic, with East Sumatra and West Burma occupying a position outboard the Lhasa terrane along the NW Australian margin and Sibusima situated on the northern Greater Indian margin.

Prior to the collision of India with Asia, the evolution of island arcs and resultant crustal formation in the now-disrupted easternmost Tethys are poorly constrained. Here, we report for the first time zircon U-Pb and Hf isotopic data from Mesozoic granitoids in Sumatra, Indonesia. Our analyses identified three magmatic episodes at 214–201 Ma, 148–143 Ma, and 102–84 Ma, respectively, with a drastic change in magmatic zircon εHf(t) values from –13.1 to +17.7 in the Late Triassic granitoids, which reveals a fundamental restructuring of the arc system in Sumatra. Subsequently, all Jurassic to Late Cretaceous granitoids have exclusively positive zircon εHf(t) values (+17.7 to +10.2), consistent with juvenile arc development owing to subduction of the easternmost Tethyan lithosphere beneath Sumatra. Such highly positive zircon εHf(t) values of the Sumatran granitoids, in general accordance with those of the Gangdese arc system in South Asia, are markedly higher than those (+13.7 to –14.7) of broadly contemporaneous Cordilleran arcs in Americas and Zealandia. Our findings from the easternmost Tethys provide new insights into not only the tectono-magmatic evolution of eastern Tethys, but also its crucial role in global juvenile crustal growth.