Phanerozoic magmatic tempos of North China

- Late Paleozoic continental arc magmatism in North China had a tempo of 60 m.y.
- Magmatic flare-ups were associated with increasing degrees of crustal melting.
- Magmatic lulls were associated with influxes of depleted mantle melts into the arc.
- Crustal shortening generated flare-ups, and delamination occurred during lulls.
- Mesozoic magmatic tempos in North China may be driven by similar processes.

Detrital zircons from northeast China record cyclic magmatism along the northern and eastern margins of the North China block during late Paleozoic time and Mesozoic time, respectively. The late Paleozoic zircons record three magmatic flare-ups with a period of ∼60 m.y. that occurred within a magmatic arc constructed along the Paleoasian (northern) margin of North China, and are accompanied by negative εHf(t) excursions representing shortening and increased crustal melting over the duration of each flare-up. The intervening magmatic lulls are accompanied by rapid positive εHf(t) excursions signifying influxes of juvenile magma into the arc, probably during extension and foundering of underlying melt residua. The lack of similar isotopic patterns in zircons derived from contemporaneous intrusions into older continental settings inboard of the arc indicate that this process was restricted to the arc itself. Mesozoic magmatism in North China occurred along the Paleo-Pacific margin following closure of the Paleoasian Ocean, and exhibits a ∼50 m.y. periodicity that is out-of-phase with that of the Paleozoic arc. Although the tectonic setting of North China during Mesozoic time is complex and still controversial, it is possible that this younger periodicity is governed by similar processes as those that dominated the Paleozoic arc. This is a testable hypothesis that warrants further attention. Crustal shortening was widespread in North China during Mesozoic time, and documented lithosphere removal events in eastern North China occurred during the Mesozoic magmatic lulls. Lithospheric thickening/foundering cyclicity, well-documented in Cordilleran arc systems, may be a common process in continental arcs through space and time.

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