| Abstrakt: |
Cyclical change in subduction angle is the favorable mechanism to elucidate the cyclicity of continental arc magmatism, however, the role of episodic tectonics and variation of the lithosphere in overriding plates is much underestimated. Here we focus on structural, magnetic, and gravitational features of the Late Jurassic to Early Cretaceous granites in the Mesozoic Paleo‐Pacific arc system of the North China block. By unraveling the emplacement process and regional tectonics, we establish a three‐staged extension‐contraction cycle with crustal thickness variation controlling the magmatic flux and behavior. The Late Jurassic extension produced high‐flux crustal‐derived magma (1.87 × 103 km2/Myr), but the thick crust >45 km accumulated large granitic batholiths by multi‐feeders emplacement at the middle‐lower crust and prevented magma ascent and eruption. Subsequently, the Latest Jurassic to Earliest Cretaceous contraction resulted in the magmatic lull and thickened crust of ca. 60 km, fueling crustal material for the ensuing magmatism. In the Early Cretaceous, intense crustal extension thinned the crust to 30 km and largely enhanced the magmatic flux (3.03 × 103 km2/Myr). The magma is prone to penetrate the thin crust with an intensive eruption. A small amount of magma was stored, and the emplacement was controlled by ductile detachments or normal faults. Our model emphasizes episodic the deformation of lithosphere and associated crustal thickness variation in controlling magma production, which may shed new light in understanding the magmatic cyclicity under continuous subduction. Plain Language Summary: The magmatic cycle is key to forecasting volcanic eruption for hazard assessment. On a long‐time scale, the paleo‐magmatic cyclicity including alternating flare‐ups and lulls provides the case to study its driving forces. It is traditionally considered that the magmatic cyclicity is controlled by the subducted plate, however, it fails to explain whether magma erupts or stores, and why it emplaces variably in the different cycles. Taking the Late Mesozoic North China block as an example, we highlight that the overriding plate that experiences episodic variations of crustal deformation and crustal thickness plays an important role in the magmatic cyclicity. When the crustal thickness of the overriding plate was more than 45 km at the Late Jurassic, magma is prone to storage than eruption, and multi‐pulsed magma emplacement is predominated under this extensional regime. Afterward, the Latest Jurassic‐Earliest Cretaceous crustal shortening and thickening (ca. 60 km) prevent magma formation. When the crust thinned to 30 km during the Early Cretaceous, the magma was able to rise to the upper crust, and even to erupt. The magma emplacement is controlled by ductile detachments or by normal faults. Key Points: Feedback between regional tectonics and magmatism account for the Late Mesozoic magmatic lulls/fare‐ups in the North China blockEpisodic variation in tectonics and crustal thickness controlled the magma behavior and associated emplacement mechanismsOverriding‐plate process is key to understanding the magmatic cyclicity under continuous subduction [ABSTRACT FROM AUTHOR] |
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