Magma chamber processes in Early Cretaceous Shangzhuang layered mafic intrusion from the North China Craton

Abstract

The Fe–Ti ore‐bearing Shangzhuang mafic intrusion in the Yanshan Orogenic Belt, north of the North China Craton, is characterized by compositional layering with troctolite, noritic gabbro and gabbro from the bottom to the top. The intrusive complex formed through fractionation of Fe‐, Ti‐ and Mg‐rich mafic hydrous magma. Here, we present a systematic petrological and mineral data on the various rock types from this intrusion. The plagioclase laths exhibit Na‐enriched rims with homogeneous cores and X_An content decreasing towards the margin, induced by sluggish coupled inter‐diffusion of (Ca + Al) versus (Na + Si). The reactions also resulted in amphibole and orthopyroxene rims surrounding olivine. Subsolidus equilibrium is indicated by Fe–Ti oxide lamellae in pyroxenes. The H₂O content of the primary magma is estimated to be less than 2.5 wt.%, and initial crystallization temperature in the magma chamber is estimated as approximately 884 °C at a pressure of 3.45 kbar. The formation of the parent magma was due to the thermal–chemical erosion through mantle upwelling, basaltic underplating and heat input from convection of deep asthenosphere mantle, widely associated with the large‐scale Mesozoic lithospheric thinning beneath the North China Craton. Final emplacement of the Shangzhuang intrusion is related to the intra‐continental extensional setting, at a depth of approximately 14.5 km, suggesting large‐scale, post‐emplacement uplift and exhumation of the Yanshan Orogenic Belt in the Late Jurassic and Early Cretaceous. Copyright © 2016 John Wiley & Sons, Ltd.