Polyphase Deformation of the Weihai-Rongcheng UHP Unit Rocks, NE Sulu： Insights into the Tectonic Evolution of the Dabie-Sulu UHP and HP Belts, China

摘要

Different scales of structural data reveal a complex deformation history of ultrahigh- pressure (UHP) rocks exposed in the Weihai-Rongcheng area, NE Sulu (northern Jiangsu-eastern Shandong), eastern China. Excluding pre-UHP deformations, at least five major sequential deformational stages (D1–D5) are recognized. The first deformation (D1) produced a weak foliation and lineation in massive eclogites. The foliated eclogite with a dominant foliation containing a stretching and mineral lineation was developed during the D2 deformation. Both the D1 and D2 deformations occurred under UHP metamorphic conditions, and are well preserved in the eclogite bodies. D3 structures which developed shortly after the formation of granulite/amphibolite facies symplectites are characterized by imbricated associations marked by a regional, steeply dipping foliation, compositional layering, eclogite boudinage, isoclinal folds and reverse ductile shear zones. The D3 deformation was accompanied by decompressional partial melting. A regional, gently dipping amphibolite facies foliation and stretching lineation, low-angle detachments, and dome- and arc-shaped structures formed during the D4 deformation stage dominate to some degree the map pattern of the Weihai-Rongcheng UHP domain. The last stage of deformation (D5) gave rise to the final exhumation of the UHP rocks. D5 is characterized by development of brittle-dominated high-angle faulting associated with emplacement of large volumes of undeformed granite plutons and dykes dated at 134–100 Ma. The deformational and metamorphic sequence followed by the UHP rocks in the Weihai-Rongcheng area is similar to that studied in the entire Dabie-Sulu UHP and HP metamorphic belts from microscopic to mapping scale. Based on structural data, combined with available petrographic, metamorphic and geochronological data, a speculative tectonic evolutionary model for the Dabie-Sulu UHP and HP belts is proposed, involving continental subduction/collision between the Sino-Korean and Yangtze cratons and subsequent polyphase exhumation histories of the UHP and HP metamorphic rocks.