Structural Relationships along a Neoarchean Arc‐Continent Collision Zone, North China Craton

Abstract

The Archean North China craton is composed of the Western block, Eastern block, and the intervening Central orogenic belt. A 4–10-km-wide and 85-km-long tectonic melange belt informally called the Zanhuang tectonic melange is documented in the Zanhuang Massif of the Central orogenic belt, separating the Eastern block from an Archean arc terrane in the Central orogenic belt. The melange belt contains a structurally complex tectonic mixture of metapelites, metapsammites, marbles, and quartzites mixed with exotic tectonic blocks of volcanic, mafic, and ultramafic rocks, metabasalts that locally include relict pillow structures, and tonalite-trondhjemite-granodiorite (TTG) gneisses. The Zanhuang tectonic melange marks the suture of an arc-continent collisional zone between the Western Zanhuang Massif in the Central orogenic belt and the Eastern block of the North China craton, and it is one of the best-preserved Archean tectonic melanges in the world. Here, using zircon U-Pb dating of various types of blocks from the Zanhuang melange, we show that the formation and associated deformation of the Zanhuang melange occurred in the Neoarchean (ca. 2.5 Ga). High-precision (1:20–1:200) lithostructural mapping of three key outcrops reveals details of the internal fabrics and kinematics of the melange and regional structural relationships along the arc-continent collisional zone. A synthesis of studies on the tectonic evolution of the North China craton, coupled with our new fabric and kinematic analysis of the Zanhuang melange, further constrains the initial amalgamation timing and geometry of the arc-continent collision between the Fuping arc terrane in the Central orogenic belt and the Eastern block with a northwest-dipping subduction polarity. The asymmetric structures and mixture of different blocks and matrices with folding and thrusting events in the Zanhuang melange record kinematic information that is consistent with the tectonic setting of an accretionary wedge that was thrust over the passive margin of the Eastern block by 2.5 Ga. Lithostructural mapping shows that the classic melange and fold-and-thrust structures along the Neoarchean arc-continent collisional zone are broadly similar to Phanerozoic collisional belts.