Archean blocks and their boundaries in the North China Craton: lithological, geochemical, structural and P-T path constraints and tectonic evolution

suggests that the basement of the North China Craton can be divided into Ea stern and Western Blocks, separated by major crustal boundaries that roughl y correspond with the limits of a 300 km wide zone, called the Trans-North China Orogen. The Eastern Block consists predominantly of Late Archean domi form tonalitic-trondhjemitic-granodioritic (TTG) batholiths surrounded by a nastomosing networks and linear belts of open to tight synforms of minor vo lcanic and sedimentary rocks metamorphosed from greenschist to granulite fa cies at similar to2.5 Ga, with anticlockwise P-T paths. Some Early to Middl e Archean rocks are locally present in the Eastern Block, but their tectoni c history is unclear due to reworking by the 2.5 Ga tectonothermal event. T he Western Block has a Late Archean assemblage, structural style and metamo rphic history similar to that of the Eastern Block, but it differs in the a bsence of early to middle Archean assemblages and in being overlain by and interleaved with Paleoproterozoic khondalites, which were affected by a sim ilar to1.8 Ga metamorphic event involving clockwise P-T paths. A mantle plu me model is proposed for the formation and evolution of Late Archean baseme nt rocks in the Eastern and Western Blocks based on a combination of extens ive exposure of TTG gneisses, affinities of mafic rocks to continental thol eiitic basalts, presence of voluminous komatiitic rocks, dominant diaprism- related domiform structures, anticlockwise P-T paths, and a short time span from the primary emplacement of TTG and ultramafic to mafic rocks until th e onset of regional metamorphism. Between the two blocks is the Trans-North China Orogen which is bounded by two major fault systems and is composed o f Late Archean to Paleoproterozoic TTG gneisses and granitoids, interleaved with abundant sedimentary and volcanic rocks that are geochemically interp reted as having developed in magmatic are and intra-arc basin environments. These rocks underwent multiple phases of compressional deformation and pea k high-pressure metamorphism followed by rapid exhumation during the Late P aleoproterozoic at similar to1.8 Ga as a result of collision between the Ea stern and Western Blocks, resulting in the amalgamation of the North China Craton. (C) 2001 Elsevier Science B.V. All rights reserved.