Alpine-style tectonic nappe stacking in an Archean suture zone: Quantitative structural profile places constraints on orogenic architecture

We report the structural geometry and stacking sequence of an Archean Alpine-style sub-horizontal fold/thrust nappe pile in the Precambrian basement of the Zanhuang massif, northern China, to provide a quantitative basis for discussing the tectonism style during Archean orogenesis. The first-order geometric restoration and field-based anatomy enables us to subdivide this fold/thrust nappe pile into the top-most Black Rock Temple nappe, a lower giant sheath-folded nappe, the Zhaimen recumbent nappe, and the lowermost Buddha nappe, which all have major ductile shear zones at their bases, and likely merge into a single décollement at depth. The internal structures, lithologies, and deformation sequences illustrate that the individual nappes were derived from different tectonic belts of an ancient paleo-ocean before they were emplaced. During transportation and emplacement, the nappes underwent progressive ductile shearing and recorded the tectonic history from far-traveled 2.7–2.5 Ga oceanic, fore-arc, arc, and continental margin sequences thrusting, to arc/proto-continental collision at 2.5 Ga. This work explicitly unravels the displacement of nappes accomplished by a combination of rigid body translation along thrusts and internal strain by ductile deformation. The rigid body translation is illustrated by the dominance of nappe gliding on the basal shear surfaces for the large-scale horizontal tectonic transportation. The internal strain related displacement is best-illustrated by the high-strain recumbent giant sheath fold. Comparison of the lateral displacements and structural history of the Archean Zanhuang nappes with those of the Swiss Alps and other Phanerozoic orogenic belts reveals remarkable similarities but few differences, providing positive evidence for horizontal plate tectonics in the Archean. The similar architecture and structural history of many orogenic belts from the Archean to Cenozoic implies that Archean orogenic geotherms, the duration of orogenic events, and the fundamental processes of tectonic evolution have remained relatively constant for the past 2.7 Ga.