Abstract: Many fold structures are well-preserved in mid-lower crustal detachment fault zones owing to progressive shearing along the fault zone during exhumation of metamorphic core complexes. These fold structures, like host rocks, bear important information on the evolution of the detachment fault zone. In this paper, we studied the various fold structures from the Jinzhou detached fault zone of the Liaonan metamorphic core complex. Based on the relationship between mylonitic foliation and fold, the folds are subdivided into pre-, syn-, and post-shearing folds. The syn-shearing folds can be further grouped into early (a1), mid (a2) and late (a3) syn-shearing folds. The transition from early to late syn-shearing is ascribed to progressive shearing during the detachment faulting. By means of morphological and crystallographic fabric analysis and quartz paleothermometry, we performed preliminary examination on the formation mechanism of folds along the detachment fault to provide constraints to the detachment faulting process in southern Liaoning. Our study shows that differences in macroscopic characteristics or relationship between foliation and folds of different stages, as well as morphological and crystallographic fabric characteristics of quartz grains in the folded rocks, can provide corroborative evidence for determining and restoring formation mechanism of folds. We suggest that the folds from the detachment fault zone result from progressive shearing under the combined effects of buckling and rheological properties of folded layers. During progressive shearing, a1 and a2 stage folds are dominated by buckling, while a3 stage fold is attributed primarily to flexural slip. Folding mainly occurred at a temperature range of 500 to 380 ℃. The detachment fault zone evolution maintained a relatively steady strain state overall from the early to late stage, while a weak contraction occurred in the NE-SW direction during the regional NW-SE extension in the Jinzhou detachment fault zone.

Key words: fold, detachment fault, metamorphic core complex, quartz crystallographic preferred orientations, dynamic recrystallization