The Hengshan low-angle normal fault zone: Structural and geochronological constraints on the Late Mesozoic crustal extension in South China

Thermal evolution of the Hengshan extensional dome in central South China and its tectonic implications: New insights into low-angle detachment formation

“…Obviously, this time is at least 14 Myr later than the intrusion of the Hengshan composite granitoids, revealing that the composite granitoids were pre-kinematic and represented two discrete phases of preceding magmatic activity. In addition, previous 40 Ar/ 39 Ar thermochronologic analysis of muscovite from three mylonitic rocks has suggested that the ductile shear zone cooled to~350°C at 108-97 Ma (Li et al, 2013). Structurally upward toward the detachment fault are marked by increased brittle deformation intensity and retrograded metamorphism, as expressed by the development of a~5 m thick slightly foliated cataclasite zone (Fig.…”

“…Notably, the ductile shear zone was permeated by dikes of albitite, and the albite therein suffered from strong stretching and displayed consistent shear features with the country rocks, implying that the albitite dikes were synkinematically emplaced. SHRIMP U-Pb zircon age of the albitite dikes constrains the onset time of ductile shearing and thus crustal extension in the Hengshan region to be 136 Ma (Li et al, 2013). Obviously, this time is at least 14 Myr later than the intrusion of the Hengshan composite granitoids, revealing that the composite granitoids were pre-kinematic and represented two discrete phases of preceding magmatic activity.…”

“…2). These data, coupled with previously published structural observations and geochronological/thermochronological ages (Li et al, 2013), allow us to evaluate the thermal and mechanical evolution of footwall rocks, and the slip rate, magnitude, and initial geometry of the Hengshan detachment fault. These results aid in testing geological models for the formation and evolution of the low-angle detachment fault.…”

“…4D-E). Optical measurements of quartz c-axis orientations show a simultaneous operation of basal b aN and prism baN slips, indicating a deformation temperature ranging from 300 to 500°C (Li et al, 2013). Petrographic observations are expressed by ribbon and dynamically recrystallized quartz, synkinematic growth and elongation of micas, and brittle fracturing and rotation of feldspars ( Fig.…”

“…136 Ma, based on high accuracy U-Pb analyses of zircons from syn-kinematic albitite intrusions, and (3) lower plate metamorphic rocks underwent significant exhumation and unroofing at ca. 108-97 Ma, revealed by 40 Ar/ 39 Ar analysis of syn-kinematic muscovites from the shear-zone mylonites (Li et al, 2013). Although it is clear that the exhumation of the lower plate metamorphic rocks was solely attributed to slip on the Hengshan detachment fault, the cooling history of the extensional dome and thus the rate, duration, and formation mechanism of the low-angle Hengshan detachment fault, remain poorly constrained.…”