Post‐orogenic evolution of the <scp>M</scp>esozoic <scp>M</scp>icang <scp>S</scp>han <scp>F</scp>oreland <scp>B</scp>asin system, central <scp>C</scp>hina

Abstract

Abstract [Correction added after online publication 3 August 2010 ‐ ‘prelate’ has been changed to ‘pre‐late’ throughout the text]. Using apatite fission track and ( U‐Th‐Sm )/ He thermochronology, we report the low‐temperature thermal history of the M esozoic M icang S han F oreland B asin system, central C hina. This system, comprising the H annan D ome hinterland, the northern S ichuan F oreland B asin and the intermediate frontal thrust belt (FB), shares a common boundary with three major tectonic terrains – M esozoic Q inling‐ D abie O rogen, M esozoic S ichuan F oreland B asin and C enozoic elevated T ibetan Plateau. Results show: (1) a relatively rapid pre‐late C retaceous cooling episode in the H annan D ome; (2) a mid‐ C enozoic cooling phase ( ca . 50°C at ca . 30 ± 5 Ma) within the northern S ichuan Basin; and (3) possible late C enozoic cooling ( ca . 25°C at ca . 16 ± 4 Ma) within the H annan D ome‐FB, a phase which has also been reported previously from adjacent regions. The pre‐late C retaceous cooling episode in the H annan D ome is attributed to coeval tectonism in nearby regions. Mid‐ C enozoic cooling in the northern S ichuan B asin can possibly be attributed to either one of or a combination of shortening of the basin, onset of the A sian monsoon and drainage adjustment of the Y angtze R iver system, all of which are related to growth of the T ibetan P lateau. Possible late C enozoic cooling in the hinterland and nearby regions is also probably related to the northeastward growth of the T ibetan P lateau. However, previous studies suggest a northeastward propagation for onset of cooling from the eastern T ibetan P lateau to western Q inling in response to northeastward lower crust flow from the central T ibetan P lateau. The timing of apparent late C enozoic cooling in the H annan D ome hinterland, at an intermediate locality, is not consistent with this trend, and supports a previous model suggesting northeastern growth of the T ibetan P lateau through reactivation of WE trending strike‐slip faults.