Abstract:
Abstract: [Objective] As an essential component of the East Asian continental margin, the southeastern coastal region of China records a complex history of regional tectonics, magmatism, and geomorphological associated with the subduction of the Paleo-Pacific/Pacific Plate. This region serves as an ideal window for studying ocean-continent interactions related to subduction zones. During the Cretaceous period, influenced by the rollback of the Paleo-Pacific Plate, a giant rhyolitic volcanic belt approximately 1200 km in length developed along the southeastern coast of China. Among the provinces in this region, Zhejiang hosts the largest preserved area of rhyolitic volcanic rocks and retains the most well-preserved volcanic structures. Previous studies have extensively investigated the geochronology, petrology, geochemistry, and metallogenesis of these rhyolitic volcanic rocks, however, their uplift and cooling history has been largely overlooked. [Methods] This study conducted apatite fission track dating and HeFTy thermal history modeling on the central facies intrusive rocks (quartz syenite, syenite and monzonite) of the calderas at Yandang Mountain and Shenxianju areas. [Results] All the apatite fission track dates from the Yandang Mountain and Shenxianju areas show chi-squared possibility P(χ
2) ≥ 0.05 which indicating that the fission track dates of all specimens follow a Poisson distribution and belong to a single age population. Twenty of total thirty-two specimens from the Yandang Mountain area yielded apatite fission track ages (pooled age and central age) between 31 Ma to 40 Ma, seven of total thirty-two specimens gave apatite fission track ages between 41 Ma to 50 Ma, with only five of total thirty-two specimens yielded apatite fission track ages ranging from 51 Ma to 61 Ma. For the Shenxianju area, the apatite fission track ages are predominantly (sixteen of total twenty-five specimens) distributed between 31 Ma to 40 Ma, with some specimens (seven of total twenty-five specimens) show ages ranging between 41 Ma to 50 Ma and a few of them (two of total twenty-five specimens) yielded age between 51 Ma to 61 Ma. Furthermore, the single grain apatite fission track ages of the specimens from Yandang Mountain and Shenxianju area both show unimodal distribution with a peak of 33 Ma. The mean confined track lengths of the specimens from Yandang Mountain area varying between ~11.12 μm and ~14.09 μm with unimodal track length distributions. Specimens from Shenxianju area yielded mean confined track lengths of ~11.11 to ~14.44 μm, which also show a unimodal track length distribution pattern. The mean Dpar values of specimens from Yandang Mountain area ranging from 0.78 μm to 1.04 μm, while for those from Shenxianju area display mean Dpar values vary from 0.86 μm to 1.12 μm. The HeFTy thermal history modeling reveals a rapid exhumation and cooling event occurred from the early-Eocene to the earliest Oligocene for both Yangdang Mountain (48 Ma to 33 Ma) and Shenxianju (52 Ma to 32 Ma) areas. The cooling rates of this event vary from ca. 8 ℃/Myr to 20 ℃/Myr for Yandang Mountain area and ca. 5 ℃/Myr to 16 ℃/Myr for Shenxianju area respectively. [Conclusion] Our new apatite fission track dating and HeFTy thermal history modeling results help identify an exhumation and cooling event of the Yangdang Mountain and Shenxianju areas during the early-Eocene to the earliest Oligocene epoch. Based on the results of this study and regional tectonic setting analysis, the early-Eocene to the earliest Oligocene exhumation and cooling event in the study areas is interpreted as being initially controlled by the subduction of the Izanagi-Pacific Plate ridge and later driven by the combined effects of the India-Eurasia continental collision and the rollback of the Pacific Plate. [Significance] This study provide important low-temperature thermal geochronological constraints on the Phanerozoic regional tectonic and geomorphological evolution of the southeast Zhejiang province.