ObjectiveAs 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 features 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.
MethodsThis 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 in the Yandang Mountain and Shenxianju areas.
ResultsAll the apatite fission track dates from the Yandang Mountain and Shenxianju areas show chi-squared probability P(χ2) ≥ 0.05, indicating that the fission track dates of all specimens follow a Poisson distribution and belong to a single age population. Twenty of the total thirty-two specimens from the Yandang Mountain area yielded apatite fission track ages (pooled age and central age) between 40 Ma and 31 Ma, seven of the thirty-two specimens gave apatite fission track ages between 50 Ma to 41 Ma, with only five of the thirty-two specimens yielding apatite fission track ages ranging from 61 Ma to 51 Ma. For the Shenxianju area, the apatite fission track ages are predominantly (sixteen of the twenty-six specimens) distributed between 40 Ma and 31 Ma, with some specimens (eight of the twenty-six specimens) showing ages ranging from 50 Ma to 41 Ma and a few of them (two of the twenty-six specimens) yielding ages between 61 Ma and 51 Ma. Furthermore, the single-grain apatite fission track ages of the specimens from both the Yandang Mountain and Shenxianju areas show a unimodal distribution with a peak at 33 Ma. The mean confined track lengths of the specimens from the Yandang Mountain area vary between ~11.12 μm and ~14.09 μm with unimodal track length distributions. Specimens from the Shenxianju area yielded mean confined track lengths of ~11.11 to ~14.44 μm, also showing a unimodal track length distribution pattern. The mean Dpar values of specimens from the Yandang Mountain area range from 0.78 μm to 1.04 μm, while those from the Shenxianju area display mean Dpar values varying from 0.86 μm to 1.12 μm. The HeFTy thermal history modeling reveals a rapid exhumation and cooling event occurring from the early-Eocene to the earliest Oligocene for both the 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.
ConclusionOur new apatite fission track dating and HeFTy thermal history modeling results help identify an exhumation and cooling event in 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 provides important low-temperature thermal geochronological constraints on the Phanerozoic regional tectonic and geomorphological evolution of southeastern Zhejiang province.
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