Zircon U–Pb chronology on plutonic rocks from northeastern Cambodia

Abstract

Zircon U–Pb geochronology was carried out on plutonic rocks from Phnom Daek, Phnom Koy Rmeas, Svay Chras, Kon Mom, Koh Nheak, Andong Meas, Oyadav South, Svay Leu, and Phnom Soporkaley. The zircon U–Pb ages from the plutonic rocks determined in this study can be roughly divided into two groups. One is the Late Permian to Triassic ages of 278–202 Ma for the Phnom Daek, Phnom Koy Rmeas, Oyadav South, Svay Leu, and Phnom Soporkaley, and the other is the early Cretaceous ages of 118–98 Ma for the Svay Chras, Kon Mom, Koh Nheak, and Andong Meas samples. The plutonic rocks from Phnom Daek, Phnom Koy Rmeas, Svay Leu, Oyadav South, and Phnom Soporkaley were likely formed by magmatic activity in the Loei Fold Belt. These plutonic rocks were likely formed in an extensional setting and/or a region where the continental crust was thin. The plutonic rocks of Svay Chras, Kon Mom, Koh Nheak, and Andong Meas were likely formed by magmatic activity in the Dalat-Kratie Fold Belt, related to the NW-directed subduction of the Paleo-Pacific Ocean plate. These plutonic rocks are thought to correspond to the Dinhquan suite in southern Vietnam. The Kon Mom and Koh Nheak plutonic rocks fall within the alkaline series, which suggests that the magma genesis was deep and far from the western Paleo-Pacific Ocean plate. Magmatic activity in the Dalat-Kratie Fold Belt migrated oceanward as a whole during the Cretaceous.

Early Cretaceous volcanic-arc magmatism in the Dalat-Kratie Fold Belt of eastern Cambodia: implications for the lithotectonic evolution of the Indochina terrane

“…We interpret these inherited zircons as being derived from an older period of spatially associated subduction-related magmatism as they have similar Hf isotopic values (ε Hf (t) = +13.2-+16.8) as the emplacement age zircons (ε Hf (t) = +12.1-+17.0). Moreover, the inherited Early Cretaceous (112-118 Ma) ages overlap with reported rock ages throughout the Dalat-Kratie Fold Belt of Vietnam and Cambodia (Nguyen et al, 2004a;Shellnutt et al, 2013;Hennig-Breitfeld et al, 2021;Kasahara et al, 2021;Nong et al, 2021). The Late Paleozoic (335-296 Ma) inherited zircons are contemporaneous with Middle Carboniferous Sun and McDonough (1989).…”

“…The zircon U-Pb geochronology results of the surface rocks yielded Albian ages (O05c = 107.5 ± 0.3 Ma; O20 = 109.1 ± 0.4 Ma). Moreover, sample O20 has inherited zircons that range in Breitfeld et al, 2020;Hennig-Breitfeld et al, 2021;Kasahara et al, 2021;Nong et al, 2021;Nong et al, 2022). Specifically, they correlate to a period of subduction-related (130-90 Ma) magmatism along the western margin of the Paleo-Pacific Ocean (Taylor and Hayes, 1983;Metcalfe, 2006;Yang, 2013;Hennig-Breitfeld et al, 2021;Waight et al, 2021).…”

“…The more widespread I-type Early Cretaceous granitic batholiths are related to the subduction of the Paleo-Pacific Ocean crust beneath Indochina and contemporaneous with Yanshanian magmatism along the coast of eastern China. The Late Cretaceous A-type granitic rocks that crop out in southern Vietnam are interpreted to be related to post-collision extensional stress associated with trench retreat and slab rollback of the Paleo-Pacific Ocean (Zhou et al, 2006;Shellnutt et al, 2013;Cheng et al, 2019;Hennig-Breitfeld et al, 2021;Kasahara et al, 2021;Waight et al, 2021;Nong et al, 2022).…”

“…The Dalat-Kratie Fold Belt is composed of Triassic to Cretaceous sedimentary rocks and volcano-plutonic rocks that are overlain by Quaternary basalt (Zaw et al, 2014). The granitic rocks are primarily of Cretaceous (130-75 Ma) ages, although Carboniferous (332 ± 5 Ma), Permian (277 ± 2 Ma), and Triassic (202 ± 0.4 Ma; 238 ± 0.3 Ma; 211 ± 1.7 Ma; 248.9 ± 2.4 Ma) mafic and silicic igneous rocks are also present in the region (Nguyen et al, 2004a;Nguyen et al, 2004b;Shellnutt et al, 2013;Cheng et al, 2019;Hennig-Breitfeld et al, 2021;Kasahara et al, 2021).…”

“…The Cretaceous rocks record two distinct periods of granitic magmatism related to the subduction of the Paleo-Pacific plate. The more voluminous, older rocks are attributed to volcanic-arc magmatism and contemporaneous with the Late Yanshanian Orogeny of East Asia whereas the younger (<90 Ma) rocks are correlated with post-collisional magmatism (Nguyen et al, 2004a;Nguyen et al, 2004b;Shellnutt et al, 2013;Cheng et al, 2019;Hennig-Breitfeld et al, 2021;Kasahara et al, 2021). Located within the Dalat-Kratie Fold Belt of eastern Cambodia is the previously unstudied Snoul pluton.…”