Geochemical and zircon U-Pb geochronological constraints on late mesozoic Paleo-Pacific subduction-related volcanism in southern Vietnam

Abstract

Late Mesozoic volcanic rocks comprising mainly basalt and basaltic-andesite to dacite occur in south-central Vietnam (Dalat zone) and to a lesser extent in southwestern Vietnam (Bay Nui area). Mineral and whole-rock chemistry indicate a calc-alkaline affinity for samples in the Dalat zone and a high-K calc-alkaline to shoshonitic affinity for rocks in the Bay Nui area. Mineral characteristics and variation diagrams of selected elements suggest that fractional crystallization dominated during magma differentiation. The Bay Nui volcanic rocks generally are more enriched in potassium and LILEs (large-ion lithophile elements) than volcanic rocks from the Dalat zone, which may indicate a more evolved nature or crustal assimilation. The similar chemical characteristics and eruption/emplacement age range of volcanic and plutonic rocks (ca. 90–110 Ma) of equal silica concentration indicate that the magma feeding the volcanic eruptions had the same source as that of the plutonic rocks. The observed mineral and whole-rock compositions with enrichment in LILEs, depletion in HFSEs (high field strength elements), and noticeably negative Nb, Ta, and Ti anomalies are characteristic for arc signatures. Zircon U-Pb geochronological data for the volcanic rocks indicate an age range of 95–105 Ma for the eruption. These geochemical and geochronological data link this Late Mesozoic volcanism with continental arc magmatism driven by the subduction of the Paleo-Pacific beneath eastern Indochina. Zircon xenocrysts with a likely magmatic origin cluster around 350 Ma and 250 Ma, indicating two earlier magmatic events most likely related to the subduction of the Paleo-Tethys beneath western Indochina and the subsequent Indosinian orogeny.

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

“…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 reported ages of the Dalat-Kratie granites are mostly between ~120 Ma and ~80 Ma and show a chemical transition from Cordilleran I-type granites to post-collisional (A-type) granites over time (Nguyen et al, 2004a;Nguyen et al, 2004b;Shellnutt et al, 2013;Hennig-Breitfeld et al, 2021). Although there is a compositional transition from I-type granite to A-type granite, there does not appear to be a spatial correlation as the older I-type granites (120-115) geographically overlap with the younger I-type granites (110-90 Ma) and the A-type granites (<90 Ma) (Nguyen et al, 2004a;Nguyen et al, 2004b;Shellnutt et al, 2013;Cheng et al, 2019;Kasahara et al, 2021;Hennig-Breitfeld et al, 2021;Waight et al, 2021;Nong et al, 2022). However, there is a distinct change in the Sr-Nd isotopic compositions of the I-type granites in Cambodia compared to the granites of similar age in Vietnam (Figure 9).…”

“…During the Early Triassic, the Indochina terrane collided and accreted to the South China Block whereas during the Late Triassic it was affected by collision and accretion of the Sukhothai and Sibumasu terranes (Lepvrier et al, 2008;Burrett et al, 2021;Jiang et al, 2021). Furthermore, the Paleo-Pacific plate subducted beneath the Indochina terrane beginning in the Early Cretaceous and was responsible for the generation of widespread Cordilleran Batholiths throughout the Dalat-Kratie Fold Belt of southern Vietnam and eastern Cambodia (Nguyen et al, 2004a;Nguyen et al, 2004b;Shellnutt et al, 2013;Cheng et al, 2019;Hennig-Breitfeld et al, 2021;Nong 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).…”

Causes of Late Cretaceous subduction termination below South China and Borneo: Was the Proto-South China Sea underlain by an oceanic plateau?

“…Today, the subduction zone along the east Asian margin continues as far as Taiwan, where it connects to plate boundaries of the Philippines. However, geological records of arc magmatism and accretionary complexes show that until the Late Cretaceous (~80 Ma) a Paleo-Pacific subduction zone was active along South China, through Hainan, Vietnam and Cambodia as far as southern Borneo (e.g., Jahn et al, 1990;Lapierre et al, 1997;Xu et al, 1999;Shellnut et al, 2013Shellnut et al, , 2023Breitfeld et al, 2017Breitfeld et al, , 2022Hennig et al, 2017;Nong et al, 2021Nong et al, , 2022Hennig-Breitfeld et al, 2021;Waight et al, 2021;Hiu et al, 2022).…”