Early Paleozoic medium-pressure metamorphism in central Vietnam: evidence from SHRIMP U-Pb zircon ages

Abstract

To constrain the timing of collisional event in the Indochina block, SHRIMP U-Pb dating and REE analyses of zircon were carried out for two paragneiss samples of the Kham Duc Complex, central Vietnam. Both samples contain kyanite, staurolite, and zoisite as relics from an early metamorphic stage (M1), and biotite and sillimanite as major minerals constituting the foliation formed during the late metamorphic stage (M2). The change in mineral assemblages indicates a clockwise P-T path composed of a high-or medium-P + low-T stage (M1) and a subsequent low-P + high-T stage (M2). The U−Pb concordia ages of zircon rims are 447 ± 6 Ma and 452 ± 6 Ma for the two samples, respectively. These results are distinctly different from the available Ar-Ar mineral ages of 254-225 Ma. Following the clockwise P-T path and phase equilibrium analyses of the Complex, we suggest that the zircon rims were formed near peak temperatures during the decompression. The ~450 Ma zircon rim thus gives the minimum age constraint for a possible crustal thickening event during Early Paleozoic, whereas the reported Permo-Triassic Ar-Ar ages would result from an Indosinian overprint. This Early Paleozoic event is most likely related to a collisional orogeny between the Indochina and South China blocks. Late Neoproterozoic to Neoarchean ages are recorded from detrital zircon cores of the Kham Duc Complex, the Kontum Massif and Truong Son Belt, suggesting that their protoliths might have derived from sediments at the Gondwana margin.

Zircon U-Pb geochronology and heavy mineral composition constraints on the provenance of the middle Miocene deep-water reservoir sedimentary rocks in the Yinggehai-Song Hong Basin, South China Sea

“…9) (Hoa et al, 2008;Liu et al, 2012). The Early Paleozoic granitoids within the Truong Son Belt occur mainly in the southwest of the orogenic belt, and gives aged of 460e430 Ma (Carter et al, 2001;Lan et al, 2003;Usuki et al, 2009Usuki et al, , 2013Wang et al, 2016a). Metamorphism occurred during the Indosinian Orogeny dated between 250 and 245 Ma (Lepvrier et al, 1997;Carter et al, 2001;Nagy et al, 2001;Roger et al, 2007).…”

Late Miocene provenance change on the eastern margin of the Yinggehai-Song Hong Basin, South China Sea: Evidence from U–Pb dating and Hf isotope analyses of detrital zircons

“…Rocks of early PermianeTriassic arc magmatism (280e270 Ma and 250e240 Ma) are widely distributed in this belt (Hoa et al, 2008;Liu et al, 2012). In addition, the Early Paleozoic granitoids within the Truong Son Belt are mainly located in the southwest of the orogenic belt, with ages of 460e430 Ma (Carter et al, 2001;Lan et al, 2003;Usuki et al, 2009).…”

Detrital zircon U–Pb geochronology, Lu–Hf isotopes and REE geochemistry constrains on the provenance and tectonic setting of Indochina Block in the Paleozoic

“…Early Paleozoic to Mesozoic magmatic rocks are widely distributed within the Truong Son Belt were emplaced during Ordovician-Silurian (470-420 Ma), late Carboniferous-early Permian (300-280 Ma), late Permian to middle Triassic (270-245 Ma) and middle-late Triassic (245-200 Ma) (Carter et al, 2001;Hoa et al, 2008;Usuki et al, 2009;Tran et al, 2014;Shi et al, 2015).…”

“…4), suggestive of a short transportation from the local source region. Coeval granitic rocks in the Truong Son Belt and adjacent areas yield zircon ages ranging from 460 to 400 Ma (Carter et al, 2001;Usuki et al, 2009;Tran et al, 2014;Shi et al, 2015), and were likely the source of the detritus. In addition, the range of ages in our samples yielded εHf(t) values of − 11.83 to +11.15 with model ages between 674 Ma and 1847 Ma (Appendix A), suggesting that they were derived from reworking of Mesoproterozoic crust (1200-1850 Ma) and some juvenile crustal materials older than 670 Ma.…”