Early Paleoproterozoic magmatism in the Yangtze Block: Evidence from zircon U-Pb ages, Sr-Nd-Hf isotopes and geochemistry of ca. 2.3 Ga and 2.1 Ga granitic rocks in the Phan Si Pan Complex, north Vietnam

Abstract

Our understanding of the early evolution of the Yangtze Block is limited by the sparsely dispersed nature of pre-Neoproterozoic exposures. New, integrated petrographic, zircon U-Pb age and Hf-Nd isotope analyses, and whole-rock geochemical data for early Paleoproterozoic granites in the Phan Si Pan Complex provides new insights into the evolution of the Yangtze Block as well as its role in the Pre-Nuna supercontinent. LA-ICP-MS zircon U-Pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207 Pb/ 206 Pb ages of 2306 ± 12 Ma and 2096 ± 15 Ma, respectively. Zircons from the quartz monzonite have ε Hf(t) values ranging from-4.1 to-2.1, corresponding to T DM2 model ages of 3002-2890 Ma, whereas zircons in the gneissic granite have ε Hf(t) values between-0.95 and +1.72 and corresponding T DM2 model ages of 2660-2516 Ma, which are consistent with their whole-rock Nd isotope values. Geochemically, the quartz monzonites are I-type granites. Combined with their relatively high Sr/Y ratios and low Y concentrations, as well as fractionated REE patterns with relatively high LREE but low HREE concentrations, they were probably generated by partial melting of the thickened middle-lower crust under elevated temperature. Geochemical and isotopic signatures suggest that the ca. 2.1 Ga gneissic granites are high-K calc-alkaline, ferroan A-type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material. The Phan Si Pan complex has a distinct early Paleoproterozoic crustal evolution history compared with the other crustal provinces of the Yangtze Block, suggesting independent histories that were not unified until the late Paleoproterozoic during the assembly of Nuna. Moreover, the magmatism and tectonic evolution of the north Vietnam region is broadly similar to that of the Arrowsmith Orogen of the Rae craton in Laurentia suggesting a potential spatial linkage. The geologic record of the Yangtze Block does not support an early Paleoproterozoic shutdown of plate tectonics.

Neoarchean and Paleoproterozoic K-rich granites in the Phan Si Pan Complex, north Vietnam: Constraints on the early crustal evolution of the Yangtze Block

“…This interpretation is consistent with the distinct sources and melting conditions of Archean TTGs in the different Archean basement units Wang and Dong et al, in press), and different magmatic and metamorphic records in distinct Archean components of the Yangtze Block ( Fig. 13; Zhao et al, 2019b).…”

“…Although an increasing number of pre-Neoproterozoic rocks have been reported in the Yangtze Block over the past few years (Guo et al, 2015;Wang et al, 2018a;Xiang et al, 2018;Zheng et al, 2006;Zhang et al, 2019), the nature of the Precambrian crystalline basement to the block and its evolutionary record remain unclear. For example, the isolated and spatially separated nature of the Archean rocks in the block has led to speculation as to whether they represent a single, evolving segment of crust or a series of independent fragments that were subsequently amalgamated (Ling et al, 2001;Wang et al, 2018b;Wang et al, 2018c;Zhao et al, 2019b;G. Zhou et al, 2018).…”

Nature and Evolution of Pre‐Neoproterozoic Continental Crust in South China: A Review and Tectonic Implications

“…The ca. 2.1 Ga granites, by contrast, show ferroan A-type granite characters, and were interpreted to form from partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material (Zhao et al, 2019b).…”

Late Paleoproterozoic to Early Mesoproterozoic Mafic Magmatism in the SW Yangtze Block: Mantle Plumes Associated With Nuna Breakup?

“…Archean crystalline basement rocks are sporadically exposed in the northern portion of the Yangtze Block, represented by Kongling Complex, which is dominated by tonalite‐trondhjemite‐granodiorite (TTG) suites as old as ~3.45 Ga and associated metasedimentary rocks (Gao et al, 2011; Guo et al, 2014). More recently, available data show that late Archean to early Paleoproterozoic magmatic rocks are also exposed in the northern and southwestern Yangtze Block, typified by the Zhongxiang (2.85–2.65 Ga), Douling (2.5 Ga), Yudongzi (2.8–2.48 Ga), Houhe (2.08 Ga), and Phan Si Pan (2.28–2.19 Ga) complexes (Figure 1b) (e.g., Chen et al, 2019; Hui et al, 2017; Wang, Deng, et al, 2018; Wu et al, 2012, 2014; Zhao et al, 2019). Most of these Archean‐Paleoproterozoic rocks underwent upper amphibolite to granulite facies metamorphism at circa 2.08–1.83 Ga (e.g., Wang et al, 2016; Yin et al, 2013; Zhang et al, 2006) (Figure 1b), contemporaneous with the global collisional orogenesis possibly related to the assembly of the Nuna supercontinent (Zhao et al, 2002).…”