Discovery of Paleoproterozoic rapakivi granite on the northern margin of the Yangtze block and its geological significance

Abstract

The Huashanguan rapakivi pluton in Zhongxiang, Hubei Province, China, is the first discovered Proterozoic rapakivi pluton in the Yangtze block. Based on field and petrographical observations, a typical rapakivi texture was found in the northern portion of the Huashanguan granitic pluton. Almost all the K-feldspar phenocrysts were round to oval in shape and most had plagioclase coatings known as rapakivi phenocrysts. Alkali feldspars and quartz had two or more generations. Petrochemically, the Huashanguan rapakivi granites were characterized as having high values of Si, K, Fe, Th, U, La, Ga, Ce, Sm and LREE, low values of Ca, Mg, Sr, Nb, Y and HREE, and a negative Eu anomaly. These geochemical characteristics of the Huashanguan granites were concordant with typical rapakivi granites, and had an affinity to A-type granites. LA-ICP-MS U-Pb zircon dating also was conducted. The dating yielded a 207 Pb/ 206 Pb weighted mean age of 1851±18 Ma (MSWD =1.2), which represents the age of the pluton emplacement. The age of 803±170 Ma at the lower intercept in the concordia diagram corresponds to the age of a later deformation event which affected the pluton, and suggests that the Huashanguan pluton was influenced by Neoproterozoic thermo-tectonic events after its formation. The discovery of Paleoproterozoic Huashanguan rapakivi granites indicates continental rifting or a post-orogenic extensional event that took place in the Paleoproterozoic in the Yangtze block. These events may be related to the breakup of the Paleoproterozoic Columbia supercontinent.

Mid-Neoproterozoic angular unconformity in the Yangtze Block revisited: Insights from detrital zircon U–Pb age and Hf–O isotopes

“…The ca. 1.86 Ga zircon grains have similar age and Hf isotope compositions with A-type granites (Xiong et al, 2009;Zhang et al, 2011) and mafic dykes in the northern Yangtze Block. Thus, those detrital zircons in Mid-Neoproterozoic sedimentary rocks were most likely derived from the locally exposed Paleoproterozoic mafic-granitic rocks in the northern Yangtze Block.…”

Mature Archean continental crust in the Yangtze craton: Evidence from petrology, geochronology and geochemistry

“…Nonetheless, current research indicates that the age of the Quanqitang pluton is 1854 Ma [3,8,14], and the age of the Huanshanguan pluton is 1851 Ma [15]. Hence, both of these plutons are middle-late Paleoproterozic in age, and they share the same tectonic setting associated with rifting of the Columbia supercontinent during the Paleoproterozic.…”

“…To date within the Yangtze craton, the Quanqitang granite and Huashanguan pluton have been recorded as the oldest K-granites [4,8,15], the age of which are middle Paleoproterozoic (ca. 1850 Ma).…”

Formation and evolution of Precambrian continental lithosphere in South China

“…Peng et al (2009) found a dolerite dyke with similar U-Pb ages around 1.85 Ga and ε Hf (t) values of −6.3 to 0.5 in the Kongling complex, implying that they were derived from partial melting of an enriched mantle source. Zhang et al (2011) reported an A-type granite with a U-Pb age of 1851±18 Ma at Zhongxiang, to the east of the Kongling complex. As shown in Fig.…”