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 207Pb/206Pb 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.
Highlights
The Huashanguan rapakivi pluton in Zhongxiang, Hubei Province, China, is the first discovered Proterozoic rapakivi pluton in the Yangtze block
Archean rocks are widely exposed in the North China block, and there are many records of the Proterozoic tectonothermal events related to the amalgamation and breakup of the Columbia supercontinent [10,15,16,17,18,19,20,21,22,23,24], including the Miyun Proterozoic typical rapakivi granites in Beijing [5,6,7,10]
There have been no reports of any Paleoproterozoic rapakivi granites within the Yangtze block
Summary
The Huashanguan rapakivi pluton in Zhongxiang, Hubei Province, China, is the first discovered Proterozoic rapakivi pluton in the Yangtze block. 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. Archean rocks are widely exposed in the North China block, and there are many records of the Proterozoic tectonothermal events related to the amalgamation and breakup of the Columbia supercontinent [10,15,16,17,18,19,20,21,22,23,24], including the Miyun Proterozoic typical rapakivi granites in Beijing [5,6,7,10]. As a result of dynamic metamorphism, the intrusions and the country rocks suffered a certain degree of deformation1)
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