Geochemistry of extrusive rocks at Khun Dan Prakan Chon Dam site, Nakhon Nayok Province, Thailand

Abstract

The extrusive rock samples were collected from outcrops at Khun Dan Prakarn Chon Dam site, Nakhon Nayok Province. They are parts of the Pre-Cretaceous Khao Yai Volcanics located at the southern end of the western Loei-Petchabun-Nakhon Nayok Volcanic Subbelt. Petrological study found that the extrusive rock samples can be classified into four groups: felsic pyroclastic rocks, felsic volcanic lava flows, mafic pyroclastic rocks, and mafic-to-intermediate volcanic/hypabyssal rocks. Geochemical characteristics of the extrusive rock samples, however, can be divided into two groups which are mafic-to-intermediate extrusive rocks and felsic extrusive rocks. Although the major and some trace element signatures of these extrusive rocks are identical to those of typical calc-alkalic magmas, the tectonic discrimination diagrams for least-altered rocks showed that they were different in the magmatic suite and erupting episode; and discriminant diagrams can be successfully used to identify the tectonic environments of extrusive rocks and to evaluate the tectonic setting of a region. Incompatible trace element plot on the tectonic discrimination diagrams for the mafic-to-intermediate extrusive rock samples indicated high affinity with a within-plate tectonic setting, while felsic extrusive rock samples had high affinity with continental volcanic arc tectonic setting. In addition, the tectonic setting of these mafic-to-intermediate extrusive rock samples could be correlated to the Khiao Andesite located in the east of studied area. Dykes could be associated with multiple arc magmatism in Loei Fold Belt and resulted in the subduction in the Late Permian.