Magma mingling of Early Paleozoic intrusive rocks in western Kangxiwar, West Kunlun, China

Early Paleozoic intrusive rocks are widespread north of Sanshilifang. They may be divided into the intermediate-basic, intermediate-acid and acid types. The intermediate-basic rocks consist predominantly of pyroxene diorite. The dark-colored minerals are commonly pyroxene and plagioclase is mostly andesine. Intermediate-acid rocks are dominated by quartz diorite, which has an inhomogeneous petrofabric and in which deep-seated, dark-colored xenoliths are commonly seen. Most of these xenohths have clear-cut boundaries with their host rocks, while a few show transitional phenomenon. Under the microscope, association of unbalanced minerals and enclosure by antiphase minerals may be observed and the features of mingling of magma are conspicuous. Acid intrusive rocks are composed mainly of medium- and coarse-grained monzogranite. They contain a small number of xenoliths, whose features are the same as intermediate-acid intrusive rocks. Intermediate-basic rocks and acid rocks represent two successive continental crustal vertical growths respectively. The first mantle differentiation and continental crustal vertical growth occurred in the study area in the Cambrian, while the second extensive intrusion of basic magma occurred during post-orogenic derooting in the West Kunlun in the Late Ordovician-Early Silurian and its heat source resuited in large-scale partial melting of lower crustal material, thus generating large amount of granitic magma and leading to the second vertical growth of continental crust.