Ages of the Hongshan granite and intruding dioritic dyke swarms, in western Junggar, Xinjiang, NW China: Evidence form LA-ICP-MS zircon chronology
新疆西准噶尔红山岩体及其中闪长质岩墙的时代——来自锆石LA-ICP-MS定年的证据

Dykes preserve important information which indicates the magma intrusion history and geodynamical environment. In order to reconstruct the Late Paleozoic geodynamical conditions of western Junggar and Central Asia, the large number of dark dioritic dykes, emplaced in Hongshan granitic pluton, in western Junggar, were studied by remote sensing interpretation, field investigation and sample analysis. It is revealed that there are two groups of dykes, namely the ring dykes and the non-ring dykes, emplaced in Hongshan granitic pluton. From the ring centre to margin the thickness and grain size of the ring dykes decrease gradually. The non-ring dykes, without obvious variety in thickness and grain size, cut the ring dykes at many outcrops. The zircon 206Pb/238U ages of the ring dykes, the non-ring dykes and the host rock were obtained, by LA-ICP-MS zircon U-Pb dating, including 3 samples from the ring dykes, 2 samples from the non-ring dykes and 1 sample from the host rock were analyzed. Their ages are 304±1Ma, 302±1Ma and 303±1Ma for the ring dykes, 302±1Ma and 302±1Ma for the non-ring dykes, and 304±1Ma for the host rock. Considering these chronology data and the contact relationships among the ring dykes, the non-ring dykes and the host rock, the host rock was formed at 304Ma, the ring dykes are formed at 303Ma, and the non-ring dykes are formed at 302Ma, approximately. These chronology data imply that there were different kinds of magma intrusions in western Junggar and the fractures filled by later dioritic magma were formed in Late Carboniferous, and provide reliable time constrains for further study of Late Paleozoic geodynamical conditions in western Junggar and Central Asia.