Petrogenesis of the Mesozoic Malage complex pluton in the East Inner Mongolia：Constraints on the regional tectonic evolution

 In this paper, Zircon U-Pb age and whole rock geochemical analyses of the Malage complex pluton in the southern part of the Xing 'an Block are reported, in order to further understand the important scientific problem of spatio-temporal scope of influence of two tectonic systems (Mongolia-Okhotsk Ocean and Paleo-Pacific) in Northeast China. The study shows that the Malage complex pluton is composed of two stages of granite, the early stage is the lithologic combination of quartz monzonite diorite, monzogranite and alkali-feldspar granite, and indicate that they intruded at 225 ± 1Ma and 220 ± 2Ma, i.e., late Triassic; The granite-porphyry intruded at 124±1Ma, i.e., late Early Cretaceous. The granites of the two stages is I-type granite and belongs to the high K calc-alkaline series, but the difference lies in the high degree of differentiation of late granite-porphyry. They are characterized by enrichment of large ion lithophilic elements (Rb, Ba, K) and light rare-earth elements (LREE), different degrees of loss (Ta, Nb, P, Ti) in high field strength elements (HFSE) and heavy rare-earth elements (HREE), low total rare earths (ΣREE=34.25×10^-6~217.91×10^-6), different degrees of europium loss(δEu=0.40~0.84). Combined with geological setting, the Malage complex pluton indicates that the influence range of Late Triassic Mongolian-Okhotsk Ocean subduction may have reached the southern part of the Xing'an block; In late Early Cretaceous, the regional structure was in an extensional setting, which was inferred to be the result of the joint action of the extension after the closure of the Mongolia-Okhotsk Ocean and retreat of the Paleopacific subduction, especially closely associated with the latter.