华北地块北缘晚古生代－早中生代岩浆活动期次、特征及构造背景

Tectonic evolution of northern North China Block (NCB) and its relation with the Central Asia Orogenic Belt (CAOB) during the Late Paleozoic to Early Mesozoic period have aroused considerable interest among earth scientists in recently years. A summary of the recently obtained zircon U-Pb or 39Ar-40Ar ages of the Late Paleozoic-Early Mesozoic magmatic rocks in the northern margin of NCB indicates that at least three stages of magmatism including Devonian (400~360 Ma), late Early Carboniferous to Middle Permian (330~265 Ma) and latest Permian to Triassic (250~200 Ma) occurred during the Late Paleozoic to Early Mesozoic period. The main components of the Devonian magmatism are syenite and monzonite, together with some other rocks such as monzodiorite, alkaline granite, rhyolite and maficultramafic rocks. These rocks exhibit high alkali content (K2O+Na2O) and have alkaline to high K calc-alkaline, metaluminous or weak peraluminous geochemical features. Rocks from the late Early Carboniferous-Middle Permian intrusive suite are composed mainly of diorite, quartz diorite, granodiorite and granite, with some gabbro and tonalite. The late Early Carboniferous-Middle Permian magmatic rocks have variable SiO2 content and calc-alkaline to high K calc-alkaline, metaluminous or weak peraluminous geochemical features. Some of the late emplaced magmatic rocks (latest Early Permian-Middle Permian) display shoshonitic or alkaline geochemical compositions, indicating a trend of transition from calc-alkaline to shoshonitic or alkaline series during magmatic evolution. The latest Permian magmatic rocks consist mainly of monzogranite, K-feldspar granite, syenite, monzonite, mafic-ultramafic rocks and some intermediate-felsic volcanic rocks. They are characterized by high content of SiO2, K2O and alkali (K2O+Na2O) and display geochemical signatures ranging from highly fractionated Ⅰ-type to A-type. Magmatic evolution exhibits a transition trend from high K calc-alkaline series in the early stage to the coexistence of alkaline and high K calc-alkaline series during the late stage. Compared with the Devonian and late Early Carboniferous to Middle Permian rocks, the latest Permian to Triassic magmatic rocks show much more extensive distribution. The wide distribution of the Late Paleozoic to Early Mesozoic magmatic rocks indicates a very complex tectonomagmatic history of the northern margin of the NCB during the Late Paleozoic to Early Mesozoic period. The Devonian rocks are probably related to post-collisional extension after the arc-continental collision between the Early Paleozoic Bainaimiao arc belt and the northern margin of the North China Craton during the latest Silurian to earliest Devonian period. The late Early Carboniferous to Middle Permian intrusive rocks are interpreted as subduction-related magmatic rocks emplaced in an Andean-style continental margin arc during the southward subduction of the Paleo-Asian oceanic plate beneath the NCB. The formation of large quantities of latest Permian to Triassic magmatic rocks might have resulted from post-collisional/post-orogenic lithospheric extension after final collision and suturing of the Mongolian arc terranes with the NCB.