The causes of the high-pressure granulite Shandong Peninsula granitic light-colored veins

Thin layers and lenses of granitic leucosome are widely distributed within high-pressure (HP) mafic granulite from the Early Precambrian metamorphic basement of Shandong Peninsulu, SE North China Craton. They are parallel to, or cross-cut, foliations in the host rocks at different scales and show evidence of coalescence and migration to form centimeter-to decimeter-scale segregations. A combined study of mineral inclusions, cathoduluminescence (CL) images, U-Pb LA-ICP-MS dates, and in-situ trace element compositions of zircon provide clear evidence on the nature and timing of partial melting within the Early Precambrian metamorphic basement of Shandong Peninsula. Most zircons as newly crystals commonly show perfectly euhedral shapes, have pronounced oscillatory zoning and contain felsic mineral inclusions, such as quartz (Qtz) + K-feldspar (Kfs) + plagioclase (PI) ± apatite (Ap). The REE patterns are remarkably flat for the HREE with strongly and moderately negative Eu anomalies (Eu/Eu * = 0. 13 ∼ 0. 65) and pronounced positive Ce anomalies (Ce/Ce* =11 ∼32). These new zircons show dispersive U content (31 × 10-6 ∼779 × 10 -6) with pronounced low Th content (0. 03×10-6 ∼ 1. 3 × 10-6) and Th/U ratio (<0. 0081). This strongly suggests that the new zircons are anatectic in origin and that the granitic leucosomes within HP granulite may be injected melts, derived from nearly meta-supracrustal rocks, such as khondalite series. Abundant U-Pb spot analyses of the anatectic zircons reveal a meaningful age of partial melting within the Early Precambrian metamorphic basement of Shandong Peninsula. Forty anatectic zircon domains from granitic leucosome sample HP1 yield consistent U-Pb ages of 1870±11Ma to 1843 ±20Ma (2a), with a weighted mean of 1859. 6 ±2. 2Ma (MSWD =0.74). These data together with previous studies imply that the Early Precambrian metamorphic basement within Shangdong Peninsulu experienced a Paleoproterozoic partial melting event, which was probably associated with a post-peak middle-low pressure granulitefacies stage of 'hot' exhumation rather than a peak HP granulite-facies stage. This partial melting event induced extensive retrograde metamorphism of the HP granulites and their country rocks distributed within the Shandong Peninsula.