关键词: 孔兹岩系, 大理岩, 长石砂岩, LA-ICP-MS锆石U-Pb, 古元古代

Abstract:

Our research area is located in Jining, the eastern section of the Khondalite belt in the western block of the North China craton, where the khondalite series is composed of garnet-biotite gneiss in the lower part and marble in the upper part. Several layers of felsic gneiss interbedded with thin marble layers are found, and the parental rock of the felsic gneiss is defined as feldsparthic sandstone by petrographical study, zircon characteristics and restoring the protolithic types. After LA-ICP-MS zircon U-Pb dating of the felsic gneiss, 72 zircon data are obtained from 70 zircon grains, among which the youngest detrital zircon data is (2 091±20) Ma that can represent the lower limit of felsic gneiss formation age; And the weighted average ²⁰⁷Pb/²⁰⁶Pb apparent age of the 19 metamorphic zircon concentrated between 1.8-1.9 Ga is (1 852±15) Ma（MSWD=0.7）, can represent the upper limit of deposition age of the original rock of the felsic gneiss. Based on the previous research results, we could conclude that in Jining area, marbles in the khondalite series were formed in the Paleoproterozoic Era between (1 852±15) Ma and (2 091±20) Ma, and underwent the regional metamorphism in (1 852±15) Ma. This suggests that marbles are the important component of the khondalite series; In the Khondalite belt across the western block of the North China craton, a large scale of granitic intrusion had existed in the source region of protolith of the khondalite series. However, there are different material source regions in every part of the belt; the protoliths of the khondalite series is not the in-situ deposition of fragmentary materials provided by the nearby Archean rocks, but alien tectonic rock sheet mingled with the nearby Archean rocks by Late Paleoproterozoic tectonic processes.

Key words: khondalite series, marble, feldspar sandstone, LA-ICP-MS zircon U-Pb, Paleoproterozoic