冀北红旗营子杂岩的锆石、独居石年代学及地质意义

Zircon and monazite geochronology of the Hongqiyingzi complex, northern Hebei, China

较为详细的SHRIMP、LA-ICPMS锆石U-Pb年代学和独居石电子探针Th-U-Pb化学法定年揭示,隆化-凤山地块的石英闪长质片麻岩和石榴黑云二长花岗质片麻岩分别形成于2484Ma和2180Ma,同时存在3164～2553Ma的锆石记录和约1854Ma的变质改造事件;细粒二长花岗岩形成于413Ma,独居石内核记录了约628Ma的继承年龄。凤山-丰宁地块的钾长花岗质糜棱片麻岩、角闪黑云石英闪长质片麻岩和黑云母二长花岗岩分别形成于1876Ma、1838Ma和1810Ma,其中存在2042～1904Ma的捕获锆石,遭受了1756Ma、1694Ma和313.5Ma的多期改造,其中晚古生代的构造-岩浆-变质事件的改造尤为强烈。赤城-崇礼地块的角闪黑云花岗闪长质片麻岩分别形成于2535Ma和2529～2480Ma,石榴英云闪长质片麻岩和石榴黑云斜长变粒岩分别形成于1871Ma和1841Ma,发现有约2602Ma的继承锆石,并记录了从古元古代到晚古生代多阶段的改造事件,尤其清楚地记录了343～320Ma的地质事件。结合前人的年代学资料,综合分析上述地质年代学的特征,认为红旗营子杂岩从东到西可能由不同来源的微陆块组成,这些微陆块都经历了晚古生代的构造-岩浆-变质事件,可能在古生代晚期才与华北克拉通北缘拼贴。

Detailed SHRIMP and LA-ICPMS zircon U-Pb isotopic dating and EMPA monazite Th-U-Pb chemical dating revealed the zircon and monazite geochronology of three blocks. In the Longhua-Fengshar block, quartz dioritic gneiss and garnet-biotite monzonitic gneiss formed at 2484 and 2180 Ma respectively, and the zircons preserved the record between 3164 and 2553 Ma and the metamorphic event at -1854 Ma; fine-grained monzonite formed at 413 Ma, while the core of monazite in this rock recorded an inherited age of-628 Ma. In the Fengshan-Fengning block, the granitic mylonite gneiss, amphibole-biotite-quartz dioritic gneiss and biotite monzonite formed at 1876, 1838 and 1810 Ma respectively, which contain xenocrystal zircom ranging in age between 2042 and 1904 Ma; these rocks were subjected to polyphase reworking at 1756, 1694 and 313.5 Ma, especially the Late Paleozoic tectonic-magmatic-metamorphic event. In the Chicheng-Chongli block,amphibole-biotite granodioritic gneiss formed at 2535 and 2529-2480 Ma, while the garnet tonalitic gneiss and garnet-biotite-plagioclase fine-grained gneiss formed at 1871 and 1841 Ma respectively; these rocks contain ~2602 Ma old inherited zircon and recorded multi-stage reworking events fi＇om Paleoproterozoic to Late Paleozoic, particularly the geological event between 343 and 320 Ma. The above geochronological data, together with the data of other researchers, suggest that the Hongqiyingzi complex may be composed of microblocks of different origins, all of which experienced the Late Paleozoic tectonic-magmatic-metamorphic event, indicating that these microblocks were not amalgamated with the northern margin of the North China croton until the Late＇ Paleozoic.