胶莱盆地早白垩世瓦屋夼组砂岩中碎屑锆石U-Pb-Hf同位素组成及其构造意义

摘要

LA-ICP-MS U-Pb dating and in situ Hf isotope analysis were carried out for the detrital zircons to constrain the depositional age and provenance of the Wawukuang Formation, which is believed as the earliest unit of the Laiyang Group in the Jiaolai Basin, and its implications. Most of these detrital zircons from the feldspar quartz sandstone in the Wawukuang Formation are magmatic in origin, which are euhedral-subhedral and display oscillatory zoning in CL images; whereas few Late Triassic detrital zircons are metamorphic in origin and structureless in CL images. U-Pb isotopic dating of 82 zircon grains yields age populations at ca. 129 Ma, 158 Ma, 224 Ma, 253 Ma, 461 Ma, 724 Ma, 1851 Ma and 2456 Ma. U-Pb dating and Hf isotopic results indicate that:1) the Wawukuang Formation deposited during the Early Cretaceous (129–106 Ma);2) the detrital zircons with the ages of 1851 Ma and 2456 Ma mainly sourced from the Precambrian basement rocks of the North China Craton;the Neoproterozoic (729–721 Ma) magmatic zircons and the Late Triassic (226–216 Ma) metamorphic zircons sourced from the Su-Lu terrane; The Late Paleozoic detrital zircons could source from the Late Paleozoic igneous rocks in the northern margin of the North China Craton;the Late Triassic (231–223 Ma) magmatic zircons and the 158–129 Ma zircons sourced from the coeval igneous rocks in the Jiaobei and Jiaodong;3) the deposition age and provenance of the Jiaolai Basin are different from those of the Hefei Basin; 4) the recognition of clastic sediments from the Su-Lu terrane in the Wawukuang Formation suggests that the Su-Lu terrane was under denudation in the Early Cretaceous.%本文报道了胶莱盆地莱阳群最底部瓦屋夼组长石石英砂岩中碎屑锆石的LA-ICP-MS U-Pb年代学和原位Hf同位素分析结果，进而约束了瓦屋夼组砂岩的沉积时代和物源及其构造意义。碎屑锆石多数呈自形–半自形晶，发育岩浆生长环带，暗示它们为岩浆成因；少数晚三叠世锆石呈均匀无结构的阴极发光特点，缺乏岩浆环带，暗示它们为变质锆石。82个谐和年龄的峰值分别为129 Ma、158 Ma、224 Ma、253 Ma、461 Ma、724 Ma、1851 Ma和2456 Ma。上述定年结果结合原位Hf同位素分析表明：(1)瓦屋夼组的沉积时代为早白垩世(129~106 Ma)；(2)1851 Ma、2456 Ma年龄的锆石主要来源于华北克拉通前寒武纪基底岩石；新元古代(729~721 Ma)岩浆锆石和晚三叠世(226~216 Ma)变质锆石来源于苏鲁造山带；晚古生代锆石记录了华北克拉通北缘同时代的岩浆事件；晚三叠世(231~223 Ma)岩浆锆石和158~129 Ma锆石则与胶北、胶东同时期的岩浆事件相对应；(3)胶莱盆地与合肥盆地具有不同的沉积时代和物源属性；(4)瓦屋夼组中苏鲁造山带物源的存在，暗示苏鲁高压–超高压变质岩石至少在早白垩世时期已经出露地表。