冈瓦纳大陆边缘罗斯运动的岩浆活动时代:来自北维多利亚地松散沉积物锆石年龄的证据

Detrital zircon age from the glacial and littoral deposit,Northern Victoria Land,Antarctica:Implications for the timing of magmatic activity of the Ross Orogeny on the Gondwana continental margin

横穿南极大陆中部的横贯南极山脉是早古生代时期古太平洋向东冈瓦纳活动大陆边缘俯冲形成的罗斯造山带,该阶段的地层沉积、变形变质以及花岗质岩浆侵入代表了罗斯运动的演化过程。由于岩浆活动与沉积地层和变形变质在时代上存在明显差异,罗斯运动的时代仍缺乏精确的限定。通过采集北维多利亚地难言岛地区冰碛物和海岸沉积物中的松散砂砾石样品,并进行碎屑锆石U-Pb测年得出:4件不同粒径的冰碛物和海岸沉积样品中的碎屑锆石年龄峰谱具有单一峰谱的特征,年龄区间为2443~323 Ma,主要集中于530~450 Ma之间,峰值年龄约为485 Ma;锆石Th/U比值均大于0.1,而且以>0.4为主,其CL图像也具有明显的振荡环带,稀土元素特征主体具有岩浆锆石的特征,反映了样品物源区岩浆活动的时代特征。碎屑锆石年龄组成与周缘地区岩浆活动和陆内变形以及沉积地层时代基本一致,表明北维多利亚地及其周缘地区在罗斯运动晚期陆内变形阶段的岩浆活动应持续至450 Ma,这可能代表了罗斯运动结束的时代,该结果为冈瓦纳大陆边缘罗斯运动的构造演化过程提供了新的约束。

The Transantarctic Mountains across the central Antarctic continent are the Ross orogenic belt formed by westward subduction of the Paleo-Pacific underneath the East Gondwana active continent margin in the early Paleozoic.The sedimentary,deformation and metamorphism,and granitic magmatic intrusion in this stage represent the process of the Ross Orogeny.Due to the significant difference in age among the three elements mentioned above,there is no precise time defined on the Ross Orogeny.In this paper,detrital zircon U-Pb dating of gravel and sand samples from moraines and coastal sediments in the Inexpressible Island of Northern Victoria Land was carried out.The ages of four samples with different gravel diameters range from 2443 to 323 Ma and are mainly concentrated between 530~450 Ma,with a peak age of~485 Ma.Most of the zircons show oscillatory zoning in CL images and have Th/U ratios great than 0.1(mainly>0.4),with REE characteristics indicating a magmatic origin.Therefore,these ages reflect the timing of magmatic activity in the provenance of the loose sediment samples.The age composition of detrital zircons is consistent with the age of magmatic intrusion,intracontinental deformation and depositional stratigraphy in the surrounding areas,suggesting that the magmatic activity in the Northern Victoria Land and its surrounding areas might have lasted up to 450 Ma in the intracontinental deformation stage,which may represent the end time of the Ross Orogeny.These results provide a new constraint for the tectonic evolution of the Ross Orogeny on the Gondwana continental margin.