扬子北缘下高川盆地上泥盆统铁矿梁组沉积物源分析

下高川盆地为扬子地块和秦岭造山带结合处的特殊构造单元，其构造演化与相邻的构造单元存在明显差异，晚泥盆世尤为突出。为全面理解下高川盆地的构造演化，重点研究了下高川盆地上泥盆统铁矿梁组砂岩的沉积物源。以石英砂岩为研究对象，分析重矿物组成，进而进行电气石电子探针分析和LA-MC-ICP-MS锆石U-Pb定年。砂岩样品的闪锌矿、白钛石、钛铁矿重矿物组合说明其物源为岩浆岩。电气石电子探针分析结果表明，铁矿梁组石英砂岩主要来自于变质板岩和变质砂岩，少量为贫锂花岗岩类、伟晶岩和细晶岩。砂岩锆石U Pb年龄谱分析表明，铁矿梁组砂岩的主要物源来自425~530 Ma的天水和丹凤花岗岩、佛坪片麻岩、清水英安岩，以及578~982 Ma的柞水（黑沟）碱性花岗岩、天水和西峡的花岗质片麻岩、丹凤和卢氏的花岗岩。另外，1 015~1 551 Ma的佛坪黑云母斜长片麻岩，1 658~1 957 Ma的太白和宝鸡花岗岩、佛坪片麻岩，2 329~2 502 Ma的丹凤石榴黑云斜长片麻岩和2 625~3 147 Ma的商南太古宙结晶基底岩石均经历多次搬运，为扬子北缘下高川盆地提供次要物源。综合区域资料，晚泥盆世的物源大致来自北部，同时古地理格局表现为天水、丹凤、清水、西峡等地区岩体隆升剥蚀，成为物源区，而在华北古陆与扬子北缘下高川盆地之间可能存在多个较小古陆，如佛坪也属于物源区。

Analysis of Sediment Provenance of Upper Devonian Tiekuangliang Formation in Xiagaochuan Basin,the Northern Margin of Yangtze Plate

Xiagaochuan Basin is a special tectonic unit between Yangtze Block and Qinling orogen. The tectonic evolution of Late Devonian is obviously different from that of the adjacent tectonic units. In order to understand the tectonic evolution of Xiagaochuan Basin, the sediment provenance of sandstone of Upper Devonian Tiekuangliang Formation was studied. Taking quartz sandstone as the research object, heavy mineral assemblages were analyzed, and then the tourmaline electron microprobe analysis and LA-MC-ICP-MS zircon U-Pb dating were determined, respectively. The heavy mineral assemblages of sphalerite, leucite and ilmenite indicate that they can be provided by magmatic rocks. The tourmaline electron microprobe analysis shows that the sandstone from Tiekuangliang Formation is mainly from metapelites and metapsammites, and a small amount of Li-poor granitoids and associated pegmatites and aplites. The zircon U-Pb age spectra of sandstone suggest that the provenance of sandstone from Tiekuangliang Formation mainly comes from the rocks with the ages of 425-530 Ma and 578-982 Ma. The 425-530 Ma rocks are Tianshui and Danfeng granites, Foping gneiss and Qingshui dacite; the 578-982 Ma rocks are Zhashui (Heigou) alkaline granite, Tianshui and Xixia gneisses, and Danfeng and Lushi granites. Furthermore, the rocks including 1 015-1 551 Ma Foping biotite plagioclase gneiss, 1 658-1 957 Ma Taibai and Baoji granites, and Foping gneiss, 2 329-2 502 Ma Danfeng garnet gneiss, and 2 625-3 147 Ma Shangnan Archean crystalline basement, have undergone several transportation and provided secondary provenance from Xiagaochuan Basin, the northern margin of Yangtze Plate. Based on the regional data, the Late Devonian provenance is roughly from the north. Meantime, the paleogeographic pattern shows that the rocks in Tianshui, Danfeng, Qingshui and Xixia areas are uplifted and eroded, becoming the provenance areas. Moreover, there are many small oldlands between North China paleoland and Xiagaochuan Basin, the northern margin of Yangtze Plate, such as Foping, which is also the provenance area.