南秦岭佛坪泥盆纪砂岩锆石U—Pb定年及Hf同位素分析：对物质源区和构造环境的制约

Detrital zircon U-Pb geochronology and Devonian sandstone in the southern on the material sources and Hf isotopic compositions of Qinling belt： Constrain tectonic setting

泥盆纪地层广泛分布于南秦岭地区，为揭示南秦岭地质演化过程提供了重要的信息。目前，对于南秦岭泥盆纪沉积物源、构造环境存在争议，相关泥盆纪物质源区地壳生长仍旧缺乏深入讨论。本文通过对采自南秦岭佛坪地区泥盆纪砂岩碎屑锆石U-Pb年代学研究揭示，样品中锆石年龄主要分布于500—400Ma和1300—700Ma，少量为-1．85Ga、-2．5Ga和-2．7Ga。这些碎屑锆石U—Pb年龄和相应Hf同位素数据表明，该时期碎屑物质主要来自于南、北秦岭和华北板块南缘，缺少来自扬子板块北缘的物源供给。综合已发表的刘岭群碎屑锆石Hf同位素数据，我们识别出南秦岭泥盆纪物质源区存在3期地壳生长事件，并且分别对应于北秦岭早古生代（500—407Ma）弧岩浆岩事件、华北板块南缘新太古末期一古元古代早期（-2．5Ga）和新太古代中期（-2．7Ga）的岩浆事件。结合累积曲线分布特征和前人研究成果，我们认为刘岭群该时期为前陆盆地沉积环境。

The Devonian strata are widely distributed in the southern Qinling area, and provide significant information for revealing geological evolution of the southern Qinling belt. It is still disputing for material sources and tectonic setting of the Devonian sediments in the Southern Qinling belt, and relevant discussion of crustal growth is absent. Based on zircon U-Pb geochronology of the sandstone from the Devonian sediments in the Foping area, southern Qinling belt, it is show that the detrital zircon grains were dominantly formed at 500 - 400 Ma and 1 300 - 700 Ma. In addition, a few older zircon populations with U-Pb ages of - 1.85 Ga, - 2.5 Ga and - 2.7 Ga were also discovered. Detrital zircon U-Pb ages integrated with Hf isotope analysis show that the clastic materials were mainly derived from the southern Qinling belt, the northern Qinling belt and the southern northern China block, but lack of detritus from the northern margin of the Yangtze block. Combined with the previous published Hf isotopic data of the Liuling Group, the Devonian detrital zircons in the southern Qinling belt have recorded three significant crustal growth events in their sedimentary sources, which are corresponding to the Early Paleozoic magmatic event （500 - 407 Ma） in the northern Qinling belt, the Neoarchaean-Paleoproterozoic （ - 2.5 Ga） and Neoarchaean （ - 2.7 Ga） magmatic events in the southern northern China block, respectively. Based on the previous studies and the distribution characteristics of cumulative curves, we consider that the Liuling Group was in a foreland basin environment during this time.