华北克拉通南缘小秦岭地区新太古代晚期-古元古代晚期岩浆构造热事件:锆石U-Pb-Hf同位素和地球化学证据

为了探讨华北克拉通南缘早前寒武纪形成演化，对华北克拉通南缘小秦岭地区早前寒武纪变质基底花岗质片麻岩开展了SHRIMP U-Pb锆石定年、Hf同位素组成及地球化学组成研究，获得了2个TTG片麻岩样品~2.50 Ga的岩浆锆石年龄和时代相近的变质锆石年龄，岩浆锆石ε_Hf（t）值为0.71~4.37；1个花岗质片麻岩样品的岩浆锆石年龄为~2.30 Ga，ε_Hf（t）值为－1.21~0.11.它们也记录了古元古代晚期变质锆石年龄或显示古元古代晚期构造热事件影响的存在.岩石以轻重稀土强烈分异为特征，大离子亲石元素相对富集，Nb、P、Ti相对亏损.在小秦岭地区首次发现新太古代晚期TTG岩石，并识别出新太古代晚期构造热事件.现有资料支持华北克拉通南缘与华北克拉通其他地区具有类似的早前寒武纪形成演化历史的认识.但是，华北克拉通南缘以2.3 Ga左右岩浆作用十分发育而显示出独特性. 

Late Neoarchean-Late Paleoproterozoic Magmato-Tectonothermal Events in the Xiaoqinling Area,Southern Margin of the North China Craton,as Documented by Zircon U-Pb-Hf Isotope Analyses and Whole-Rock Geochemistry

This paper reports SHRIMP U-Pb dating results and MC-ICPMS Hf isotopes of zircons as well as whole-rock geochemical compositions on granitoidic rocks from the early Precambrian basement in the Xiaoqinling area, southern margin of the North China Craton. Two TTG gneiss samples have ~2.50 Ga and slightly younger ages for magmatic and metamorphic zircons, respectively, with magmatic zircons having ε_Hf(t) values of 0.71 to 4.37. One granitic gneiss sample has a magmatic zircon age of ~2.30 Ga and ε_Hf(t) values of -1.21 to 0.11. All samples have recorded late Paleoproterozoic metamorphic ages or the influence of the event. The rocks are similar in element composition, showing strong light to heavy REE differentiation and enrichment in LILE and depletion in Nb, P and Ti. Combined with early work, the identification of late Neoarchean TTG rocks and tectonothermal event support the conclusion that the southern margin of the North China Craton is similar in early Precambrian geological history to others all over the craton. However, the former shows its peculiarity in widespread developement of ~2.3 Ga magmatism.