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华夏腹地南岭东段的桃溪群麻粒岩相变质岩的岩石化学和锆石的U-Pb-Hf同位素研究显示,其原岩是一种低成熟度的碎屑沉积岩.碎屑物质主要来源于新元古代中期(~736Ma)的花岗质(或流纹质)岩石,混有少量新太古代-古元古代物质.这期新元古代岩浆活动的时代与扬子地块第二期岩浆活动的时代一致.Hf同位素特征指示新元古代花岗质岩石是古元古代幔源地壳物质再循环(部分熔融)的产物.该变质岩原岩沉积于晚新元古代,在早古生代被挤压俯冲带到下地壳深部,在480Ma左右发生了部分熔融和结晶作用,大约在443Ma发生了麻粒岩相变质作用.这一时期形成的锆石显示了大的Hf同位素变化,εHf(t)值从?13.2增加到2.36,且具有随年龄变小εHf(t)值增加的趋势,表明在部分熔融和变质过程中有明显的地幔物质加入.计算显示该麻粒岩演化到晚中生代具有与邻区一些过铝花岗质岩石相似的同位素组成,暗示这种麻粒岩相变质岩很可能是南岭东段一些中生代过铝花岗岩的源岩.
The petrochemical and zircon U-Pb-Hf isotope studies of Taoxi Group granulite facies metamorphic rocks in the eastern Nanling area of Huaxia hinterland show that the protolith is a low-maturity clastic sedimentary rock. The granitic (or rhyolitic) rocks, derived from the mid-Neoproterozoic (~ 736 Ma), are mixed with a small amount of Neo-Archean-Paleoproterozoic material. The Neoproterozoic magmatic activity and the second phase of the Yangtze block The age of magmatic activity is consistent with the Hf isotopic characteristics indicating that the Neoproterozoic granitic rocks were the product of the recycle (partial melting) of the Paleoproterozoic crustal material that was deposited in the late Neoproterozoic and was squeezed in the Early Paleozoic Pressure subduction to the lower part of the lower crust, partial melting and crystallization took place around 480Ma, and granulite facies metamorphism occurred at about 443Ma. The zircons formed during this period showed large changes in Hf isotopes, and εHf (t) Increasing from? 13.2 to 2.36 and showing an increasing εHf (t) value with age, indicating significant mantle material addition during partial melting and metamorphism. Calculations show that this granulite evolved into a late Mesozoic with Some peraluminous granite rocks in the vicinity are similar Isotopic composition, suggesting that granulite facies metamorphic eastern Nanling probably through some of Mesozoic granites aluminum source rock.