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报道了平水群角斑质岩石的LA-ICP-MS锆石U-Pb年龄和Hf同位素以及全岩地球化学组成,讨论了其岩石成因和地质意义.研究结果表明,来自平水群的角斑岩形成于(904±8)~(906±10)Ma.地球化学组成上,这些中酸性岩浆岩相对富集轻稀土,亏损重稀土和高场强元素(Nb,Ta,Ti和P),类似于岛弧环境下岩浆作用的产物.这些角斑岩具极高的锆石初始Hf同位素组成[εHf(t)=8.6~15.4],能较好地对应其全岩初始Nd同位素组成[εNd(t)=6.4~7.9],远超过一般壳源岩石的Nd-Hf同位素体系.因此,它们可能是新元古代早期弧-陆碰撞过程中对年轻岛弧地壳即时再造的产物.结合锆石Hf模式年龄,认为扬子板块东南缘除了有Grenville期(1.3~1.1Ga)的地壳生长外,在新元古代早期(约1000~900Ma),局部(平水地区)可能还存在一次非常重要的年轻岛弧地壳生长事件.
The LA-ICP-MS zircon U-Pb age, Hf isotope and whole-rock geochemistry of the hornblende from Pingshui Group are reported, and the genesis and geologic significance of the rocks are discussed.The results show that the porphyry from the Pingshui Group (904 ± 8) to (906 ± 10) Ma. These intermediate-acidic magmatic rocks are relatively enriched in light rare earths, depleted in heavy rare earths and high-field elements (Nb, Ta, Ti and P) They are the product of magmatic activity under island arc environment.These horn porphyries have extremely high initial Hf isotopic composition of zircon [εHf (t) = 8.6 ~ 15.4], corresponding well with the initial Nd isotope composition of whole rock [εNd ( t) = 6.4 ~ 7.9], far exceeding the Nd-Hf isotopic compositions of the general crustal rocks, and therefore they may be the products of the immediate re-creation of the young island arc crust during the early Neoproterozoic arc- In the early Neoproterozoic (about 1000-900 Ma), there may be a very important young island arc in the local (Pingshui area) besides the Grenville (1.3 ~ 1.1Ga) crustal growth on the southeast margin of the Yangtze plate. Crustal growth events.