北淮阳地区中生代火山岩成岩年代学及构造动力学背景

来源期刊:中南大学学报(自然科学版)2021年第2期

论文作者:张德贤 郭兆清

文章页码:478 - 489

关键词:锆石U-Pb年龄;Hf同位素;火山岩;构造动力学背景;北淮阳

Key words:zircon U-Pb age; Hf isotope; volcanic rocks; geodynamic setting; North Huaiyang

摘    要:北淮阳地区火山岩分布广泛,其喷发可分为3个旋回且为连续喷发。利用锆石U与Pb质量分数之间的关系即U-Pb测年和Hf同位素分析技术,选取北淮阳地区舒城、晓天、响洪甸、金刚台及信阳等地区的火山岩进行研究。研究结果表明:北淮阳地区舒城、晓天、响洪甸、金刚台及信阳等地区的火山岩的年龄分别为(126.29±0.80),(124.90±0.50),(131.17±0.83),(129.10±3.20)和(130.20±2.10) Ma,表明该地区火山均沿着深大断裂几乎同时间断性喷发,喷发时限在126~135 Ma之间;火山岩中锆石的初始铪同位素标准化值εHf(t)为-18.74~-35.26,由此计算所得亏损地幔的两阶段模式年龄变化范围为2.4~3.2 Ga,表明该地区火山岩主要由太古宙再循环基底地壳熔融而成,来源于下地壳;大别造山带早白垩世拆沉作用造成造山带核部和北淮阳构造带之间的差异性隆升,在北淮阳构造带内形成滑覆伸展构造,同时,拆沉作用引起上地幔和下部地壳部分熔融形成的岩浆快速上升,从而出现强烈的火山喷发,形成大规模的早白垩世火山岩盆地。

Abstract: Volcanic rocks are widely distributed in North Huaiyang area, and their eruptions can be divided into three cycles. The zircons in volcanic rocks from Shucheng, Xiaotian, Xianghongdian, Jingangtai and Xinyang in North Huaiyang area were selected for U-Pb dating and Hf isotope analyses. The results show that zircon ages of Shucheng Xiaotian, Xianghongdian, Jingangtai and Xinyang are (126.29±0.80), (124.90±0.50), (131.17±0.83), (129.10±3.20) and (130.20±2.10) Ma, respectively, indicating that all the volcanoes erupt simultaneously along the deep fault and regional faults, and activated age is from 126 Ma to 135 Ma. The initial Hf isotopic normalized values of zircon εHf(t) varies from -18.74 to -35.26, and calculated two-stage model ages ranges from 2.4 Ga to 3.2 Ga, indicating that volcanic rocks in this area are mainly originated from the Archaean recycled basement crust, which is derived from the lower crust. The early Cretaceous delamination of the Dabie orogenic belt results in the differential uplift between the core of the orogenic belt and the North Huaiyang structural belt, forming a sliding extensional structure in the North Huaiyang structural belt. Magmas from the partial melting of the upper mantle and lower crust caused by the delamination increase rapidly, then results in the strong volcanic eruption and forms a large-scale volcanic basin during the early Cretaceous.

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