Jacobs J, Paoli G, Rocchi S, Ksienzyk A K, Sirevaag H, Elburg M A
Department of Earth Science, University of Bergen, P.O.Box 7800, 5020, Bergen, Norway.
Dipartimento di Scienze della Terra, Università di Pisa, Pisa, I-56126, Italy.
Sci Rep. 2018 Feb 9;8(1):2704. doi: 10.1038/s41598-018-20979-w.
We have traced the particle path of high-pressure metasedimentary rocks on Elba Island, Northern Apennines, with the help of a U-Pb-Hf detrital zircon study. One quarter of the analysed zircons are surprisingly young, 41-30 Ma, with a main age peak at ca. 32 Ma, indicating an unexpected early Oligocene maximum deposition age. These Oligocene ages with negative εHf indicate a volcanic source region in the central-southern Alps. Though young by geological means, these zircons record an extraordinary geodynamic history. They originated in a volcanic arc, during the convergence/collision of the the Adria microplate with Europe from ca. 65 to 30 Ma. Thereafter, the Oligocene zircons travelled ca. 400 km southward along the Adria margin and the accretionary prism to present-day Tuscany, where they were subducted to depths of at least 40 km. Shortly thereafter, they were brought to the surface again in the wake of hinge roll back of the Apennine subduction zone and the resulting rapid extensional exhumation. Such a zircon roller coaster requires a microplate that has back-to-back subduction zones with opposing polarities on two sides.
我们借助U-Pb-Hf碎屑锆石研究，追踪了亚平宁山脉北部厄尔巴岛上高压变质沉积岩的颗粒路径。四分之一的分析锆石年龄出奇地年轻，为41 - 30 Ma，主要年龄峰值约为32 Ma，表明存在一个意外的渐新世早期最大沉积年龄。这些具有负εHf值的渐新世年龄表明其源区为阿尔卑斯山脉中南部的一个火山源区。尽管从地质角度看这些锆石很年轻，但它们记录了一段非凡的地球动力学历史。它们起源于一个火山弧，时间大约在65至30 Ma期间，当时亚得里亚微板块与欧洲板块汇聚/碰撞。此后，渐新世锆石沿着亚得里亚边缘和增生楔向南移动约400公里至现今的托斯卡纳地区，在那里它们被俯冲到至少40公里的深度。此后不久，随着亚平宁俯冲带的枢纽回滚以及由此产生的快速伸展剥露，它们再次被带到地表。这样的锆石“过山车”历程需要一个在两侧具有相反极性的背对背俯冲带的微板块。
