期刊
GEOLOGICAL SOCIETY OF AMERICA BULLETIN
卷 135, 期 11-12, 页码 2767-2796出版社
GEOLOGICAL SOC AMER, INC
DOI: 10.1130/B36332.1
关键词
-
The highest structural level of the Naxos metamorphic core complex, the Zas Unit, records blueschist-facies metamorphism at ca. 50 Ma during subduction, followed by crustal thickening and Barrovian metamorphism reaching peak conditions at ca. 20-15 Ma. It is suggested that the Barrovian metamorphism resulted from a 30-35 million year period of crustal thickening prior to extension, while extension led to exhumation and cooling of the crust.
Metamorphic core complexes are classically interpreted to have formed during crustal extension, although many also occur in compressional environments. New U-(Th)-Pb allanite and xenotime geochronologic data from the structurally highest Zas Unit (Cycladic Blueschist Unit) of the Naxos metamorphic core complex, Greece, integrated with pressure-temperature-time (P-T-t) histories, are incorporated into a thermal model to test the role of crustal thickening and extension in forming metamorphic core complexes. Metamorphism on Naxos is diachronous, with peak metamorphic conditions propagating down structural section over a -30-35 m.y. period, from ca. 50 Ma to 15 Ma. At the highest structural level, the Zas Unit records blueschist-facies metamorphism (-14.5-19 kbar, 470-570 degrees C) at ca. 50 Ma, during northeast-directed subduction of the Adriatic continental margin. The Zas Unit was subsequently extruded toward the SW and thrust over more proximal continental margin and basement rocks (Koronos and Core units). This contractional episode resulted in crustal thickening and Barrovian metamorphism from ca. 40 Ma and reached peak kyanite-sillimanite-grade conditions of -10-5 kbar and 600-730 degrees C at 20-15 Ma. Model P-T-t paths, assuming conductive relaxation of isotherms following overthrusting, are consistent with the clockwise P-T-t evolution. In contrast, extension results in exhumation and cooling of the crust, which is inconsistent with key components of the thermal evolution. Barrovian metamorphism on Naxos is therefore interpreted to have resulted from crustal thickening over a -30-35 m.y. time period prior to extension, normal faulting, and rapid exhumation after a thermal climax at ca. 15 Ma.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据