Complex Paleozoic magmatic and metamorphic evolution in the Argentera Massif (Western Alps) resolved with U-Pb dating
Complex Paleozoic magmatic and metamorphic evolution in the Argentera Massif (Western Alps) resolved with U-Pb dating
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发表时间：
2001
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通讯作者：
D. Rubatto;U. Schaltegger;B. Lombardo;R. Compagnoni
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作者：
D. Rubatto;U. Schaltegger;B. Lombardo;R. Compagnoni
用U-Pb测年法研究了Gesso-Stura地体（西北部，外结晶地块）阿尔卑斯山前岩浆作用和变质作用的时间。榴辉岩中锆石的常规ID-TIMS分析将辉长岩原岩的侵入时间限定在462 ± 6 Ma，与同一样品的离子探针年龄457 ± 6 Ma一致。无论其原始岩浆分区，从榴辉岩的锆石遭受铅损失在一个或多个热事件。较低的不一致截距（323 ± 12 Ma）和离子探针测得的最年轻锆石环（330 ± 5 Ma）将最后一次变质事件，即华力西斜长角闪岩相变质作用的时代限定为纳穆里期。变质安山岩中的锆石表明酸性岩浆结晶于晚奥陶世，结晶时间为443 ± 3 Ma。对华力西期深熔作用影响下的二长岩进行锆石离子探针测年，得到侵入年龄为332 ± 3 Ma。我们的研究结果有助于重建前阿尔卑斯山的演化的Gesso-Stura地形的Alterntera基底，记录了几个岩浆和变质事件之间的时间跨度早奥陶世和晚石炭世。定年岩石中锆石的行为对U-Pb年代学具有一定的意义
The timing of pre-Alpine magmatism and metamorphism in the Gesso-Stura Terrain (NW Argentera massif, External Crystalline Massifs) has been investigated by U-Pb dating. Conventional ID-TIMS analysis of zircons from an eclogite constrained the intrusion of the gabbroic protolith at 462 ± 6 Ma, in agreement with an ion microprobe age of 457 ± 6 Ma on the same sample. Regardless of their pristine magmatic zoning, the zircons from the eclogite suffered lead loss during one or more thermal events. A lower discordia intercept (323 ± 12 Ma) and the youngest zircon rim dated by ion-microprobe (330 ± 5 Ma) constrain the age of the last of these events, i.e. the Variscan amphibolite-facies metamorphism, to the Namurian. Zircon from a metadacite indicates that the acid magma crystallised during Late Ordovician at 443 ± 3 Ma. Ion microprobe dating of zircon from a monzonite affected by Variscan anatexis yielded an intrusion age of 332 ± 3 Ma. Our results help reconstructing the pre-Alpine evolution of the Gesso-Stura terrain of the Argentera basement, which records several magmatic and metamorphic events in the time span between Early Ordovician and Late Carboniferous. The zircon behaviour in the dated rocks bears some implications for U-Pb geochronology