Contemporaneous plutonism and strike‐slip faulting: A case study from the Tonale fault zone north of the Adamello pluton (Italian Alps)
Contemporaneous plutonism and strike‐slip faulting: A case study from the Tonale fault zone north of the Adamello pluton (Italian Alps)
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DOI：
10.1029/2003tc001515
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发表时间：
2004-06
期刊：
影响因子：
4.2
通讯作者：
Michael Stipp;B. Fügenschuh;L. Gromet;Holger Stünitz;Stefan M. Schmid
中科院分区：
文献类型：
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作者：
Michael Stipp;B. Fügenschuh;L. Gromet;Holger Stünitz;Stefan M. Schmid
对东托纳勒断裂带沿着同时期深成岩作用和走滑断层作用的野外、显微构造和年代学研究为岩浆侵位、接触变质和剪切作用之间的相互关系提供了新的见解，并为亚得里亚海周围断裂系统提出了新的时间限制。岩体侵位与剪切作用虽然不是相互作用的结果，但在接触变质作用中是相互作用的。Tonale复合断裂带的性质随其靠近Adamello岩体的北方边缘而变化很大，从西部的一对绿片岩相糜棱岩带（北方糜棱岩带）和碎裂断裂带，到东部的由北方糜棱岩带、碎裂断裂带和第二糜棱岩带（南方糜棱岩带）组成的断裂带，后者是由同生剪切和接触变质作用形成的。持续的走滑运动导致变形接触晕的伸缩和平流冷却。最北端的Adamello侵入体（Avio为34.6 - 1.0 Ma，Presanella为32.0 - 2.3 Ma）的新U/Pb锆石年龄确定了接触变质作用的开始。Rb-Sr和K-Ar冷却年龄和新的锆石裂变径迹年龄提供了证据，表明侵入后迅速冷却至300°C以下，即，大约3千万年前，与环境温度约为250°C时的浅地壳侵位一致。激变的右旋走滑断层作用持续到20 Ma左右，这时Tonale断层带被一些较小的左旋剪切和Giudicarie断层所抵消。因此，沿着Bergell岩体以东的Periadriatic断层系统的右行走滑运动沿着持续了大约3500万至2000万年前。
A field, microstructural, and geochronological study of contemporaneous plutonism and strike‐slip faulting along the eastern Tonale fault zone provides new insights into the interrelationships between magmatic emplacement, contact metamorphism and shearing, and it places new time constraints for the Periadriatic Fault System. Although pluton emplacement and shearing were not caused by each other, they mutually interacted during contact metamorphism. The character of the composite Tonale fault zone varies considerably with its proximity to the northern margin of the Adamello pluton, from a paired greenschist facies mylonite belt (Northern mylonite zone) and cataclastic fault zone in the west, to a fault zone consisting of Northern mylonite zone, Cataclastic fault zone and a second mylonite belt (Southern mylonite zone) formed by contemporaneous shearing and contact metamorphism in the east. Ongoing strike‐slip motion led to telescoping and advective cooling of the deforming contact aureole. New U/Pb zircon ages for the northernmost Adamello intrusions (the Avio at 34.6‐1.0 Ma and the Presanella at 32.0‐2.3 Ma) date the onset of contact metamorphism. Rb‐Sr and K‐Ar cooling ages and new zircon fission track ages provide evidence that postintrusive cooling to below 300°C was achieved rapidly, i.e., approximately 30 Myr ago being consistent with a shallow crustal emplacement at ambient temperatures of approximately 250°C. Cataclastic dextral strike‐slip faulting continued until about 20 Ma, when the Tonale fault zone became offset by a number of minor sinistral shears, and by the Giudicarie fault. Hence dextral strike‐slip motion along the Periadriatic Fault System east of the Bergell pluton lasted from approximately 35–20 Myr ago.