Hot fluid pumping along shallow-level collisional thrusts: The Monte Rentella Shear Zone, Umbria Apennine, Italy

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• 作者：F. Meneghini^a ; ^{meneghini@dst.unipi.it} ; F. Botti^a ; ^{fbotti@dst.unipi.it} ; L. Aldega^b ; ^{luca.aldega@uniroma1.it} ; C. Boschi^c ; ^{c.boschi@igg.cnr.it} ; S. Corrado^d ; ^{corrado@uniroma3.it} ; M. Marroni^a ; ^c ; ^{marroni@dst.unipi.it} ; L. Pandolfi^a ; ^c ; ^{pandolfi@dst.unipi.it}
• 关键词：Shallow level collisional thrusts ; Fluid-driven fault-fracture mesh ; Vitrinite reflectance ; C and O stable isotopes ; Northern Apennines
• 刊名：Journal of Structural Geology
• 出版年：2012
• 期刊代码：52_01918141
• 类别：ear
• 出版时间：April, 2012
• 卷：37
• 期：Complete
• 页码：36-52
• 文件大小：4857 K

摘要

The characteristics of a shallow-level shear zone that is representative of the deformation in the external sectors of the Northern Apennine fold-and-thrust belt are described. The characterization involved an integrated approach using microstructural analysis of deformation fabrics, vitrinite reflectance measurements, XRD analysis on clay minerals and carbon and oxygen stable isotopes analyses. This data set provides the evidence that the thrust was active at very shallow depths (ca. less than 3聽km), with maximum paleotemperatures ranging from 60掳 to 100-110聽掳C. The regime during fault activity evolved through cycles of compaction and dilation linked to transient build up of fluid overpressure and injection. The alternating cycles of fluids supply generated a fault-fracture mesh with a complex network of blocky and striped veins that formed at temperatures ranging from 150掳 to 200聽掳C, not compatible with the conditions in the host rocks. This evidence implies that the shear zone was flooded by hot fluids coming upward from diagenetic and low-grade metamorphic dehydration of clay minerals active at deeper structural levels. The fluids were thus highly channelled and focused where deformation also focused, producing a local pronounced isotopic difference between fluids and host rock.