The Palomares brittle-ductile Shear Zone of southern Spain

Ruud Weijermars

doi:10.1016/0191-8141(87)90022-8

The Palomares brittle-ductile Shear Zone of southern Spain

Ruud Weijermars^*

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

82 Scopus citations

Abstract

The Palomares Shear Zone is a major Neogene-Quaternary strike-slip zone which transects the crust of the Betic Cordillera in SE Spain. The shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology. It is emphasized that the formation of the Palomares Shear Zone was not an isolated tectonic event, but part of a complex Neogene tectonic history. The Neogene evolution of the Betic-Rif orogen and its central Alboran Basin is characterised by the following events: (1) emplacement of the Alboran Diapir with resulting nappe-shedding from the overlying crust between 25 and 20 Ma ago; (2) onset of the subsidence of the Alboran Basin between 20 and 15 Ma ago due to cooling of the Alboran Diapir and the overlying crust; (3) formation of the Cabo de Gata Volcanic Chain between 15 and 8 Ma ago; and (4) refolding of the nappe sheets in the Betic-Rif orogen into a basin and range structure about 7 Ma ago. Continuous activity of the Crevillente Fault of southern Spain may have occured over a period from 20 Ma ago up to the present. The interrelated Palomare Fault in SE Spain was probably formed between 15 and 8 Ma ago and seem to be active still. The Palomares Shear Zone affects a rock volume 44 km wide, at least 80 km long and 30 km deep. A shear strain-distance diagram constructed across the Palomares Shear Zone and its axial Palomares Fault involves a new method to estimate or constrain the shear strain magnitude along brittle-ductile shears. The typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the Palomares Fault are of the order 10^-13-10^-14 s^-1. The tensor shear strain rate along the Palomares Fault itself is of the order 10^-12s^-1 and the time averaged relative displacement rate of its walls is about 2 mm a^-1. The range of strain rates within the Palomares Shear Zone are interpreted to be due to a combination of various flow-softening mechanisms: geometric, structural, thermal and strain-rate softening. These softening mechanisms might explain the difference in vertically averaged viscosities of 10²⁰ Pa s and 10²⁵ Pa s or lower suggested for the crustal rocks in the Palomares Fault proper and that of the relatively rigid boundaries of the Palomares Shear Zone, respectively.

Original language	English
Pages (from-to)	139-143,145-157
Journal	Journal of Structural Geology
Volume	9
Issue number	2
DOIs	https://doi.org/10.1016/0191-8141(87)90022-8
State	Published - 1987
Externally published	Yes

Bibliographical note

Funding Information:
Acknowledgements--I thank the following members of the University of Amsterdam: Drs Th. B. Roep for many clarifying discussions on the geology of the Neogene basins of SE Spain and Professors Emeriti J. J. Hermes and W. P. de Roever for general discussions on the tectonic evolution of SE Spain. I also thank Dr O. J. Simon (Amsterdam) for introducing me to the intricacies of the Betic Cordillera and Dr J. P. Plan (Oxford) for supervision of my 4 months of M.Sc. field mapping in 1979. Dr. A. Allen of the University of Cork (Ireland) is thanked for advice on shear zone motions and critical comments on the original manuscript and also Professor C, J. Talbot and Miss K. Gloersen for criticising and typing, respectively, various later versions in Uppsala. Final draftwork of Figs. 7, 10 and l 1 was kindly done by Mrs C. Werstr6m All other drafts were completed by the author. The final manuscript was prepared after detailed comments of Drs. J. H. Behrmann, J. C. Bousquet and S. H. Treagus during JSG's review procedure. My work was made possible by a postgraduate teaching assistantship at the University of Amsterdam between 1981 and 1983 and grants of the Swedish Natural Science Research Council (NFR) since 1983.

ASJC Scopus subject areas

Geology

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10.1016/0191-8141(87)90022-8

Cite this

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title = "The Palomares brittle-ductile Shear Zone of southern Spain",

abstract = "The Palomares Shear Zone is a major Neogene-Quaternary strike-slip zone which transects the crust of the Betic Cordillera in SE Spain. The shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology. It is emphasized that the formation of the Palomares Shear Zone was not an isolated tectonic event, but part of a complex Neogene tectonic history. The Neogene evolution of the Betic-Rif orogen and its central Alboran Basin is characterised by the following events: (1) emplacement of the Alboran Diapir with resulting nappe-shedding from the overlying crust between 25 and 20 Ma ago; (2) onset of the subsidence of the Alboran Basin between 20 and 15 Ma ago due to cooling of the Alboran Diapir and the overlying crust; (3) formation of the Cabo de Gata Volcanic Chain between 15 and 8 Ma ago; and (4) refolding of the nappe sheets in the Betic-Rif orogen into a basin and range structure about 7 Ma ago. Continuous activity of the Crevillente Fault of southern Spain may have occured over a period from 20 Ma ago up to the present. The interrelated Palomare Fault in SE Spain was probably formed between 15 and 8 Ma ago and seem to be active still. The Palomares Shear Zone affects a rock volume 44 km wide, at least 80 km long and 30 km deep. A shear strain-distance diagram constructed across the Palomares Shear Zone and its axial Palomares Fault involves a new method to estimate or constrain the shear strain magnitude along brittle-ductile shears. The typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the Palomares Fault are of the order 10-13-10-14 s-1. The tensor shear strain rate along the Palomares Fault itself is of the order 10-12s-1 and the time averaged relative displacement rate of its walls is about 2 mm a-1. The range of strain rates within the Palomares Shear Zone are interpreted to be due to a combination of various flow-softening mechanisms: geometric, structural, thermal and strain-rate softening. These softening mechanisms might explain the difference in vertically averaged viscosities of 1020 Pa s and 1025 Pa s or lower suggested for the crustal rocks in the Palomares Fault proper and that of the relatively rigid boundaries of the Palomares Shear Zone, respectively.",

author = "Ruud Weijermars",

note = "Funding Information: Acknowledgements--I thank the following members of the University of Amsterdam: Drs Th. B. Roep for many clarifying discussions on the geology of the Neogene basins of SE Spain and Professors Emeriti J. J. Hermes and W. P. de Roever for general discussions on the tectonic evolution of SE Spain. I also thank Dr O. J. Simon (Amsterdam) for introducing me to the intricacies of the Betic Cordillera and Dr J. P. Plan (Oxford) for supervision of my 4 months of M.Sc. field mapping in 1979. Dr. A. Allen of the University of Cork (Ireland) is thanked for advice on shear zone motions and critical comments on the original manuscript and also Professor C, J. Talbot and Miss K. Gloersen for criticising and typing, respectively, various later versions in Uppsala. Final draftwork of Figs. 7, 10 and l 1 was kindly done by Mrs C. Werstr6m All other drafts were completed by the author. The final manuscript was prepared after detailed comments of Drs. J. H. Behrmann, J. C. Bousquet and S. H. Treagus during JSG's review procedure. My work was made possible by a postgraduate teaching assistantship at the University of Amsterdam between 1981 and 1983 and grants of the Swedish Natural Science Research Council (NFR) since 1983.",

year = "1987",

doi = "10.1016/0191-8141(87)90022-8",

language = "English",

volume = "9",

pages = "139--143,145--157",

journal = "Journal of Structural Geology",

issn = "0191-8141",

publisher = "Elsevier Ltd.",

number = "2",

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T1 - The Palomares brittle-ductile Shear Zone of southern Spain

AU - Weijermars, Ruud

N1 - Funding Information: Acknowledgements--I thank the following members of the University of Amsterdam: Drs Th. B. Roep for many clarifying discussions on the geology of the Neogene basins of SE Spain and Professors Emeriti J. J. Hermes and W. P. de Roever for general discussions on the tectonic evolution of SE Spain. I also thank Dr O. J. Simon (Amsterdam) for introducing me to the intricacies of the Betic Cordillera and Dr J. P. Plan (Oxford) for supervision of my 4 months of M.Sc. field mapping in 1979. Dr. A. Allen of the University of Cork (Ireland) is thanked for advice on shear zone motions and critical comments on the original manuscript and also Professor C, J. Talbot and Miss K. Gloersen for criticising and typing, respectively, various later versions in Uppsala. Final draftwork of Figs. 7, 10 and l 1 was kindly done by Mrs C. Werstr6m All other drafts were completed by the author. The final manuscript was prepared after detailed comments of Drs. J. H. Behrmann, J. C. Bousquet and S. H. Treagus during JSG's review procedure. My work was made possible by a postgraduate teaching assistantship at the University of Amsterdam between 1981 and 1983 and grants of the Swedish Natural Science Research Council (NFR) since 1983.

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N2 - The Palomares Shear Zone is a major Neogene-Quaternary strike-slip zone which transects the crust of the Betic Cordillera in SE Spain. The shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology. It is emphasized that the formation of the Palomares Shear Zone was not an isolated tectonic event, but part of a complex Neogene tectonic history. The Neogene evolution of the Betic-Rif orogen and its central Alboran Basin is characterised by the following events: (1) emplacement of the Alboran Diapir with resulting nappe-shedding from the overlying crust between 25 and 20 Ma ago; (2) onset of the subsidence of the Alboran Basin between 20 and 15 Ma ago due to cooling of the Alboran Diapir and the overlying crust; (3) formation of the Cabo de Gata Volcanic Chain between 15 and 8 Ma ago; and (4) refolding of the nappe sheets in the Betic-Rif orogen into a basin and range structure about 7 Ma ago. Continuous activity of the Crevillente Fault of southern Spain may have occured over a period from 20 Ma ago up to the present. The interrelated Palomare Fault in SE Spain was probably formed between 15 and 8 Ma ago and seem to be active still. The Palomares Shear Zone affects a rock volume 44 km wide, at least 80 km long and 30 km deep. A shear strain-distance diagram constructed across the Palomares Shear Zone and its axial Palomares Fault involves a new method to estimate or constrain the shear strain magnitude along brittle-ductile shears. The typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the Palomares Fault are of the order 10-13-10-14 s-1. The tensor shear strain rate along the Palomares Fault itself is of the order 10-12s-1 and the time averaged relative displacement rate of its walls is about 2 mm a-1. The range of strain rates within the Palomares Shear Zone are interpreted to be due to a combination of various flow-softening mechanisms: geometric, structural, thermal and strain-rate softening. These softening mechanisms might explain the difference in vertically averaged viscosities of 1020 Pa s and 1025 Pa s or lower suggested for the crustal rocks in the Palomares Fault proper and that of the relatively rigid boundaries of the Palomares Shear Zone, respectively.

AB - The Palomares Shear Zone is a major Neogene-Quaternary strike-slip zone which transects the crust of the Betic Cordillera in SE Spain. The shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology. It is emphasized that the formation of the Palomares Shear Zone was not an isolated tectonic event, but part of a complex Neogene tectonic history. The Neogene evolution of the Betic-Rif orogen and its central Alboran Basin is characterised by the following events: (1) emplacement of the Alboran Diapir with resulting nappe-shedding from the overlying crust between 25 and 20 Ma ago; (2) onset of the subsidence of the Alboran Basin between 20 and 15 Ma ago due to cooling of the Alboran Diapir and the overlying crust; (3) formation of the Cabo de Gata Volcanic Chain between 15 and 8 Ma ago; and (4) refolding of the nappe sheets in the Betic-Rif orogen into a basin and range structure about 7 Ma ago. Continuous activity of the Crevillente Fault of southern Spain may have occured over a period from 20 Ma ago up to the present. The interrelated Palomare Fault in SE Spain was probably formed between 15 and 8 Ma ago and seem to be active still. The Palomares Shear Zone affects a rock volume 44 km wide, at least 80 km long and 30 km deep. A shear strain-distance diagram constructed across the Palomares Shear Zone and its axial Palomares Fault involves a new method to estimate or constrain the shear strain magnitude along brittle-ductile shears. The typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the Palomares Fault are of the order 10-13-10-14 s-1. The tensor shear strain rate along the Palomares Fault itself is of the order 10-12s-1 and the time averaged relative displacement rate of its walls is about 2 mm a-1. The range of strain rates within the Palomares Shear Zone are interpreted to be due to a combination of various flow-softening mechanisms: geometric, structural, thermal and strain-rate softening. These softening mechanisms might explain the difference in vertically averaged viscosities of 1020 Pa s and 1025 Pa s or lower suggested for the crustal rocks in the Palomares Fault proper and that of the relatively rigid boundaries of the Palomares Shear Zone, respectively.

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The Palomares brittle-ductile Shear Zone of southern Spain

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