A reappraisal of the Sibson‐Scholz fault zone model: The nature of the frictional to viscous (“brittle‐ductile”) transition along a long‐lived, crustal‐scale fault, Outer Hebrides, Scotland

Tectonics - Tập 20 Số 5 - Trang 601-624 - 2001
Jonathan B. Imber, R. E. Holdsworth, C. A. BUTLER, R. A. Strachan

Tóm tắt

The widely cited Sibson‐Scholz conceptual fault zone model suggests that seismically active, upper crustal brittle faults pass downward across a predominantly thermally controlled transition at 10–15 km depth into ductile shear zones in which deformation occurs by aseimic viscous creep. The crustal‐scale Outer Hebrides Fault Zone (OHFZ) in NW Scotland has been described as the type example of such a continental fault zone. It cuts Precambrian basement gneisses and is deeply exhumed, allowing direct study of the deformation products and processes that occur across a wide range of crustal depths. A number of fault rock assemblages are recognized to have formed during a long‐lived displacement history lasting in excess of 1000 Myr. During Caledonian movements that are recognized along much of the 190 km onshore fault trace, brittle, cataclasite‐bearing faults in the west of the OHFZ are unequivocally overprinted to the east by a younger fabric related to a network of ductile shear zones. Field observations and regional geochronological data demonstrate that there is no evidence for reheating of the fault zone due to thrust‐related crustal thickening or shear heating. Microstructural observations show that the onset of viscous deformation was related to a major influx of hydrous fluids. This led to retrogression, with the widespread development of new finegrained phyllosilicate‐bearing fault rocks (“phyllonites”), and the onset of fluid‐assisted, grain size‐sensitive diffusional creep in the most highly deformed and altered parts of the fault zone. Phyllonitic fault rocks also occur in older, more deeply exhumed parts of the fault zone, implying that phyllonitization had previously occurred at an earlier stage and that this process is possible over a wide temperature (depth) range within crustal‐scale faults. Our data provide an observational basis for recent theoretical and experimental studies which suggest that crustal‐scale faults containing interconnected networks of phyllosilicate‐bearing fault rocks will be characterized by long‐term relative weakness and shallow (∼5 km) frictional‐viscous transition zones. Similar processes acting at depth may provide an explanation for the apparent weakness of presently active structures such as the San Andreas Fault.

Từ khóa


Tài liệu tham khảo

Binns P. E. R.McQuillin N.Kenolty The geology of the Sea of the HebridesRep. 73/14 44 Inst. Geol. Sci. HMSO London 1974.

10.1130/0091-7613(1994)022<0147:SBICBI>2.3.CO;2

10.1016/0191-8141(80)90045-0

10.1016/0191-8141(93)90132-T

Butler C. A. Basement fault reactivation: The kinematic evolution of the Outer Hebrides Fault Zone Scotland Ph.D. thesis Univ. of Durham Durham England 1995.

10.1144/gsjgs.152.5.0743

10.1144/gsjgs.146.6.0921

Coward M. P. The structural and metamorphic geology of South Uist Outer Hebrides Ph.D. thesis Univ. of London London England 1969.

10.1144/sjg08010001

10.1016/0040-1951(90)90033-5

10.1130/0016-7606(1974)85<1515:CATGOF>2.0.CO;2

10.1029/92TC00850

10.1093/petrology/25.4.894

10.1144/GSL.SP.1987.027.01.04

Fettes D. J., 1992, Geology of the Outer Hebrides

Fowler C. M. R., 1990, The Solid Earth

10.1016/0191-8141(94)00093-F

10.1144/gsjgs.133.3.0257

10.1016/S0191-8141(97)00080-1

10.1016/0040-1951(89)90122-4

10.1029/JB095iB06p08647

10.1016/0040-1951(94)90026-4

Hippertt J. F., 1994, Direct observation of porosity in quartzite and phyllonite, Neues Jahrb. für Mineral., 166, 239

10.1016/S0191-8141(97)00083-7

10.1016/0191-8141(92)90053-Y

10.1144/gsjgs.154.1.0073

10.1144/GSL.SP.2001.184.01.07

Imber J. Deformation and fluid‐rock interaction along the reactivated Outer Hebrides Fault Zone Scotland Ph.D. thesis Univ. of Durham Durham England 1998.

10.1144/gsjgs.154.1.0105

10.1130/0091-7613(1988)016<1064:FIRR>2.3.CO;2

10.1016/0040-1951(87)90160-0

10.1130/0091-7613(1994)022<0443:LPAAIO>2.3.CO;2

10.1016/0191-8141(89)90039-4

10.1029/JB085iB11p06185

10.1029/91JB01506

10.1144/gsjgs.146.2.0253

10.1144/sjg06020214

10.1144/GSL.SP.1992.062.01.16

10.1144/gsjgs.150.4.0653

10.1016/0191-8141(92)90052-X

10.1144/jgs.157.5.1009

Maltman A., 1994, Continental Deformation, 143

10.1016/0191-8141(93)90156-5

10.1130/0091-7613(1990)018<0824:MTMIDR>2.3.CO;2

Miyashiro A., 1994, Metamorphic Petrology

10.1144/gsjgs.131.2.0213

10.1016/0040-1951(88)90280-6

10.1046/j.1525-1314.1996.00347.x

10.1017/S0016756801005325

10.1038/312628a0

10.1016/0012-821X(72)90286-5

10.1144/gsjgs.149.1.0127

10.1111/j.1525-1314.1995.tb00249.x

10.1016/S0074-6142(08)62835-1

10.1144/gsjgs.156.6.1061

10.1144/gsjgs.140.5.0725

10.1144/GSL.SP.2001.186.01.01

Schmid S. M., 1991, Controversies in Modern Geology: Evolution of Geological Theories in Sedimentology, Earth History and Tectonics, 339

10.1007/BF01848693

Scholz C. H., 1990, The Mechanics of Earthquakes and Faulting

10.1029/92JB00620

10.1016/0040-1951(81)90276-6

10.1111/j.1365-246X.1975.tb06195.x

10.1144/gsjgs.133.3.0191

Sibson R. H. The Outer Hebrides Thrust: Its structure mechanism and deformation environment Ph.D. thesis Univ. of London London England 1977.b.

Sibson R. H., 1982, Fault zone models, heat flow, and the depth distribution of earthquakes in the continental crust of the United States, Bull. Seismol. Soc. Am., 72, 151

10.1144/gsjgs.140.5.0741

10.1144/GSL.SP.1990.054.01.02

10.1093/petrology/36.2.563

10.1038/299338a0

Snoke A. W., 1988, Fault‐Related Rocks: A Photographic Atlas

10.1144/gsjgs.131.2.0183

10.1111/j.1365-2117.1988.tb00008.x

10.1144/GSL.SP.1992.062.01.03

10.1029/1998TC900033

10.1016/S0191-8141(99)00164-9

Strachan R. A., 2000, Geological History of Britain and Ireland, 52

10.1016/0012-8252(92)90014-K

10.1016/S0264-8172(98)00064-6

10.1016/S0191-8141(96)00075-2

10.1016/0191-8141(80)90005-X

10.1144/sjg07020139

Walker J. A study of the deformation environment of the Outer Hebrides Fault Zone Ph.D thesis Univ. of London London England 1990.

Walsh J. J., 2001, The Nature and Tectonic Significance of Fault Zone Weakening, Geol. Soc. Spec. Publ., 157

10.1016/S0016-7878(77)80001-1

10.1016/S0191-8141(96)00059-4

10.1144/GSL.SP.1987.027.01.15

10.1098/rsta.1986.0026

10.1144/sjg29010001

10.1016/S0191-8141(99)00019-X

Wintsch R. P., 1995, Fluid‐rock reaction weakening of fault zones, J. Geophys. Res., 100, 13021, 10.1029/94JB02622

Yardley B. W. D., 1989, An Introduction to Metamorphic Petrology

10.1038/35011181

Thông tin
Thông tin xuất bản

Tectonics

Tập 20 Số 5

601-624

Thông tin tác giả