Evidence for sinistral movement on the Peel Fault System in serpentinites, Glenrock Station, N.S.W.

Abstract

The serpentinites in the Glenrock shown that the present shape of these continents Station area contain mesoscopic and microscopic is the result of both accretion and dis•ermion of structures resembling those observed in mylonites. terranes of various sizes and age. These terranes These structures have been developed during are fault bounded and characterised by a geolomovement on the Peel Fault System, a major suture gical history different from their neighbouts extending for over 270 km in the Southern New [Howell et al, 1985]. Displacement along the England Fold Belt. The earliest structure to faults may vary from a few kilometres to many develop is a fine, penetrative schistosity (Sl); thousands of kilometers. textural evidence suggests that Sl is a plane of In Eastern Australia, several terranes have flattening and is parallel to the XY plane of the been recognised in the New England Fold Belt (see finite strain ellipsoid. Overprinting it at an inset, Figure 1), a north trending, Palaeozoic angle of 45 o or less, are a set of microshears structure extending approximately 1600 km in (S 2) which show a sinistral sense of movement N.S.W. and Queensland [Cawood and Leitch, 1985]. according to vergence relationships and kinematic The southern portion of this belt is divided into indicators. Less commonly developed at this time the Tablelands Complex and the Tamworth Belt was another set of microshears with a dextral [Runnegar, 1974], and Zone A and B by Leitch displacement of the first foliation. Superposed [1974]. Distinctive rock sequences, structural on all early foliations is a second set of styles and types of metamorphism occur in these microshears (S 3) which folds and displaces in a zones. Scheibner [1985] recognises five suspect left lateral sense, earlier foliations. A terranes in the Tablelands Complex; Cawood and chrysotile fibre lineation was produced during Leitch [1985], however, reco•nise only four. both shearing events. Dividing the Tablelands Complex and the Microscopic features indicate that the Tamworth Belt is the Peel-Manning Fault System, a serpentine minerals behaved in a plastic fashion major suture extending for approximately 270 km during the formation of S• and in a brittle(Figure 1). It is delineated by lenticular masses plastic fashion while the microshears were being of serpentinite of varying size and shape, formed, suggesting that shearing took place at containing exotic blocks which have been carried shallower depths in the crust. from the deeper levels of the crust and mantle. The geometry of the foliations and the Geophysical studies, relationships between the chrysotile lineations reveals that the movement on serpentinites and the associated sediments, and the Peel Fault System is dominantly strike-slip. cleavage orientation within the serpentinites Movement on this zone appears to have been short suggest that the Peel Fault System dips vertically lived occurring between 262 and 270 Ma. This fact or steeply to the east [Crook, 1963; Ramsay and and the observation that shear strain has not been Stanley, 1976; Leitch, 1980; Glen and Butt, high, suggests that the strike-slip displacement 1981; Offlet and Williams, 1985]. Little is was not substantial. Thus the serpentinites in known of the attitude of the Manning River Fault the Glenrock Station area record evidence for a System. sinistral, dominantly strike-slip movement on the This suture occurs close to a long-lived, Peel Fault System. Palaeozoic convergent plate margin and separates forearc basin from accretionary-subduction complex Introduction rocks. At the beginning of the Permian, the plate In the last decade, major advances have been vector orientation changed resulting in the develmade in the unravelling of the tectonic history of opment of a strike-slip margin [Roberts and Engel, the continents bordering the Circum-Pacific 1986]. Strike-slip movement taken up by the Peel region, particularly North America. Studies have Fault System at this time was later terminated Copyright 1987 by the American Geophysical Union. 141 Geodynamics Series Terrane Accretion and Orogenic Belts Vol. 19 Copyright American Geophysical Union •. • Complex •/ \• .': :' i ! '..•]•k ••.,• • :: :::::::7::::: .... •o • •_ • INEF•_• :::•:•/•: '••• 0 I 2Km• MF ,• • J ......... • .. • I II 8YDNE ': • • • • •.•.•. .... ::•:;:::::.. • ..::.. . .... •:::-.:.::;:..: . . • •0 ' '• I• • ===================================== :•::::::•.'::::::: -x• • • . .• '• 4• ======================================== ...... ,, , ....... ......... ••• ========================== -4•' • ' • s '' • .... , • ':•::::::•;:•• ...... • •;' ' ...... '• ..... • •e . :• •% , . .•% '.% ', V , • • • ...... •lTl' s V V V s s • , s •