U-Pb ages on titanite and apatite from the Darling Range granite: implications for Late Archaean history of the southwestern Yilgarn Craton

Titanite and apatite U-Pb ages are reported for granites from the Darling R ange Batholith and a mafic granulite from the southwestern part of the Arch aean Yilgarn Craton of Western Australia. The results provide constraints o n the post-emplacement temperature history of the batholith and the southwe stern Yilgarn Craton. The similarity of titanite and apatite ages (at ca 26 30 Ma) in the eastern part of the batholith and the adjacent metamorphic be lt suggest that this region cooled from ca 650 degrees C to 500 degrees C w ithin a time span represented by the uncertainties in the age measurements. In the western part of the batholith, titanite grains from one granite sam ple show two clearly resolved, concordant ages of 2637 +/- 5 Ma and 2615 +/ - 3 Ma and apatite ages from the granites are consistent at ca 2575 Ma. Thi s is interpreted as evidence that the western part of the batholith cooled at a slower rate than the eastern part. To explain this it is proposed that greater uplift in the west has exposed deeper granites than those exposed in the east. This model is supported by gravity and seismic profiles across the southern Yilgarn that suggest that the craton has been tilted with upl ift being greater in the west. Westward uplift can also explain the progres sive change in Rb-Sr biotite ages across the batholith; from ca 500 Ma in t he west to ca 2.5 Ga in granites to the east. The U-Pb systems of apatite f rom granites from the western part of the batholith have been slightly dist urbed at ca 420 Ma, suggesting that in addition to uplift there was a rehea ting along the western margin of the craton possibly associated with contin ental rifting and movement on the Darling Fault. (C) 1999 Elsevier Science B.V. All rights reserved.