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 Range Batholith and a mafic granulite from the southwestern part of the Archaean Yilgarn Craton of Western Australia. The results provide constraints on the post-emplacement temperature history of the batholith and the southwestern Yilgarn Craton. The similarity of titanite and apatite ages (at ca 2630 Ma) in the eastern part of the batholith and the adjacent metamorphic belt suggest that this region cooled from ca 650 degrees C to 500 degrees C within a time span represented by the uncertainties in the age measurements. In the western part of the batholith, titanite grains from one granite sample 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. This 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 uplift being greater in the west. Westward uplift can also explain the progressive change in Rb-Sr biotite ages across the batholith; from ca 500 Ma in the west to ca 2.5 Ga in granites to the east. The U-Pb systems of apatite from granites from the western part of the batholith have been slightly disturbed at ca 420 Ma, suggesting that in addition to uplift there was a reheating along the western margin of the craton possibly associated with continental rifting and movement on the Darling Fault. (C) 1999 Elsevier Science B.V. All rights reserved.