LA-ICPMS U-Pb geochronology of detrital rutile from North Gondwana Cambro-Ordovician sandstones is reported for the first time. Our sampling sites in Israel, Jordan and Ethiopia are situated thousands of kilometers apart thus providing a continental-scale perspective on the cooling and unroofing history of the provenance of the great Cambro-Ordovician sandstone sheet. Detrital rutiles in the Cambrian sandstone of Israel and Jordan define a unimodal age concentration at 0.59–0.58 Ga, preceding the timing of major orogenic sutures and predating the final assembly of Gondwana. Cooling to below the rutile U-Pb closure temperature followed continental-scale Pan-African granitoid intrusion at 0.63–0.60 Ga, signifying that rather than representing high-grade metamorphism the detrital rutile age spectra reflect widespread resetting, cooling and exhumation associated with late to post-tectonic igneous activity. The unimodal 0.59–0.58 Ga age spectra do not change significantly up the Cambrian sequence, implying exhumation prior to Cambrian sedimentation generated ample crustal material with an almost uniform U-Pb rutile signature that was prone to deliver immense amounts of detritus. Therefore, rather than reflecting progressive erosion of Cambrian Supermountains, the North Gondwana Cambrian sandstone represents secondary denudation of an already-exhumed metamorphic basement. Alongside the older (0.59–0.58 Ga) detrital rutile population, which dominates the Cambrian sequence, 0.55 Ga detrital rutiles first appear in the Ordovician of Jordan while 0.54 Ga rutile locally dominates the Ordovician from Ethiopia, some 2000 km upstream the Cambro-Ordovician fluvial system, close to its headwaters. The Ordovician drainage basin has thus been extended to include crustal vestiges that were exhumed coeval with Gondwana consolidation, but it is likely that most of the rock carapace that has been eroded from consolidating Cambrian orogenic sutures has been delivered to the south (modern coordinates).
Bibliographical noteFunding Information:
This research was supported by the G.I.F., the German-Israeli Foundation for Scientific Research and Development (grant number 1248-301.8/2014 ). A. Abbo is grateful to the Azrieli Foundation for the award of an Azrieli Fellowship. We thank Y. Ben-Dor and K. Kolodner for providing additional samples from southern Israel and Jordan, and to G. Gutiérrez-Alonso for a trial sample from northern Spain. Y. Geller is thanked for technical assistance in mineral separation, and L. Marko for invaluable analytical support at GUF. This manuscript benefited from reviews by G. Meinhold and two anonymous reviewers, all reviews are greatly appreciated.
© 2017 International Association for Gondwana Research
- Cambro-Ordovician sandstone
- Detrital rutile
- Neoproterozoic Pan-African orogeny
- North Gondwana
- U-Pb geochronology