Extension-related volcanism is thought to have ceased along the Newfoundland margin at the end of the Early Cretaceous (Grant and McAlpine, 1990), with the youngest igneous rocks recovered from the shelf (96.4 Ma; exploration well) and Newfoundland Seamounts (97.7 Ma; dredge) as summarized in Pe-Piper et al. (1990). Younger volcanic rocks (~59 Ma) are limited to rift zones to the north, east, and west of Greenland (Pe-Piper et al., 1990).
One of the more interesting sedimentological discoveries of Leg 210 was the isolated volcanic input at ~60 Ma in Core 210-1276A-15R, near the Unit 2/3 boundary. Shipboard petrographic observations showed this interval to contain felsic(?) and mafic epiclastic volcanic debris. The timing of this input at Site 1276, as verified by mica ages of ~57 Ma by Wilson and Hiscott (this volume), corresponds to a major uplift event followed by extensive magmatism and rifting off southeastern Greenland (e.g., Larson and Saunders, 1998). As documented at Site 917, the Greenland volcanism was bimodal with dacitic and basaltic end-members, and this bimodal episode was relatively short lived (61–60 Ma). It is possible that an event of this magnitude could have produced a submarine sediment pulse (fan) that crossed the Mid-Atlantic Ridge via a major transform zone and extended 1000 km south to the vicinity of Site 1276. Alternatively, the volcanic debris may have been derived from the little-studied Cretaceous Newfoundland Seamounts (Pe-Piper et al., 1990) located south of Site 1276 or perhaps some as-yet undocumented source on Grand Banks. In support of a seamount source, Davis et al. (2002) have shown through submersible sampling and mapping of seamount systems off the Pacific coast of North America that seamount reactivation may occur during regional tectonic reorganizations. In some cases during this rejuvenation phase, the seamounts can build to sea level and produce epiclastic debris like that observed in Core 210-1276A-15R.
Although several samples from Core 210-1276A-15R were collected for this study, they contained little to no volcaniclastic material. Two samples were point counted (Table T1), with LmlvLs%Lv ranging from 0.0% to 6.9%. However, significant (LmLvLs%Lv > 5%) volcanic contributions to the section were first noted in the Santonian samples and continue into the Eocene, suggesting that the few percent volcanic debris could be a background signal. It should be noted that Sample 210-1276A-15R-4, 123 cm, contained the highest percentage of mica (11%) in the Site 1276 section, and ages provided by Wilson and Hiscott (this volume) are consistent with a coeval volcanic source. However, geochemical studies of mudstones across this interval show no evidence of volcanic input (Robertson, this volume). The lack of tuffaceous fines suggests that the source of the bed described shipboard was different from the source providing fine background sediments. Questions remain as to the source(s) and modes of supply of volcanic material to this margin, as well as its Iberian conjugate, where volcaniclastics are also present, as shown below.
A review of the thin sections prepared from the ~60-Ma interval recovered on the Iberian margin shows them to contain heretofore unrecognized mafic to felsic(?) volcanic detritus: Samples 149-897C-62R-1, 123 cm (Fig. F18), 173-1068A-7R-2, 82 cm (Fig. F19), and 173-1069A-7R-2, 82 cm (Fig. F20). Their composition is masked by extreme alteration of glass to clay minerals; however, the common occurrence of black tachylitic microlitic fragments is consistent with a mafic source, and the presence of highly vesiculated pumice suggests a felsic component as well (Fig. F20). As with Site 1276, some of the debris is rounded and interpreted as epiclastic. This debris could have been derived from reactivated volcanic centers in the Lusitania Basin or perhaps on the Tore Seamount that lies along trend with the Newfoundland Seamounts (Fig. F4). These observations suggest the volcanic reactivation or exotic influx of volcanic material was not limited to the Newfoundland margin and was a punctuated (~60 Ma) but widespread event across the North Atlantic region.