Long-lived early Cretaceous seamount volcanism in the Mariana Trench, Western Pacific Ocean

An alkaline volcanic rock sample, peralkaline rhyolite pillow lava, in addition to some radiolarian-bearing pelagic sedimentary rocks, were collected by the Japanese submersible Shinkai 6500 from Quesada Seamount on the oceanward slope of the Mariana Trench. 40Ar-39Ar dating resulted in a plateau age of 129.3 +/- 2.6 Ma, which is approximately 10 Myr younger than the radiolarian age of the oldest intercalated tuffaceous radiolarian claystone of early Berriasian age (approximately 140 Ma). Fragments of volcanic glass that are of alkali-basalt (hawaiite) composition may indicate that this tuffaceous claystone was formed during the shield-building volcanic stage. Because the peralkaline rhyolite is a very differentiated volcanic rock and commonly erupts in the post-shield stage, we interpret that the activity lasted for a long period (approximately 10 Myr). This long-lived shield-building stage may be due to the slow moving rate of the Pacific Plate during the Early Cretaceous. (C) 2002 Elsevier Science B.V. All rights reserved.