Petrology and Geochemistry of Ordovician K-Bentonites in New York State: Constraints on the Nature of a Volcanic Arc

Ordovician K-bentonites of eastern North America

“…Accompanying volcanogenic mineral grains include biotite, feldspar, quartz, apatite, zircon, leucoxene, or anatase, plus sulfide and carbonate minerals. Delano et al (1990) reported garnet in K-bentonites from New York State and concluded that it represented transported source material from the lower crust. Yost et al (1994) reported amphiboles in several Swedish K-bentonite beds and concluded on the basis of major element ratios, that they were not derived directly from parental magma.…”

“…Both primary phenocryst and whole rock chemical analyses have provided much useful information concerning original magmatic composition and have further contributed to interpretations of the tectonic settings of source volcanoes (Delano et al, 1990;Roberts and Merriman, 1990;Huff et al, 1993). Detailed studies of immobile large-ion lithophile (LIL) elements and rare-earth elements (REE) indicate most source volcanoes were associated with collision-margin tectonism and that the parental magmas were silicic in nature.…”

“…Thus twinning alone is an inaccurate guide to the origin of feldspar grains. Delano et al (1990) analyzed garnets in Ordovician K-bentonites from New York State and concluded that they represent the influence of a high-pressure regime, probably the lower crust, on the composition of the parent magma. They further concluded that this constrained the tectonic setting of the source volcanoes to, most likely, an active plate-margin setting.…”

Late Ordovician (Chatfieldian) catastrophic volcanism and abrupt carbonate platform-interior subsidence: A tectonic link across a Taconian foreland basin (Quebec Embayment) due to inherited crustal weakness

“…Elevated values of loss on ignition (LOI; on October 14, 2011 gsabulletin.gsapubs.org Downloaded from (Delano et al, 1990;Berkley and Baird, 2002). When calculated on a LOI-free basis, the Verulam bentonite has SiO 2 and TiO 2 values that are lower, and Al 2 O 3 and K 2 O values that are higher, than those associated with the typical gray shale of the upper Verulam Formation ( Table 2).…”

“…Delano et al (1990) considered the first process to explain the origins of what appears to be the only other reported lithic-bearing (Fig. 2).…”