Bimodal volcanism Bimodal volcanism Bimodal volcanism is the eruption of both mafic and felsic lavas from a single volcanic centre with little or no lavas of intermediate composition. This type of volcanism is normally associated with areas of extensional tectonics, particularly rifts. Most occurrences of bimodal volcanism are associated with thinning of the crust and the presence of such rocks in metamorphic sequences has been used to provide evidence for past rifting events. Most examples come from areas of active continental rifting such as the Basin and Range Province. Bimodal volcanism has also been described from areas of transtension, the early phases
Grayson Glades Natural Area Preserve Grayson Glades Natural Area Preserve Grayson Glades Natural Area Preserve is a Natural Area Preserve located in Grayson County, Virginia. Its centerpiece is an extremely rare wetland type known as a "mafic fen", which are situated upon soils rich in magnesium and fed by springs. The site is at the headwaters of a small stream system supporting additional mafic fens. Among the rare species found on the property are tuberous grass-pink ("Calopogon tuberosus"), ten-angled pipewort ("Eriocaulon decangulare" var. "decangulare"), large-leaved grass-of-parnassus ("Parnassia grandifolia"), queen-of-the-prairie ("Filipendula rubra"), sticky false-asphodel ("Triantha glutinosa") and Canada burnet ("Sanguisorba canadensis"). The preserve is owned and