Search results for "lawsonite"

Origin of potassic postcollisional volcanic rocks in young, shallow, blueschist-rich lithosphere

2020

Unusually high Th/La in K-rich orogenic rocks may indicate shallow blueschist-rich sources in accretionary settings.

Crystal structure of SrMn2(Si2O7)(OH)2 H2O, a new mineral of the lawsonite type

1992

Crystal with the composition SrMn 2 [Si 2 O 7 ](OH) 2 .H 2 O were found in a sugilite, serandite-pectolite rich sample from the Wessels Mine, Kalahari, South Africa. The crystal structure of the nex compound with space group Cmcm, a = 6.255(1), b = 9.034(2), c = 13.397(2) A, Z = 4 was determined from X-ray single-crystal data (R = 0.048). The structure is of the lawsonite type where Al is completely replaced by Mn 3+ and Ca by Sr. [Mn 3+ O 6 ] octahedra forming edge-sharing chains parallel to a exhibit a Jahn-Teller distortion with four short and two long Mn 3+ -O distances. Sr is in eight-fold coordination and H 2 O is disordered on a split position. Together with orientite, macfallite, ru…

Geochemical characteristics of lawsonite blueschists in tectonic mélange from the Tavşanlı Zone, Turkey: Potential constraints on the origin of Medit…

2019

Constraints on the sources of post-collisional K-rich magmatism: The roles of continental clastic sediments and terrigenous blueschists

2017

Abstract The possible role of continental sediments in the generation of potassium-enriched lavas of the Alpine-Himalayan belt depends on their melting behaviour either during subduction or during post-collisional relaxation. Although usually classed as orogenic lavas, these volcanic rocks may result from re-melting of newly formed mantle lithosphere 30–40 million years after collision ends, and can thus be considered as the first stage of intraplate volcanism. The potassic component in these volcanics is characterized by a high Th/La signature for which there are two competing explanations: melting of subducted continental clastic sediments, and the involvement of lawsonite blueschists in …