Page 218 - Caldera Volcanism Analysis, Modelling and Response

Characterisation of Archean Subaqueous Calderas in Canada 193

from eruption a by flows transport pelagic fluids

directly water, of water via laminar turbidity and from as or quiescence. and floor lithofacies subsurface diagenesis

facies: fountaining from Collapse in hydroclastic Transport low-concentration (1) (2) pyroclastic resulted facies tremors; or currents volcanic pervasive hydrothermal and

Pyroclastic magmatic insulation carapace. results and fragmentation. and currents: and flows Reworked autoclastic failure turbidity during intracaldera margin Iron-formation by of percolation seeps) cold

(b-1) a with steam fountain ingestion high- density mass slope by rain Locus: caldera (b-2) formed (and

autoclastic divided a (ii) stratified well feature stratified graded ca. tuff magnetite mm-cm- rip-up

lithofacies: and facies & facies 7–20 m-thick, breccia 51 m-thick, upper an tuff-lapilli lithofacies dyke of deposits irregular clasts, and clasts contain vesicles. and 1–5 m-thick in deposited laminated and lithofacies: of units in large iron-
(2)

Volcaniclastic pyroclastic pyroclastic Pyroclastic basal a (i) tuff lapilli to up (iii) and tuff turbiditic Volcaniclastic screens in Pyroclastic with beds amoeboid-shaped blocky with pyroclasts beds; quartz-filled pyroclastic facies: tuff lapilli graded Iron-formation 5–100 cm-thick jasper-magnetite as and beds bande

(b-1) (1) reworked facies. into: massive middle lapilli 2 m-thick tuff. preserved swarm. massive beds tuff 30–60% Reworked autoclastic and massive, beds (b-2) and scale clasts. formation.

Iron- lithofacies

Volcaniclastic and lithofacies formation

(b)

Lower but (ages as
2,732–2,734Ma in described Stage and flows deposit terminate lobe

ca. Dykes Formational crosscut pyroclastic 2,728–2,730 Ma) locally endogenous
Age: Dykes