Page 225 - Caldera Volcanism Analysis, Modelling and Response

A
Lower formational stage I

B Lower formational stage II

C
Middle formational stage

Figure 5 Evolution of the Hunter Mine caldera based on physical volcanology, sedimentology,
faults and precise U--Pb zircon ages (modi¢ed from Mueller and Mortensen, 2002). (A) Incipi-
ent submarine caldera subsidence structure with ring fractures and a central moat zone com-
posed of felsic volcanic £ows and domes.The intracaldera £oor developed a horst and graben
structure. (B) Continued subsidence in central portion of volcanic structure during ¢rst caldera
phase with magmatic-fountaining eruptions and autoclastic dome fragmentation processes.
(C) Emplacement of the Roquemaure sill and in£ation of the central subsidence structure.
(D) Well-developed second caldera event with a major dome-building phase and the extrusion
of ma¢c tholeiitic pillowed £ow at the caldera walls. Note formation of banded iron-formation
deposits on the caldera £oor. (E) Extensive hydrothermal alteration and banded iron-formation
associated withVMS (modi¢ed from Mueller and Mortensen, 2002).