The Miocene Costa Giardini diatreme, Iblean Mountains, southern Italy: model for maar-diatreme formation on a submerged carbonate platform

Abstract

In this paper we present a model for the growth of a maar-diatreme complex in a shallow marine environment. The Miocene-age Costa Giardini diatreme near Sortino, in the region of the Iblei Mountains of southern Sicily, has an outer tuff ring formed by the accumulation of debris flows and surge deposits during hydromagmatic eruptions. Vesicular lava clasts, accretionary lapilli and bombs in the older ejecta indicate that initial eruptions were of gas-rich magma. Abundant xenoliths in the upper, latedeposited beds of the ring suggest rapid magma ascent, and deepening of the eruptive vent is shown by the change in slope of the country rock. The interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts of variable size and amount. The occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle-lower part of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity. Intrusions of nonvesicular magma, forming plugs and dikes, occur on the western side of the diatreme, and at the margins, close to the contact between breccia deposits and country rock; they indicate involvement of volatile-poor magma, possibly during late stages of activity. We propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a rampart that isolated for a short time the inner crater from the surrounding marine environment. This allowed explosive activity to draw down the water table in the vicinity of the vent and caused deepening of the explosive center. A subsequent decrease in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water, at which time the hyaloclastite was deposited. Emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and unconsolidated, locally forming peperites. The sheltered, low-energy lagoon filled with marine limestones mixed with volcaniclastic material eroded from the surrounding ramparts. Ultimately, lagoonal sediments accumulated in the crater until subsidence or erosion of the tuff ring caused a return to normal shallow marine conditions.

Geochronology of the Tumpangpitu Porphyry Au-Cu-Mo and High-Sulfidation Epithermal Au-Ag-Cu Deposit: Evidence for Pre- and Postmineralization Diatremes in the Tujuh Bukit District, Southeast Java, Indonesia

“…The crater above the diatreme vents at Tumpangpitu is interpreted to have formed by phreatomagmatic to phreatic explosions and subsequent sedimentary infill. This intra-maar sequence shares many similarities with the "crater infill breccia" described by many authors, such as at Wau, PNG by ; at Agua Rica, Argentina by Landtwing et al (2012) and diatremes not related to porphyry-epithermal districts (Calvari and Tanner, 2010;White and Ross, 2011), including kimberlites (Sparks, 2013). The upper facies breccia at Tumpangpitu dips centripetally at 10 -20˚ (influenced locally by underlying hostrock; phase 2 diorite; Figs.…”

“…The presence of accretionary lapilli and low-angle cross stratification, in combination with features such as slumping along faults, channelling of beds and lack of sag structures beneath large fragments, suggests that low temperature, wet pyroclastic base surge deposits overlie fall out and co-surge fallout ash fall deposits (e.g., Lorenz and Kurszlaukis, 2007;Calvari and Tanner, 2010;Sutopo, 2013). Base surge deposits are ubiquitous products of maar-forming phreatomagmatic or phreatic eruptions (Moore, 1967;Fisher and Waters, 1970;Lorenz, 1973;Walter, 1984).…”

“…Deposits from slumping suggest that the early explosive activity produced deposits located closer to the initial eruptive vent than the preserved material exposed in outcrops at Tanjung Jahe. The accretionary lapilli may have formed in eruption columns of tephra ejected as Surtseyan jets and then fallen as a component of ash or, more probably, grew in the base surges themselves (Lorenz, 1973;Calvari and Tanner, 2010).…”

“…In contrast to the well-bedded facies in the upper levels of the Tumpangpitu diatreme, the breccia in the lower part of the diatreme lacks distinct bedding, and is well-mixed, massive and poorly sorted similar to lower facies diatreme breccias elsewhere (e.g., Landtwing et al, 2002;Cannell et al, 2005;Lorenz and Kurszlaukis, 2007;Davies et al, 2008a;Calvari and Tanner, 2010;White and Ross, 2011).…”

An Overview of the Monogenetic Volcanic Fields of the Western Pannonian Basin: Their Field Characteristics and Outlook for Future Research from a Global Perspective

“…The result of this is a significant volume of excavated country rocks, the formation of mass deficit that eventually leads to a gradual collapse, and the formation of volcanic debris-filled volcanic conduit, or diatreme (White & Ross, 2011). The mechanism of the formation of a diatreme is far from well-known, and there is still argument about whether it is magmatic gas (Stoppa, 1996;Stoppa & Principe, 1997;Sparks et al, 2006;Walters et al, 2006;Suiting & Schmincke, 2009;2010) or magma and water explosive interaction (Lorenz, 1973;1986;Zimanowski et al, 1986;Wohletz & Heiken, 1992;Mastrolorenzo, 1994;Zimanowski et al, 1995;Zimanowski et al, 1997;Calvari & Tanner, 2011) that drives the energy release that fragments the country rocks. However, there is agreement that the resulting subsurface pipe is a volcanic and non-volcanic debris dominated zone with collapsed blocks of wall rock and complex arrays of juvenile particle enriched sub-vertical regions (Lorenz & Kurszlaukis, 2007;White & Ross, 2011).…”