Author Affiliations
13DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff CF10 3YE, UK
2Present address: BP Exploration, Wellheads Avenue, Farburn Industrial Estate, Dyce, Aberdeen AB21 9PD, UK (e-mail: Robert.Evans2@uk.bp.com)
3BP Azerbaijan, Villa Petrolea, 2 Neftchilar Prospekti, Baku, Azerbaijan
4CeREES (Centre for Research into Earth Energy Systems), Department of Earth Sciences, University of Durham, Science Labs, Durham DH1 3LE, UK
Circular depressions bounded by inward-dipping faults found at the upper terminations of large mud volcano systems (>500 m diameter) are termed ‘mud volcano summit calderas’.
From new mapping and comparison with previously identified examples we describe a series of common structural and morphological features found at a number of calderas and propose a mechanism for caldera formation.
A typical example consists of concentric deformational and volcanic zones including an outermost topographic rim, inward-dipping circular fault system, ‘moat’ and raised central ‘pedestal’ of freshly extruded mud volcanic sediment.
This distinctive ‘moat and pedestal’ morphology can be explained in terms of the quantity and rheology of extruded mud, and appears characteristic of calderas from the South Caspian Basin and elsewhere.
The association of fresh mud volcanic deposits with the calderas in combination with extensive literature on caldera modelling leads us to conclude that the most likely causal mechanism is subsidence as a result of evacuation of fluids and sediment from shallow structural levels during eruptions.
Summit calderas mapped in this study characterize dormant periods of mud volcanism in subaerial and submarine settings, and appear to be a common structural element in the extrusive domain of mud volcano systems.
Received February 1, 2007.
Accepted February 1, 2008.
© 2008 The Geological Society of London
Structural controls on mud volcano vent distributions: examples from Azerbaijan and Lusi, east Java
Journal of the Geological Society, July 2011, v. 168:1013-1030,
Structural controls on mud volcano vent
distributions: examples from Azerbaijan and Lusi,
east Java
Author Affiliations
1 CeREES (Centre for Research into Earth Energy Systems), Department of Earth Sciences, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK
2 Present address: Hess Services Ltd., London, WC2N 6AG, UK
3 Institute of Petroleum Engineering, Heriot–Watt University, Edinburgh EH14 4AS, UK
4 Tectonics, Resources and Exploration (TRaX), Australian School of Petroleum Geoscience, University of Adelaide, Adelaide, SA, 5005, Australia
↵*Corresponding author (e-mail: KSRoberts@Hess.com)
Scientific Editing By Tim Needham.
Abstract:
Structural mapping, nearest neighbour and two-point azimuth statistical analysis of mud volcano vent distributions from nine examples in Azerbaijan and the Lusi mud volcano in east Java are described.
Distributions are non-random, forming alignments subparallel to faults within anticlines, ring faults, conjugate faults and detachment faults; this finding confirms a spatial relationship and supports a model for subsurface flow along these features as well as showing fractionation at depth.
As fracture and fault orientations are related to structures such as anticlines and the in situ stress state they are therefore predictable.
We use vent distributions in Azerbaijan, where the structural geology is well constrained, to propose what controls the distribution of 169 vents at the Lusi mud volcano.
This mud volcano system shows evidence for initial eruptions along a NE–SW trend, parallel to the Watukosek fault, changing to eruptions that follow east–west trends, subparallel to regional fold axes.
Our analysis indicates that regions east and west of the Lusi mud volcano are more likely to be affected by new vents than those to the north and south, owing to probable onset of elongate caldera collapse within a 10 km diameter of the central vent.
Sector collapse of mud volcanoes, Azerbaijan
Journal of the Geological Society, January 2011, v. 168:49-60,
Sector collapse of mud volcanoes, Azerbaijan
Author Affiliations
1 CeREES (Centre for Research into Earth Energy Systems), Department of Earth Sciences, Durham University, Science Laboratories, South Road, Durham DH1 3LE, UK
2 Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK
3 3DLab, School of Earth, Ocean and Planetary Sciences, Cardiff University, Cardiff CF10 3YE, UK
*Corresponding author (e-mail: k.s.roberts@dur.ac.uk)
Scientific Editing By Tim Needham.
Abstract:
Field data collected from mud volcanoes in Azerbaijan are used to describe a process in mud volcano development that involves portions of the constructional edifices collapsing outwards in ‘thin-skinned' slides.
These events create kilometre-scale scarps that are tens of metres in height, arcuate in plan view, elongate and facing downdip.
Similar morphological features occur on igneous volcanoes and have been described as ‘sector collapse' structures.
The largest sector collapses in igneous volcanoes involve some 1012 tons of mobilized material; equivalent structures in mud volcanoes are several orders of magnitude smaller.
We employ a shape parameter that can be utilized in field and satellite-based mapping, to distinguish between slope failure and eruptive deposits.
Three mud volcanoes with kilometre-scale sector collapses are described and controlling mechanisms are reviewed.
The updip domains of these collapses are characterized by fluid escape, showing that there is also linkage to deeper mud volcano structure.
The observations are reconciled in a model consisting of a deflating mud chamber that triggers thin-skinned sector collapse.
The updip domain of the sector collapse is localized above a deep-seated zone of volume loss and the downdip domain of the collapse runs down the edifice flank onto the surrounding plain.
Footnotes
Received July 1, 2010.
Accepted September 13, 2010.
© The Geological Society of London