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SIGNIFICANCE OF MUD VOLCANISM - Kopf - 2002 - Reviews of ...
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6 Sep 2002 ... Achim J. Kopf ... Volume 40, Issue 2, pages 2-1–2-52, May 2002 ... This paper summarizes the main thrusts in mud volcano research as well as ...
significance of mud volcanism - Berkeley Seismological Laboratory
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dance of mud volcanoes (terms in italic are defined in the ... Reviews of Geophysics, 40, 2 / May 2002 ..... Italy (A.Kopf, unpublished data, 2002)) and 30 cm.
Distribution and characters of the mud diapirs and mud volcanoes ...
http://www.gep.ncu.edu.tw/upload/focus/30/2014_Shu-Kun_Hsu_JAES1.pdf
21 Oct 2013 ... These mud volcanoes generally occur on tops of the diapiric structures. Moreover , the ... brook, 1988; Pérez-Belzuz et al., 1997; Kopf, 2002).
Tectonics and mud volcano development in the Gulf of Cidiz
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In this work we present images of the mud volcano plumbing systems and the ... volcanism and tectonics (Kopf,2002; Huguen et al., 2004; Panahi,. 2005) ...
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2003; Kholodov, 2002; Kopf, 2002). Recent developments in seismic exploration and seafloor imaging have led to the discovery of mud volcanoes not only ..
SIGNIFICANCE OF MUD VOLCANISM
Achim J. Kopf
Scripps Institution of Oceanography
University of California at San Diego
La Jolla, California, USA
Received 10 November 2000; revised 11 December 2001; accepted 12 December 2001; published 6 September 2002.
SIGNIFICANCE OF MUD VOLCANISM
Achim J. Kopf
Scripps Institution of Oceanography
University of California at San Diego
La Jolla, California, USA
Received 10 November 2000; revised 11 December 2001; accepted 12 December 2001; published 6 September 2002.
[1] Mud volcanism and diapirism have puzzled geoscientists for ϳ2 centuries.
They have been described onshore and offshore in many places on Earth, and although they occur in various tectonic settings, the majority of the features known to date are located in compressional tectonic scenarios.
This paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described.
Mud volcanoes show variable geometry (up to tens of kilometers in diameter and several hundred meters in height) and a great diversity regarding the origin of the fluid and solid phases.
Gas (predominantly methane), water, and mud may be mobilized at subbottom depth of only a few meters but, in places, can originate from several kilometers depth (with minor crustal or mantle input).
The possible contribution of mud extrusion to global budgets, both from quiescent fluid emission and from the extrusive processes themselves, is important.
In regions where mud volcanoes are abundant, such as the collision zones between Africa and Eurasia, fluid flux through mud extrusion exceeds the compaction-driven pore fluid expulsion of the accretionary wedge.
Also, quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and, hence, to greenhouse climate.
KEYWORDS: mud volcanism; extrusion; fluid venting; convergent margin; diapirism
Citation: A. J. Kopf, Significance of mud volcanism, Rev. Geophys., 40(2), 1005, doi:10.1029/2000RG000093, 2002.
SUMMARY AND CONCLUSIONS
[56] Despite the variability in appearance, deepseated mud volcanoes have a number of features in common:
(1) a connection with rapidly deposited, overpressured, thick argillaceous sequences of mostly Tertiary age as parent beds;
(2) the incorporated fragments of underlying rocks and other structural associations;
(3) a relationship to regional tectonics and seismicity or to petroleum reservoirs; and
(4) the presence or influx of gaseous and liquid fluids to facilitate diapiric intrusion and extrusion.
[57] Mud volcanoes act as “windows” to depths otherwise inaccessible to sampling, as gas, liquid, and solid particles from up to several kilometers are transported to the Earth’s surface.
There is a steadily increasing number of new discoveries of mud volcanoes from improved geophysical exploration techniques. As plate convergence and fluid cyclicity have been two fundamental processes throughout Earth’s evolution, one can
safely assume that mud extrusion may have played a prominent role over long periods.
[58] The growing importance of mud volcanism as an efficient dewatering mechanism in active convergent margin scenarios has been acknowledged in recent work [Kopf et al., 2001].
At least on a regional scale, these researchers have shown that fluid flux by MVism may exceed that from compaction.
Moreover, such MV fluids are typically enriched in volatile and (some) trace elements, so that high back flux rates of these elements into the hydrosphere have an impact on geochemical cycling [Deyhle and Kopf, 2001]. Hence the significance of mass transfer through mud intrusion and extrusion will influ- ence future fluid budget estimates. From the small numberof gas flux estimates through mud volcanoes, it can be estimated that the annual amount of methane globally emanated through MVs is _108 to 2 _ 109 m3.
Although this number appears small when compared to other sources of gas emission, it may be a conservative estimate of their contribution over wide periods during Earth’s evolution. Regardless of the small number of fossil examples preserved, MVs are likely to have been common dewatering and devolatilization features with a significant overall contribution to the earlier Earth’s atmosphere.
[59] Continued seafloor mapping will undoubtedly identify more MVs, even if the study is not dedicated to these features. Given the present-day knowledge and technology, side-scan surveys for clasts and carbonate crusts or pockmark depressions on the seafloor, heat flow studies, or methane composition in the water column will also add to the discovery of new mud volcanoes.
Some of these observations may even hint toward regions rich in hydrocarbons, either to exploit them for fossil fuel or to prevent hazards.
[60] Future mud volcano studies should focus on refined strategies of long-term observatories of the fluid discharge through features onshore and offshore.
Sampling techniques to collect pristine waters and gases are of particular importance.
As it is clearly impossible to cover wide MV areas with long-term observatories, suitable targets for well-defined case studies have to be
identified to assess global budgets.
For drilling of transects and installation of long-term observatories, the Mediterranean Ridge/Black Sea/Caucasus region or the Barbados Ridge would be good choices. With the type of examples carefully chosen, the assessment of the role of mud volcanoes in global budget estimates may improve significantly.
INTRODUCTION AND STRUCTURAL OUTLINE
[2] Mud intrusion and extrusion are well-known phenomena whereby fluid-rich, fine-grained sediments ascend within a lithologic succession because of their buoyancy.
These processes have long been recognized as related to the occurrence of petroleum, regional volcanic and earthquake activity, and orogenic belts (see theenlightening presentation by Ansted [1866]).
The abundance of mud volcanoes (terms in italic are defined in the glossary, after the main text) was first examined systematically on a broad scale by Higgins and Saunders [1974].
These authors mostly focused on mud volcanoes on land, and they used industry drill-hole data to establish relationships between mud volcanism, hydrocarbons, and regional tectonics.
The onshore mud volcanoes and their important role in predicting petroleum reservoirs have been summarized by Rakhmanov [1987].
Recent improvements in seafloor imagery and seismic exploration led to the discovery of countless mud extrusive provinces all over the world (Figure 1).
In fact, compared to the compilation by Higgins and Saunders [1974], more than twice as many occurrences are presently known, the number gradually increasing through time.
Most importantly, mud volcanoes occur along convergent plate margins where fluid-rich sediment is accumulated in deep-sea trenches at high rates.
Such deposits then enter the subduction factory, where liquids and volatiles are released due to increasing compactional stress and temperature.
Studies of geophysical data and samples of mud volcanoes have considerably improved the understanding of the mechanics, driving forces, and
evolution of the features through the most recent Earth history [e.g., Barber et al., 1986; Brown, 1990]. In addition, deep ocean drilling and submersible studies shed crucial light on eruptivity, emission of volatiles, and potential hazard originating from violent mud extrusion [e.g., Robertson et al., 1996; Bagirov et al., 1996a; Kopf, 1999].
The wealth of results attests that mud extrusion predominantly occurs in collisional settings, with mostly pore fluids during early (often marine) stages and with hydrocarbons at later stages (often on land [e.g., Jakubov et al., 1971; Tamrazyan, 1972; Speed and Larue, 1982]).
Although quantification of fluid and mud discharge in mud volcanoes is not easy because of their short-lived nature and inaccessibility on the seafloor, first-order estimates regarding flux rates have recently been attempted for various features and regions [e.g., Henry et al., 1996; Kopf and Behrmann, 2000; Etiope et al., 2002].
When put into a broader context, such estimates indicate that mud extrusion contributes significantly to fluid back flux from the lithosphere to the hydrosphere.
Figure 1. Occurrence of mud volcanoes (MVs) on Earth. Numbers refer to section heading nomenclature
of Appendix A as well as to Table 1.
long wide parts of large accretionary prisms (like the Barbados or Mediterranean Ridges), hundreds of features can cause fluid expulsion at rates exceeding those at the frontal part of the prism (see discussion by Kopf et al.[2001]).
Provided that the process of mud volcanism has been equally common in the past, these features have been major players in fluid and gas budgets and in geochemical cycling in collision zones.
[3] In this paper, the general terminology, as well as the distribution of mud volcanism on Earth in its tectonic context, is introduced (section 2).
Key issues concerning the nature of mud extrusion dynamics will be discussed.
These include the influence of the physical properties of the gaseous, aqueous, and solid phases, as well as processes like rapid sediment accumulation, enhanced fluid pressures, gas hydrate stability, and geochemical processes (see section 3).
Combined with geophysical investigations and results from modeling, quantitative studies estimate
(1) mobilization depth of the different phases (section 4),
(2) material flux with time, and
(3) the impact of mud volcanism on global budgets (section 5).
Finally, a compilation of the literature on mud volcanoes appears in Appendix A.
This summary closely resembles the review by Higgins and Saunders [1974], with the more recent discoveries added.
Appendix A covers the early description of enigmatic mud features [e.g., Goad, 1816; Abich, 1857] up to the most recent studies [e.g., Bouriak et al., 2000; Delisle et al., 2002; Etiope et al., 2002] and is divided into regional sectiondiscussed.
These include the influence of the physical properties of the gaseous, aqueous, and solid phases, as well as processes like rapid sediment accumulation, enhanced fluid pressures, gas hydrate stability, and geochemical processes (see section 3).
Combined with geophysical investigations and results from modeling, quantitative studies estimate
(1) mobilization depth ofthe different phases (section 4),
(2) material flux with time, and
(3) the impact of mud volcanism on global budgets (section 5).
Finally, a compilation of the literature on mud volcanoes appears in Appendix A.
This summary closely resembles the review by Higgins and Saunders [1974], with the more recent discoveries added.
Appendix A covers the early description of enigmatic
mud features [e.g., Goad, 1816; Abich, 1857] up to themost recent studies [e.g., Bouriak et al., 2000; Delisle etal., 2002; Etiope et al., 2002] and is divided into regional sections.