**2. Observations consistent with serpentosphere source**

The hot, hydrothermal, serpentosphere-sourced, mud volcanic model integrates with several recent observations that are problematic for existing models. These observations include the following:


#### **2.1 Density-driven mineral fractionations**

Mineral paragenesis in the combined Weissliegend-Kupferschiefer-Zechstein sequence can be characterized as a density-driven fractionation process. Heavier minerals generally appear earlier and deeper in the sequence in the Kupferschiefer and lighter minerals appear later and higher in the Zechstein sequence.

The intimate association of hydrocarbon generation coinciding with sulfide deposition is shown in **Figure 3**, where a small diapiric body of zoned sulfides projects into the soft marls of the lower Zechstein at the hydrocarbon generation horizon. This relationship demonstrates the hydrogenation effect induced by sulfide deposition from chloride-rich brines, per the chemistry shown in **Figure 2**. The diapir-like shape of the sulfide mineralization can be inferred to represent a smallscale analog of the vertical pipe-like features present throughout the Kupferschiefer. The entire depositional sequence appears to be more or less coeval and occurred under soft, mud slurry conditions that were migrating upward from high pressure to low pressure.

Fractionation occurs at all scales within the Kupferschiefer section. At the broad system scale, mineral densities generally become lighter up-section and with decreasing age (**Table 1**). At the deposit scale (**Figure 4**), pipe-like features have been

**Figure 3.**

*Immiscible bornite-chalcopyrite-injectite with covellite, solid state exsolution into soft, carbonaceous-dolomitic muds of the Zechstein dolostone, mounted on a stylolite of massive bitumen hydrocarbon. Spremberg DH 131. //Nic. [2].*

intersected by drillholes beneath the Rudna mound. At the district scale (**Figure 5**), a, high-density, heavy, noble element suite (Au, PGE, U) is associated with the latestage, Rote Fäule and is present near deep-seated pipes or fault conduits, such as the Odra fault, as documented by Kucha [9]. Many of Kucha's observations anticipate the perspectives offered here. Deep-seated pipe structures might be located beneath high density, uranium-rich, gamma anomalies along and near the Odra fault [9, 10].

The early, high-density, copper-rich mineral suite occurs at the base of the Kupferschiefer in the famous, high copper-grade, T-1 unit and in the more recently mined, Weissliegend basal unit of the Zechstein in the Rudna area of southwest Poland. The copper facies and kerogen mainly formed during the widespread Stage 1 episode.

After a short pause, chalcopyrite-sphalerite- and lesser galena were deposited in the basal Zechstein dolomitic marls. The lead facies and bitumen corresponds to Stage 2. Low-density hydrocarbons and calcitic marls co-formed and continued to form after the dolomitic marls along with pyritic sulfides. The final phases of Zechstein deposition were associated with a low density, saline mineral suite. Within this saline mineral suite, a density-driven zoning is apparent. Higher density anhydrite occurs in the lower cycles and lower density, magnesium-potassium halides (carnallite, kieserite, and sylvite) occur in the higher cycles. Halite deposition is widespread, but appears to be maximized in the middle cycles.

#### **2.2 Carbon isotopes**

Carbon isotope data for the Kupferschiefer are also consistent with other isotope data that indicate a deep serpentosphere source. The δ13C isotope data for all Kupferschiefer samples are shown in **Figure 6** and range from 23 to 28‰ [11–18]. The Kupferschiefer carbon isotopes completely overlap those of oceanic serpentinite seawater peridotite inclusions. Carbon isotopes from Kupferschiefer plot in the middle of the serpentinite-peridotite-kerogen oil window.

Important additional carbon isotope correlations include those for dissolved kerogen (DOC) in deep sea water, saline, hydrothermal fluids from deep marine


### *Generation of Mud Volcanic Systems Sourced in Dehydrated Serpentospheric Mantle DOI: http://dx.doi.org/10.5772/intechopen.105689*

#### **Table 1.**

*Paragenetic sequence and zoning integrated with mineral densities for the Kupferschiefer-Zechstein section (youngest at top).*

seeps hosted in basalt on the Juan de Fuca Ridge, and a partial overlap with serpentine-sourced hydrothermal fluids emanating from white smokers at Lost City in the central Atlantic Ocean. There is also a complete overlap with carbon isotopes in world-wide oil. This carbon isotope correlation allows the inference that the serpentosphere described below is the ultimate source of oil, carbonaceous shale, and metallization in the Kupferschiefer.

#### **2.3 Sulfur isotopes**

An isotopic feature that is unique to the Kupferschiefer-Zechstein sulfide system is the extremely light sulfur isotope data at Lubin (**Figure 7**) [19]. In chalcocitedigenite samples, the <sup>δ</sup>32S reaches values as low as 39.9‰. Pyrite samples are

#### **Figure 4.**

*Deposit-scale cross section of the Rudna deposit showing that smaller-scale pipe structures are also present at larger scales (modified from [11]).*

#### **Figure 5.**

*Regional metal zoning in the greater Lubin district and its geographic relationship to the deep-seated Odra fault (adapted from [9]).*

*Generation of Mud Volcanic Systems Sourced in Dehydrated Serpentospheric Mantle DOI: http://dx.doi.org/10.5772/intechopen.105689*

#### **Figure 6.**

*Carbon 13 isotopes in the Kupferschiefer compared with δ13C isotope data from world-wide, serpentine-related and other rocks (Kupferschiefer data from [11–14] for Konrad data, [15] for Lost City and other data, [16] for deep seawater, and [17] for basaltic fluids from Juan de Fuca Ridge (as modified from data in [18]).*

anomalous and range from 42.01 to 44.9‰. In the early-stage chalcocitedigenite-bornite assemblage in the lower to middle Kupferschiefer, sulfur isotopes range between about 31 and 40‰.

#### **Figure 7.**

*Sulfur isotopes at the Lubin copper mine (modified from [19]). Abbreviations: P = pyrite; Ch = chalcocite; D = digenite; B = bornite; C = chalcopyrite; S = sphalerite; G = galena; K = covellite; and T = tennantitetetrahedrite. Values of <sup>δ</sup>34S range from 10.23 to 7.65‰ for tennantite-tetrahedrite.*

In contrast, in the overlying carbonate-marl Kupferschiefer and marl Zechstein carbonates, sulfur isotopes range between 31 and 20‰. Presumed late-stage tennantite-tetrahedrite veins exhibit distinct heavy δ34S-enriched sulfur isotopes. Similar sulfur isotope patterns were documented by Spieth [2] in the Kupferschiefer deposit at Spremberg, Germany. Hence, the paragenetic sequence of light reductive sulfur isotopes transitioning upward to heavy oxidized sulfur isotopes for Kupferschiefer types of deposits appears to be a general characteristic of the deposit type.

Given the high temperature of the sulfide mineralization documented by Spieth and Keith and others [1, 2], these low values cannot be explained by microbial reduction. Some other reductive mechanism or source is required. Serpentinization of peridotite is the only other known geologic process that we are aware of that can create light δ34S isotopes (**Figure 8**). These light δ34S serpentines then become a source for subsequent steatization reactions during mantle heat overprinting, such as may have occurred at the end of the Permian.

Extremely light sulfur isotopes that are associated with late disseminated pyrite in the overlying Zechstein limestones may be explained by low-temperature, conventional microbial reduction in the classic portrayals by Wedepohl [20] for the Kupferschiefer. However at Kupferschiefer, the microbial signature is inferred to be superimposed on an already light sulfur isotope condition that is serpentinitesourced as in **Figure 8**.

*Generation of Mud Volcanic Systems Sourced in Dehydrated Serpentospheric Mantle DOI: http://dx.doi.org/10.5772/intechopen.105689*

**Figure 8.**

*Comparison of the sulfide and sulfate isotope compositions of serpentinites from Liguria, the Iberian Margin, the Atlantis Massif, and the MARK area (modified from [19] and including data from references therein).*

Only one rock type, oceanic serpentinite, exhibits extremely light sulfur isotopes. When compared with the sulfur isotopes in sulfides in Kupferschiefer rocks [2], it can be argued that brines that were sourced in the serpentine-steatite reaction chamber were buffered at similar low oxidation states. Significantly, oceanic serpentinites have been identified in the Caledonian basement immediately to the southeast of the Lubin and Konrad Kupferschiefer mineral systems southeast of Wroclaw.

An upward-lightening sulfur isotope pattern was observed by Sawlowicz and Wedepohl [21] in the Weissliegend sand extrudite mounds at Rudna. The upwardlightening pattern of sulfur isotopes ranged from <sup>δ</sup>34S of <sup>39</sup>‰ at the bottom of the chalcocite rhythmite section to 44‰ at the top of a composited rhythmite section. The presence of generally light sulfur isotopes allows the interpretation that deep, serpentinite-sourced brines for the slurries began to deposit chalcocite at the base of the Weissliegend. Hydrogen reduction associated with progressive chalcocite deposition from chloride-hydrogen sulfide brines would have led to production of increasingly lighter δ34S isotopes similar to the broader pattern observed by Kościński in **Figure 7** [19] and the light sulfur isotope signature of reduced serpentinite sequences.

#### **2.4 Deep-sourced chemistry and mineralogy in the Zechstein saline succession**

Keith and others [1] also hypothesized that much of the saline mass residing in the thick (up to 2000 m), Zechstein saline sequence is not derived from surface evaporative processes, but instead consists of saline, exhalative, chemical, hydrothermal brine products derived from deep serpentinite sources. The concept of a deep serpentine source is supported by the frequent occurrence of talc and magnesium chlorite (clinochlore) in muds, and even serpentine (antigorite) in muds at a number of localities (**Figure 1**) in the Zechstein [1]. An additional serpentine mud locality was reported from the Morsleben salt diapir [6]. Both the Morsleben and

Gorleben salt diapirs contain high-lithium brines that were interpreted to represent basement-sourced metamorphic brines [6] and that fit the dehydration narrative discussed below.

Authigenic, Herkimer-habit, quartz crystals contain carnallite in hot, brine fluid inclusions that homogenized at over 200°C in Zechstein salt diapirs. Additional fluid inclusion data reported by Vovnyuk and Czapowski [22] showed that in sylvite-stable, potassium-rich salines, two sets of fluid inclusions were present. The first set ranged from 50° to 62°C, indicating warm hydrothermal conditions attended high-potassium sylvite precipitation from 'basin brines'. The second set ranged from 82° to 135°C, indicating hot hydrothermal conditions. From the perspective of the deep, hot, serpentine-sourced, mud-volcanic model, these brines may have been sourced at much deeper levels in the crust. For example, sylvite has been reported from fluid inclusions in the Weissliegend copper ore, along with potentially primary atacamite reported by Michalik [23].

The rare mineral rokühnite (iron chloride, also known as 'black carnallite') is locally common in carnallite-rich zones at several locations in the Zechstein. To date, rokühnite is not found in other saline localities. The presence of rokühnite may suggest special conditions in the underlying basement whereby both copper and iron were transported in chloride-rich brine to be deposited in overlying carnallite zones of the Zechstein saline sequences.

## **3. Brine source in the serpentosphere**

#### **3.1 Description of serpentosphere**

Keith and others [24] defined the serpentosphere as a thin (about one to ten kilometers thick), nearly continuous, global-scale layer of serpentinite rock that occurs between the crust and mantle. The serpentosphere is composed mainly (90%) of serpentine group minerals (**Table 2**) [25–27]. An expanded description of the serpentosphere is included here because the serpentosphere concept is important to the Kupferschiefer origin. Chemical compositions of the three main serpentine group minerals were selected by non-chemical criteria by Page [25] and are shown in **Table 2**.

The serpentosphere occurs at the transition between the oceanic crust and the peridotitic mantle, which is widely referred to as the Moho (Mohorovicic geophysical discontinuity). The Moho is characterized by a change in P-wave seismic velocities (Vp) that range from 6.8 to 8.2 km/sec (**Figure 9**). These velocities are also characteristic of serpentine, as characterized by petrophysical laboratories. When interpreting seismic velocity profiles and sections, Vp velocities of 6.8 to 7.3 km/sec indicate lizardite serpentinite and velocities of 7.3 to 7.8 km/sec indicate antigorite serpentinite in serpentinites that have been about 50% serpentinized [26].

Thicker initial serpentosphere material (about 2.5 km thick) may be generated at relatively shallow depths adjacent to slower spreading ridges, such as the Southwest Indian Ridge [28]. Thinner serpentosphere (about 1.5 km thick) may be generated at moderately fast spreading ridges, such as the mid-Atlantic ridge (shown in **Figure 9**).

More recent geophysical work has produced seismic-reflection images of the rocks that comprise the Moho (**Figure 10**). For example, the seismic reflection studies of the northeast Pacific have imaged a reflector layer about 3 km thick beneath a 200 km-long seismic line [29]. The reflectance texture is consistent with shearing that has produced a mylonitic fabric induced by creep of the upper oceanic crust above the peridotitic mantle.

Recent seismic evidence now suggests that the Moho is not simply a geophysical feature, but rather is a thin layer of serpentine-dominated rock. Such rocks have


*Generation of Mud Volcanic Systems Sourced in Dehydrated Serpentospheric Mantle DOI: http://dx.doi.org/10.5772/intechopen.105689*

#### **Table 2.**

*Average composition of serpentine group minerals (data from [25, 27]).*

#### **Figure 9.**

*Seismic habitats and P seismic wave velocities of the serpentosphere (modified from [28]). Light green lines indicate lizarditic serpentosphere P wave velocities. Dark green lines indicate antigoritic serpentosphere P wave velocities.*

been long known, starting with the observations by Steinmann [30] in ophiolite belts that are now sutured into continents. Hess [31] was the first researcher to suggest that there might be a globally distributed layer of serpentinite beneath the ocean basins. Hess noted that serpentine-bearing ophiolites have a world-wide distribution in suture zones within continents [31], which is consistent with the presence of the serpentosphere beneath continental areas.

#### **Figure 10.**

*Deep seismic image (200 km long) in the northeast Pacific showing the Moho as a zone of subhorizontal reflectors about 3 km thick (modified from [29]).*

### **3.2 Tectonic settings of serpentosphere**

Serpentosphere occurs in four tectonic settings shown in **Figure 11**. Briefly, serpentosphere is made by hydrolysis of mantle peridotites adjacent to oceanic spreading centers (upper left diagram in **Figure 11**). The serpentosphere is then subducted under normal subduction conditions beneath an aesthenosphere-mantle hanging wall (lower left part of diagram), where it sequentially dehydrates to produce hydrous metaluminous arc magmatism in the hanging wall that ultimately intrudes the upper crust to make magmatic arcs.

#### **Figure 11.**

*Schematic diagrams of four major tectonic settings for the serpentosphere (green line) as discussed in this paper. Upper left: generation of serpentosphere at oceanic rift spreading centers. Lower left: subduction of serpentosphere in normally dipping subduction zones. Upper right: flat subduction of oceanic serpentosphere beneath continental crust during oceanic crust-continent assemblies. Lower right: continental rifting and dehydration of formerly underplated serpentosphere by mantle heating during continental breakups.*

*Generation of Mud Volcanic Systems Sourced in Dehydrated Serpentospheric Mantle DOI: http://dx.doi.org/10.5772/intechopen.105689*

A less familiar geotectonic setting is flat subduction beneath typically continental upper plates (upper right part of diagram). In such cases, dehydration of the serpentosphere can produce extensive melting of crustal material in the upper plate to produce peraluminous granitoids.

Subsequent rifting of crust that has experienced previous episodes of flat subduction (lower right part of diagram) can then be systematically dehydrated by mantle heat. The continental rift setting is the tectonic setting envisioned for Kupferschiefer-Zechstein types of deposits.

#### *3.2.1 Oceanic rift tectonic settings*

Formation of serpentosphere is started near oceanic spreading centers at the mantle-crust contact (**Figure 12** with the explanation in **Figure 13**). Oceanic fluids are pushed down by the weight of the overlying water column into the oceanic fracture system to the contact between the gabbroic oceanic crust layer and the underlying peridotitic mantle. Regional-scale serpentinization reactions occur at that contact and produce low temperature lizardite/chrysotile serpentine [32].

Formation of the serpentosphere results from serpentinization (i.e., hydration) of mantle peridotite by seawater (Eq. (1)). The hydration involves adding water and accompanying elements (especially chlorine and carbon) from the seawater into serpentine. The main serpentine group mineral produced at this stage is the relatively low temperature mineral lizardite, along with magnetite and a brine component. Compared to antigorite, lizardite serpentines are much more oxidized and more hydrous.

Magnetite formation produces considerable hydrogen, which can react with existing carbon in the peridotite to make additional kerogen products, which are shown in Eq. (2). The process is exothermic and heat is released during the reaction. These reactions are important regulators for global climate and, ultimately, hydrothermal hydrocarbon formation.

Simplified serpentinization reaction under supercritical conditions (Eq. (1)).

6 Mg1*:*5Fe0*:*<sup>5</sup> SiO4 <sup>þ</sup> 8 Hð Þ! 2O 3Mg3Si2O5ð Þ OH <sup>4</sup> <sup>þ</sup> Fe3O4 <sup>þ</sup> H2 <sup>þ</sup> H2O <sup>þ</sup> Heat*:*

Olivine þ Seawater ! Serpentine lizardite ð Þþ Magnetite þ Brine þ Heat (1)

Simplified serpentinization reaction with carbon under supercritical conditions (Eq. (2)).

$$\begin{aligned} &\text{6(Mg}\_{1.5}\text{Fe}\_{0.5})\text{SiO}\_{4} + 0.04\text{C} + 8(\text{H}\_{2}\text{O}) + 0.24\text{HCO}\_{3} \rightarrow \text{Mg}\_{3}\text{Si}\_{2}\text{O}\_{5}(\text{OH})\_{4} \\ &+ \text{Fe}\_{3}\text{O}\_{4} + 0.01\text{HC} + 0.45\text{H}\_{2} + 0.04\text{HC} + 0.09\text{CH}\_{4} + 0.04\text{CHO} \\ &+ \text{0.1CO}\_{2} + 1.44\text{H}\_{2}\text{O} + \text{Heat}. \end{aligned}$$

$$\begin{aligned} \text{Olivine} &+ \text{Carbon in oilivine} + \text{Seawater} + \text{Bicarbonate} \\ &\rightarrow \text{Serpente}(\text{lizarlite}) + \text{Magntite} + \text{Korogen} + \text{Methanol} \end{aligned} \tag{2}$$

þ Formate þ Carbon dioxide þ Water þ Heat*:*

Once the serpentinization reaction is initiated, continued seawater flux maintains the reaction. Hence, the thickness of the serpentosphere increases progressively away from spreading centers. At the mid-ocean ridge, serpentosphere thickness is near zero, whereas in oceanic crust adjacent to continents well away from the ridge, serpentosphere thicknesses may range up to 10 km or more.

Lizardite serpentosphere is produced under lower pressure, lower greenschistgrade, hydrothermal, metamorphism/hydration of mantle peridotites in oceanic ridge settings. Brine leakage from this reaction (Eq. (1)) produces white smokers (calcite with minor brucite), such as the white smoker field at Lost City in the central Atlantic Ocean. At the on-ridge setting, oceanic brines leach gabbro to produce sulfide-rich black smokers. The carbon in serpentinite is largely added from seawater as shown in Eq. (2).

The extended serpentine reaction (Eq. (2)) introduces carbon into the serpentinebrine system. The carbon component is probably introduced as bicarbonate or dissolved kerogen (DOC in the literature). These carbon compounds are then reacted into the serpentine-brine product system as varying amounts of dissolved kerogen (HC), methane (CH4), formate (CHOO), and carbon dioxide (CO2) brine products. Recent literature shows that reduced carbon species are also present in the deep oceans beneath about 2 km [16] and in submarine vents [17].

*Generation of Mud Volcanic Systems Sourced in Dehydrated Serpentospheric Mantle DOI: http://dx.doi.org/10.5772/intechopen.105689*

Both oxidized and reduced carbon sources can be cycled down to the Moho contact where the serpentosphere and its resultant brine products are made. The brine products can then be cycled back up through the overlying oceanic crust to make submarine vents, such as Lost City, and pock marks on the ocean floor.

In this broader perspective, derivative products, such as oil and life, began their evolution in seawater with serpentine as an important mediator. An important link to creation of life is the presence of formate shown in Eq. (2). Formate potentially is the starting platform on which amino acids, RNA, and ultimately DNA can polymerize. The plastic nature of serpentine also functions as a tectonic 'grease' that facilitates plate tectonics.

Compared to the parent peridotite, serpentinites are more magnetic and are lower in density [27]. The coincidence of a magnetic high with a gravity low gives a geophysical signature that can indicate the position of serpentinites at depth beneath or adjacent to ore deposits and oil accumulations, such as richer vents, like Rudna in the Polish Kupferschiefer.

#### *3.2.2 Normal-dip subduction tectonic settings*

Antigorite serpentosphere is produced via dehydration of lizardite serpentosphere between 300 and 400°C [32] in both normal-dip settings (oceancontinent collisions) and flat subduction settings (continent-continent collisions). The more familiar type of antigorite serpentosphere is formed in normally dipping subduction zones and is later incorporated into alpine collisional orogens as the well-known alpine serpentinites.

#### *3.2.3 Flat-subduction tectonic settings*

A less familiar type of antigorite serpentosphere is formed in flat or shallowly dipping subduction zones. A detailed schematic of flatly subducting oceanic serpentosphere beneath continental crust is shown in **Figure 14** with the legend in **Figure 15**. Flat subduction of serpentosphere is frequently coupled with trenchdirected thrust faults that can provide conduits for deep-sourced brines that were generated during dehydration of the underplating serpentosphere.

An example is the latest Laramide, flat subduction beneath western North America in the Paleocene-Eocene. Kerogen in the flatly subducting serpentosphere is typically a high-hydrogen, Type I kerogen that is linked to Type I petroleum accumulations, such as those found in Wyoming, Colorado, and Utah in the Green River, hypersaline shale horizons. In the case of the Kupferschiefer, flat subduction of the Iapetus Ocean serpentosphere beneath northern Europe occurred 135 Ma earlier, making serpentinite available for later dehydration.

Flat subduction of serpentosphere material is a very under-rated geotectonic process. Mature continental areas are characterized by thick Moho, which may be several times thicker than oceanic Moho. The increased thickness may be due to accumulation of several oceanic serpentosphere layers during numerous, previous, flat subduction episodes at the ends of previous orogenies. These thick serpentosphere layers may be variously dehydrated during subsequent rift episodes associated with continental breakups throughout geologic time.

#### *3.2.4 Continental rift tectonic settings*

Once serpentospheric materials have been emplaced beneath continental areas by flat subduction, subsequent rifting of the continents creates opportunities for systematic dehydration of the serpentosphere by mantle heat fluxes. Such situations

#### **Figure 14.**

*Schematic cross section of flat subduction emphasizing southwestern North America features, such as the Green River shales [33]. Explanation is in Figure 15.*

occurred in North America and Europe during the breakup of the Pangea supercontinent near the end of the Permian. A schematic cross section of the results of the dehydration and diapiric processes in rift tectonic settings is shown on **Figure 16** [1]).

A distinguishing feature of rifting and continental breakups is the penetration of the decompression cone down into the deep, lower mantle aesthenosphere. When this deeper penetration occurs, resulting more alkaline diapirs may ascend and interact with the dehydrating serpentospheric material at the base of the rifting and extending continent. These deep interactions may lead to the production of more potassium-rich, alkaline, hydrocarbon deposits (Type II) and their associated brine deposits. These more potassic brines, in turn, lead to the production of much more potassium-rich salines, which precipitate minerals like carnallite and sylvite.

In contrast, in rifting of previously flatly subducted oceanic crust, there is no decompression cone. Instead, shallow, upper mantle, depleted peridotites are hydrated and produce much more sodium-enriched brines that, in turn, lead to sodium-rich trona and nahcolite deposits, such as the Green River hypersaline deposits in the western U.S.

**Figure 15.** *Explanation for Figure 14.*

## **3.3 Application to kupferschiefer-zechstein sequence**

When the above observations are applied to the crust beneath the part of southwestern Poland that contains the Kupferschiefer-Zechstein, a deep serpentosphere pattern is present (**Figure 17**). In the central Polish velocity profile shown in **Figure 17**, low-angle, lensoid-shaped packages with Vp (P-wave) velocities [34]

**Figure 16.**

*Schematic model of serpentine diapirs in rift settings, modeled on the Viking Graben structure in the North Sea between Norway and Great Britain in Kupferschiefer time and explanation(from [1]).*

that are consistent with both lizardite and antigorite serpentinites are present beneath southwest Poland.

A more detailed diagram of geophysical profiles for the Lubin area (**Figure 17**) has been modified to show the possible relationship of the Kupferschiefer deposits at Lubin and Konrad to metalliferous plumes originating in continental serpentosphere (expressed by numerous sub-parallel reflectors between 6 and 11 seconds). The plumes utilize a deep-seated fault system, which includes faults that penetrate the crust (such as the Odra fault) and which is indicated by breaks/ troughs in the magnetic profile. These are adjacent to the Sudetic block, basement high indicated by the gravity high (**Figure 17**).

Gravity and magnetic profiles for a geophysical line that traverses the Kupferschiefer type deposits on either side of the Fore-Sudetic gravity high [35] show coupled, low-gravity and high-magnetic features are present (**Figure 17**). The gravity low/magnetic high features indicate the possible presence of deep serpentinite. These features may coincide with a deep-seated feeder system that connects deep serpentosphere crust to the Konrad Kupferschiefer system on the south side and the Lubin system on the north side of the Fore-Sudetic high (**Figure 17**).

The importance of deep-seated basement flaws, such as the Odra fault system in Poland, is shown in **Figure 17**. These faults focus heat flow, as well as deep-seated gas fluxes, such as helium that could be generated via serpentinization processes. The presence of such faults can help initiate serpentinite dehydration processes in the lower crust by focusing heat flow from the underlying mantle during continental breakups. An example of continental breakups is the attempted breakup of Pangea in northern Europe in Late Permian. Such a process may have led to development of the Kupferschiefer-Zechstein in the upper crust.

*Generation of Mud Volcanic Systems Sourced in Dehydrated Serpentospheric Mantle DOI: http://dx.doi.org/10.5772/intechopen.105689*

**Figure 17.** *Serpentosphere (Moho) beneath Rudna-Konrad-Spremberg Kupferschiefer (modified from [35]).*

The position of the Lubin district and the Odra fault projected to the section line is of relevance to the mud-volcanic origin of the Kupferschiefer-Zechstein presented in this article. The Odra fault projection coincides with a prominent deflection of the middle crust velocity packages that extend down to the presumed serpentospherevelocity lenses in the lower crust (**Figure 18**). For a serpentinite-sourced, ascending, hot brine-mud plume, the upward travel distance is only about 20 km.

Notably, the inferred Caledonide serpentospheric basement is identified in basement massifs southwest of the European Suture zone shown on **Figure 18**, but does not occur to the northeast of the suture. To our knowledge, no Kupferschiefertype deposits and no deep serpentosphere geophysical signatures are present northeast of this suture. Thus, the European Suture may place an eastern limit on the occurrence of Kupferschiefer-type systems. The lack of Caledonide basement northeast of the European Suture further emphasizes the inference that the presence of serpentosphere is a necessary condition for the occurrence of Kupferschiefer-type systems.

The presence of serpentinite-bearing ultramafic complexes in the basement of uplifts adjacent to Kupferschiefer types of deposits is also important (**Figure 19**). The nearby presence of ultramafic sources, such as the Jordanów-Gogolów serpentinite massif [36], is particularly relevant to the deposits in the Lubin district. Rodingite from this massif was dated at 400 Ma [37]. Fluid inclusions within the dated zircons have yielded homogenization temperatures ranging from 268 to 290° C at about 1 kbar. These data place constraints on the temperatures, pressures, and timing of emplacement of serpentospheric materials in the basement beneath the Kupferschiefer and the hydrothermal event associated with rodingite formation.

#### **Figure 18.**

*Map of Poland and nearby areas showing Teisseyre-Tornquist Zone (TTZ), northeast of which there are no Kupferschiefer type deposits and possibly no underlying Caledonide continental serpentosphere and showing location of the greater Lubin-Kupferschiefer district and its possibly related, deep-seated Odra fault [34]. BT Baltic Terrane, EA Eastern Avalonia, FSS Fennoscandia-Sarmatia Suture, MLSZ Mid-Lithuanian Suture Zone, PLT Polish–Latvian Terrane, RG Rønne Graben, RFH Ringkobing-Fyn High, STZ Sorgenfrei-Tornquist Zone,TTZ Teisseyre-Tornquist Zone, VDF Variscan Deformation Front. The area of Bohemian Massif is highlighted in dark green. The Trans-European Suture Zone separates thick and cold Precambrian crust from younger, thin and hot Paleozoic crust. Yellow star shows the location of Libiąż earthquake, which was recorded at LUMP seismic stations. Yellow line shows the LUMP profile (modified from [34]).*

*Generation of Mud Volcanic Systems Sourced in Dehydrated Serpentospheric Mantle DOI: http://dx.doi.org/10.5772/intechopen.105689*

**Figure 19.**

*Map showing the geographic relationship between the Kupferschiefer deposits and potential ultramafic sources in the Variscan/Caledonide basement (maps modified from [36] and [37]).*

The rodingitization event 135 Ma earlier was not the event that created Kupferschiefer mineralization. The serpentosphere emplacement circa 400 Ma, however, was a necessary precursor condition for the ultimate formation of the Kupferschiefer. Without the presence of the Caledonide serpentosphere, the Kupferschiefer could not have happened. During lizarditization of the oceanic peridotites, key ingredients (such as fluorine, sulfur, copper, and others) were added to the lizardite. These elements would later be added to the Kupferschiefer brines during later dehydration events, starting in the uppermost Permian.

With respect to the continental serpentosphere, data suggest that the serpentospheric materials were emplaced beneath northern Europe during the lowangle subduction event of the Iapetus Ocean circa 400 Ma. This material was then affected by mantle-heat-driven dehydration beneath the Odra and related fault systems beginning about 265 Ma, approximately 135 Ma after the emplacement of the Caledonide serpentosphere. The result is hypothesized to be the Kupferschiefer-Zechstein mineralization.
