**5. Alteration of peperites**

Microfacies of peperites has been an essential tool in recognition of alteration of peperites as it encompasses the change in mineral and chemical composition of juvenile clasts and the mingling sediment, and more rarely, the formation of interstitial cement. Juvenile blocky clasts dispersed in abundant siliciclastic silt commonly underwent only devitrification, the alteration of glassy juvenile clasts with perlitic

### **Figure 11.**

*(A) an intimate mixture of elongate altered clasts of sediment (S) and juvenile clasts (L); (B) sediment (S) entrained into lava flow (L) through a laminar boundary layer. The arrow shows the entrainment direction. The elongated sediment clast soon becomes thinner (t). Along the first obstacle it becomes thicker (T) by enclosing the phenocryst, and then becomes thinner by avoiding the second phenocryst; (C) microstructure of peperite indicating turbulent flow (t) by disrupted and convoluted sediment layers (S) in lava (L); (D) an intimate mixture of elongated clasts of sediment (S) and juvenile clasts (L); (E) platy juvenile clasts (L) formed by penetration of magma into fine-grained volcanic ash (T); (F) juvenile clasts (jc) and fluidised sediment (S) developed owing to the intrusion of the Kramarica Sill. The sediment is altered to iron oxides and the larger juvenile clast to laumontite (Lmt).*

cracks may involve the formation of laumontite and Fe-oxides (**Figure 9A**). The mingling sediment is, in general, unaltered except for locally developed iron oxides.

Peperites with denser population of juvenile clasts, and particularly juvenile clasts having irregular fluidal or amoeboid shape, that mingled with siliciclastic silt are commonly altered to laumontite or laumontite and iron oxides. The host sediment commonly remained unaltered (**Figure 13A**).

Some juvenile clasts are replaced by the assemblage of laumontite, albite, quartz, actinolite and epidote (**Figure 13B**), or laumontite, albite, quartz, pumpellyite, incipient epidote and chlorite, or laumontite, prehnite, quartz, chlorite and

**315**

**Figure 12.**

*Submarine Stratovolcano Peperite Syn-Formational Alteration - A Case Study of the Oligocene…*

incipient epidote, or laumontite, analcime and interlayered chlorite-smectite. Incipient epidote [53] refers to some μm to a few 10 μm sized, oval and highly birefringent grains. If the mingling sediment was siliciclastic silt it is often altered to

*(A) the arrows (i) and (r) show the directions of magma penetration in intergranular space of volcaniclastic turbidite deposit. The arrow (o) indicates the cessation of penetration along a volcanic rock fragment (VRF); (B) penetration of magma (arrows) into volcaniclastic turbidite deposit by pushing aside crystal grains (cg). The cessation of penetration resulted in the formation of a juvenile clast (jc); (C) penetration of magma (m) stopped by crystal grains, the direction is marked by arrows, VRF – volcanic rock fragments; (D) stacked phenocrysts (Ph) of augite and a glassy constituent of magma (g) that penetrated somewhat further into volcaniclastic* 

If the mingling sediment was fine-grained pyroclastic deposit the alteration minerals commonly resemble those in the juvenile clasts. The most extensive alteration underwent the clasts composed of fine-grained pyroclastic deposit that were incorporated into lava flow, or fine-grained pyroclastic sediment that was entrained into lava flow through lamination boundary layers (**Figure 13C**). A common alteration assemblage is albite, prehnite, quartz, iron oxides and chlorite or interlayered chlorite-smectite with more than 80% of chlorite layers [54]. In the advanced stage of mingling (**Figure 11A**) the alteration of sediment commonly remained the same

Penetration of the host sediment into juvenile clasts had immediate impact to its alteration. Before the sediment penetrated juvenile clasts and also in the initial stage of formation of droplets it commonly remained unaltered (**Figure 10B,C**), but with advanced penetration and subsequent dispersion into the juvenile clasts, and the transformation of shape from irregular to spherical and oval, the alteration advanced as well (**Figure 10E, 13D**). Such inclusions of the host sediment closely resemble vesicle fillings and could be easily misinterpreted. Common alteration minerals are laumontite (**Figure 13D**), and the assemblages of or prehnite, laumontite and quartz (**Figure 13E**), or pumpellyite, albite, quartz and chlorite (**Figure 13F**), or laumon-

microcrystalline quartz, incipient epidote and iron oxides.

*turbidite deposit, the arrows mark the directions of magma penetration.*

while the juvenile clasts can be altered to iron oxides and chlorite.

tite, prehnite, quartz, epidote and chlorite.

*DOI: http://dx.doi.org/10.5772/intechopen.95480*

*Submarine Stratovolcano Peperite Syn-Formational Alteration - A Case Study of the Oligocene… DOI: http://dx.doi.org/10.5772/intechopen.95480*

### **Figure 12.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

cracks may involve the formation of laumontite and Fe-oxides (**Figure 9A**). The mingling sediment is, in general, unaltered except for locally developed iron oxides. Peperites with denser population of juvenile clasts, and particularly juvenile clasts having irregular fluidal or amoeboid shape, that mingled with siliciclastic silt are commonly altered to laumontite or laumontite and iron oxides. The host sedi-

*(A) an intimate mixture of elongate altered clasts of sediment (S) and juvenile clasts (L); (B) sediment (S) entrained into lava flow (L) through a laminar boundary layer. The arrow shows the entrainment direction. The elongated sediment clast soon becomes thinner (t). Along the first obstacle it becomes thicker (T) by enclosing the phenocryst, and then becomes thinner by avoiding the second phenocryst; (C) microstructure of peperite indicating turbulent flow (t) by disrupted and convoluted sediment layers (S) in lava (L); (D) an intimate mixture of elongated clasts of sediment (S) and juvenile clasts (L); (E) platy juvenile clasts (L) formed by penetration of magma into fine-grained volcanic ash (T); (F) juvenile clasts (jc) and fluidised sediment (S) developed owing to the intrusion of the Kramarica Sill. The sediment is altered to iron oxides and the larger* 

Some juvenile clasts are replaced by the assemblage of laumontite, albite, quartz, actinolite and epidote (**Figure 13B**), or laumontite, albite, quartz, pumpellyite, incipient epidote and chlorite, or laumontite, prehnite, quartz, chlorite and

ment commonly remained unaltered (**Figure 13A**).

**314**

**Figure 11.**

*juvenile clast to laumontite (Lmt).*

*(A) the arrows (i) and (r) show the directions of magma penetration in intergranular space of volcaniclastic turbidite deposit. The arrow (o) indicates the cessation of penetration along a volcanic rock fragment (VRF); (B) penetration of magma (arrows) into volcaniclastic turbidite deposit by pushing aside crystal grains (cg). The cessation of penetration resulted in the formation of a juvenile clast (jc); (C) penetration of magma (m) stopped by crystal grains, the direction is marked by arrows, VRF – volcanic rock fragments; (D) stacked phenocrysts (Ph) of augite and a glassy constituent of magma (g) that penetrated somewhat further into volcaniclastic turbidite deposit, the arrows mark the directions of magma penetration.*

incipient epidote, or laumontite, analcime and interlayered chlorite-smectite. Incipient epidote [53] refers to some μm to a few 10 μm sized, oval and highly birefringent grains. If the mingling sediment was siliciclastic silt it is often altered to microcrystalline quartz, incipient epidote and iron oxides.

If the mingling sediment was fine-grained pyroclastic deposit the alteration minerals commonly resemble those in the juvenile clasts. The most extensive alteration underwent the clasts composed of fine-grained pyroclastic deposit that were incorporated into lava flow, or fine-grained pyroclastic sediment that was entrained into lava flow through lamination boundary layers (**Figure 13C**). A common alteration assemblage is albite, prehnite, quartz, iron oxides and chlorite or interlayered chlorite-smectite with more than 80% of chlorite layers [54]. In the advanced stage of mingling (**Figure 11A**) the alteration of sediment commonly remained the same while the juvenile clasts can be altered to iron oxides and chlorite.

Penetration of the host sediment into juvenile clasts had immediate impact to its alteration. Before the sediment penetrated juvenile clasts and also in the initial stage of formation of droplets it commonly remained unaltered (**Figure 10B,C**), but with advanced penetration and subsequent dispersion into the juvenile clasts, and the transformation of shape from irregular to spherical and oval, the alteration advanced as well (**Figure 10E, 13D**). Such inclusions of the host sediment closely resemble vesicle fillings and could be easily misinterpreted. Common alteration minerals are laumontite (**Figure 13D**), and the assemblages of or prehnite, laumontite and quartz (**Figure 13E**), or pumpellyite, albite, quartz and chlorite (**Figure 13F**), or laumontite, prehnite, quartz, epidote and chlorite.

### **Figure 13.**

*(A) juvenile clasts (white) altered to laumontite (Lmt), iron oxides (o) and chlorite (Chl). The composition of the mingling siliciclastic sediment (S) remained largely unaltered; (B) a juvenile clast altered to laumontite (Lmt), epidote (Ep) and actinolite (Ac); (C) a clast of fine-grained pyroclastic deposit incorporated in a lava flow has been altered to albite (Ab), quartz (Qtz), chlorite (Chl) and Fe-oxides (o). Some clasts underwent magma assimilation (ma); (D) the mingling fine-grained pyroclastic deposit (S) formed a large oval inclusion in a juvenile clast that has been partially altered into laumontite (Lmt). Smaller inclusions are altered to pumpellyite (Pmp) and quartz, some small spherical inclusions are unaltered (o) and the other replaced by chlorite (Chl). juvenile clasts (jc); (E) an inclusion of fine-grained pyroclastic deposit (s) in a juvenile clast altered to prehnite (Prh) and laumontite (Lmt); (F) inclusions of fine-grained pyroclastic deposit in a juvenile fragment (brownish) altered to pumpellyite (Pmp), epidote (Ep), quartz (Qtz) and albite (Ab). Volcanic glass in the juvenile clast is locally replaced by chlorite (Chl).*

Platy juvenile clasts related to penetration of magma into the host sediment are commonly extensively altered into laumontite and iron oxides (**Figure 11E**). The same assemblage typically replaces irregularly shaped juvenile clasts in peperites formed during the emplacement of the Krmarica Sill (**Figure 11F**).

The alteration of peperites related to coarse-grained host sediment is characterised by chlorite, interlayered chlorite-smectite with more than 90% of chlorite layers, quartz, and sometimes incipient epidote. Laumontite and other zeolites, and pumpellyite, prehnite and epidote are uncommon (**Figure 12A**-**D**).

**317**

*Submarine Stratovolcano Peperite Syn-Formational Alteration - A Case Study of the Oligocene…*

**stratovolcano-hosted hydrothermal system in the Smrekovec Volcanic** 

The stratovolcano-hosted hydrothermal system with convective-advective flow

**6. Peperite alteration in the succession of volcanic deposits and the** 

regime of hydrothermal fluids (**Figure 3**), and another important event in the evolution of hydrothermal alteration of volcanic deposits was the emplacement of the Kramarica Sill. Consequently, volcanic deposits underwent alteration related to diverse processes and different superimposed stages of hydrothermal activity [37]. The largest source of geothermal energy and hydrothermal fluids in the time span

of volcanic activity some 28-23 mya [43] was a deep igneous body. The alteration resulting from an elevated geothermal gradient is characterised by clinoptilolite, heulandite, analcime, smectite and interstratified smectite-chlorite. The convective flow of hydrothermal fluids occurred primarily through fracture systems and the most typical mineral formed owing to hydrothermal activity is laumontite. Where the fractures were densely distributed, the adjacent rock was altered as well. Laumontite occurs as interstitial cement and replaces volcanic glass and intermediate plagioclases in assemblage with albite, and the principal phyllosilicate mineral is chlorite or interstratified chlorite-smectite with over 80% of chlorite layers. Advective outflow of hydrothermal fluids preferentially occurred through highpermeability layers of the stratovolcano edifice, and laumontite, chlorite, albite and more rarely prehnite are typical minerals encountered in coarse-grained rocks such as volcaniclastic breccias. The adjacent, lower-permeability layers contain authigenic minerals with lower temperature stability ranges, namely clinoptilolite, heulandite, analcime and interlayered chlorite-smectite (**Figures 5** and **6**) [37, 38]. Stilbite locally occurs as vein mineral and was developed during late-stage of hydrothermal activity. The emplacement of the Kramarica Sill (**Figure 2**) was related to the formation of new vent along the Periadriatic Line. Thermal effects of the emplacement promoted a number of progressive alteration reactions such as from laumontite to prehnite, laumontite to yugawaralite, or interlayered chlorite-smectite to chlorite. During the cooling of the sill, local hydrothermal conditions persisted and controlled retrograde reactions such as from prehnite to yugawaralite, from prehnite to laumontite, from laumontite to heulandite or analcime and from chlorite to inter-

The formation of alteration minerals in volcanic-hydrothermal systems is a complex process affected by temperature, pressure, composition of reacting fluids, porosity, permeability and initial composition of the host-rock, duration of hydrothermal activity and superimposed thermal (or hydrothermal) regimes [55, 56]. Nevertheless, there is a general relationship between temperature and the formation of alteration minerals, and some mineral assemblages can be used to interpret temperatures within a geothermal system (**Figure 14**). For heulandite and stilbite, laumontite, yugawaralite, pumpellyite and actinolite widely accepted temperature stability ranges are 100-120°C, 120-220°C, 172-234°C, 200-310°C, 220-310°C and 280-460°C [52, 55–65]. Incipient, fine-grained and poorly crystallised epidote has been encountered in hydrothermal systems of the Philippines [53, 55] and the Nisyros Island [63], respectively, in the temperature range of 180-220°C although epidote generally forms at temperatures higher than 240°C [64, 65]. The temperature stability range of 245-265°C has been reported for mixed-layer R0 and

R1 chlorite-smectite from Nesjavellir geothermal field, Iceland [66].

*DOI: http://dx.doi.org/10.5772/intechopen.95480*

layered corrensite-chlorite [37, 38, 54].

**7. Discussion**

**Complex**

*Submarine Stratovolcano Peperite Syn-Formational Alteration - A Case Study of the Oligocene… DOI: http://dx.doi.org/10.5772/intechopen.95480*
