**4. The spectrum of architecture and lithofacies of volcanic structures: internal versus external-factor implications**

In this study, 318 domes, 303 lava flows, 268 scoria cones, 14 maars, and 4 tuff cones have been identified. This identification is primarily based on the morphological aspects of the volcanic edifices, which is characterized by the dominant

eruption style and number or combination of eruption phases following Bishop [53] and Walker [54] (**Figures 1** and **2**).

*Scoria cones* (**Figure 5a**) are mainly characterized by circular to elliptical shape in plan-view, showing different landforms as ideal (e.g., La Poruña), gully, horseshoe, tilted, amorphous or crater row that in some cases display lava flows associated (e.g., Negros de Aras volcanic field). These lava flows (**Figure 5b**) are mainly characterized by ʻaʻā flow structures associated with early (e.g., Del Inca) or late-stage (e.g., Ajata) eruptions with channel, ogive, leeve, lobe, and breakout lobe structures.

### **Figure 5.**

*Volcano types from northern Chile. a) Poruñita scoria cone (Ollagüe stratovolcano in the background). b) Scoria cone and lava flows from Negros de Aras monogenetic volcanic field. c) La Torta de Tocorpuri dome. d) Chao dome with its pyroclastic deposit (PD) and lava dome stages (I, II, and III) (Google earth™ image). e) La Espinilla maar-dome and Del Indio dome (DI). f) Tilocálar Norte lava flow. g) Ajata lava flows. h) Cerro Tujle maar. i) Alitar maar, fumaroles occur in white areas (Alitar stratovolcano in the background). j) Luna de Tierra tuff cone (Ollagüe stratovolcano in the background).*

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*An Overview of the Mafic and Felsic Monogenetic Neogene to Quaternary Volcanism…*

*Domes* (**Figure 5c**) of northern Chile are characterized by a pile up of lava in large thicknesses over their vents. They are often referred to as *tortas* (pies or pancakes) (e.g., La Torta de Tocorpuri), controlled by the slope angle of the preeruptive surface, viscosity, effusion rate, phenocryst contents, and in some cases, related to early pyroclastic density currents (e.g., Chao). Overall, domes (**Figure 5d**) show coulee (e.g., Chao), lobate (e.g., Chascón), platy (e.g., Pabellón-Apacheta), and axisymmetric (e.g., Chillahuita) landform structures. Few domes (**Figure 5e**) in

*Lava flows* (**Figure 5f**) are mainly characterized by a jumble of irregular and coherent block of lava (up to meters), across with smooth, planar, and angular surfaces. They can be classified as ʻaʻā (e.g., El Negrillar) and blocky (e.g., Tilocálar Norte) lavas, and may display a simple (e.g., Ajata) or compound (e.g., Tilocálar Sur) landform with several features as a channel, ogive, leeve, lobe, and breakout

*Maars* (**Figure 5h**) show a characteristic landform characterized by a preserved crater that cut into the pre-eruptive landscape (e.g., Tujle). The crater cavities reach from 30 m to 200 m deep; they are partially sediment filled with a crater diameter from 300 m to 3 km. Sulfur deposits (e.g., Juan de la Vega maar), fumaroles (e.g., Alitar maar), and domes (e.g., La Espinilla) are present in maar volcanoes associ-

*Tuff cones* (**Figure 5j**) in northern Chile display a horseshoe landform, a wider crater relative to basal diameter than the scoria cones, exhibiting a crater rim from a flat surface up to 10 m dominated by salt deposits. They are mainly associated with

The monogenetic volcanic centers (mafic and felsic volcanism) are characterized by the heterogeneity of volcanic products, which can be mainly classified into eight lithofacies based on field observation, componentry and sedimentological

1.*Bombs and lapilli beds* (BL): This lithofacies is mainly found both at the base and the summit of scoria cones. It is poorly sorted, reversed graded to massive and mostly clast-supported, and consists of poorly to non-agglutinated juvenile clasts (**Figure 6a** and **b**). BL lithofacies is interpreted as the result of

2.*Lapilli and ash beds* (LA): This lithofacies is mainly located at the base of scoria cones. It is well sorted, normal or reversed graded to massive, with parallel or cross-lamination, and mostly clast-supported with non-agglutinated juvenile clasts (**Figure 6c**). This lithofacies is interpreted as the result of hydromagmatic

3.*Agglutinated to spatter bomb and lapilli beds* (AS): This lithofacies is mainly found at the summit of scoria cones or pyroclastic deposits. It comprises a brittle core and fluid rim to completely fluid clasts (spatter) that agglutinate moderately forming beds (up to 5 m thick) (**Figure 6d**). LA lithofacies is

4.*Welded scoria to clastogenic lavas* (CL): This lithofacies is mainly located at the summit of scoria cones and pyroclastic deposits. It is formed by scoria of lapilli and bombs size fragments highly welded (coalesced), forming dense agglutinate layers (clastogenic lava) (**Figure 6e**). CL lithofacies is interpreted as the result of

interpreted as the result of Hawaiian to transitional eruptions.

ated with events that appear late of the maar eruptions (**Figure 5e**–**i**).

*DOI: http://dx.doi.org/10.5772/intechopen.93959*

lobe structures (**Figure 5g**).

characteristics such as:

eruptions.

Strombolian eruptions.

Hawaiian to transitional eruptions.

salt plains or *salares* (e.g. Luna de Tierra).

northern Chile occur within craters (e.g., La Espinilla).

*An Overview of the Mafic and Felsic Monogenetic Neogene to Quaternary Volcanism… DOI: http://dx.doi.org/10.5772/intechopen.93959*

*Domes* (**Figure 5c**) of northern Chile are characterized by a pile up of lava in large thicknesses over their vents. They are often referred to as *tortas* (pies or pancakes) (e.g., La Torta de Tocorpuri), controlled by the slope angle of the preeruptive surface, viscosity, effusion rate, phenocryst contents, and in some cases, related to early pyroclastic density currents (e.g., Chao). Overall, domes (**Figure 5d**) show coulee (e.g., Chao), lobate (e.g., Chascón), platy (e.g., Pabellón-Apacheta), and axisymmetric (e.g., Chillahuita) landform structures. Few domes (**Figure 5e**) in northern Chile occur within craters (e.g., La Espinilla).

*Lava flows* (**Figure 5f**) are mainly characterized by a jumble of irregular and coherent block of lava (up to meters), across with smooth, planar, and angular surfaces. They can be classified as ʻaʻā (e.g., El Negrillar) and blocky (e.g., Tilocálar Norte) lavas, and may display a simple (e.g., Ajata) or compound (e.g., Tilocálar Sur) landform with several features as a channel, ogive, leeve, lobe, and breakout lobe structures (**Figure 5g**).

*Maars* (**Figure 5h**) show a characteristic landform characterized by a preserved crater that cut into the pre-eruptive landscape (e.g., Tujle). The crater cavities reach from 30 m to 200 m deep; they are partially sediment filled with a crater diameter from 300 m to 3 km. Sulfur deposits (e.g., Juan de la Vega maar), fumaroles (e.g., Alitar maar), and domes (e.g., La Espinilla) are present in maar volcanoes associated with events that appear late of the maar eruptions (**Figure 5e**–**i**).

*Tuff cones* (**Figure 5j**) in northern Chile display a horseshoe landform, a wider crater relative to basal diameter than the scoria cones, exhibiting a crater rim from a flat surface up to 10 m dominated by salt deposits. They are mainly associated with salt plains or *salares* (e.g. Luna de Tierra).

The monogenetic volcanic centers (mafic and felsic volcanism) are characterized by the heterogeneity of volcanic products, which can be mainly classified into eight lithofacies based on field observation, componentry and sedimentological characteristics such as:


*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

and Walker [54] (**Figures 1** and **2**).

eruption style and number or combination of eruption phases following Bishop [53]

eruptions with channel, ogive, leeve, lobe, and breakout lobe structures.

*Scoria cones* (**Figure 5a**) are mainly characterized by circular to elliptical shape in plan-view, showing different landforms as ideal (e.g., La Poruña), gully, horseshoe, tilted, amorphous or crater row that in some cases display lava flows associated (e.g., Negros de Aras volcanic field). These lava flows (**Figure 5b**) are mainly characterized by ʻaʻā flow structures associated with early (e.g., Del Inca) or late-stage (e.g., Ajata)

**256**

**Figure 5.**

*Volcano types from northern Chile. a) Poruñita scoria cone (Ollagüe stratovolcano in the background). b) Scoria cone and lava flows from Negros de Aras monogenetic volcanic field. c) La Torta de Tocorpuri dome. d) Chao dome with its pyroclastic deposit (PD) and lava dome stages (I, II, and III) (Google earth™ image). e) La Espinilla maar-dome and Del Indio dome (DI). f) Tilocálar Norte lava flow. g) Ajata lava flows. h) Cerro Tujle maar. i) Alitar maar, fumaroles occur in white areas (Alitar stratovolcano in the* 

*background). j) Luna de Tierra tuff cone (Ollagüe stratovolcano in the background).*

### **Figure 6.**

*Field photographs of lithofacies of the monogenetic volcanoes in northern Chile. a) Lithofacies BL from Poruñita scoria cone. b) Lithofacies BL from La Poruña scoria cone. c) Lithofacies LA from Negros de Aras scoria cones. d) Lithofacies AS from Ajata scoria cone. e) Lithofacies CL from Tilocálar Sur pyroclastic deposit. f) Lithofacies LAL from Cerro Overo maar.*


**259**

**Figure 7.**

*An Overview of the Mafic and Felsic Monogenetic Neogene to Quaternary Volcanism…*

monogenetic), and as an isolated vent. Lava flow lithofacies is characterized by three primary vertical levels (**Figures 7e** and **8a**–**e**). This lithofacies flowed, reaching length up to 11 km and piling up from low to large thicknesses (< 1 m – 400 m), and based on their morphology, it can be classified as lava flows or domes. LF lithofacies is mainly interpreted as the result of Strombolian eruptions.

*Field photographs of lithofacies of the monogenetic volcanoes in northern Chile. a) Lithofacies LAL showing a juvenile fragment with cauliflower-shaped from Cerro Overo maar. b) Lithofacies P showing a mingling of juvenile material and unconsolidated host sediment from Tilocálar Sur pyroclastic deposit. c) La Poruña lava flow and scoria cone. d) Lithofacies LD showing the* boccas *of the Ajata scoria cone with levee structures of the Ajata 3 lava flow. e) Lithofacies LD showing the primary three principal levels of this lithofacies* 

*(top auto-breccia, core, and basal auto-breccia) from El País lava flow field.*

8.*Raft blocks* (RB): This lithofacies corresponds to mounds or blocks of agglutinate to welded pyroclasts located on top of lava flows and associated with scoria cones (**Figure 8f** and **g**). The individual blocks are the result of the cone rafting (RB lithofacie), which initially were the product of Strombolian style eruptions.

The spectrum of architecture and lithofacies of volcanic structures involve several interactions between internal and external processes. It is affected by the continuous degassing and interactions of the magma with the environment at different levels en-route during its ascent from the source to the surface, resulting in a volcanic eruption that can be explosive or effusive [55]. In many cases,

*DOI: http://dx.doi.org/10.5772/intechopen.93959*

*An Overview of the Mafic and Felsic Monogenetic Neogene to Quaternary Volcanism… DOI: http://dx.doi.org/10.5772/intechopen.93959*

### **Figure 7.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

5.*Lapilli and ash beds with lithic fragments* (LAL): This lithofacies is mainly

*Field photographs of lithofacies of the monogenetic volcanoes in northern Chile. a) Lithofacies BL from Poruñita scoria cone. b) Lithofacies BL from La Poruña scoria cone. c) Lithofacies LA from Negros de Aras scoria cones. d) Lithofacies AS from Ajata scoria cone. e) Lithofacies CL from Tilocálar Sur pyroclastic deposit.* 

6.*Peperite* (P): This lithofacies is located at the base of scoria cones and pyroclastic deposits, overlying the pre-eruptive surface. It is mainly a mingling of juvenile material and unconsolidated host sediment (**Figure 7b**). P lithofacies is interpreted as the result of magma-wet sediment/shallow water eruptions.

7.*Lava flow* (LF): This lithofacies is found at the flank and ring plain of stratovolcanoes, both at the base and at the summit of scoria cones (from *boccas*) (**Figure 7c** and **d**), at the crater of other volcanic edifices (polygenetic or

as the result of hydromagmatic eruptions.

*f) Lithofacies LAL from Cerro Overo maar.*

found both at the base and the summit of scoria cones and pyroclastic deposits. It is moderately sorted, normal or reversed graded to massive and mostly clastsupported deposits with abundant lithic fragments (>20%) locally moderate to no agglutination/welding (**Figures 6f** and **7a**). LAL lithofacies is interpreted

**258**

**Figure 6.**

*Field photographs of lithofacies of the monogenetic volcanoes in northern Chile. a) Lithofacies LAL showing a juvenile fragment with cauliflower-shaped from Cerro Overo maar. b) Lithofacies P showing a mingling of juvenile material and unconsolidated host sediment from Tilocálar Sur pyroclastic deposit. c) La Poruña lava flow and scoria cone. d) Lithofacies LD showing the* boccas *of the Ajata scoria cone with levee structures of the Ajata 3 lava flow. e) Lithofacies LD showing the primary three principal levels of this lithofacies (top auto-breccia, core, and basal auto-breccia) from El País lava flow field.*

monogenetic), and as an isolated vent. Lava flow lithofacies is characterized by three primary vertical levels (**Figures 7e** and **8a**–**e**). This lithofacies flowed, reaching length up to 11 km and piling up from low to large thicknesses (< 1 m – 400 m), and based on their morphology, it can be classified as lava flows or domes. LF lithofacies is mainly interpreted as the result of Strombolian eruptions.

8.*Raft blocks* (RB): This lithofacies corresponds to mounds or blocks of agglutinate to welded pyroclasts located on top of lava flows and associated with scoria cones (**Figure 8f** and **g**). The individual blocks are the result of the cone rafting (RB lithofacie), which initially were the product of Strombolian style eruptions.

The spectrum of architecture and lithofacies of volcanic structures involve several interactions between internal and external processes. It is affected by the continuous degassing and interactions of the magma with the environment at different levels en-route during its ascent from the source to the surface, resulting in a volcanic eruption that can be explosive or effusive [55]. In many cases,

### **Figure 8.**

*Field photographs of lithofacies of the monogenetic volcanoes in northern Chile. a) South dome (Guallatiri volcano area) showing the three primary levels of this lithofacies. Red areas indicate foliated lava sequences that are described in Watts et al. [26] in ref.s therein. b) El Ingenio (also called La Celosa) felsic dome (Ollagüe volcano area) exhibiting a* torta *type morphology. c-d) mafic enclaves from El Ingenio dome and south dome, respectively. e) Flow structures of El Mani dome. f) Scoria cone from Negros de Aras showing a horseshoe morphology associated with lava flow and with agglutinated material deposited on the summit crater. g) Lithofacies RB of unconsolidated and agglutinated pyroclastic material located at the distal part of the lava flow of Figure 8f from Negros de Aras.*

the outcrops of monogenetic volcanic centers are covered by some debris flank due to desert physical weathering and mass movements or covered by eolian deposits. Nevertheless, integrating the different lithofacies identified and the cross-sections from different edifices are possible to build the history of the eruptive style involved in the formation of the monogenetic volcanoes of northern Chile.

In general, scoria cones are composed of the lithofacies that indicate a rapid and continuous evolution from the Strombolian eruption style (lithofacies BL) to Hawaiian and Transitional styles (lithofacies AS and CL). This transition is characterized from the base to the upper levels by poorly sorted, reversed graded to massive and mostly clast-supported deposits, which consist of poorly to nonagglutinated juvenile clasts, to the summit by clastogenic lavas and welded agglutinated bomb (e.g., Ajata, La Poruña, Del Inca, Negros de Aras scoria cones). In addition, magmatic effusive stages are associated with the lithofacies LF (lava flow)

**261**

**Figure 9.**

*An Overview of the Mafic and Felsic Monogenetic Neogene to Quaternary Volcanism…*

and RB (raft blocks). They are represented by lava flows at the base or the summit of the scoria cones (e.g., Ajata, La Poruña, Del Inca, Negros de Aras scoria cones), and mounts from the volcanic edifice of scoria cones at the lava flows (e.g., Negros de Aras), respectively. That means scoria cones show a range of magmatic activity

Nevertheless, in some cases (e.g., Negros de Aras scoria cones), hydrovolcanic records may be identified either at the summit or at the bases of the scoria cones (**Figure 9**). This corresponds to the lithofacies LAL (lapilli and ash beds with lithic fragments) and LA (Lapilli and ash beds), which suggest magma-water interactions during the initial (e.g., Poruñita scoria cone) or later phases (e.g., Negros de Aras scoria cones), where shallow water levels are available. This characteristic is also recognized at the base in some pyroclastic deposits (e.g., Tilocálar Sur), where fluidal and jigsaw-fit textures are locally preserved (lithofacies P) (**Figure 7b**).

*a) Schematic drawing of monogenetic volcanic landforms of northern Chile, showing the conceptual link between monogenetic and polygenetic volcanoes and their relationship with their environmental setting. The numbers indicate the volcanic landforms detailed in the diagram of the theoretical link/transition between eruptive styles, eruption phases, and volcanic landforms for monogenetic volcanoes of northern Chile. Examples of Chilean volcanoes in each case. b) Cerro Overo maar. c) Scoria cone from Negros de Aras with a crater* 

*associated with a phreatomagmatic eruptive phase. d) Tilocálar Sur maar.*

*DOI: http://dx.doi.org/10.5772/intechopen.93959*

from explosive to effusive styles (**Figure 9**).

*An Overview of the Mafic and Felsic Monogenetic Neogene to Quaternary Volcanism… DOI: http://dx.doi.org/10.5772/intechopen.93959*

and RB (raft blocks). They are represented by lava flows at the base or the summit of the scoria cones (e.g., Ajata, La Poruña, Del Inca, Negros de Aras scoria cones), and mounts from the volcanic edifice of scoria cones at the lava flows (e.g., Negros de Aras), respectively. That means scoria cones show a range of magmatic activity from explosive to effusive styles (**Figure 9**).

Nevertheless, in some cases (e.g., Negros de Aras scoria cones), hydrovolcanic records may be identified either at the summit or at the bases of the scoria cones (**Figure 9**). This corresponds to the lithofacies LAL (lapilli and ash beds with lithic fragments) and LA (Lapilli and ash beds), which suggest magma-water interactions during the initial (e.g., Poruñita scoria cone) or later phases (e.g., Negros de Aras scoria cones), where shallow water levels are available. This characteristic is also recognized at the base in some pyroclastic deposits (e.g., Tilocálar Sur), where fluidal and jigsaw-fit textures are locally preserved (lithofacies P) (**Figure 7b**).

### **Figure 9.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

the outcrops of monogenetic volcanic centers are covered by some debris flank due to desert physical weathering and mass movements or covered by eolian deposits. Nevertheless, integrating the different lithofacies identified and the cross-sections from different edifices are possible to build the history of the eruptive style involved

*Field photographs of lithofacies of the monogenetic volcanoes in northern Chile. a) South dome (Guallatiri volcano area) showing the three primary levels of this lithofacies. Red areas indicate foliated lava sequences that are described in Watts et al. [26] in ref.s therein. b) El Ingenio (also called La Celosa) felsic dome (Ollagüe volcano area) exhibiting a* torta *type morphology. c-d) mafic enclaves from El Ingenio dome and south dome, respectively. e) Flow structures of El Mani dome. f) Scoria cone from Negros de Aras showing a horseshoe morphology associated with lava flow and with agglutinated material deposited on the summit crater. g) Lithofacies RB of unconsolidated and agglutinated pyroclastic material located at the distal part of the lava* 

In general, scoria cones are composed of the lithofacies that indicate a rapid and continuous evolution from the Strombolian eruption style (lithofacies BL) to Hawaiian and Transitional styles (lithofacies AS and CL). This transition is characterized from the base to the upper levels by poorly sorted, reversed graded to massive and mostly clast-supported deposits, which consist of poorly to nonagglutinated juvenile clasts, to the summit by clastogenic lavas and welded agglutinated bomb (e.g., Ajata, La Poruña, Del Inca, Negros de Aras scoria cones). In addition, magmatic effusive stages are associated with the lithofacies LF (lava flow)

in the formation of the monogenetic volcanoes of northern Chile.

**260**

**Figure 8.**

*flow of Figure 8f from Negros de Aras.*

*a) Schematic drawing of monogenetic volcanic landforms of northern Chile, showing the conceptual link between monogenetic and polygenetic volcanoes and their relationship with their environmental setting. The numbers indicate the volcanic landforms detailed in the diagram of the theoretical link/transition between eruptive styles, eruption phases, and volcanic landforms for monogenetic volcanoes of northern Chile. Examples of Chilean volcanoes in each case. b) Cerro Overo maar. c) Scoria cone from Negros de Aras with a crater associated with a phreatomagmatic eruptive phase. d) Tilocálar Sur maar.*

On the other hand, lava flows and lava domes are characterized by the lithofacies LF (lava flow), suggesting a magmatic effusive nature with different morphological features (**Figure 9**). The main differences between lava flows (e.g., El País lava flow field; **Figure 7e**) and lava domes (e.g., Tinto dome; **Figure 8a**) are the changes in the viscosity, volatile content, and magma ascent rate [55]. These features control the magma degassing during their ascent from the source to the surface, and therefore, the fragmentation processes [56]. Despite these differences, deposits that are inferred to represent explosive phases have been found at the base of the lava domes (e.g., Chao dome), which corresponds to the initial stages of pyroclastic deposits characterized by bombs and lapilli beds (lithofacies BL).

Maars (e.g., Cerro Overo) and tuff cones (e.g., Luna de Tierra) are characterized by LAL (lapilli and ash beds with lithic fragments) and LA (Lapilli and ash beds) lithofacies, which are associated with hydromagmatic eruptions, suggesting magma-water interactions. These phreatomagmatic and Surtseyan eruptions may be associated with external factors that trigger the magma-water interaction at different degrees of ratio and different depths of magma-water interaction [57]. The maars are mainly associated with areas characterized by i) folded ignimbrite basement (e.g., Tilomonte ridge for Tilocálar Sur maar, Cerro Tujle ridge for Cerro Tujle maar or Altos del Toro Blanco ridge for Cerro Overo maar), ii) groundwater aquifers (e.g., Monturaqui-Tilopozo-Negrillar aquifer for Tilocálar Sur maar), and iii) salt flats or lagoons as discharge zones (e.g., Salar de Atacama for Cerro Tujle maar or Laguna Lejía for Cerro Overo maar) (**Figure 9**). In contrast, tuff cones are located at low topographic positions filled with poorly consolidated sediments as salt flats (e.g., Salar de Carcote for Luna de Tierra) or caldera basins (e.g., La Pacana caldera for Corral de Coquena), where the resulting tephra came from phreatomagmatic eruptions through shallow surface water [58] (**Figure 9**).

Overall, the architecture spectrum and the volcanic lithofacies of the monogenetic centers of northern Chile (**Figure 9**) are similar to those reported for the northern Puna region (Argentina) by Maro and Caffe [59] and Maro et al. [60]. This suggests a wide range of eruptive styles involved in the eruption history of this small-volume volcanism, and in some cases, large volume as well. Nevertheless, in northern Chile, this range of eruptive styles is characterized by effusive (e.g., Ajata lava flows or Tinto dome) and/or explosive magmatic (e.g., Tilocálar Sur or Chao dome) activities dominated by Strombolian to Hawaiian/Transitional styles (e.g., La Poruña scoria cone), and hydromagmatic activities, as phreatomagmatic (e.g., Cerro Overo maar) or Surtseyan (e.g., Luna de Tierra tuff cone) styles, which were often simultaneous or alternating during the growth of the monogenetic volcanoes in northern Chile (**Figure 9**).
