**3. Volcano-tectonic implications: the relationship between vent locations and the structural elements**

In this study, 907 monogenetic volcanic centers were identified in northern Chile (**Figure 2**). Among which, 306 centers correspond to parasitic monogenetic volcanoes associated with polygenetic volcanoes (**Figure 2a**), which are at the flank of stratovolcanoes linked to crustal/edifice magma storage [45], and 601 centers correspond to individual monogenetic volcanoes (**Figure 2a**). The monogenetic centers

### **Figure 2.**

*Distribution of monogenetic volcanoes across northern Chile based on a) their relationship with polygenetic volcanoes and b) their volcanic landform.*

**253**

**Table 1.**

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

show a variety of volcanic structures such as domes (35.1%), lava flows (33.4%), scoria cones (29.6%), maars (1.5%), and tuff cones (0.4%) (**Figure 2b**). These centers can be found as isolated centers (e.g., Cerro Punta Negra), clusters (e.g., Purico-Chaskón complex), or forming small volcanic fields (e.g., Negros de Aras). Using the location of the total number of the monogenetic volcanoes (i.e. 905), the average nearest neighbor analysis can be used to differentiate the distribution of each kind of monogenetic landforms (e.g., [3, 46]). The average nearest neighbor analysis shows R-statistic values of 0.71 for all monogenetic volcanoes of northern Chile, 0.74 for domes, 0.69 for scoria cones, and 0.62 for lava flows (**Table 1**). These value ranges are identified as a clustered distribution of volcanic centers [46]. For maars and tuff cones, the average nearest neighbor analysis was not obtained due to the small number of centers identified (18 monogenetic centers that are 1.9% of the

On the other hand, using the total number of monogenetic volcanoes (i.e. 907) and the area in which the monogenetic volcanoes are distributed in northern Chile

decrease in eruptive centers from Miocene (268 monogenetic centers) to Pliocene (258 monogenetic centers), and a later increase in the Pleistocene (363 monogenetic centers) (**Figure 3**). Domes and scoria cones abundance show the same trend mentioned before, whereas lava flows, maars, and tuff cones display a trend to increase from Miocene to Pleistocene (**Figure 3**). The activity during the Holocene (18 monogenetic centers) is mainly dominated by dome eruptions (**Figure 3**). The temporal evolution of the monogenetic volcanoes from older to younger shows a migration from south to north with a concentration in the central part of northern Chile (cluster 3: Antofagasta Central). Based on the kernel density map, the monogenetic volcanoes of northern Chile may be mainly grouped into five regional clusters (**Figure 4a**). These distributions of volcanic centers display a high density of features and a preferred elongation trending. Monogenetic centers are alienated NW-SE preferentially for clusters 1 and 2, N-S, NW-SE, and NE–SW for cluster 3, NE–SW for cluster 4, and WNW-ESE and NW-SE for cluster 5 (**Figure 4a**). The volcanic structures distribution across the northern Chile map (**Figure 4b**) exhibits that scoria cones and domes are mainly associated with NNW–SSE, NW-SE, and WSW-ENE tectonic structures and lineaments, in decreasing order of frequency. Lava flows are mainly aligned N-S and NW-SE, while maars and tuff cones occur mainly along N-S, NW-SE, and WSW-ENE trending tectonic structures and lineaments, in decreasing order of frequency. The distribution of magma paths suggests that for Miocene, the main direction of the shortening of structures at the upper crust should have been about E-W, WNW-ESE, and NNW–SSE [47]. This is consistent with the development of N-S and NNE–SSW reverse faults and folds reported for cluster 2 (Antofagasta Norte; **Figure 4a**), cluster 3 (Antofagasta Central; **Figure 4a**) and cluster 4 (Antofagasta Sur; **Figure 4a**), and WSW-ENE structures for cluster 5

**Feature Ro (km) Re (km) R-statistic ZR Pattern** All monogenetic structures 2.56 3.61 0.71 −16.63 Clustered Domes 4.51 6.05 0.74 −8.71 Clustered Lava flows 3.85 6.2 0.62 −12.62 Clustered Scoria cones 4.57 6.45 0.69 −9.48 Clustered

*Ro: Observed Mean Distance; Re: Expected Mean Distance; R-statistic: Nearest Neighbor Ratio; ZR: Z-score.*

*Results for the average nearest neighbor in northern Chile.*

), the area that envelopes all the monogenetic volcanic centers identi-

. The temporal distribution is characterized by a

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

total) to generate a statistically significant result.

(46,610 km2

fied is of 1.95 x 10-2 centers/km2

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

show a variety of volcanic structures such as domes (35.1%), lava flows (33.4%), scoria cones (29.6%), maars (1.5%), and tuff cones (0.4%) (**Figure 2b**). These centers can be found as isolated centers (e.g., Cerro Punta Negra), clusters (e.g., Purico-Chaskón complex), or forming small volcanic fields (e.g., Negros de Aras).

Using the location of the total number of the monogenetic volcanoes (i.e. 905), the average nearest neighbor analysis can be used to differentiate the distribution of each kind of monogenetic landforms (e.g., [3, 46]). The average nearest neighbor analysis shows R-statistic values of 0.71 for all monogenetic volcanoes of northern Chile, 0.74 for domes, 0.69 for scoria cones, and 0.62 for lava flows (**Table 1**). These value ranges are identified as a clustered distribution of volcanic centers [46]. For maars and tuff cones, the average nearest neighbor analysis was not obtained due to the small number of centers identified (18 monogenetic centers that are 1.9% of the total) to generate a statistically significant result.

On the other hand, using the total number of monogenetic volcanoes (i.e. 907) and the area in which the monogenetic volcanoes are distributed in northern Chile (46,610 km2 ), the area that envelopes all the monogenetic volcanic centers identified is of 1.95 x 10-2 centers/km2 . The temporal distribution is characterized by a decrease in eruptive centers from Miocene (268 monogenetic centers) to Pliocene (258 monogenetic centers), and a later increase in the Pleistocene (363 monogenetic centers) (**Figure 3**). Domes and scoria cones abundance show the same trend mentioned before, whereas lava flows, maars, and tuff cones display a trend to increase from Miocene to Pleistocene (**Figure 3**). The activity during the Holocene (18 monogenetic centers) is mainly dominated by dome eruptions (**Figure 3**).

The temporal evolution of the monogenetic volcanoes from older to younger shows a migration from south to north with a concentration in the central part of northern Chile (cluster 3: Antofagasta Central). Based on the kernel density map, the monogenetic volcanoes of northern Chile may be mainly grouped into five regional clusters (**Figure 4a**). These distributions of volcanic centers display a high density of features and a preferred elongation trending. Monogenetic centers are alienated NW-SE preferentially for clusters 1 and 2, N-S, NW-SE, and NE–SW for cluster 3, NE–SW for cluster 4, and WNW-ESE and NW-SE for cluster 5 (**Figure 4a**). The volcanic structures distribution across the northern Chile map (**Figure 4b**) exhibits that scoria cones and domes are mainly associated with NNW–SSE, NW-SE, and WSW-ENE tectonic structures and lineaments, in decreasing order of frequency. Lava flows are mainly aligned N-S and NW-SE, while maars and tuff cones occur mainly along N-S, NW-SE, and WSW-ENE trending tectonic structures and lineaments, in decreasing order of frequency. The distribution of magma paths suggests that for Miocene, the main direction of the shortening of structures at the upper crust should have been about E-W, WNW-ESE, and NNW–SSE [47]. This is consistent with the development of N-S and NNE–SSW reverse faults and folds reported for cluster 2 (Antofagasta Norte; **Figure 4a**), cluster 3 (Antofagasta Central; **Figure 4a**) and cluster 4 (Antofagasta Sur; **Figure 4a**), and WSW-ENE structures for cluster 5


### **Table 1.**

*Results for the average nearest neighbor in northern Chile.*

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

rocks ([43] and references therein).

**locations and the structural elements**

tion of heavy rare earth elements (HREE) in volcanic rocks [28].

melting-assimilation-storage-homogenization (MASH), and assimilation by deple-

Paleozoic, Mesozoic, and Miocene-Oligocene continental volcanic and sedimentary rocks; ii) Paleozoic and Mesozoic marine sedimentary rocks; iii) Precambrian and Paleozoic metamorphic rocks; and iv) Paleozoic, Mesozoic, and Paleocene intrusive

The Central Andes is known as the home of "andesitic" magmatism [36]; nevertheless, lava and pyroclastic rocks of dacitic, rhyolitic, and occasionally basaltic andesite and basaltic composition volcanic rocks also occur in the CVZ, building calderas, extensive ignimbrite sequences, stratovolcanoes and monogenetic volcanoes [44].

**3. Volcano-tectonic implications: the relationship between vent** 

In this study, 907 monogenetic volcanic centers were identified in northern Chile (**Figure 2**). Among which, 306 centers correspond to parasitic monogenetic volcanoes associated with polygenetic volcanoes (**Figure 2a**), which are at the flank of stratovolcanoes linked to crustal/edifice magma storage [45], and 601 centers correspond to individual monogenetic volcanoes (**Figure 2a**). The monogenetic centers

*Distribution of monogenetic volcanoes across northern Chile based on a) their relationship with polygenetic* 

The magmatic activity of the CVZ has been continuous from the Upper Oligocene to the present day [42]. The basement is mainly comprised by i)

**252**

**Figure 2.**

*volcanoes and b) their volcanic landform.*

**Figure 3.**

*a) Temporal distribution of monogenetic volcanic landforms across northern Chile. b) Histogram of the temporal distribution of monogenetic volcanic landforms during Miocene, Pliocene, Pleistocene, and Holocene.*

(Atacama; **Figure 4a**) in previous studies [48]. During the Pliocene to Holocene, the main direction of shortening inferred to have been E-W, NE–SW, WNW-ESE, and NNW–SSE direction of contraction, in decreasing order of frequency. This is consistent with the N-S and NW-striking normal faults, NE-striking reverse faulting, NW-SE, and WSW-ENE strike-slip faults reported in previous studies [20, 48].

The spatial–temporal correlation of monogenetic centers, combined with the tectonic structures within northern Chile, allows the identification of three different structural styles of monogenetic volcanoes (Figure A.1), as has been suggested by Le Corvec et al. [2] for monogenetic volcanism and by Tibaldi et al. [49] for the CVZ. The first case (Figure A.1a) corresponds to a compressional environment mainly characterized by N-S and NNE–SSW reverse faults and folds over the monogenetic feeding conduits. Nevertheless, in this case, the magmatic plumbing system has been associated with the development of normal or strike-slip faults allowing the ascent of magmas to the surface such as the Tilocálar complex [22] at the south of the Salar de Atacama basin into the cluster 3 (Antofagasta Central; **Figure 4**). The second scenario (Figure A.1b) is mainly characterized by N-S and NW-SE, striking normal faults into an extensional environment. This case has been reported to scoria cones, lava flows, and mainly domes into the Ollagüe region and San Pedro-Linzor volcanic chain area [16, 50], which correspond to cluster 2 (Antofagasta Norte; **Figure 4**). The last scenario (Figure A.1c) corresponds to a strike-slip environment mainly

**255**

**Figure 4.**

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

characterized by NW-SE left lateral and WSW-ENE strike-slip faults. Monogenetic volcanism associated with this scenario has been mainly reported by Tibaldi et al. [49] for cluster 3 (Antofagasta Central; **Figure 4**), Baker et al. [20], and González-Ferrán et al. [51] for cluster 5 (Atacama; **Figure 4**). These scenarios have also been reported in others areas of monogenetic volcanism in the CVZ of the Andes such as the Uyuni region by Tibaldi et al. [50], Antofagasta de la Sierra Basin by Báez et al. [52], or in the southern Puna Plateau by Haag et al. [3]. These interpretations were developed based on the distribution and alignment of the monogenetic centers. Therefore, it is essential to consider that the tectonic structures have been formed before of the magma intrusion that originated monogenetic centers. In this context, the emplacement of these volcanic centers was favored by these tectonic structures.

*a) Kernel density map for monogenetic volcanoes and the main clusters identified. The numbers represent the main regions: 1. Arica-Iquique, 2. Antofagasta Norte, 3. Antofagasta Central, 4. Antofagasta Sur, and 5.* 

*Atacama. b) Map of the major fault systems and lineaments across northern Chile.*

**4. The spectrum of architecture and lithofacies of volcanic structures:** 

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

**internal versus external-factor implications**

*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 4.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

(Atacama; **Figure 4a**) in previous studies [48]. During the Pliocene to Holocene, the main direction of shortening inferred to have been E-W, NE–SW, WNW-ESE, and NNW–SSE direction of contraction, in decreasing order of frequency. This is consistent with the N-S and NW-striking normal faults, NE-striking reverse faulting, NW-SE, and WSW-ENE strike-slip faults reported in previous studies [20, 48]. The spatial–temporal correlation of monogenetic centers, combined with the tectonic structures within northern Chile, allows the identification of three different structural styles of monogenetic volcanoes (Figure A.1), as has been suggested by Le Corvec et al. [2] for monogenetic volcanism and by Tibaldi et al. [49] for the CVZ. The first case (Figure A.1a) corresponds to a compressional environment mainly characterized by N-S and NNE–SSW reverse faults and folds over the monogenetic feeding conduits. Nevertheless, in this case, the magmatic plumbing system has been associated with the development of normal or strike-slip faults allowing the ascent of magmas to the surface such as the Tilocálar complex [22] at the south of the Salar de Atacama basin into the cluster 3 (Antofagasta Central; **Figure 4**). The second scenario (Figure A.1b) is mainly characterized by N-S and NW-SE, striking normal faults into an extensional environment. This case has been reported to scoria cones, lava flows, and mainly domes into the Ollagüe region and San Pedro-Linzor volcanic chain area [16, 50], which correspond to cluster 2 (Antofagasta Norte; **Figure 4**). The last scenario (Figure A.1c) corresponds to a strike-slip environment mainly

*a) Temporal distribution of monogenetic volcanic landforms across northern Chile. b) Histogram of the temporal distribution of monogenetic volcanic landforms during Miocene, Pliocene, Pleistocene, and Holocene.*

**254**

**Figure 3.**

*a) Kernel density map for monogenetic volcanoes and the main clusters identified. The numbers represent the main regions: 1. Arica-Iquique, 2. Antofagasta Norte, 3. Antofagasta Central, 4. Antofagasta Sur, and 5. Atacama. b) Map of the major fault systems and lineaments across northern Chile.*

characterized by NW-SE left lateral and WSW-ENE strike-slip faults. Monogenetic volcanism associated with this scenario has been mainly reported by Tibaldi et al. [49] for cluster 3 (Antofagasta Central; **Figure 4**), Baker et al. [20], and González-Ferrán et al. [51] for cluster 5 (Atacama; **Figure 4**). These scenarios have also been reported in others areas of monogenetic volcanism in the CVZ of the Andes such as the Uyuni region by Tibaldi et al. [50], Antofagasta de la Sierra Basin by Báez et al. [52], or in the southern Puna Plateau by Haag et al. [3]. These interpretations were developed based on the distribution and alignment of the monogenetic centers. Therefore, it is essential to consider that the tectonic structures have been formed before of the magma intrusion that originated monogenetic centers. In this context, the emplacement of these volcanic centers was favored by these tectonic structures.
