**5. Magmatic processes: textural and petrological evidence**

Petrographically, products from scoria cones, lava flows, maars, and tuff cones comprise mainly aphyric rocks (e.g., SC2). On the other hand, domes can be variable from aphyric (e.g., La Albondiga) to porphyritic rocks, which in some cases show mafic enclaves (e.g., Tinto dome). Overall, samples are characterized by hypocrystalline, hypidiomorphic, and hyalopilitic textures, where aphyric rocks show 40–50% vol. microphenocryst and microlite content, whereas porphyritic rocks exhibit 20–50% vol. phenocryst. The main mineral assemblage corresponds to euhedral to subhedral clinopyroxene (15% vol.; max 1.15 mm) and plagioclase (25–40% vol.; max 7 mm) with subordinated olivine (5% vol.; max 0.9 mm) and Fe–Ti oxide phases (1% vol.; max 0.2 mm). Nevertheless, in some cases, orthopyroxene (3% vol.; max 0.4 mm) and hydrous minerals, such as amphibole (**Figure 10a**),

**263**

**Figure 10.**

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

*Photomicrographs and micro-vesiculated photos are showing typical petrographic textures of monogenetic volcanoes products from northern Chile. Thin sections under cross-polarized- (a, c-h) and plane-parallel- (b) light. a) Amphibole breakdown/reaction rim with skeletal and sieve textures from Cerro Tujle maar. b) Mafic and felsic bands are showing mingling texture from El Maní dome. c) Olivine phenocryst showing skeletal growth from SC2 scoria cone. d) Quartz xenocryst resorbed and rimmed mainly by clinopyroxenes from Tilocálar Sur lava flow. e) Plagioclase with sieve and reabsorption textures and showing zoned rim from Luna de Tierra tuff cone. f) Fluidal texture showing olivines with absorption and skeletal growth textures from Cerro Overo maar. g) Silicic product from El Ingenio dome. h) the diktytaxitic-like texture of the groundmass of the enclave from El Ingenio dome. Mineral abbreviations are amphibole (amp), plagioclase (Pl), Clinopyroxene* 

*(Cpx), olivine (Ol), quartz (Qz), K-feldspar (Fsp), Biotite (Bt), opaque mineral (Opq).*

*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 10.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

characterized by bombs and lapilli beds (lithofacies BL).

matic eruptions through shallow surface water [58] (**Figure 9**).

**5. Magmatic processes: textural and petrological evidence**

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

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 phreatomag-

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

Petrographically, products from scoria cones, lava flows, maars, and tuff cones comprise mainly aphyric rocks (e.g., SC2). On the other hand, domes can be variable from aphyric (e.g., La Albondiga) to porphyritic rocks, which in some cases show mafic enclaves (e.g., Tinto dome). Overall, samples are characterized by hypocrystalline, hypidiomorphic, and hyalopilitic textures, where aphyric rocks show 40–50% vol. microphenocryst and microlite content, whereas porphyritic rocks exhibit 20–50% vol. phenocryst. The main mineral assemblage corresponds to euhedral to subhedral clinopyroxene (15% vol.; max 1.15 mm) and plagioclase (25–40% vol.; max 7 mm) with subordinated olivine (5% vol.; max 0.9 mm) and Fe–Ti oxide phases (1% vol.; max 0.2 mm). Nevertheless, in some cases, orthopyroxene (3% vol.; max 0.4 mm) and hydrous minerals, such as amphibole (**Figure 10a**),

**262**

in northern Chile (**Figure 9**).

*Photomicrographs and micro-vesiculated photos are showing typical petrographic textures of monogenetic volcanoes products from northern Chile. Thin sections under cross-polarized- (a, c-h) and plane-parallel- (b) light. a) Amphibole breakdown/reaction rim with skeletal and sieve textures from Cerro Tujle maar. b) Mafic and felsic bands are showing mingling texture from El Maní dome. c) Olivine phenocryst showing skeletal growth from SC2 scoria cone. d) Quartz xenocryst resorbed and rimmed mainly by clinopyroxenes from Tilocálar Sur lava flow. e) Plagioclase with sieve and reabsorption textures and showing zoned rim from Luna de Tierra tuff cone. f) Fluidal texture showing olivines with absorption and skeletal growth textures from Cerro Overo maar. g) Silicic product from El Ingenio dome. h) the diktytaxitic-like texture of the groundmass of the enclave from El Ingenio dome. Mineral abbreviations are amphibole (amp), plagioclase (Pl), Clinopyroxene (Cpx), olivine (Ol), quartz (Qz), K-feldspar (Fsp), Biotite (Bt), opaque mineral (Opq).*

biotite, or sideromelane (10% vol; max 5 mm) can also be found. The main textures correspond to fluidal, reabsorption, and disequilibrium textures, such as mingling (**Figure 10b**), skeletal (**Figure 10c**), and resorbed edges rimmed by a network of clinopyroxenes (**Figure 10d**), sieve texture, and zoned rims (**Figure 10e**). The groundmass (50–80% vol.) is glassy with a microlites of plagioclase > clinopyroxene > olivine > amphibole/biotite > orthopyroxene, and opaque phases, where tabularshaped microlites display flow structures (**Figure 10f**). In general, the mafic inclusions commonly are fine-grained and microvesiculated and range from 2 to 20 cm in size (**Figure 10g**). They exhibit crystal assemblages of plagioclase, pyroxene, amphibole, biotite, olivine, and quartz. The groundmass shows mainly plagioclase > pyroxene > amphibole and rare biotite and Fe-Ti oxides, with acicular phases and diktytaxitic texture (vesicles with plagioclase around cavity; **Figure 10h**).

In general, products of monogenetic centers in northern Chile contain two or three plagioclase populations. The first one is characterized by defined edges and no resorption features (**Figure 10e**). The second population of plagioclase show inner zones with sieve texture overgrown by euhedral rims of plagioclase, and plagioclase that is thoroughly sieved (**Figure 10e**). The last population of plagioclase exhibits oscillatory zoning and, in some cases, coarse-sieve texture and smooth edges. The mineral assemblage consists of plagioclase, olivine, orthopyroxene, and clinopyroxene, in order of decreasing abundances, with amphibole and opaque mineral (e.g., magnetite and ilmenite) as minor phases for mafic products, and plagioclase, amphibole, biotite, quartz, K-feldspar, pyroxene, titanite and opaque mineral (e.g., magnetite and ilmenite), in order of decreasing abundances, with apatite and zircon as accessory phases for felsic products. For mafic products, olivines are present in samples showing reabsorption features characterized by different types of skeletal crystal morphologies (**Figure 10f**). Pyroxene is commonly recognized as individual crystal, and as reaction rims on olivine crystals or glomerocrystals. Quartz xenocrysts are also identified and are resorbed and rimmed by a network of mafic microlites (e.g., clinopyroxene) (**Figure 10d**). For felsic products, quartz crystals have rounded edges; amphibole and biotite show euhedral to subhedral habits affected by the intense breakdown (**Figure 10g**). Overall, the groundmass is very finely crystalline, with microlites of plagioclase, ortho- and clinopyroxene, olivine, amphibole, and opaque minerals with interstitial glass (**Figure 10**).

These characteristics correspond to disequilibrium textures, giving evidence of magma mixing, heating of the reservoirs where the crystals are located or assimilation of crustal rocks, fast ascent, cooling, and decompression (e.g. [61]). The mixing processes correspond to mechanical mixing processes or mingling [62], which occur when mafic magma had insufficient interaction time with the felsic magma to generate a chemical mixing [62]. This process occurs at around 0.1–10 km depth [63], developed in different degrees, being evidenced by mafic enclaves (e.g., Tinto dome) and alternating mafic and felsic bands (e.g., El Maní dome) with flow structures [64]. Assimilation and fractional crystallization can be interpreted by the role of amphibole fractionation and plagioclase crystallization, respectively [32]. Whereas, all rims on amphibole and biotite phenocrysts suggest a fast magma ascent as a consequence of decompression [65].

Geochemically, based on the total alkali-silica diagram (after [66]), mafic monogenetic volcanism in northern Chile range mainly from basaltic andesite to dacitic in composition, which corresponds to scoria cones, lava flows, domes, maars, and tuff cones (**Figure 11a**). On the other hand, felsic products range from dacitic to rhyolitic composition, which corresponds to domes (**Figure 11a**). All the samples have calc-alkaline composition (not shown; after [72]), whilst mafic and felsic samples are mainly in the medium-K and high-K fields, respectively (not shown; after [73]). Based on geochemical compositional variations (Sr/Y, Sm/Yb,

**265**

**Figure 11.**

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

*a) Total alkalis–silica diagram (after [66]). b) SiO2 vs. Sr./Y diagram. c) SiO2 vs. La/Sm diagram. d) SiO2 vs. Dy/Yb diagram. The segmented lines correspond to the two group areas described in the text. e-f) comparison of whole-rock 87Sr/86Sr and 143Nd/144Nd ratios of monogenetic volcanoes with elevation (continuous line) and crustal thickness (dashed line), respectively. Arc front means elevation and crustal thickness profiles taken from Scott et al. [67]. SC: Scoria cone; LF: Lava flow; D: Dome; E: Enclave; M: Maar. g) 87Sr/86Sr vs. 143Nd/144Nd diagram; EMI (enriched mantle I) green area from Lucassen et al. [68] and references therein; the gray area from Scott et al. [67] and orange area from Franz et al. [69]. h) 87Sr/86Sr vs. SiO2 diagram. Arrows of differentiation trends (with relative mineral contribution) after Mamani et al. [70] and Delacour et al. [71]. Grt: Garnet; Cpx: Clinopyroxene; amp: Amphibole; Pl: Plagioclase; AFC: Assimilation fractional* 

*crystallization; FC: Fractional crystallization; ATA: Assimilation during turbulent magma ascent.*

*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 11.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

biotite, or sideromelane (10% vol; max 5 mm) can also be found. The main textures correspond to fluidal, reabsorption, and disequilibrium textures, such as mingling (**Figure 10b**), skeletal (**Figure 10c**), and resorbed edges rimmed by a network of clinopyroxenes (**Figure 10d**), sieve texture, and zoned rims (**Figure 10e**). The groundmass (50–80% vol.) is glassy with a microlites of plagioclase > clinopyroxene > olivine > amphibole/biotite > orthopyroxene, and opaque phases, where tabularshaped microlites display flow structures (**Figure 10f**). In general, the mafic inclusions commonly are fine-grained and microvesiculated and range from 2 to 20 cm in size (**Figure 10g**). They exhibit crystal assemblages of plagioclase, pyroxene, amphibole, biotite, olivine, and quartz. The groundmass shows mainly plagioclase > pyroxene > amphibole and rare biotite and Fe-Ti oxides, with acicular phases and

diktytaxitic texture (vesicles with plagioclase around cavity; **Figure 10h**).

In general, products of monogenetic centers in northern Chile contain two or three plagioclase populations. The first one is characterized by defined edges and no resorption features (**Figure 10e**). The second population of plagioclase show inner zones with sieve texture overgrown by euhedral rims of plagioclase, and plagioclase that is thoroughly sieved (**Figure 10e**). The last population of plagioclase exhibits oscillatory zoning and, in some cases, coarse-sieve texture and smooth edges. The mineral assemblage consists of plagioclase, olivine, orthopyroxene, and clinopyroxene, in order of decreasing abundances, with amphibole and opaque mineral (e.g., magnetite and ilmenite) as minor phases for mafic products, and plagioclase, amphibole, biotite, quartz, K-feldspar, pyroxene, titanite and opaque mineral (e.g., magnetite and ilmenite), in order of decreasing abundances, with apatite and zircon as accessory phases for felsic products. For mafic products, olivines are present in samples showing reabsorption features characterized by different types of skeletal crystal morphologies (**Figure 10f**). Pyroxene is commonly recognized as individual crystal, and as reaction rims on olivine crystals or glomerocrystals. Quartz xenocrysts are also identified and are resorbed and rimmed by a network of mafic microlites (e.g., clinopyroxene) (**Figure 10d**). For felsic products, quartz crystals have rounded edges; amphibole and biotite show euhedral to subhedral habits affected by the intense breakdown (**Figure 10g**). Overall, the groundmass is very finely crystalline, with microlites of plagioclase, ortho- and clinopyroxene, olivine, amphibole, and opaque minerals with interstitial glass (**Figure 10**).

These characteristics correspond to disequilibrium textures, giving evidence of magma mixing, heating of the reservoirs where the crystals are located or assimilation of crustal rocks, fast ascent, cooling, and decompression (e.g. [61]). The mixing processes correspond to mechanical mixing processes or mingling [62], which occur when mafic magma had insufficient interaction time with the felsic magma to generate a chemical mixing [62]. This process occurs at around 0.1–10 km depth [63], developed in different degrees, being evidenced by mafic enclaves (e.g., Tinto dome) and alternating mafic and felsic bands (e.g., El Maní dome) with flow structures [64]. Assimilation and fractional crystallization can be interpreted by the role of amphibole fractionation and plagioclase crystallization, respectively [32]. Whereas, all rims on amphibole and biotite phenocrysts suggest a fast magma

Geochemically, based on the total alkali-silica diagram (after [66]), mafic monogenetic volcanism in northern Chile range mainly from basaltic andesite to dacitic in composition, which corresponds to scoria cones, lava flows, domes, maars, and tuff cones (**Figure 11a**). On the other hand, felsic products range from dacitic to rhyolitic composition, which corresponds to domes (**Figure 11a**). All the samples have calc-alkaline composition (not shown; after [72]), whilst mafic and felsic samples are mainly in the medium-K and high-K fields, respectively (not shown; after [73]). Based on geochemical compositional variations (Sr/Y, Sm/Yb,

ascent as a consequence of decompression [65].

*a) Total alkalis–silica diagram (after [66]). b) SiO2 vs. Sr./Y diagram. c) SiO2 vs. La/Sm diagram. d) SiO2 vs. Dy/Yb diagram. The segmented lines correspond to the two group areas described in the text. e-f) comparison of whole-rock 87Sr/86Sr and 143Nd/144Nd ratios of monogenetic volcanoes with elevation (continuous line) and crustal thickness (dashed line), respectively. Arc front means elevation and crustal thickness profiles taken from Scott et al. [67]. SC: Scoria cone; LF: Lava flow; D: Dome; E: Enclave; M: Maar. g) 87Sr/86Sr vs. 143Nd/144Nd diagram; EMI (enriched mantle I) green area from Lucassen et al. [68] and references therein; the gray area from Scott et al. [67] and orange area from Franz et al. [69]. h) 87Sr/86Sr vs. SiO2 diagram. Arrows of differentiation trends (with relative mineral contribution) after Mamani et al. [70] and Delacour et al. [71]. Grt: Garnet; Cpx: Clinopyroxene; amp: Amphibole; Pl: Plagioclase; AFC: Assimilation fractional crystallization; FC: Fractional crystallization; ATA: Assimilation during turbulent magma ascent.*

Dy/Yb, and La/Sm ratio contents), monogenetic products can be divided into two types (**Figure 11b**-**d**). A group with high contents of Sr./Y, Sm/Yb, Dy/Yb, and La/ Sm ratio shows deep assimilation under high pressures and thick crust assimilation garnet signature [70]. The second group has low Sr./Y, Sm/Yb, Dy/Yb, and La/ Sm ratios, and displays shallow assimilation with amphibole and clinopyroxene fractionation [74].

Eruptive products of monogenetic volcanoes of northern Chile show values between 0.705–0.708 for 87Sr/86Sr, and 0.5122–0.5126 for 143Nd/144Nd (**Figure 11e**-**g**). These values are higher than expected for magmas derived from the asthenospheric mantle, and relatively restricted compared to isotopic data of stratovolcanoes from the CVZ (**Figure 11e**). Overall, less differentiated products show 87Sr/86Sr values lower (< 0.707) than more differentiated products (> 0.707) (**Figure 11e,f**). The 87Sr/86Sr vs. SiO2 diagram shows that assimilation and fractional crystallization (AFC) occur at different degrees and levels during the magmatic ascent from the source to the surface (**Figure 11h**). Fractional crystallization processes characterize these products, with a low degree of contamination and increasing HREE depletion (e.g., Dy, Yb, or Y), which suggest residual garnet of mantle melting enhanced by lithospheric delamination [75]. Nevertheless, a group of samples of mafic lava flows and scoria cones displays a reverse isotopic behavior of decreasing 87Sr/86Sr ratio values with the increasing of the SiO2 (**Figure 11h**). This trend cannot be explicated by mixing processes where is an increase of LILE content compared with HFSE or by AFC processes that expect an enrichment of 87Sr/86Sr ratio values during the differentiation [76]. In this context, assimilation during turbulent ascent process has been proposed (ATA; [77, 78]). This ATA process generates a selective fusion and assimilation of felsic crust, enriching of LILE (e.g., Sr or Rb; **Figure 11b**) compared with HFSE (e.g., Y or La; **Figure 11b,c**), and an enrichment of radiogenic strontium (**Figure 11e**, **f**, and **h**) like the more evolved silicic products over a relatively short time [77, 79].

On the other hand, the felsic products can be explained by the presence of a magma reservoir located in the middle-shallow crust (e.g., polybaric crystallization using the amphibole thermobarometer; [80, 81]). Two feeding reservoir systems have been identified for silicic magmas at ~4–8 km depth (~740–840°C) and at ~15–20 km (~940–1000°C) depth, respectively [80, 81]. In addition, meltingassimilation-storage-homogenization (MASH; [76]) zones have been interpreted and identified by petrological and seismic tomographic studies at ~15–40 km depth such as Altiplano-Puna Magma Body (APMB), Lazufre Magma Body (LMB) or Incahuasi Magma Body (IMB) [82–84]. These magmatic reservoirs are associated with a magmatic flare-up and magmatic steady-stage during the formation of the large ignimbrite deposits and growth of stratovolcanoes in northern Chile [85, 86]. This suggests that after these magmatic phases (flare-up and steady stage), the formation of shallow magmatic reservoirs (at 4–8 km depth) could have been formed as remnants of these eruptions. These would have been fed by a magmatic system of super-eruption scale (e.g., APMB, LMB, or IMB) of dacitic magmas and by new magma batches of less-evolved magmas [32, 87], triggering silicic eruptions of large volume with mafic inclusions as enclaves.

Therefore, based on the geochemical and isotopic compositional variations, the monogenetic volcanic products of northern Chile are characterized by two groups of magmas. One of them presents a magma evolution dominated by a high-pressure garnet source at deepest crust levels [71, 88] (**Figure 12**) characterized by different magmatic processes as FC, AFC, and ATA (**Figure 12**). The second group of magmas presents a magma evolution dominated by low-pressure garnet-free source middle-upper crust level to shallow crustal levels. This group of magmas is characterized by crystallizing of amphibole during the magma ascent (e.g. [32, 87]), and by AFC magmatic processes with different mixing degree (**Figure 12**).

**267**

**6. Concluding remarks**

*model were taken from [75].*

and vice versa).

**Figure 12.**

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

Monogenetic volcanism in northern Chile (18–28° Lat. S) is represented by 907 centers characterized by small (e.g., SC2 scoria cone) and large-volume (e.g., La Torta de Tocorpuri dome) volcanic structures. It exhibits a wide range of composition, from basaltic andesite (e.g., Cerro Overo) to rhyolite (e.g., Corral de Coquena) and a wide spectrum of volcanic landform, lithofacies, and hydromagmatic and magmatic eruptive styles (with the transition from explosive to effusive,

*Conceptual model diagram of the magmatic system for monogenetic volcanoes in northern Chile. This model relates mantle-derived magmas with felsic upper crustal partially molted levels of magma storages such as shallow pre-eruptive reservoirs and large magmatic bodies (e.g., Altiplano-Puna Magma body). Processes during the magma ascent from source to the surface, such as MASH (melting-assimilation-storagehomogenization), mixing, AFC (assimilation fractional crystallization), ATA (assimilation during turbulent magma ascent) or magma-water interaction (phreatomagmatism). Distribution of these zones is constrained by stratigraphic [33–35], petrologic and thermobarometric [29, 79, 87–89], and geophysical [82–84] data. Partial melting and assimilation of lithospheric mantle by delaminated material at the base of the lithosphere* 

Among these eruptive styles, the most abundant activity corresponds to effusive and Strombolian eruptions. In contrast, the fewer frequency activities are the phreatomagmatic and Surtseyan eruptions (**Figure 3**), which is concordant with an arid climate in northern Chile from the Miocene [41, 90]. This could be related to the degree of glaciation because when everything is too cold and frozen, not a lot of water can infiltrate to become groundwater. At the same time, in warmer periods,

meltwater can form lakes or flow toward basins from the peaks.

*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 12.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

fractionation [74].

Dy/Yb, and La/Sm ratio contents), monogenetic products can be divided into two types (**Figure 11b**-**d**). A group with high contents of Sr./Y, Sm/Yb, Dy/Yb, and La/ Sm ratio shows deep assimilation under high pressures and thick crust assimilation garnet signature [70]. The second group has low Sr./Y, Sm/Yb, Dy/Yb, and La/ Sm ratios, and displays shallow assimilation with amphibole and clinopyroxene

Eruptive products of monogenetic volcanoes of northern Chile show values between 0.705–0.708 for 87Sr/86Sr, and 0.5122–0.5126 for 143Nd/144Nd (**Figure 11e**-**g**). These values are higher than expected for magmas derived from the asthenospheric mantle, and relatively restricted compared to isotopic data of stratovolcanoes from the CVZ (**Figure 11e**). Overall, less differentiated products show 87Sr/86Sr values lower (< 0.707) than more differentiated products (> 0.707) (**Figure 11e,f**). The 87Sr/86Sr vs. SiO2 diagram shows that assimilation and fractional crystallization (AFC) occur at different degrees and levels during the magmatic ascent from the source to the surface (**Figure 11h**). Fractional crystallization processes characterize these products, with a low degree of contamination and increasing HREE depletion (e.g., Dy, Yb, or Y), which suggest residual garnet of mantle melting enhanced by lithospheric delamination [75]. Nevertheless, a group of samples of mafic lava flows and scoria cones displays a reverse isotopic behavior of decreasing 87Sr/86Sr ratio values with the increasing of the SiO2 (**Figure 11h**). This trend cannot be explicated by mixing processes where is an increase of LILE content compared with HFSE or by AFC processes that expect an enrichment of 87Sr/86Sr ratio values during the differentiation [76]. In this context, assimilation during turbulent ascent process has been proposed (ATA; [77, 78]). This ATA process generates a selective fusion and assimilation of felsic crust, enriching of LILE (e.g., Sr or Rb; **Figure 11b**) compared with HFSE (e.g., Y or La; **Figure 11b,c**), and an enrichment of radiogenic strontium (**Figure 11e**, **f**, and **h**) like

the more evolved silicic products over a relatively short time [77, 79].

volume with mafic inclusions as enclaves.

On the other hand, the felsic products can be explained by the presence of a magma reservoir located in the middle-shallow crust (e.g., polybaric crystallization using the amphibole thermobarometer; [80, 81]). Two feeding reservoir systems have been identified for silicic magmas at ~4–8 km depth (~740–840°C) and at ~15–20 km (~940–1000°C) depth, respectively [80, 81]. In addition, meltingassimilation-storage-homogenization (MASH; [76]) zones have been interpreted and identified by petrological and seismic tomographic studies at ~15–40 km depth such as Altiplano-Puna Magma Body (APMB), Lazufre Magma Body (LMB) or Incahuasi Magma Body (IMB) [82–84]. These magmatic reservoirs are associated with a magmatic flare-up and magmatic steady-stage during the formation of the large ignimbrite deposits and growth of stratovolcanoes in northern Chile [85, 86]. This suggests that after these magmatic phases (flare-up and steady stage), the formation of shallow magmatic reservoirs (at 4–8 km depth) could have been formed as remnants of these eruptions. These would have been fed by a magmatic system of super-eruption scale (e.g., APMB, LMB, or IMB) of dacitic magmas and by new magma batches of less-evolved magmas [32, 87], triggering silicic eruptions of large

Therefore, based on the geochemical and isotopic compositional variations, the monogenetic volcanic products of northern Chile are characterized by two groups of magmas. One of them presents a magma evolution dominated by a high-pressure garnet source at deepest crust levels [71, 88] (**Figure 12**) characterized by different magmatic processes as FC, AFC, and ATA (**Figure 12**). The second group of magmas presents a magma evolution dominated by low-pressure garnet-free source middle-upper crust level to shallow crustal levels. This group of magmas is characterized by crystallizing of amphibole during the magma ascent (e.g. [32, 87]), and

by AFC magmatic processes with different mixing degree (**Figure 12**).

**266**

*Conceptual model diagram of the magmatic system for monogenetic volcanoes in northern Chile. This model relates mantle-derived magmas with felsic upper crustal partially molted levels of magma storages such as shallow pre-eruptive reservoirs and large magmatic bodies (e.g., Altiplano-Puna Magma body). Processes during the magma ascent from source to the surface, such as MASH (melting-assimilation-storagehomogenization), mixing, AFC (assimilation fractional crystallization), ATA (assimilation during turbulent magma ascent) or magma-water interaction (phreatomagmatism). Distribution of these zones is constrained by stratigraphic [33–35], petrologic and thermobarometric [29, 79, 87–89], and geophysical [82–84] data. Partial melting and assimilation of lithospheric mantle by delaminated material at the base of the lithosphere model were taken from [75].*
