5.a. Estimation of physicochemical crystallization conditions

Using the available thermobarometric models and the obtained compositions for clinopyroxene and amphibole, we were able to estimate the prevailing temperatures, pressures, oxygen fugacities and the water contents of the crystallization environments related to each of the studied plutons. These constraints are crucial for understanding the processes that control magma generation and evolution and for reconstructing the thermal and emplacement history of the Jurassic plutonic rocks exposed in southern Colombia. The results (average values) are summarized in Table 2; the full dataset is listed in supplementary Tables S2b and S2c.

Table 2. Estimated mean values of crystallization physicochemical parameters of the studied Jurassic arc-related plutonic occurrences

Thermobarometry calculations based on: T1 and P1 = Cpx-thermobarometry calibrations by Wang et al. (Reference Wang, Hou, Wang, Zhang, Zhang, Pan, Marxer and Zhang2021); T2 = amphibole-plagioclase thermometer by Holland and Blundy (Reference Holland and Blundy1994) (expression B); P2 = Al-in-hornblende barometer by Mutch et al. (Reference Mutch, Blundy, Tattitch, Cooper and Brooker2016); Depths were determined based on pressure conditions, assuming an equivalent 3.8 km pressure gradient for the average crustal density of 2.7 g cm^{− 3}; Physico-chemical conditions of magmas (logf _O2, H₂Omelt) according to amphibole-only calibrations by Ridolfi (Reference Ridolfi2021).

5.a.1. Temperature

Petrographic observations have indicated that clinopyroxene is an early-crystallized phase found exclusively in the monzodiorite, quartz monzodiorite and quartz monzonite facies of Associations I and II from UMV. Therefore, by measuring the crystallization temperature of clinopyroxene, it is possible to estimate the near-liquidus temperature of the parental magmas for the corresponding magma series. The model proposed by Wang et al. (Reference Wang, Hou, Wang, Zhang, Zhang, Pan, Marxer and Zhang2021), unlike other thermometers that rely on additional information from melt compositions or coexisting minerals (e.g. Liang et al. Reference Liang, Sun and Yao2013; Putirka et al. Reference Putirka, Johnson, Kinzler, Longhi and Walker1996; Putirka, Reference Putirka2008), depends solely on the clinopyroxene compositions and the resulting temperatures appear to be more accurate on the average, as evidenced by comparisons in Wieser et al. (Reference Wieser, Kent and Till2023). In our calculations, we assumed an average H₂O content in the melt of ∼4.0 wt %, according to the broadly estimated water contents in mafic arc magmas (Plank et al. Reference Plank, Kelley, Zimmer, Hauri and Wallace2013). The estimated clinopyroxene temperatures in both associations overlap but are higher on average for the monzodiorite and quartz monzodiorite rocks of Association I (970°C–1087°C) as compared to those quartz monzodiorites and monzonites of Association II (988°C–1011°C) see Table 2. Considering that clinopyroxenes were among the first crystallized mineral phases, these results are interpreted to represent thermal conditions near the liquidus of the older magmas within the UMV domain.

The amphibole-plagioclase thermometer developed by Holland and Blundy (Reference Holland and Blundy1994) is a widely accepted model for estimating the close-to-solidus crystallization temperatures of hydrous magmas within arc magmatic systems. In our study, the criteria for its application have been consistently met in all investigated plutonic rock samples, defined by the typical mineral assemblage of quartz + plagioclase + K-feldspar + hornblende + biotite + titanite + magnetite + apatite. For comparison, the new Ti-Amp thermometer of Liao et al. (Reference Liao, Wei and Rehman2021), which is based on the titanium content of calcic amphibole-bearing igneous and high-grade metamorphic rocks, was also applied in this study.

We obtained variable crystallization temperatures for the distinct plutons in which mostly diorite, monzodiorites and quartz monzodiorites facies record higher T conditions relative to quartz monzonites, granodiorites and granites. Temperatures determined by the plagioclase-hornblende thermometer in the plutonic occurrences constituted by Association IV display the highest temperatures, ranging from 691°C to 761°C (±40), followed by Association I and III, with temperatures between 656°C–747°C (±40) and 655°C–708°C (±40), respectively. In contrast, Association II results in the lowest temperatures range from 647°C to 673°C (±40). Regarding the amphibole-only thermometer, the calculated crystallization temperatures are mostly consistent with those mentioned above, with plutons in Association IV yielding 671°C–873°C (±35), Association I 656°C–766°C (±35) and Association III 601°C–691°C (±35), except for samples in Association II, which exhibit considerable underestimations about the close-to-solidus temperature conditions between 467°C and 517°C (±35). Of note, there are underestimations in specific samples from Associations I and III from the obtained temperatures by using the model of Liao et al. (Reference Liao, Wei and Rehman2021), as evidenced by the greater standard deviations of the data compared to those obtained using the Holland and Blundy (Reference Holland and Blundy1994) model (see Supplementary Table S4). Therefore, we opted to show only the plagioclase-hornblende temperature estimations in Table 2 and Fig. 9a.

Figure 9. Crystallization conditions for the distinctive petrographic facies associations of the Jurassic arc-related plutonic occurrences in southern Colombia: (a) Temperature vs pressure vs depth diagram. Dotted curves correspond to the H₂O contents necessary for water saturation of the melt taken from Holtz et al. (Reference Holtz, Behrens, Dingwell and Johannes1995); (b) logfO₂ vs. temperature showing the Ni-NiO (NNO) and QFM (Quartz-Fayalite-Magnetite) buffers for amphibole compositions from Ridolfi et al. (Reference Ridolfi, Renzulli and Puerini2010); (c) Pressure dependence of H₂O solubility diagram at 800°C after Holtz et al. (Reference Holtz, Behrens, Dingwell and Johannes1995).

Differences in temperature crystallization conditions among the four association groups can be attributed to variations in the magmatic processes and/or the degree of fractionation that occurred in each plutonic body. They may suggest that the entire Jurassic plutonic arc magmatic system in southern Colombia underwent distinct thermal histories, which influenced the observed contrasting mineral compositions and textures. In the case of the clinopyroxene-bearing rocks, the amphibole-derived temperatures are in general agreement with those clinopyroxene-derived, as amphibole was relatively late in the crystallization sequence; however, in the case of Association II, the amphibole temperatures are significantly lower approaching the expected close-to-solidus temperatures, and the resulting temperature gap is much large (up to c. 300°C), suggesting amphibole late re-equilibration. On the other hand, thermal conditions recorded by the amphibole-bearing rocks, in which amphibole crystallized at intervals above the solidus temperatures ranging between ≥700°C and ≤800°C, in general, suggest an early crystallization stage of this phase in the mineral sequences of Associations I and IV. In this sense, when compared to the zircon saturation temperatures recorded by these rocks (with mean values of 718°C, Table 1; see also Chavarría et al. Reference Chavarría, Bustamante, Cardona and Bayona2021), zircon appears to be a relatively late magmatic phase in the crystallization history of the more evolved granites in the studied region.

5.b. Plutonic evolution and implications for the Jurassic magmatic arc in southern Colombia

The physicochemical conditions and observed textural and compositional variations of minerals within the studied occurrences provide valuable insights into the petrogenetic processes that controlled the magmatic history and differentiation of the Jurassic arc in southern Colombia. In particular, the estimated crystallization parameters indicate that plutons within the UMV and SCC domains were formed in distinct magma reservoirs, where fractionation processes occurred at multiple crustal depths along the arc plutonic system, arguably related to different plumbing systems.

The differences in the emplacement depths between these domains can be explained by internal structural controls, in which the regional fault systems (Fig. 2) that extend along the region seem to be separating the UMV and SCC crustal blocks. In this section, we provide a broad understanding of the tectono-magmatic evolutionary history during the construction of the Jurassic arc by integrating the available field observations, whole-rock elemental and isotopic compositions and U-Pb zircon crystallization ages of the studied plutonic occurrences with the acquired mineral compositions and related thermobarometry. Additionally, for comparison, we illustrated the mineral compositional evolutionary paths observed of the main rock-forming phases in terms of Mg# and An parameters, as shown in Fig. 10.

Figure 10. Summary of Mg# numbers of clinopyroxene, orthopyroxene, amphibole, biotite and An content of plagioclase for the analyzed samples and their reported zircon U-Pb ages of Jurassic arc-related plutonic occurrences in southern Colombia. Of note, unfilled symbols correspond to plagioclase and amphibole data from Chavarría et al. (Reference Chavarría, Bustamante, Cardona and Bayona2021).

Magma generation in the UMV domain has been linked to a tectonic episode of crustal thickening during the early phase subduction that occurred between 190 and 180 Ma and resulted in the development of an arc crustal column of about ∼40 to 50 km paleodepth (Chavarría et al. Reference Chavarría, Bustamante, Cardona and Bayona2021). We propose that in this scenario of thick crust, the massive influx of magma prompted the partial melting of ancient Precambrian rocks at relatively high pressures, causing the generation of high-K (up to 5.3 wt % K₂O, cf. Table 1) metaluminous calc-alkaline magmas within a well-defined MASH zone (melting, assimilation, storage, homogenization; Hildreth and Moorbath, Reference Hildreth and Moorbath1988) found in this older magmatic episode. It is argued that the estimated high-pressure crystallization of clinopyroxene (∼6 kbar) from the more primitive monzodiorite rock in Association I (Table 2) reflects the initial fractionation of its deep MASH zone as illustrated in Fig. 11. Therefore, we hypothesize that crustal assimilation and/or magma mixing processes played significant roles in the differentiation of the UMV magmas.

Figure 11. Conceptual approach to the magmatic arc system and processes involved in the Jurassic plutonism in southern Colombia.

The constraints on magma reservoir conditions, derived from the amphibole compositions, indicated that UMV magmas appeared to be relatively oxidized and enriched in water content (Fig. 9 and Table 2). The subsequent fractional crystallization of these magmas resulted in the differentiation of the three distinct Associations I, II and III, under varying high to low pressure and temperature conditions, with emplacement depths ranging from mid- to upper-crustal levels along the arc column. During magma ascent, UMV melts likely incorporated significant crustal materials as suggested by the heterogeneous positive and negative Hf isotopic compositions from plutons in Association III (Garcia, unpub. PhD thesis, São Paulo Univ. Brazil, 2018), the presence of inherited Neoproterozoic zircons in plutons of Association III (Rodríguez et al. Reference Rodríguez, Arango, Zapata and Bermúdez2018), unradiogenic Nd isotopic values of most of the arc-related rocks in the region (Leal-Mejía et al. Reference Leal-Mejía, Shaw, Melgarejo, Cediel and Shaw2019) and elevated concentrations of large ion lithophile elements (LILEs) and rare earth elements (REEs), reaching up to 2186 and 265 ppm, respectively, within all UMV plutonic rocks (Table 1). The presence of Precambrian metamorphic rocks and Paleozoic sediments in the region (Gomez et al. Reference Gomez, Schobbenhaus and Montes2019; Ibañez-Mejia, Reference Ibañez-Mejia, Gómez and Mateus–Zabala2020) suggests the availability of fertile lithologies that can undergo partial melting within the lower crust, especially when mantle-derived magmas are emplaced into the crust.

Evidence of the magma mixing process during the formation of the UMV plutons include the widespread occurrence of microgranular mafic (dioritic) enclaves (Table S2) and related mafic and felsic syn-plutonic dikes from field observations (e.g. García-Chinchilla and Vlach, Reference García-Chinchilla and Vlach2019; Rodríguez-García et al. Reference Rodríguez-García, Correa-Martínez, Zapata-Garcia, Arango-Mejía, Obando-Erazo, Zapata-Villada, Bermudez, Gómez and Mateus–Zabala2020a). The corona and sieve textures observed in ortho- and/or clinopyroxenes, showing partial replacement by amphibole or biotite (Figs. 3, 8a and 10) are also potential indicators of magma reservoirs undergoing magma mixing/mingling processes (Baxter and Feely, Reference Baxter and Feely2002; Kamacı and Altunkaynak, Reference Kamacı and Altunkaynak2019; Schaaf et al. Reference Schaaf, Corona-Chávez, Ortiz Joya, Solís-Pichardo, Arrieta García, Hernández Treviño and Poli2021; Koua et al. Reference Koua, Sun, Li, Li, Xie, Sun, Li, Yang, Zhang and Mondah2022; Sousa et al. Reference Sousa, Conceição, Soares, Fernandes and da Silva Rosa2022). Additionally, the changing magmatic conditions recorded in the compositional zoning of clinopyroxenes and amphiboles in Associations I and III likely suggest the replenishment of magma batches into pre-existing magma reservoirs, leading to disequilibrium conditions and mixing processes during the crystallization of primitive UMV magmas. Based on the petrological features described above, along with the similar geochemical trace element compositions (Table 1) and coexisting fractionation patterns observed in the different mafic and felsic rocks from the UMV domain (see Rodríguez et al. Reference Rodríguez, Arango, Zapata and Bermúdez2018), we argue that the mixing/mingling of magmas might serve as a complementary petrological process in the lower crust MASH zone, contributing to the magmatic evolutionary history of the UMV rocks. This process may potentially explain the wide variability of the plutonic rocks in the region. However, to fully evaluate the specific contributions of the role of mixing and/or crustal assimilation, further investigations should employ geochemical and isotopic models.

During the first interval of magmatic evolution from c. 195 to 183 Ma, mineral chemistry results reveal the significant role of clinopyroxene, fractionating at different pressures between 6 and 2 kbar (Table 2), in driving the differentiation of early-formed monzodiorite, quartz monzodiorite (Association I) and monzonite and quartz monzonite (Association II) rocks. The observed evolutionary trends in these rocks include the extensive crystallization of clinopyroxene with a range of Mg# values from 0.78 to 0.53, plagioclase with varying An_57-12 contents and the subsequent crystallization of Mg-rich amphiboles (Mg# = 0.75–0.44; Fig. 10). Crystallization of Mg-rich annite with Mg# evolutionary trends from 0.57 to 0.41 record the next stage of solidification of the early UMV magmas in the arc system. Moreover, this early magmatism is notably characterized by distinct intrusion events of Association I and II intrusions at mid- to upper-crustal depths, as previously estimated. Considering the established steady-state scenario that characterized the onset of subduction-driven magmatism within this Jurassic arc (Bustamante et al. Reference Bustamante, Cardona, Bustamante and Vanegas2019), we can only speculate about the existence of localized structural heterogeneities within the arc crustal column. These variations in the stress regime might have facilitated the continuous ascent of less voluminous magmas along vertically arc-parallel faults, such as the Agrado-Betania and Fraile-Pava faults, depicted in Fig. 2. Consequently, smaller, and relatively more, homogeneous intrusions and stocks like those grouped in Association II were emplaced at shallower crustal levels in the central UMV region (Fig. 11). This hypothesis gains support from the spatial relationships observed, where Association II bodies intruded the volcanic sequences of the Saldaña Formation, representative of the primary component of the arc volcanic front within the Jurassic magmatic system.

Between ∼180 and 165 Ma, the magmas in the UMV domain evolved through plagioclase and amphibole-dominated fractionation, reflected in the compositional trends of An_46-1 and Mg# 0.74–0.49, respectively (Fig. 10), resulting in the formation of granodiorite and granite rocks (Association III). Of note, the more evolved granites exhibit slight variations in the intensive crystallization parameters, characterized by higher f _o2 oxidation but lower H₂O_melt values when compared to the intermediate rocks of Associations I and II (Fig. 9 and Table 2). These differences are arguably attributed to enhanced crustal assimilation interactions during magma ascent within the plumbing system (Blatter et al. Reference Blatter, Sisson and Hankins2013; Humphreys et al. Reference Humphreys, Brooker, Fraser, Burgisser, Mangan and McCammon2014; Grocke et al. Reference Grocke, Cottrell, de Silva and Kelley2016). These processes caused the destabilization of the amphibole crystals and the subsequent formation or re-equilibrate biotite, as evidenced in the shallower emplacement plutons of Associations II and III (Figs. 3, 8 and 10). Comparing the crystallization sequences of the UMV plutonic rocks, we have observed overlapping mineral evolutionary trends among contemporaneous granodiorites of Association I and granites of Association III emplaced at ∼162 to 163 Ma (Fig. 10). This suggests similar magmatic differentiation trends occurred in both the western and eastern parts of the UMV domain, supporting the idea that the older (∼195 to 165 Ma) Jurassic magmatic episode of arc construction in southern Colombia was developed within a stationary subduction setting (Bustamante et al. Reference Bustamante, Cardona, Bustamante and Vanegas2019).

Bustamante et al. (Reference Bustamante, Archanjo, Cardona and Vervoort2016) suggest that the tectonic regime changed to a more oblique subduction setting during the younger (∼165 to 145 Ma) Jurassic magmatic episode. This tectonic scenario could have potentially led to the underplating of new mantle-derived melts and the formation of a distinct magma reservoir within a thinned crust, at depths of ∼25–45 km (Chavarría et al. Reference Chavarría, Bustamante, Cardona and Bayona2021). Isotopic data from Sr, Nd, Pb and Hf compositions consistently indicate an increasingly juvenile signature in the magmatic record between 165 and 129 Ma (Cochrane et al. Reference Cochrane, Spikings, Gerdes, Winkler, Ulianov, Mora and Chiaradia2014a; Bustamante et al. Reference Bustamante, Archanjo, Cardona and Vervoort2016; Quandt et al. Reference Quandt, Trumbull, Altenberger, Cardona, Romer, Bayona, Ducea, Valencia, Vásquez, Cortes and Guzman2018; Leal-Mejía et al. Reference Leal-Mejía, Shaw, Melgarejo, Cediel and Shaw2019). This is further supported by the distinct redox conditions recorded by the plutonic occurrences of Association IV (Fig. 9 and Table 2). These conditions reflect the addition of less oxidizing slab fluids ascending in the mantle wedge, resulting in the formation of moderately oxidized and hydrous calc-alkaline medium-K magmas (up to 3.9 wt % K₂O), with discrete LILEs and REEs concentrations (reaching up to 1197 and 119 ppm, respectively; Table 1). Subsequently, the development of magma fractionation processes within a mid-crustal MASH zone likely led to the crystallization of the younger Jurassic plutons within the SCC domain.

Although the examined samples of Association IV from the Ibague Batholith and Payande Stock in the SCC domain are limited, we were able to identify key aspects that provide insights into the potential magmatic processes involved in the formation of these younger Jurassic plutons. Our mineral chemistry data suggest that SCC magmas have been differentiated by primary fractionation of plagioclase with varying An_57-12 contents, and amphibole and biotite with Mg# values from 0.69 to 0.54 and 0.54 to 0.58, respectively (Fig. 10). We hypothesize that the diorite facies, with cumulate amphibole + plagioclase texture and crystallized under high pressure, records the accumulation of crystal from the melt at the base of the younger magma chamber. Thermobarometry supports this interpretation, suggesting that this rock likely represents the root of the intrusive Southern Ibague Batholith established at mid-crust levels (Table 2). Previous studies suggest that the formation of this intrusive body in the region involved multiple intrusions, evidenced by continuous magma pulses from c. 171 to 137 Ma (Leal-Mejía et al. Reference Leal-Mejía, Shaw, Melgarejo, Cediel and Shaw2019; Rodríguez-García et al. Reference Rodríguez-García, Ramírez, Zapata, Correa-martínez, Sabrica, Obando, Estudios, Especiales and Colombiano2022). These multiple injection events are further supported by the contrasting crystallization pressure and temperature conditions of the diorite and monzogranite rocks in the Southern Ibague Batholith, indicating a late magmatic re-equilibration process, as discussed in the previous section. Indeed, the common occurrence of concentric-zoned plagioclase crystals within this association (Figs. 3 and 4) suggests extensive crystal fractionation during the evolution of the SCC magmas. Therefore, we propose that magmatic differentiation may have persisted after the early magma injections, allowing later, more evolved magmas to ascend and reach the uppermost crust. This is supported by the shallower emplacement depths of the granodiorite and monzogranite rocks in the SCC domain (Fig. 11).

5.c. Late Jurassic to Early Cretaceous fragmentation and exhumation of the magmatic arc

Our constraints on the emplacement depth of the Jurassic plutonic rocks from the UMV and SCC domains in southern Colombia have provided minimum exhumation values for several segments of the Jurassic magmatic arc. The inferred paleodepths exhibit a total exhumation pattern that partially aligns with the modern geomorphic provinces of the Northern Andes. The westernmost plutonic basement rocks of the SCC domain exhibit the highest amount of total exhumation of ∼15 km, while the eastern basement rocks of the UMV demonstrate total exhumation values ranging from 12 to 5 km, with minor intra-basin exhumation between 2 and 4 km within the UMV. These results support the models suggesting that the Central Cordillera in the SCC domain has undergone more prolonged deformation and exhumation compared to other provinces in the Northern Andes (Zapata et al. Reference Zapata, Zapata-Henao, Cardona, Jaramillo, Silvestro and Oboh-Ikuenobe2021).

Six of the investigated occurrences are situated within coherent structural basement blocks overlain by Cretaceous strata, indicating rock exhumation between magma crystallization and sediment deposition. Hence, the inferred paleodepth values presented in this study provide a constraint on the magnitude of deformation during this period. The Late Jurassic to Early Cretaceous exhumation inferred from thermobarometry data includes ∼10 km in the Sombrerillo Batholith and the Paez and Algeciras Massifs, ∼6 km in the Mocoa Batholith and the Altamira Massif and >4 km in the Astilleros, Anchique and Payande Stocks. The absence of distinct Cretaceous unconformities in the remaining structural blocks domain precludes any inferences about this exhumation event.

This major exhumation event can be correlated to either terrane collision and crustal thickening during the Late Jurassic (Blanco-Quintero et al. Reference Blanco-Quintero, García-Casco, Toro, Moreno, Ruiz, Vinasco, Cardona, Lázaro and Morata2014; Bustamante et al. Reference Bustamante, Archanjo, Cardona and Vervoort2016), the onset of crustal extension (Zapata et al. Reference Zapata, Patiño, Cardona, Parra, Valencia, Reiners, Oboh-Ikuenobe and Genezini2020) or a combination of both. Detrital zircon fission-track ages obtained from the Cretaceous strata in the Upper Magdalena Basin suggest a Jurassic to Early Cretaceous exhumation event (Calderon-Diaz et al. Reference Calderon-Diaz, Zapata, Cardona, Parra, Sobel, Patiño, Valencia, Jaramillo-Rios and Glodny2024). Nevertheless, these age populations lack the resolution to determine whether this exhumation was triggered by collisional or extensional tectonic processes. A zircon fission-track age derived from the Astilleros Pluton implies that in this specific structural block, exhumation took place around 124 Ma. This finding aligns more closely with exhumation associated with extensional tectonic activity (Valencia-Gómez et al. Reference Valencia-Gómez, Cardona, Zapata, Monsalve, Marín, Rodríguez-Cuevas, Sobel, Parra and Glodny2024).

Several questions and observations can be addressed based on this dataset. The eastern segment of the Central Cordillera and the Algeciras Massif exhibit higher exhumation values, followed by the Mocoa Batholith, while lower values are observed within the Upper Magdalena Basin. This pattern resembles the modern basin configuration, suggesting a plausible control of these past events on subsequent deformation phases. Moreover, it implies a long-lived deformation history of the fault systems limiting these structural blocks (e.g. La Plata-Chusma, Agrado-Betania and Algeciras Fault systems). In either compressional or extensional tectonics, such amounts of exhumation would have resulted in a substantial sedimentary influx into extensional or flexural basins associated with the exhumed blocks. However, the absence of sedimentary strata from this period remains enigmatic. We present compelling evidence of significant Late Jurassic to Early Cretaceous rock exhumation. Nonetheless, the tectonic precursors, refined spatial-temporal patterns and the absence of associated sedimentation remain as open research questions.