Contemporaneous eruption of calc-alkaline and ... - Springer Link

Contrib Mineral Petrol (2005) 150: 423–440 DOI 10.1007/s00410-005-0015-x

O R I GI N A L P A P E R

Gerardo Carrasco-Nu´n˜ez Æ Kevin Righter Æ John Chesley Lee Siebert Æ Jose´ Jorge Aranda-Go´mez

Contemporaneous eruption of calc-alkaline and alkaline lavas in a continental arc (Eastern Mexican Volcanic Belt): chemically heterogeneous but isotopically homogeneous source Received: 24 October 2004 / Accepted: 16 June 2005 / Published online: 6 October 2005 Ó Springer-Verlag 2005

Abstract Nearly contemporaneous eruption of alkaline and calc-alkaline lavas occurred about 900 years BP from El Volcancillo paired vent, located behind the volcanic front in the Mexican Volcanic Belt (MVB). Emission of hawaiite (Toxtlacuaya) was immediately followed by calc-alkaline basalt (Rı´ o Naolinco). Hawaiites contain olivine microphenocrysts (Fo67–72), plagioclase (An56–60) phenocrysts, have 4–5 wt% MgO and 49.6–50.9 wt% SiO2. In contrast, calc-alkaline lavas contain plagioclase (An64–72) and olivine phenocrysts (Fo81–84) with spinel inclusions, and have 8–9 wt% MgO and 48.4–49.4 wt% SiO2. The most primitive lavas in the region (Rı´ o Naolinco and Cerro Colorado) are not as primitive as parental melts in other arcs, and could represent either (a) variable degrees of melting of a subduction modified, garnet-bearing depleted mantle source, followed by AFC process, or (b) melting of two distinct mantle sources followed by AFC processes. These two hypotheses are evaluated using REE, HFSE, and Sr, Os and Pb isotopic data. The Toxtlacuaya flow and the Y & I lavas can be generated by combined fractional crystallization and assimilation of gabbroic granulite, starting with a parental liquid similar to the Communicated by T.L. Grove. G. Carrasco-Nu´n˜ez (&) Æ J. J. Aranda-Go´mez Centro de Geociencias, Campus UNAM Juriquilla, Quere´taro, Qro 76230, Me´xico E-mail: [email protected] Tel.: +52-442-238-1116 Fax: +52-442-238-1129 K. Righter Mail Code KT, NASA Johnson Space Center, 2101 NASA Road One, Houston, TX 77058, USA J. Chesley Department of Geosciences, University of Arizona, Gould-Simpson Building# 77, Tucson, AZ 85721, USA L. Siebert Global Volcanism Program, Smithsonian Institution, Washington, DC 20013-7012, USA

Cerro Colorado basalt. Although calc-alkaline and alkaline magmas commonly occur together in other areas of the MVB, evidence for subduction component in El Volcancillo magmas is minimal and limited to 15%; Fig. 7c). These high F values are unreasonable for sub-alkaline melts and would produce a melt with major and trace element characteristics unlike either of the primitive CPVC melts (Kushiro 1998). However, the alkaline Young Lava Series basalts (Cerro Colorado) can be reproduced by 3% melting of such a source with a small amount of garnet to explain the HREE (Fig. 7d). The sub-alkaline Rı´ o Naolinco basalt can be reproduced by 5–7% melting of such a source with a small amount of garnet (2%) to explain the HREE (Fig. 7e). Therefore, the REE patterns of both primitive CPVC melts can be satisfied by melting of a 90% depleted, 10% enriched, garnet-bearing mantle that has been modified by an addition of a small (0.5–0.7%) amount of subduction component. The HFSE (Ti, Ta, Nb, and Hf) are incompatible and largely insoluble in fluids, making them useful elements to see through the potential effects of subduction modification of a mantle source. Recently, however, the insoluble nature of Hf and Zr has been challenged (e.g., Grove et al. 2002). For this reason, we have chosen Ti and Nb to model the contributions of depleted or

enriched mantle for the generation of the CPVC primitive melts. Using the batch partial melting models of Michael (1988) and partition coefficient data of Grove et al. (2002), the concentrations of Nb and Ti in liquids derived from 1 to 15% melting of both incompatible element enriched and depleted mantle have been calculated for comparison with the primitive lavas from the CPVC (Fig. 8a). It is clear that these elements fall between the two enriched and depleted end members for all degrees of partial melting, but the compositions of both ‘‘primitive’’ liquids can be reproduced by melting of approximately 85% depleted/15% enriched mantle (heavy curve in Fig. 8a). Rı´ o Naolinco lavas can be produced by 6% melting, whereas the Young Lavas (Cerro Colorado) can be produced by 3% partial melting of the same source. This modeling and result is very similar to the findings of Wallace and Carmichael (1999), who examined Nb–Zr–Ti compositions of basalt from the Sierra Chichinautzin in the central MVB. Similarly, Ti/Y and Nb/Y ratios for the basaltic lavas in this study indicate a depleted source (Fig. 8b), plotting near the MORB field (cf, Pearce and Peate 1995). Also, Ba/Zr and Nb/Zr ratios (after Leeman et al. 1990) are

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Fig. 6 87Sr/88Sr versus 187Os/188Os and Ni versus 187Os/188Os for the Rı´ o Naolinco and Toxtlacuaya samples as well as AFC trends calculated for a subduction-modified mantle melt and a granulite assimilant (Table 8). AFC modeling was done using the equations presented by DePaolo (1981) with Ma/Mc=0.66, and values in Table 8. For the mantle melt (90% DM and 10% EM), 187 Os/188Os=0.13, 87Sr/86Sr=0.7033, Sr=300 ppm, Ni=400 ppm, and Os=100 ppt. Tick marks are 2% assimilant increments. Ni–Os isotope trends are calculated for D(Ni)=7 and 10, and for crustal 187 Os/188Os=0.5–1.8, to illustrate the variation caused by these parameters. Values for the host lava are as follows: 187 Os/188Os=0.13, 87Sr/86Sr=0.704, Sr=590 ppm, Ni=160 ppm, and Os=50 ppt. Again, the mantle melt represents melt of a 90% depleted mantle and 10% enriched mantle, and has had 0.5% subduction component added (Table 8) with isotopic composition: 187 Os/188Os=0.13 and 87Sr/86Sr=0.70365

consistent with derivation from a depleted source and one that has been minimally affected by subduction fluids (Fig. 8c). Sr and Pb isotopes have been used by Petrone et al. (2003) to suggest that variations in the mantle sources of calc-alkaline and alkaline lavas from western MVB were a mixture of depleted mantle, enriched mantle and a subduction component, where two different magmas are present. In contrast, the calc-alkaline and IA magmas from the CPVC are consistent with derivation from a largely depleted (90% depleted/10% enriched) mantle plus a small (1–2%) subduction component (Fig. 9), indicating a similar mantle source. It is interesting to

point out that the alkaline magmas from El Volcancillo apparently come from a mostly depleted mantle source, in contrast with the alkaline lavas from the western MVB that are derived from an enriched source. Finally, examination of Sm/Nd and Lu/Hf versus an indicator of the degree of fractionation such as MgO (Fig. 10) reveals that a single parental liquid such as that derived from melting of a 90%DM10%EM mantle source could account for both the subalkaline and alkaline suites by modification of that melt during AFC processes. Because even the most primitive melts show evidence for crustal contamination, we favor this model over those involving multiple mantle sources. As for El Volcancillo, the sequential eruption of compositionally different magma batches might be similar to that documented during the 9-year-long eruption of Paricutı´ n volcano, which was explained by combined fractional crystallization and crust assimilation processes (McBirney et al. 1987). Furthermore, the chemical variations of the 1986–1992 Pu’u O’o eruption were attributed to progressive melting of a predominantly homogeneous mantle (Garcı´ a et al. 1996). Calc-alkaline basalts from the western Mexican Volcanic Belt, and the Michoaca´n–Guanajuato and Sierra Chichinautzin volcanic fields commonly show evidence for a subduction component in terms of elevated Ba/Nb ratios (Carmichael et al. 1996; Wallace and Carmichael 1999; Chesley et al. 2002). In contrast, the CPVC basalts show only minor evidence for a subduction component, as they exhibit lower Ba/Nb at a given Zr/Nb value (Fig. 11). Ba/Nb falls off the trend defined by calc-alkaline and alkaline basalt from the MVB. Also, Ba/Zr and Nb/Zr values for the CPVC lavas are not elevated above the MORB–OIB field of Leeman et al. (1990), indicating only a minor role for subduction component (Fig. 8c). In summary, it is evident from the REE and Ti–Nb– Y–Ba–Zr data (Figs. 7 and 8), and the Sr–Pb isotope and trace element data that both the Rı´ o Naolinco and Toxtlacuaya parental lavas could have been derived from melting of a subduction modified, largely depleted mantle. Both magmas rose into a crust dominated by granulite rocks belonging to the Oaxaquia terrane and underwent different processes during their ascent to the surface. We surmise that the injection of the calcalkaline Rı´ o Naolinco magma triggered the eruption of the hawaiiitic Toxtlacuaya magma. The Toxtlacuaya hawaiites cannot be derived from the Rı´ o Naolinco magmas by simple fractional crystallization or AFC, but instead from a more alkaline parent magma (Cerro Colorado) modified by AFC processes. This parent was not necessarily derived from melting of an enriched mantle, but rather by small degrees of melting of a largely depleted mantle.

Implications for arc volcanism The occurrence of both calc-alkaline and alkaline (OIBlike or IA) magmas in many arcs has usually led to the

436 Fig. 7 Rare earth element (REE) diagram for Rı´ o Naolinco and Young Lava Series (Cerro Colorado), along with calculated patterns for melting of different mantle sources. a Melting of a depleted mantle (DM) with variable amounts of residual garnet in the source, at 5% melting; (b) melting of an enriched mantle (EM) with variable amounts of garnet in the mantle source at 5% melting; (c) depleted mantle (spinel lherzolite) with 1% subduction component (SC) added, and variable extents of melting. d 90% DM and 10% EM with 0.7% SC added, and with variable amounts of residual garnet in the mantle source and 3% melting; (e) 90% DM and 10% EM with 0.5% SC added, and with variable extents of melting of a garnetbearing mantle source (5, 6, and 7% melting). The last two calculated patterns match the Cerro Colorado and Rı´ o Naolinco lavas and indicate that these two primitive lavas could be derived from variable extents of melting of a garnetbearing, subduction-modified mantle. All data normalized to chondrites (Nakamura 1974). Partition coefficients and end members used in the modeling are listed in Table 8

conclusion that the sub-arc mantle is heterogeneous, consisting of a mixture of depleted, enriched and subduction-modified reservoirs. For example, contemporaneous alkaline and calc-alkaline volcanism is common along the front of the western sector of the MVB (Lange and Carmichael 1990, 1991; Wallace and Carmichael 1992; Carmichael et al. 1996; Righter and Rosas-Elguera 2001). Other regions where this occurs in the MVB are the Colima and Sangangu¨ey volcanoes (Luhr and

Carmichael 1985a; Nelson and Livieres 1986), and the Michoaca´n–Guanajuato (Luhr and Carmichael 1985b), and Chichinautzin volcanic fields (Wallace and Carmichael 1999). The distribution pattern is also observed in the Central America volcanic chain, where the volcanic front consists of large subalkaline composite volcanoes, and just behind the front there are fields of transitional or alkaline cinder cones (Alvarado and Carr 1993). Furthermore, both alkaline and calc-alkaline lavas occur

437 b

Fig. 8 a Nb and TiO2 concentrations for primitive lavas from Rı´ o Naolinco and Cerro Colorado (Young Lavas). Also shown are the concentrations of Nb and TiO2 in liquids derived from 1 to 15% melting of both incompatible element enriched (dotted line), depleted (dot–dashed line) and mixed 85% depleted/15% enriched mantle (heavy line). Tick marks are 1% melting increments. These calculations used the batch partial melting models of Michael (1988) and partition coefficient from Table 8. Rı´ o Naolinco lavas can be produced by 6% melting of a 85% depleted/15% enriched mantle, whereas the Cerro Colorado (Young Lavas) can be produced by 3% partial melting of the same source. b Ti/Y versus Nb/Y for basaltic lavas (>7 wt% MgO) from the Mexican Volcanic Belt, including the western region (Nelson and Carmichael 1984; Righter and Carmichael 1992; Righter et al. 1995; Righter and Rosas-Elguera 2001), and the central region (Luhr and Carmichael 1985b; Hasenaka and Carmichael 1987; Wallace and Carmichael 1999; Blatter et al. 2001). N-MORB, E-MORB and OIB fields from Pearce and Peate (1995). Rı´ o Naolinco and Young Lavas Series samples plot in the depleted (MORB) region. c Ba/Zr versus Nb/Zr for the same samples as in (b) illustrating again that the Rı´ o Naolinco and Young Lavas Series samples plot in the depleted (MORB) region and have been only minimally affected by subduction fluids compared to many other basaltic magmas in the MVB. MORB–OIB field as used by Leeman et al. (1990)

The possibility of deriving alkaline magmas from a subduction modified or metasomatized source was explored by Hesse and Grove (2003). Their experimental results, coupled with detailed trace element and isotopic data for an absarokite series from western Mexico, demonstrated the possibility of deriving such unusual melts from depleted mantle. This is of special interest in

together in the Aleutians (Nye and Stelling 2000), the Cascades (Leeman et al. 1990; Conrey et al. 1997), and the Andes (Hildreth and Moorbath 1988). It has been proposed that these contrasting types of volcanism in the MVB form in response to mantle plumes (Ma´rquez et al. 1999), rifting (Sheth et al. 2000; Verma 2003), or slab windows (Ferrari 2004). However, in contrast with other places (e.g., Volynets et al. 1983; Strong and Wolff 2003) where the sequential eruption of compositionally contrasting magmas is attributed to mantle source heterogeneity, the present example demonstrates that the contemporaneous occurrence of calc-alkaline and alkaline volcanism can be produced by variable degrees of melting of the same or a similar mantle source.

Fig. 9 87Sr/86Sr vs 206Pb/204Pb diagram showing enriched mantle and depleted mantle end members as well as subduction component (modified from Petrone et al. 2003). Also shown are mixing curves between subduction fluids and mantle along the enriched–depleted line. The mixing lines are widened by variable fluid:melt ratios (after Petrone et al. 2003). The variable Pb isotopic values for the Rı´ o Naolinco samples are most likely due to variable amounts of crustal assimilation (see discussion of Os, Sr isotopes, and Ni). Modeling values are given in Table 8

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Fig. 11 Zr/Nb versus Ba/Nb diagram for the CPVC lavas. Note the systematic offset of lavas from other parts of the MVB towards samples unaffected by subduction such as Hawaiian basalts (Chen et al. 1991) and Iceland basalts (Wood 1978). Circles are calcalkaline basalts (CAB) and triangles are intraplate alkaline (IA) basalts (data sources are: Nelson and Carmichael 1984; Luhr et al. 1989; Lange and Carmichael 1990, 1991; Righter and Carmichael 1992; Righter et al. 1995; Carmichael et al. 1996). All solid symbols are from CPVC

Conclusions

Fig. 10 Sm/Nd and Lu/Hf versus MgO for the CPVC lavas and crustal reservoirs. A common parental mantle melt that underwent assimilation of different kinds of crust could give rise to the variation observed in both the Rio Naolinco and Old lavas, as well as the Toxtlacuaya and Young and Intermediate Lavas. Crustal sources (open squares) are from Rudnick and Fountain (1995) and mantle sources (dashed lines) are from Norman and Garcia (1999)

the case of western Mexico, because depleted mantle melts have not been previously recognized or identified as they have in other arcs (e.g., Righter 2000). The production of subalkaline and alkaline magmas from a depleted mantle source in the CPVC presents a similar situation. But an important difference is the role of later crustal interaction. Later differentiation/contamination (AFC processes) has altered the primitive CPVC magmas further, thus creating additional differences from the parent. This could be a relatively common phenomenon, and is likely to be an important issue in continental arcs worldwide. The minor role of the subduction component in the EMVB may be due to the unusual plate geometry there. The shallow subduction angle of the Cocos Plate beneath the North American Plate yields a very long span of subducted oceanic crust (500–600 km) before the slab is beneath the CPVC. As a result of the long length of subduction, the slab must undergo extensive metamorphism and dehydration and the sediments may be scraped off as it descends beneath the arc (e.g., Gutschler and Peacock 2003).

Chemically and physically contrasting lavas erupted contemporaneously from a paired vent at El Volcancillo. Their chemical signatures suggest that they could have been produced by different degrees of melting of a similar mantle source, or by melting of two different mantle sources. We favor the former, because it is consistent with the bulk of the geochemical data. The chemical characteristics of the Toxtlacuaya hawaiites reflect modification by crustal contamination (granulite rocks) and crystal fractionation processes in small batches. Although the Rı´ o Naolinco calc-alkaline basalts are related to a similar mantle source as the Toxtlacuaya hawaiites, they were produced at higher temperature and underwent less extensive AFC processes in the lower crust. The production of subalkaline and hawaiitic lavas from different degrees of melting of a similar largely depleted mantle source (followed by later differentiation/ contamination processes) is unusual for arcs, where such diversity is usually explained by melting of heterogeneous (enriched and depleted) mantle. In contrast to other parts of the MVB, only a weak subduction component (sediments or fluids) is recorded. Acknowledgements Funding for this work was mainly provided by CONACYT 27554-T, 44549-T, and PAPIIT 104401 grants to GC. Logistics were provided by Centro de Geociencias. KR and JC were funded by NSF grants EAR 9814891 and 0125773. Analytical work undertaken in the University of Arizona under the care of M. Baker and J. Ruiz. Juan Va´zquez and Cresencio Gardun˜o prepared thin sections for petrography. Rufino Lozano and Patricia Giro´n performed major chemical analyses by XRF and Sonia Angeles determined the FeO values by titration, all at UNAM. The manuscript has also benefited greatly from the thorough reviews of B. Leeman, R.M. Conrey, and editorial handling by T.L. Grove. We appreciate previous reviews by D Barker, P Stelling, D Geist, and especially P Wallace.

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