(Southern Mexico): Implications for the Evolution of the Iapetus and Rheic Oceans: Reply

Pressure-temperature-time evolution of high-pressure rocks of the Acatlán Complex (southern Mexico): Implications for the evolution of the Iapetus and Rheic Oceans: Reply

Ricardo Vega-Granillo1,†, Oscar Talavera-Mendoza2, Diana Meza-Figueroa1, Joaquin Ruiz3, Margarita López-Martínez4, and George E. Gehrels3 1Departamento de Geología, Universidad de Sonora, Rosales y Encinas S/N, Hermosillo, Sonora 83000, México 2Unidad Académica de Ciencias de la Tierra, Universidad Autónoma de Guerrero, A.P. 197, Taxco, Guerrero 40200, México 3Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA 4Departamento de Geología, Centro de Investigación Cientíﬁ ca y de Educación Superior de Ensenada (CICESE), Km 107 Carr, Tijuana-Ensenada, Ensenada, Baja California, México

We thank Keppie et al. (2008) for their com- the merger as a single group. In the following The youngest detrital zircon cluster in blue- ment that allows us to expand the discussion on sections, we answer each aspect discussed by schists (200–390 °C; 6–9 kbar) (Vega-Granillo the geology and metamorphic evolution of the Keppie et al. (2008) in their comment. et al., 2007) of the Ixcamilpa suite has a peak Acatlán Complex of southern Mexico. In our of ca. 477 Ma (U-Pb, zircon; Talavera-Mendoza paper (Vega-Granillo et al., 2007), we provide ONE OR THREE HP METAMORPHIC et al., 2005) indicating a maximum Early Ordo- geologic, petrologic, thermobarometric, and EVENTS IN THE ACATLÁN COMPLEX? vi cian depositional age. As indicated above, geochronologic evidence of three distinctive the age of eclogitic metamorphism in the high-pressure (HP) metamorphic events of Early Three distinct HP metamorphic events are Xayacatlán suite predates that age. Accordingly, Ordovician, Late Ordovician–Silurian, and Silu- defi ned in the Acatlán Complex by fi eld rela- the eclogite metamorphism of Xayacatlán and rian ages overprinting the Acatlán Complex; tionships and petrologic and thermobarometric the blueschist metamorphism of Ixcamilpa are these events affect three different lithological determinations along with U-Pb and 40Ar/39Ar unrelated. In our paper, we clearly stated that suites, under contrasting pressure-temperature geochronologic data. In the Olinalá area, in the ages for deposition and blueschist meta- (P-T) conditions. This new concept differs from southern Acatlán, lower P (~350–450 °C; morphism in Ixcamilpa are bracketed between the classical idea proposed by Ortega-Gutiérrez ~3–5 kbar) metabasites of the El Rodeo suite are ca. 477 Ma, the age of the youngest detrital (1978), who considered a single HP metamor- thrust over medium-temperature (~490–610 °C; zircon cluster, and the 323 ± 6 Ma 40Ar/39Ar phic event in the Acatlán Complex affecting ~12–13 kbar) eclogitic rocks of the Xayacatlán age yielded by phengite of that suite. However, diverse lithologies; this concept is endorsed by suite. The contrasting P-T conditions indicate we indicate that the absence of detrital zircons Keppie et al. (2008). The comment by Keppie metamorphism in both suites occurred before of Silurian and Devonian age would suggest a et al. (2008) is basically focused on geochrono- their tectonic juxtaposition. The thrust fault is in- Late Ordovician depositional age. As correctly logic data and disregards other critical evidence truded by granites of 476 ± 8 Ma (U-Pb, zircon ; argued by Keppie et al. (2008), the absence of such as fi eld relationships and petrologic or Talavera-Mendoza et al., 2005). In the same area, such zircons can be due to other factors than an thermobarometric constraints, which support eclogitic rocks of the Xayacatlán suite are intruded undeveloped source. A depositional age for the our interpretations. Keppie et al. (2008), follow- by post-eclogitic leucogranites of 478–471 Ma Ixcamilpa suite younger than Late Ordovician is ing the stratigraphic scheme of Ortega-Gutiérrez (U-Pb, zircon; Talavera-Mendoza et al., 2005). therefore feasible. However, the younger depo- et al. (1999), merge the Xayacatlán and The same relationship occurs at Mimilulco and sitional age reinforces our conclusion that rocks Esperanza granitoids units into the Piaxtla Piaxtla, where granites of 461 ± 9 Ma and 474 ± of the Ixcamilpa suite are unrelated to those of Group just based on the HP overprinting meta- 16 Ma (U-Pb, zircon; Talavera-Mendoza et al., the Xayacatlán suite, and that HP events affect- morphism. Consequently, they regard it as 2005) intrude Xayacatlán eclogitic rocks. None ing both suites must occur at different times. unnecessary to specify which unit they are re- of the intruding granites bear evidence of HP The Esperanza granitoids in central Acatlán ferring to—determined age or geologic relation- metamorphism, but they do show evidence of yield 442–440 Ma ages (U-Pb, zircon; Ortega- ship; therefore, they ambiguously mention to the local dynamic metamorphism under greenschist- Gutiérrez et al., 1999; Talavera-Mendoza et al., lithological units or events overprinting them by to amphibolite-facies conditions (Vega-Granillo, 2005; Vega-Granillo et al., 2007), and conse- their geographic location. However, Talavera- 2006). At Mimilulco, the Middle Ordovician quently, they are younger than eclogitic meta- Mendoza et al. (2005) indicate that the Piaxtla leucogranite transects the eclogitic foliation and morphism of the Xayacatlán suite (<478 Ma). Group is actually composed of four geneti- engulfs xenoliths of Xayacatlán eclogitic rocks Esperanza typical granitoids intrude a sedi- cally unrelated units (Xayacatlán, Ixcamilpa, (Fig. 1A). This geologic and geochronologic evi- mentary sequence whose deposit age cannot Esperanza, and Tecolapa), proving artifi cial dence indicates that eclogitic metamorphism in be better constrained than 719–440 Ma (Vega- the Xayacatlán suite occurred before leucogranite Granillo et al., 2007). Granites and sediments are †E-mail: [email protected] intrusion ~478–461 Ma. intruded by mafi c dikes of unknown age. Then,

GSA Bulletin; September/October 2009; v. 121; no. 9/10; p. 1460–1464; doi: 10.1130/B26514.1; 1 ﬁ gure.

Xayacatlán suite The proposal of a single HP metamorphic Grt-Cld Micaschist Eclogite and event of Mississippian age affecting all HP suites and quartzite Eclogite facies Grt-amphibolite Eclogite facies foliation Eclogite facies of Acatlán requires substantiation. It is well Meta-leucogranite xenolith epidote amphibolite known that in the Patlanoaya region, in central to greenschist facies Acatlán, both HP and low-pressure (LP) meta- 461 ± 9 Ma (1) Mylonitic (U-Pb, zircon) foliation morphic rocks are overlain by a sedimentary unit named the Patlanoaya Formation, which A 1 m contains fossils of Late Devonian (Famennian, 374.5–359.2 Ma according to Gradstein et al., 2004) to Early Permian (Guadalupian) age Esperanza suite (Brunner, 1987; Vachard et al., 2000; Vachard San Francisco de Asís and Flores de Dios, 2002). Near the base of the Lithodeme Grt-micaschist and Patlanoaya Formation there are more than 50 m Quartzite Mg-taramite Eclogite 374 ± 4 Ma (3) Eclogite Facies of basal conglomerate, and there is no evidence Eclogite facies 40 39 345 ± 2 Ma (3) ( Ar/ Ar, phengite 430 ± 10 Ma (2) 40 39 of tectonic shearing affecting the contact. The ( 40Ar/ 39 Ar, phengite) in pods within ( Ar/ Ar, amphibole) Grt-augen gneiss eclogite) Eclogite facies oldest fossils are mostly older than the age pro- 440±15Ma(1) xenolith posed by Keppie et al. (2008) for their HP meta- Granitic pegmatite (U-Pb zircon) Meta-leucogranite unmetamorphosed amphibolite facies morphic event in the Acatlán (~353–341 Ma). 346 ± 4 Ma (3) 372 ± 8 Ma (1) (40 Ar/ 39 Ar, white mica) (U-Pb zircon) According to our thermobarometric data, HP metamorphism in the central band of Acatlán (Esperanza suite) occurred at ~15–17 kbar cor- Locally migmatized responding to ~50–60 km depth (Vega-Granillo B metasediments et al., 2007). Evidently, deposition of the Late 1 m Devonian and Lower Mississippian Patlanoaya beds and eclogitic metamorphism cannot oc- Figure 1. (A) Cartoon displaying the geologic relationships in the Xayacatlán Suite. (1) Inter- cur simultaneously. Patlanoaya strata partially preted as magmatic age (Talavera-Mendoza et al., 2005); Grt—garnet, Cld—chloritoid. overlying the HP rocks necessarily imply their (B) Cartoon displaying the geologic relationships in the Esperanza suite. (1) Interpreted as previous exhumation; consequently, the HP magmatic ages; (2) interpreted as the eclogite-facies metamorphism age; (3) interpreted metamorphism in central Acatlán must have oc- as cooling ages (all ages in (B) from Vega-Granillo et al., 2007). curred before Late Devonian. In our view, the ages of post-eclogitic leucogranite 372 ± 8 Ma (U-Pb zircon; Vega-Granillo et al., 2007), leucogranites, sediments, and mafi c dikes underwent Murphy et al., 2006; Vega-Granillo et al., 2007), cratic pods in eclogite 374 ± 2 Ma (Ar-Ar phen- a high-temperature (~730–830 °C; 15–17 kbar) suggesting they were deposited in different gite; Vega-Granillo et al., 2007), as well as the eclogite-facies metamorphism (Vega-Granillo basins . Additionally, the obtained P-T path for dates of zircon overgrowths in eclogite obtained et al., 2007), which transformed these rocks into the Ixcamilpa suite corresponds to simple sub- by Middleton et al. (2007), date the migmatiza- high-grade gneisses, quartz-feldspar schists, duction, whereas the P-T path for the Esperanza tion event succeeding the eclogitic event not the quartzites, garnet mica schists, and eclogites. suite corresponds to continental collision (Vega- eclogitic event itself. These lithologies make up the Esperanza suite. Granillo et al., 2007). Therefore, the blueschist Subsequently, the Esperanza suite rocks were in- event in the Ixcamilpa suite and the eclogitic GEOCHRONOLOGY truded by post-eclogitic muscovite leucogranite event in the Esperanza suite cannot be the same (Fig. 1B) yielding a crystallization age of 372 ± whether or not they could be coeval. Keppie et al. (2008) challenge some of our 8 Ma (U-Pb zircon; Vega-Granillo et al., 2007). Keppie et al. (2008) propose a single HP 40Ar/39Ar ages, particularly those yielding older Accordingly, the age of the HP metamorphism metamorphic event of Mississippian age based ages than their own. Amphibole in eclogite from in the Esperanza rocks is restricted by the Lower on a single concordant, U-Pb age of 346 ± 3 Ma the Esperanza suite yields an isochron age of Silurian 442–440 Ma crystallization age of the 98 (Middleton et al., 2007) obtained from zircon 430 ± 5 Ma, which we regard as the age of the Esperanza granitoids and the Late Devonian overgrowths in eclogite. They mention U-Pb zir- eclogitic metamorphism in that suite. In the fi rst 372 ± 8 Ma age of post-eclogitic leucogranite. con ages from decompression migmatites yield- instance, amphibole older age can be explained As a consequence, eclogitic metamorphism ing similar ages (~347–330 Ma) (Middleton et al., by its higher closure temperature in relation to in the Esperanza suite cannot be related to the 2007) and a phengite age yielding a 40Ar/39Ar the white mica (e.g., Geyh and Schleicher, 1990). Early Ordovician eclogitic metamorphism of plateau of 351 ± 2 Ma interpreted as the cooling Keppie et al. (2008) argue that the isochron of the Xayacatlán rocks. On the other hand, in the through ~350 °C (Murphy et al., 2006). They do the eclogite (sample RAC-201) includes points Ixcamilpa suite, the lithology and geologic set- not fi nd evidence of older thermal events. Even that force the correlation line and that the high- ting have an oceanic affi nity, in contrast to those though all ages cited by Keppie et al. (2008) temperature fraction in one of the experiments of the Esperanza suite, which are continental were obtained in the San Francisco de Asis area yielding an age of 526 ± 12 Ma is evidence of (De la Cruz-Vargas, 2004; Murphy et al., 2006). (part of our Esperanza suite) in the central re- excess argon and that, consequently, the plateau Furthermore, the detrital zircon age plot of the gion, they interpreted these ages as dating the age obtained with the other fractions is invalid. Ixcamilpa suite has a pattern clearly different HP metamorphism in the whole Acatlán Com- However, the difference observed on the am- from those of the Xayacatlán and Esper anza plex (Xayacatlán, Ixcamilpa, and Esperanza) re- phibole age spectra is an artifact of the heating suites (Talavera-Mendoza et al., 2005, 2006; gardless of the differences indicated previously. schedule, because the diagram concentrates

Geological Society of America Bulletin, September/October 2009 1461 Vega-Granillo et al. results from two different techniques (Fig. 8F et al. (2008), such a process in the Acatlán Com- tism postdating eclogitic metamorphism in the in Vega-Granillo et al., 2007). A six-step ex- plex remains tentative. Scaillet (1998) stated Xayacatlán suite; (3) a 442–441 Ma plutonic periment conducted on the multigrain sample that excess argon is not an ineluctable feature suite forming part of the Esperanza suite (as heated with the Ta-furnace gave an integrated of HP–ultrahigh-pressure (UHP) metamor- defi ned in Vega-Granillo et al., 2007) in central age of 438.7 ± 6 Ma defi ned by four fractions phism, and that in some cases the interpretation Acatlán; and (4) a ca. 371 Ma (Yañez et al., 1991; representing up to 90% of released 39Ar. Other of excess argon can prevent alternative geologic Vega-Granillo et al., 2007) magmatism that in- two-step results obtained through a single-grain, interpretations. Furthermore, factors other than cludes the La Noria pluton and leucogranites laser fusion experiment yielded an integrated age excess argon have been proposed to explain intruding the Esperanza suite in central Acatlán. of ~419 ± 5 Ma. A third, three-step, single-grain, geologically meaningful older 40Ar/39Ar ages in The 478–461 Ma rocks intrude exclusively the laser fusion experiment gave two plateaus of metamorphic HP minerals (Maurel et al., 2003). Xayacatlán suite, postdating its eclogitic meta- ~418 ± 4 and ~315 ± 4 Ma, suggesting the possi- For example, some rocks, blocks, or parts of a morphism. Only the Late Devonian leucogran- bility of two thermal events. All but the fi rst frac- sequence, can avoid Ar resetting when the lack ite intruding the eclogitic rocks of the Esperanza tion of each experiment were combined to defi ne of penetrative deformation reduces hydrother- suite is regarded by us as decompression melts. the isochron age of 430 ± 5 Ma, with (40Ar/36Ar) mal circulation and diminishes diffusion in min- We did not fi nd evidence of Lower Silurian i = 332 ± 20, which is our best age estimate for erals. Another possible reason to preserve older granitoids intruding the Xayacatlán suite, and the amphibole (complete argon results are in the ages can be the grain size (Maurel et al., 2003). we never considered the Lower Silurian gran- GSA Data Repository of Vega-Granillo et al., The Ar is released from minerals through diffu- itoids in the central band as decompression 2007). This age is concordant within uncer- sion, and diffusion is easier and more complete melts as suggested by Keppie et al. (2008). tainty with a 418 ± 18 Ma, U-Pb monazite age in smaller size grains than in larger grains. Thus, obtained by Ortega-Gutiérrez et al. (1999) from the 2-cm crystals of phengite yielding the Late TECTONIC MODEL the Esperanza gneiss regarded as recording the Devonian (374 ± 2 Ma) age could retain that eclogitic metamorphism. older age because of their size without excess Arguing the existence of a single HP meta- Large (~2 cm) phengite crystals are con- Ar being involved. morphic event of Mississippian age based on a spicuous in some eclogites from Santa Cruz few U/Pb and 40Ar/39Ar ages and some paleo- Organal, where they crystallize into 6- to SOME IMPORTANT REMARKS magnetic data, Keppie et al. (2008) confront 10-cm-wide veins and pods. Two experiments our tectonic model. In a previous section we on that phengite yielded identical and simple In their comment, Keppie et al. (2008) demonstrated that the development of a HP 40Ar/39Ar spectra with an integrated age of misinterpreted some of our statements. They metamorphism of Mississippian age synchro- 374 ± 2 Ma. That age is in agreement with the mentioned for example that evidence of an nously with sedimentation of Patlanoaya strata Late Devonian 372 ± 8 Ma age (U-Pb zircon; Ordovician–Silurian HP metamorphism in over the same HP rocks is simply untenable. Vega-Granillo et al., 2007) of leucogranite tran- Santa Cruz Organal remains tentative. In our Moreover, a single HP metamorphism cannot secting the eclogitic body. Keppie et al. (2008) work, we do not propose such an age for the explain the fi eld relationships of HP rocks and suggest that this age may imply excess argon HP metamorphism in that locality. In this zone associated plutonic rocks, as well as petrologic because other of our and their 40Ar/39Ar ages we proposed a Silurian (~430–418 Ma) age for and thermobarometric differences presented in of phengites yielded younger ages. However, the HP metamorphism imposed only over the our paper (Vega-Granillo et al., 2007), infor- 40Ar/39Ar spectra are very simple and do not Esperanza suite. However, a pre–478 Ma age mation that was neglected in the Keppie et al. show evidence of excess argon (some detailed for the eclogitic metamorphism is proposed for (2008) comment. notes on the Ar geochronology are included in the Xayacatlán suite, in western Acatlán. Paleomagnetic studies in the Acatlán Com- the GSA Data Repository). Keppie et al. (2008) also mentioned that we plex have produced contrasting results and The Esperanza suite and the Late Devonian proposed an orogenic tectonic setting for the varied models (e.g., Fang et al., 1989; Böhnel, leucogranite are transected by an undeformed Esperanza granitoids. The geochemistry of the 1999; Alva-Valdivia et al., 2002). Quantifi cation and unmetamorphosed granitic pegmatite. The Esperanza granitoids is out of the scope of our of the displacement critically depends upon the large (>2 cm) white mica crystals from this peg- paper, and we do not assign the Esperanza gran- ages of the magnetizations and resolutions of matite yielded a 40Ar/39Ar isochron age of 346 ± itoids to a particular tectonic setting. In fact, we the structural attitudes. The Acatlán Complex 4 Ma (Early Mississippian). The isochron age do not regard the mafi c dikes of the Esperanza is polydeformed with some lithologies experi- was calculated with 35 combined fractions of suite (San Francisco de Asis lithodeme) of encing two or three phases of isoclinal folding three laser step-heating experiments and one Ordovician age as suggested by Keppie et al. (Vega-Granillo, 2006). Except for some work bulk sample analysis. That age is also chal- (2008), because they transect the Lower Silu- on microtectonics of small areas (e.g., Weber lenged by Keppie et al. (2008), who adduce ex- rian Esperanza gneiss of 440 ± 15 Ma (Vega- et al. 1997; Malone et al., 2002), the nature, cess argon. However, we do not fi nd evidence Granillo et al., 2007), and consequently must kine matics, and age of the deformation in Acat- of excess argon in the correlation diagram from be younger. lán is just beginning to be studied in detail. Even that pegmatite; sample RAC-188 (GSA Data Finally, Keppie et al. (2008) indicate that we the Permian beds overlying the Acatlán Com- Repository of Vega-Granillo et al., 2007). interpreted the Esperanza granitoids as decom- plex are folded and locally dynamically meta- Excess argon has been interpreted in am- pression melts following HP metamorphism. morphosed (Vega-Granillo, 2006). Based on phiboles and phengites from some HP terrains The Esperanza granitoids unit as originally Alva-Valdivia et al. (2002), Keppie et al. (2008) yielding anomalously older ages, whereas inde- defi ned by Ortega-Gutiérrez (1978) is actually argue that paleomagnetic data for Permian rocks pendent evidence (geologic and/or geochrono- composed of four distinct and unrelated plutonic indicate a latitudinal position relative to North logic) proves a younger age of metamorphism suites (Talavera-Mendoza et al., 2005): (1) a America similar to its present location, contra- (e.g., Arnaud and Kelley, 1995; El-Shazly et al., 1165–1043 Ma plutonic suite referred to as dicting our paleogeographic model for that time. 2001). With the evidence presented by Keppie the Tecolapa suite; (2) a 478–461 Ma magma- However, Alva-Valdivia et al. (2002) recognized

1462 Geological Society of America Bulletin, September/October 2009 Reply to comment by Keppie et al. that “… our dataset is not suffi ciently robust to ACKNOWLEDGMENTS Zulaf, G., and Kraft, P., eds., The Geology of Peri- Gondwana: The Avalonian–Cadomian Belt, Adjoining enable constraints about the tectonic evolution This work was supported by a Consejo Nacional de Cratons and the Rheic Ocean: Geological Society of of the studied area.” Furthermore, the most ac- Ciencia y Tecnología (CONACYT) grant (J32549-T) America, Special Paper, v. 423, p. 489–509. cepted paleogeographic reconstructions of Pan- to DMF and two National Science Foundation grants Miller, B.V., Stewart, K.G., Miller, C.F., and Thomas, C.W., (EAR-9708361 and EAR-9628150) to GG and JR. 2000, U-Pb ages from the Bakersville Eclogite: Taco- gea during the Permian place South America nian eclogite metamorphism followed by Acadian and overlapping most of southern Mexico, implying REFERENCES CITED Alleghanian cooling: Geological Society of America an allochtonous origin for terranes of that region Abstracts with Programs, v. 32, no. 2, p. A-62. Alva-Valdivia, L.M., Goguitchaichvli, A., Grajales, M., Murphy, J.B., Keppie, J.D., Nance, R.D., Miller, B.V., Dostal , (Pindell and Dewey, 1982; Pindell, 1985, 1994; Flores de Dios, A., Urrutia-Fucugauchi, J., Rosales, C., J., Middleton, M., Fernández-Suarez, J., Jeffries, T.E., Handschy et al., 1987; Pindell and Kennan , and Morales, J., 2002, Further constraints for Permo- and Storey, C.D., 2006, Geochemistry and U-Pb proto- Carboniferous magnetostratigraphy: Case study of the lith ages of eclogitic rocks of the Asís Lithodeme, 2001). In their study on the Acatlán area, Fang sedimentary sequence from San Salvador-Patlanoaya Piaxtla Suite, Acatlán Complex, southern Mexico: et al. (1989) mention evidence of displacement (Mexico): Comptes Rendus Geoscience, v. 334, p. 1–7, Tectonothermal activity along the southern margin of of the Acatlán terrane relative to North America doi: 10.1016/S1631-0713(02)01821-7. the Rheic Ocean: The Geological Society of London, Arnaud, N.O., and Kelley, S., 1995, Evidence for excess Ar v. 163, p. 683–695, doi: 10.1144/0016-764905-108. but point out that the ages of the magnetiza- during high pressure metamorphism in the Dora-Maira Ortega-Gutiérrez, F., 1978, Estratigrafía del Complejo Acat- tions and resolutions of the structural attitudes (western Alps, Italy), using a ultra-violet laser ablation lán en la Mixteca Baja, Estados de Puebla y Oaxaca: 40 39 are not well constrained. Thus, from our point microprobe Ar/ Ar technique: Contributions to Min- Revista Insituto de Geología, Universidad Nacional eralogy and Petrology, v. 121, p. 1–11, doi: 10.1007/ Autónoma de México, v. 2, no. 2, p. 112–131. of view, Keppie et al. (2008) do not provide s004100050086. Ortega-Gutiérrez, F., Elías-Herrera, M., Macías-Romo, robust geochronologic or paleomagnetic evi- Böhnel, H., 1999, Paleomagnetic study of Jurassic and Cre- C., and López, R., 1999, Late Ordovician-Early taceous from the Mixteca terrane (Mexico): Journal of Silurian continental collisional orogeny in southern dence to dismiss our tectonic model for the South American Earth Sciences, v. 12, p. 87–93, doi: Mexico and its bearing on Gondwana-Laurentia con- Acatlán Complex. 10.1016/S0895-9811(99)00038-3. nections: Geology, v. 27, p. 719–722, doi: 10.1130/ Brunner, P., 1987, Microfacies y microfósiles de las rocas 0091-7613(1999)027<0719:LOESCC>2.3.CO;2. carbonatadas del Paleozoico de San Salvador Pat- Pindell, J.L., 1985, Alleghenian reconstruction and the sub- CONCLUDING REMARKS lanoaya, Puebla, México: Revista de la Sociedad Mexi- sequent evolution of the Gulf of Mexico, Bahamas, cana de Paleontología, v. 1, p. 98–124. and proto-Caribbean Sea: Tectonics, v. 4, p. 1–39, doi: Deciphering the tectonic evolution of De la Cruz-Vargas, J.C., 2004, Geoquímica de esquistos 10.1029/TC004i001p00001. polymetamorphosed orogens such as the Acat- azules y eclogitoides del Complejo Acatlán: Evidencia Pindell, J.L., 1994, Evolution of the Gulf of Mexico and the de una zona de subducción del Paleozoico en el Sur Caribbean, in Donovan, S.K., and Jackson, T.A., eds., lán Complex using exclusively a geochrono- de México [M.S. thesis]: Hermosillo, Universidad de Caribbean Geology: An Introduction: Kingston, Uni- logic approach can lead to an overinterpretation Sonora, 88 p. versity West Indies Publishers’ Association, p. 13–39. El-Shazly, A.E., Broecker, M.S., Hacker, B.R., and Pindell, J.L., and Dewey, J.F., 1982, Permo-Triassic recon- of the ages. The ages must be consistent with Calvert, A.T., 2001, Formation and exhumation of struction of western Pangea and the evolution of the other lines of evidence such as geologic rela- blueschists and eclogites from NE Oman: New con- Gulf of Mexico/Caribbean region: Tectonics, v. 1, tionships, stratigraphy, petrology, geochemistry, straints from Rb-Sr and 40Ar/39Ar dating: Journal p. 179–211, doi: 10.1029/TC001i002p00179. of Metamorphic Geology, v. 19, p. 233–248, doi: Pindell, J.L., and Kennan, L., 2001, Kinematic evolution thermobarometry, and microtectonics, in order 10.1046/j.1525-1314.2001.00309.x. of the Gulf of Mexico and Caribbean, in Fillon, R., to reduce misinterpretations. Studies of small Fang, W., Van der Voo, R., Molina-Garza, R., Moran-Zenteno, et al., eds., Transactions of the Gulf Coast Section So- areas of complex terrains are necessary to defi ne D., and Urrutia-Fucugachi, J., 1989, Paleomagnetism of ciety of Economic Paleontologists and Mineralogists the Acatlán terrane, southern México: Evidence for ter- (GCSSEPM ) 21st Annual Bob F. Perkins Research critical geologic aspects and to acquire well- rane rotation: Earth and Planetary Science Letters, v. 94, Conference, Petroleum Systems of Deep-Water Ba- controlled geochronologic, geochemical, and p. 131–142, doi: 10.1016/0012-821X(89)90089-7. sins: Houston, Texas, p. 193–220. Geyh, M.A., and Schleicher, H., 1990, Absolute age deter- Scaillet, S., 1998, K-Ar (40Ar/39Ar) Geochronology of ultra- structural data. However, some prudence must minations: Berlin, Springer-Verlag, 503 p. high pressure rocks, in Hacker, B.R., and Liou, J.G., be taken in extrapolating data and interpreta- Gradstein, F.M., Ogg, J.G., and Smith, A.G., eds., 2004, A eds., When Continents Collide: Geodynamics and tions to different areas, particularly if discrepan- Geologic Time Scale Cambridge, Cambridge Univer- Geochemistry of Ultrahigh-pressure Rocks: Nether- sity Press, 589 p. lands, Kluwer Academic Publishers, p. 161–201. cies in the geologic record exist. Handschy, J.W., Keller, G.R., and Smith, K.J., 1987, The Shervais, J.W., Dennis, A.J., McGee, J.J., and Secor, D., Our interpretation concerning the existence Ouachita system in northern Mexico: Tectonics, v. 6, 2003, Deep in the heart of Dixie: Pre-Alleghanian of three separate HP events in the Acatlán Com- p. 323–330, doi: 10.1029/TC006i003p00323. eclogite and high-P granulite metamorphism in Jamieson, R.A., 1990, Metamorphism of an early Paleo- the Carolina terrane, South Carolina, USA: Jour- plex is a more comprehensive model to explain zoic continental margin, western Baie Verte Peninsula nal of Metamorphic Geology, v. 21, p. 65–80, doi: its metamorphic evolution because it is consis- Newfoundland: Journal of Metamorphic Geology, v. 8, 10.1046/j.1525-1314.2003.00416.x. p. 269–288, doi: 10.1111/j.1525-1314.1990.tb00473.x. Talavera-Mendoza, O., Ruiz, J., Gehrels, G.E., Meza- tent with all sorts of available data. As detailed Keppie, J.D., Nance, R.D., Murphy, J.B., Miller, B.V., Dostal, Figueroa, D.M., Vega-Granillo, R., and Campa- in our paper, a set of HP metamorphic events, J., and Ortega-Rivera, A., 2008, Comment on paper by Uranga , M.F., 2005, U-Pb geochronology of the of similar age, affecting analogous petrotectonic Vega-Granillo et al., 2007, Pressure-temperature -time Acatlán Complex and implications for the Paleozoic evolution of high-pressure rocks of the Acatlán Com- paleogeog raphy and tectonic evolution of southern assemblages, under comparable P-T condi- plex (southern Mexico): Implications for the evolution Mexico: Earth and Planetary Science Letters, v. 235, tions, has been described in the Appalachian- of the Iapetus and Rheic Oceans: Geological Society of p. 682–699, doi: 10.1016/j.epsl.2005.04.013. Caledonian chain, where they are related to the America Bulletin, v. 119, p. 1249–1264. Talavera-Mendoza, O., Ruiz, J., Gehrels, G.E., Meza- McKerrow, W.S., Mac Niocaill, C., and Dewey, J.F., 2000, Figueroa, D., Vega-Granillo, R., and Valencia, V., closure of the Iapetus Ocean (e.g., Jamieson, The Caledonian Orogeny redefi ned: The Geological 2006, U-Pb geochronology of the Acatlán Complex 1990; McKerrow et al., 2000; Miller et al., 2000; Society of London, v. 157, no. 6, p. 1149–1154. and implications for the Paleozoic paleogeography Malone, J.R., Nance, R.D., Keppie, J.D., and Dostal, J., 2002, and tectonic evolution of southern Mexico: Earth and Van Staal, 1994, 2007; Shervais et al., 2003). In Deformational history of part of the Acatlán Complex: Planetary Science Letters, v. 245, p. 476–480, doi: view of the available evidence, the correlation Late Ordovician–Early Permian orogenesis in southern 10.1016/j.epsl.2006.03.017. of the Acatlán Complex with the Appalachian- Mexico: Journal of South American Earth Sciences, Vachard, D.A., and Flores de Dios, A., 2002, Discovery of v. 15, p. 511–524, doi: 10.1016/S0895-9811(02)00080-9. latest Devonian/earliest Mississippian microfossils in Caledonian orogen remains the best hypothesis. Maurel, O., and Monié, P.P., Respaut, J.P., Leyreloup, A.F., San Salvador Patlanoaya (Puebla, México): Biogeo- The model proposing a single Mississippian HP and Maluski, H., 2003, Pre-metamorphic 40Ar/39Ar and graphic and geodynamic consequences: Comptes Ren- event affecting all the HP suites of the Acatlán U–Pb ages in HP metagranitoids from the Hercynian dus Geoscience, v. 334, p. 1095–1101, doi: 10.1016/ belt (France): Chemical Geology, v. 193, p. 195-214. S1631-0713(02)01851-5. Complex is an oversimplifi cation and requires Middleton, M., Keppie, J.D., Murphy, J.B., Miller, B.V., and Vachard, D., Flores de Dios, A., Buitrón, B.E., and Grajales, fundamental explanations about the geologic Nance, R.D., 2007, P-T-t constraints on exhumation M., 2000, Biostratigraphie par fusilines des calcaires following subduction in the Rheic Ocean: Eclogitic Carboniferes et Permienes de San Salvador Pat lanoaya relationships of the Acatlán Complex and its Asis Lithodeme, Piaxtle Suite, Acatlán Complex, (Puebla, Mexique): Geobios, v. 33, p. 5–33, doi: sedimentary cover. southern Mexico, in Linnemann, U., Nance, R.D., 10.1016/S0016-6995(00)80145-X.

Geological Society of America Bulletin, September/October 2009 1463 Vega-Granillo et al.

Van Staal, C.R., 1994, Brunswick subduction complex in the Acatlán, Puebla, México: Implicaciones tectóni- region, Puebla: Geoﬁ sica International, v. 36, no. 2, Canadian Appalachians: Record of the Late Ordovi- cas [Ph.D. thesis]: México, Universidad Nacional p. 63–76. cian to Late Silurian collision between Laurentia and Autónoma de México, 344 p. Yañez, P., Ruiz, J., Patchett, P.J., Ortega-Gutiérrez, F., and the Gander margin of Avalon: Tectonics, v. 13, p. 946– Vega-Granillo, R., Talavera-Mendoza, O., Meza-Figueroa, Gehrels, G.E., 1991, Isotopic studies of the Acatlán 962, doi: 10.1029/93TC03604. D., Ruiz, J., Gehrels, G.E., López-Martínez, M., and complex, southern Mexico: Implications for Paleo- Van Staal, C.R., 2007, Pre-Carboniferous metallogeny of De la Cruz-Vargas, J.C., 2007, Pressure-temperature- zoic North American tectonics: Geological Society of the Canadian Appalachians, in Goodfellow, W.D., time evolution of high-pressure rocks of the Acatlán America Bulletin, v. 103, p. 817–828, doi: 10.1130/ ed., Mineral deposits of Canada: A synthesis of major Complex (southern Mexico): Implications for the 0016-7606(1991)103<0817:ISOTAC>2.3.CO;2. deposit-types, district metallogeny, the evolution of evolution of the Iapetus and Rheic Oceans: Geological geological provinces, and exploration method: Mineral Society of America Bulletin, v. 119, p. 1249–1264, doi: MANUSCRIPT RECEIVED 16 JULY 2008 Deposit Division, Geological Association of Canada, 10.1130/B226031.1. REVISED MANUSCRIPT RECEIVED 24 NOVEMBER 2008 Special Publication 5, p. 793–818. Weber, B., Meschede, M., Ratschbacher, L., and Frisch, W., MANUSCRIPT ACCEPTED 28 APRIL 2009 Vega-Granillo, R., 2006, Petrología, termobarometría y 1997, Structure and kinematic history of the Acatlán análisis estructural en la región NW del Complejo Complex in the Nuevos Horizontes—San Bernardo Printed in the USA

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