The Arizona-Sonora porphyry copper cluster is one of the most productive provinces of this type on Earth. There, upper-crustal deposits emplaced between Late Cretaceous and Early Eocene, subsequently ...exhumed and developed supergene enrichment profiles. Despite the Basin and Range regional extension, these shallow intrusions and associated mineralization were preserved in eastern Sonora in the exhumed footwalls of normal faults. In order to better constrain their exhumation history, we performed a thermobarometrical (Al-in-hornblende) and thermochronological (apatite U–Pb and fission-track) study on the La Caridad and Suaqui Verde porphyry copper deposits. On the one hand, thermobarometry allows us to determine that the Suaqui Verde porphyry copper emplaced at 4.8 ± 0.9 km-depth, which implies that Cu–Mo mineralization may occur deeper than the ~2–4 km depth classically proposed for porphyry copper. On the other hand, using thermobarometry and inverse modeling of thermochronologic data obtained for individual and drill core samples, we reconstruct the thermal history of these porphyry copper. After a very fast post-emplacement cooling, numerical models suggest that cooling of rocks was slow and mainly monotonous during exhumation. Indeed, our data do not record an acceleration of the exhumation in eastern Sonora during the Basin and Range regional extension (between ~25 and 12 Ma). However, inverse modeling of fission-track data obtained along a drill core in La Caridad allows us to reconstruct the evolution of the geothermal gradient through time, which is in agreement with the regional geodynamics. Overall, it cannot be excluded that Oligocene volcanic rocks protected the ore deposits from erosion, even if they remained relatively thin (<500 m-thick). We propose that eastern Sonora was characterized by Basin and Range extension distributed on numerous normal faults with small offsets, which allowed to preserve the upper crustal part of the Cretaceous-Paleogene magmatic arc and its numerous associated porphyry copper systems.
•Thermal histories of the Suaqui Verde and La Caridad porphyry copper deposits are reconstructed.•Evolution of the geothermal gradient through time in La Caridad is in agreement with the regional geodynamics.•Basin and Range extension is not recorded by accelerated cooling and exhumation, suggesting that deformation was distributed on numerous normal faults with small offsets in Eastern Sonora.
A new data set combining thermobarometry, geo‐thermochronology, chronostratigraphic, and structural analyses highlights the tectono‐thermal evolution of the St. Martin granodiorite from its ...emplacement to its surface exposure. The described vertical motions in this part of the upper plate of the Lesser Antilles subduction zone since 30 Myrs are linked to the migration of the Lesser Antilles volcanic arc toward the plate interior. Results suggest that the St. Martin granodioritic pluton emplaced at 4–5 km depth and underwent a four‐step history: (a) 30–27 Ma, emplacement along N20–40° transtensive structures oblique to the trench followed by, (b) 27–24 Ma, rapid post‐emplacement cooling and exhumation (∼0.6 mm/yr) controlled by perpendicular to the trench N45° trending structures, (c) 24–9 Ma, slow subsidence (0.01 mm/yr) and development of carbonate platforms associated to tectonic quiescence, westward migration of the arc, and subsequent cooling of the crust, (d) 9 Ma to present‐day, exhumation (∼0.25 mm/yr) and uplift of Neogene carbonate platforms mainly along N45° faults that likely accommodate the progressive trench curvature since 30 Ma. Pecube forward modeling using this scenario reproduces both the observed present‐day geometry and thermochronometric ages. A similar sequence of events is observed in the Virgin Islands. Along with our new data, this suggests a southward migration of the deformation associated with the opening of the Anegada Trough.
Key Points
The tectono‐thermal history of the St. Martin Oligocene granodiorite is reconstructed
Exhumation occurred during two periods: between 27 and 24 Ma and since 9 Ma, along N45° trending normal faults
Regionally, exhumation rates suggest a southward migration of the deformation associated with the opening of the Anegada Trough
We present a study based on new and compiled geochronological and geochemical data to assess the tectonomagmatic evolution of Mexico from the Late Cretaceous and Eocene (~90–40 Ma). review of the ...literature highlights the striking geological differences observed in southwestern US and Mexico and particularly south of the classical Laramide province. Current tectonic models for western Mexico indicate that the continental margin of Mexico was fully consolidated by ~90 Ma, with the final accretion of the Alisitos and Guerrero arc terranes. Since then, east-faced subduction with a regular lowering of the slab dip persisted up to ca. 40 Ma, when compression and calc-alkaline magmatism ceased along the entire Cordillera. The sustained magmatic arc activity along the herein defined “Cretaceous-Eocene Mexican Magmatic Arc” (CEMMA), leads us to recommend abandoning the use of the term “Laramide magmatism” in Mexico. We define the CEMMA as an arc that trends NW-SE along most of western Mexico, but scattered outcrops occur also in central and eastern Mexico. The CEMMA composition ranges from gabbro to alkali granite, but hornblende ± biotite granodiorites are by far the most abundant type of rocks. Coeval volcanic rocks have been deeply eroded, but andesite-dominated sequences are partially preserved in the eastern part of the arc, particularly below the Cenozoic volcanic rocks of the Sierra Madre Occidental. The geochemical database that we present include 729 samples and shows that the CEMMA formed in a typical continental magmatic arc environment (calc-alkaline–metaluminous signatures and #Mg’s < 68). However, rocks from the eastern part of the arc reach more alkaline compositions, particulry due to larger K2O uptakes in the magma away from the trench. REE plots are characterized by negative slopes and negative to slightly positive Eu anomalies. Multielement spectra reveal negative anomalies of NbTa, Ti and P, coupled with positive anomalies of U, K and Pb. Initial values of 87Sr/86Sr and εNd range from 0.7031 to 0.7137 and from +6.2 to −8.3, respectively, suggesting mixing of variable proportions of crustal materials with the mantle-derived magmas. These elemental and isotopic features are typical of continental margin magmatic arcs. In this context, sustained generation of calc-alkaline magma under these conditions yielded outstanding conditions to form a diversity of metallic ores, particularly porphyry copper deposits, in the region of Arizona-New Mexico- Sonora, located just south of the classical Laramide province. Although the ages along the CEMMA can be roughly explained by partial melting of a metasomatized section of the mantle above the region of amphibole instability (~100 km), plutons with crystallization ages of ~90 Ma in eastern Sonora, and even more to the east in Durango and Zacatecas, are older than expected. We consider that these plutons were generated by more discrete magma pulses linked to the dehydration of the phlogopite deeper in the slab (~200 km).
The deformation that characterizes the Laramide province ends south of the Colorado Plateau, and then it does not affect the Late Cretaceous-Eocene magmatic arc rocks of Mexico. Display omitted
•The Late Cretaceous-Eocene magmatic arc activity in Mexico.•Laramide province features do not continue south of the Colorado Plateau.•Despite a large age overlap there is a clear migration of the arc to the east.•The eastern part of the arc reaches more alkaline compositions.•Two sites for magma generation are interpreted to explain the age distribution.
In their paper, Barrón-Díaz et al. (2019a) present new geochronological and thermobarometric data of rocks of the Bamori Ranch area, Caborca region, Sonora, Mexico. The authors interpret the ...greenschist facies of Neoproterozoic and Paleozoic strata as a result of contact metamorphism close to supposed extended granodioritic intrusions that emplaced during Laramide time (90–40 Ma). In our opinion, this interpretation is poorly constrained. Based on previous geological studies as well as a re-evaluation of presented thermobarometric data, we propose that greenschist facies metamorphism and 40Ar-39Ar ages described by the authors can be the result of a regional metamorphism event that developed during the Laramide orogeny in northwestern Sonora.
The Mediterranean geodynamic system is an exceptional natural laboratory to study the complexities of back-arc extension during subduction rollback. Corsica is a key locality that recorded the Alpine ...subduction-collision history followed by 30Ma of the Apennines slab rollback, responsible for the successive opening, from West to East, of the Liguro-Provençal basin and the Tyrrhenian Sea. The overall strain pattern of the Alpine metamorphic units of Alpine Corsica is studied through a synthesis of i) available geological maps, ii) geochronological data and iii) newly acquired structural data relative to successive events of ductile and brittle extension. Three main stages of extension are recorded: 1/ Syn-metamorphic Oligocene extension accommodated by N140° trending ductile shear zones, that correspond to the reactivation of a major Alpine thrust; 2/ Burdigalian ramp-flat extension with N60°–70° trending fault zones that controlled the deposition of onshore piggy-back basins (e.g. St Florent basin), and 3/ Serravalian N–S trending fault zones. From a geodynamical point of view, these successive extensional deformations in Alpine Corsica can be correlated to the history of the Apennines slab rollback. The two first stages are related to a southeastward rollback of the Appennines slab that successively triggered: 1/ Continental rifting in Oligocene leading to the opening of the Liguro-Provençal basin and 2/ Burdigalian extension with N60°–70° trending fault zone, oblique to the Alpine thrust that, after a counterclockwise rotation of the Corso-Sardinian block, became unable to accommodate extension. Finally, the third stage that gave NS-trending fault zones developed in Serravalian, at the onset of Tyrrhenian rifting, related to an eastward rollback of the Apennines slab, as a response of slab tearing in Sicily.
•We evidence three stages of extension in Alpine Corsica.•Oligocene extension accommodated by N140° trending fault zones.•Burdigalian ramp-flat extension controlled by N60°–70° trending fault zones.•Serravalian N–S trending fault zones.•Alpine Corsica has recorded the Apennines slab rollback history.
Despite a long history of plate convergence at the western margin of the South American plate that has been ongoing since at least the Early Paleozoic, the southern Peruvian fore‐arc displays little ...to no evidence of shortening. In the light of this observation, we assess the deformation history of the southern Peruvian fore‐arc and its geodynamic implications. To accomplish this, we present a new structural and geo‐thermochronological data set (zircon U‐Pb, mica 40Ar/39Ar, apatite and zircon fission‐track and zircon (U‐Th)/He analyses) for samples collected along a 400 km long transect parallel to the trench. Our results show that the Mesoproterozoic gneissic basement was mainly at temperatures ≤350°C since the Neoproterozoic and was later intruded by Jurassic volcanic arc plutons. Along the coast, a peculiar apatite fission‐track age pattern, coupled with field observations and a synthesis of available geological maps, allows us to identify crustal‐scale tilted blocks that span the coastal Peruvian fore‐arc. These blocks, bounded by normal faults that are orthogonal to the trench, suggest post‐60 Ma trench‐parallel extension that potentially accommodated oroclinal bending in this region. Block tilting is consistent with the observed and previously described switch in the location of sedimentary sources in the fore‐arc basin. Our data set allows us to estimate the cumulative slip on these faults to be less than 2 km and questions the large amount of trench‐parallel extension suggested to have accommodated this bending.
Key Points
New geo‐thermochronological data set along a 400 km long trench‐parallel profile
Southern Peruvian fore‐arc deformation history and its linkage to oroclinal bending
Crustal‐scale block tilting occurs contemporaneously to oroclinal bending
New data on the stratigraphy, biostratigraphy, detrital zircon U-Pb, and Hf isotope geochronology of a Lower Cretaceous succession of the Bisbee Group in northern Sonora, Mexico that accumulated in ...the Altar-Cucurpe sub-basin help to constrain ages of their formations and documents the detrital provenance. These tectonically shortened strata, studied in the Arizpe area, crop out in the Cerro La Ceja block (CCB) composed of the upper Morita Formation, the complete Mural Limestone, and Cintura Formations, and the lower part of La Juana Formation. The Sierra Los Azulitos block (SAB), composed of the Mural Limestone, is thrust eastward over the CCB. A measured section of the Mural Limestone in the SAB block includes the upper Tuape Shale, Los Coyotes, Cerro La Puerta, and part of the Cerro La Espina members whose age is constrained as upper Aptian to lower Albian based on benthic and planktonic foraminifera, bivalves and echinoderms. The age of the boundary between the Morita and Tuape Shale Member is constrained by detrital zircon maximum depositional ages (MDA) of 115.8 ± 1.1 Ma and 113.9 ± 0.8 Ma, respectively. The MDA of the upper Mural is 111.6 ± 1.6 Ma and the MDA of basal Cintura Formation is 108.8 ± 1.1 Ma. The La Juana Formation has upper Albian bivalves and echinoderms.
About one-quarter of the detrital zircon grains dated from the five sandstone samples have Proterozoic ages with age peaks that clearly indicate provenance from basement rocks of southwestern Laurentia. More than two-thirds of the grains are of Jurassic and Early Cretaceous age in about the same proportions, and have main peaks at 166, 150, and 118 Ma. The Jurassic grains may have sources in rocks of the Jurassic Cordilleran continental magmatic arc of southwestern North America, and the most probable sources for the Cretaceous grains are arcs of the Peninsular Ranges batholith that by that time were located adjacent to coastal Sonora. Jurassic and the Early Cretaceous zircons dated from 195.3 to 106.8 Ma both have mixed εHf(t) values that range from 9.53 to -21.28, and TDM model ages between 0.4 to 0.8 Ga for the primitive grains, and 0.8 to 1.3 Ga for the more evolved zircons. The probable source for the Jurassic grains with negative εHf values might be local granites of that age in northern Sonora that have Neoproterozoic TDM model ages. In contrast, sources for the Jurassic zircon with positive Hf values may be Jurassic igneous and metaigneous rocks of the Peninsular Ranges Batholith of the Californias, although data reported are scarce. Similarly, the Early Cretaceous detrital zircon grains with mixed positive and negative εHf values may have provenance from igneous rocks of the Peninsular Ranges Batholith-Sierra Nevada magmatic arc.
In this study, we investigate the Lesser Antilles forearc basin, focusing on the late Pliocene to Pleistocene sedimentary archives in order to track the occurrence of extreme events triggered by ...enhanced subduction‐related tectono‐volcanic activity. We identify late Piacenzian deposits covering a major regional erosional surface, displaying sedimentary dykes and large marine boulders embedded in a mixed continental–marine matrix, characteristic of tsunamites. We interpret this episode of platform emersion and the successive cataclysmic deposits as resulting from enhanced tectonic activity at the interface of the subduction zone, synchronous with the initiation of the Lesser Antilles volcanic arc. We then discuss the implications in terms of the mechanical behaviour of the Lesser Antilles subduction zone.
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