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Papers by Martin Valencia

Scientific Investigations Report, 2010

Journal of South American Earth Sciences, 2006

... late 1970s (eg, Coney and Reynolds, 1977, Gastil and Krummenacher, 1977, McDowell and Clabaug... more ... late 1970s (eg, Coney and Reynolds, 1977, Gastil and Krummenacher, 1977, McDowell and Clabaugh, 1979, Damon et al., 1983a, Damon et al., 1983b, Silver and Chappell, 1988, Kimbrough et al., 2001, Staude and Barton, 2001, Henry et al., 2003 and Ortega-Rivera, 2003). ...

Canadian Journal of Earth Sciences, 2003

Los Alisos prospect is a porphyry copper deposit located in northeastern Sonora, at about 10 km n... more Los Alisos prospect is a porphyry copper deposit located in northeastern Sonora, at about 10 km northeast of La Caridad mine. It is a relatively small deposit, characterized by an intense hypogene oxidation zone exposed over 20 km 2 . According to the new U-Pb zircon dates reported in this work, the oldest rocks outcropping in this region consist of andesitic volcanic flows of Late Cretaceous age dated at 73.6 ± 1.0 Ma, which were intruded during the Paleocene by a 60.2 ± 0.8 Ma old quartz-feldspar porphyry stock. These rocks were unconformably covered by Eocene-Oligocene rhyolite lava flows and tuffs. Locally, these rocks were in turn covered by a sequence of conglomerate and sandstone with basaltic lava flows, which regionally correlates with the Miocene Baucarit Formation. The geochemical and isotopic composition of the quartz-feldspar porphyry is characterized by a light rare earth enriched pattern (LREE), coupled with Sr and eNd initial values of 0.7067 and -5.5, respectively. ...

Ore Geology Reviews, 2016

Abstract Late Cretaceous to early Eocene volcanic and plutonic rocks that crop out in the Nacozar... more Abstract Late Cretaceous to early Eocene volcanic and plutonic rocks that crop out in the Nacozari quadrangle compose the Laramide magmatic arc in northeastern Sonora, northwestern Mexico. The purpose of this work is to characterize the arc rocks based on new cartography, stratigraphy, U-Pb and K-Ar geochronology, and major, trace and isotope geochemical data and interpret them in the regional context of evolution of the arc. The study area lies within the Proterozoic Mazatzal crustal block which is limited to the south by the Caborca block. The volcanic rocks regionally correlate with the Tarahumara Formation and consist of volcanic flows, breccias, tuffs and volcaniclastic sandstones with an estimated thickness of 4 km. They range in composition from andesite to rhyolite and have isotopic ages from 76.8 ± 0.4 to 57.1 ± 0.4 Ma. The granitic plutons and rhyolitic domes that intrude them yielded ages from 59.3 ± 0.8 to 53.3 ± 1.6 Ma. Initial 87 Sr/ 86 Sr and epsilon Nd values for these rocks vary from 0.70553 to 0.70841 and − 3.7 to − 8.5, respectively, and have 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb isotope ratios that range from 18.05 to 19.05, 15.52 to 15.63, and 38.25 to 39.07, respectively. Regional integration of our U-Pb ages suggests that the volcanic activity lasted between ca. 81 and 57 Ma, with two main peaks of activity at 74.5 and 61 Ma. Similarly, regional magmatic activity indicated by dated plutons initiated at ca.91 and ended by 50 Ma, after main peaks of activity at 71 and 60–55 Ma. The plutonism between 91 and 80 Ma was subordinate and regionally restricted to coastal and central Sonora and might represent an older event unrelated to the Laramide arc. Two K-Ar cooling ages of 55.4 ± 0.7 and 48.5 ± 0.7 Ma obtained from La Purica granite dated at ca. 59 Ma (U-Pb) in the study area, correlate regionally with a possible event of rapid uplift between 68 and 50 Ma. The geochemical composition of the studied rocks indicate high-K, calc-alkaline, metaluminous to weakly peraluminous compositions, typical of subduction arc-related magmas which characterize the Laramide magmatic belt in northwestern Mexico. The Nd, Sr and Pb isotope compositions of these and other samples documented for northeastern Sonora, closely correlate with isotope signatures of the Mazatzal crustal block in southeastern Arizona and differ from those in the Caborca block, which display affinity with the Mojave-Yavapai province. The data also allow to best constrain the location of the boundary between the Mazatzal and Caborca crustal blocks in east-central Sonora.

Geological Society of America Bulletin, Apr 2000

The Arizpe and Bacanuchi Quadrangles provide a geologic history representative of the north-centr... more The Arizpe and Bacanuchi Quadrangles provide a geologic history representative of the north-central part of Sonora, where lithologies are dominated by late Mesozoic and Cenozoic igneous rocks. In this study, new geologic mapping, 40Ar/39Ar dating, and geochemical analyses have been combined to provide a stratigraphic framework for this area. Ten lithostratigraphic units and several igneous and tectonic events can be recognized. The oldest outcropping rocks are Lower Cretaceous strata of the Bisbee Group, which along with the Picacho conglomerate record a middle Cretaceous compressive tectonic event and associated sedimentation. Laramide igneous activity is widespread and represented by (1) highly altered andesitic flows and volcaniclastic rocks (Arroyo Alcaparros andesitic rocks) of late Campanian to Maastrichtian age, (2) less altered andesitic and dacitic flows (Cerro Las Jarillas volcanic rocks) of late Paleocene age, and the intrusive bodies of (3) Sierra El Manzanal granodiorite and (4) Rancho Vaquería quartz monzonite. The Sierra El Manzanal granodiorite was emplaced at ca. 68 Ma on the basis of a 40Ar/39Ar biotite age (67.97 ± 0.19 Ma) and cooled relatively rapidly according to less precise 40Ar/39Ar hornblende and K-feldspar ages from the same sample (64.8 ± 1.0 Ma and 62.8 ± 0.3 Ma, respectively). The Cerro Las Jarillas volcanic rocks are slightly younger (40Ar/39Ar biotite age of 58.67 ± 0.17 Ma). The Rancho Vaquería quartz monzonite was emplaced at ca. 57 Ma (40Ar/39Ar biotite age of 56.73 ± 0.14 Ma and a less precise 40Ar/39Ar hornblende age of 55.0 ± 0.7 Ma); a protracted cooling history of this pluton is indicated by the age spectrum of K-feldspar from the same sample. A probable magmatic lull and denudation seem to have occurred between middle and late Eocene time and probably until the early Oligocene. Subsequently, rhyolitic to mafic volcanism began close to late Oligocene time and lasted until the early Miocene. Felsic volcanism is represented by the Cerro Cebadéhuachi volcanic rocks, from which 40Ar/39Ar hornblende ages of 27.25 ± 0.09 and 27.32 ± 0.06 Ma and a biotite age of 26.97 ± 0.06 Ma were obtained at three different localities. The Mesa Pedregosa volcanic rocks represent the transition to younger, mafic volcanic activity that occurred during the late Oligocene, as indicated by a sanidine 40Ar/39Ar age of 25.48 ± 0.05 Ma. This late Oligocene and early Miocene magmatism was paired by two episodes of extensional deformation. The first phase is characterized by northwest-striking normal faults and folds, which expose the deepest structural levels of the area, and by the related basin fill, the Bacanuchi conglomerate. The second phase is represented by north-striking normal faults and by the syntectonic basin fill, the Arizpe conglomerate. Basaltic andesite volcanic flows at the base of the Arizpe conglomerate yielded 40Ar/39Ar (whole-rock) ages of 23.52 ± 0.17 and 21 ± 0.20 Ma. The extensional deformation (27 to 23 Ma) in the study area is coeval with the development of metamorphic core complexes in neighboring areas of Sonora and with the onset of extension in southern Sonora. The mafic volcanic rocks and clastic sedimentary units associated with this extension resemble the basin fills that in other parts of Sonora are assigned to the Báucarit Formation.

Geochemical information from samples representing each of the igneous events displayed high-K calc-alkalic and mostly metaluminous compositions. The older units including the Arroyo Alcaparros andesitic rocks, the Cerro Las Jarillas volcanic rocks, the Sierra El Manzanal granodiorite, and the Rancho Vaquería quartz monzonite are characterized by steep chondrite-normalized REE (rare earth element) slopes and generally well-developed negative Eu anomalies, suggesting garnet and plagioclase removal in the source. The younger igneous events including the Cerro Cebadéhuachi and Mesa Pedregosa volcanic rocks, and the basaltic flows associated with the Arizpe conglomerate, showed basin-shaped REE slopes with no Eu anomalies, suggesting clinopyroxene or amphibole fractionation.

… Society of America …, 2001

… Society of America …, 2000

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… SOCIETY OF AMERICA, 2007

… Journal of Earth …, 2003

... to the Pacific side (Fig. 7d). One likely explanation to this behavior may be involvement of ... more ... to the Pacific side (Fig. 7d). One likely explanation to this behavior may be involvement of deep sea clay in the magma source, according to the average content of Sr in these sediments (Faure 1986). In any case, the lateral variations ...

International geology …, 1999

The geochemistry of Laramide granitic rocks from central Sonora was studied to relate possible co... more The geochemistry of Laramide granitic rocks from central Sonora was studied to relate possible compositional variations to the assimilation of different crustal sources. Most of the studied rocks are granodiorites collected near the southern boundary of the Paleozoic North American continent. North of this boundary, the Laramide plutons intruded a thick section of Upper Proterozoic and Paleozoic miogeoclinal strata, whereas