- Mexico
Este trabajo presenta un mapa geológico del Estado de Sonora, México, que fue compilado a la escala 1:1,000,000, y está acompañado de una base de datos isotópicos. Ambos se elaboraron a partir de la compilación de trabajos publicados y se... more
Este trabajo presenta un mapa geológico del Estado de Sonora, México, que fue compilado a la escala 1:1,000,000, y está acompañado de una base de datos isotópicos. Ambos se elaboraron a partir de la compilación de trabajos publicados y se incluyen observaciones e interpretaciones propias. El trabajo es la actualización de una versión publicada en 2006 que fue elaborada sobre mapas topográficos base y se digitalizó generando nuevos datos vectoriales, adicionándole el mapa de relieve. El mapa se forma por 33 unidades cartográficas reconocidas por sus litologías y edades, y muestra 1,129 edades U-Pb, K-Ar y 40Ar/39Ar de rocas ígneas y de mineralización en Re-Os.
Abstract This work reports on the geology and U–Pb LA-ICPMS zircon geochronology of a crustal section that is part of the Jurassic magmatic arc in the Magdalena quadrangle of north-central Sonora, Mexico. This rock succession is variably... more
Abstract This work reports on the geology and U–Pb LA-ICPMS zircon geochronology of a crustal section that is part of the Jurassic magmatic arc in the Magdalena quadrangle of north-central Sonora, Mexico. This rock succession is variably metamorphosed and strained as it was affected by Late Cretaceous shortening, intruded by early Tertiary granitoids, and further exhumed in the lower plate of the early Miocene Magdalena metamorphic core complex. The older and more extensively exposed Jurassic unit is the >3.5 km thick Sierra Guacomea rhyolite that is composed of massive to poorly bedded rhyolite, bedded quartz-phyric rhyolitic ignimbrite and interbedded ash-fall tuffs and quartz-rich sandstone beds. Three rhyolite samples collected at different localities of its outcrops yielded concordia ages of 175.2 ± 0.9, 171.7 ± 0.6, and 171.4 ± 0.7 Ma. The quartz-phyric Rancho La Vibora, Los Vallecitos, and the Agua Caliente rhyolitic domes that are associated with the Sierra Guacomea rhyolite yield concordia ages of 176 ± 0.8, 174.4 ± 0.9 and 173.1 ± 0.8 Ma, respectively. The Rancho Los Pozos unit composed of interbedded rhyolitic ash-fall tuff and flows, sandstone, siltstone and subordinate limestone beds has an estimated thickness of 600 m and yielded a crystallization concordia age of 170.7 ± 0.6 Ma from a rhyolite bed. The porphyritic El Rincon granite that intrudes into the Sierra Guacomea rhyolite yields crystallization ages of 167.43 ± 0.42 and 164.4 ± 0.7 in samples from different localities. The La Jojoba metasandstone that consists of foliated, quartz-rich to arkosic clastic strata of fluvial origin is at least 900 m thick; detrital zircons dated from three sandstone samples yielded dominantly Jurassic zircon grains with peak ages at 172, 170, and 163.7 Ma, and a combined maximum depositional age of ca. 163 Ma. The younger plutons are the porphyritic El Nopalito granite that has an interpreted crystallization age of 160.8 ± 0.6 Ma, and the leucocratic, two-mica, garnet-bearing La Cebolla granite that yielded a concordia age of 158.1 ± 1 Ma. These granitic intrusions record the waning magmatic pulses of the arc, in the study quadrangle, but their volcanic equivalents were not identified. Inherited zircon grains in the volcanic and plutonic units are only of Jurassic age, except by two Proterozoic zircon grains yielded by the El Nopalito granite. The El Salto granite augen gneiss is a xenolith dated at 1071.9 ± 5 Ma that indicates the presence of Grenvillian basement in the study area. Major- and trace-element geochemical data indicate that the volcanic and plutonic units are silica-rich, mostly high K calc-alkaline to shoshonitic rocks associated with a continental margin arc setting. The plutons are mostly peraluminous, and in conjunction with trace element geochemistry data, they suggest crustal assimilation of magmas emplaced in a probably thickened continental crust. Chondrite-normalized REE patterns and primitive mantle-normalized trace element diagrams also suggest partial melting and fractional crystallization processes. The ages obtained indicate that the arc in the study area developed from ca. 176 to 158 Ma, encompassing a 17 m.y. interval of magmatism and associated sedimentation. Regional correlation and geochronologic published data indicate that the arc crustal section of the Magdalena quadrangle is part of the Jurassic magmatic arc that regionally lasted from ca. 190 to 158 Ma.
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The Morita Formation is a Lower Cretaceous unit of the Bisbee Group that crops out in northern Sonora and southeastern Arizona where it was deposited within the Altar-Cucurpe, and Huachuca sub-basins of the Bisbee basin, respectively. In... more
The Morita Formation is a Lower Cretaceous unit of the Bisbee Group that crops out in northern Sonora and southeastern Arizona where it was deposited within the Altar-Cucurpe, and Huachuca sub-basins of the Bisbee basin, respectively. In northern Sonora it either overlies strata of the Upper Jurassic Cucurpe Formation, the Glance Conglomerate, or strata of the Lower Cretaceous Cerro de Oro/Rancho La Colgada formations, and it grades upward into the Mural Limestone. In this
contribution we characterize the stratigraphy, petrography and detrital zircon geochronology of the Morita Formation along a ca. 60 km-long northwest-southeast transect that includes the complete columns of the Mule Mountains in southeastern Arizona and the sierras San Jos�e, Anibacachi and Rancho Búfalo area in northeastern Sonora. Thickness of these sections varies from a minimum of 555 m in Sierra Anibacachi to a maximum of 855 m in Rancho Búfalo. In most sections, the lower half of the Morita consists of reddish siltstone and mudstone with pedogenic calcareous nodules with interbeds of mostly single-storey sandstone bodies, which changes to isolated multi-storey sandstone bodies in its upper half. In contrast, the lower part of the Rancho Búfalo column consists of reddish mudstone/siltstone with isolated, fining-upward, clast-supported, fine-pebble conglomerate beds that grades into reddish to purple, brown and green mudstone/siltstone with isolated, single-storey to multi-storey sandstone beds of its upper part. Lithofacies association in the Morita Formation suggest it is of fluvial origin but ichnofossils and local herringbone- and flaser-cross bedding in its upper part indicate intermitent marginal marine sedimentation preceding the transgression that deposited the overlying Mural shelf.
Sandstone composition of the Mule and San Jos�e mountains is dominantly feldspatho-quartzose indicating dominant provenance from basement uplift and transitional continental areas, while composition at Sierra Anibacachi and Rancho Búfalo ranges from feldspatho litho-quartzose to litho-quartzose, indicating provenance from recycled orogen. Detrital zircon grains dated from samples of all the studied sections share very similar populations of Proterozoic to Mesozoic ages,
but the Mesoproteozoic and Triassic grains compose ca. 64% of the total grains. Detrital zircon grains of Lower Cretaceous age that are only present in samples from the bottom of the Mule and San Jos�e Mountains help to constrain a maximum depositional age of 125.5 � 0.8 Ma for inception of sedimentation of the Morita Formation in this region. According to this age and to observed stratigraphic relationships, we interpret that the lower contact of the Morita Formation is a
disconformity with the underlying Glance Conglomerate, or with the Cerro de Oro Formation in northeastern Sonora. Similarly, according to regional stratigraphic relationships and age data known from the Cucurpe-Tuape region, in north-central Sonora, the age of this unit may be constrained to the Aptian stage, in Sonora, from ca. 125 to 115 Ma. Regional isopach curves confirm merging of the sub-basins in northeastern Sonora, continuous sedimentation of the Morita Formation, and presence of the Cananea high separating them.
contribution we characterize the stratigraphy, petrography and detrital zircon geochronology of the Morita Formation along a ca. 60 km-long northwest-southeast transect that includes the complete columns of the Mule Mountains in southeastern Arizona and the sierras San Jos�e, Anibacachi and Rancho Búfalo area in northeastern Sonora. Thickness of these sections varies from a minimum of 555 m in Sierra Anibacachi to a maximum of 855 m in Rancho Búfalo. In most sections, the lower half of the Morita consists of reddish siltstone and mudstone with pedogenic calcareous nodules with interbeds of mostly single-storey sandstone bodies, which changes to isolated multi-storey sandstone bodies in its upper half. In contrast, the lower part of the Rancho Búfalo column consists of reddish mudstone/siltstone with isolated, fining-upward, clast-supported, fine-pebble conglomerate beds that grades into reddish to purple, brown and green mudstone/siltstone with isolated, single-storey to multi-storey sandstone beds of its upper part. Lithofacies association in the Morita Formation suggest it is of fluvial origin but ichnofossils and local herringbone- and flaser-cross bedding in its upper part indicate intermitent marginal marine sedimentation preceding the transgression that deposited the overlying Mural shelf.
Sandstone composition of the Mule and San Jos�e mountains is dominantly feldspatho-quartzose indicating dominant provenance from basement uplift and transitional continental areas, while composition at Sierra Anibacachi and Rancho Búfalo ranges from feldspatho litho-quartzose to litho-quartzose, indicating provenance from recycled orogen. Detrital zircon grains dated from samples of all the studied sections share very similar populations of Proterozoic to Mesozoic ages,
but the Mesoproteozoic and Triassic grains compose ca. 64% of the total grains. Detrital zircon grains of Lower Cretaceous age that are only present in samples from the bottom of the Mule and San Jos�e Mountains help to constrain a maximum depositional age of 125.5 � 0.8 Ma for inception of sedimentation of the Morita Formation in this region. According to this age and to observed stratigraphic relationships, we interpret that the lower contact of the Morita Formation is a
disconformity with the underlying Glance Conglomerate, or with the Cerro de Oro Formation in northeastern Sonora. Similarly, according to regional stratigraphic relationships and age data known from the Cucurpe-Tuape region, in north-central Sonora, the age of this unit may be constrained to the Aptian stage, in Sonora, from ca. 125 to 115 Ma. Regional isopach curves confirm merging of the sub-basins in northeastern Sonora, continuous sedimentation of the Morita Formation, and presence of the Cananea high separating them.
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The Triassic and Jurassic geology of northern Sonora encompasses important events that are linked to the late Paleozoic history of the region. The fossiliferous El Antimonio Group in the Sierra del Álamo includes the upper... more
The Triassic and Jurassic geology of northern Sonora encompasses important events that are linked to the late Paleozoic history of the region. The fossiliferous El Antimonio Group in the Sierra del Álamo
includes the upper Permian-Triassic Antimonio, and Río Asunción formations and the Hettangian-Sinemurian Sierra de Santa Rosa Formation. These formations consist of upward-fining sequences from I to XIV that represent fluvial to shallow and deep marine environments of deposition. The Triassic/Jurassic boundary in this region is a hiatus represented by a disconformity between sequence IX of the Río Asunción formations and sequence X of the Sierra de Santa Rosa Formation.
The shallow to deep marine succession of the Sierra de Santa Rosa composes the upper part of the Sierra de Santa Rosa Formation that ranges in age from late Sinemurian to early Pliensbachian. Ages of the Permian to Triassic plutonic rocks of northwesternmost Sonora, the Mojave Desert and the Jurassic continental margin Nazas arc that crossed through northern Sonora, are also well recorded by igneous clasts and detrital zircon grains that have been dated from the El Antimonio Group and other Jurassic formations of this region. The upper Oxfordian-lower Tithonian Cucurpe Formation in north-central Sonora recorded the onset of continental extension and incursion of marine waters from the Gulf of Mexico into northwestern Mexico, once activity of the Jurassic magmatic arc ended.
includes the upper Permian-Triassic Antimonio, and Río Asunción formations and the Hettangian-Sinemurian Sierra de Santa Rosa Formation. These formations consist of upward-fining sequences from I to XIV that represent fluvial to shallow and deep marine environments of deposition. The Triassic/Jurassic boundary in this region is a hiatus represented by a disconformity between sequence IX of the Río Asunción formations and sequence X of the Sierra de Santa Rosa Formation.
The shallow to deep marine succession of the Sierra de Santa Rosa composes the upper part of the Sierra de Santa Rosa Formation that ranges in age from late Sinemurian to early Pliensbachian. Ages of the Permian to Triassic plutonic rocks of northwesternmost Sonora, the Mojave Desert and the Jurassic continental margin Nazas arc that crossed through northern Sonora, are also well recorded by igneous clasts and detrital zircon grains that have been dated from the El Antimonio Group and other Jurassic formations of this region. The upper Oxfordian-lower Tithonian Cucurpe Formation in north-central Sonora recorded the onset of continental extension and incursion of marine waters from the Gulf of Mexico into northwestern Mexico, once activity of the Jurassic magmatic arc ended.
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The Cabullona basin in northeastern Sonora is a continental depocenter whose origin is related to the adjacent Sierra Anibacachi uplift that bounds its tectonic eastern flank. Its exposed, mostly fluvial and lacustrine sedimentary fill,... more
The Cabullona basin in northeastern Sonora is a continental depocenter whose origin is related to the adjacent Sierra Anibacachi uplift that bounds its tectonic eastern flank. Its exposed, mostly fluvial and
lacustrine sedimentary fill, the Cabullona Group, was deposited between 81.9 ± 0.7 and 69.8 ± 0.7 Ma and its outcrops extends for 70 km from north to south. The oldest measured stratigraphic column of the
Cabullona Group is the Los Atolillos column of the southern part of the basin, but its base is not exposed. A basal conglomerate in the younger El Malacate (ca. 80 Ma), Cuauhtemoc (ca. 75 Ma) and San Joaquín
(ca. 70 Ma) columns onlaps deformed basement rocks. The type section in which the Cabullona Group was previously named is herein referred as the Naco section and is dated ~73-72 Ma. The younger strata
of the Cabullona Group correspond to the fluvial San Joaquín column that onlaps the eastern tectonic
boundary of the basin and to the lacustrine Esqueda column. These columns are dated at ca. 70 Ma and
may represent the late evolution of the Cabullona basin.
Sandstone petrography and detrital zircon geochronology are used to infer provenance of sediments of
the Cabullona Group. Sandstones consist of lithic arkose to feldespathic litharenite, indicating provenance
from dissected to transitional volcanic arc, but samples of the El Malacate column classify as arkose
and lithic arkose with possible provenance from basement uplift of Sierra Los Ajos; litharenite from the
Esqueda column indicate arc provenance. Detrital zircons yielded mostly Proterozoic and Mesozoic ages
with age peaks at ca. 1568, 167, 100, 80 and 73 Ma indicating possible provenance from the Precambrian
basement rocks and the Jurassic continental magmatic arc that underlie the region, the Alisitos arc and La
Posta plutons in Baja California, and from the Laramide magmatic arc of Sonora.
The Cabullona basin developed nearly contemporaneous to the early, eastwards migrating Laramide
magmatic arc that located to the west of the basin, and to a tectonic shortening that occurred in northern
Sonora during Late Cretaceous time. In the older columns of the Cabullona Group and in columns of the
northern part, the early arc had a distal influence during sedimentation as shown by interbedded ash fall
tuffs and minor rhyolitic flows, but sections in the southern part of the basin record more abundant
rhyolitic ash-fall tuffs and flows indicating the arc proximity. An important regional flare-up of the arc at
ca. 74 Ma is recorded by the Ejido Ruiz Cortines column, while the upper part of the Cabullona Group was
interdigitating with rhyolitic rocks by 70 Ma. The Cabullona basin started to form during the shortening
event whose age is constrained between ca. 93 and 76 Ma according to U-Pb ages of the syntectonic
Cocospera Formation of northern Sonora and from Laramide arc rocks that overlie it. Ages and correlation
of the Cocospera and the Altar formations may indicate that a Laramide tectonic front extended from
north-central Sonora to the Caborca region and whose trace may correspond to a westward extension of
the San Antonio fault.
lacustrine sedimentary fill, the Cabullona Group, was deposited between 81.9 ± 0.7 and 69.8 ± 0.7 Ma and its outcrops extends for 70 km from north to south. The oldest measured stratigraphic column of the
Cabullona Group is the Los Atolillos column of the southern part of the basin, but its base is not exposed. A basal conglomerate in the younger El Malacate (ca. 80 Ma), Cuauhtemoc (ca. 75 Ma) and San Joaquín
(ca. 70 Ma) columns onlaps deformed basement rocks. The type section in which the Cabullona Group was previously named is herein referred as the Naco section and is dated ~73-72 Ma. The younger strata
of the Cabullona Group correspond to the fluvial San Joaquín column that onlaps the eastern tectonic
boundary of the basin and to the lacustrine Esqueda column. These columns are dated at ca. 70 Ma and
may represent the late evolution of the Cabullona basin.
Sandstone petrography and detrital zircon geochronology are used to infer provenance of sediments of
the Cabullona Group. Sandstones consist of lithic arkose to feldespathic litharenite, indicating provenance
from dissected to transitional volcanic arc, but samples of the El Malacate column classify as arkose
and lithic arkose with possible provenance from basement uplift of Sierra Los Ajos; litharenite from the
Esqueda column indicate arc provenance. Detrital zircons yielded mostly Proterozoic and Mesozoic ages
with age peaks at ca. 1568, 167, 100, 80 and 73 Ma indicating possible provenance from the Precambrian
basement rocks and the Jurassic continental magmatic arc that underlie the region, the Alisitos arc and La
Posta plutons in Baja California, and from the Laramide magmatic arc of Sonora.
The Cabullona basin developed nearly contemporaneous to the early, eastwards migrating Laramide
magmatic arc that located to the west of the basin, and to a tectonic shortening that occurred in northern
Sonora during Late Cretaceous time. In the older columns of the Cabullona Group and in columns of the
northern part, the early arc had a distal influence during sedimentation as shown by interbedded ash fall
tuffs and minor rhyolitic flows, but sections in the southern part of the basin record more abundant
rhyolitic ash-fall tuffs and flows indicating the arc proximity. An important regional flare-up of the arc at
ca. 74 Ma is recorded by the Ejido Ruiz Cortines column, while the upper part of the Cabullona Group was
interdigitating with rhyolitic rocks by 70 Ma. The Cabullona basin started to form during the shortening
event whose age is constrained between ca. 93 and 76 Ma according to U-Pb ages of the syntectonic
Cocospera Formation of northern Sonora and from Laramide arc rocks that overlie it. Ages and correlation
of the Cocospera and the Altar formations may indicate that a Laramide tectonic front extended from
north-central Sonora to the Caborca region and whose trace may correspond to a westward extension of
the San Antonio fault.
A succession of Triassic to Jurassic strata occurs in the vicinity of Caborca, Mexico, where the Antimonio, Río Asunción, and Sierra de Santa Rosa Formations contain a nearly continuous marine section deposited in previously reported... more
A succession of Triassic to Jurassic strata occurs in the vicinity of Caborca, Mexico, where the Antimonio, Río Asunción, and Sierra de Santa
Rosa Formations contain a nearly continuous marine section deposited in previously reported shallow basin environments. The Sierra de
Santa Rosa Formation is known to be Early Jurassic, but with an 18 m.y. uncertainty in age. Here we establish the ages of the three members
of the Sierra de Santa Rosa Formation as early Sinemurian to middle Toarcian. Detrital zircon U-Pb geochronology from a set of 2334 grains
along with ammonite zonation is used to establish depositional ages and to support the interpretation of the formation as being deposited
in a retroarc basin. We find 2 zircon populations of 199 Ma and 192 Ma that mark the onset of Early Jurassic magmatic activity in the formation.
Older Neoproterozoic and Early Devonian populations not attributable to local sources imply a robust Early Jurassic exchange with
southwestern Laurentian eolianites. Here we also establish the ages of three fossiliferous units containing solitary and colonial corals in the
Sierra de Santa Rosa Formation. The end-Triassic mass extinction decimated coral reefs worldwide and reports of Early Jurassic corals have
been particularly rare in North America. The ages indicate an earlier regional recovery for North American corals than previously proposed;
this has implications for understanding postextinction reef recovery.
Rosa Formations contain a nearly continuous marine section deposited in previously reported shallow basin environments. The Sierra de
Santa Rosa Formation is known to be Early Jurassic, but with an 18 m.y. uncertainty in age. Here we establish the ages of the three members
of the Sierra de Santa Rosa Formation as early Sinemurian to middle Toarcian. Detrital zircon U-Pb geochronology from a set of 2334 grains
along with ammonite zonation is used to establish depositional ages and to support the interpretation of the formation as being deposited
in a retroarc basin. We find 2 zircon populations of 199 Ma and 192 Ma that mark the onset of Early Jurassic magmatic activity in the formation.
Older Neoproterozoic and Early Devonian populations not attributable to local sources imply a robust Early Jurassic exchange with
southwestern Laurentian eolianites. Here we also establish the ages of three fossiliferous units containing solitary and colonial corals in the
Sierra de Santa Rosa Formation. The end-Triassic mass extinction decimated coral reefs worldwide and reports of Early Jurassic corals have
been particularly rare in North America. The ages indicate an earlier regional recovery for North American corals than previously proposed;
this has implications for understanding postextinction reef recovery.
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Several Proterozoic basement units crop out in the Sonora State of NW Mexico, and the same can be correlated with crustal provinces of southern Laurentia in the neighboring southwestern USA. Zircon U–Pb and Hf isotopic determinations in... more
Several Proterozoic basement units crop out in the Sonora State of NW Mexico, and the same can be correlated with crustal provinces of southern Laurentia in the neighboring southwestern USA. Zircon U–Pb and Hf isotopic determinations in more than 300 grains separated from igneous and metaigneous rocks from these units indicate that the crystalline basement in Sonora is made up of different components, which are from west to east: (1) The Caborca–Mojave province to the west, characterized by the so-called Bámori Complex, have U–Pb ages between 1696 and 1772 Ma, with moderately juvenile to slightly evolved εHf values, yielding TDM ages of ca. 2.1–2.4 Ga; (2) in the intermediate area, east of Hermosillo, the Palofierral and La Ramada orthogneiss units yield an age of 1640 and 1703 Ma, respectively, both having juvenile εHf with the Palofierral overlapping the depleted mantle curve at ca. 1.65 Ga; and (3) in the northeastern Sonora, samples from the southern extension of the Mazatzal province, represented by the Pinal Schist, yielded ages between 1674 and 1694 Ma, with moderately juvenile to juvenile εHf values and a TDM age of ca. 1.9 Ga. In addition, a suite of post-tectonic granites was also studied in Caborca (San
Luis granite) as well as in northeastern Sonora (Cananea
granite), both yielding ages of ca. 1.44 Ga with moderately
juvenile εHf values ranging from −1 to +8 and TDM dates
of ca. 1.8–1.9 Ga and 1.6–1.7 Ga, respectively. These two
isotopically contrasting provinces may imply the existence
of a Proterozoic paleo-suture. However, if the Palofierral
gneiss, of which the Hf signature straddles the depleted
mantle array, is taken as the source for the 1.44 Ga Cananea
granite, then the location of such a suture zone should lay
farther south than the proposed trace of the Mojave–Sonora
megashear.
Luis granite) as well as in northeastern Sonora (Cananea
granite), both yielding ages of ca. 1.44 Ga with moderately
juvenile εHf values ranging from −1 to +8 and TDM dates
of ca. 1.8–1.9 Ga and 1.6–1.7 Ga, respectively. These two
isotopically contrasting provinces may imply the existence
of a Proterozoic paleo-suture. However, if the Palofierral
gneiss, of which the Hf signature straddles the depleted
mantle array, is taken as the source for the 1.44 Ga Cananea
granite, then the location of such a suture zone should lay
farther south than the proposed trace of the Mojave–Sonora
megashear.
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Plutonic rocks of the Puerta del Sol area, in central Sonora, represent the extension to the south of the El Jaralito batholith, and are part of the footwall of the Sierra Mazatán metamorphic core complex, whose low-angle detachment fault... more
Plutonic rocks of the Puerta del Sol area, in central Sonora, represent the extension to the south of the El Jaralito batholith, and are part of the footwall of the Sierra Mazatán metamorphic core complex, whose low-angle detachment fault bounds the outcrops of plutonic rocks to the west. Plutons in the area record the magmatic evolution of the Laramide arc and the Oligo-Miocene syn-extensional plutonism in Sonora. The basement of the area is composed by the ca. 1.68 Ga El Palofierral orthogneiss that is part of the Caborca block. The Laramide plutons include the El Gato diorite (71.29 ± 0.45 Ma, U-Pb), the El Pajarito granite (67.9 ± 0.43 Ma, U-Pb), and the Puerta del Sol grano-diorite (49.1 ± 0.46 Ma, U-Pb). The younger El Oquimonis granite (41.78 ± 0.32 Ma, U-Pb) is considered part of the scarce magmatism that in Sonora records a transition to the Sierra Madre Occidental magmatic event. The syn-extensional plutons are the El Garambullo gabbro (19.83 ± 0.18 Ma, U-Pb) and the Las Mayitas granodiorite (19.2 ± 1.2 Ma, K-Ar). A migmatitic event that affected the El Palofierral orthogneiss, El Gato diorite, and El Pajarito granite between ca. 68 and 59 Ma might be related to the emplacement of the El Pajarito granite. The plutons are metaluminous to slightly peraluminous, with the exception of El Oquimonis granite, which is a peraluminous two-mica, garnet-bearing granite. They are mostly high-K calc-alkaline with nearly uniform chondrite-normalized REE and primitive-mantle normalized multielemental patterns that are characteristic of continental margin arcs and resemble patterns reported for other Laramide granites of Sonora. The Laramide and syn-extensional plutons also have Sr, Nd and Pb isotopic ratios that plot within the fields reported for Laramide granites emplaced in the Caborca terrane in northwestern and central Sonora. Nevertheless, and despite their geochemical affinity to continental magmatic arcs, the El Garambullo gabbro and Las Mayitas granodiorite are syn-extensional plutons that were emplaced at ca. 20 Ma during development of the Sierra Mazatán metamorphic core complex. The 40 Ar/ 39 Ar and K-Ar ages obtained for the El Palofierral orthogneiss, the Puerta del Sol granodiorite, the El Oquimonis granite, and the El Garambullo gabbro range from 26.3 ± 0.6 to 17.4 ± 1.0 Ma and are considered cooling ages associated with the exhumation of the metamorphic core complex. RESUMEN El área de Puerta del Sol, en el centro de Sonora, se encuentra en la parte sur del batolito El Jaralito y es parte de la placa inferior del complejo de núcleo metamórfico de la Sierra Mazatán, cuya falla de despegue limita sus afloramientos en su parte occidental. La geología la forman varios plutones que registran la evolución magmática del arco Laramide hasta el plutonismo sinextensional del Oligioceno-Mioceno de Sonora. El basamento del área lo forma el ortogneis El Palofierral cuya edad de ca. 1.68 Ga (U-Pb) lo hace pertenecer al basamento del bloque Caborca. Los plutones laramídicos incluyen a la diorita El Gato (71.29 ± 0.45 Ma, U-Pb), el granito El Pajarito (67.9 ± 0.43 Ma, U-Pb) y la granodiorita Puerta del Sol (49.1 ± 0.46 Ma, U-Pb). El granito El Oquimonis (41.78 ± 0.32 Ma, U-Pb) es un plutón más joven considerado parte del escaso magmatismo regional transicional al de la Sierra Madre Occidental. Los plutones sinextensionales están representados por el gabro El Garambullo (19.83 ± 0.18 Ma, U-Pb) y la granodiorita Las Mayitas (19.2 ± 1.2 Ma, K-Ar). Un evento migmatítico que ocurrió entre ca. 68 y 59 Ma afectó al ortogneis El Palofierral, a la diorita El Gato y al granito El Pajarito y pudiera estar relacionado a la intrusión de este último. Los plutones del área son metaluminosos a ligeramente peraluminosos, con excepción del granito El Oquimonis que es peraluminoso, de dos micas y con granate. Estas rocas son principalmente calcialcalinas, altas en K,
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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... more
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 87Sr/86Sr and epsilon Nd values for these rocks vary from 0.70553 to 0.70841 and − 3.7 to − 8.5, respectively, and have 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb 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 Púrica 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.
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... 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.,... 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). ...
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U-Pb ages and Nd isotope values of Proterozoic rocks in Sonora, Mexico, indicate the presence of Caborca-type basement, predicted to lie only south of the Mojave-Sonora mega-shear, 40 km north of the postulated megashear. Granitoids have... more
U-Pb ages and Nd isotope values of Proterozoic rocks in Sonora, Mexico, indicate the presence of Caborca-type basement, predicted to lie only south of the Mojave-Sonora mega-shear, 40 km north of the postulated megashear. Granitoids have U-Pb zircon ages of 17631737 ...
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New ornithomimid material discovered from the Upper Cretaceous Packard Shale Formation, (Cabullona Group) of Sonora, Mexico is described. The material includes a partial skeleton, which is assigned to a new genus and species, Tototlmimus... more
New ornithomimid material discovered from the Upper Cretaceous Packard Shale Formation, (Cabullona Group) of Sonora, Mexico is described. The material includes a partial skeleton, which is assigned to a new genus and species, Tototlmimus packardensis. This new taxon differs from other ornithomimids in having five unique characteristics that separate it from other northamerican ornithomimids: (1) a distinctively articulation between metatarsals, where the distal ends of metatarsals II and IV contact directly with the distal facet of metatarsal III; (2) a metatarsal III with a weakly ginglymoid distal articular face; (3) the medial and lateral sides of metatarsal III are shaped into the form of metatarsals II and IV, so all distal ends fit together when they articulate; (4) an asymmetrical and narrow pedal ungual with shallow grooves in both medial and lateral sides; and finally, (5) the presence of a deep sulcus on the ventromedial edge, close to the articular end. Phylogenetic analysis suggests that Tototlmimus packardensis corresponds to a derived ornithomimid included in the Northamerican clade, forming a monophyly with Ornithomimus. Tototlmimus packardensis is the first definitive ornithomimid described for Mexico, and represents one of the southernmost occurrences in the Western Interior Basin of North America.
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We used petrofacies analysis, carbon, oxygen and strontium isotope data to interpret the isotopic variations in the carbonate rocks of the Mural Formation of Sonora (Sierra San José section), Mexico. The petrographic study reveals a range... more
We used petrofacies analysis, carbon, oxygen and strontium isotope data to interpret the isotopic variations in the carbonate rocks of the Mural Formation of Sonora (Sierra San José section), Mexico. The petrographic study reveals a range of lithofacies from wackestone to packstone. The analyzed limestones show significant negative δ18O values (-18.6 to -10.9 VPDB) and δ13C values ranging from negative to positive (-2.6 to +2.5‰ VPDB). The absence of correlation between δ13C and δ18O values suggests a primary marine origin for the δ13C values of limestones from the Sierra San José section. The limestones have large variations in 87Sr/86Sr values (0.707479 to 0.708790). Higher 87Sr/86Sr ratios in various levels of the studied section suggest that most of the sediments were derived from the Proterozoic basement of the Caborca block during Early Cretaceous time. A decrease in 87Sr/86Sr ratios at certain levels indicates an influx of lesser amounts of radiogenic Sr that could have been caused by contribution of sediments from the Triassic and Jurassic volcanic rocks.
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The source of volcanic material in the Upper Triassic Chinle Formation on the Colorado Plateau has long been speculated upon, largely owing to the absence of similar-age volcanic or plutonic material cropping out closer than several... more
The source of volcanic material in the Upper Triassic Chinle Formation on the Colorado Plateau has long been speculated upon, largely owing to the absence of similar-age volcanic or plutonic material cropping out closer than several hundred kilometers distant. These strata, however, together with Upper Triassic formations within El Antimonio and Barranca Group sedimentary rocks in northern Sonora, Mexico, yield important clues about the inception of Cordilleran magmatism in Triassic time.
Volcanic clasts in the Sonsela Member of the Chinle Formation range in age from ca. 235 to ca. 218 Ma. Geochemistry of the volcanic clasts documents a hydrothermally altered source region for these clasts. Detrital zircons in the Sonsela Member sandstone are of similar age to the clasts, as are detrital zircons from the El Antimonio and Barranca Groups in Sonora. Most noteworthy about the Colorado Plateau Triassic zircons, however, are their Th/U ratios, which range from ~1 to 3.5 in both clast and detrital zircons. Thorium/uranium ratios in the Sonoran zircons, in contrast, range from ~0.4 to ~1.
These data, together with rare-earth-element geochemistry of the zircons, shed light on likely provenance. Geochemical comparisons support correlation of clasts in the Sonsela Member with Triassic plutons in the Mojave Desert in California that are of the same age. Zircons from these Triassic plutons have relatively low Th/U ratios, which correspond well with values from El Antimonio and Barranca Group sedimentary rocks, and support derivation of the strata, at least in part, from northern sources. The Sonsela Member zircons, in contrast, match Th/U values obtained from Proterozoic through Miocene volcanic, volcaniclastic, and plutonic rocks in the eastern and central Mojave Desert. Similarly, rare-earth-element compositions of zircons from Jurassic ignimbrites in the Mojave Desert, though overlapping those of zircons from Mojave Desert plutons, also closely resemble those from Sonsela Member zircons. We use these data to speculate that erosion of Triassic volcanic fields in the central to eastern Mojave Desert shed detritus that became incorporated into the Chinle Formation on the Colorado Plateau.
Volcanic clasts in the Sonsela Member of the Chinle Formation range in age from ca. 235 to ca. 218 Ma. Geochemistry of the volcanic clasts documents a hydrothermally altered source region for these clasts. Detrital zircons in the Sonsela Member sandstone are of similar age to the clasts, as are detrital zircons from the El Antimonio and Barranca Groups in Sonora. Most noteworthy about the Colorado Plateau Triassic zircons, however, are their Th/U ratios, which range from ~1 to 3.5 in both clast and detrital zircons. Thorium/uranium ratios in the Sonoran zircons, in contrast, range from ~0.4 to ~1.
These data, together with rare-earth-element geochemistry of the zircons, shed light on likely provenance. Geochemical comparisons support correlation of clasts in the Sonsela Member with Triassic plutons in the Mojave Desert in California that are of the same age. Zircons from these Triassic plutons have relatively low Th/U ratios, which correspond well with values from El Antimonio and Barranca Group sedimentary rocks, and support derivation of the strata, at least in part, from northern sources. The Sonsela Member zircons, in contrast, match Th/U values obtained from Proterozoic through Miocene volcanic, volcaniclastic, and plutonic rocks in the eastern and central Mojave Desert. Similarly, rare-earth-element compositions of zircons from Jurassic ignimbrites in the Mojave Desert, though overlapping those of zircons from Mojave Desert plutons, also closely resemble those from Sonsela Member zircons. We use these data to speculate that erosion of Triassic volcanic fields in the central to eastern Mojave Desert shed detritus that became incorporated into the Chinle Formation on the Colorado Plateau.
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The Laramide magmatic arc in the Arizpe-Mazocahui quadrangle of north-central Sonora, Mexico, is composed of volcanic rocks assigned to the Tarahumara Formation and several granitic plutons that intrude it. The arc was built over... more
The Laramide magmatic arc in the Arizpe-Mazocahui quadrangle of north-central Sonora, Mexico, is composed of volcanic rocks assigned to the Tarahumara Formation and several granitic plutons that intrude it. The arc was built over juxtaposed crustal basements of the Caborca and Mazatzal provinces. A basal conglomerate of the >4-km-thick Tarahumara Formation overlies deformed Proterozoic igneous rocks and Neoproterozoic to Early Cretaceous strata, thus constraining the age of a contractional tectonic event that occurred between Cenomanian and early Campanian time. The lower part of the Tarahumara Formation is composed of rhyolitic ignimbrite and ash-fall tuffs, andesite flows, and interbedded volcaniclastic strata, and its upper part consists of rhyolitic to dacitic ignimbrites, ash-fall tuffs, and volcaniclastic rocks. The Tarahumara Formation shows marked lateral facies change within the study area, and further to the north it grades into the coeval fluvial and lacustrine Cabullona Group. The age of the Tarahumara Formation is between ca. 79 and 59 Ma; the monzonitic to granitic plutons have ages of ca. 71–50 Ma. The informally named El Babizo and Huépac granites, La Aurora and La Alamedita tonalities, and the Puerta del Sol granodiorite compose the El Jaralito batholith in the southern part of the area.
Major and trace element composition of the Laramide igneous rocks shows calc-alkaline differentiation trends typical of continental magmatic arcs, and the isotope geochemistry indicates strong contribution from a mature continental crust. Initial 87Sr/86Sr values range from 0.70589 to 0.71369, and εNd values range from –6.2 to –13.6, except for the El Gueriguito quartz monzonite value, –0.5. The Nd, Sr, and Pb isotopic values of the studied Laramide rocks permit comparison with the previously defined Laramide isotopic provinces of Sonora and Arizona. The El Gueriguito pluton and Bella Esperanza granodiorite in the northeastern part of the study area along with plutons and mineralization of neighboring northern Sonora have isotopic values that correspond with those of the southeastern Arizona province formed over the Mazatzal basement (Lang and Titley, 1998; Bouse et al., 1999). Isotopic values of the other Laramide rocks throughout the study area are similar to values of provinces A and B of Sonora (Housh and McDowell, 2005) and to those of the Laramide Pb boundary zone of western Arizona, while the Rancho Vaquería and La Cubana plutons in the northernmost part of the area have the isotopic composition of the Proterozoic Mojave province of the southwestern United States. These data permit us to infer that a covered crustal boundary, between the Caborca block with a basement of the Mojave or boundary zone and the Mazatzal province, crosses through the northeastern part of the area. The boundary may be placed between outcrops of the El Gueriguito and Rancho Vaquería plutons, probably following a reactivated Cretaceous thrust fault located north of the hypothesized Mojave-Sonora megashear, proposed to cross through the central part of the area.
Major and trace element composition of the Laramide igneous rocks shows calc-alkaline differentiation trends typical of continental magmatic arcs, and the isotope geochemistry indicates strong contribution from a mature continental crust. Initial 87Sr/86Sr values range from 0.70589 to 0.71369, and εNd values range from –6.2 to –13.6, except for the El Gueriguito quartz monzonite value, –0.5. The Nd, Sr, and Pb isotopic values of the studied Laramide rocks permit comparison with the previously defined Laramide isotopic provinces of Sonora and Arizona. The El Gueriguito pluton and Bella Esperanza granodiorite in the northeastern part of the study area along with plutons and mineralization of neighboring northern Sonora have isotopic values that correspond with those of the southeastern Arizona province formed over the Mazatzal basement (Lang and Titley, 1998; Bouse et al., 1999). Isotopic values of the other Laramide rocks throughout the study area are similar to values of provinces A and B of Sonora (Housh and McDowell, 2005) and to those of the Laramide Pb boundary zone of western Arizona, while the Rancho Vaquería and La Cubana plutons in the northernmost part of the area have the isotopic composition of the Proterozoic Mojave province of the southwestern United States. These data permit us to infer that a covered crustal boundary, between the Caborca block with a basement of the Mojave or boundary zone and the Mazatzal province, crosses through the northeastern part of the area. The boundary may be placed between outcrops of the El Gueriguito and Rancho Vaquería plutons, probably following a reactivated Cretaceous thrust fault located north of the hypothesized Mojave-Sonora megashear, proposed to cross through the central part of the area.
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Stratigraphy, sedimentology, and geochronology of the Upper Jurassic Cucurpe Formation in north-central Sonora, Mexico, provide new insights into Late Jurassic rifting along the southwestern margin of Laurentia. The Cucurpe Formation is... more
Stratigraphy, sedimentology, and geochronology of the Upper Jurassic Cucurpe Formation in north-central Sonora, Mexico, provide new insights into Late Jurassic rifting along the southwestern margin of Laurentia. The Cucurpe Formation is the fill of the Altar-Cucurpe Basin. This basin developed upon attenuated crust of the Triassic–Middle Jurassic continental arc and was part of the Arivechi-Cucurpe seaway; a narrow marine embayment oriented parallel to and located west of the Chihuahua trough. The Cucurpe Formation unconformably overlies Middle Jurassic arc assemblages and represents upward-coarsening marine prodeltaic deposits. New U-Pb zircon geochronology and a Kimmeridgian ammonite (Idoceras cf. I. densicostatum) constrain its age to between ca. 158 and 149 Ma. Detrital zircon ages from the unconformably overlying Lower Cretaceous Bisbee Group indicate a maximum depositional age of 139 ± 2 Ma (2σ error), demonstrating a hiatus of at least 10 m.y. between Jurassic and Cretaceous strata. Detrital zircon ages and petrographic data indicate the provenance of Cucurpe Formation and lowermost Bisbee strata. The lower part of the Cucurpe was derived dominantly from Middle Jurassic volcano-sedimentary successions. The upper part of the Cucurpe Formation was largely derived from syneruptive volcanic material equivalent to the Ko Vaya volcanic suite of southern Arizona and northern Sonora. Lowermost Bisbee strata were derived from Middle Jurassic arc rocks and exhumed Caborcan basement, Paleozoic–Lower Jurassic sedimentary cover, and Lower Cretaceous intermediate volcanic rocks. Revised stratigraphy of the Cucurpe-Tuape region indicates that several conglomeratic units, formerly interpreted as Late Jurassic pull-apart basin deposits, are not of Late Jurassic age.