Yavapai Orogeny Research Articles

Resolving pressure differences within the Grand Canyon Precambrian basement: Implications for Proterozoic tectonics

Abstract Burial pressures (depths) within mountain belts place fundamental constraints on the growth and stabilization of continental crust. We report precise metamorphic pressures for ca. 1.7 Ga rocks from the Upper Granite Gorge (UGG) of the Grand Canyon (southwestern United States) and, for the first time, resolve pressure variations across this continuous exposure of mid-crustal rocks. We applied quartz-in-garnet (QuiG) barometry and pseudosection modeling to determine pressures in domains (“blocks”) with evidence of higher and lower peak metamorphic grades. New pressure-temperature (P-T) paths constructed using this integrated approach show that a hot block sample reached 7 kbar and a cold block sample never surpassed 5 kbar, revealing an ~2 kbar P difference between hot and cold blocks and delineating distinct P-T paths for these domains in the UGG. Our findings suggest that hot and cold blocks were likely metamorphosed at different crustal levels within a pre-Yavapai, Paleoproterozoic orogen and were subsequently juxtaposed during and/or after the Yavapai Orogeny at mid-crustal levels. The deformation that produced differential vertical displacement of crustal blocks post-dated peak metamorphism and could reflect extensional collapse of a large orogen and/or renewed folding and thrusting at the Paleoproterozoic Laurentian plate margin.

Heterogeneous multi-stage accretionary orogenesis — Evidence from the Gunnison block in the Yavapai Province, southwest USA

Proterozoic rocks exposed in the southwestern U.S.A. represent one of the best examples of crustal growth by arc-related magmatism and accretionary orogenesis. Within the Southwest the 1.8–1.7 Ga Yavapai Province is widely regarded as a classic example of juvenile arc crust, however 1.8–2.5 Ga inherited zircon and Nd and Hf model ages have been recognized near Gunnison in central Colorado. These data have led to questions regarding the extent and nature of pre-1.8 Ga crustal material and the genesis of the Yavapai Province. We present evidence for a geochemically distinct, spatially restricted crustal block underlain by pre-1.8 Ga crust material (referred to here as the Gunnison block) in central to western Colorado within the Yavapai Province. The Gunnison block is characterized by 1.8–1.9 and 2.4–2.6 Ga inherited zircon, Pb isotopic systematics (μ = 9.8 ± 0.1, κ = 3.7 ± 0.1) elevated relative to 1.8 Ga depleted mantle values, 1.8–2.5 Ga Nd and Hf model ages, and a distinct pressure-temperature-time history. The geochemical data are consistent with mixing between juvenile 1.8 Ga and pre-1.8 Ga sources. The older crustal component is most similar to the isotopically enriched Mojave Province of eastern California and western Arizona, suggesting greater similarities between these provinces than previously recognized. Monazite and xenotime petrochronology indicate ca. 1.75–1.74, 1.72–1.69, 1.67, and 1.47–1.38 Ga tectono-metamorphic events. These data suggest that the Gunnison block accreted to other components of the Yavapai Province outboard of Laurentia at 1.75–1.74 Ga. The composite Yavapai Province was accreted to the margin of Laurentia during the 1.72–1.69 Ga Yavapai orogeny. Later overprinting is associated with the ∼1.68–1.60 Ga Mazatzal and ∼1.47–1.37 Ga Picuris orogenies. Identification of distinct crustal terranes within the Yavapai Province supports models involving multiple arcs and back-arcs that were progressively assembled prior to their accretion to Laurentia, perhaps akin to the present-day Banda Sea in Indonesia.

Geochemical evidence for evolving Proterozoic crustal thickness and orogenic styles in southwestern Laurentia

It has long been challenging for researchers to track the crustal thickness and mode(s) of crustal modification in ancient convergent margins, limiting evaluation of the tectonic styles and processes that modify continental crust during orogenesis. We present trace element igneous geochemical crustal thickness proxies that quantitatively track the crustal thickness evolution of the long-lived Proterozoic active margin in the southwestern U.S.A. We integrate these results with geobarometric data to constrain the mode of crustal modification. The data indicate a complex record of crustal thickness change in space and time and evolving orogenic styles. Geochemical proxies at 1.84–1.72 Ga are consistent with 20–40 km thick magmatic arcs that were locally thickened to ∼50 km during ∼1.75 Ga tectonism. During the Yavapai orogeny, 1.72–1.69 Ga, a ∼200-km-wide belt of 50-60 km thick crust extended from southern California to northern Colorado and was rapidly thinned and exhumed by ∼1.68 Ga. Crustal thickening and thinning during the Yavapai orogeny largely occurred by shortening and exhumation, respectively, in the upper 25 km of the crust. Subsequent 1.68–1.60 Ga tectonism involved crustal growth, local crustal thickening, and low-P, high-T metamorphism, consistent with extensional accretionary orogenesis. The 1.47–1.37 Ga Picuris orogeny was associated with 50–60 km thick crust across much of the Southwest and involved crustal shortening with ∼10 km of magmatic underplating. Advective heat from the emplacement of ferroan granites in the mid-crust likely contributed to elevated geothermal gradients and rheologically weakened the crust. Our results suggest evolving orogenic styles in the Southwest from 1.75–1.69 Ga short-lived crustal thickening associated with terrane accretion to 1.69–1.60 Ga largely extensional accretionary orogenesis, and regional, long-lived crustal thickening at 1.47–1.37 Ga involving extensive basaltic underplating. Contrasting with some recent hypotheses, our data document a complex middle Proterozoic record for the Southwest that was not orogenically quiescent or tectonically stagnant but involved complex mountain building styles.

Unraveling 800 Ma of pegmatite formation in the western Grenville Front tectonic Zone near Sudbury, Canada

The origin of pegmatites has been at the core of petrological research for decades, but despite much effort their origin remains controversial – protracted fractionation of a causative felsic magma versus anatexis of an appropriate protolith. To address this controversy, we present the results of U-Pb analyses (zircon (n = 774), monazite (n = 230), xenotime (n = 295)) for 32 well characterized pegmatites from an extensive swarm of felsic dike rocks outcropping, along a 12 km transect ca. 12 km south of Sudbury (Ontario, Canada) in the westernmost part of the Grenville Front Tectonic Zone (GFTZ). Collectively these rocks exhibit a remarkably large morphological, textural and mineralogical variation related to the crystallization of three distinct pegmatite-forming events that span 800 Ma. The derived concordant U-Pb ages of the dated phases coincide with the late Paleoproterozoic (ca. 1740 Ma) Yavapai orogeny, the Mesoproterozoic (ca. 1450–1430 Ma) Chieflakian event, and the early Neoproterozoic (ca. 1000–970 Ma) Grenville orogeny. Field observations and related geochemical data suggest the two older events are genetically related to regional magmatism (i.e., fractionation of a progenitor), whereas the Neoproterozoic pegmatites were generated via partial melting of an appropriate protolith at depth. The data therefore support a duality of models for pegmatite genesis. We emphasize the important role of imaging (CL and BSE) as an integral part of our protocol, as this revealed widespread coupled dissolution-precipitation (CDP) replacement textures and metamictization in both zircon and xenotime, the latter due to high U contents (i.e., >1000 pm). Interestingly, the Neoproterozoic pegmatites show similar U(±Th), Nb(±Ta) and REE enrichments like their contemporaneous Sveconorwegian counterparts. Many zircons record U-Pb system resetting at ca. 220–200 Ma which is possibly related to the far-field effects of the onset of the Central Atlantic Magmatic Province (CAMP) related to the opening of the Atlantic Ocean. Finally, this study shows that anatexis is a viable process of rare-element pegmatite formation, even in areas rich in potential parental granites, which suggests that anatectic rare-element pegmatites might be globally under-recognized.

Monazite and xenotime petrochronologic constraints on four Proterozoic tectonic episodes and ca. 1705 Ma age of the Uncompahgre Formation, southwestern Colorado, USA

Abstract The Proterozoic tectonic evolution of the southwestern USA remains incompletely understood due to limited constraints on the timing and conditions of the tectono-metamorphic phases and depositional age of metasedimentary successions. We integrated multi-scale compositional mapping, petrologic modeling, and in situ geochronology to constrain pressure-temperature-time paths from samples of Paleoproterozoic basement gneisses and overlying quartzites in southwestern Colorado, USA. Basement gneiss from the western Needle Mountains records metamorphic conditions of 600 °C at 0.75 GPa at 1764 ± 9 Ma and ~575 °C at 1741 ± 10 Ma. Gneiss sampled from drill core near Pagosa Springs, Colorado, records conditions of 700 °C at 1748 ± 9 Ma, 800 °C at 1.1 GPa at 1650 ± 40 Ma, 540 °C at 1570 ± 36 Ma, and 440 °C at 1424 ± 12 Ma. The Uncompahgre Formation was deposited at ca. 1705 Ma, as constrained by detrital monazite (1707 ± 8 Ma) and xenotime (1692 ± 40, 1725 ± 50 Ma), metamorphic xenotime (1650 ± 10 Ma), and published 40Ar/39Ar and detrital zircon data. Compositions of ca. 1705 Ma detrital monazite and xenotime are consistent with derivation from a garnet-bearing source in the Yavapai orogenic hinterland. The Vallecito Conglomerate and Uncompahgre Formation record macroscopic folding and greenschist-facies metamorphism at 1650 ± 10 Ma and temperatures of 270 °C to >570 °C at 1470–1400 Ma. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon geochronology yielded dates of 1775 ± 18 Ma from the Twilight Gneiss and 1696 ± 7 Ma from the Bakers Bridge Granite, supporting previous isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates. The Eolus Granite yielded a date of 1463 ± 6 Ma, which is older than previous 1.44–1.43 Ga ID-TIMS dates. The newly dated granite of Cataract Gulch is 1421 ± 12 Ma. In situ analysis of detrital and meta-morphic monazite and xenotime, igneous zircon, and quantitative thermobarometry, integrated with previously published constraints, indicate multiple tectonic episodes after the emplacement of 1800–1760 Ma arc-related rocks. The region experienced greenschist- to amphibolite-facies metamorphism (M1) from 1760 Ma to 1740 Ma, which was followed by the intrusion of granites at 1730–1695 Ma and deposition of the Uncompahgre Formation at ca. 1705 Ma, contemporaneous with the Yavapai orogeny. Metamorphism at 1680–1600 Ma was characterized by greenschist-facies conditions near Ouray, Colorado, and granulite-facies conditions near Pagosa Springs (M2) during the Mazatzal orogeny. From 1470 Ma to 1400 Ma, greenschist- to amphibolite-facies metamorphism (M3) and largely granitic plutonism occurred during the protracted Picuris orogeny. These results demonstrate the power of monazite and xenotime analyses to constrain depositional ages, provenance, and pressure-temperature-time (P-T-t) paths to resolve the compound orogenic history that is characteristic of most mountain belts.

Evaluating the Magnitudes of Weathering and Potassium Metasomatism in Paleosols: Examples from Proterozoic, Cambrian, and Cretaceous Paleosols in Midcontinental Laurentia

Six Proterozoic, two Cambrian, and two Cretaceous paleosols in the Lake Superior region of midcontinental Laurentia were investigated in detail. All but the Cretaceous paleosols experienced potassium metasomatism, which resulted in the precipitation of muscovite in Proterozoic paleosols or illite and microcline in Cambrian paleosols. A comparison of the magnitude of potassium metasomatism among the paleosols is provided by depth-normalized mass flux (DNMF), where DNMF=1000×[(mass flux)/(depth of weathering)], which normalizes for different thicknesses of weathering profiles. Average DNMF values for the total addition of K2O are 0.98 ± 0.19 mol cm−3 for the Proterozoic paleosols and 1.27 ± 0.06 mol cm−3 for the Cambrian paleosols. The ages of potassium metasomatism were determined by 40Ar/39Ar isotopic dating of metasomatic muscovite in the Proterozoic McGrath, Ville Marie, and Baraboo paleosols, which yielded ages of 1742 ± 3, 1589 ± 3, and 1467 ± 11 Ma, respectively, the former being coeval with the Yavapai orogeny and the latter with the Baraboo orogeny. Metasomatic microcline in the Cambrian Trempealeau paleosol yielded a plateau age of 488.0 ± 1.0 Ma, which corresponds to the age of the Cambrian-Ordovician boundary. SiO2, CaO, and Na2O were substantially removed from the paleosols by weathering, as was K2O (before metasomatism). The average total amount of SiO2, CaO, Na2O, and K2O removed was 17.6% ± 1.9% from six Proterozoic paleosols, 28.5% ± 4.2% from two Cambrian paleosols, 36.5% ± 8.6% from two Cretaceous paleosols, and 34.2% ± 2.7% from five modern soils. The greater magnitude of weathering in the Phanerozoic weathering profiles compared with the Proterozoic ones, despite lower levels of CO2 in the Phanerozoic atmosphere, may reflect the emergence of land plants at ∼500 Ma and their profound effects on weathering.

Growth, overprinting, and stabilization of Proterozoic provinces in the southern Lake Superior region

New geochronologic data in the southern Lake Superior region provide key information on the timing and nature of tectonic activity that pre-and post-date initial Paleoproterozoic growth of Laurentia during the geon 18 Penokean orogeny. The obducted Pembine ophiolite formed along the edge of a Paleoproterozoic ocean basin at least 30 m.y. prior to Penokean island arc/microcontinent accretion beginning at 1860 Ma. Following Penokean orogenesis, intrusion of mafic dikes at 1817 ± 2 Ma indicate a period of extension that coincided with a 30 m.y. gap in orogenic felsic magmatism at 1835–1805 Ma (between the Penokean and Yavapai orogenies) and likely represents relaxation of Penokean compression and a tectonic switch to intra-arc extension related to initiation of Yavapai subduction. Subsequent Yavapai arc accretion (1750–1720 Ma) resulted in pervasive ductile deformation of the dikes and host rocks at temperatures of ~700 °C, previously attributed to Penokean deformation. Geon 16 Mazatzal overprinting of the accreted Penokean and Yavapai provinces was widespread but of overall lower metamorphic grade (greenschist facies), and the thermal effects of the 1476–1470 Ma shallow level Wolf River batholith was limited to a 10–15 km wide contact zone surrounding the intrusion.In contrast to the Archean Superior Province to the north, Paleoproterozoic terranes in the southern Lake Superior area experienced widespread low-temperature reheating and cooling of shallow crustal levels at ca. 1.1–1.0 Ga attributed primarily to magmatic underplating with little subsequent Neoproterozoic exhumation. In the southern Lake Superior region widespread magmatic underplating likely thickened, strengthened, and stabilized Proterozoic Penokean-Mazatzal lithosphere but destabilized Archean cratonized Superior Province lithosphere to the north.

Neoarchean and Paleoproterozoic events in the Minnesota River Valley subprovince, with implications for southern Superior craton evolution and correlation

The lithologic diversity and protracted geologic history of the Minnesota River Valley (MRV) gneiss terrane at the southern margin of the Archean Superior Province provide key perspectives on the growth and modification of this craton. Innovations in geochronology, specifically the application of the chemical abrasion technique to remove Pb-loss domains in zircon, and the tandem use of in situ geochemistry and precise isotope dilution age analysis for establishing the petrologic context of radioisotopic ages, are yielding new insights into these old rocks. First, U-Pb geochronology on a variety of plutonic to mesoscale intrusive rocks from the Morton and Montevideo blocks of the MRV provide precise constraints on the Neoarchean (2603–2584 Ma) Sacred Heart orogeny, which sutured the Mesoarchean gneisses of the MRV to the southern margin of the Superior craton in an episode of contractional deformation, high-grade metamorphism, and voluminous plutonism. Second, we report the first radioisotopic age constraints on the St. Leo and Taunton belts of greenstone and supracrustal rocks within the Yellow Medicine shear zone, an inferred lithosphere-scale structure juxtaposed between the Morton and Montevideo gneisses. Titanite from a metadiorite intrusion into the St. Leo belt yields igneous (∼2539 Ma) and metamorphic (∼2510 Ma) ages, confirming the Archean provenance of the host greenstones and revealing a latest Neoarchean episode of magmatism and deformation focused along and within the shear zone. Third, a new ∼1781 Ma U-Pb zircon age for one of a number of small granitic plugs in the southern Montevideo block confirms its correlation to the more voluminous East-Central Minnesota Batholith and its origin in the Yavapai orogeny. Again later magmatism was focused along the Yellow Medicine shear zone suggesting the lithosphere-scale significance of that structure. This more resolved history for the Neoarchean to Proterozoic evolution of the southern Superior craton provides new opportunities to test Archean craton correlations and reconstructions, including links to the Wyoming and Slave cratons.

The Paleoproterozoic Vishnu basin in southwestern Laurentia: Implications for supercontinent reconstructions, crustal growth, and the origin of the Mojave crustal province

The formation of the Mojave crustal province has been a persistent enigma in models of the Proterozoic tectonic history of southwestern Laurentia. It is composed of similarly-aged 1.8–1.7 Ga rocks as the adjacent Yavapai province, yet shows evidence of much older (>2.2 Ga) lithospheric components in all isotopic systems. We present >700 new U-Pb analyses and >350 new Lu-Hf analyses of zircon from the oldest metasedimentary and plutonic rocks of the Mojave province to better understand its origin and evolution. Six metasedimentary rocks have detrital zircon age populations dominated by ∼1.87 and 2.4–2.7 Ga grains. This age distribution is like the Vishnu Schist in Grand Canyon and we suggest that together they comprise a regional turbidite basin that we name the Vishnu basin. Cross cutting relationships indicate that deposition of the Vishnu basin proceeded from west to east (present coordinates) from ∼1.8 to 1.75 Ga. The Vishnu basin extends from central Arizona to the Transverse Ranges in California and possibly beyond the present boundaries of Laurentia to previously adjacent cratonic blocks. We propose the Mawson continent as the source of Vishnu basin detritus, and hence favor Nuna accretion at ∼1.8 Ga. Paleoproterozoic plutons that intrude the Vishnu basin sampled in this study range in age from 1791 ± 15 to 1691 ± 15 Ma. Plutons show a systematic change in Hf-isotope composition through time and space. The oldest plutons in the western Mojave province have the most isotopically evolved signatures and contain inherited zircon cores and xenocrysts with age and Hf-isotope characteristics that suggest they were derived from Vishnu basin sediments and/or 1.8–2.7 Ga lower crust. The Hf-isotope composition of plutons becomes more radiogenic (juvenile) from west-to-east and from old-to-young. The magnitude of Hf-isotope variation requires increased influence of depleted mantle sources through time. Hf-isotope compositions of the younger 1.7–1.68 Ga syn-to-post orogenic granites show more evolved compositions attributed to lower crustal melting due to crustal thickening during the Yavapai orogeny.

Redefining the metamorphic history of the oldest rocks in the southern Rocky Mountains

Proterozoic rocks exposed in the Rocky Mountains of New Mexico record the history of the assembly of North America, providing insight into crustal growth, accretion, and recycling. Here, we present six well-constrained Lu-Hf garnet ages showing that regional amphibolite-facies metamorphism and deformation occurred between 1.46 and 1.40 Ga. The samples come from the kyanite, sillimanite, and andalusite zones of the “Al 2 SiO 5 triple-point terrane” of northern New Mexico. Porphyroblast-matrix textures in dated samples provide definitive evidence for garnet growth during three phases of deformation associated with crustal thickening during the development of a regional-scale north-vergent contractional orogenic belt. The development of first-generation deformation fabrics is constrained to a period between 1.46 and ca. 1.45 Ga; second-generation deformation fabrics are constrained to the period 1.42−1.40 Ga; and third-generation fabrics were formed after ca. 1.40 Ga. Our results demonstrate that crustal-scale structures and regional metamorphism in northern New Mexico are both the result of a Mesoproterozoic orogenic event, the Picuris orogeny. We found no evidence for amphibolite-facies metamorphism during the Paleoproterozoic Mazatzal or Yavapai orogenies in northern New Mexico.

New structural, metamorphic, and U–Pb geochronological constraints on the Blezardian Orogeny and Yavapai Orogeny in the Southern Province, Sudbury, Canada

New structural and geochronological data are presented for two orogenic events, the Blezardian and Yavapai orogenies, which affected the Paleoproterozoic Southern Province near Sudbury, Ontario, Canada. The Southern Province comprises ca. 2452 Ma metavolcanic rocks and metasedimentary rocks of the Huronian Supergroup, which were deposited along the southern margin of the Archean Superior craton during its evolution from a rifted to passive continental margin. Emplacement of the ca. 2415 Ma Creighton pluton during rifting was followed by its deformation and the development of a penetrative gneissic fabric during the ca. 2415 − ca. 2219 Ma Blezardian Orogeny. New laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) U–Pb zircon ages of 2343 ± 17 and 2344 ± 47 Ma on two granitic dikes that cut this fabric provide a new minimum age of ca. 2.34 Ga for the Blezardian Orogeny. The Sudbury area was then impacted by a large extraterrestrial bolide at ca. 1.85 Ga and deformed during the Penokean Orogeny. The southern part of the Southern Province was later reworked by regional folding and north-directed thrusting during the younger 1.7 Ga Yavapai Orogeny. The 1744 ± 29 Ma Eden Lake Complex was emplaced and deformed during this event, which produced a strong foliation overprinting the complex. The foliation formed at pressures of 2.8–4 kbar (1 kbar = 100 MPa) and temperatures of 540–565 °C and was intruded by a weakly deformed 1704 ± 13 Ma old granitic dike, bracketing the Yavapai event between 1744 ± 29 and 1704 ± 13 Ma in the Sudbury segment of the Southern Province. Crustal thickening associated with the Yavapai event resulted, locally, in minor pressure increases before or during regional metamorphism as revealed by phase equilibria modeling in the Raft Lake area; this evolution may be recorded elsewhere in the Ontario segment of the Southern Province.

Correlating Proterozoic synorogenic metasedimentary successions in southwestern Laurentia: New insights from detrital zircon U-Pb geochronology of Paleoproterozoic quartzite and metaconglomerate in central and northern Colorado, U.S.A.

Detrital zircon ages from quartzite and metaconglomerate exposed in the Park Range, Front Range, and Sawatch Range of northern and central Colorado reveal new information about age and provenance trends within the Yavapai province of southwestern Laurentia and provide a critical test of regional correlations. Six samples from the three exposure areas—the Lester Mountain area in the Park Range, Coal Creek area in the Front Range, and Collegiate Peaks area in the Sawatch Range—are dominated by Paleoproterozoic detrital zircon that define a relatively narrow range of peak ages between 1772 and 1701 Ma. The unimodal character of most age spectra and the age of the dominant age-probability peaks indicate that the metasedimentary successions were derived largely from local sources within the ca. 1.78–1.70-Ga Yavapai province. Age-probability peaks between 1830 Ma and 2716 Ma are attributed to older source regions to the north and northeast such as the Trans-Hudson orogen, Black Hills, or Wyoming province. However, the percentage of older grains is relatively minor and decreases to almost zero from north to south. Maximum depositional ages constrained by the youngest age populations are 1763 Ma, 1717 Ma, and 1701 Ma for the respective localities from north to south. All of the metasedimentary successions were deformed and metamorphosed after deposition, and quartzite at one locality is intruded by ca. 1672-Ma plutons. On the basis of similarities between outcrop characteristics, structural style, and comparison of detrital zircon age spectra, we correlate the two southern localities with a regional suite of quartzite successions deposited ca. 1.70 Ga following the culmination of the Yavapai orogeny. The northern succession represents an earlier cycle of sedimentation predating ca. 1750-Ma deformation in the northern Yavapai province. The southward progression of ages is consistent with regional tectonic models for the evolution of the Paleoproterozoic accretionary provinces in southern Laurentia, and the multiple cycles of sedimentation suggest that basin formation and collapse were important processes in the tectonic evolution of the continent.

Tectonic model for the Proterozoic growth of North America

This paper presents a plate-scale model for the Precambrian growth and evolution of the North American continent. The core of the North American continent (Canadian shield) came together in the Paleoproterozoic (2.0–1.8 Ga) by plate collisions of Archean continents (Slave with Rae-Hearne, then Rae-Hearne with Superior) as well as smaller Archean continental fragments (Wyoming, Medicine Hat, Sask, Marshfield, Nain cratons). The resulting Trans-Hudson orogen was a collisional belt similar in scale to the modern Himalayas. It contains mainly reworked Archean crust, but remnants of juvenile volcanic belts are preserved between Archean masses. The thick, buoyant, and compositionally depleted mantle lithosphere that now underlies North America, although dominantly of Archean age, took its present shape by processes of collisional orogenesis and likely has a scale of mantle heterogeneity similar to that exhibited in the overlying crust. In marked contrast, lithosphere of southern North America (much of the conti nental United States) was built by progressive addition of a series of dominantly juvenile vol canic arcs and oceanic terranes accreted along a long-lived southern (present coordinates) plate margin. Early juvenile additions (Pembine-Wausau, Elves Chasmarcs) formed at the same time (1.84–1.82 Ga) the core was assembling. Following final assembly of the Archean and Paleoproterozoic core of North America by 1.8 Ga, major accretionary provinces (defined mainly by isotopic model ages) were added by arc-continent accretion, analogous to present-day convergence between Australia and Indonesia. Also similar to Indonesia, some accreted terranes contain older continental crustal material [Archean(?) Mojavia], but the extent and geometry of older crust are not well known. Accretionary provinces are composed of numerous 10 to 100 km scale terranes or blocks, separated by shear zones, some of which had compound histories as terrane sutures and later crustal-assembly structures. Major northeast-trending provinces are the Yavapai province (1.80–1.70 Ga), welded to North America during the 1.71–1.68 Ga Yavapai orogeny; the Mazatzal province (1.70–1.65 Ga), added during the 1.65–1.60 Ga Mazatzal orogeny; the Granite-Rhyolite province (1.50–1.30 Ga), added during the 1.45–1.30 Ga tectonic event associated with A-type intracratonic magmatism; and the Llano-Grenville province (1.30–1.00 Ga), added during the 1.30–0.95 Ga broader Grenville orogeny. During each episode of addition of juvenile lithosphere, the transformation of juvenile crust into stable continental lithosphere was facilitated by voluminous granitoid plutonism that stitched new and existing orogenic boundaries. Slab roll back created transient extensional basins (1.70 and 1.65 Ga) in which Paleoproterozoic quartzite-rhyolite successions were deposited, then thrust imbricated as basins were inverted. The lithospheric collage that formed from dominantly juvenile terrane accretion and stabilization (1.8–1.0 Ga) makes up about half of the present-day North American continent. Throughout (and as a result of) this long-lived convergent cycle, mantle lithosphere below the accretionary provinces was more hydrous, fertile, and relatively weak compared to mantle lithosphere under the Archean core.

Proterozoic tectonic evolution of the Sangre de Cristo Mountains, southern Colorado, U.S.A.

Field studies and U-Pb geochronology in the Sangre de Cristo Mountains, southern Colorado, provide new constraints on the Proterozoic tectonic evolution of southern Laurentia. Protoliths for basement gneisses and amphibolites were formed in an arc environment and underwent early penetrative deformation and metamorphism (D1 and M1) during formation of the Yavapai province. D1 deformation produced penetrative, subvertical, northwest-striking fabrics (S1) in rocks exposed throughout the range and is interpreted to have occurred during long-lived arc formation and accretion across northwest-striking tectonic boundaries. The ages of D1 and M1 are constrained by a suite of 1750–1730-Ma calc-alkaline intrusions in the southern part of the range and might have occurred as late as ca. 1710 Ma in the northern part of the range. The northeast-striking tectonic grain that was developed regionally during the culmination of the Yavapai orogeny is not recognized locally. Post-orogenic granitoid plutons were emplaced at 1695±2 Ma and 1682±3 Ma, broadly coeval with deposition of locally derived quartzite at the surface. Magmatism and sedimentation during this time are interpreted to represent contemporaneous responses to crustal extension during the ca. 60-m.y. inter-orogenic period between the Yavapai and Mazatzal orogenic events. D2 deformation is interpreted to represent the Mazatzal orogeny locally, and involved northwest-directed shortening and dextral shear localized along subvertical, northeast-trending high-strain zones. D2 was accompanied by amphibolite-facies metamorphism (M2) at 1637±6 Ma, and the quartzite is inferred to have been deformed during this time. Mesoproterozoic deformation (D3) produced a northeast-striking, subvertical tectonic foliation and localized shear zones between 1420 and 1412 Ma. D3 deformation was bracketed by the emplacement of two newly dated granitic intrusions at 1434±2 Ma and 1407±6 Ma. The map-scale geometry of these intrusions and coeval deformational fabrics suggest that ca. 1.4-Ga granites were emplaced into a broadly compressional stress field during subhorizontal northwest–southeast shortening. These new data and observations indicate that ca. 1.4-Ga granites are not anorogenic, consistent with tectonic models suggesting that widespread magmatism was broadly synchronous with intracontinental orogenesis at ca. 1.4 Ga.

Three Proterozoic Orogenic Episodes and an Intervening Exhumation Event in the Black Canyon of the Gunnison Region, Colorado

U/Pb zircon/titanite geochronology, in situ monazite geochronology, and 40Ar/39Ar thermochronology provide an unusually complete data set for reconstructing the tectonic history of Proterozoic rocks exposed in the Black Canyon, Gunnison, Colorado. These new geochronologic data record three protracted orogenic episodes and an exhumation event between orogenic pulses: (1) Yavapai orogeny (1741–1689 Ma), (2) exhumation marked by an angular unconformity beneath post‐Yavapai, pre‐Mazatzal quartzites, (3) Mazatzal orogeny (postquartzite deposition), and (4) 1434–1403 Ma intracratonic tectonism. Supracrustal rocks of the Black Canyon succession were deposited or crystallized at or prior to $$1741\pm 4$$ Ma and were intruded by the $$1713\pm 2$$ Ma Pitts Meadow granodiorite. Paleoproterozoic high‐temperature metamorphism (>650°C) associated with the Yavapai orogeny occurred between 1741 and 1690 Ma. Deposition of interorogenic quartzites took place after ∼1700 Ma. The Vernal Mesa monzogranite was emplaced at $$1434\pm 2$$ Ma followed by metamorphism ($$\sim 600^{\circ }\pm 50^{\circ }$$C and $$\sim 3\pm 1$$ kbar) at $$\leq 1403\pm 23$$ Ma. 40Ar/39Ar thermochronology records Mesoproterozoic middle crustal temperatures of 350°–500°C, with the highest temperatures occurring near the Vernal Mesa monzogranite and the NE‐striking Black Canyon shear zone. The area cooled through 350°C by ∼1385 Ma but variably cooled through 300°C from 1370 to 1100 Ma, suggesting long‐term residence of rocks above the 250°C isotherm at ∼10 km crustal depths. When these results are combined with geologic data to construct generalized pressure/temperature/time/deformation paths (PTtD), a new template for the evolution of Proterozoic rocks of southwestern Colorado and the southwestern United states emerges.

Age, provenance, and tectonic setting of Paleoproterozoic quartzite successions in the southwestern United States

New field studies combined with U-Pb zircon geochronology constrain the ages of deposition and sedimentary provenance of Paleoproterozoic quartzite successions exposed in the southwestern United States. Orthoquartzites were deposited in short-lived basins at two times (ca. 1.70 and 1.65 Ga) during crustal assembly of southern Laurentia. The more voluminous ca. 1.70 Ga successions occur in southern Colorado, northern New Mexico, and central Arizona and are interpreted here to be time correlative, though not necessarily deposited in the same basins. Detrital zircon from quartzites and metaconglomerates exposed in southern Colorado and northern New Mexico is characterized by a single population with a relatively narrow range of ages (1.80–1.70 Ga) and minimal Archean input (<5% of grains analyzed). Peak detrital zircon ages (1.76–1.70 Ga) vary slightly from location to location and mimic the age of underlying basement. Unimodal detrital populations suggest local sources and a first-cycle origin of the orthoquartzites within a short time interval (1.70–1.68 Ga) during unroofing of local underlying basement. The maximum age of quartzite exposed at Blue Ridge, Colorado, is constrained by the 1705–1698 Ma coarse-grained granitoid basement on which quartzite was deposited unconformably. The minimum age of Ortega Formation quartzite (New Mexico) is constrained by ca. 1680–1670 Ma metamorphic monazite overgrowths. These dates agree with direct ages on the lower Mazatzal Group, Arizona, and suggest that orthoquartzite deposition occurred over a wide region during and soon after the ca. 1.70 Ga Yavapai orogeny. Regional structural arguments and the thrust style of quartzite deformation suggest that the metasedimentary successions were deformed during the ca. 1.66–1.60 Ga Mazatzal orogeny, thus making them important time markers separating the Yavapai and Mazatzal orogenic events. Our model for syntectonic deposition involves extensional basin development followed by thrust closure, possibly due to opening and closing of slab rollback basins related to outboard subduction. The first-cycle origin of orthoquartzites near the end of the arc collisions of the Yavapai orogeny seems to contrast sharply with their extreme compositional maturity. This can be explained in terms of protracted, extreme diagenesis and/or special environmental influences that enhanced chemical weathering but were unique to the transitional atmosphere and ocean chemistry of the Proterozoic. Similarities among quartzites exposed throughout the southwestern United States and along the Laurentian margin suggest that they represent a widespread regional, and perhaps global, episode of sedimentation involving a distinctive syntectonic setting and unique climatic conditions, a combination that might make these units a signature lithology for Paleoproterozoic time.

Paleoproterozoic tectonic history of the Cerbat Mountains, northwestern Arizona: Implications for crustal assembly in the southwestern United States

Structural mapping, metamorphic analysis, and U-Pb geochronology from the Cerbat Mountains of northwestern Arizona place new constraints on the tectonic significance and timing of the boundary between the Mojave and Yavapai Proterozoic crustal provinces in the southwestern United States. The Cerbat Mountains are the easternmost range that exhibits wholly Mojave Pb isotopic signatures, yet their Paleoproterozoic structural history is strikingly similar to that of the Yavapai province. Two pervasive deformational events are recognized in the Cerbat Mountains. D1 fabrics are well preserved in the northern Cerbat Mountains, and are characterized by a north-northwest−striking, moderately northeast-dipping foliation (S1) that is axial planar to macroscopic recumbent folds that we interpret to be west to southwest vergent. Similar structures have been documented locally in the Yavapai province. D1 is bracketed between 1740 and 1721 Ma in the Cerbat Mountains on the basis of U-Pb zircon ages of the Big Wash granite (1737 ± 4.3 Ma) and the Diana and Chloride granites (1719 ± 1.2 and 1721 ± 2.4 Ma, respectively). D2 fabrics dominate the central and southern Cerbat Mountains and include a subvertical, northeast-striking foliation that truncates and transposes S1. D2 is bracketed between 1721 and 1682 Ma, on the basis of U-Pb ages of the Diana and Chloride granites and post-D2 granite dikes in the eastern Cerbat Mountains (1682.5 ± 2.4 Ma). The structural style, orientation, and timing of D1 and D2 fabrics in the Cerbat Mountains are identical to those of the Yavapai province. Supracrustal rocks within the Cerbat Mountains were subjected to two periods of metamorphism that correspond temporally to the two periods of deformation. The early phase occurred at 675–725 °C and 5–6 kilobars. The later phase occurred at 650– 700 °C and 3.5–4.5 kilobars. We propose that the Mojave and Yavapai provinces were sutured together between ca. 1740 and 1720 Ma during regional D1 deformation. Collisional orogenesis in the eastern Mojave province may have resulted in the tectonic burial of rocks in the Cerbat Mountains to depths of 20 km. D2, between 1720 and 1682 Ma, corresponds to the widespread Yavapai orogeny, and is interpreted to record accretion of the amalgamated Mojave-Yavapai terrane to Proterozoic terranes that are now located in Colorado.

Medicine Bow orogeny: Timing of deformation and model of crustal structure produced during continent-arc collision, ca. 1.78 Ga, southeastern Wyoming

A four-dimensional model for the evolution of the late-Paleoproterozoic Cheyenne belt arc-continent suture is presented based on available geologic mapping, structural analysis, geophysical constraints, geobarometry, geochronology, and isotopic data. All of the data are consistent with a southeast-dipping suture and deformation that lasted from 1.78 Ga to at least 1.76 Ga, and possibly as late as 1.74 Ga. Archean crustal components and/or detritus were subducted at least 30 to 70 km south of the trace of the suture. There is considerable variation in crustal structure and tectonic evolution along strike of the Cheyenne belt. Thick-skinned, intracratonic uplift along the Laramie Peak shear zone and synorogenic emplacement of the Horse Creek anorthosite complex occurred in the east, whereas low-grade metamorphism and late cataclastic thrust faulting occurred in the west. Some of this lateral variation may reflect the influence of preexisting crustal features such as high-angle normal faults and crustal heterogeneities related to ca. 2.0-Ga rifting, whereas other differences may reflect variations in collision geometry. The lithospheric architecture of this arc-continent suture created compositional and structural anisotropies that influenced later deformation and magmatism, such as the generation and emplacement of the 1.43-Ga Laramie anorthosite complex and location of Paleozoic diamond-bearing diatremes. In this paper, the term “Medicine Bow orogeny” is proposed to describe the ca. 1.78-Ga arc-continent collision that formed the Cheyenne belt suture, and the subsequent structural evolution of the orogenic zone, which may have continued to ca. 1.74 Ga. The orogenic belt trends from southeastern Wyoming to northeastern Nevada, a distance of ∼1900 km. This term is invoked to differentiate the tectonic history along the Cheyenne belt from both the Yavapai orogeny to the south, and Central Plains orogeny to the east, because these orogenies include younger rocks and younger deformation. The arc terrane involved in the Medicine Bow orogeny is probably 50 to 100 km wide, and it makes up the basement of northern Colorado and continues at least as far south as the Soda Creek-Fish Creek shear zone in north-central Colorado. Accretion during the Medicine Bow orogeny represents a substantial addition to the North American continent.

Pseudostratigraphy and origin of the Early Proterozoic Payson ophiolite, central Arizona

The Payson ophiolite (ca. 1.73 Ga), exposed within the Early Proterozoic orogenic belt of central Arizona, is a shallow-dipping, pseudostratigraphic sequence of gabbro, sheeted dikes, and submarine volcanic rocks, partly disjointed by later intrusion and deformation. An older basement complex occurs as roof pendants in the gabbro and screens in the sheeted dike complex and was tilted and eroded prior to development of the ophiolite. Gabbro-dike mingling and mutual intrusion in the transition from gabbro to sheeted dikes indicates that the dikes are rooted in the gabbro. Analysis of detailed measured sections of well-exposed sheeted dikes (600 m) reveals 90%–100% dikes with lateral variations in the proportions of tonalitic or dacitic dikes and basement screens. The transition from sheeted dikes to submarine basalts is abrupt and marked by a stratigraphically continuous zone of intensely altered rocks. The sheeted dike complex, pseudostratigraphic structure, and synmagmatic hydrothermal alteration of the Payson ophiolite are diagnostic of a crustal section formed by sea-floor spreading. The Payson ophiolite intrudes, and is intruded by, arc granitoids and is overlain by arc-derived volcanic and sedimentary rocks. A model of an intra-arc basin formed along an arc parallel strike-slip fault is proposed to account for (1) screens of older arc crust, (2) inferred arc-parallel extension, and (3) juxtaposition of the ophiolite with a distinct arc terrane prior to regional convergent deformation and accretion of the arc to North America during the Yavapai orogeny (ca. 1.70 Ga).

A Summary of the Orogenic Epochs in the Geologic History of North America

Next article FreeA Summary of the Orogenic Epochs in the Geologic History of North AmericaEliot BlackwelderEliot Blackwelder Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 22, Number 7Oct. - Nov., 1914 Article DOIhttps://doi.org/10.1086/622180 Views: 389Total views on this site Citations: 17Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Arlo Brandon Weil, Adolph Yonkee The Laramide orogeny: Current understanding of the structural style, timing, and spatial distribution of the classic foreland thick-skinned tectonic system, (Jan 2023): 707–771.https://doi.org/10.1130/2022.1220(33)Tsilavo Raharimahefa, Bruno Lafrance, Douglas K. Tinkham, Fernando Corfu New structural, metamorphic, and U–Pb geochronological constraints on the Blezardian Orogeny and Yavapai Orogeny in the Southern Province, Sudbury, Canada, Canadian Journal of Earth Sciences 51, no.88 (Aug 2014): 750–774.https://doi.org/10.1139/cjes-2014-0025J. J. Schwartz, A. W. Snoke, F. Cordey, K. Johnson, C. D. Frost, C. G. Barnes, T. A. LaMaskin, J. L. Wooden Late Jurassic magmatism, metamorphism, and deformation in the Blue Mountains Province, northeast Oregon, Geological Society of America Bulletin 123, no.9-109-10 (Jun 2011): 2083–2111.https://doi.org/10.1130/B30327.1Arthur W. Snoke, Calvin G. Barnes The development of tectonic concepts for the Klamath Mountains province, California and Oregon, (Jan 2006): 1–29.https://doi.org/10.1130/2006.2410(01)Gary G. Gray Structural and tectonic evolution of the western Jurassic belt along the Klamath River corridor, Klamath Mountains, California, (Jan 2006): 141–151.https://doi.org/10.1130/2006.2410(07)Charlotte M. Allen, Calvin G. Barnes Ages and some cryptic sources of Mesozoic plutonic rocks in the Klamath Mountains, California and Oregon, (Jan 2006): 223–245.https://doi.org/10.1130/2006.2410(11)Kevin R. Chamberlain, Arthur W. Snoke, Calvin G. Barnes, Jonathan C. Bushey New U-Pb radiometric dates of the Bear Mountain intrusive complex, Klamath Mountains, California, (Jan 2006): 317–332.https://doi.org/10.1130/2006.2410(15)Bradley R. Hacker, Mary M. Donato, Calvin G. Barnes, M. O. McWilliams, W. G. Ernst Timescales of orogeny: Jurassic construction of the Klamath Mountains, Tectonics 14, no.33 (Jul 2010): 677–703.https://doi.org/10.1029/94TC02454Gregory D. Harper, Jason B. Saleeby, Matthew Heizler Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California-Oregon: U/Pb zircon and 40 Ar/ 39 Ar geochronology, Journal of Geophysical Research: Solid Earth 99, no.B3B3 (Sep 2012): 4293–4321.https://doi.org/10.1029/93JB02061Steven H. Edelman Relationships between kinematics of arc-continent collision and kinematics of thrust faults, folds, shear zones, and foliations in the Nevadan orogen, northern Sierra Nevada, California, Tectonophysics 191, no.3-43-4 (Jun 1991): 223–236.https://doi.org/10.1016/0040-1951(91)90058-ZGregory D. Harper, James E. Wright Middle to Late Jurassic tectonic evolution of the Klamath Mountains, California-Oregon, Tectonics 3, no.77 (Jul 2010): 759–772.https://doi.org/10.1029/TC003i007p00759Jason B. Saleeby, Gregory D. Harper, Arthur W. Snoke, Warren D. Sharp Time relations and structural-stratigraphic patterns in ophiolite accretion, west central Klamath Mountains, California, Journal of Geophysical Research 87, no.B5B5 (Jan 1982): 3831.https://doi.org/10.1029/JB087iB05p03831Jason B. Saleeby, Cathy Busby-Spera, J. S. Oldow, G. C. Dunne, J. E. Wright, D. S. Cowan, N. W. Walker, R. W. Allmendinger Early Mesozoic tectonic evolution of the western U.S. Cordillera, (): 107–38.https://doi.org/10.1130/DNAG-GNA-G3.107W. B. Harland Interpretation of stratigraphical ages in orogenic belts, Geological Society, London, Special Publications 3, no.11 (Jun 2022): 115–135.https://doi.org/10.1144/GSL.SP.1969.003.01.07Hans Bürgl The orogenesis in the andean system of colombia, Tectonophysics 4, no.4-64-6 (Oct 1967): 429–443.https://doi.org/10.1016/0040-1951(67)90009-1R. H. Dott Mesozoic-cenozoic tectonic history of the southwestern Oregon coast in relation to cordilleran orogenesis, Journal of Geophysical Research 70, no.1818 (Dec 2012): 4687–4707.https://doi.org/10.1029/JZ070i018p04687Richard A. Sonder Die erdgeschichtlichen Diastrophismen im Lichte der Kontraktionslehre, Geologische Rundschau 13, no.33 (Nov 1922): 217–272.https://doi.org/10.1007/BF01799789