Eastern Klamath Mountains Research Articles

Nature and timing of Late Devonian–early Mississippian island-arc magmatism in the Northern Sierra terrane and implications for regional Paleozoic plate tectonics

Abstract The Northern Sierra terrane is one of a series of Paleozoic terranes outboard of the western Laurentian margin that contain lithotectonic elements generally considered to have originated in settings far removed from their present relative locations. The Lower to Middle Paleozoic Shoo Fly Complex makes up the oldest rocks in the terrane and consists partly of thrust-imbricated deep-marine sedimentary strata having detrital zircon age signatures consistent with derivation from the northwestern Laurentian margin. The thrust package is structurally overlain by the Sierra City mélange, which formed within a mid-Paleozoic subduction zone and contains tectonic blocks of Ediacaran tonalite and sandstone with Proterozoic to early Paleozoic detrital zircon populations having age spectra pointing to a non–western Laurentian source. Island-arc volcanic rocks of the Upper Devonian Sierra Buttes Formation unconformably overlie the Shoo Fly Complex and are spatially associated with the Bowman Lake batholith, Wolf Creek granite stock, and smaller hypabyssal felsic bodies that intrude the Shoo Fly Complex. Here, we report new results from U-Pb sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) dating of 15 samples of the volcanic and intrusive rocks, along with geochemical studies of the dated units. In addition, we report U-Pb laser ablation–inductively coupled plasma–mass spectrometry ages for 50 detrital zircons from a feldspathic sandstone block in the Sierra City mélange, which yielded abundant Ordovician to Early Devonian (ca. 480–390 Ma) ages. Ten samples from the composite Bowman Lake batholith, which cuts some of the main thrusts in the Shoo Fly Complex, yielded an age range of 371 ± 9 Ma to 353 ± 3 Ma; felsic tuff in the Sierra Buttes Formation yielded an age of 363 ± 7 Ma; and three felsic hypabyssal bodies intruded into the Sierra City mélange yielded ages of 369 ± 4 Ma to 358 ± 3 Ma. These data provide a younger age limit for assembly of the Shoo Fly Complex and indicate that arc magmatism in the Northern Sierra terrane began with a major pulse of Late Devonian (Famennian) igneous activity. The Wolf Creek stock yielded an age of 352 ± 3 Ma, showing that the felsic magmatism extended into the early Mississippian. All of these rocks have similar geochemical features with arc-type trace-element signatures, consistent with the interpretation that they constitute a petrogenetically linked volcano-plutonic system. Field evidence shows that the felsic hypabyssal intrusions in the Sierra City mélange were intruded while parts of it were still unlithified, indicating that a relatively narrow time span separated subduction-related deformation in the Shoo Fly Complex and onset of Late Devonian arc magmatism. Following recent models for Paleozoic terrane assembly in the western Cordillera, we infer that the Shoo Fly Complex together with strata in the Roberts Mountains allochthon in Nevada migrated south along a sinistral transform boundary prior to the onset of arc magmatism in the Northern Sierra terrane. We suggest that the Shoo Fly Complex arrived close to the western Laurentian margin at the same time as the Roberts Mountains allochthon was thrust over the passive margin during the Late Devonian–early Mississippian Antler orogeny. This led to a change in plate kinematics that caused development of a west-facing Late Devonian island arc on the Shoo Fly Complex. Due to slab rollback, the arc front migrated onto parts of the Sierra City mélange that had only recently been incorporated into the accretionary complex. In the mélange, blocks of Ediacaran tonalite, as well as sandstones having detrital zircon populations with non–western Laurentian sources, may have been derived from the Yreka and Trinity terranes in the eastern Klamath Mountains, where similar rock types occur. If so, this suggests that these Klamath terranes were in close proximity to the developing accretionary complex in the Northern Sierra terrane in the Late Devonian.

Dilution and propagation of provenance trends in sand and mud: Geochemistry and detrital zircon geochronology of modern sediment from central California (U.S.A.)

Integrated, multi-method provenance studies of siliciclastic sedimentary deposits are increasingly used to reconstruct the history of source-to-sink transport, paleogeography, and tectonics. Invariably, analysis of large-scale depositional systems must confront issues regarding how to best sample the system and adequately cope with the details of sediment mixing. Potential biases including variations in grain size, sediment flux, and mineral concentration may cause provenance tracking tools to misrepresent the contributions of source-areas that contribute to large drainage networks. We have acquired U-Pb detrital zircon data from modern sand and whole-rock geochemistry from mud sampled from the Sacramento-San Joaquin drainage of central California to elucidate conditions that can skew provenance trends along the course of a major river system. This drainage network is fed by headwaters that tap the Mesozoic pluton-dominated southern Sierra Nevada, the Paleozoic-Mesozoic wallrock and volcanic-dominated northern Sierra Nevada, the ultramafic-dominated eastern Klamath Mountains, and the intermediate to mafic Cascades volcanic arc. Analysis of the results indicates that detrital zircon provenance trends effectively record source variations for the southern, granite-dominated portion of the drainage network where contrasts in lithology and inferred zircon fertility are relatively minor. In these circumstances, mixture modeling of U-Pb detrital zircon data calibrated with a measure of zircon fertility approximates relative sediment flux contributed by individual drainages. Alternatively, in the northern parts of the system, source regions underlain by ultramafic and/or volcanic rocks are poorly represented, or entirely missing, in downstream detrital zircon records. In some cases, mud geochemistry data more faithfully represent sediment provenance trends. Sampling performed at the confluence of the Sacramento, American, Mokelumne, and San Joaquin Rivers within the Sacramento-San Joaquin Delta region yields a detrital zircon age distribution that is indistinguishable from that of an independently established database of Sierra Nevada batholith crystallization ages. However, when the combined river flows along a recently established passage to the Pacific through the San Francisco Bay region, dredged sediment is found to be significantly contaminated by locally eroded material from the Franciscan Complex and other rocks that crop out within the Coast Ranges. Large variation of Zr concentrations measured throughout the Bay area document that significant hydrodynamic fractionation impacts sediment delivery through this segment of the system. The more Sierra Nevada-like detrital zircon age distribution yielded by a piston-core sample from the continental slope may be explained by either early-stage unroofing of the Coast Ranges or more efficient sand delivery from the delta to the Pacific by a free-flowing river driven by a low stand in sea level.

Sedimentology, petrology, and structure of the Moffet Creek Formation, Eastern Klamath Mountains, Northern California

Sedimentology, petrology, and structure of the Moffet Creek Formation, Eastern Klamath Mountains, Northern California

Thermotectonic evidence for two-stage extension on the Trinity detachment surface, Eastern Klamath mountains, California

We present integrated fission-track and (U-Th)/He analysis of a reconnaissance suite of 8 apatite samples along a transect crossing the footwall of the Trinity Detachment Surface, a variably preserved low-angle extensional structure in the Eastern Klamath Mountains of California. These thermochronological data display significant variation when plotted along the extension lineation evident on exposed remnants of the fault, and the combined ages, together with the fission track length variation observed, require two discrete episodes of exhumation associated with extension on this structure. Consistent mid-Cretaceous fission-track ages indicate continuation of earlier slip on the detachment surface and/or erosional exhumation to bring upper greenschist facies footwall rocks into the brittle upper crustal domain. This phase of exhumation continued until c. 80 Ma, terminating while currently exposed samples were still 2 to 3 km below the surface. Final exhumation of the footwall block occurred in a second discrete episode initiating at c. 20 to 23 Ma, contemporaneous with development or re-activation of extension on the La Grange Fault to the south.

Provenance of the Pythian Cave conglomerate, northern California: implications for mid-Cretaceous paleogeography of the U.S. Cordillera

Provenance analysis of middle Cretaceous sedimentary rocks can help distinguish between disparate tectonic models of Cretaceous Cordilleran paleogeography by establishing links between sediment and source, as well as between currently separated basins. This study combines new detrital zircon age data and compositional data with existing provenance data for the Pythian Cave conglomerate, an informally-named unit deposited unconformably on the eastern Klamath Mountains, to test possible correlations between the Pythian Cave conglomerate and similar-age deposits in the Hornbrook Formation and the Great Valley Group. These provenance results indicate that restoring Late Cretaceous clockwise rotation of the Blue Mountains adds a significant sediment source for Cretaceous basins previously associated with only the Klamath Mountains (e.g., the Pythian Cave conglomerate and Hornbrook Formation) or a combined Klamath-Sierran source (e.g., Great Valley Group). Comparison of the Pythian Cave conglomerate with the Klamath River Conglomerate and the Lodoga petrofacies suggests that the Pythian Cave conglomerate system was separate from the nearby Hornbrook Formation and was probably related to the Lodoga petrofacies of the Great Valley Group.

New fusulinids from Lower Permian turbidites at Conglomerate Mesa, southeastern Inyo Mountains, east-central California

Seven previously unrecognized fusulinid species from Lower Permian (Wolfcampian and Leonardian) turbidites near Conglomerate Mesa in east-central California, four of which are named as new species, are here described and figured. the four new species areSchwagerina merriami, S. wildei, Parafusulina mackevetti, andSkinnerella rossi.These fusulinid species have close affinities to similar taxa in Texas and northeastern Nevada, and they are distinct from some other faunas of slightly different age in the Conglomerate Mesa area that are dominated by endemic species and other species with Eastern Klamath Mountains affinities.

New Permian fusulinids from Conglomerate Mesa, southeastern Inyo Mountains, east-central California

In the Conglomerate Mesa area in the southeastern Inyo Mountains, east-central California, a series of distinctive fusulinid assemblages ranging in age from late Artinskian to Kungurian or Roadian was developed in units 7–10 of the sedimentary rocks of Santa Rosa Flat (part of the Owens Valley Group). The fauna of unit 7 shows some eastern Klamath Mountains affinity, but most of the species in unit 7 and the lower half of unit 8 are highly endemic and comprise three new genera with 12 new species, two unusual unassigned forms, and two other new species assigned to previously described genera. New taxa include: Crenulosepta new genus with five new species, C. inyoensis, C. delicata, C. fusiformis, C. rossi, and C. wahlmani; Nigribaccinus new genus with three new species, N. giganteus, N. elegans, and N.? nestelli; and the new genus Inyoschwagerina with four new species, I. magnifica, I. elayeri, I. elongata, and I.? linderae. Cuniculinella Skinner and Wilde, 1965, is represented by one new species, C. parva, and Skinnerella Coogan, 1960 by one new species, S.? mcallisteri. Faunas from the upper half of unit 8, unit 9, and unit 10 have a strong West Texas affinity. New species from these units are Skinnerella davydovi, S. hexagona, Parafusulina cerrogordoensis, P. complexa, P. halli, P. owensensis, and P. ubehebensis.

New Permian fusulinids from Conglomerate Mesa, southeastern Inyo Mountains, east-central California

In the Conglomerate Mesa area in the southeastern Inyo Mountains, east-central California, a series of distinctive fusulinid assemblages ranging in age from late Artinskian to Kungurian or Roadian was developed in units 7–10 of the sedimentary rocks of Santa Rosa Flat (part of the Owens Valley Group). The fauna of unit 7 shows some eastern Klamath Mountains affinity, but most of the species in unit 7 and the lower half of unit 8 are highly endemic and comprise three new genera with 12 new species, two unusual unassigned forms, and two other new species assigned to previously described genera. New taxa include:Crenuloseptanew genus with five new species,C. inyoensis,C. delicata,C. fusiformis, C. rossi, andC.wahlmani;Nigribaccinusnew genus with three new species,N. giganteus, N. elegans, andN.?nestelli; and the new genusInyoschwagerinawith four new species,I.magnifica, I.elayeri, I. elongata, andI.?linderae. CuniculinellaSkinner and Wilde, 1965, is represented by one new species,C. parva, andSkinnerellaCoogan, 1960 by one new species,S.?mcallisteri.Faunas from the upper half of unit 8, unit 9, and unit 10 have a strong West Texas affinity. New species from these units areSkinnerella davydovi, S. hexagona, Parafusulina cerrogordoensis, P. complexa, P. halli, P. owensensis, andP. ubehebensis.

Joseph Silas Diller (1850-1928): Pioneer of Southern Cascadian Geology, California and Oregon

Joseph Silas Diller worked as a United States Geological Survey (USGS) geologist for some forty years, from 1883 to 1923. While his principal interest was in petrography, he was responsible for production of numerous geological maps, reconnaissance surveys and economic geologic studies. A majority of these were in Southern Cascadia, the complex region of southern Oregon and northern California that encompasses portions of the eastern Great Basin, Sierra Nevada, Cascade Volcanic, Great Valley, Klamath Mountains and Coast Ranges geologic provinces. Among his achievements were the production of six maps as part of the USGS Geologic Atlas Folio Series, in-depth reports on the evolution of Crater Lake and Lassen Peak, detailed descriptions of several mining districts, and the preparation of sets of hand specimens, thin sections and descriptions for colleges and universities. He was also a specialist on asbestos, coal, placer gold and chromic iron ore. He is perhaps best remembered for his studies of Crater Lake and analysis of Tertiary peneplanation and regional uplift.

ORDOVICIAN “SPHINCTOZOAN” SPONGES FROM PRINCE OF WALES ISLAND, SOUTHEASTERN ALASKA

Abstract A faunule of silicified hypercalcified “sphinctozoan” sponges has been recovered from a clast of Upper Ordovician limestone out of the Early Devonian Karheen Formation on Prince of Wales Island in southeastern Alaska. Included in the faunule are abundant examples of the new genus Girtyocoeliana, represented by Girtyocoeliana epiporata (Rigby and Potter), and Corymbospongia adnata Rigby and Potter, along with rare Corymbospongia amplia n. sp., and Girtyocoelia(?) sp., plus common Amblysiphonella sp. 1 and rare Amblysiphonella(?) sp. 2. The assemblage is similar to that from Ordovician clasts from the eastern Klamath Mountains of northern California. This indicates that the Alexander terrane of southeastern Alaska is related paleogeographically to the lithologically and paleontologically similar terrane of the eastern Klamath Mountains. This lithology and fossil assemblage of the clast cannot be tied to any currently known local rock units on Prince of Wales Island. Other clasts in the conglomerate...

Comparison of charcoal and tree-ring records of recent fires in the eastern Klamath Mountains, California, USA

Fire-history reconstructions are based on tree-ring records that span the last few centuries and charcoal data from lake-sediment cores that extend back several thousand years. The two approaches have unique strengths and weaknesses in their ability to depict past fire events and fire regimes, and most comparisons of these datasets in western conifer forests have focused on sites characterized by high-severity crown fires. Tree-ring and charcoal data spanning the last 300 years in four watersheds in the montane forests of the Klamath Mountains provided an opportunity to compare the records in a fire regime of frequent low- to moderate-severity surface events. The charcoal data were obtained from small lakes, and tree-ring records were derived from fire-scar chronologies at multiple sites within each watershed. The comparison indicates that the tree-ring records detected individual fires not evident in the lake-sediment profiles, whereas the charcoal data disclosed variations in fuel loading and general levels of burning at broader spatial scales. Regional burning in the late 19th and early 20th centuries was evident in the lake-sediment records, and both datasets registered a decline in fire activity in the late 20th century. Thus, the two types of data provide complementary as well as supplementary information on past fire conditions.

Concordant paleolatitudes for Neoproterozoic ophiolitic rocks of the Trinity Complex, Klamath Mountains, California

[1] New paleomagnetic results from the eastern Klamath Mountains of northern California show that Neoproterozoic rocks of the Trinity ophiolitic complex and overlying Middle Devonian volcanic rocks are latitudinally concordant with cratonal North America. Combining paleomagnetic data with regional geologic and faunal evidence suggests that the Trinity Complex and related terranes of the eastern Klamath plate were linked in some fashion to the North American craton throughout that time, but that distance between them may have varied considerably. A possible model that is consistent with our paleomagnetic results and the geologic evidence is that the Trinity Complex formed and migrated parallel to paleolatitude in the basin between Laurasia and Australia–East Antarctica as the Rodinian supercontinent began to break up. It then continued to move parallel to paleolatitude at least through Middle Devonian time. Although the eastern Klamath plate served as a nucleus against which more western components of the Klamath Mountains province amalgamated, the Klamath superterrane was not accreted to North America until Early Cretaceous time. INDEX TERMS: 1525 Geomagnetism and Paleomagnetism: Paleomagnetism applied to tectonics (regional, global); 5475 Planetology: Solid Surface Planets: Tectonics (8149); 8157 Tectonophysics: Evolution of the Earth: Plate motions—past (3040); 9350 Information Related to Geographic Region: North America; 9619 Information Related to Geologic Time: Precambrian

Volcanisme triasique calco-alcalin a shoshonitique du Nevada occidental

Volcanisme triasique calco-alcalin a shoshonitique du Nevada occidental

Postglacial vegetation and fire history, eastern Klamath Mountains, California, USA

Pollen and high-resolution charcoal data from Bluff Lake and Crater Lake, California, indicate simi lar changes in climate, vegetation and fire history during the last 15 500 years. Pollen data at Bluff Lake suggest that the vegetation between c. 15 500 and 13 100 cal. BP consisted of subalpine parkland with scattered Pinus and Abies. After 13 100 cal. BP a relatively closed forest of P. monticola, P. contorta and Abies developed, and fire-event frequency was low. The inferred climate then was cooler and wetter than present. Pinus and Quercus vaccinifolia dominated at both sites during the early Holocene, when conditions were warm and dry. As climate became wetter and cooler in the late Holocene, Abies spp. at both sites and Tsuga mertensi ana at Crater Lake increased in importance, displacing Pinus and Quercus. The two lake records have similar trends in fire history, with high event frequencies at c. 8400, 4000 and 1000 cal. BP and low values at c. 4800 cal. BP. The fire and vegetation history at both sites suggests a similar response to large-scale changes in climate during the Holocene.

Supra‐Subduction Zone Ophiolite Formed in an Extensional Forearc: Trinity Terrane, Klamath Mountains, California

The Paleozoic Trinity terrane is a massif of ultramafic rock and mafic intrusive complexes that forms the basement of eugeoclinal rocks in the eastern Klamath Mountains. The origin of the Trinity terrane has been particularly enigmatic and several mutually exclusive origin models have been proposed: (1) mantle diapir; (2) slice of obducted monogenetic oceanic lithosphere; (3) monogenetic backarc‐basin lithosphere; (4) forearc lithosphere; and (5) volcanic arc basement. We have compiled new and existing field, petrographic, geochronologic, isotopic, and whole‐rock chemical data for the Trinity terrane to evaluate these models and conclude that the Trinity terrane is an supra‐subduction zone ophiolite whose mafic intrusive complexes record subduction‐related magmatism and forearc extension that occurred during the inception of intraoceanic subduction. According to this extensional forearc model, all four terranes in the eastern Klamath Mountains evolved principally during the inception and evolution of a si...

Silurian plutonism in the Trinity terrane (Neoproterozoic and Ordovician), Klamath Mountains, California, United States

New data indicate that the Trinity terrane of northern California is a polygenetic composite terrane rather than a single slice of oceanic lithosphere. We suggest approximately one third of the Trinity terrane consists of Silurian intrusive rocks that represent the roots of a previously unrecognized Silurian magmatic arc. Crosscutting relations and U‐Pb zircon isotopic data document at least one early Paleozoic deformation in the Trinity terrane of northern California. A ductile shear zone between Neoproterozoic metagabbro and Ordovician(?) harzburgite is intruded by the Upper Silurian China Mountain pluton. This evidence indicates a major early Paleozoic shear zone formed in the eastern Klamath Mountains after the Middle Ordovician but prior to Late Silurian plutonism.

Palynology and plate tectonics — a case study on cretaceous terrestrial sediments in the eastern Klamath mountains of northern California, U.S.A.

Abstract The western part of the North American Cordillera is thought to be made up of a collage of allochthonous crustal fragments formed in a variety of tectonic settings at some distance west of their present location. Paleontological and radiometric age dating of the rocks associated with these terranes is critical in understanding their geological history. The basal conglomeratic unit of the Hornbrook Formation (Klamath River Conglomerate) and isolated exposures of some unnamed, undated conglomerates at the Pythian Cave locality, 40 km northwest of Mt. Shasta and south of the town of Yreka, California, both lie nonconformably over the basement rocks that form the Yreka‐Trinity composite microplate in Hornbrook Basin. Palynological data indicate that the geologic age of the unnamed conglomerates at Pythian Cave is middle Albian, and that of the Klamath River Conglomerate is middle Cenomanian. This study also shows that the Pythian Cave conglomerates have a different source, and have formed in a differ...

Early Paleozoic Blueschist from the Schist of Skookum Gulch, Eastern Klamath Mountains, Northern California

Late Ordovician blueschist from the schist of Skookum Gulch, eastern Klamath Mountains, California, is the oldest known blueschist in California and one of the oldest in North America. Lawsonite-bearing glaucophane schist occurs as lenses intimately interlayered with chlorite schist, quartz-albite schist, and dolomite marble. Detailed investigation of a portion of the Skookum Gulch schist demonstrates that these rock types share a common deformational and metamorphic history. The first deformation occurred during blueschist metamorphism and produced similar-style isoclinal folds and an axial-planar foliation. During subsequent deformations, parallel-style open to tight folds and local kink bands deformed foliation but produced no recognizable recrystallization. Major and selected trace elements, analyzed by XRF for 12 samples of mafic schist, show that the protoliths were broadly basaltic in composition ($$SiO_{2} mostly ranges from 46 to 53 wt \%$$) and that ocean-floor basalt affinities are suggested by...

Ordovician-Silurian tectonism in northern California:The Callahan event

Middle Ordovician to Early Silurian volcanism, plutonism, metamorphism, deformation, and sedimentation in the Yreka and Trinity terranes, eastern Klamath Mountains, northern California, are considered to be related phenomena that occurred in response to an episode of tectonism known as the Callahan event. A diverse array of evidence is used to construct a tectonic model for the Callahan event that involves a subduction zone, a magmatic arc, and a back-arc spreading center, and to show that tectonism likely occurred within the framework of the North American continental margin. Evidence pertaining to subduction polarity is meager, but is consistent with an eastward dip. The Callahan event represents the earliest Phanerozoic convergent-margin tectonic event recognized within the U.S. Cordillera.

The origin of geochemical variations in a late permian volcanic arc, eastern klamath mountains, California

Volcanic are remnants present in the eastern Klamath terranes record an intermittent volcanism from Ordovician to Early Jurassic times. The Upper Permian volcanics (Nosoni, Dekkas and Bully Hill formations) consist mainly of andesites with minor basalts and rhyolites, metamorphosed in the prehnite-pumpellyite facies. Their petrographic and geochemical characters indicate a mature island-arc setting, but their tholeiitic affinity suggests an intra-oceanic environment. Nd isotopic compositions of the Nosoni-Dekkas lavas ( εNd T = +4 to +8), as well as a preferential enrichment of light rare-earth over high-field-strength elements and systematic negative Ce anomalies, point to MORB-type mantle sources contaminated by a few percent of slab-derived sediments. Large variations in the chondrite-normalized La/Yb ratio (0.95 to 3.7) are interpreted in terms of variable depth and degree of partial melting. Two distinctive basalt-types are found at the top of the Nosoni Formation (Dekkas Saddle) and the Bully Hill Formation. The former are high-Mg basalts showing a strong enrichment in incompatible elements (La/Yb ∼ 50, 8.7 ppm Th, ∼ 50 ppm Nb) but low TiO 2, Al 2O 3, Yb, Zr and Sr contents, with a pronounced positive Eu anomaly. They may result from small degrees of partial melting of a refractory peridotitic source enriched by felsic melts derived from subducted MORB, with garnet in the residue. These lavas probably record a transient anomalous thermal regime in the deepest part of the subduction zone, and can be compared to some extent to the arc alkali series. On the other hand, the Bully Hill basalt shows boninitic affinities and probably originated from a shallower lithospheric mantle source. The large range of compositions recorded by the Permian arc lavas gives evidence of efficient extraction of melts segregated at different depths.