Tuff Breccia Research Articles

西南北海道，長万部地域の新第三紀火山岩類のＫ‐Ａｒ年代

Oshamanbe district is on the northern extension of the so-called green tuff district in northeastern Japan, and the sedimentary rocks in a sea area and volcanic rocks from Miocene to Pleistocene widely distribute. The authors carried out the geological survey of this district, and published the results as the geological features in Oshamanbe district. The volcanic rocks distributing in this district range from andesite to dacite and rhyolite. Their lithofacies are mostly volcanic breccia and tuff breccia, accompanied by lava and dikes. This time, the measurement of the age of these volcanic rocks was carried out, and the stratigraphical table made by the authors was investigated. It is considered that those age values offer important information for determining the age of the Setana formation. The outline of the geological features, the samples for the measurement, the method of measurement of Ar isotopic ratio and K, and the results of measurement are reported. As the results, 4.38 - 4.47 Ma were obtained for Garogawa volcanic rocks, and 2.59 Ma for Shamanbesan volcanic rocks. The period of sedimentation of the Setana formation was from the latter period of Pliocene to pleistocene. (Kako, I.).

日本海東縁の飛島に産する中新世深海底ソレアイト型玄武岩

Abyssal tholeiites are found from Tobishima Island in Japan Sea, 40km northwest from Sakata, northeastern Japan. These basalts (Tobishima basalts), including lava flows, minor dikes, epiclastic lapilli tuff and tuff breccia, and hyaloclastite, were formed under water, and overlie acidic volcanic rocks. The basaltic lavas and dikes containing less than 10% of olivine and plagioclase phenocrysts are uniform in composition, but show various degrees of alteration. They are similar to abyssal tholeiites in composition of groundmass augite and coexisting phenocrysts of olivine and plagioclase. In addition, Tobishima basalts plot in the field of abyssal tholeiites in the tectonic discrimination diagrams of FeO*/MgO-TiO2, FeO*/MgO-FeO*, Y-Zr/Y, Y-Cr, TiO2-P2O5, Ti-Cr and Ti-Ni. The submarine and bimodal character of the volcanism at Tobishima suggests the possibility of Middle Miocene age instead of Early Miocene as was previously deduced from K-Ar dating.

Self-glazing ceramic tiles based on acidic igneous glasses

A technology was derived to produce self-glazing ceramic tiles based on single-component systems of acidic igneous (volcanic) glasses. A weakly alkaline solution of NaOH or KOH was used as the sealing water to activate the sintering process. Tests conducted on the self-glazing ceramic tiles showed that their water absorption amounts to 2.5-8%, linear shrinkage is 3.2-7%, and frost resistance amounts to 35-70 cycles. The application of acidic igneous glasses as the main raw material for the production of ceramic facing tiles made it possible to widen the raw material base and simplify the technology for fabricating ceramic facing tiles at lower cost. The use of waste products when processing perlite-bearing rocks, when carrying out mining and cutting of tuffs, slags, and tuff breccia for recovering cut materials was recommended.

Deep marine arc apron deposits and syndepositional magmatism in the Alisitos group at Punta Cono, Baja California, Mexico

ABSTRACTRocks exposed at Punta Cono include very fine‐grained to coarse‐grained tuffs, lapilli tuffs, and tuff breccias deposited in a deep marine environment. Syndepositional basaltic intrusive activity was common. In one locality a hyaloclastite‐peperite complex formed. Slumped sections with fluidal basalt ‘clasts’, derived from intrusions that entered the sediment pile from below, are present elsewhere. Abundant soft‐sediment folds in fine‐grained laminated subaqueous fall‐out tuff suggest steep gradients; these are cut by shallow channels filled with coarse‐grained tuff, lapilli tuff, and rare tuff breccia. The combination of marine fossils, extreme textural immaturity, abundant slump features, and syndepositional magmatism indicates deposition upon the submarine flanks of an active volcano.Recognition of magma‐wet sediment interaction is hampered in volcaniclastic rocks because of the similarity between host and intrusive fragments. Products of magma‐water‐sediment interactions at Punta Maria include: (1) jigsaw‐puzzle hyaloclastite, formed by non‐explosive hydroclastic fragmentation of magma upon contact with water and water‐bearing sediment; (2) peperites, produced by mixing of magma with sediment; and (3) an unusual tuff breccia unit, the result of non‐explosive mixing of ‘wisps’of lava with sediment during remobilization of an unconsolidated section. Low‐explosivity magma‐water‐sediment interactions are favoured by relatively high hydrostatic pressures in sub‐wave base settings.

岩手県九戸郡山形村の凝灰角れき岩のＫ‐Ａｒ年代

Tuff breccia was found in Yamagata-mura, Kunohe-gun, Iwate-Prefecture. This tuff breccia contains many granitic and andesitic rocks with a small numbr of chert fragments. The matrix part of the tuff breccia is characterized by the presence of coarse, euhedral or corroded hornblende crystals. K-Ar age of the hornblende is dated as 16.1±2.0 Ma, and therefore, the tuff breccia is considered to be formed at the Middle Miocene in age. At the northern Kitakami Mountains, the area of Neogene magmatism should have been more extended 10 km to the east than that was considered before.

千葉県館山市船形磨崖仏十一面観音像の劣化と水・岩石相互作用

Daifukuji Temple rock-cliff Budda sculpture which is located halfway up on the hill near the coast of Tateyama, Chiba Prefecture was carved in 8th century on the Neogene andesitic tuff and tuff breccia alternated bed. It is sheltered by a beautiful wooden construction. The Neogene andesitic tuff and tuff breccia are composed chiefly of augite, hypersthene, hornblende, plagioclase, and volcanic glass with subordinate amounts of fine-grained magnetite, pyrite (probably biogenic), hematite and limonite. The surface of Budda sculpture is covered by a thick, up to several mm, crust or scab composed chiefly of minerals such as gypsum, thenardite, epsomite, mirabilite with minor amounts of halite, sylvite, aragonite and copiapite. Rain water penetrates into the rock of the hill where sculpture is located and the water easily comes out after interaction with rocks and evaporates from the surface of rock-cliff. The water coming out from rock mass has high contents of Ca, Na, Cl, HCO3 and SO4 with subordinate amounts of K and Mg. Gypsum-rich scab or crust was formed by the evaporation of such type of groundwater on the rock-mass surface. The growth of thus formed scabs or crusts and their falling off must be major reasons why the sculpture has been decayed so badly as shown by Fig 4. Modes of occurrence of gypsum-rich scabs and indoor experiments using bore-hole cores taken from the Neogene volcanogenic sediments mass on which the sculpture was carved indicate that the increase in the thickness of the gypsum-rich scabs is unbelievably fast, probably more than 0.15mm/year. The repeated cycle of the growth of gypsum-rich scab or crust on the surface of Neogene volcanic sedimentary rock mass and their falling off should be stopped to prevent the forth decay of this Budda sculpture. The best ways to solve this problem are considered to be (1) to minimize the down permeation of groundwater from the top surface through interstitial void and joint of Neogene volcanogenic formation by making open drainage space at the above and/or back side of the rock-cliff sculpture or by covering the top surface of the hill by unpermeable facing and (2) to keep the humidity of the room of rock-cilff sculpture as high as possible to minimize the evaporation of water extracted from the surface of the sculpture.

Relationship between Rock Alteration and Landslides in the Noboribetsu District, Southwest Hokkaido

Triggered by severe local rainfall in September, 1983, a large number of landslides occurred on slopes in the southern foot of the somma of Kuttara Caldera, SW Hokkaido. On the basis of slope movement features, they were classified mainly into two types: slump and debris-slide. Almost all the slump type landslides took place on slopes within a rock alteration zone in the southwestern part of the foot; whereas, the debris-slide type landslides showed a scattered distribution in the study area. Tuff breccia, parent rock in the alteration zone, was intensely altered to clay hydrothermally.The alteration increased with increasing depth and is characterized by considerable amounts of montmorillonite and sulfides. The slipping surfaces of landslides of this type were found in the depth of tuff breccia formation. On the other hand, the slipping surfaces of debris-slide type landslides were found in a clayey crust that was formed by weathering of the surface part of the tuff breccia formation. The clayey crust is of several tens of centimeters in thickness and is composed mainly of halloysite and/or metahalloysite. It is likely that the degree and process of rock alteration played a very important role in controlling the type and distribution of landslides in the study area.

Early Proterozoic bimodal volcanic rocks in central Colorado, U.S.A., Part I: Petrography, stratigraphy and depositional history

Early Proterozoic metamorphic rocks of the Salida area include two exceptionally well-preserved sections of undeformed volcanogenic rocks: a northern section nearly 4000 m thick and a southern section 1700 m thick. The stratigraphic and lithologic character of the sections are the same, indicating that they were formed contemporaneously in the same subaqueous environment. The suite is strongly bimodal, consisting of felsic volcaniclastic rocks (50%), mafic volcanic and volcaniclastic rocks (22%), and gabbro/diabase sheets (23%). The remaining rocks are mostly pelitic metasediments. The felsic rocks, which dominate the upper portions of both sections, comprise four distinct facies: crystal-lithic tuff breccia, crystal-lithic lapilli-breccia tuff, bedded tuff, and massive tuff. Lithic fragments are typically foreign, dominated by pelitic material. Crystal clasts are feldspar, mainly plagioclase, and quartz. Sequences of these facies, representing cycles of eruptive activity, are uniform in thickness and extend along strike for the entire width of Precambrian exposure, up to 4 km, but individual facies units, especially the coarser ones, are limited in their lateral extent. Individual sequences average about 100 m thick, but continuous exposures of felsic rocks locally exceed 600 m. Primary sedimentary structures and vertical and lateral variations indicate deposition, typically following remobilization as debris flows and turbidites, in a shallow marine environment of low relief. Mafic volcanic and volcaniclastic rocks form accumulations up to 600 m thick and extend uniformly for several kilometers along strike, although individual units are more restricted laterally. The principal rock types are basalt flows, basaltic lithic breccia, pillow lava/pillow breccia, bedded basaltic lapillistone, and laminated basaltic tuff, all deposited in a submarine setting. Accumulations, typically including several types, are interbedded with felsic rocks, but mechanical mixing of mafic and felsic volcaniclastics is rare, suggesting separate eruptive centers for the mafic and felsic volcanics. The northern section may be more proximal than the southern section, as indicated by the greater abundance of flows, the thicker sheets of gabbro, and the greater abundance of mafic rocks relative to felsic rocks. Gabbro/diabase sheets, up to 350 m thick and dominantly concordant, intrude throughout both sections. They are characterized by lack of internal differentiation, simple mineralogy consisting of plagioclase and hornblende, pseudomorphous after pyroxene, and sub-ophitic texture. The minor pelitic material indicates that the area was accessible to continental sediment sources, although their location is not known. The Salida bimodal volcanic suite is part of a more extensive accumulation of similar 1700–1800 Ma supracrustal rocks that extends west to the Gunnison area and perhaps south into northern New Mexico.

Anatomy of a middle Miocene Valles-type caldera cluster: Geology of the Okueyama volcano-plutonic complex, southwest Japan

A deeply eroded root of a Miocene Valles-type caldera cluster is exposed in the Okueyama volcano-plutonic complex in Kyushu, southwest Japan. The complex shows the relationship between an ash-flow caldera and a vertically zoned granitic batholith. The igneous activity of this complex began with the eruption of the Sobosan dacitic tuff and collapse of the Sobosan cauldron (18 × 13 km). After an erosion interval, the Katamukiyama aphyric rhyolitic lavas were erupted to form a thick lava plateau, followed by the eruption of Katamukiyama dacitic tuffs concurrent with the formation of the Katamukiyama cauldron (12 × 6 km). Some dikes of felsite and tuff breccia and a stock of hypersthene-biotite granodiorite are closely related to this stage of volcanism. After an erosional interval, eruption of the Sobosan andesitic and dacitic lavas and pyroclastics constructed three large stratovolcanoes, and their eruptive centers migrated from SW to NE. Stocks of pyroxene-bearing quartz monzodiorite to porphyritic granophyre intruded the centers of the stratovolcanoes, and are probably vent-filling intrusives. After an erosional interval, the Kunimidake rhyolitic tuff erupted to form the Okueyama cauldron (33 × 23 km). The Sobosan and Katamukiyama cauldrons subsided again during this stage; large ring-shaped dikes of granite porphyry were formed as vent-filling intrusives of this volcanism. The Okueyama granitic batholith, the product of the final magmatic activity in this complex, is a solidified resurgent magma chamber displaying vertical zonation, which intruded to 3 km beneath the surface. In this zoned pluton, upper biotite granite (74-70 wt. % SiO 2) gradually changes to lower hornblende-biotite granodiorite (66-65 wt. % SiO 2). The age of the batholithic pluton given by K-Ar dating is about 14 Ma, and the igneous activity of the Okueyama complex would have lasted for a relatively short time span during the middle Miocene.

U–Pb zircon ages in supracrustal and plutonic rocks; North Spirit Lake area, Northwestern Ontario

The North Spirit Lake greenstone belt in the Sachigo Subprovince of the Superior Province comprises parts of three sequences of volcanic and sedimentary rocks; the main (youngest) is separated from the older sequences by an unconformity to disconformity. The belt is bounded by large granitoid batholiths and was metamorphosed under greenschist to, locally, hornblende–cordierite facies. U–Pb zircon dating was performed on volcanic, sedimentary, and plutonic rocks in order to establish an absolute chronology for the evolution of the area.A tuff breccia in the lowermost supracrustal sequence is dated at 3023 ± 2 Ma. Zircons from a tuff in the middle sequence show complex U–Pb relationships; although they do not allow a precise age determination, the data suggest that the tuff formed sometime between 2950 and 2800 Ma ago. Zircons from a quartz arenite, also in the middle sequence, yield a simple data pattern and define an age of [Formula: see text], suggesting derivation of the sediment from a uniform source of this age. A zircon analysis from a tonalitic clast in a conglomerate at the base of the upper sequence yields a minimum age of 2975 Ma. The clast may have had the same origin as the zircons in the quartz arenite. Another tonalitic clast from the same conglomerate yields a slightly older age of 3001 ± 3 Ma. No remnant of these tonalites can be recognized in the field, suggesting that they have been largely removed during subsequent erosional processes.Two subvolcanic intrusions from the upper sequence yield zircon ages of 2743 ± 2 and 2731 ± 2 Ma, respectively. A crystal tuff, also in the upper sequence, contains two generations of zircons: newly formed magmatic zircons, which date the extrusion of the tuff at 2735 ± 10 Ma, and older grains with a minimum age of 2862 Ma, which represent inherited zircons. This tuff was thus generated at least in part by anatectic melting of >2862 Ma crust.A quartz diorite from MacDowell Lake in the adjacent Berens River Subprovince yields an age of 2744 ± 2 Ma. A mafic inclusion in the quartz diorite contains amoeboidal, strongly fractured zircons, which point to an intercept age of about 2727 Ma. This age could either reflect a metamorphic event or represent a geologically meaningless mixed age.

Pyroclastic rocks: another manifestation of ultramafic volcanism on Gorgona Island, Colombia

Tertiary ultramafic volcanism on Gorgona Island, Colombia, is manifested not only by komatiite flows, but also by a more voluminous sequence of tuff breccias, which is cut by comagmatic picrite dikes. The ultramafic pyroclastic rocks are chaotic to stratified mixtures of angular to subrounded glassy picritic blocks and a fine grained volcaniclastic matrix that consists primarily of plastically-deformed, glassy globules. The entire deposit is interpreted to have formed by an explosive submarine eruption of phenocryst-laden picritic magma. MgO contents of tuff breccias and picrite dikes range from 21 to 27 wt%. Relative to nearby komatiite flows, these rocks are MgO-rich, and FeO-, TiO2- and Ni-poor. HREE concentrations are very low (<seven times chondrite), and similar to those of the komatiites, whereas the LREE are extremely fractionated ((Ce/Sm)N<0.2), indicating derivation from a more highly depleted mantle source region. Nd isotopic data suggest a cogenetic relationship between the picritic magma that formed the tuff breccia and associated dikes and that which produced the komatiite flows. Nevertheless Pb isotopic data as well as whole rock geochemistry preclude such a connection, either due to olivine fractionation/accumulation or to different degrees of partial melting. These ultramafic rock types crystallized from magmas which most likely were extracted from distinct mantle source regions.

Eruptive style and construction of shallow marine mafic tuff cones in the Narakay Volcanic Complex (Proterozoic, Hornby Bay Group, Northwest Territories, Canada)

Abstract The Early Proterozoic (1663 Ma) Narakay Volcanic Complex, exposed in Great Bear Lake (Northwest Territories, Canada), is a bimodal suite of basalt and rhyolite erupted in a continental setting and consisting largely of pyroclastic rocks interlayered with shallow marine sedimentary rocks of the Hornby Bay Group. Mafic pyroclastic rocks consist of lapilli tuff, tuff, tuff breccia and agglomerate that represent the remnants of small subaerial tuff cones (0.5 to 2 km in diameter) that in most cases have subsided into the volcanic conduit. Stratification styles, sedimentary structures and grain morphologies in pyroclastic rocks reflect variations in the water:magma ratio during eruptions and have been used to help elucidate eruptive mechanisms and reconstruct volcanic edifices. Basaltic pyroclasts are commonly bounded by fracture surfaces and are morphologically similar to modern pyroclasts produced by thermal quench fragmentation or steam-blast disruption of magma. Most fragments have low vesicularity and scoria is only locally abundant which indicates that eruptive energy was supplied mostly by water—melt interaction rather than exsolution of magmatic gases. Cored bombs and lapilli, fusiform bombs, and pyroclasts similar in texture to those of Strombolian cinder and agglutinate spatter, are uncommon but are stratigraphically widespread and imply the occurrence of Strombolian eruptions, presumably when water access to the vent was impeded. Massive bedding is typical of the tuffs and, in addition to the poorly sorted ash-rich nature of the tuffs, implies deposition from water- and/or steam-rich hydrovolcanic eruption clouds and cypressoid jets by airfall and dense pyroclastic flows. Uncommon well-stratified and sorted ash and lapilli tuff record airfall and pyroclastic flow(?) deposition from eruption clouds rich in magmatic gases. Base surge deposits are uncommon and occur only in the subaerial portion of a sequence of tuffs inferred to record the progradation of a cone-margin surge platform into standing water. Few of the tuff cone deposits display a systematic vertical sequence of stratification styles, structures and grain morphologies. This indicates that either the eruptive style varied irregularly between hydrovolcanic and Strombolian and/or that pyroclasts of different origin were mixed during eruptions.

Coarse-Grained Volcaniclastic Sediments and Associated Penecontemporaneous Volcanism, Alisitos Group, Baja California, Mexico: ABSTRACT

Volcaniclastic rocks of Cretaceous age make up the Alisitos group, which is exposed over large areas of northern Baja California, Mexico, and is inferred to have been deposited within an island arc. Intimately intermixed penecontemporaneous intrusive, extrusive, and fragmental volcanic rocks characterize many of the intra-arc deposits within the Alisitos. Peperites, formed by mixing of magma and wet sediment, are useful for demonstrating contemporaneity of volcanism and sedimentation. Peperites were recently discovered at the type locality of the Alisitos group at Punta China, only 25 km south of Ensenada, Mexico. These intrude a 50-m thick section, dominated by mafic lithic lapilli tuff breccias and lava flows, that accumulated in a nearshore to beach environment. Near Punta Maria (about 100 km north of Guerrero Negro), coarse-grained volcaniclastics interpreted to have been deposited on a north to northwest-facing submarine slope are exposed in sea cliffs. Ammonite (Pervinquieria.) and belemnite fossils suggest a Cretaceous age and marine deposition for the Punta Maria sequence. Horizontal burrows and lack of wave reworking indicate subwave-base depth for most of the section. The most common rock types in the sequence are andesitic lithic lapilli tuff and tuff breccia, deposited from nonturbulent high-concentration sediment gravity flows (density-modified grainmore » flow). Comparison of the Punta Maria and Punta China sections suggests that hydrostatic pressure and depositional slope play important roles in controlling the magma/sediment interaction. At Punta China, a shallow-water association was intruded by small sills, resulting in a highly dispersed peperite (explosive interaction). The Punta Maria section, comprising deeper water slope deposits, was intruded by a larger magma body that partly ingested a limestone and produced a thick carapace of hyaloclastite (nonexplosive interaction).« less

Depositional features of rhyolitic and andesitic volcaniclastic rocks of the Mineral King submarine caldera complex, Sierra Nevada, California

Abstract Rhyolitic and lesser andesitic pyroclastic rocks and lava flows are interstratified with marine sedimentary rocks deposited in shelf to basinal environments early Jurassic time. Voluminous (> 25 km 3 ) thick tabular sheets of rhylite ash-flow tuff accumulated within caldera collapse structures. Small (1–10 km 3 ) andesitic stratocones also formed. The andesitic units show abundant features typical of subaqueous deposition, including sorting, bedding, grading of single beds or overall grading of bedded sequences, and soft-sediment deformation. The rhyolite ash-flow tuffs show much less evidence of interaction with water during transport and deposition but are nonetheless believed to have been deposited subaqueously. The andesite stratocones have a thick core facies of amygdaloidal lava flows, hyaloclastites, and massive tuff breccias and an apron facies of bedded and sorted lapilli tuffs, lahars, tuff turbidites and subaqueous fallout tuffs. The rhyolite ash-flow sheets, in contrast, consist dominantly of massive, unsorted, unbedded and pumiceous ash-flow tuffs which resemble subaerially deposited ash-flow tuffs; however, each ash-flow sheet passes gradationally upward and distally into a bedded facies which was sorted by water during deposition. The bedded facies composes only 5–15% of each ash-flow sheet. The bedding is defined by: (1) discontinuous, crudely defined layers of blocks, lapilli, and ash within single flow units and (2) fallout layers and debris flow deposits interstratified with flow units at the distal end of each ash-flow tuff sheet. The former may be segregations that formed by shear between differentially flowing laminae within a single flow unit. The latter may have formed by settling and remobilization of material which was winnowed from the distal end of each flow unit during its subaqueous transport. Turbulent mixing with the water column was important during small-volume pulsating andesitic eruptions, whereas silicic pyroclastics were deposited from highly concentrated plug or laminar flows fed by steady, voluminous eruptions.

Geochemistry and tectonic significance of the mafic volcanic blocks in the Dunnage mélange, north central Newfoundland

Abundant volcanic blocks are present in the Dunnage mélange. These mafic volcanic rocks consist predominantly of pillow lava, tuff breccia, isolated pillow–tuff breccia, and minor amounts of ropy lava.Major- and trace-element compositions of the basalts reveal that these volcanics do not resemble calc-alkaline or low-potassium island-arc suites. Rather, the majority of the samples are enriched-type ocean-floor tholeiites, whereas some show alkali basalt affinities. Discrimination diagrams suggest that these basalts may have been erupted as within-plate basalts. However, the chemical composition of the volcanic blocks is most similar to that of basalts generated at bathymetric highs located astride (or slightly off) mid-ocean ridges.The geochemistry of the Dunnage mélange basalts is very similar to that of the mafic volcanic rocks from the nearby Summerford Group and the Lawrence Head Formation. This correlation is further supported by sedimentary and petrographic evidence and by partial age equivalency.

Vein formation and distribution, Ohio and Mt. Baldy districts, Marysvale, Piute County, Utah, USA

The Ohio and Mt. Baldy mining districts near Marysvale, Utah, are situated within a calc-alkalic rock assemblage of the Bullion Canyon Volcanics. The assemblage is divisible into three portions: 1) a lower laharic sequence of epiclastic breccias and autobreccias, 2) a middle portion containing mostly lava flows, including a dacite flow with cupola magma characteristics, and tuff and lapilli breccias, and 3) an upper portion containing a local volcanic vent complex and the ash-flow Delano Peak Tuff Member.

Correlation of the Rockland Ash Bed, a 400,000-Year-Old Stratigraphic Marker in Northern California and Western Nevada, and Implications for Middle Pleistocene Paleogeography of Central California

Outcrops of an ash bed at several localities in northern California and western Nevada belong to a single air-fall ash layer, the informally named Rockland ash bed, dated at about 400,000 yr B.P. The informal Rockland pumice tuff breccia, a thick, coarse, compound tephra deposit southwest of Lassen Peak in northeastern California, is the near-source equivalent of the Rockland ash bed. Relations between initial thickness of the Rockland ash bed and distances to eruptive source suggest that the eruption was at least as great as that of the Mazama ash from Crater Lake, Oregon. Identification of the Rockland tephra allows temporal correlation of associated middle Pleistocene strata of diverse facies in separate depositional basins. Specifically, marine, littoral, estuarine, and fluvial strata of the Hookton and type Merced formations correlate with fluvial strata of the Santa Clara Formation and unnamed alluvium of Willits Valley and the Hollister area, in northwestern and west-central California, and with lacustrine beds of Mohawk Valley, fluvial deposits of the Red Bluff Formation of the eastern Sacramento Valley, and fluvial and glaciofluvial deposits of Fales Hot Spring, Carson City, and Washoe Valley areas in northeastern California and western Nevada. Stratigraphic relations of the Rockland ash bed and older tephra layers in the Great Valley and near San Francisco suggest that the southern Great Valley emerged above sea level about 2 my ago, that its southerly outlet to the ocean was closed sometime after about 2 my ago, and that drainage from the Great Valley to the ocean was established near the present, northerly outlet in the vicinity of San Francisco Bay about 0.6 my ago.

Stratigraphic and sedimentologic evidence of a submarine island-arc volcano in the lower Mesozoic Peñon Blanco and Jasper Point Formations, Mariposa County, California

Research Article| October 01, 1985 Stratigraphic and sedimentologic evidence of a submarine island-arc volcano in the lower Mesozoic Peñon Blanco and Jasper Point Formations, Mariposa County, California NICHOLAS L. BOGEN NICHOLAS L. BOGEN 1Lamont-Doherty Geological Observatory, Columbia University, Palisades, New York 10964 Search for other works by this author on: GSW Google Scholar Author and Article Information NICHOLAS L. BOGEN 1Lamont-Doherty Geological Observatory, Columbia University, Palisades, New York 10964 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1985) 96 (10): 1322–1331. https://doi.org/10.1130/0016-7606(1985)96<1322:SASEOA>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation NICHOLAS L. BOGEN; Stratigraphic and sedimentologic evidence of a submarine island-arc volcano in the lower Mesozoic Peñon Blanco and Jasper Point Formations, Mariposa County, California. GSA Bulletin 1985;; 96 (10): 1322–1331. doi: https://doi.org/10.1130/0016-7606(1985)96<1322:SASEOA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Detailed mapping in the foothills of the central Sierra Nevada has revealed that the Lower Jurassic Peñon Blanco Formation and the newly named Jurassic-Triassic Jasper Point Formation occupy the core of a previously unrecognized anticline of Late Jurassic age that plunges gently southeastward, exposing the Upper Jurassic Mariposa Formation on its limbs. The Jasper Point Formation consists of >900 m of massive, pillowed, and brecciated basalt overlain by as much as 100 m of varicolored radiolarian chert; these units resemble layers 2 and 1 of the oceanic crust, respectively. The Peñon Blanco Formation is composed of as much as 5 km of coarse, augite- and plagioclase-bearing volcaniclastic rocks and lesser flows that appear to have originated at a common vent. Fine tuff at the base of the formation is interbedded with, and overlies, the Jasper Point chert gradationally.A restored section of the Peñon Blanco Formation suggests that the volcanic rocks define a single, composite volcano that probably originated as part of an island arc. Voluminous volcanidastic detritus that composes most of the volcano may have been produced at great depth, possibly by hyaloclasis, autoclasis, or mass wasting. Much of the detritus was deposited as turbidites of tuff and tuff breccia that define an extensive volcanic apron that thickens and coarsens upward over hundreds of metres, suggesting progradation. Submarine clastic processes thus dominated the construction of the volcano. Fragmentation of most of the erupted material probably occurred at or near the vent, and subsequent distribution of the detritus around the vent by epiclastic processes formed a distinctive Stratigraphic sequence. These hypotheses may be tested by dredging young, deeply submerged island-arc volcanoes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Late Cenozoic volcanic rocks of the Clearwater – Wells Gray area, British Columbia

The Clearwater – Wells Gray area of east-central British Columbia includes a succession of late Cenozoic, alkali olivine basalt flows that lie east of the extensive Chilcotin lavas and define the eastern end of the Anahim Volcanic Belt. The rocks are petrographically similar to but less altered than the Chilcotin basalts. The volcanic activity spanned at least two episodes of glacial advance and produced both subaerial flows and a subaqueous facies comprising pillow lava, pillow breccia, and tuff breccia, locally intercalated with fluvial gravels and sand. Four morphological assemblages have been recognized. An early glacial assemblage, characterized by tuyalike forms, gives K – Ar dates of 0.27 – 3.5 Ma. These circular features are surrounded by a deeply dissected valley-filling assemblage of subaerial and minor subaqueous flows and tuff breccia that rest locally on lag gravel and till. Subaerial flows in this assemblage give K – Ar dates of 0.15 – 0.56 Ma. Whitehorse Bluffs, a volcanic centre composed of crudely laminated tuff cut by high-level dykes, may be a source of some of these valley-filling flows. A late interglacial assemblage is composed of subaerial pyroclastic material, transitional deposits, and deposits that are clearly subaqueous. Volcanic activity in the area culminated with the formation of pyroclastic cones, blocky lava flows, and pit craters that postdate the last Cordilleran glaciation.

An Archean volcanic—Exhalative system adjacent to a trondhjemite stock near Wawa, Ontario

Abstract A trondhjemite stock intrudes an Archean succession metamorphosed to the greenschist facies at Gutcher Lake near Wawa, Ontario, Canada. This regional metamorphism also modified the stock and its partly enveloping aureole of epidote—hornblende hornfels. Mafic metavolcanic rocks in the greenstone succession are derived from pillowed flow, amygdular flow, massive flow or sill, and minor hyaloclastites that include pillow breccia. Stratiform lenses of felsic metavolcanic rocks are derived from massive flow or tuff, crystal tuff, lapilli tuff and volcanic breccia. Chalcopyrite and native gold coexist in stringers and veins of quartz, pyrrhotite and pyrite in a layered assemblage with cherty iron-formation at the stratigraphic top of the stock. Ego Mines Ltd. reports 348 000t averaging 1.60% copper and 3.77 g t −1 gold. The deposition of pillowed and amygdular lavas on the Archean sea-floor was interrupted by the venting of felsic magma that yielded viscous flows and pyroclastic tuffs. Heat emanating from the rising stock caused seawater to convect in the volcanic sequence. Hot modified seawater debouched onto an interflow trough above the stock, mixed with ambient seawater, and precipitated aprons of sulphidic mud and chert amongst clastic sediment. Down-slope slumping culminated in a stratified assemblage with pockets of debris-flow breccia. Compaction and de-watering of this package concentrated some of the dispersed sulphide material into fractures to form veins. The stock and the intruded succession was then metamorphosed to the greenschist facies.