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A talk to the Summer batch of Hacker School students – HackerSchoolTalk/ at master · johnmyleswhite/HackerSchoolTalk. Off Vancouver. Is Canada, salmon fishing effort is concentrated around topographic features and thermal boundaries (Borstad et al ).
– cretaceous plutonic rocks: Topics by
Zircon ages and wide-ranging trace element concentrations suggest crystallization mainly in differentiated melt pockets in high-crystallinity magmas that may repeatedly freeze and thaw. Not all zircons survive recycling into undersaturated magmas, in which zircon will dissolve given enough time, depending on temperature and dissolved volatiles.
Recent zircon geochronologic results for volcanic and plutonic rocks lend credence to the “mush model” of rhyolite genesis and batholith consolidation. Crystal-poor rhyolites and leucogranites are melts segregated by compaction or gas-driven filter pressing from granitoid crystal mush emplaced incrementally in the middle to upper crust and powered by basaltic magma repeatedly injected into the lower reaches of the mush column.
Balance between heat loss and basaltic influx determines whether the mush freezes or partially thaws at any given time, blurs internal contacts in resulting plutons , and can produce large volumes of crystal-rich ignimbrite or rapid separation and eruption of crystal-poor rhyolite.
Zircon U-Pb dating of the plutonic rocks indicates that they were formed at ca. These ages are consistent with Eocene-Oligocene tholeiite and calc-alkaline arc magmatism in the Izu-Bonin-Mariana IBM Arc and exclude several previous models for the origin of the Mineoka-Setogawa ophiolitic rocks.
The geochemical characteristics of these plutonic rocks are similar to those of the Eocene-Oligocene IBM tholeiite and calc-alkaline volcanic rocks as well as to the accreted middle crust of the IBM Arc, the Tanzawa Plutonic Complex. Moreover, their lithology is consistent with those of the middle and lower crust of the IBM Arc estimated from the seismic velocity structure.
Additionally, the presence of the Mineoka-Setogawa intermediate to felsic plutonic rocks supports the hypothesis that intermediate magma can form continental crust in intra-oceanic arcs. The Shir-Kuh pluton Central Iran : Magnetic fabric evidences for the coalescence of magma batches during emplacement. It is composed of peraluminous rocks , corresponding to ilmenite-bearing S-type granites compositionally ranging from granodiorites to leucogranites.
These rocks show a continuum in their chemistry attributed to progressive differentiation. This allows using the anisotropy of magnetic susceptibility technique to tempt establishing the relative chronology between emplacements of magma batches in the pluton.
The rather low susceptibility magnitudes Km pluton. The magnetic fabrics data magnetic lineation and foliation maps, K, P and T parameters , complemented by field and microstructural observations, reveal that two feeder zones at least, as characterized by areas having steep lineations ascribed to magma flow likely issued from the base of the brittle crust, served as conduits for the magmas.
The early Cretaceous age of the pluton , the orientations of the feeding zones, the overall lineation directions throughout the pluton , as well as the S-type nature of the magmas call for a dextral transpressive regime which might have been active in the back-arc region located above the subducting eastern branch of the Neo-Tethys.
Combined anisotropy of magnetic susceptibility AMS , structural, and field studies document a clear pattern of magmatic flow radiating from at least three subvertical conduits pluton , matching the expected pattern for laccolithic emplacement. Ascent conduits within the Big Hole Canyon pluton are coincident with the fold axis of an anticline above a thrust ramp, suggesting that the magma ascended up the fault of the fault-bend-fold.
Preliminary thermal modeling indicates that the BHCp was emplaced in , years, likely between periods of regional shortening deformation.
Rapid magma ascent rates calculated by dike flow modeling and implied by entrained wall- rock xenoliths may indicate sequential magma injection into the pluton ; an absence of chill margins between phases within the pluton indicates that sequential injections must have taken place quickly enough that the magmas did not have time to cool below the solidus temperature.
The geometry and location of the BHCp suggest that magma used a pre-existing fault as a mechanical discontinuity for both ascent and emplacement. Continued intrusion of magma had a sufficient amount of driving pressure to stretch, shear, and lift the roof of the pluton.
Detailed field mapping, structural studies, AMS, and thermobarometry indicate that the Late Cretaceous Big Hole Canyon pluton was emplaced as a laccolith at the top of a pre-existing fault-bend-fold in the frontal portion of the Sevier fold-thrust belt. Late-stage sinking of plutons. Many granodiorite to diorite plutons in the Great Basin of western North America are surrounded by rim monoclines or anticlines that suggest relative downward movement of the plutons while wall rocks were hot and ductile.
We propose that such plutons rise to a level of approximately neutral buoyancy and then founder as their densities increase??? Late-stage sinking of intermediate to mafic plutons should be common when wall rocks are rich in weak, low-density minerals such as quartz and calcite. Structures related to sinking will overprint those related to initial pluton emplacement and may be mistaken for regional tectonic structures.
Tonalite and trondhjemite plutonism in the western Chugach Mountains, so. Alaska: an example of near trench magmatism. In the northern Chugach Mountains of southern Alaska a suite of granitoid plutons were emplaced in a near-trench setting in mid-Early Cretaceous time. The plutons intrude both the then continental edge marked by Jurassic igneous and metamorphic rocks of the Peninsular terrane and the accretionary prism composed of the Early Cretaceous McHugh Complex.
Field, petrographic and geochemical data classify the plutonic rocks as ranging from a hornblende-biotite tonalite to a biotite trondjhemite. Most of the rocks are post-metamorphic and show hypidiomorphic granular textures. Locally, however, the rocks are weakly foliated and quartz shows grain size reduction serrate textures indicative ofmore » minor ductile strain; suggesting some strain following emplacement. Two possible petrographic models fit the data. The entail a fractional crystallization-assimilation model and a partial melting of a low temperature hydrothermally altered basalt.
The tectonic mechanism responsible for this unusual event is elusive but two models are allowable: 1 a ridge-trench encounter; and 2 melting along thrust planes during initiation of subduction – a mechanism analogous to melting along great crystalline thrust sheets.
Emplacement, rapid burial, and exhumation of Ma plutons in southeastern Alaska. In southeastern Alaska, granodiorite-tonalite plutons of the Admiralty-Revillagigedo belt intruded the Jurassic- Cretaceous Gravina belt along the eastern side of the Alexander terrane around 90 Ma. These plutons postdate some deformation related to a major contractional event between the previously amalgamated Wrangellia and Alexander terranes and the previously accreted terranes of the North American margin.
We studied the aureole mineral assemblages of these plutons near Petersburg, Alaska, determined pressure and temperature of equilibration, and examined structures that developed within and adjacent to these plutons. Parallelism of magmatic and submagmatic fabrics with fabrics in the country rock indicates synchroneity of pluton emplacement with regional deformation and suggests that magma transport to higher crustal levels was assisted by regional deformation.
Replacement of andalusite by kyanite or sillimanite indicates crustal thickening soon after pluton emplacement. Regional structural analysis indicates the crustal thickening was accomplished by thrust burial.
Thermobarometric analyses indicate the aureoles reached near-peak temperatures of to ?? C at pressures of to MPa. Structural observations indicate there was contractional deformation before, during, and after emplacement of the Ma plutons. Initial exhumation of the Admiralty-Revillagedo belt in the Petersburg area may have occurred along a thrust west of the pluton belt within the Gravina belt. Thermochronology of Cretaceous batholithic rocks in the northern Peninsular Ranges batholith, southern California: Implications for the Late Cretaceous tectonic evolution of southern California.
Miggins, Daniel P. The thermochronology for several suites of Mesozoic metamorphic and plutonic rocks collected throughout the northern Peninsular Ranges batholith PRB was studied as part of a collaborative isotopic study to further our understanding of the magmatic and tectonic history of southern California.
Notable characteristics of the various ages from different dating methods include: 1 Zircon. Guidelines to classification and nomenclature of Arabian felsic plutonic rocks. Well-defined procedures for classifying the felsic plutonic rocks of the Arabian Shield on the basis of petrographic, chemical and lithostratigraphic criteria and mineral-resource potential have been adopted and developed in the Saudi Arabian Deputy Ministry for Mineral Resources over the past decade.
A number of problems with conventional classification schemes have been identified and resolved; others, notably those arising from difficulties in identifying precise mineral compositions, continue to present difficulties.
The petrographic nomenclature used is essentially that recommended by the International Union of Geological Sciences. Problems that have arisen include the definition of: 1 rocks with sodic, zoned or perthitic feldspar, 2 trondhjemites, and 3 alkali granites. Chemical classification has been largely based on relative molar amounts of alumina, lime and alkalis, and the use of conventional variation diagrams, but pilot studies utilizing univariate and multivariate statistical techniques have been made.
The classification used in Saudi Arabia for stratigraphic purposes is a hierarchy of formation-rank units, suites and super-suites as defined in the Saudi Arabian stratigraphic code. For genetic and petrological studies, a grouping as ‘associations’ of similar and genetically related lithologies is commonly used.
In order to indicate mineral-resource potential, the felsic plutons are classed as common, precursor, specialized or mineralized, in order of increasing exploration significance. The oldest metamorphic episode s postdates Middle Permian magmatism and predates the intrusion of Late Triassic Ma granitoids into the Fortymile River assemblage Taylor Mountain assemblage of previous papers.
In the eastern Eagle quadrangle, rapid and widespread Early Jurassic cooling is indicated by??? We interpret these Early Jurassic ages to represent cooling resulting from northwest-directed contraction that emplaced the Fortymile River assemblage onto the Nasina assemblage to the north as well as the Lake George assemblage to the south. This cooling was the final stage of a continuum of subduction-related contraction that produced crustal thickening, intermediate- to high-P metamorphism within both the Fortymile River assemblage and the structurally underlying Lake George assemblage, and Late Triassic and Early Jurassic plutonism in the Fortymile River and Nasina assemblages.
We interpret the Early Cretaceous metamorphic cooling, in most areas, to have resulted from regional extension and exhumation of the lower plate, previously tectonically thickened during Early Jurassic and older convergence.
Late Paleozoic crustal history of central coastal Queensland interpreted from geochemistry of Mesozoic plutons : The effects of continental rifting. The eastern margin of Australia is understood to be the result of continental rifting during the Cretaceous and Tertiary. These isotopic signatures are much less evolved than the Late Carboniferous-Permian batholith that many Cretaceous plutons intrude. As rocks ranging in age from about Ma are well exposed near Bowen, we can track magma evolution through time.
The significant change of magma source occurred much earlier than the Cretaceous based on the fact that Triassic granites in the same area are also isotonically primitive. We attribute the changes of magma composition to crustal rifting during the Late Permian and earliest Triassic. The Cretaceous rocks actually latest Jurassic to Cretaceous , Ma themselves show compositional trends with time.
Rocks of appropriate mineralogy for Al-in-hornblende geobarometry yield pressures ranging from to 80 MPa for rocks ranging in age from to Ma, respectively. More significantly, this older group is relatively compositionally restricted, and is Sr-rich, and Y- and Zr-poor compared to Ma rocks.
This younger groups is bimodal, being comprised principally of basalts and rhyolites granites. REE patterns for a given rock type, however, do not differ with age tribute these relatively subtle trace element differences to small differences in conditions T, aH2O at the site of melting. Cretaceous crustal rifting can explain the range of rock types and the spatial distribution of rocks Cretaceous intrusions. A subduction-related setting is assigned to the Ma.
U-Pb zircon geochronology of plutonism in the northern Peninsular Ranges batholith, southern California: Implications for the Late Cretaceous tectonic evolution of southern California. Previously noted petrologic, mineralogic, and textural differences delineated four major zonations from west to east and raised the need for detailed geochemical and isotopic work. U-Pb zircon geochronology establishes that these zonations are essentially temporally separate. Despite petrologic differences, a relatively smooth progression of magmatism is seen from west to east.
A fourth zone is defined by magmatism at ca. The age data presented here differ slightly from those presented in earlier work for similar rocks exposed across the middle and southern portions of the Peninsular Ranges batholith in that our data define a relatively smooth progression of magmatism from west to east, and that the transition from western-type to eastern-type plutonism is interpreted to have occurred at ca.
The progressive involvement of older crustal components in the enrichment of eastern Peninsular Ranges batholith—type magma sources is documented by the occurrence of Proterozoic zircon inheritance within samples of the eastern part of the batholith. U-Pb ages and Hf isotope compositions of zircons in plutonic rocks from the central Famatinian arc, Argentina.
Otamendi, Juan E. The Famatinian arc formed around the South Iapetus rim during the Ordovician, when oceanic lithosphere subducted beneath the West Gondwana margin.
We present combined in situ U-Th-Pb and Lu-Hf isotope analyses for zircon to gain insights into the origin and evolution of Famatinian magmatism. Zircon crystals sampled from four intermediate and silicic plutonic rocks confirm previous observations showing that voluminous magmatism took place during a relatively short pulse between the Early and Middle Ordovician Ma. Typical tonalites and granodiorites that contain zircons with evolved Hf isotopic compositions formed upon incorporating meta sedimentary materials into calc-alkaline metaluminous magmas.
The evolved Hf isotope ratios of zircons in the subduction related plutonic rocks strongly reflect the Hf isotopic character of the metasedimentary contaminant, even though the linked differentiation and growth of the Famatinian arc crust was driven by ascending and evolving mantle magmas. Geochronology and Hf isotope systematics in plutonic zircons allow us understanding the petrogenesis of igneous series and the provenance of magma sources.
However, these data could be inadequate for computing model ages and supporting models of crustal evolution. K-Ar geochronology of basement rocks on the northern flank of the Huancabama deflection, Ecuador.
The Huancabamba deflection, a major Andean orocline located at the Ecuador-Peru border, constitutes an important geologic boundary on the Pacific coast of South America. Crust to the north of the deflection is oceanic and the basement is composed of basic igneous rocks of Cretaceous age, whereas crust to the south is continental and felsic rocks of Precambrian to Cretaceous age make up the basement. The northern flank of the Huancabamba Deflection in El Oro Province, Ecuador, is underlain by Precambrian polymetamorphic basic rocks of the Piedras Group; shale, siltstone, sandstone, and their metamorphosed equivalents in the Tahuin Group in part of Devonian age ; concordant syntectonic granitic rocks ; quartz diorite and alaskite of the Maroabeli pluton ; a protrusion of serpentinized harzburgite that contains a large inclusion of blueschist-facies metamorphic rocks , the Raspas Formation, and metamorphic rocks north of the La Palma fault.
This is interpreted as an uplift age and is consistent with a regional metamorphism of Paleozoic age. A nearby sample from the Piedras Group that yielded a hornblende K-Ar age of ? Biotite from quartz diorite of the mesozonal Maroabeli pluton yields a Late Triassic age ?
Emplacement of the pluton may postdate regional metamorphism of the Tahuin Group. This age is believed to date the isostatic rise of the encasing serpentinized harzburgite as movement along a subjacent subduction zone ceased, and it is synchronous with the age of the youngest lavas of a coeval volcanic arc in eastern Ecuador. A Late Cretaceous K-Ar age The case for simultaneous deformation, metamorphism and plutonism : an example from Proterozoic rocks in central Arizona.
The syntectonic 1. Synchronous plutonism and deformation is indicated by syn-shortening dikes, sills, and veins; parallel magmatic and solid state fabrics; fabrics in xenoliths; and a foliation triple point.
Synchronous deformation and metamorphism is indicated by porphyroblast inclusion geometries that document the synmetamorphic development of the S2 cleavage. The pluton was emplaced adjacent to the Shylock shear zone during progressive shortening.
Emplacement of granite as NE-trending sheets was facilitated by temporal partitioning of transpressional convergence into strike-slip and dip-slip components. At the scale of the pluton ‘s aureole and on the relatively rapid time scale of 10 6 y, regional deformation and metamorphism were punctuated by thermal softening and increased diffusion rates.
Data suggests that accretion of Proterozoic arcs in Arizona involved diachronous pluton -enhanced deformation and associated high temperature-low pressure regional metamorphism. Exposed paleo-arcs, such as the Rosario segment of the Cretaceous Alisitos Arc in Baja California, Mexico, provide an opportunity to explore the evolution of arc crust through time.
Remarkable 3-D exposures of the Rosario segment record crustal generation processes in the volcanic rocks and underlying plutonic rocks. In this study, we explore the physical and geochemical connection between the plutonic and volcanic sections of the extensional Alisitos Arc, and elucidate differentiation processes responsible for generating them. Upper crustal volcanic rocks have a coherent stratigraphy that is km thick and ranges in composition from basalt to dacite.
The most felsic compositions The most mafic compositions The transition to deeper plutonic rocks is clearly an intrusive boundary, where plutonic units intrude the volcanic units. Plutonic rocks are dominantly a quartz diorite main phase with a more mafic, gabbroic margin. A transitional zone is observed along the contact between the plutonic and volcanic rocks , where volcanics have coarsely recrystallized textures.
Most, but not all, samples are low K. REE patterns are relatively flat with limited enrichment. We interpret plutonic and volcanic units to have similar geochemical relationships, where liquid lines of descent show the evolution of least to most evolved magma types. We provide a model for the formation and magmatic evolution of the Alisitos Arc. Age and tectonic setting of Mesozoic metavolcanic and metasedimentary rocks , northern White Mountains, California.
Mesozoic metavolcanic and metasedimentary rocks in the northern White Mountains, eastern California and western Nevada, are separated from lower Paleozoic and Precambrian rocks by Jurassic and Cretaceous plutons.
The large stratigraphic hiatus across the plutons is called the Barcroft structural break. The Barcroft Granodiorite has been thrust westward over most of the Mesozoic section. It is everywhere in fault contact with overturned metasedimentary rocks on the west side of the range, rocks which were previously thought to be upright and the oldest part of the Mesozoic section. Metamorphic facies map of Southeastern Alaska; distribution, facies, and ages of regionally metamorphosed rocks.
Nearly all of the bedrock in Southeastern Alaska has been metamorphosed, much of it under medium-grade conditions during metamorphic episodes that were associated with widespread plutonism. The oldest metamorphisms affected probable arc rocks near southern Prince of Wales Island and occurred during early and middle Paleozoic orogenies. The predominant period of metamorphism and associated plutonism occurred during Early Cretaceous to early Tertiary time and resulted in the development of the Coast plutonic -metamorphic complex that extends along the inboard half of Southeastern Alaska.
Middle Tertiary regional thermal metamorphism affected a large part of Baranof Island. Geochemical constraints on the link between volcanism and plutonism at the Yunshan caldera complex, SE China. Our results imply that volcanic and plutonic rocks in caldera systems may provide unique constraints on the evolution of the magmatic system in which both the erupting melt and the residual crystalline material are being preserved.
The Strawberry mine roof pendant, 90 km northeast of Fresno, Calif. The metasedimentary rocks are a former miogeosynclinal sequence of marl and limestone now metamorphosed to calc-silicate hornfels and marble. A pelecypod found in the calc-silicate hornfels has been tentatively identified as a Mesozoic bivalve, possibly Inoceramus pseudomytiloides of Early Jurassic age.
These metasedimentary rocks are similar in lithology, structure, and gross age to the metasedimentary rocks of the Boyden Cave roof pendant and are assigned to the Lower Jurassic Kings sequence. The younger metaigneous rocks are metamorphosed shallow-in trusi ve rocks that range in composi tion from granodiorite to rhyolite. These rocks are similar in composition and age to the metavolcanic rocks of the surrounding Merced Peak quadrangle and nearby Ritter Range, and probably represent necks or dikes that were one source for the meta volcanic rocks.
The roof pendant is intruded by several plutons , ranging in composition from dioritic to highly felsic, that constitute part of the granodiorite of Jackass Lakes, also M middle Cretaceous age. The contemporaneous suites of metaigneous, metavolcanic, and plutonic rocks in the region represent a middle Cretaceous period of calc-alkalic volcanism and plutonism in the central Sierra Nevada and are interpreted as part of an Andean-type volcanic- plutonic arc.
Three deformations are documented in the roof pendant. The first deformation is reflected only in the metasedimentary rocks and consists of northeast-to east-west-trending folds.
Similar structures occur in the Boyden Cave roof pendant and in the Calaveras Formation and represent a Middle Jurassic regional deformation. Evidence of the second deformation occurs in the metasedimentary and metaigneous rocks and consists of folds, faults, minor structures, and. The origins of high-silica igneous rocks are debated, as they may be products of high-degree fractional crystallization or low-degree partial melting.
They may play a role in the generation of intermediate igneous rocks and are responsible for large, ash-rich volcanic eruptions. High-silica granites and rhyolites in the Sierra Nevada, California, and the Colorado Mineral Belt CMB are investigated using isotope geochemistry to better understand how they bear on these questions.
High-silica granites in both suites have relatively high concentrations of middle rare earth and high field strength elements. Data for these and other discrete high-silica plutons in the batholith suggest they were derived from titanite-free sources in the deep crust, unlike similarly felsic parts of zoned intrusive suites. High-silica granites of the SIS have supracrustal O in zircon, crustal Sr and Nd whole rock isotopic compositions, and negative Ce anomalies suggesting the SIS granites may have been derived from oceanic sedimentary sources.
In contrast, KIS granites have mantle-like isotopic compositions. The location and geochemistry of the KIS suggests it may have resulted from backarc magmatism in the mid- Cretaceous Sierra. Volcanic and plutonic rocks in the central CMB were emplaced during the Laramide orogeny and subsequent Oligocene-Eocene volcanic flare-up.
Strontium and Nd data suggest the Ma Twin Lakes pluton and igneous rocks as young as 24 Ma were derived from a persistent mafic lower crust or enriched lithospheric mantle source. Groundwater from Lower Cretaceous rocks in Kansas.
Sandstones in Lower Cretaceous rocks contain supplies, of water that may be adequate to meet increasing present and future demands for supplemental municipal and domestic use in central and western Kansas. An estimated 70 to 80 million acre-feet 86, to 99, cubic hectometers of water containing less than 1, milligrams per liter dissolved solids may be acceptable for use at the present An additional 10 to 15 million acre-feet 12, to 18, cubic hectometers containing 1, to 3, milligrams per liter dissolved solids is estimated to be available for use in the future with appropriate desalinization.
The rocks dip from a structural high in the southwest part of the State to structural lows in the northwest and north-central part. Depth below land surface increases generally northwestward to about 2, feet meters ; thickness of the rocks increases westward, nearly zero to about feet meters.
The rocks consist chiefly of marine to nonmarine shale and silt- stone interbedded with coastal to deltaic sandstone. The interbedded sandstone, which composes about one-third of the rocks , consists of one or more lenses that thicken westward to about feet meters in the central part of western Kansas. The yield of water to individual wells is related to areal extent, thickness, and interconnection of the sand lenses and to grain size and cementation of the sand.
Large amounts of water may be pumped by wells where loosely cemented sand lenses are interconnected. Wells commonly yield adequate supplies for domestic and stock use; reported yields from municipal and irrigation wells range from about to 2, gallons per minute 6 to liters per second.
Recharge to the Lower Cretaceous-rocks occurs in the area of outcrop and from hydraulically connected saturated Cenozoic rocks , especially in the southern part of the State. Dyman, T. More than 5, m 17, ft of Cretaceous strata are present in southwestern Montana, less than m 1, ft in eastern South Dakota. The asymmetry resulted from varying rates of subsidence due to tectonic and sediment loading.
The strata consist primarily of sandstone, siltstone, mudstone, and shale. Conglomerate is locally abundant along the western margin, whereas carbonate is present in most areas of the eastern shelf. Sediment was deposited in both marine and nonmarine environments as the shoreline fluctuated during major tectonic and eustatic cycles. A discussion of Cretaceous strata from southwestern to east-central Montana, the Black Hills, eastern South Dakota, and southwestern Minnesota shows regional stratigraphy and facies relations, sequence, boundaries, and biostratigraphic and radiometric correlations.
The thick Cretaceous strata in southwestern Montana typify nonmarine facies of the rapidly subsiding westernmost part of the basin. These strata include more than 3, m 10, ft of synorogenic conglomerate of the Upper Cretaceous part of the Beaverhead Group.
West of the Madison Range, sequence boundaries bracket the Kootenai Aptian and Albian , the Blackleaf Albian and Cenomanian , and the Frontier Formations Cenomanian and Turonian ; sequence boundaries are difficult to recognize because the rocks are dominantly non-marine. Cretaceous strata in east-central Montana about 1, m; 4, ft thick lie at the approximate depositional axis of the basin and are mostly marine terrigenous rocks. Chert-pebble zones in these rocks reflect stratigraphic breaks that may correlate with sequence boundaries to the east and west.
Cretaceous rocks of the Black Hills region consist of a predominantly marine clastic sequence averaging approximately 1, m 5, ft thick. The Cretaceous System in eastern South. The post collisional magmatic activity produced several volcano- plutonic complexes in NW Anatolia Turkey during the late Oligocene- Middle Miocene. One of the major volcano- plutonic complexes, the Solarya volcano- plutonic complex is remarkable for its coeval and cogenetic plutonic Solarya pluton , hypabysal and volcanic rocks of Early Miocene Ma age.
Solarya pluton is an epizonal pluton which discordantly intruded into metamorphic and nonmetamorphic basement rocks of Triassic age. It is a N-S trending magmatic body covering an area of km2,approximatelly 20 km in length and 10 km in width.
Based on the field and petrographic studies, three main rock groups distinguished in Solarya pluton ; K-feldspar megacrystalline granodiorite, microgranite-granodiorite and haplogranite. Porphyritic and graphic-granophyric textures are common in these three rock groups.
Pluton contains magmatic enclaves and syn- plutonic dykes of dioritic composition. Hypabyssal rocks are represented by porphyritic microdiorite and porphyritic quartz-diorite. They form porphyry plugs, sheet inrusions and dykes around the pluton.
Porphyrites have microcrystalline-cryptocrystalline groundmass displaying micrographic and granophyric textures. Petrographically similar to the hypabyssal rocks , volcanic rocks are formed from andesitic and dasitic lavas and pyroclastic rocks. Plutonic , hypabyssal and volcanic rocks of Solarya volcano- plutonic complex show similar major-trace element and Sr-Nd-Pb isotopic compositions, indicating common magmatic evolution and multicomponent melt sources including mantle and crustal components.
These geochemical characteristics and isotopic signatures are considered to reflect the composition of the magmas derived from a. Distribution of manganese between coexisting biotite and hornblende in plutonic rocks.
The distribution of manganese between coexisting biotite and hornblende for 80 mineral pairs from igneous rocks of diverse provenance including Southern California, Sierra Nevada, Boulder, and Boulder Creek batholiths and the Jemez Mountains volcanics has been determined by neutron activation analysis.
Comparison of Kd values of mineral pairs with bulk chemical composition of host rocks reveals no correlation. Because initial crystallization temperatures vary with rock composition, the lack of correlation of composition with Kd suggests that the equilibrium distribution of Mn between biotite and hornblende reflects exchange at subsolidus temperatures rather than initial crystallization temperatures. The highest Kd values are for volcanic rocks , in which rapid quenching prevents subsolidus redistribution of Mn.
For sample pairs from the Southern California and Sierra Nevada batholiths there is a positive correlation of Kd with TiO2 content of biotite. An unusually large, elongate Jurassic pluton of trondhjemite, about by km in dimensions, intruded Jurassic plutonic and metamorphic rocks of the Peninsular terrane in the central Talkeetna Mountains of south-central Alaska. Muscovite and biotite yield minimum ages of Ma.
The N40[degree]E-trending body is concordant with regional structures. It is the youngest member of a subduction-related Jurassic plutonic suite in the Peninsular terrane that, along with Wrangellia, was accreted to the North American continent in the middle Cretaceous.
Biotite is the chief mafic mineral. Minormore » muscovite and garnet are common and green hornblende rare. High Al[sub 2]O[sub 3] Averages for Zr ppm and Nb 3. The pluton appears homogeneous in outcrop. Metamorphic basement rocks from SW Borneo are undated but have been suggested to be Palaeozoic. It has no sedimentary cover and the exposed basement has been widely assumed to be a crustal fragment from the Indochina-China margin.
Metamorphic rocks of the Pinoh Group in Kalimantan Indonesian Borneo are intruded by granitoid rocks of Jurassic- Cretaceous age, based on K-Ar dating, suggesting emplacement mainly between and 80 Ma.
The Pinoh metamorphic rocks have been described as a suite of pelitic schists, slates, phyllites, and hornfelses, and have not been dated, although they have been correlated with rocks elsewhere in Borneo of supposed Palaeozoic age. Pelitic schists contain biotite, chlorite, cordierite, andalusite, quartz, plagioclase and in some cases high-Mn almandine-rich garnet.
Many have a shear fabric associated with biotite and fibrolite intergrowth. Contact metamorphism due to intrusion of the granitoid rocks produced hornfelses with abundant andalusite and cordierite porphyroblasts. Granitoids range from alkali-granite to tonalite and contain abundant hornblende and biotite, with rare white mica. Zircons from granitoid rocks exhibit sector- and concentric- zoning; some have xenocrystic cores mantled by magmatic zircon.
There are four important age populations at c. Zircons from pelitic metamorphic rocks are typically euhedral, with no evidence of rounding or resorbing of grains; a few preserve volcanic textures. They record older ages than those from igneous rocks ; U-Pb ages are Cretaceous with a major population between and Ma. A single sample contains Proterozoic. Distribution, facies, ages, and proposed tectonic associations of regionally metamorphosed rocks in east- and south-central Alaska.
Most of the exposed bedrock in east- and south-central Alaska has been regionally metamorphosed and deformed during Mesozoic and early Cenozoic time. All the regionally metamorphosed rocks are assigned to metamorphic-facies units on the basis of their temperature and pressure conditions and metamorphic age.
North of the McKinley and Denali faults, the crystalline rocks of the Yukon- Tanana upland and central Alaska Range compose a sequence of dynamothermally metamorphosed Paleozoic and older? This sequence was extensively intruded by postmetamorphic mid- Cretaceous and younger granitoids. Many metamorphic-unit boundaries in the Yukon-Tanana upland are low-angle faults that juxtapose units of differing metamorphic grade, which indicates that metamorphism predated final emplacement of the fault-bounded units.
In some places, the relation of metamorphic grade across a fault is best explained by contractional faulting; in other places, it is suggestive of extensional faulting. Near the United States-Canadian border in the central Yukon- Tanana upland, metamorphism, plutonism , and thrusting occurred during a latest Triassic and Early Jurassic event that presumably resulted from the accretion of a terrane that had affinities to the Stikinia terrane onto the continental margin of North America.
Elsewhere in the Yukon-Tanana upland, metamorphic rocks give predominantly late Early Cretaceous isotopic ages. These ages are interpreted to date either the timing of a subsequent Early Cretaceous episode of crustal thickening and metamorphism or, assuming that these other areas were also originally heated during the latest Triassic to Early Jurassic and remained buried, the timing of their uplift and cooling.
This uplift and cooling may have resulted from extension. Geochemistry of Mesozoic plutons , southern Death Valley region, California: Insights into the origin of Cordilleran interior magmatism. Mesozoic granitoid plutons in the southern Death Valley region of southeastern California reveal substantial compositional and isotopic diversity for Mesozoic magmatism in the southwestern US Cordillera. Jurassic plutons of the region are mainly calc-alkaline mafic granodiorites with??
Cretaceous granitoids of the region are mainly monzogranites with?? The granitoids were generated by mixing of mantle-derived mafic melts and pre-existing crust – some of the Cretaceous plutons represent melting of Paleoproterozoic crust that, in the southern Death Valley region, is exceptionally heterogeneous. A Cretaceous gabbro on the southern flank of the region has an unuasually juvenile composition?? Ndi Geographic position of the Mesozoic plutons and comparison with Cordillera plutonism in the Mojave Desert show that the Precambrian lithosphere craton margin in the eastern Mojave Desert region may consists of two crustal blocks separated by a more juvenile terrane.
Natural radionuclides in the rocks of the Valle del Cervo Pluton in Piedmont. Monitoring of the gamma radiation in Valle del Cervo Pluton was performed by determining U and Th contents in the main rock types cropping out over the entire area and pertaining to the granitic complex, syenitic complex and monzonitic complex.
In particular, syenitic rocks were largely used as building and ornamental materials e. Sienite della Balma. All the samples are fresh and do not present joints or fractures filled with U minerals. For all the analysed rocks uranium activity is higher than thorium one.
The lowest value of radioactive concentration is referred to rocks of the granitic complex. The most active rocks are syenites. The data confirm the high activities of Valle del Cervo rock types, strongly connected with high K content of the source magma geochemical signature ; on the contrary, the activity seems to be not related to the location of the samples.
The oldest and largest pulse of plutonism was focused between Ma when fluxes were a minimum of 3. A second, smaller peak of magmatism at Ma minimum of 8. Tonalite dominates at all levels of the section. Intrusions range from large plutons to thin rocks that record less focused magmatism.
Sheeted intrusions and gently dipping tabular bodies are more common with depth. Some of these plutons fit the model that most intrusions are subhorizontal and tabular, but many do not, reflecting the complex changes in lithology and rheology in arc crust undergoing regional shortening.
The steep sheeted plutons partly represent magma transfer zones that fed the large shallow plutons , which were sites of intermittent.
In magmatic series considered to form by crystal fractionation intermediate rocks are usually much less abundant than expected. Yet, intermediate plutonic rocks , predominantly monzodiorites, are very abundant in the Neoproterozoic Timna igneous complex, S. A previously unnoticed plutonic shoshonitic suite was recently defined and mapped in Timna Litvinovsky et al. It mostly comprises intermediate rocks in a seemingly ‘continuous’ trend from monzodiorite through monzonite to quartz syenite.
Macroscale textures including gradational boundaries of mafic and felsic rocks and MME suggest that magma mixing is central in forming intermediate rocks in Timna. Our petrographic, microtextural and mineral chemistry study delineates the mode of incipient mixing, ultimate mingling and crystal equilibration in hybrid melts. Each texture has an affinity to a particular mixing region.
A modal count of these textures leads to a kinetic mixing model involving multi temporal and spatial scales necessary to form the hybrid intermediate rocks. REE patterns in zircon shows that it originated from both mafic and felsic parent melts. Whole rock Fe vs Sr plot suggests a two-stage mixing between the monzogabbro and quartz-syenite producing first mesocratic syenite, and subsequent mixing with a fractionating monzogabbro resulting in monzonitic compositions. A fractionating monzogabbro intruded into a syenitic melt sequentially.
While slowly cooling, the monzogabbro heated the immediate syenitic melt, lowering the viscosity and rheological obstruction to overturn. Early cretaceous lower crustal reworking in NE China: insights from geochronology and geochemistry of felsic igneous rocks from the Great Xing’an range. In combination with the high K2O contents 4.
The syenogranites and rhyolites are likely formed in Mongol-Okhotsk oceanic subduction setting. Incorporating other lower crust-originated felsic rocks in Erguna and Xing’an massifs and Songliao basin, it is argued that lower crustal reworking is pronounced in NE China during Early Cretaceous. Regional stratigraphic cross sections of Cretaceous rocks from east-central Arizona to the Oklahoma Panhandle. Sedimentary rocks of Cretaceous age along Transect DD” in eastern Arizona, northern New Mexico, southern Colorado, and western Oklahoma consist mainly of sandstone, siltstone, shale, limestone, and bentonite.
They accumulated as sediments in continental, nearshore marine, and offshore marine environments on the west side of a north-trending epicontinental sea. The rocks record intermittent deposition and erosion as well as regional and local subsidence and uplift possibly beginning in Aptian time about Ma and occurring in Albian through Maastrichtian time about Most of the Lower Cretaceous Berriasian through Aptian, Ma in this transect is represented by a basal unconformity.
The Cretaceous rocks and unconformities along the transect are depicted on the attached lithostratigraphic cross sections sheets 1 and 2 ; one extending from the Mogollon Rim in eastern Arizona to Pagosa Springs in southwestern Colorado and the other from Pagosa Springs, Colorado, to Kenton in western Oklahoma. The same rocks and unconformities are also represented on the attached chronostratigraphic profile sheet 3 , which was prepared mainly from surface and subsurface data shown on the lithostratigraphic cross sections.
Multiphase groundwater flow near cooling plutons. We investigate groundwater flow near cooling plutons with a computer program that can model multiphase flow, temperatures up to ?? C, thermal pressurization, and temperature-dependent rock properties. A series of experiments examines the effects of host- rock permeability, size and depth of pluton emplacement, single versus multiple intrusions, the influence of a caprock, and the impact of topographically driven groundwater flow.
We also reproduce and evaluate some of the pioneering numerical experiments on flow around plutons. Host- rock permeability is the principal factor influencing fluid circulation and heat transfer in hydrothermal systems. The hottest and most steam-rich systems develop where permeability is of the order of m2. Temperatures and life spans of systems decrease with increasing permeability.
Conduction-dominated systems, in which permeabilities are??? Pluton size, emplacement depth, and initial thermal conditions have less influence on hydrothermal circulation patterns but affect the extent of boiling and duration of hydrothermal systems. Topographically driven groundwater flow can significantly alter hydrothermal circulation; however, a low-permeability caprock effectively decouples the topographically and density-driven systems and stabilizes the mixing interface between them thereby defining a likely ore-forming environment.
Paleozoic subduction complex and Paleozoic-Mesozoic island-arc volcano- plutonic assemblages in the northern Sierra terrane.
This field trip provides an overview of the stratigraphic and structural evolution of the northern Sierra terrane, which forms a significant part of the wall rocks on the western side of the later Mesozoic Sierra Nevada batholith in California. The terrane consists of a pre-Late Devonian subduction complex Shoo Fly Complex overlain by submarine arc-related deposits that record the evolution of three separate island-arc systems in the Late Sevonian-Early Mississippian, Permian, and Late Triassic-Jurassic.
The two Paleozoic are packages and the underlying Shoo Fly Complex have an important bearing on plate-tectonic processes affecting the convergent margin outboard of the Paleozoic Cordilleran miogeocline, although their original paleogeographic relations to North America are controversial.
The third arc package represents an overlap assemblage that ties the terrane to North America by the Late Triassic and helps constrain the nature and timing of Mesozoic orogenesis. Several of the field-trip stops examine the record of pre-Late Devonian subduction contained in the Shoo Fly Complex, as well as the paleovolcanology of the overlying Devonian to Jurassic arc rocks.
Excellent glaciated exposures provide the opportunity to study a cross section through a tilted Devonian volcano- plutonic association. Additional stops focus on plutonic rocks emplaced during the Middle Jurassic arc magmatism in the terrane, and during the main pulse of Cretaceous magmatism in the Sierra Nevada batholith to the east.
An age of approx 20 m. Post-magmatic hydrothermal events approximately Tertiary in age, lowered delta 18O values and disturbed parent-daughter relationships in most of the isotopic systems investigated. The two intrusive units apparently were derived from different protoliths. Initial isotopic ratios and petrochemistry for the Louis Lake batholith are consistent with an early Archaean trondhjemitic to tonalitic source. The protolith for the Bear Ears pluton must have been subjected to high-grade metamorphism that caused loss of Rb and U prior to magma generation.
Tourmaline occurrences within the Penamacor-Monsanto granitic pluton and host- rocks Central Portugal : genetic implications of crystal-chemical and isotopic features.
Farinha; Barriga, F. Tourmalinization associated with peraluminous granitic intrusions in metapelitic host- rocks has been widely recorded in the Iberian Peninsula, given the importance of tourmaline as a tracer of granite magma evolution and potential indicator of Sn-W mineralizations.
Huang, W. Paleolatitudes for the Tibetan Himalaya Zone based on paleomagnetic inclinations provide kinematic constraints of the passive northern Indian margin and the extent of ‘Greater India’ before the India-Asia collision. The carbonates yield positive fold tests, suggesting that the remanent magnetizations have a pre-folding origin.
However, detailed paleomagnetic analyses, rock magnetic tests, end-member modeling of acquisition curves of isothermal remanent magnetization, and petrographic studies reveal that the magnetic carrier of the Jurassic carbonates is authigenic magnetite, whereas the dominant magnetic carrier of the Lower Cretaceous volcaniclastic rocks is detrital magnetite. We conclude that the Jurassic carbonates were remagnetized, whereas the Lower Cretaceous volcaniclastics retain a primary remanence.
The remagnetization of the limestones prevents determining the size of ‘Greater India’ during Jurassic time. Instead, a paleolatitude of the Tibetan Himalaya of The volcaniclastic rocks with the primary remanence, however, yielded a Lower Cretaceous paleolatitude of Tibetan Himalaya of Map showing the distribution and characteristics of plutonic rocks in the Tonopah 1 degree by 2 degrees Quadrangle, central Nevada.
The accompanying table includes the name if any of the pluton and its location, the age of the pluton either a radiometric age or an age inferred from field relations , modal composition, texture, mineralogy, hydrothermal alteration and mineralization related to the pluton , the source of mapping shown on this map, and published references on the pluton.
Radiometric ages are either published K-Ar and fission track ages or new whole- rock Rb-Sr ages determined by A. Robinson on samples collected either for this study or as part of regional Sr-isotope studies by R. Kistler and A.
Flight simulation facilities that use the central computers are described. Management of the complex, procedures for its use, and available services and resources are discussed.
This document is intended for new users of the complex, for current users who wish to keep appraised of changes, and for visitors who need to understand the role of central scientific computers at Langley. Sudhir Warier. Page 1.
HackerSchoolTalk/ at master · johnmyleswhite/HackerSchoolTalk · GitHub
These ages are interpreted to date either the timing of a subsequent Early Cretaceous episode of crustal thickening and metamorphism or, assuming that these other areas unblockes also источник статьи heated during the latest Triassic to Early Jurassic and remained buried, the timing of their uplift and cooling. The tonalites of the Tanzawa Mountains have been interpreted to represent mid-lower crustal plutonic rocks that make up the 6. Muscovite alteration ages are reported for several plutons and represent minimum ages for emplacement of these plutons.