Mountain Pluton Research Articles

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.

Petrology of the Caribou Mountain Pluton, Klamath Mountains, California

Petrology of the Caribou Mountain Pluton, Klamath Mountains, California

The Buckhorn Mountain (Crown Jewel) gold skarn deposit, Okanogan County, Washington

The gold skarn system at Buckhorn Mountain is related to the Cretaceous (?) Buckhorn Mountain pluton (diorite to granodiorite) and its associated dikes and sills. The host rocks are Pennsylvanian to Triassic (?) clastic and carbonate sedimentary rocks of the Thompson assemblage and the andesitic flows of the Brooklyn Formation. These have been altered to proximal garnet-magnetite-sulfide, intermediate garnet-pyroxene-epidote-sulfide, and distal pyroxene and hornfels assemblages. Typically, the pyroxene is iron rich (Hd (sub 20-94) ), averaging Hd 51 , and the garnet is intermediate granditc (Ad (sub 36-75) ). Retrograde epidote, calcite, amphibole, and zoisite are common. Skarn associations vary according to original lithologies; the carbonate-rich layers altered to a more garnet-magnetite rich assemblage, whereas the argillaceous and siliceous layers altered to a pyroxene dominant assemblage. Alteration in the intrusion takes many forms, including potassic, propylitic, argillic, albitization, and complete alteration to garnet-epidote-pyroxene skarn.Gold mineralization is spatially associated with a variety of skarn assemblages in locations ranging from proximal to distal. There are positive correlations of gold with epidote, magnetite, bismuthinite, native bismuth, pyrrhotite, and cobaltitc. Structure and original lithologies were important controls for fluid movement, and therefore, gold mineralization. The gold probably was carried in reduced fluids by bisulfide complexes and probably was deposited at temperatures less than 400 degrees C.Average pressure-corrected temperatures for skarn-forming fluids are 465 degrees C for prograde (garnet-pyroxene) skarn and 360 degrees C for retrograde (epidote) skarn. Fluids in skarn minerals, as measured from last ice-melting phenomena in fluid inclusions, are undersaturated, and fall within the 18 to 22 wt percent NaCl equiv range. No daughter minerals were found in any skarn mineral fluid inclusions. Liquid to vapor ratios are relatively constant, implying that there was no boiling. A comparison of prograde skarn and quartz vein fluid inclusion characteristics indicates that the two may have formed at roughly the same time from similar fluids. The skarn formed from pervasive fluid infiltration under dominantly lithostatic conditions, whereas quartz veins formed from fluids channeled along fault structures, largely under hydrostatic conditions.

Remarkable isotopic and trace element trends in potassic through sodic Cretaceous plutons of the Yukon‐Koyukuk Basin, Alaska, and the nature of the lithosphere beneath the Koyukuk terrane

During the period from 110 to 80 m.y. ago, a 450‐km‐long magmatic belt was active along the northern margin of Yukon‐Koyukuk basin and on eastern Seward Peninsula. The plutons intruded Upper Jurassic(?) and Lower Cretaceous volcanic arc rocks and Cretaceous sedimentary rocks in Yukon‐Koyukuk basin and Proterozoic and lower Paleozoic continental rocks in Seward Peninsula. Within Yukon‐Koyukuk basin, the plutons vary in composition from calc‐alkalic plutons on the east to potassic and ultrapotassic alkalic plutons on the west. Plutons within Yukon‐Koyukuk basin were analyzed for trace element and isotopic compositions in order to discern their origin and the nature of the underling lithosphere. Farthest to the east, the calc‐alkalic rocks of Indian Mountain pluton are largely tonalite and sodic granodiorite, and have low Rb (average 82 ppm), high Sr (>600 ppm), high chondrite‐normalized (cn) Ce/Yb (16–37), low δ18O (+6.5 to +7.1), low initial 87Sr/86Sr (SIR) (0.704), and high initial 143Nd/144Nd (NIR) (0.5126). These rocks resemble those modelled elsewhere as partial melts and subsequent fractionates of basaltic or gabbroic metaigneous rocks, and may be products of melting in the deeper parts of the Late Jurassic(?) and Early Cretaceous volcanic arc. Farthest to the west, the two ultrapotassic bodies of Selawik and Inland Lake are high in Cs (up to 93 ppm), Rb (up to 997 ppm), Sr, Ba, Th, and light rare earth elements, have high (Ce/Yb)cn (30, 27), moderate to low δ18O (+8.4, +6.9), high SIR (0.712, 0.710), and moderate NIR (0.5121–0.5122). These rocks resemble rocks of Australia and elsewhere that were modelled as melts of continental mantle that had been previously enriched in large cations. This mantle may be Paleozoic or older. The farthest west alkalic pluton of Selawik Hills is largely monzonite, quartz monzonite, and granite; has moderate Rb (average 284 ppm), high Sr (>600 ppm), high (Ce/Yb)cn (15–25), moderate δ18O (+8.3 to +8.6), high SIR (0.708–0.712), and moderate NIR (0.5121–0.5122). These rocks may be the product of interaction of magma derived from old continental mantle and magma derived from old continental crust. Plutons between eastern and western extremes show completely gradational variations in the concentration of K and Rb and in the isotopic compositions of Sr, Nd, and O. These plutons probably originated either by melting in a mixed source composed of a Paleozoic or older continental section (mantle + crust) overlain by Mesozoic mafic arc rocks, or by mixing of ultrapotassic to potassic magmas from continental sources (mantle + crust), and tonalitic magmas from arc sources. We infer from these results that the northwest portion of Yukon‐Koyukuk basin is underlain by a substantial continental basement of Paleozoic or greater age. This basement probably thins out to the east. There is no geochemical evidence for continental basement east of about longitude 157°, or along a belt of at least 50 km width flanking Ruby Geanticline as far to the southwest as about longitude 161°. These areas are probably underlain by oceanic and Mesozoic arc rocks.

Petrogenesis of the Ear Mountain tin granite, Seward Peninsula, Alaska

Ear Mountain is part of a belt of Cretaceous tin on the Seward Peninsula of western Alaska. Porphyritic and seriate biotite quartz monzonite and quartz syenite represent early pluton units. These were followed by equigranular and fine-grained two-mica tourmaline-bearing granite. Late units are enriched in B, F, and Na/K and are depleted in Ti, A greisen alteration assemblage of tourmaline-quartz-cassiterite-white mica + or - magnetite + or - pyrite + or - pyrrhotite + or - rutile + or - arsenopyrite is found in the granite and skarns surrounding the pluton.Granite compositions approximate the minimum in the synthetic granite system at a pressure of 0.5 kb. Compositions of fine-grained granite are shifted toward the F-enriched minimum in the synthetic system. Temperature estimates based on feldspar geothermometry range from 624 degrees to 501 degrees C and are close to the solidus temperature in the F- and B-enriched systems. Coexisting Fe-Ti oxide mineral data give temperature estimates of 625 degrees to 675 degrees C and indicate cooling along a buffered path intermediate between the quartz-fayalite-magnetite and nickel-nickel-oxide curves. Biotite compositions (Fe/Fe + Mg = 0.69-0.99) combined with the feldspar geothermometry also indicate that crystallization of the pluton followed a buffer near the nickel-nickel-oxide curve.The tin contents of Ear Mountain granites largely correlate with degree of greisen alteration. Unaltered granites contain less than 80 ppm Sn, whereas thoroughly altered granites contain over 950 ppm Sn. Tin concentrations in unaltered granitic rocks increase progressively from porphyritic to seriate to some equigranular rocks, indicating a progressive concentration of Sn with fractional crystallization. Most unaltered fine-grained granites contain low Sn values, interpreted as results from Sn lost to the evolved vapor phase.The moderately reducing, weakly peraluminous and low calcium conditions during crystallization of the Ear Mountain pluton allowed for concentration of Sn into the melt. High B and F contents in the melt promoted prolonged fractionation of the system and increased concentration of Sn. Evolution of a vapor phase removed Sn from the granitic melt and reaction of this vapor with the granite and the skarn produced the Sn-enriched greisen alteration. There is no evidence that Sn was remobilized from Sn-enriched biotites into greisen.Greisen development is not extensive at present levels of erosion. Abundant cassiterite in placers surrounding the pluton suggest much of the greisen zone has been removed by erosion. The apical parts of other tin granites on the Seward Peninsula, such as Lost River and Kougarok, have well-developed greisen zones. Ear Mountain probably resembled these systems prior to erosion.

Observations and controls on the occurrence of inherited zircon in Concord-type granitoids, New Hampshire

U-Pb analyses of zircons separated from two Concord-type plutons near Sunapee and Dixville Notch, New Hampshire, reveal differences in the pattern and magnitude of zircon inheritance which are related to differences in melt chemistry. The Sunapee pluton contains only slightly more Zr than required to saturate the melt at the peak temperature of 700 ± 30° C. Traces of inherited zircon in this separate are inferred to be present as small, largely resorbed grains. In contrast, the Long Mountain pluton, near Dixville Notch, contains about 240% more Zr than required to saturate the melt. Thus, more than half of the Zr existed as stable, inherited zircon crystals during the partial fusion event, consistent with the observation of substantial inheritance in all grain size fractions. Ion probe intra-grain analyses of zircon from the Long Mountain pluton indicate a complex pattern of inheritance with contributions from at least two Proterozoic terrenes and caution against simple interpretations of upper and lower intercepts of chords containing an inherited component. Ion probe analyses of zircons from the Sunapee pluton reveal clear evidence of U loss which results in incorrect apparent conventional U-Pb ages. Ages of crystallization for the Long Mountain and Sunapee pluton are ~350 and 354 ± 5 Ma, respectively. A Sm/Nd measurement for the Long Mountain pluton yields a depleted mantle model age of 1.5 Ga, consistent with the observed inheritance pattern. In contrast, a Sm/Nd model age for the Sunapee pluton is improbably old due to minor monazite fractionation.

New U/Pb Ages from Granite and Granite Gneiss in the Ruby Geanticline and Southern Brooks Range, Alaska

New U/Pb zircon ages from the Ray Mountains of central Alaska clarify the plutonic history of the Ruby geanticline and support earlier suggestions that the Ruby geanticline and southern Brooks Range were once parts of the same tectonostratigraphic terrane. U/Pb zircon ages of 109 to 112 Ma from the Ray Mountains pluton confirm previously reported mid-Cretaceous K/Ar ages and rule out the possibility that the earliest intrusive phase of the pluton is older than mid-Cretaceous. New U/Pb zircon ages from four granite gneiss samples in the Ray Mountains indicate a Devonian protolith age of 390 ± 12 Ma and suggest that the Ruby geanticline, like the southern Brooks Range, underwent a major plutonic event in mid-Paleozoic time.

Platinum-group element geochemistry of zoned ultramafic intrusive suites, Klamath Mountains, California and Oregon

Three postorogenic Alaskan-type ultramafic to mafic intrusive suites in the Klamath Mountains, ranging in age from 142 to 163 m.y. and intruding metavolcanic, metasedimentary, or ophiolitic cumulate ultramafie to gabbroic rocks, were examined for their platinum-group element content. The Lower Coon Mountain pluton consists of layered clinopyroxene-rich lithologies occurring in chronological sequence whereas the intrusive suite at Tincup Peak consists of a cogenetic sequence of wehrlite, clinopyroxenite, magnetite clinopyroxenite, feldspathic hornblende-magnetite clinopyroxenite, dunite-olivine clinopyroxenite, and hornblende gabbro. The ultramarie-mafic intrusive suite at Chanchelulla Peak, part of the Wildwood pluton, consists predominantly of clinopyroxenite, minor interlayered dunite, and wehrlite with minor hypabyssal gabbroic rocks. Clinopyroxene compositions in the three intrusive suites are calcium rich and range from Wo (sub 54.7) -En (sub 45.1) -Fs 19 to Wo (sub 44.9) -En (sub 43.8) -Fs (sub 11.3) and resemble clinopyroxene with alkalic affinities. Olivine ranges from Fo 72 to Fo 83 and plagioclase from An 68 to An 96 . Cyclic units of layered cumulus magnetite + spinel (+ or -ilmenite) and coarse interstitial magnetite occur at Tincup Peak and Lower Coon Mountain. All three intrusive suites contain disseminated pyrrhotite + chalcopyrite + or - pentlandite, but the Chanchelulla Peak intrusive body also contains lenticular zones of disseminated to interstitial sulfides near its contact with sulfide-bearing horn-felsic rocks.Characteristics of rocks from these three Klamath Mountains Alaskan-type intrusive suites are (1) Rh contents of near or less than 1 ppb, (2) Ir and Ru contents less than 100 and 20 ppb, (3) variable Pd contents between rock units within intrusive suites and among suites, and (4) relatively similar Pt contents within intrusive suites and among suites. Concentrations of Pd average 6.3 ppb at Lower Coon Mountain, 13.7 ppb at Chanchelulla Peak, and 36.4 ppb at Tincup Peak. Cohen-corrected abundance data for individual rock units within each intrusive suite yield a Pt/(Pt + Pd) ratio that is greater in olivine-rich rocks than in clinopy-roxenite than in gabbro suggesting chemical fractionation of Pd within intrusive suites.

Iron Variation within a Granitic Pluton as Determined by Near-Infrared Reflectance

One-hundred fifty-one previously chemically analyzed samples of tonalite from the Lakeview Mountains pluton, southern California batholith, were analyzed for their iron content using near-infrared spectrophotometry. Compared to the earlier analyses of the same sample set by X-ray fluorescence spectrog-raphy, the infrared data have higher analytical variance but clearly define patterns of compositional zonation in the pluton which are closely similar to those patterns obtained from X-ray data; petrogenetic interpretations for the pluton would be the same from either data set. Infrared spectral data can be obtained directly in the field with relatively simple instruments and field measurements can be made to average local heterogeneities that often mask significant plutonic variations.

Petrology of the Gillis Mountain pluton, Cape Breton Island, Nova Scotia

The Gillis Mountain pluton is a small composite granitoid intrusion in southeastern Cape Breton Island. It is one of the few plutons of known Devonian age in Cape Breton Island and is particularly significant because of the presence of Cu–Mo mineralization with porphyry affinities. The pluton consists of three main phases (quartz monzodiorite, porphyritic granite, and fine-grained granite) with minor late dykes of granite, granitic porphyry, and aplite. These phases probably represent a differentiation sequence from an 'I-type' parent magma of calc-alkalic affinity. All phases have been affected by phyllic and possibly potassic alteration, presumably related to the mineralization processes. However, this hydrothermal activity appears to be little reflected in the bulk chemistry of the pluton, except possibly in increased barium content and large standard deviations in the metallic elements and sulphur.

Fission-Track Dating of the Green Mountain Kimberlite Diatreme, near Boulder, Colorado

Green Mountain diatreme is at the southern end of a belt of about 90 kimberlite plutons along the eastern margin of the Laramie and Front Ranges extending from Iron Mountain, Wyoming, to near Boulder, Colorado. Fission-track ages have been obtained both from sphene and apatite from the Green Mountain pluton. The apatite age, 77.1 ± 5 m.y., apparently is a reset age, representative of when the rock mass last underwent sufficient cooling to retard fission-track annealing. The cooling event is likely associated with erosional strip­ ping during and following the Laramide Orogeny. The sphene age of 367 ± 15 m.y. (Devonian) appears to represent the time of emplacement of the pluton. The fact that this value is statistically identical with the radio­ metric age of the Schaffer No. 3 pipe, near the Colorado-Wyoming State line, supports the idea that all of the kimberlite plutons were intruded during one plutonic episode in Devonian time.

Geology and Structural Control of Geothermal System at Roosevelt Hot Springs KGRA, Beaver County, Utah: ABSTRACT

The Roosevelt Hot Springs KGRA is located in the Basin and Range province along the western flank of the Mineral Mountains. It is within the Wah Wah-Tusher mineral belt which has been the locus for rhyolitic intrusive and extrusive activity through Tertiary and into Quaternary time. The area is just east of the Sevier (Cretaceous) thrust belt and is near the margin of the Intermountain seismic belt. Geologic mapping has identified three metamorphic and plutonic units of Precambrian age, nine intrusive phases of the Tertiary Mineral Mountains pluton, three Pleistocene rhyolitic extrusive phases, and siliceous hot spring deposits of relatively recent age. Cuttings from exploration holes indicate that the Precambrian and Tertiary crystalline rocks host the present geothermal system. The structure of the area is dominated by low-angle normal faults (denudation faults) which dip to the west. The hanging wall of the principal denudation fault was intensely brecciated during the fault episode forming steep fault zones which generally strike northwest. Both these low- and high-angle fault zones show the development of intense, silicified mylonites. Adjacent to these mylonite zones, the crystalline rocks are highly fractured. East-west and northeast-trending high-angle faults cut the denudation faults and channel much of the recent hot-spring activity. The geothermal system is a high-temperature, water-dominated resource which is probably related to an igneous heat source. The low primary permeability of the reservoir rocks and the location of the geothermal field indicate structural control of the system. The reservoir geometries and permeabilities result from the intersections of the principal fault systems. End_of_Article - Last_Page 836------------

Age and origin of the Stone Mountain Granite, Lithonia district, Georgia

Research Article| July 01, 1976 Age and origin of the Stone Mountain Granite, Lithonia district, Georgia JAMES A. WHITNEY; JAMES A. WHITNEY 1Department of Geology, University of Georgia, Athens, Georgia 30602 Search for other works by this author on: GSW Google Scholar LOIS M. JONES; LOIS M. JONES 1Department of Geology, University of Georgia, Athens, Georgia 30602 Search for other works by this author on: GSW Google Scholar RAYMOND L. WALKER RAYMOND L. WALKER 2Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 Search for other works by this author on: GSW Google Scholar Author and Article Information JAMES A. WHITNEY 1Department of Geology, University of Georgia, Athens, Georgia 30602 LOIS M. JONES 1Department of Geology, University of Georgia, Athens, Georgia 30602 RAYMOND L. WALKER 2Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (7): 1067–1077. https://doi.org/10.1130/0016-7606(1976)87<1067:AAOOTS>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 JAMES A. WHITNEY, LOIS M. JONES, RAYMOND L. WALKER; Age and origin of the Stone Mountain Granite, Lithonia district, Georgia. GSA Bulletin 1976;; 87 (7): 1067–1077. doi: https://doi.org/10.1130/0016-7606(1976)87<1067:AAOOTS>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 Petrographic, geochemical, and strontium isotopic studies have been conducted on samples of the Stone Mountain Granite (leucocratic quartz monzonite) from the Lithonia district, within the Inner Piedmont province of Georgia. A Rb-Sr isochron obtained from 10 whole-rock and 3 mineral samples yielded an age of 291 ± 7 m.y. and an initial Sr87Sr86 ratio of 0.7250 ± 0.0005. Petrologic and geochemical data, combined with the high initial strontium isotopic ratio, suggest that the origin of this peraluminous quartz monzonite can best be explained by the anatexis of an older peraluminous, granitic crustal material during Late Pennsylvanian time. The depth of intrusion was probably around 12 km, with initial magma temperatures of 700°C or less. Magma generation could have occurred at depths of 22 to 28 km, depending on the regional geothermal gradient at the time. The most likely source material is the Lithonia Gneiss, which has a peraluminous, granitic composition and underlies the area.The Stone Mountain pluton extends the 300-m.y.-old intrusive belt in the southern Appalachians across the Piedmont province to just south of the Brevard lineament. Its implied depth of intrusion fits well with certain models for the development of the Inner Piedmont and Blue Ridge provinces in the Carolinas because it requires rapid removal of considerable overburden. The origin and magmatic history of this intrusive unit may find use as a model for other peraluminous granitic plutons having similar petrologic, geochemical, and isotopic characteristics. 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.

Garnet-Clinopyroxenite from the Red Mountain Pluton, Alaska

Several lens-shaped and irregular masses of garnet-clinopyroxenite occur along the north margin of the Red Mountain pluton, near Seldovia, Alaska. The pluton is composed of intercalated dunite, clinopyroxenite, and banded chromite layers. The chromite layers appear to dip toward the center of the mass, but they have been deformed, and in some places display isoclinal overturned folds. The garnet-clinopyroxenite bodies are compositionally layered and appear to have been deformed along with the host peridotite. The garnet-clinopyroxenite bodies have whole-rock compositions analogous to alkali-poor anorthite gabbro or mafic anorthosite. Garnet compositions are dominated by the pyrope, grossularite, and almandine components, and the clinopyroxene bodies are rich in Ca-Tschermaks molecule (CaAl 2 SiO 6 ). Although crystallization from the liquidus is a possibility, textures, structures, and the chemical composition of the constituent mineral phases indicate that the garnet-clinopyroxenite has equilibrated in the solid state at pressures of 15 to 25 kb and temperatures of 1100°C to 1300°C. Such P-T parameters suggest an upper-mantle origin for the garnet-clinopyroxenite and the enclosing pluton.

Mica Granites of the Kern Mountains Pluton, Eastern White Pine County, Nevada: Remobilized Basement of the Cordilleran Miogeosyncline?

Among the many granitic plutons within the Basin and Range province of western North America, those in the Kern Mountains of eastern Nevada and western Utah are unusual structurally, mineralogically, and chemically. The two largest intrusions, which together are exposed over an area of 130 sq km (51 sq mi), have well-defined border facies of leucocratic and generally aplitic rocks, or of protoclastic rock developed from coarser core-facies material. Within the core facies are abundant aplitic, leucocratic dikes. The core facies of the larger intrusion (Tungstonia Granite) is a two-mica granite with conspicuous phenocrystic books of muscovite up to 5 cm across. The smaller intrusion (Skinner Canyon Granite) lacks muscovite, and Fe-Ti oxides and sphene are constant accessory phases in it. Rb-Sr and K-Ar isotopic analyses suggest a wide range of initial Sr 87 /Sr 86 ratios, which for the most part are unusually high—to nearly 0.7246 for the Tungstonia Granite—and a complex, protracted period of magmatism and isotopic adjustment that extended from possibly Mesozoic into mid-Cenozoic time. The simplest interpretation is that the final emplacement of the Tungstonia body occurred 60 m.y. ago and that the Skinner Canyon intrusion occurred between 30 and 45 m.y. ago. The data prompt the conclusion that the magmas represent remobilized sialic basement whose model dates (assuming an initial ratio typical for mantle-derived magmas) are in excess of 1.5 b.y. The occurrence of such anatectic intrusions within the relatively intensely metamorphosed parts of the infrastructure of the Sevier orogenic belt, rather than elsewhere in the Basin and Range province, is not unexpected, and it possibly represents a more advanced evolutionary stage than do the gneiss domes previously documented within this same belt.

Emplacement of a Dike Swarm in the Buffalo Mountain Pluton, Nevada

Research Article| November 01, 1973 Emplacement of a Dike Swarm in the Buffalo Mountain Pluton, Nevada THOMAS R. NEFF THOMAS R. NEFF 1Department of Geology and Geography, Weber State College, Ogden, Utah 84403 Search for other works by this author on: GSW Google Scholar Author and Article Information THOMAS R. NEFF 1Department of Geology and Geography, Weber State College, Ogden, Utah 84403 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1973) 84 (11): 3689–3696. https://doi.org/10.1130/0016-7606(1973)84<3689:EOADSI>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 THOMAS R. NEFF; Emplacement of a Dike Swarm in the Buffalo Mountain Pluton, Nevada. GSA Bulletin 1973;; 84 (11): 3689–3696. doi: https://doi.org/10.1130/0016-7606(1973)84<3689:EOADSI>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 The Buffalo Mountain pluton in southern Humboldt County, Nevada, is cut by an extensive dike swarm. Dikes occur mainly within the plutonic rocks, although a few extend as much as 3.5 km into the surrounding sedimentary rocks. The dikes are composed of rhyolite porphyry and quartz latite porphyry or their altered equivalents.Dikes vary in width from a few centimeters to several hundred meters. In plan, individual dikes are sigmoidal or curving, and they branch and intersect intricately to form a very complex pattern. A statistical analysis of dike orientations shows a strong north trend and a weaker northwest trend.The amount of dilation produced by dike injection is approximately 1,160 m in an east-west direction. Space to accommodate dilation probably was the result of a regional east-west crustal relaxation. The dike swarm apparently formed during three overlapping stages. 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.

The Lakeview Mountains Pluton, Southern California Batholith Part II: Chemical Composition and Variation

Research Article| August 01, 1969 The Lakeview Mountains Pluton, Southern California Batholith Part II: Chemical Composition and Variation D. M MORTON; D. M MORTON California Division of Mines and Geology, Los Angeles, California Search for other works by this author on: GSW Google Scholar A. K BAIRD; A. K BAIRD Department of Geology, Pomona College, Claremont, California Search for other works by this author on: GSW Google Scholar K. W BAIRD K. W BAIRD Department of Geology, Pomona College, Claremont, California Search for other works by this author on: GSW Google Scholar Author and Article Information D. M MORTON California Division of Mines and Geology, Los Angeles, California A. K BAIRD Department of Geology, Pomona College, Claremont, California K. W BAIRD Department of Geology, Pomona College, Claremont, California Publisher: Geological Society of America Received: 11 Nov 1968 Revision Received: 23 Jan 1969 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1969, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1969) 80 (8): 1553–1564. https://doi.org/10.1130/0016-7606(1969)80[1553:TLMPSC]2.0.CO;2 Article history Received: 11 Nov 1968 Revision Received: 23 Jan 1969 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation D. M MORTON, A. K BAIRD, K. W BAIRD; The Lakeview Mountains Pluton, Southern California Batholith Part II: Chemical Composition and Variation. GSA Bulletin 1969;; 80 (8): 1553–1564. doi: https://doi.org/10.1130/0016-7606(1969)80[1553:TLMPSC]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 Major elemental analyses and specific gravity determinations were made on bulked rock samples from 162 localities over the Lakeview Mountains pluton. Mineral separates from 126 localities were also analyzed. Results show that the pluton is highly homogeneous on the large scale with high heterogeneity on the small scale. Despite the high homogeneity, all analytical results define consistent zonational patterns approximately parallel to the walls of the body and to the concordant schlieren. This zonation shows that the Lakeview Mountains pluton has a relatively basic and dense core compared to its margin and implies that the last rock to crystallize was more basic than rock formed earlier. 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.

The Lakeview Mountains Pluton, Southern California Batholith Part I: Petrology and Structure

The Lakeview Mountains pluton, a part of the southern California batholith, is a steep-walled body with a tear-shaped ground plan, exposed discontinuously over an area of 100 to 130 km 2 . It is located at an abrupt local deflection of the regional structural grain and is concordant with planar structures in the enclosing rocks. These are gabbro, granitic rocks, mixed rock composed of granitic and metamorphic rocks, and regionally metamorphosed rocks of the cordierite-amphibolite facies. Most of the adjacent granitic rocks are older than the Lakeview Mountains pluton, although some may be of the same age. The pluton is almost entirely coarse-grained hornblende-biotite quartz diorite that lacks potassium feldspar. Schlieren are ubiquitous, and small lenticular inclusions, common throughout the pluton, parallel the schlieren. The schlieren, which make the rock extremely inhomogeneous on a small scale, geometrically fall into three orientation groups. One group, the most pronounced, is concordant to the outline of the pluton and planar structures in the adjacent rocks; the other two, discordant with respect to the shape of the pluton, strike northeast and northwest. Some outcrops exhibit schlieren intersecting at a large angle, and mesoscopic fabric analysis indicates that mineral orientation of much of the massive-appearing rocks is complex on the scale of an outcrop. Granitic pegmatite dikes, masses of hypersthene gabbro, and both mafic and leucocratic quartz diorite are concentrated in the geometrically and structurally deduced center of the pluton. It is concluded that the concordant schlieren resulted from outward growth of the pluton and the discordant sets in response to regional forces. The concordance between the outline of the pluton and its wall rocks and the abrupt deflection of the regional structural grain resulted from the outward growth of the pluton. The pegmatite represents the fugitive constituents of the pluton-forming magma, and the sites of pegmatite concentration in the wider part of the tear-shaped body mark the last portions of the pluton to crystallize.

Geochemical and Structural Studies in Batholithic Rocks of Southern California: Part II, Sampling of the Rattlesnake Mountain Pluton for Chemical Composition, Variability, and Trend Analysis

New techniques of X-ray fluorescence spectrography have extended the lower atomic-number limit of determination to 0.01 weight per cent Na in silicates. As a result, chemical analyses of coarse-grained rocks can now be obtained more easily than modal analyses. This paper is a discussion of results obtained from nearly 1000 new rock analyses of samples from the Rattlesnake Mountain pluton, San Bernardino Mountains, California. The new method of obtaining chemical data from granitic rocks has necessitated reexamination of sampling methods and designs. Samples must be large enough to be rocks, not merely fragments of constituent minerals. A portable diamond drill is a practical means of decreasing bias and extending the population sampled. Trend-surface analysis of individual elements is a useful computational technique for establishing general patterns of distribution. Factor (vector) analysis makes it possible to study simultaneously the variation of many elements. A more conventional way of achieving this result is to recast chemical analyses as norms; nearly 800 such norms have been computed for this paper. High-speed computers and automatic plotting devices have proved essential for the processing and reduction of our chemical data. Hierarchical sampling enables one to analyze the variance and to measure its components on different scales, information which is essential to the justification of supposed chemical differences between rocks. Chemical mapping requires knowledge of the variance within localities, and more than one sample must be collected at each locality if this variance is to be measured. It is concluded that the analytical precision is more than adequate for this geochemical purpose; local variability in the rocks themselves is usually the limiting factor.

Geochemical and Structural Studies in Batholithic Rocks of Southern California: Part 1, Structural Geology of Rattlesnake Mountain Pluton

The Rattlesnake Mountain pluton, a funnel-shaped body of coarse-grained porphyritic quartz monzonite, is an offshoot from a batholithic mass of biotite-quartz monzonite forming the central part of the San Bernardino Mountains in Southern California. The pluton intrudes a structurally complex region of metamorphic and igneous rocks that borders the batholith on the north side of the mountains. The metamorphic rocks consist of marbles, calc-silicate hornfels, schists, quartzites, amphibolites, gneisses, granulites, and migmatites. The degree of metamorphism is in the higher grades of the almandine-amphibolite facies and of the granulite facies. Igneous rocks of the pluton range from quartz monzonite through granodiorite to quartz diorite and were emplaced at the same time as the main part of the batholith. The intrusion of the pluton was postkinematic and disrupted the regional structure. The most distinctive features of the Rattlesnake Mountain pluton are its shape and internal structure. The upper part of the funnel flares outward and is divided into several lobes and sheets separated by screens of mafic rocks. The sheets follow the funnel pattern, lying concentrically within one another and dipping inward toward a central point. The lobes are tongue-shaped and extend from the upper edge of two of the sheets. One of the lobes extends outward for more than 5 miles from the funnel. An unusual abundance of inclusions, schlieren, and dikes are present. These structures are in many cases oblique to one another; schlieren commonly cut across or are truncated by other schlieren, and inclusions lie in various orientations. Structural data were plotted on equal-area projections; in any one area, normals to the flattened surfaces of inclusions and schlieren form a pattern that commonly consists of an incomplete great circle containing a central maximum.