Plutonic Quartz Research Articles

Integrated methodology for determining provenance of detrital quartz using optical petrographic microscopy and cathodoluminescence (CL) properties

The provenance of detrital quartz is a useful predictor in frontier basin sandstone reservoirs of the availability of coarse-grained quartz grains of plutonic or high grade metamorphic origin. The standard approach is to use scanning electron microscope (SEM) panchromatic cathodoluminescence (CL) imagery and observations from an optical petrographic microscope. We describe a work flow, modified from previous literature proposals, to determine quartz provenance in detrital grains using optical petrographic microscopy and CL properties from both a hot-cathode cathodoluminescence microscope attachment (HCMA) and panchromatic SEM-CL. HCMA analysis permits better discrimination of different types of metamorphic quartz. This method is applied to a Middle Jurassic to Lower Cretaceous section in the Bandol-1 wildcat well, located in the Laurentian sub-basin south of Newfoundland. Two types of high-grade metamorphic quartz are distinguished, one with low luminescence as described in previous literature and one with medium blue CL colour and a moderate colour shift that is also known from granulite in the hinterland. Three phases of detrital supply are identified, suggesting progressive unroofing of higher grade metamorphic sources through the middle Jurassic and major input of plutonic quartz in the early Cretaceous.

Quartz types of the Eocene Broken River Formation, Mount Somers, South Island, New Zealand

ABSTRACTQuartz arenites are a very common geological feature on the South Island of New Zealand. The provenance of the quartz grains that form these arenites is not well constrained because standard point-counting techniques do not provide enough detailed information. In this study we distinguish different quartz types using scanning electron microscopy–cathodoluminescence combined with standard optical microscopy on the same individual quartz grains. This is done on a suite of samples collected from shallow marine quartz arenites of the Paleocene–Eocene Blondin Sand Member of the Broken River Formation (Eyre Group) at Mt Somers in the Canterbury basin on the South Island of New Zealand. Our results show that the volcanic quartz grains were derived from local volcanic source rocks, whereas metamorphic quartz grains may have been derived from either local source rocks of the Torlesse Supergroup or from distant metamorphic sources rocks via longshore transport. Plutonic quartz grains were exclusively derived by long-distance transport. Warm and humid climatic conditions and the presence of humic acids in the associated coal-forming depositional environment probably increased the proportion of quartz in the sampled rocks.

Provenance Analysis of Lower Cretaceous Sindong Group Sandstones in the Gyeongsang Basin, Korea, Using Integrated Petrography, Quartz Sem-Cathodoluminescence, and Zircon Zr/Hf Analysis

The Sindong Group (Aptian–Albian) in southeastern Korea is a 2–3-km-thick fluvio-lacustrine sedimentary package deposited in an elongated basin (the Nakdong Trough), which was formed by extension in an active-continental-margin setting. The provenance of the Sindong Group was studied to understand spatial and temporal variation in composition in three different parts of the basin by using integrated data on petrography, quartz SEM-cathodoluminescence (CL) analysis, and zircon Zr/Hf analysis. Although Sindong Group sandstones display wide variation in the composition of framework grains, they generally have increasing amounts of feldspar and decreasing amounts of quartz up sequence. Significant amounts of volcanic rock fragments and volcanic quartz are observed in the late-stage sediments. Metamorphic quartz is predominant in all Sindong Group sandstones, indicative of the exposure of metamorphic rocks in the source terrane, mostly from Precambrian basement and Triassic granites. The occurrence of significant amounts of plutonic quartz from early-stage sediments suggests that Jurassic granites were widely exposed in the source terranes. In addition, the episodic increase in volume of plutonic quartz content in the sequence, especially in the northern part of the basin, suggests that episodic tectonic activity occurred in the catchment. The increasing feldspar content up sequence could support the occurrence of tectonic activity in the catchments. The Zr/Hf analysis of detrital zircons revealed that the majority of zircons are of continental-crust origin formed in orogenic settings, but zircons in the lowest strata in the northern part of the basin were derived largely from anorogenic magmatic rocks of mantle origin. Our results demonstrate that source terranes for the Sindong Group have heterogeneous spatial and temporal distribution and were composed mainly of Precambrian basement and Triassic to Jurassic granitic rocks, with minor (meta)sedimentary rocks and syndepositional volcanic rocks. The detritus derived from syndepositional volcanic rocks became significant in the late stage of basin filling, representing the transition from extensional tectonism to continental-arc magmatism. The differences in characteristics of quartz SEM-CL and zircon Zr/Hf ratios in different parts of the basin are best explained by deposition on different alluvial fans and river systems.

Provenance and depositional conditions of Cretaceous–Paleogene boundary sandstones from northeastern Mexico

We compare Late Maastrichtian siliciclastic sandstone in northeastern Mexico with those representing the Cretaceous–Paleogene (K–Pg) boundary to reveal differences in provenance and depositional conditions between background sedimentation and K–Pg sand. Lithology and compositional variations are presented for the deep-water Burgos Basin and the shallow-water La Popa Basin.The Late Maastrichtian sandstones in the Burgos Basin have sharp lower contacts, contain abundant trace fossils and are separated by meter-thick marl layers. They represent sporadic mass flows from coastal areas separated by long phases of hemipelagic sedimentation. The K–Pg sandstone layers are amalgamated, contain thin marl intercalations only in the uppermost part and trace fossils are present in the top sandstone layer only. Also this succession represents mass-flow deposits, but the sand may have been deposited during a very short period. The La Popa Basin sandstones represent deltaic sedimentation interrupted by submarine channel deposition during the K–Pg boundary transition with abundant rip-up clasts and bioclasts at the base.The sandstones of the Burgos Basin are quartz to akosic wacke dominated by quartz (>90%) and some feldspar (<10%) in calcite cement and matrix. Lithic fragments are rare and dominated by chert and bioclasts. Ultra-stable heavy minerals (ZTR=50–80) and plutonic quartz grains (ca. 40% of the total quartz population) are particularly common in the K–Pg sandstones. In the Maastrichtian sandstones, metamorphic heavy minerals, particularly chlorite, clinozoisite, and tourmaline (20–50% of the heavy mineral population), and metamorphic quartz (80% of the quartz population) have higher abundances. The La Popa sandstones are subarkose to arkose and arkosic wacke and have a high abundance of feldspar (15–30%) and lithic fragments (5–20%), mainly of siltstone and carbonate. The sandstones from both basins have chemical compositions typical for recycling (Zr/Sc=12–27 and 17–140 in the Burgos and La Popa Basin, respectively) and influences from mafic source rocks (Th/Sc=0.4–1.1; Ti/Nb=350–510). Therefore we suggest that all studied successions share a common provenance with transport of recycled orogenic metasedimentary components from northwestern Mexico and magmatic arc material from western Mexico. Subsequently, longshore currents mixed the detritus with limestone clasts derived from the tectonically active Sierra Madre Oriental, which probably is the cause for compositional changes in the sandstones. Due to increased sediment input from western Mexico at the K–Pg boundary, provenance changes cannot be related to the Chicxulub impact.

Cathodolumenescence Spectra of Quartz As Provenance Indicators Revisited

Abstract We present a discrimination scheme for cathodoluminescence (CL) spectra of quartz as a tool in provenance studies. We analyzed > 1000 quartz crystals from 58 samples of different plutonic, volcanic, metamorphic, and pegmatitic rocks. The technique is based on the measurement of the relative intensity of the two main emission centers in visible light at 470–490 nm and 600–640 nm. The results confirm a red, violet, or bright to medium blue luminescence for volcanic phenocrysts, mainly bright blue colors for felsic plutonic and high-temperature metamorphic quartz, as well as brown to dark blue CL for quartz of low-temperature metamorphic origin. These and additional results for mafic plutonic (dark blue) and pegmatitic quartz (bright blue) lead to a possible discrimination with the following rock grouping: (1) volcanic quartz, (2) low-temperature metamorphic and mafic plutonic quartz, and (3) felsic plutonic, high-temperature metamorphic, and pegmatitic quartz. In the proposed scheme, 87% of the spectra are classified correctly. The three quartz groups can be taken as an estimate for the amount of volcanic, metamorphic, and plutonic quartz in sediments, unless major input from plutonic, high-temperature metamorphic, or pegmatitic quartz has taken place. Hence, despite criticism within the literature during the last decades, the CL colors of detrital quartz still can be used as provenance indicators. We finally conclude that the measurement of wavelength spectra is a fast and straightforward method to determine quartz-bearing source rocks of siliciclastic sediments.

Detrital Quartz and Zircon Combined: The Production of Mature Sand with Short Transportation Paths Along the Cambrian West Gondwana Margin, Northwestern Argentina

Abstract Quartz, the most common mineral in most sandstones, rarely is used in provenance studies. This study demonstrates the provenance-discriminatory potential of combining cathodoluminescence (CL) color wavelength spectra of quartz with morphology and in situ U-Pb ages of zircon. The Cambrian Meson Group in northwestern Argentina is used for the test of this combined methodology, because it is composed of nonmetamorphosed sandstones with > 90% quartz and a dominance of zircon among the heavy minerals. Correlation of the results from the two methods is evident: (1) both CL spectra typical for bright-luminescent quartz (red to blue; > 90%) and oscillatory zircon growth zoning (80–90%) indicate a dominance of magmatic detritus. (2) Upsection, diminishing input from euhedral 510–600 Ma zircons (70% at the base) correlates with lower amounts of volcanic quartz (40% red and violet grains at the base). Instead, plutonic quartz and abraded zircons of 550–700 Ma age prevail. The data point to the occurrence of a (nearly) synsedimentary volcanic phase, which has not been known previously. Furthermore, initial short transportation paths from nearby magmatic bodies (100–200 km) can be assumed, because of the low degree of grain abrasion and an age correlation with magmatic bodies in the region, such as the Santa Rosa de Tastil batholith, here dated at 513 +4/−5 Ma. The proximity to the source area at an initial stage indicates first-cycle sand. The maturity was probably reached by intense chemical weathering. The upsection-diminishing young, volcanic input indicates erosion of the volcanic source within a time period of millions of years. At that stage, mainly up to 1000-km-long coast-parallel transport from the Sierras Pampeanas in the south fed the depositional basin. The change in—and expansion of—the main source areas record a change to production of multicycle sand. Hence, the maturity was partly caused by sedimentary recycling. More generally, the provenance-discriminative effect of the CL of quartz, which has been doubted by some researches, can be confirmed. Therefore, the results imply that both quartz and zircon should be taken into account in provenance studies of quartz arenites.

Red thermoluminescence (RTL) sensitivity change in quartz

Abstract This study investigated changes in the thermoluminescence sensitivity of volcanic and plutonic quartz following irradiation and annealing treatments with the aim of improving the accuracy of red thermoluminescence (RTL) dating. The response to X-ray irradiation (49 Gy) and RTL readout to 450 °C at a rate of 1 °C s −1 was repeated 12 times and the sensitivity change induced by doses ranging from 49 to 293 Gy was examined. The results of these two experiments revealed that the final enhanced ratio of the sensitivity of plutonic quartz is 2.1–2.8 and 2.2–2.3 for two types of analyzed samples, much greater than that of volcanic quartz. To examine the thermal stability of quartz, several annealing treatments were performed from 300 to 900 °C for 100 min. An annealing treatment of 500 °C for 100 min resulted in a strong enhancement of RTL emission intensity for plutonic quartz, approaching the level for volcanic quartz. Finally, the single aliquot regeneration (SAR) method was applied to evaluate the absorbed dose, D e , for aliquots irradiated with a known-dose ranging from 195 to 1952 Gy. All SAR D e values obtained with volcanic quartz were in good agreement with the known dose values; whereas for plutonic quartz large uncertainties in D e were obtained due to a marked sensitivity change. The magnitude of the RTL sensitivity change of quartz depends on dose and annealing treatment, and is clearly dependent on a classification of quartz based on thermal history.

Neoproterozoic subaqueous extrusive–intrusive rocks in the Playa Hermosa Formation in Uruguay: Regional and stratigraphic significance

Volcanic rocks in southern Uruguay are linked to an extensional tectonic regime related to the post-collisional Brasiliano–Pan African orogenic cycle. The ca 580 Ma magmatic event is recorded in the Playa Hermosa Formation. In the upper section of this formation several units were defined. The basal unit is a quartz–syenite brecciated deposit, interpreted as the result of explosive episodes of shallow plutonic quartz–syenite intrusion with signs of hydrothermal alteration. Sedimentary and basaltic lithoclasts are occasionally present in the breccia, implying the emplacement of basalts before of that magmatic event. The middle unit is composed of trachytic hyaloclastites. Local distribution and textural evidence indicate that trachytic volcanic pulses have been followed by an explosive event that produced brecciated deposits. The upper unit of the studied sequence is composed of basalts with thin sedimentary intercalations. Most of the outcropping basalts display the typical micro- and macro-features of hyaloclastites; distinctive of extrusions occurred in wet sediments previous to lithification. Basaltic feeder dikes are common in the lower unit. The study of flow structures in the quartz–syenite brecciated deposits led to the recognition of two basaltic inputs. Such differences are related to the intensity of chloritic alteration, which would be related to water contamination. Basaltic peperites are one of the most impressive features of the Playa Hermosa Formation. Hyaloclastites and peperites largely represented among the studied volcanic rocks, and devitrification textures are all evidences of magma/seawater interactions. In the basaltic fragments of the peperites well preserved orange palagonite appears, while the sandstone fractions have lithic clasts of felsic volcanic rocks, such as rhyolitic lavas with perlitic cracks and lithophysae-like structures. Palagonite chemical analyses suggest marine environment and, at the same time, it proves that the studied section lacks of regional metamorphism. The felsic volcanic lithoclasts contained in sandstones could be related to the felsic volcanic lobes intercalations. The studied magmatic event is important in order to formulate correlations with other Neoproterozoic units distributed around the Dom Feliciano belt, like Camaquã and Campo Alegre basins (Brazil), and in the Kaoko belt (NW Namibia) in Africa. Also, Playa Hermosa Formation presents glacigenic features that are well documented, and reinforce the volcanism around 580 Ma in the Rio de la Plata Craton.

Time-resolved luminescence of low sensitivity quartz from crystalline rocks

Time-resolved luminescence spectra of low sensitivity natural quartz from crystalline rocks are presented. The luminescence was pulse-stimulated at 11 μ s width using 470 nm blue light from quartz separated from plutonic, metamorphic, volcanic and hydrothermal samples. Measurements were made at 20 °C. All samples show evidence of a short lifetime component less than 5 μ s long although in several cases too weak in intensity to be evaluated accurately. On the other hand, the value of the principal lifetime component varies considerably being about 86 μ s in metamorphic quartz, 18 μ s in plutonic quartz, and 100 μ s in one example of hydrothermal quartz. The results illustrate a new feature of luminescence from quartz for which lifetimes less than 5 μ s or greater than 75 μ s have never been reported at room temperature before. It is argued that the thermal provenance of the quartz and so the annealing it will have experienced influences the size of the observed lifetime. In particular, the results are explained in terms of a model consisting of three luminescence centers with the dominant lifetime linked to preferential recombination at one center depending on the thermal history of the sample and hence the hole concentration of the center.

Provenance analysis of the Paparoa and Brunner Coal Measures using integrated SEM‐cathodoluminescence and optical microscopy

An integrated approach using grain‐by‐grain comparison of SEM‐cathodoluminescence (CL) andpetrographic characteristics was applied to investigate the provenance of fluvial/lacustrine quartz‐rich lithic arenites deposited in the Late Cretaceous transtensional Paparoa Basin in New Zealand. Results show most quartz in the Paparoa Basin was derived from a relatively low grade metamorphic source, most likely the underlying metasedimentary Greenland Group. This interpretation is supported by the presence of sedimentary lithics and Greenland Group conglomerate clasts in the Paparoa members. The eastern part of the basin is characterised by the addition of detrital chlorite and muscovite, some clearly replacing potassium feldspar in retrograde metamorphic lithoclasts, the lack of plutonic quartz, and an increase in polycrystalline metamorphic quartz. All this indicates an increase in metamorphic grade of the source area to the east upward through the stratigraphic section followed by a decrease. Such a change in grain type most likely reflects the migration of the basin past the exposed metamorphic rocks of the Paparoa Metamorphic Core Complex to the northeast of the strike‐slip Paparoa Tectonic Zone. On the west side of the basin, c. 15% of quartz grains are also derived from a plutonic source, probably the Barrytown Granite pluton or similar intrusions. Our provenance information provides the first concrete evidence for sinistral strike‐slip fault movement as predicted by tectonic reconstructions.

Intensity of quartz cathodoluminescence and trace-element content in quartz from the porphyry copper deposit at Butte, Montana

Textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope (SEM-CL) refl ect the physical and chemical environment of quartz formation. Variations in intensity of SEM-CL can be used to distinguish among quartz from superimposed mineralization events in a single vein. In this study, we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events. This technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in Butte, Montana. Analyzed veins include early quartz-molybdenite veins with potassic alteration, pyrite-quartz veins with sericitic alteration, and Main Stage veins with intense sericitic alteration. CL intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions, isotopes, trace elements, etc., from specific mineralizing episodes. Furthermore, CL intensity increases proportional to temperature of quartz formation, such that plutonic quartz from the Butte quartz monzonite (BQM) that crystallized at temperatures near 750 °C luminesces with the highest intensity, whereas quartz that precipitated at ~250 °C in Main Stage veins luminesces with the least intensity Trace-element analyses via electron microprobe and laser ablation-ICP-MS indicate that plutonic quartz and each generation of hydrothermal quartz from Butte is dominated by characteristic trace amounts of Al, P, Ti, and Fe. Thus, in addition to CL intensity, each generation of quartz can be distinguished based on its unique trace-element content. Aluminum is generally the most abundant element in all generations of quartz, typically between 50 and 200 ppm, but low-temperature, Main Stage quartz containing 400 to 3600 ppm Al is enriched by an order of magnitude relative to all other quartz generations. Phosphorous is present in abundances between 25 and 75 ppm, and P concentrations in quartz show little variation among quartz generations. Iron is the least abundant of these elements in most quartz types and is slightly enriched in CL-dark quartz in pyrite-quartz veins with sericitic alteration. Titanium is directly correlated with both temperature of quartz precipitation, and intensity of quartz luminescence, such that BQM quartz contains hundreds of ppm Ti, whereas Main Stage quartz contains less than 10 ppm Ti. Our results suggest that Ti concentration in quartz is controlled by temperature of quartz precipitation and that increased Ti concentrations in quartz may be responsible for increased CL intensities.

Is Quartz Cathodoluminescence Color a Reliable Provenance Tool? A Quantitative Examination

ABSTRACT We examined cathodoluminescence (CL) colors of quartz by using red (590-780 nm), green (515-590 nm), and blue (380-515 nm) optical filters interfaced with a cathodoluminescence (CL) detector attached to a scanning electron microscope (SEM). SEM/CL images taken through these filters were captured digitally and transferred to a computer. Luminescence intensities (luminosities) of the images were measured by using available commercial software. Measured luminosities of these CL images are directly related to relative intensities of red, green, and blue CL emissions. Luminosity data were then used to construct plots that display relative luminosities of the CL images acquired through the red, green, and blue filters. An unfiltered CL image of each quartz grain, generated by photons with wavelengths ranging from 200-700 nm, was also acquired. By subtracting the numerical luminosity values of the images acquired through the red, green, and blue filters from the luminosity value of the unfiltered image, the contribution to total luminosity provided by CL emission in the near ultraviolet (UV) was calculated. The CL colors of quartz from a variety of volcanic, plutonic, and metamorphic rocks and hydrothermal deposits were examined. Volcanic quartz phenocrysts have the most restricted CL color range, with strongest emission intensity in the blue wavelength band. CL colors of plutonic quartz overlap those of volcanic phenocrysts but extend over a broader range to include quartz that displays higher intensity of red emission. CL emission in hydrothermal (vein) quartz is similar to that in plutonic quartz, although some hydrothermal quartz exhibits stronger green-CL emission than does plutonic quartz. The CL colors of metamorphic quartz exhibit the widest variation, overlapping the color fields of both volcanic and plutonic quartz and extending further into the red. CL emission in the near UV makes a significant contribution ( 5-85 percent) to the total luminosity of SEM/CL images, particularly images of plutonic quartz. Because of overlap in the CL color ranges of volcanic, plutonic, metamorphic, and hydrothermal quartz, unambiguous identification of quartz provenance on the basis of CL color alone is problematic. It is difficult to distinguish between volcanic and some plutonic quartz, and between some plutonic and hydrothermal quartz, or to distinguish magmatic quartz from metamorphic quartz that exhibits blue CL color. Only metamorphic quartz that exhibits moderately strong red emission appears distinguishable (on the basis of color) from quartz of other origins. Our work thus suggests that CL color is not a reliable indicator of quartz provenance.

Provenance interpretation of Tertiary sandstones from the Cheju Basin (NE East China Sea): a comparison of conventional petrographic and scanning cathodoluminescence techniques

Cheju Basin is a Tertiary intracratonic basin filled with largely nonmarine sediments and is located SW of the Korean Peninsula beneath the NE East China Sea. Commercial petroleum companies drilled 10 deep wells in this basin between the late 1970s and the 1990s. We obtained samples from four representative wells for provenance analysis, using both conventional petrographic techniques and scanning cathodoluminescence (SEM-CL) imaging of quartz. This paper examines differences in provenance interpretation arising from the use of two different analytical techniques. On the basis of framework mineralogy, quartz undulosity and polycrystallinity, and feldspar compositions, we interpret that Cheju Basin sediments were derived from a mixed source rock terrane. Petrographic data suggest that plutonic source rocks were predominant, metamorphic rocks less abundant, and volcanic and sedimentary least important. SEM-CL imaging of quartz from nine of the same samples examined petrographically yielded a different provenance interpretation. SEM-CL results indicate that metamorphic quartz greatly predominates over plutonic quartz in all samples. This discrepancy in interpretation probably stems from the difficulty in distinguishing between plutonic and metamorphic quartz by petrographic methods. SEM-CL analysis shows that volcanic quartz is absent in many samples, even in samples that contain modest amounts of volcanic rock fragments, probably reflecting the generally low content of quartz in many volcanic source rocks. The SEM-CL method cannot directly detect sedimentary (recycled) quartz. Thus, neither petrographic analysis of sandstones nor SEM-CL analysis of quartz may provide completely accurate interpretation of provenance, implying that an integrated approach to provenance analysis is most reliable. Our data suggest that the Cheju Basin areas may have been connected by land to a sediment source on the Korean Peninsula during Oligocene to Miocene time. Alternatively, or additionally, a land source may have existed to the northwest along a narrow massif or suture belt now inundated by the East China Sea. Regional subsidence in Pliocene time initiated the onset of marine conditions in the Cheju Basin; however, one or more of the same land sources continued to furnish sediments to the basin.

Evidence for a nonmagmatic component in potassic hydrothermal fluids of porphyry cu-Au-Mo systems, Yukon, Canada

Isotopic (H, Sr, Pb, Ar) and fluid inclusion data for hydrothermal fluids associated with potassic alteration from three Late Cretaceous porphyry Cu occurrences, west central Yukon, suggest a nonmagmatic fluid component was present in these hydrothermal fluids. Potassic stage quartz veins contain a dominant assemblage of saline and vapor-rich fluid inclusions that have δD values between −120 and −180‰. Phyllic stage quartz veins are dominated by vapor-rich fluid inclusions and have δD values that overlap with but are, on average, heavier (−117 to −132‰) than those in potassic stage quartz veins. These δD values are significantly lower than those from plutonic quartz phenocrysts (−91 to −113‰), and from values typically reported for primary fluids from porphyry-style mineralization (−40 to −100‰). The initial Sr ( 87Sr/ 86Sr i) isotopic values for the plutons are 0.7055 (Casino), 0.7048 (Mt. Nansen), and 0.7055 (Cash). The 87Sr/ 86Sr i compositions of hydrothermal K-feldspar ranges from magmatic Sr i values to more radiogenic compositions (Casino: 0.70551–0.70834, n = 8; Mt. Nansen: 0.7063–0.7070, n = 4; Cash: 0.7058, n = 1). The fluid inclusion waters from potassic quartz veins have 87Sr/ 86Sr i values that are similar to those of co-existing hydrothermal K-feldspar. The Pb isotopic compositions of hydrothermal K-feldspar show a weak positive correlation with Sr i for identical samples. Fluid inclusion waters of phyllic quartz veins also have Sr i compositions more radiogenic than the plutons. The Pb isotopic composition of pyrite and bornite from phyllic alteration veins are similar to, or more radiogenic than, hydrothermal K-feldspar Pb isotopic values. Hydrothermal K-feldspar samples yield 40Ar/ 39Ar ages (Casino = 71.9 ± 0.7 to 73.4 ± 0.8 Ma; Mt. Nansen = 68.2 ± 0.7 and 69.5 ± 0.6 Ma; Cash = 68.3 ± 0.8 Ma) similar to the U-Pb zircon, K-Ar biotite and Re-Os molybdenite ages of the Late Cretaceous plutons, with the age spectra indicating no excess 40Ar or disturbance. The 40Ar/ 36Ar values (285–292) of the K-feldspar samples are similar to the atmospheric compositions (295 ± 5) during Late Cretaceous time. The H, Sr, Pb, and Ar isotopic compositions of hydrothermal K-feldspar and quartz vein fluid inclusion waters that characterize the potassic hydrothermal fluids show evidence for an exotic component in addition to magmatic water (fluid). This component has a low δD, radiogenic Sr and Pb, and an atmospheric Ar composition. The inheritance of pre-existing isotope compositions from the host rocks, postpotassic alteration isotope exchange, or the replenishment of the magma chamber with magma of different isotopic composition cannot explain the isotope data. We suggest that to generate the observed H, Sr, Pb, and Ar isotope compositions, crustal fluids must be a component (15–94%) of potassic hydrothermal fluids in porphyry mineralization in the deposits studied.

Provenance interpretation of quartz by scanning electron microscope–cathodoluminescence fabric analysis

Research Article| September 01, 1997 Provenance interpretation of quartz by scanning electron microscope–cathodoluminescence fabric analysis Abbas Seyedolali; Abbas Seyedolali 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar David H. Krinsley; David H. Krinsley 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar Sam Boggs, Jr; Sam Boggs, Jr 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar Patrick F. O'Hara; Patrick F. O'Hara 2Kaaterskill Exploration, 691 Robinson Drive, Prescott, Arizona 86303 Search for other works by this author on: GSW Google Scholar Henning Dypvik; Henning Dypvik 3Department of Geology, University of Oslo, Blindern, P.O. Box 1047, Blindern, N-0316, Oslo, Norway Search for other works by this author on: GSW Google Scholar Gordon G. Goles Gordon G. Goles 1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272 Search for other works by this author on: GSW Google Scholar Geology (1997) 25 (9): 787–790. https://doi.org/10.1130/0091-7613(1997)025<0787:PIOQBS>2.3.CO;2 Article history first online: 02 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 Abbas Seyedolali, David H. Krinsley, Sam Boggs, Patrick F. O'Hara, Henning Dypvik, Gordon G. Goles; Provenance interpretation of quartz by scanning electron microscope–cathodoluminescence fabric analysis. Geology 1997;; 25 (9): 787–790. doi: https://doi.org/10.1130/0091-7613(1997)025<0787:PIOQBS>2.3.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 SocietyGeology Search Advanced Search Abstract We used a cathodoluminescence (CL) detector attached to a scanning electron microscope (SEM) to study patterns of variable-intensity CL in quartz grains from a variety of igneous, metamorphic, sedimentary, and shock-deformed (meteorite-impact) rocks. Distinctive fabrics in quartz grains revealed by SEM-imaged differential CL include zoning, healed fractures, complex shears, planar features (shocked quartz), dark CL streaks and patches, indistinct, mottled texture, and nondifferential (low-contrast) CL. Zoning is common in volcanic quartz and some plutonic quartz. Zoned plutonic quartz is distinguished from volcanic quartz by the presence of closed fractures and dark CL streaks and patches. Metamorphic quartz displays either an indistinct, mottled texture, or nearly uniform (nondifferential) CL. Quartz from rocks severely deformed by tectonism displays a complex pattern of multiple, small-scale shears. Quartz from meteorite-impact sites and some system boundaries is characterized by intricate patterns of planar features, presumably created by shock metamorphism. Thus, the SEM-CL fabric-analysis technique provides a rapid method for distinguishing quartz from a variety of source rocks. 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.

Lead isotopes as a provenance tool for quartz: Examples from plutons and quartzite, northeastern Minnesota, USA

The U-Pb isotope system in plutonic quartz samples approximates the crystallization age of the host granitoid and thus provides a useful provenance tool for detrital quartz grains. We present lead isotopic data and U and Pb concentrations of quartz from three Late Archean granitoids and from the Early Proterozoic Pokegama Quartzite, all in northeastern Minnesota. Lead in granitic quartz is considerably more radiogenic than in its associated whole rock host, but it is similar or only slightly more thorogenic than its host. Pb-Pb ages obtained from quartz whole-rock-leached feldspar from the Late Archean granitic plutons are consistent with existing geochronology, suggesting that the U-Pb system in quartz remained closed since crystallization. U-Pb isotopic data for detrital clear quartz populations in the Pokegama Quartzite record Late Archean ages (2550–2650), consistent with a source from the Superior Province. Lead isotopic compositions of detrital K-feldspar populations and lead and neodymium isotopic compositions of whole rocks samples from the Pokegama Quartzite also support a Superior Province source. This study highlights the potential of the lead isotope system in detrital quartz, K-feldspar and whole rocks in provenance studies of sandstones.

Static breakage of granitic detritus by ice and water in comparison with breakage by flowing water

ABSTRACTTemperature cycling between −4·5±1·0°C and 13·0±2·0°C in the presence of added water caused significant breakage of granitic detritus. Because cycling with only adsorbed water present also caused breakage, fragmentation is attributed to both the combined action of ice and adsorbed water and to the latter acting alone. Breakage evidently resulted from the gradual tensile opening of pre‐existing cracks, weakening then splitting grains. Surviving unbroken grains show evidence of a fatigue effect. Quartz split dominantly along pre‐existing subplanar microfractures whereas feldspar and biotite split along crystal cleavages.Degree of breakage and product size distribution depend on the crystalline nature of the parent material, its previous history, and the nature and duration of the breakage process. With the first two factors the same, size distributions from adsorbed water breakage alone and from that due to adsorbed water plus ice differ slightly. Both contrast strongly with those of simulated fluviatile breakage. Whereas the latter preferentially produced 2–20 μm particles (probably debris of inter‐particle collisions), static breakage split coarser grains wherever major weaknesses occurred, producing less selective product size distributions with greater proportions of loess‐sized material (about 20‐‐60 μ). Characteristic inflections in the size distribution curves of our experimentally produced debris are also shown by samples from the sola of some frost‐affected soils.Partially healed microfractures in plutonic quartz are normally spaced at about 1–10 μ—approaching the downward asymptotic comminution limit for brittle solids (about 1 μ). Surficial physical processes are capable of reducing only a small proportion of plutonic quartz to this size before its storage in sediments.

The petrochemistry and geologic implications of conglomerates from Archaean geosynclinal piles of southern India

Conglomerates are abundant in the 2.6 Ga old geosynclinal piles of southern Peninsular India and some also occur in the 3.4–3.2 Ga old greenstone belts. The conglomerates in the greenstone belts are autoclastic or pyroclastic, in contrast to the conglomerates in the geosynclinal piles, which generally contain graywackes indicative of sedimentation by turbidity currents.Analyses of 104 pebbles and 28 matrices from the 2.6 Ga-old conglomerates and petrological data show that their source areas were made up of basic–ultrabasic volcanics, trondhjemitic–tonalitic acid plutonics, and phyllite–amphibolite–quartzite–chert–ironstone metasediments. The variations in the composition of the trondhjemite–tonalite pebbles from the Shimoga, Bababudan, Chitradurga, and Gadag geosynclinal piles indicate the significant overall low abundance and differences in the availability of free plutonic quartz for sedimentation. The abundance of Na2O in the matrices and associated graywackes may be due to the high Na2O content of detrital plagioclase fragments derived from trondhjemites and tonalites. The Na2O contents of Archaean graywackes do not appear to be a result of post-depositional albitization of plagioclase. The scarcity of K-rich pebbles, and the K-depleted nature of most of the matrices, indicate that the earlier acid plutonic rocks associated with the true greenstone belts were mainly trondhjemitic–tonalitic in character, and K-rich acid plutonism was largely a post-geosynclinal development. The plutonic source terranes of the geosynclinal piles are similar in some aspects to those of much younger geosynclines throughout the world.

Comparison of the Trace Element Content of Plutonic, Volcanic, and Metamorphic Quartz from Southwestern Montana

Systematic differences in the content of Ti, Mg, and Fe, in quartz of plutonic, volcanic, and metamorphic origins are reflected by spectrographic analyses of 36 samples of Holocene fluvial sand from southwestern Montana. The differences should be directly applicable to provenance interpretations of Tertiary basin-fill sand in Montana. More uniform trace-element contents are found in plutonic quartz (Tiσ = 8 ppm, Feσ = 14 ppm, and Mgσ = 3 ppm) than in metamorphic and volcanic quartz (Tiσ = 24 ppm, Feσ = 73 ppm, and Mgσ = 18 pm). Moreover, less Fe and Mg are found in plutonic quartz (Fe = 19 pm and Mg = 5 ppm) than in metamorphic and volcanic quartz (Fe = 107 ppm and Mg = 22 ppm). Mean Ti content is different for quartz derived from different batholiths; Ti = 72 ppm for Boulder batholith quartz versus Ti = 31 ppm for Tobacco Root batholith quartz.

Technique for Assessment of Particle Breakage in Natural and Artificial Environments

ABSTRACT Direct assessment of particle breakage, in both natural and artificial environments, is made possible by comparing the strengths of suites of particles which have survived a process with the strengths of suites, otherwise similar, that have not been involved in the process. The `fragmentation load,' the load required to bring about breakage of an individual particle between parallel plane surfaces, is the basic quantity used. It is measured in a slightly modified unconfined compression test machine. Fragmentation of coarse plutonic quartz appears to be a major process in a stream.