Igneous petrology Research Papers - Academia.edu (original) (raw)

The Matachewan Large Igneous Province (LIP) is interpreted to have formed during mantle plume-induced continental break-up during the early Proterozoic. When the Matachewan LIP is reconstructed to its original configuration, the dyke... more

Snowflakes and silicate mushes are two examples of the terrestrial regimes that may be characterized as partially solidified systems. Change of phase in clouds and magma chambers as well as in the earth's mantle and core introduces a... more

Snowflakes and silicate mushes are two examples of the terrestrial regimes that may be characterized as partially solidified systems. Change of phase in clouds and magma chambers as well as in the earth's mantle and core introduces a variety of phenomena to challenge both the mathematical modeler and the experimentalist intent upon understanding the nature of such processes. Paralleling the efforts of researchers in the natural sciences, metallurgists and materials scientists have extensively investigated solidification in alloy melts to discover the controlling mechanisms for undesirable behavior such as melt segregation, freckling (Figure 1), and crystal dislocation. Unfortunately, most of the studies, whether in the geosciences or in material sciences, have focused on highly specialized problems with little or no attempt at generalizing the results or methods to other physical systems. During May 12-16, 1986, at the Stanford University Conference Center at Fallen Leaf Lake, ...

Copyright 2009, Society of Petroleum Engineers This paper was prepared for presentation at the 2009 SPE/EAGE Reservoir Characterization and Simulation Conference held in Abu Dhabi, UAE, 19–21 October 2009. This paper was selected for... more

Copyright 2009, Society of Petroleum Engineers This paper was prepared for presentation at the 2009 SPE/EAGE Reservoir Characterization and Simulation Conference held in Abu Dhabi, UAE, 19–21 October 2009. This paper was selected for presentation by an SPE ...

A geochemically and mineralogically diverse group of granitoids is present within an area of 900 km 2 in the southern Snake Range of eastern Nevada. The granitoids exposed range in age from Jurassic through Cretaceous to Oligocene and... more

A geochemically and mineralogically diverse group of granitoids is present within an area of 900 km 2 in the southern Snake Range of eastern Nevada. The granitoids exposed range in age from Jurassic through Cretaceous to Oligocene and include two calcic intrusions, two different types of two-mica granites, and aplites. The younger intrusions appear to have been emplaced at progressively more shallow depths.

A geochemically and mineralogically diverse group of granitoids is present within an area of 900 km 2 in the southern Snake Range of eastern Nevada. The granitoids exposed range in age from Jurassic through Cretaceous to Oligocene and... more

A geochemically and mineralogically diverse group of granitoids is present within an area of 900 km 2 in the southern Snake Range of eastern Nevada. The granitoids exposed range in age from Jurassic through Cretaceous to Oligocene and include two calcic intrusions, two different types of two-mica granites, and aplites. The younger intrusions appear to have been emplaced at progressively more shallow depths.

The Deccan volcanic, representing basaltic flows of Cretaceous-Eocene age, are the most extensive geological formation of Peninsular India. They cover total area of 80% area of Maharashtra state. Keyword:Geological Study , amygdaloidal ,... more

The Deccan volcanic, representing basaltic flows of Cretaceous-Eocene age, are the most extensive
geological formation of Peninsular India. They cover total area of 80% area of Maharashtra state.
Keyword:Geological Study , amygdaloidal , solidification , Soil texture.

This report documents several new findings concerning the geology and mineral potential of the central East Tintic Mountains, Utah. For example, fission-track ages and 40Ar/39Ar ages which we report suggest that some of the volcanism and... more

This report documents several new findings concerning the geology and mineral potential of the central East Tintic Mountains, Utah. For example, fission-track ages and 40Ar/39Ar ages which we report suggest that some of the
volcanism and alteration in this area is as old as 37.4 to 35.3 Ma. This early episode of volcanism was contemporaneous with lacustrine deposition; the overlying volcanic rocks and cross-cutting intrusions range in age from about 34.5 to 33.6 Ma. This implies that a large caldera related to the eruption of the younger Packard Quartz Latite and Fernow Quartz Latite is not present in this area . However, our data suggest that a smaller caldera related to the eruption of the tuff member of the Copperopolis Latite may be present. We note that many monzonite dikes and intrusions in this area are hornblende bearing and are correlative in modal and chemical composition with the productive Silver City Stock rather than the barren Sunrise Peak Stock. The large areas of hydrothermal alteration which surround these intrusions
exhibit many similarities to the well-studied alteration halos in the East Tintic District. The age, composition, and field relationships of the post-lacustrine volcanic rocks suggest that they may represent, in part, the extrusive equivalents of the monzonite dikes and Silver City Stock. Our work suggests that the Silver City Stock and related intrusions may be part of one of the youngest (33.6 ± 0.2 Ma) igneous events in the central East Tintic Mountains, but not as young as previously suggested (ca. 31.5 Ma). In addition, our recent work has documented the existence of unusually large (and abundant) magmatic sulfides in lava vitrophyres and vent-facies biotite latite dikes, which are the surface expressions of the Silver City Quartz Monzonite intrusions in this area. In addition, preliminary analytical data suggest that the sulfides host most (-75%) of the Ag present in the latites. The East Tintic Mountains are potentially the first locality, worldwide, where Ag in mesothermal veins can be demonstrated to be derived from degassed Ag-bearing magmatic sulfides. Consequently, the central East Tintic
Mountains are a favorable area for exploration for Ag (Pb-Zn-Cu-Au) ore bodies because: 1) productive monzonite intrusions are present, and 2) Paleozoic rocks favorable for ore deposition may be present beneath relatively thin volcanic cover because the area is not entirely enclosed within a caldera.

Chemical and Sr isotopic zoning patterns in plagioclase megacrysts from gabbroic dykes in the Gardar Province can be used to elucidate magma-chamber and emplacement processes. The megacrysts occur either as single crystals or assembled as... more

Chemical and Sr isotopic zoning patterns in plagioclase megacrysts from gabbroic dykes in the Gardar Province can be used to elucidate magma-chamber and emplacement processes. The megacrysts occur either as single crystals or assembled as anorthosite xenoliths. The size of the megacrysts varies from <1 cm to 1 m. They consist of a large core with variable zonation (An58–39) and a relatively small (<600 µm), normally zoned rim (An62–27). The contact between core and rim is sharp and marked by a sharp increase in anorthite content which can reach 11 mol% An. This gap is interpreted as having formed during dyke emplacement due to a sudden pressure release. Some of the megacryst cores show a fairly constant composition whereas others exhibit an unusual wavy-oscillatory zoning which has not been reported elsewhere to our knowledge. The oscillatory zoning has wavelengths of up to 2,500 µm and a maximum amplitude of 7 mol% An. It is interpreted as reflecting movements of the crystals in the magma reservoir. The Sr isotopic composition of one crystal shows a radiogenic inner core ((87Sr/86Sr)i=0.7044) and a less radiogenic outer core ((87Sr/86Sr)i=0.7039–0.7036). The lack of a significant change between outer core and rim ((87Sr/86Sr)i=0.7037) is consistent with formation of the more An-rich rim due to pressure release. Variations in the core may be related to movements of the crystal and/or magma mixing. A trace-element profile across a megacryst shows a small increase in Sr and small decreases in Ba and La contents of the recalculated melt composition across the core-rim boundary, whereas P, Ce, Nd and Eu remain constant. Melt compositional changes upon emplacement are therefore considered to be of minor importance. Constant ratios of incompatible trace elements in the megacryst cores indicate a dominant influence of a lower crustal source on trace-element budgets.

High-silica topaz-bearing rhyolites of Cenozoic age are widely distributed across the western USA and Mexico. They are characteristically enriched in fluorine (> 0.2 wt.%) and incompatible lithophile elements (eg Li, Rb, Cs, U, Th, Be).... more

High-silica topaz-bearing rhyolites of Cenozoic age are widely distributed across the western USA and Mexico. They are characteristically enriched in fluorine (> 0.2 wt.%) and incompatible lithophile elements (eg Li, Rb, Cs, U, Th, Be). In addition to topaz, the rhyolites contain garnet, bixbyite, pseudobrookite, hematite and fluorite in cavities or in their devitrified groundmasses. Magmatic phases include sanidine, quartz, oligoclase and Fe-rich biotite.

The Al Haruj intra-continental Volcanic Province (AHVP), located at the southwestern margin of the Sirt Basin, hosts the most extensive and recent volcanic activity in Libya-which is considered typical for plate interiors. From north to... more

The Al Haruj intra-continental Volcanic Province (AHVP), located at the southwestern margin of the Sirt Basin, hosts the most extensive and recent volcanic activity in Libya-which is considered typical for plate interiors. From north to south the AHVP is divided into two subprovinces, namely Al Haruj al Aswad and Al Haruj al Abiyad. The total area of the AHVP is around 42,000km 2. Despite the great size of the AHVP, its volcano-tectonic evolution and activity have received very little attention and are poorly documented and understood. Here we present new field data, and analytical and numerical results, on the volcano-tectonics of the AHVP. The length/thickness ratio of 47 dykes and volcanic fissures were measured to estimate magmatic overpressure at the time of eruption. The average dyke (length/thickness) ratio of 421 indicates magmatic overpressures during the associate fissure eruptions of 8-19MPa (depending on host-rock elastic properties). Spatial distributions of 432 monogenetic eruptions sites/points (lava shields, pyroclastic cones) in the AHVP reveal two main clusters, one in the south and another in the north. Aligned eruptive vents show the dominating strike of volcanic fissures/feeder-dykes as WNW-ESE to NW-SE, coinciding with the orientation of one of main fracture/fault zones. Numerical modelling and field 2 observations suggest that some feeder-dykes may have used steeply dipping normal-fault zones as part of their paths to the surface.

The world's largest mined rare-earth element deposits are associated with alkaline magmatism, making it important to understand the mechanisms leading to magmatic and hydrothermal element enrichment. We present results from... more

The world's largest mined rare-earth element deposits are associated with alkaline magmatism, making it important to understand the mechanisms leading to magmatic and hydrothermal element enrichment. We present results from late-differentiation-stage hydrothermal veins of the Jbel Boho alkaline complex in the district of Bou Azzer in the Anti-Atlas of Morocco, which show high light-REE enrichments. The REE mineralized veins occur around a syenitic pluton at the centre of the complex and consist of quartz-jasper and quartz veins which contain at least two silica generations. Only the second quartz generation is associated with LREE mineralization. The predominant REE-host mineral is the Ca-LREE-fluorcarbonate synchysite-(Ce), mainly present as anhedral crystals up to 200 μm. Some very small anhedral rhabdophane-(Ce) grains were also found in a synchysite-bearing quartz vein. Thermometric studies on mainly liquid-vapour-solid fluid inclusions in quartz crystals in the synchysite-bearing veins suggest very high salinity (32 to 37 wt% NaCl equiv.) of the mineralizing fluid. Homogenization temperatures from 150° to 250 °C provide the minimum temperature conditions in which the quartz veins were formed.
Based on recent experimental data, we propose a model for the formation of hydrothermal REE-Ca-F carbonate deposits in the veins, involving the transport of REE as chloride complexes at low pH conditions in the presence of fluoride ions. The deposition of synchysite is proposed to result from neutralization of this fluid by mixing of hydrothermal ore fluids with carbonate-rich meteoric water or by interaction with already existing carbonates in the vein, As well as raising the pH, this interaction also provides the Ca+ and CO32– ions needed for REE precipitation as Ca-F carbonates.
The barren veins show two types of mineralogy and REE patterns: quartz-carbonate veins with enrichment of LREE over HREE and iron-rich jasper-bearing veins with quite flat REE pattern and high HREE. The LREE/HREE fractionation in these veins seems to be controlled by an interplay of two factors: 1) a low activity of ligands like Cl, which favours LREE transport and (2) the mineralogical control, by which HREE having similar ionic radii to Fe2 + will be preferred over LREE.

Computerized evaluation of Vibroseis similarity test data is the logical consequence of the increasing quality requirements for signal reproducibility and for synchronization of vibrators. The differences in start time and phase as well... more

Computerized evaluation of Vibroseis similarity test data is the logical consequence of the increasing quality requirements for signal reproducibility and for synchronization of vibrators. The differences in start time and phase as well as an indication of local phasing problems between any two Vibroseis signals can be obtained from an analysis of the difference of their respective phase spectra. This method appears to be accurate and stable with respect to harmonics which usually plague the signals from transducers monitoring the motion of the vibrators'base plates.

The probability of the occurrence of porphyry copper ore associated with subduction zone of the Neo-Tethys ocean and volcanic arc of Iran (Urumieh-Dokhtar) justifies the necessity of exploration and prospection of this type of ore in... more

The probability of the occurrence of porphyry copper ore associated with subduction zone of the Neo-Tethys ocean and volcanic arc of Iran (Urumieh-Dokhtar) justifies the necessity of exploration and prospection of this type of ore in Iran. Zafarghand index and Kahang deposit of porphyry copper-molybdenum located in Isfahan province, center of Iran using Satellite data interpretations were discovered in the years of 2010 and 2003, respectively. Geological studies have indicated the presence of argillic and propylitic alteration halos associated with porphyry copper systems. The 250 rock samples were systematically collected at a sampling distance of 100 m and in the center of the porphyry system by a distance o f 50 m in Zafarghand. Also, 377 samples of lithogeochemicals (185 rock samples and 192 soil samples) were extracted systematically from Kahang deposit. The study of geochemical data of rock and soil samples showed similarity of these two types of mineralization with other mineralization of porphyry copper-molybdenum elsewhere in the world. Finally, the comparison of geochemical anomalies copper with rock units and alteration zones showed that atmospheric waters had washed out the copper in some of these zones and probably the supergene zone was formed in depth as porphyry copper-molybdenum deposit.

Seminar Report on Quartz Mineral and the Vein Quartz Deposits of Sri Lanaka.

The Betul crystalline complex (BCC) forms a conspicuous litho-tectonic unit of the Central Indian Tectonic Zone (CITZ). The BCC occurs in central part of CITZ in between the northern Mahakoshal belt and southern Sausar belt and comprises... more

The Betul crystalline complex (BCC) forms a conspicuous litho-tectonic unit of the Central Indian Tectonic Zone (CITZ). The BCC occurs in central part of CITZ in between the northern Mahakoshal belt and southern Sausar belt and comprises of three distinct rock associations, i) Supracrustal rocks, ii) Mafic-Ultramafic suites and iii) Syn-to post-kinematic granitic rock and bimodal volcanics. The rocks of BCC have undergone three phases of progressive deformation and its environs were evolved near continental margin arc. Two phases of granitic emplacements are evident in BCC. Geochemical characterisation of basement granitoids of the BCC was carried out during the present work. The geochemical characteristics of these granitoids are comparable with I-type granites, which are metaluminous to peraluminous in nature and belongs to medium to high-K calc-alkaline series that displays characteristics of typical volcanic arc granites related to the active continental margin.

High-K calc-alkaline granitoids exposed in Mubi area, northeastern Hawal massif forms an integral part of the well-exposed syn-to post-collisional plutons in eastern Nigeria. The evolution of the rocks can be linked to the thermo-tectonic... more

High-K calc-alkaline granitoids exposed in Mubi area, northeastern Hawal massif forms an integral part of the well-exposed syn-to post-collisional plutons in eastern Nigeria. The evolution of the rocks can be linked to the thermo-tectonic period of faulting, uplift, cooling, fractionation, and high-level magmatism, which initiated granite intrusion and associated rocks during the Paleoproterozoic. A total of nine granitic rocks, constituting seven biotite granites of varying grain sizes and two porphyritic granites were sampled in Mubi area to shed new light regarding their petrochemistry. Detailed investigations indicate that the study area constitutes majorly Pan African granitoids. The massif has S-type strongly peraluminous geochemical signature, high-K calc-alkaline, magnesian, granodi-orite, exemplified by high ASI (averagely 0.81-1.59), low Na 2 O (average 2.09 wt. %), and CaO (average 2.37 wt%). More so, they exhibit low FeO t /(FeO t + MgO) ratios (0.64-0.80 wt%), low to moderate Na 2 O+K 2 O-CaO ratio (2.41-5.41 wt%), high Na 2 O+K 2 O (average 6.42 wt%), and K 2 O/Na 2 O ratios (average 2.11 wt%), as well as high Mg# (30.49-50.22), low molar CaO/(MgO + FeO t) (0.19-0.63 wt%), and molar Al 2 O 3 /(MgO + FeO t) ratio (2.10-4.31 wt%). Discrimination diagram shows that the granitoids are products of sedimentary protolith (metagreywacke) formed within a syn-collision and supra-crustal setting. The constituent mineral assemblages in the granitoids (quartz, plagioclase, alkali feldspar, bio-tite, hornblende, titanite, and iron oxides) from the northeastern Hawal massif are obviously related to the condition of evolution and compositions of the protolith. The manganese ore and associated minerals in the area are controlled by the N-S pegmatitic quartz, which is part of the Cameroon Volcanic Line. The manganese minerals are hydrothermally generated from rising thermal waters due to pressure decline and subsequent reactions with the crystalline igneous rocks, which consequently triggered the precipitation of manganese oxides of metallurgical grade (44.36-49.56 wt%) that can be further processed into desired metallic alloy to meet the required industrial standards. ARTICLE INFO

geology fundamentals mc graw hill 2015, lastest version

Myron G. Best
Brigham Young University

This study is aimed at recognizing possible sources of dispersion of density measurements of welded ignimbritic rocks by helium pycnometer. The values of bulk density and solid fraction volume, useful for volcanological studies as well as... more

This study is aimed at recognizing possible sources of dispersion of density measurements of welded ignimbritic rocks by helium pycnometer. The values of bulk density and solid fraction volume, useful for volcanological studies as well as for a complete definition of the mechanical properties of these rocks, commonly used for present or historical buildings, are often tricky to obtain, due to the presence of micropores and the high tor-tuosity of the porous network. Three samples representative of different lithofacies of Miocene ignimbrites from San Pietro Island (SW Sardinia, Italy), have been used here to tune up a density measurement method. Basing on a statistical study of the density data derived from different analytical strategies, we propose a specific procedure for determining to measure density of welded ignimbritic rocks. Several measurements (runs) are performed on the undisturbed and on powered specimens of the three samples, using two different methods of gas-purging of the pycnometer: flow and pulse purging modes, respectively. The main factors that can produce a source of accidental errors are: uncontrolled fluctuations in temperature of the instrument, pollution of the sample (e.g., moisture), intrinsic petrophysical characteristics (e.g., pore tortuosity) of ignimbritic rocks. Conversely, the main systematic errors introduced in the measurements revealed to be related to the selected time and mode of gas-purging of the instrument during the first steps of the analysis. Using an appropriate sequence of contiguous cycles, accuracy and precision of data can be optimized, thus excluding systematic errors. The results show that in the first cycle, regardless of the purge time (or pulses), the values of density and standard deviations are always higher compared to the second and the third cycles. Basing on the analysis of our data, we propose that the better procedure to obtain an accuracy data is using 10-run cycles and considering the average value of the last seven measures.

The Tecolotlan valley is a small graben ~110 km southwest of Guadalajara in the northeastern corner of the Jalisco block of west-central Mexico. The graben trends roughly north-south, is ~10 km wide and 20 km long, with ~500 m of... more

The Tecolotlan valley is a small graben ~110 km southwest of Guadalajara in the northeastern corner of the Jalisco block of west-central Mexico. The graben trends roughly north-south, is ~10 km wide and 20 km long, with ~500 m of topographic relief. It is bounded to the east by a horst of Cretaceous (Albian/Cenomanian) limestone and to the west by a block of Late Cretaceous volcaniclastic sedimentary rocks, lava fl ows, and ignimbrites (one is 77 Ma). These volcanic rocks have chemical and mineralogical affi nities with continental volcanic arc sequences and record a history of arc volcanism and sedimentation during the Late Cretaceous. The sequence (over 300 m thick) consists of rhyolitic ash-fl ow tuffs and trachytic lava fl ows (lacking pillow structures) interbedded with volcanic debris fl ow deposits, arkosic fl uvial sand-stones, and volcanic conglomerates. This suggests that by the Late Cretaceous the continental arc was emergent, but probably still low-standing as it continued to accumulate sediment after the closure of the Arperos oceanic basin and accretion of the Guerrero arc terrane to Mexico. The Tecolotlan valley contains discontinuously deposited latest Miocene to Recent sediments that are important for their record of extension, magmatism, and diverse vertebrate fauna. Neogene basin fi ll is divided into older, Late Hemphillian age (ca. 5–4.8 Ma) sedimentary rocks (~50–60 m) that are mostly fi ne-grained fl uvial and overbank deposits, and younger, Late Blancan–Recent (younger than ca. 2.7 Ma) sediments (up to 30 m thick) that consist of coarse-grained, high-energy, fl uvial deposits. Intercalated with the basin-fi ll sedimentary rocks are isolated lava fl ows and pyro-clastic-fall beds. It appears that volcanism and extension in the Tecolotlan graben occurred simultaneously with a period of increased volcanic activity along the ESE-WNW–trending Tepic-Zacoalco graben. Although extension and volcanism ceased by

The Southeast Anatolian ophiolites outcropping in the Southeast Anatolian Orogenic Belt (Southeast of Turkey) mark the closure of the southern branch of the Neotethys Ocean associated with the collision between the Arabian Plate and... more

The Southeast Anatolian ophiolites outcropping in the Southeast Anatolian Orogenic Belt (Southeast of Turkey) mark the closure of the southern branch of the Neotethys Ocean associated with the collision between the Arabian Plate and Anatolian microplate. We present new geochemical, zircon U-Pb age, zircon Lu-Hf, and Sr-Nd isotopic data on the Southeast Anatolian Ophiolites to understand their formation ages, magma genesis, and geotectonic implications. The ophiolites, which are related to island arc igneous rocks, consist of mantle peridotites and crustal rocks (less dunite, gabbros, sheeted dykes, massive, and pillow basalts). The flat rare-earth element (REE) patterns, depletion in Nb and Ta, and enrichment in LILEs (Ba, Rb, Th, Sr, Pb) of gabbros suggest close similarities with very low Ti (boninitic) lavas found in the forearc regions. Using laser ablation inductively coupled plasma-mass spectrometry, zircon separated from leucogabbros, diabase dykes, and plagiogranites yield U-Pb ages of 92 and 83 Ma, which are interpreted to represent the formation ages of the ophiolites. The zircons in the gabbros and plagiogranites are dominated by positive εHf(t) values (between +3.1 and + 17.45) with a few negative εHf(t) values. High εHf(t) features are consistent with derivation from Mid-oceanic Ridge Basalt (MORB)-source mantle. The negative εHf(t) values of the zircons suggest the involvement of subducted sedimentary rocks. The southeast Anatolian ophiolites represent an SSZ-type ophiolite and are part of the Late Cretaceous oceanic lithosphere of the southern branch of the Neotethys Ocean that opened during the Late Triassic and closed during the Late Cretaceous.

Author:
Marjorie Wilson
Department of Earch Sciences, University of Leeds

Monica Price
Kevin Walsh

What are Minerals?
What are Rocks?
Rock Identification
Mineral Identification