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Geochemistry and petrogenesis of the Catoctin Volcanic Province, central AppalachiansBadger, Robert L. 04 March 2009 (has links)
The Catoctin Volcanic Province represents a sequence of rift related tholeiitic magmas erupted during late Precambrian opening of the Iapetus ocean basin. Three transects have been mapped across the province in northern Virginia in order to demonstrate that there is a mappable stratigraphy and to provide a framework upon which to construct a chemical stratigraphy. Chemical analyses of multiple samples from single flows containing a contrast in fabric development and mineral assemblages indicate that portions of flows with poorly developed fabric and retaining igneous textures and relict clinopyroxenes have been least affected by hydration reactions and are more likely to retain igneous geochemical signatures.
Using primarily the less mobile oxides TiO₂, AlO₃, MgO, FeO, and P₂O₅ the chemical stratigraphy for each traverse can be divided into chemical subunits. Each subunit can be modeled by fractional crystallization predominantly of plagioclase and clinopyroxene. Chemical discontinuities between subunits suggest new magma sources or rejuvination of existing magma chambers. The overall geochemical signature of the magmas can be modeled through gabbro fractionation from a picritic source.
Sr isotopic data from only those samples that have been least affected by fluid interaction indicate the magmas evolved from a Sr isotopically depleted mantle source and the age of eruption was at approximately 570 Ma. A depleted Sr<sub>i</sub> is in sharp contrast to enriched signatures for a sequence of proximally located tholeiites erupted during Mesozoic rifting between North America and northern Africa, suggesting that if the Mesozoic signature is reflecting contamination by a subducted slab component (Pegram, 1986) this contamination event must have been post Catoctin time.
The 570 Ma age of eruption is the fIrst isotopically determined age that is consistent with stratigraphic and paleontologic data. When contrasted with dates of 650-730 for other rift related magmas in the southern and central Appalachians, the 570 Ma age suggests a two stage rift event, the first one failed while the second succeeded at opening the Atlantic ocean basin. / Ph. D.
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Petrogenesis of the Willis Mountain and East Ridge kyanite quartzite, Buckingham County, VirginiaCochrane, Judith Christian January 1986 (has links)
The kyanite quartzites of the Willis Mountain and East Ridge deposits in Buckingham County, Virginia hosts the world's largest kyanite mine and constitute the largest known reserves of kyanite. The stratiform kyanite quartzite is overlain and underlain by quartz-muscovite schists which are in turn enveloped by biotite-amphibole gneiss of the Cambrian Chopawamsic formation, metamorphosed volcanic and volcaniclastic rocks. The entire package of rocks has been metamorphosed to amphibolite grade peak conditions of 6.5 kb and 600°C. The kyanite quartzite is very similar in bulk composition and accessory mineralogy to high-alumina rocks of probable hydrothermal origin in North Carolina, South Carolina, and Georgia, and to active stratiform hydrothermal alteration zones in Tatun, Taiwan and Otake, Japan. The major difference among these deposits is the type of aluminosilicate phase present, a reflection of the grade of metamorphism, with kaolinite and pyrophyllite appearing in unmetamorphosed deposits, pyrophyllite and andalusite appearing in zones of greenschist grade, and kyanite appearing in zones of amphibolite grade. Data from active alteration zones and mineral equilibria suggest that the kyanite quartzite was formed from intermediate volcanic rocks by hydrothermal action of acidic fluids (pH 2 to 4) at a temperature between 100 and 200°C under mildly oxidizing conditions. Alumina and silica were residually enriched as alkali and alkaline earth cations were extracted from the rock by hydrolysis. The surrounding quartz-muscovite schist was formed in the same manner by less acidic, cooler fluids. The adjacent biotite-amphibole gneiss also shows signs of partial hydrothermal alteration, such as residual enrichment of alumina represented by a kyanite and/or sillimanite-staurolite-gedrite assemblage. / M.S.
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Petrogenesis of the reversely zoned Turtle pluton, Southeastern CaliforniaAllen, Charlotte M. January 1989 (has links)
Few plutons with a reversed geometry of a felsic rim and mafic core have been described in the geologic literature. The Turtle pluton of S.E. California is an intrusion composed of a granitic rim and granodioritic core and common microgranitoid enclaves. Field observations, mineral textures, and chemistries, major and trace element geochemistry, and isotopic variability support a petrogenetic model of in situ, concomitant, magma mixing, and fractional crystallization of rhyolitic magma progressively mixed with an increasing volume of andesitic magma, all without chemical contribution from entrained basaltic enclaves. Hornblende geobarometry indicates the Turtle pluton crystallized at about 3.5 kb. A crystallization sequence of biotite before hornblende (and lack of pyroxenes) suggests the initial granitic magma contained less than 4 wt% H₂0 at temperatures less than 780°C. U-Pb, Pb-Pb, Rb-Sr and oxygen isotope studies indicate the terrane intruded by the Turtle pluton is 1.8 Ga, that the Turtle pluton crystallized at 130 Ma, that the Target Granite and garnet aplites are about 100 Ma, and that these intrusions were derived from different sources. Models based on isotopic data suggest the rhyolitic end member magma of the Turtle pluton was derived from mafic igneous rocks, and was not derived from sampled Proterozoic country rocks. Similarity of common Sr and Pb isotopic ratios of these rocks to other Mesozoic intrusions in the Colorado River Region suggest the Turtle pluton and Target Granite have affinities like rocks to the east, including the Whipple Mountains and plutons of western Arizona. P-T-t history of the southern Turtle Mountains implies uplift well into the upper crust by Late Cretaceous time so that the heating and deformation events of the Late Cretaceous and Tertiary observed in flanking ranges did not affect the study area. / Ph. D.
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Petrogenesis of the Springfield Granodiorite, southeast Pennsylvania PiedmontBecker, Mona Louise 09 May 2009 (has links)
The Springfield pluton intrudes the Wissahickon schist in the southeast Pennsylvania Piedmont. The mineralogy of the pluton. in order of decreasing abundance is plagioclase, quartz, microcline, biotite, epidote (often with allanite cores) and trace amounts of hornblende. Accessory minerals include sphene, magnetite, apatite and zircon. The magmatic assemblage of quartz+two feldspars+biotite+sphene+hornblende+magnetite permits its utilization of AI-in-hornblende as a geobarometer (Schmidt, 1992) and yields a pressure estimate of 9 kbars. The initial 87Sr/86Sr ratio of 0.708, suggests an evolved source for the magma with respect to mantle compositions, while a Rb-Sr whole rock age of 457 ± 9 Ma suggests a link between peak metamorphic conditions (Crawford and Crawford, 1980; Crawford and Mark, 1987, Sinha, 1988) and magmatism. The pluton is metaluminous to weakly peraluminous, with the aluminum saturation index (ASI) < 1.15. Si02 contents range from 64.1 to 75.1 wt. percent, with all other elements showing a correlation (either positive or negative) with the Si02. The pluton is correlated with two similar bodies to the south, Ellicott City, Maryland and Ellisville, Virginia. The spatial and temporal relationships of the plutons, including the two mica Gunpowder granite, Maryland record a magmatic axis associated with high pressures (>5.0 kb) of emplacement of magmas. / Master of Science
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The petrogenesis of the Nelshoogte pluton: The youngest and most compositionally variable TTG pluton in the Barberton Granite-Greenstone TerrainMatsumura, Risa 04 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2014 / ENGLISH ABSTRACT: The compositions of tonalite-trondhjemite-granodiorite (TTG)-series rocks from the
Barberton Granite-Greenstone Terrain (BGGT) of Southern Africa vary in terms of major
element concentrations (leuco-trondhjemites to tonalites), trace elements (e.g. Sr, Rb, REE)
and degree of HREE depletion [(La/Yb)N ~ 0.50 - 121]. These geochemical parameters have
been interpreted to have significance for the geodynamic processes that produced TTG
magmas, particularly the depth of the source. In the Nelshoogte pluton, trondhjemite
emplacement occurred prior to and during (D2)-tectonism, and hornblende-bearing
tonalites/granodiorites occur as intrusive plugs within the trondhjemite. The geochemical
range portrayed by the ca. 3230 Ma Nelshoogte pluton covers almost the whole range
portrayed by all the TTG rocks of the BGGT, formed in the time interval 3550 to 3230 Ma.
U-Pb zircon dating reveals no significant differences in apparent ages between the
trondhjemites and tonalites of the Nelshoogte pluton; all lie between ca. 3240 and 3220 Ma.
A/CNK- and Ti-maficity correlations within the Nelshoogte pluton show behaviour typical of
I-type granitic rocks, confirming the metamafic character of the source and the involvement
of a peritectic garnet and clinopyroxene component in the magmas. The REE and traceelement
patterns resemble those of both ca. 3450 Ma TTG plutons and other ~ 3230 Ma TTG
plutons in the BGGT. This suggests that these different generations of TTG magmas were
generated from similar sources and by similar processes. The geochemical details are
consistent with a metamafic source which underwent melting at high pressure. This TTG
source was fundamentally different from the more potassic source/s that produced the
younger 3100 Ma granites. Additionally, high Zr/Sm and low Nb/Ta ratios in the Barberton
TTG rocks suggest that the Nelshoogte pluton originated as a group of chemically distinct
magmas, in a similar way to other ~ 3200 Ma TTGs. The protoliths of ~ 3450 Ma plutons and
~ 3200 Ma plutons might typically be rutile-bearing eclogite and/or 10 to 30 % garnet
bearing amphibolite.
The geochemical features of the Barberton TTGs suggest similar source compositions, but
different pressures of partial melting. For the ca. 3230 Ma plutons, the rocks of the Badplaas
pluton and the Nelshoogte trondhjemites/tonalites correspond to the high-pressure magmas,
as reflected by high Sr content, as well as high Sr/Y and (La/Yb)N ratios. In contrast, the
Kaap Valley TTGs and Nelshoogte granodiorites reflect the melting of a similar source at
moderate pressure. Furthermore, the Hf isotope data; Hft (+ 0.1 to + 1.9) and TDM model ages (3330 - 3230 Ma), suggest that the source rocks are ~ 20 to 100 Myr older than the
pluton. / AFRIKAANSE OPSOMMING: Die samestellings van tonaliet-trondhjemiet-granodioriet (TTG)-reeks gesteentes vanaf die
Baberton Graniet-Groensteen terrien (BGGT) van Suiderlike Afrika verskil in terme van
hoofelement konsentrasies (leuko-trondhjemiete tot tonaliete), spoorelemente (bv. Sr, Rb en
seldsameaarde-elemente(SAE)) en ook van swaar seldsameaarde-element (SSAE) uitputting
[(La/Yb)N ~ 0.50 - 121]. Deur interpritasie is daar vasgestel dat hierdie geochemiese
beperkings betekenis dra vir die geodinamiese prosesse wat TTG magmas produseer het, en
veral vir die diepte van die bron. In die Nelshoogte pluton het trondhjemiet inplasing voor en
gedurende (D2)-tektonisme voorgekom en horingblende-draende tonaliet/granodioriet kom
voor as intrusiewe proppe binne-in die trondhjemiet. Die geochemiese reeks wat uitgebeeld is
deur die ~ 3230 Ma Nelshoogte pluton ondersteun byna die hele reeks wat uitgebeeld is deur
al die TTG gesteentes van die BBGT wat gevorm het gedurende die tydsinterval 3550 tot
3230 Ma. U-Pb sirkoon datering openbaar geen merkwaardige verskille in ouderdomme
tussen die trondhjemiete en tonaliete van die Nelshoogte pluton nie. Al die ouderdomme lê
tussen 3240 en 3220 Ma.
A/CNK- en Ti-mafisiteit korrelasies binne die Nelshoogte pluton toon die tipiese gedrag van
I-tipe granitiese gesteentes, en bevestig sodoende die metamafiese karakter van die bron,
asook die betrokkenheid van ‘n peritektiese granaat en klinopirokseen component in die
magmas. Die seldsameaarde-element en spoorelement patroone lyk soos dié van albei ~ 3450
Ma plutons en ander ~ 3230 Ma TTG plutons in die BGGT. Dit stel voor dat hierdie
verskillende generasies van TTG magmas genereer was vanaf soortgelyke bronne en ook
deur soortgelyke prosesse. Die geochemiese besonderhede stem ooreen met ‘n metamafiese
bron wat smelting teen hoë druk ondergaan het. Hierdie TTG bron het fondamenteel verskil
van die meer kalium-ryke bron/ne wat die jonger 3100 Ma graniete prodiseer het. In ‘n
eenderse manier as ander ~ 3200 Ma TTG gesteentes, stel hoë Zr/Sm en lae Nb/Ta
verhoudings in die Baberton TTG gesteentes verder voor dat die Nelshoogte pluton ontstaan
het as ‘n groep chemies verskillende magmas. Die protoliete van ~ 3450 Ma plutons en ~
3200 Ma plutons mag dalk tipies rutiel-draende eklogiet en/of 10 tot 30% granaat draende
amfiboliet wees.
Die geochemiese aspekte van die Baberton TTGs stel eenderse bron komposisies, maar
verskillende drukke van gedeeltelike smelting voor. Vir die ~ 3230 Ma plutons stem die
gesteentes van die Badplaas pluton en die Nelshoogte trondhjemiete/tonaliete ooreen met die hoë druk magmas, soos weerspieël deur hoe Sr inhoud, sowel as hoe Sr/Y en (La/Yb)N
verhoudinge. In kontras weerspiel die Kaap Valley TTGs en Nelshoogte granodioriet die
smelting van ‘n eenderse bron teen matige druk. Verder stel die Hf isotoop data; Hft (+ 0.1
to + 1.9) en TDM model ouderdomme (3330 - 3230 Ma) voor dat die bron gesteentes ~ 20 to
100 Mjr ouer is as die pluton.
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Petrogenesis of permian flood basalts and mafic-ultramafic intrusions in the Jinping (SW China) and Song Da (Northern Vietnam) districtsWang, Yan, 王焰 January 2006 (has links)
published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy
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The geochemical evolution of the Aucanquilcha Volcanic Cluster : prolonged magmatism and its crustal consequencesWalker, Barry Alan 20 July 2011 (has links)
The interaction of magma with continental crust at convergent margins is fundamental to
understanding if and how continents grow. Isotopic and elemental data constrain the
progressive stages of development of the magmatic underpinnings of the long-lived
Aucanquilcha Volcanic Cluster (AVC), situated atop the thick continental crust of the
central Andes in northern Chile. Whole rock data are used in conjunction with mineral
compositions to infer processes that gave rise to eleven million years of intermediate,
dominantly dacite, arc volcanism. A pulse of volcanic activity at the AVC between ~5
and 2 Ma is bracketed by more sluggish rates. We document chemical changes in the
lavas that accompany this eruptive evolution. Trace element data suggest that crystal
fractionation and magma mixing were the dominant mechanisms generating the diversity
observed in the AVC whole rock data. Fractionation was dominant during early and
waning stages of magmatism, and magma mixing was an important process during the
high flux period. Peak thermal maturity of the AVC underpinnings coincided with the
high magma flux and likely promoted open system processes during this time. Mineral
compositions from zircon, amphibole, pyroxene, and Fe-Ti oxides confirm the
importance of material recycling in the production of evolved AVC rocks. Various
geothermometers were employed to calculate the pre-eruptive conditions of AVC magma
using mineral compositions. Pressure estimates from amphibole and two-pyroxene
barometry indicate crystallization depths of 1 ��� 5 kb and 4 ��� 6 kb, respectively.
Temperature estimates from zircon, Fe-Ti oxides, amphiboles, and pyroxenes indicate
temperatures ranging from ~700��C to 1100��C. Zircon temperatures are always the
lowest (700��C - 950��C), and pyroxene temperatures are always the highest (1000��C -
1100��C), with Fe-Ti oxide and amphiboles temperatures falling in between. U-Pb ages
from zircons and thermometry from individual samples evidence the thermal maturation
and consolidation of the underpinnings below the AVC, presumably culminating in a
large, crystal-rich mush zone where magmas were trapped and processed. It is in these
middle to upper crustal zones where magmatic diversity is attenuated and giant, relatively
homogeneous batholiths are formed. Isotopes of AVC lavas are similar to values
observed from other central Andes volcanic centers. Lead isotopes are consistent with
the AVC's location within a Pb isotope transition zone between the Antofalla and
Arequipa basement terranes. Oxygen and Sr isotopic ratios are high and Nd isotopic
ratios low with respect to a depleted mantle. Through time, ������Sr/������Sr values of AVC
lavas progressively increase from lows of ~0.70507 to ~0.70579 (upper values of 0.70526
to 0.70680), and ��Nd values decrease from highs of -1.0 to -4.6 (lows of -1.6 to -7.3).
Similarly, O isotopes (�������O) show a slight increase in base level through time from lows
of 6.5��� to 7.0��� (highs of 6.75��� ��� 7.5���). Dy/Yb and Sm/Yb ratios also increased
systematically from highs of 2.11 to 3.45, and 2.76 to 6.67, respectively. Despite the
temporal isotopic variation, there is little isotopic variation with indices of fractionation,
suggesting this signal is the consequence of deep magmatic processing, here attributed to
an expanding zone of melting, assimilation, storage, and homogenization (MASH) of
mantle-derived magma in the deep crust. Upward expansion brought the MASH zone
into contact with rocks that were increasingly evolved with respect to Sr and Nd isotopes,
explaining the isotopic shifts. Downward expansion of the MASH zone enhanced garnet
stability during basalt fractionation, explaining the increased Dy/Yb and Sm/Yb ratios.
Mass balance calculations involving Sr, Nd, and O isotope modeling are consistent with a
crustal component making up 10 - 30% of AVC lavas, implying that although the history
of central Andean magmatism is replete with large scale crustal recycling, the current
phase is largely a crust formation event. / Graduation date: 2012
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Migmatization and volcanic petrogenesis in the La Grande greenstone belt, QuebecLiu, Mian. January 1985 (has links)
No description available.
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Migmatization and volcanic petrogenesis in the La Grande greenstone belt, QuebecLiu, Mian. January 1985 (has links)
No description available.
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Petrogenesis of the Precambrian Bevos and Musco groups, St. Francois Mountains igneous complex, MissouriKoch, Richard J. January 1978 (has links)
Call number: LD2668 .T4 1978 K623 / Master of Science
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