The middle Paleozoic tectonic history of the Laurentian Arctic margin is contentious. Terranes that have been interpreted to have Baltican and Siberian affinities are thought to have been transferred outboard of the Arctic margin of Laurentian into the Panthalassa Ocean. The timing and mechanism(s) of this translation are poorly understood. Refining models requires better constraints, which are provided by studying the Paleozoic geology of terranes thought to be displaced during this time period: 1) Alexander terrane, 2) Pearya terrane, and 3) the Arctic Alaska terrane. The Alexander terrane is divided into the Craig and Admiralty subterranes. The timing of the juxtaposition of the two subterranes has been the subject of recent debate. Devonian sedimentary rocks in the Craig and Admiralty subterranes have nearly identical detrital zircon signatures suggesting that the two subterranes have been linked since the Devonian. Stratigraphic differences between the subterranes are explained by interpreting the Admiralty subterrane as a deep water basin adjacent to the Craig subterrane. The Pennsylvanian to Permian strata of the Craig and Admiralty subterrane have detrital zircon that, while different from each other, are consistent with derivation from Wrangellia. This supports links between the Craig and Admiralty subterranes, and reinforces the idea that Wrangellia was built on Alexander basement. The Pearya shear zone is a large scale sinistral structure that could be involved in the displacement of outboard terranes; however, the timing of displacement on the Pearya shear zone is not well constrained. Titanite aligned parallel to the fabric of the Pearya shear zone yielded middle Paleozoic ages (ca. 380 Ma). Two stages of monazite growth are described based on age. The oldest monazite formed around 980 Ma, consistent with zircon crystallization ages of the protolith. An Upper Ordovician age (ca. 460) is reported for the second phase of monazite growth. The monazite and titanite ages suggest that displacement accommodated by the Pearya shear zone was episodic. The Upper Ordovician tectonic event is interpreted to represent the approach of the Pearya terrane to the Franklinian margin, while the titanite ages are thought to date continued sinistral displacement in the middle Paleozoic post-accretion that may be related to strike-slip migration of outboard terranes. The tectonic setting of the Arctic Alaska terrane in the Middle to Late Devonian is poorly constrained. Geochronology, geochemistry and field mapping of igneous rocks from the North Slope subterrane provide new clues into the tectonic history. The intrusions yielded 370-362 Ma zircon U-Pb ages that are younger than plutons that intrude the Hammond and Coldfoot subterranes of the Arctic Alaska terrane. Whole rock geochemistry of the northern Yukon intrusions suggest that they formed in an arc setting. Field mapping suggests that all intrusions are found to the northeast of the Porcupine shear zone. Coeval intrusions with similar geochemistry are located on Northern Axel Heiberg and Ellesmere Islands. Correlation between these intrusions is inconsistent with the widely held rift setting for the Arctic Alaska terrane intrusions and suggest that the overlying Endicott group was deposit in a foreland basin rather than a rift flank.

Thesis advisor: J. Christopher Hepburn / The Shrewsbury quadrangle was geologically mapped at a scale of 1:24,000. The quadrangle spans the entire Nashoba terrane, a belt of amphibolite-grade rocks related to an early Paleozoic peri-Gondwanan arc. Petrofabric studies of fault-rocks indicated that the final motion on several major shear zones - Ball Hill fault, Sulfur Hill shear zone, and Assabet River fault - was sinistral strike-slip with an oblique NW over SE thrust component. Monazites from these shear zones were dated using an electron microprobe. Regional metamorphism (M1) took place around 420 Ma. A second regional metamorphism (M2) produced anatectic conditions around 394Ma. A group of dates in the range 360-385 Ma indicates that the Nashoba terrane was also affected by Neoacadian metamorphism and/or deformation. Major shear zones were active throughout the Devonian and may have persisted into the Carboniferous. / Thesis (MS) — Boston College, 2007. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

A variety of world-class mineral deposits occur in Mesozoic and Tertiary rocks of the Guerrero terrane. New Pb isotope analyses of various crustal units and ores from distinct subterranes of the Guerrero terrane are presented to trace metal sources in these deposits and infer source reservoirs. New Sr and Nd isotope results are provided to gain insight into the provenance of the crustal rocks from the Guerrero terrane. Triassic schist samples from the Arteaga Complex and Triassic-Jurassic phyllite and slate samples from the Tejupilco metamorphic suite contain radiogenic Pb (206Pb/204Pb = 18.701-19.256) relative to bulk earth models. Cretaceous sedimentary rocks of the Zihuatanejo Sequence are more radiogenic (206Pb/204Pb = 18.763-19.437) than samples from the Huetamo Sequence (206Pb/204Pb = 18.630-18.998). Tertiary intrusive rocks from La Verde, Inguaran, La Esmeralda, and El Malacate plot to the right of the average Pb crust evolution curve of Stacey and Kramers (206Pb/204Pb = 18.705-19.033). Ores from the La Verde and La Esmeralda porphyry copper deposits yield isotopic ratios (206Pb/204Pb = 18.678-18.723) that are generally less radiogenic than the host igneous rocks, but plot within the field defined by the sedimentary rocks from the Huetamo Sequence. Tertiary intrusive rocks from the Zimapan and La Negra districts in the Sierra Madre terrane plot above and to the right of the Stacey-Kramers reference line (206Pb/204Pb = 18.804-18.972). Lead isotope ratios of ore minerals from the Zimapan and La Negra skarn mines (206Pb/204Pb = 18.775-18.975) resemble those of the associated igneous rocks, implying a magmatic Pb input in the skarn deposits. New Sr and Nd isotope data on metamorphic rocks (87Sr/86Sr = 0.707757-0.726494 and 143Nd/144Nd = 0.512109-0.512653) suggest that the basement of the Guerrero terrane originated from sources that had been derived from an old cratonic area. The narrow ranges and generally low 87Sr/86Sr ratios (0.704860-0.705755) and 143Nd/144Nd values (0.512765-0.512772) above that of bulk earth for igneous rocks from Inguaran, El Malacate, and La Esmeralda suggest a relatively low degree of crustal contamination. However, the isotopic values for the La Verde site (87Sr/86Sr = 0.708784 and 143Nd/144Nd = 0.512640) may indicate the involvement of a more evolved crustal component.

Thesis advisor: J C. Hepburn / Thesis advisor: Yvette D. Kuiper / Metasedimentary rocks of the Merrimack terrane (MT) originated as a thick cover sequence on Ganderia consisting of sandstones, calcareous sandstones, pelitic rocks and turbidites. In order to investigate the age, provenance and stratigraphic order of these rocks and correlations with adjoining terranes, detrital zircon suites from 7 formations across the MT along a NNE-trending transect from east-central Massachusetts to SE New Hampshire were analyzed by U-Pb LA-ICP-MS methods on 90-140 grains per sample. The youngest detrital zircons in the western units, the Worcester, Oakdale and Paxton Formations, are ca. 438 Ma while those in the Kittery, Eliot and Berwick Formations in the northeast are ca. 426 Ma. The Tower Hill Formation previously interpreted to form the easternmost unit of the MT in MA, has a distinctly different zircon distribution with its youngest zircon population in the Cambrian. All samples except for the Tower Hill Formation have detrital zircon age distributions with significant peaks in the mid-to late Ordovician, similar abundances of early Paleozoic and late Neoproterozoic zircons, significant input from ~1.0 to ~1.8 Ga sources and limited Archean grains. The similarities in zircon provenance suggest that all units across the terrane, except for the Tower Hill Formation, belong to a single sequence of rocks, with similar sources and with the units in the NE possibly being somewhat younger than those in east-central Massachusetts. The continuous zircon age distributions observed throughout the Mesoproterozoic and late Paleoproterozoic are consistent with an Amazonian source. All samples, except the Tower Hill Formation, show sedimentary input from both Ganderian and Laurentian sources and suggest that Laurentian input increases as the maximum depositional age decreases. / Thesis (MS) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Geology and Geophysics.

Thesis advisor: J. Christopher Hepburn / The Nashoba terrane is a highly metamorphosed and sheared Paleozoic tectonic block in eastern Massachusetts. The metamorphic rocks that compose the terrane are intruded by a series of diorites, tonalites, and granites. The Andover Granite is a complex multiphase granitic suite found in the northern part of the Nashoba terrane and is composed of both foliated and unfoliated granites as well as a granodiorite phase. The Sgr Group of granites is a series of unfoliated granites exposed along the Nashoba-Avalon terrane boundary. New crystallization ages for the foliated Andover Granite and the Sudbury Granite, southernmost body of the Sgr Group of granites, are presented. CA-TIMS U-Pb geochronology on zircons collected from these granites yielded 419.43 ± 0.52 Ma and 419.65 ± 0.51 Ma crystallization ages for the foliated Andover Granite and a 420.49 ± 0.52 Ma crystallization age for the Sudbury Granite. Geochemical and petrographic analysis of these granites indicate that the foliated Andover Granite is a high-K calc-alkaline, peralmuminous, S-type, biotite + muscovite granite and the Sudbury granite is high-K calc-alkaline, metaluminous to slightly peraluminous, I-type, biotite granite. These two granites are interpreted to have formed from the anatexis of either Nashoba terrane metasedimentary rocks and/or its underlying basement just prior to the Acadian orogeny. It is proposed that when Silurian diorite/tonalite magmas intruded into the Nashoba terrane, the influx of magmatic heat was sufficient to trigger crustal melting and promote granite genesis. This petrogenetic scenario fits well with regional tectonic models showing the Silurio-Devonian convergence of Avalonia towards Ganderia (which formed the eastern side of composite Laurentia at the time) in the northern Appalachians. Prior to the collision of Avalonia to composite Laurentia, mafic and intermediate composition arc magmas intruded the eastern Ganderian margin. The large amount of heat that accompanied these intrusions is believed to have contributed to Acadian metamorphism and influenced the formation of granitic plutons along the margin. It is therefore proposed that the plutonic record of the Nashoba terrane shows that by the Late Silurian - Early Devonian, Avalonia was still outboard of Laurentia in the vicinity of southern New England. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Thesis advisor: John E. Ebel / Passive teleseismic data were collected with a 17-station broadband seismic array deployed from Vermont to Massachusetts. The purpose of the array was to detect changes in crustal seismic velocity structure related to the regional tectonostratigraphic terranes using receiver functions. Ps conversions from the Moho and mid-crust were observed and a cross-section of the crustal structure beneath the seismic array was produced. The crustal cross-section reveals a synclinal structure related to the Taconic orogeny, a remnant Iapetan oceanic slab, a plausible surface-location of the Red Indian Line, and several terrane boundaries that can be projected from their proposed surface locations into the deeper crust based on crustal-horizon offsets observed in the receiver function data. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Magister Scientiae - MSc (Earth Science) / The Kliprand dome is a poorly investigated structure located in the central part of the high grade Garies Terrane of the western Namaqua Sector (NS) of the Namaqua-Natal Metamorphic Province (NNMP). This structure is host to a diverse variety of supracrustal rocks comprising predominantly metapelites and quartzites of the Kamiesberg Group, the streaky augen gneiss, an enigmatic pink gneiss (official name the Lekkerdrink Gneiss) of which the origin is obscure, the metasomatic charnockites along with the pre- to syn-tectonic two-pyroxene granulites (or gabbro-norite) of the Oorkraal Suite. Large bodies of garnet-quartz-feldspar granite, believed to be the products of dehydration melting during peak metamorphism, are referred to as the Ibequas Granite. The transformation of these sediments and volcanic rocks into gneisses and migmatitites was accomplished by intense regional metamorphism during the 1.2-1.0 Ga Namaqua Orogeny. In order to unravel the tectonic evolution of the Kliprand dome, a structural, lithogeochemical, isotopic and geochronological study was undertaken.

>Magister Scientiae - MSc / The study area Koekoeb B is a farm that falls under the Kakamas Terrane which in turn falls under the Gordonia Subprovince in the Namaqua-Natal Metamorphic Province, South Africa. This area was chosen due to lack in literature about its lithology. Koekoeb B is comprised of metasedimentary rocks of the Biesje Poort Subgroup and granitoids of the Keimoes Suite. The Kakamas Terrane was deposited in an intracratonic basin between the Kaapvaal Craton and the Namaqua continental mass. The sediments were buried with time and experienced metamorphism due to burial pressures and temperatures. The area experienced folding as a result of the collision of the newly formed Kakamas Terrane and the Bushmanland segment with the Kaapvaal Craton during a Wilson Cycle. During subduction and collision the metasedimentary rocks were intruded by what is known as the Keimoes Suite. The most abundant intrusive rock in Koekoeb B is the Friersdale Charnockite. It is considered the youngest with Rb-Sr ages around 1080-1090 Ma. The Gordonia Subprovince experienced such intense deformation that continuous folds formed and there is even evidence of parasitic folds. Northwest striking shear zones developed as a result of the continued compression of the Namaqua mass with the adjacent north easterly Kaapvaal Craton. The folds and shear zones formed under four major deformational events Two months were spent acquiring orientation data (direction of dip and dip) in the field. A Clar compass was used to measure the dip direction and dip readings of bedding, cleavage, joints and lineations. The orientation data was imported into Move® software to create a geological map. Samples collected from the field were used to produce thin sections for petrography studies using the petrographic microscope. Conclusions were drawn from the analysis of the data. Koekoeb B experienced regional metamorphism and folding when the Kakamas Terrane collided with the Kaapvaal Craton. The area was subdivided into four subareas based on the strike and dip data generated on the geological map. The synoptic β-axis diagram determined that the subareas are of the same generation but the fold axes orientations vary slightly. Because the study area did not include the shear zones no conclusive reason can be given but it can be assumed that the variation is due to movement along the shear zone or as a result of the intrusion of the Keimoes Suite. The area later experienced brittle deformation which is evident from the large number of joints found; the joints cut across the folds and show a different stress regime from the folds. Conjugate joints were observed on the field and plotted on stereonets. The results showed a vertical sigma two which confirmed that Koekoeb had been affected not only by compression tectonics but by the strike-slip movement on the shear zone.

No description available.

This study utilised U-Pb geochronology, and 40Ar/39Ar and (U-Th)/He thermochro-nology to delineate arc magmatism, metamorphism, and exhumation of the pericratonic Yukon-Tanana terrane in the McQuesten map area of west-central Yukon, Canada. SHRIMP U-Pb ages delineate Mid to Late Paleozoic arc magmatism and fit key units into the regional lithotectonic framework of the terrane. The juxtaposition of unmetamorphosed and predomi-nantly undeformed Devono-Mississippian rocks in the northwest of the study area with polydeformed and up to amphibolite facies metamorphosed rocks in the southwest suggests a crustal-scale discontinuity, the Willow Lake fault, bounds the two domains. The asymmetric distribution of 40Ar/39Ar ages across the fault suggest it is extensional, and was active in the Early Jurassic. Zircon (U-Th)/He ages delineate erosion of rocks in the northwest through the upper crust during the Late Triassic and Late Jurassic to Early Cretaceous followed by Mid-dle Cretaceous erosion of the southwestern domain and possibly fault reactivation.