Remagnetization of the Scott Peak Formation Associated with Tertiary Igneous Activity: a Comparative Study of Two Deformed Carbonate

Lehigh University Lehigh Preserve

Theses and Dissertations

1994 Remagnetization of the Scott eP ak formation associated with tertiary igneous activity : a comparative study of two deformed carbonate structures in the Lost River Range, Idaho Elizabeth R. Sherwood Lehigh University

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Recommended Citation Sherwood, Elizabeth R., "Remagnetization of the Scott eP ak formation associated with tertiary igneous activity : a comparative study of two deformed carbonate structures in the Lost River Range, Idaho" (1994). Theses and Dissertations. Paper 273.

This Thesis is brought to you for free and open access by Lehigh Preserve. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Lehigh Preserve. For more information, please contact [email protected]. AUTHOR: Sherwood, Elizabeth R.

TITLE: Remagnetization of the Scott Peak Formation Associated with Tertiary Igneous Activity: A Comparative Study of Two Deformed Carbonate...

DATE: May 29,1994 Remagnetization of the Scott Peak Formation associated with Tertiary igneous activity: A comparative study of two deformed carbonate structures in the Lost River Range, Idaho

Elizabeth R. Sherwood

A Thesis Presented to the Graduate and Research Committee of Lehigh University in Candidacy for the Degree of Master of Science

m Geological Sciences

Lehigh University May 17, 1994

--'1

ACKNOWLEDGEMENTS

I would like to express my gratitude to Kenneth P. Kodama, my thesis advisor, for teaching me the essentials of paleomagnetism and for his guidance throughout this project.

I would also like to thank committee members Gray Bebout, PB Meyers, and Dave

Anastasio for contributions to my field work and thesis; Art Goldstein for providing good ." advice and teaching me good field skills; and Theresa Messina for sharing the field work and providing encouragement throughout this project

Special thanks to Michael Krol for endlessly discussing fluid flow models with me, for his support, and for teaching me to go over one hurdle at a time. And, most of all,

Paul, Michael, Matthew and Andrew for always believing in me; and to my parents for setting a good example and for being the only people who realize my full capabilities.

Paleomagnetic measurements were supported by National Science Foundation grant

#EAR-9105879. Field work was supported by National Geographic Society grant

#473892 and National Science Foundation grant #EAR-9017334, both to D. 1. Anastasio and D. M. Fisher.

ill TABLE OF CONTENTS

List of Figures v

Abstract 1

Introduction 4

Geologic History 7 Doublespring Duplex 11 Willow Creek Anticline 15

Methods 19

Results 22

Discussion 44 Remanence Carriers 44 Age ofMagnetization and Tectonic Implications 52

Conclusions 60

References 61

Appendices 67

Vita 73

IV LIST OF FIGURES

Figure Title Page 1 Regional map of central Idaho 8 2 Geologic map of northern Lost River Range 9 3 Stratigraphic column 10 4 Sketch of Doublespring duplex 12 5 Trend of duplex fold axis 13 6 Sketch of Willow Creek anticline 17 7 Trend of anticline fold axis 18 8 Zijderveld diagrams-duplex 23 9 Site mean directions-duplex 24 10 Zijderveld diagrams-anticline 25 11 ,$ite mean directions-anticline 26 12 'Fold test-duplex 27 13 Fold test-anticline 28 14 Coercivity spectrum-duplex 30 15 Coercivity spectrum-anticline 31 16 Coercivity spectrum-duplex & anticline 32 17 IRM Acquisition-duplex 33 18 IRM Acquisition-anticline 34 19 IRM Acquisition-duplex & anticline 35 20 IRM-Thermal-duplex & anticline: MX 36 21 IRM-Thermal-duplex & anticline: MX 37 22 IRM-Thermal-duplex & anticline: MY 38 23 AMS-duplex: top bed 40 24 AMS-duplex: shear zone 41 25 AMS-duplex: bottom bed 42 26 AMS-anticline 43 27 SEM photographs: iron sulfides 47 28 EDS graph: iron sulfides 48 29 SEM photographs: magnetites 49 30 EDS graph: magnetites 50 31 EDS graph: copper 51 32 Angular Dispersion of VGPs 53 33 Time scale with magnetic polarity 55 34 Apparent Polar Wander Path 57

v Abstract

The Lost River Range in south-central Idaho is the westernmost of a series of NW SE trending ranges north of the Snake River Plain, within the Basin and Range province of the western United States. During the Late Cretaceous Sevier orogeny, folding and thrusting defonned the Upper Mississippian and Lower Pennsylvanian carbonate rocks along the eastern edge of the Great Basin and extended westward toward the Laramide defonnation front The western boundary of the Lost River Range is delineated by the seismically active Lost River Fault (Crone, 1988). Miocene-Holocene extension (Ross, 1947) created the structural basins to the east and west ofthe Lost River Range. The purpose of this project is to study the remagnetization ofthe two large-scale Upper Mississippian defonned carbonate structures, the Doublespring duplex and Willow Creek anticline, located within the Lost River-Arco Hills thrust sheet, in an attempt to isolate the effects ofthe emplacement of the Challis Volcanics unit on paleomagnetic remanence. Both structures carry a postfolding, Tertiary thermoviscous and/or chemical remagnetization. The Doublespring duplex is composed of three folds that make up one horse ofmassively bedded, cherty-silty limestone, of the Upper Mississippian Scott Peak Formation. This project concentrates on the middle ofthe three anticlinal folds that comprise the duplex. The duplex trends NW-SE, parallel to the Lost River Range, plunges 11° toward N23°W, and dips homoclinally 25° toward N700E. Therefore, the transport direction is inferred to be N700E, a projection of the dip direction. The Willow Creek anticline is located approximately 12 km south of the Doublespring duplex. The Willow Creek anticline is characteristic ofregional scale folds of the Lost River Range. This anticline has an angular hinge with a close chevron core which widens upsection to a conjugate box geometry. ~ The fold axis of this upright, parallel, asymmetrical, decollement fold plunges 07" towards N37"W (Messina, 1993). The Willow Creek anticline has a calculated fold amplitude of 1.5 km and a wavelength of 1.3 km (Messina, 1993). Although the anticline contains the entire upper Paleozoic stratigraphy of

1 the Lost River Range, the Scott Peak limestone unit was sampled around one bed of the anticline for easy comparison to the duplex results. The Doublespring duplex records a reversed Tertiary direction (245°, -57"). A similar, but steeper, reversed polarity direction (229°, _82°) was isolated from the Willow Creek anticline. Both magnetizations failed the fold test at the 99% confidence level (McElhinny, 1964). Ifthe plunge is removed from the folds before unfolding, and if it is assumed that these folds were remagnetized during the extensive, regional Tertiary magmatic event, and their magnetizations are compared to Diehl, et al.'s (1983) Eocene paleopole for western North America, the anticline magnetization is statistically indistinguishable with an Eocene direction. However, two possibilities are suggested for the duplex: a clockwise vertical axis rotation of 60° or folding followed by westward tilting associated with the tilting ofthe volcanics. The disparity between the rotation of the duplex and the non-rotation ofthe anticline can be explained by block rotations resulting from NE striking normal faulting between the folds and throughout the range (Janecke, 1992). Janecke (1992) calls for Cenozoic extension along normal faults in three distinct episodes and in three different directions (Janecke, 1992). Episode 1 occurred at about 49-48 Ma with NW-SE extension (Janecke, 1992). Episode 2 occurred between 48 and 46 Ma, when the extension direction flipped to WSW-ENE to SW-NE, and is considered to be the most significant extensional event in east central Idaho, coincident with Challis volcanism (Janecke, 1992). The region extended NE-SW along Miocene and younger SW dipping Basin and Range faults at 46 Ma during episode 3 (Janecke, 1992). Rock magnetic experiments (coercivity spectrum analysis and IRM acquisition) have identified a low coercivity signal (magnetite) and a high coercivity, secondary signal (with overlapping coercivity spectra of a fme-grained sulfide (probably pyrrhotite), and goethite due to weathering). Scanning electron microscopy identified iron sulfides within magnetite grains. The Tertiary direction is carried by the high coercivity fraction in the duplex, which is suspected to be an iron sulfide brought in by the Tertiary fluids and

2 precipitated out as pyrrhotite. After detennining that the postfolding magnetizations had a Tertiary pole, it was necessary to identify possible causes of remagnetization of the structures. Initially, the data suggested that the region underwent a remagnetization event due to the migration of pore fluids through the fold and thrust belt system. The most plausible models for explaining the postfolding, Tertiary pole appeared to be either a thennoviscous remagnetization as a result ofTertiary magmatic activity; a chemical overprint due to the migration of mineral rich hydrothennal fluids; or some combination of these two processes. The driving force of hydrothennal fluid flow is most likely the extensive magma chamber that underlies much of south-eentral Idaho.

3 Introduction

Initially, the purpose ofthis project was to study the effects of deformation on magnetic remanence. Previously, similar work had been done on hematite in clastic rocks (e.g., red beds) in which the remanence was rotated by bedding parallel shear (Stamatakos

and Kodama, 1991a; 1991b). However, to date, only Kodama (1988) has attempted to document the effects of deformation on remanence in non-hematite bearing rocks, such as carbonates. In this study the carbonates were remagnetized, so synfolding deformation had minimal effect on the remanence. Therefore, when the study was initially conceived, the

main objective was to determine how remanence varies with shear strain in carbonates in conjunction with previously conducted kinematic analyses of two different structures (a duplex and an anticline) from upper Paleozoic rocks of the Lost River Range, Idaho. A

second objective was to use the results of this rock magnetic study to evaluate previous paleomagnetic studies of thrust sheet rotation in the western U.S. (Janecke, et. al., 1991; McWhinnie, et al., 1990; Schwartz and Van der Voo, 1984; Grubbs and Van der Voo, 1976) in order to determine whether the rotated magnetic declinations were due to rigid

body rotations or grain-scale strain. To accomplish the objectives of this study required the measurement of paleomagnetic remanence (primary and secondary), which could then be correlated with incremental strain history of the duplex and anticline, in addition to characterization of the magnetic remanence carrier and measurement of magnetic fabric with anisotropy of anhysteretic remanence.

One valuable aspect of this study would have been the comparison of deformation by two different folding kinematics, and their effect on remanence. Although it was previously believed that the Doublespring duplex underwent flexural flow (Hedlund, et al.,

1994) and the large-scale Willow Creek Valley anticline was subjected to flexural slip

4 (Messina, 1993) despite the close proximity (-12 Ian) of the two structures, with subsequent analysis ithas become apparent that the deformation of both folds was a combination of the two fold kinematics, and not end-member cases (Messina, 1993). Therefore, from anisotropy of anhysteretic remanence (AAR; McCabe et al., 1985) and incremental strain studies, ifthe orientation ofmagnetic fabric is subparallel with the non coaxial strain history of the structures, fInite strain could be compared with any deflection of the paleomagnetic vector, to study the effects of grain-scale strain on remanence. The direction that this project took was to be determined by the results of a paleomagnetic fold test (Graham, 1949). Ifthe remanence passed the fold test, and therefore was a pre-folding magnetization, then it would be necessary to determine whether grain scale strain during folding rotated the magnetic grains. However, ifthe magnetization was post-folding, it is a remagnetization due to either a thermal resetting of existing grains or the growth of new grains. Asynfolding magnetization pattern could be due to a prefolding remanence that was rotated by strain (Kodama, 1988). Thus, ifthe magnetization was found to be syndeformational, then itmust be determined ifthe shear zone underwent a separate magnetization event than that of the top and bottom beds of the duplex. After identifying a postfolding magnetization, the effect of shear strain on remanence was no longer relevant to this study. Instead, the focus shifted to an investigation of a possible remagnetization (CRM) event by pore fluids migrating through the fold and thrust belt system (Gillett and Taylor, 1985; McCabe and Elmore, 1989) which would be responsible for the postfolding magnetization. It is suspected that the fluids are responsible for mass transfer in this region (Hedlund,et al., 1993). Hydrothermal fluids migrating through the fold and thrust belt system (Criss, et al., 1991; Constantopoulos, 1988; Criss, et al., 1985; Criss and Champion, 1984; Criss, et al., 1984) could cause a chemical remagnetization of the carbonate rocks. Given the fIne grained nature of the rocks which comprise the Doublespring duplex, it is unlikely that

5 fluids would be able to travel through the matrix of the beds, and more likely migrated through a shear zone which follows the middle bed of one of the folds in the duplex. It appears that sheared material has been removed in the hinge of the fold, which may be a result of the structure being "pinned" at the hinge during deformation. Field observations of the shear zone revealed calcite veins in chert, extending oblique to bedding. One way to test whether fluids flushed through the shear zone would be to distinguish differences in remanence vector directions between the shear zone and its surrounding beds due to different times of remagnetization. Variations may also be due to different amounts of strain affecting the structure. Paleomagnetic remanence can be used to investigate the presence of fluid flow by identifying chemical remagnetization (CRM); (McCabe and Elmore, 1989). CRM affects primary remanence by chemically altering or reprecipitating magnetic minerals with a new remanence direction.

6 Geologic llistory

The Lost River Range in south-central Idaho is the westernmost of a series of NW SE trending ranges north of the Snake River Plain, within the Basin and Range province of the western United States (Figure 1; Fisher and Anastasio, 1994; Janecke, 1992; Link, et. al., 1992; Rember and Bennett, 1979; Maple, et. al., 1965; Ross, 1947). To the west of the range extends the Lost River Fault, which is seismically active today (Crone, 1988; Crone and Machette, 1984). The eastern boundary is delineated by the Lemhi Range, however, the Lost River Range is immediately surrounded by structural basins formed by the Miocene-Holocene extensional event (Ross, 1947). During the Late Cretaceous Sevier orogeny, folding and thrusting deformed the Upper Mississippian and Lower Pennsylvanian carbonate rocks along the eastern edge of the Great Basin and extended westward toward the Laramide deformation front (Armstrong and Ward, 1991). The Tertiary extensional event subsequently deformed this region (Bennett, 1986) with large block rotations resulting from NE-striking normal faulting (Janecke, 1992). The two structures analyzed in this study are informally named the Doublespring duplex and Willow Creek Valley anticline (Hedlund, et al., 1994; Messina, 1993), located within the Lost River-Arco Hills thrust sheet of the northern Lost River Range (Figure 2). The Lost River Range stratigraphy is composed ofUpper Paleozoic rocks, from the Mississippian McGowan Creek Formation up through the Pennsylvanian Snaky Canyon Formation (Figure 3). The region was entirely overlain by the Challis Volcanics Group, which was emplaced during two Tertiary magmatic events dated at 48 and 46 Ma by 40Art39Ar thermochronology (Janecke and Snee, 1993; Janecke, 1992). Hydrothermal alteration has been documented within the Lost River Range (Criss, et aI., 1991; Criss, et al., 1985; Criss and Champion, 1984; Criss, et al., 1984). Copper mineralization in particular has been attributed to Tertiary meteoric hydrothermal systems affecting the Mackay and Custer county area (Criss, et al., 1991). Mackay is the town closest to the two folds, both ofwhich are located within Custer county.

7 44°

113°

l1li Volcanic rocks 8 Plutonic bodies ~~~~~ Twin Peaks caldera Tuff

/ Normal Faults

Figure 1. Regional map of central Idaho showing the areal distribution of the Challis Volcanics Group. Shaded inset box indicates the field area of this study. The Doublespring duplex is located at 44 0 20', 113 0 50', and the Willow Creek anticline is located at 44 0 10', 113 0 53'. The extensive nonnal faults within the Lost River Range are in the proximity of the anticline (map modified from Janecke and Snee, 1993). 8 113° 55' 113° 50'

44° 27'

D Quaternary

, IITertiary volcanics

Upper Paleozoic

r:-:::::::::-:::I...... Antler Flysch ...... -_ .

~ Lower Paleozoic

o 5km eM 1M ..

44° 09' 1-_1IIIIiII.li~~~"-'-'~~ 113° 55' 113° 50'

Figure 2. Geologic map of northern Lost River Range, south-central Idaho. Inset boxes indicate the location of the Doublespring duplex on the eastern margin of Christian Gulch and the Willow Creek anticline within the Upper Willow Creek Valley (modified from Messina, 1993). 9 Formation and Lithology

Snaky Canyon thick bedded sandy limestone with lenses of chert

Bluebird Mountain thin bedded sandy limestone. Area Bilk thick bedded limestone Surrett Canyon thick bedded cherty limestone

South Creek 8 thin bedded cherty limestone o :"'_-.-_._---.": o ;;.-:.-:.-:.---.~ -.:::t ;-_"'::'".---.:".:: Scott Peak r'-;-_••--.----.~ :"'.-:.-.-:.-_-:.,,:..-:.._---.:: r'-••••---.:".~ s:: :"'_....-.:"_..:: medium to thick bedded .0.ro 1;"".:"_._-_-:.-_":.~--.._-:.---~ cherty-silty limestone 0. r'':-_'''::'"':-_-~ .-II) ~--.------. II) r".-.-.-.-.-.;; .-en ;::".-:.-----.":. en ~_ ------.~ .- :"'-.._-----.":. ~ ------... Middle Canyon thin bedded cherty-silty fine grained limestone ...... - . McGowan Creek .....-_-._----_- .... calcareous siltstone interbedded with silty micritic limestone

Lost River-Areo Hills Thrust

Figure 3. Stratigraphic column of Lost River Range, Idaho. Paleozoic carbonate stratigraphy from McGowan Creek through Snaky Canyon Fonnations. The duplex is composed of only the Scott Peak Formation, while the anticline is composed of the entire upper Paleozoic stratigraphy (modified from Messina, 1993).

10 The tectonic framework of the area is controlled predominantly by the Late Cretaceous Sevier Orogeny and· the Cenozoic extensional event. The Sevier Orogeny is responsible for the progressive eastward development of the NW trending ranges of . Montana and Idaho, including the Lost River Range. Following the deformation (and creation of the Doublespring duplex and Willow Creek anticline), the region was entirely overlain by the Challis Volcanics Group between 48 and 46 Ma. The Challis volcanics erupted through flssure vents and calderas throughout the region (Norman and Mertzman, 1991). Although the volcanics have been eroded, they are still present in sporadic patches throughout the Lost River Range, as well as atop several mountain peaks (Mapel, et al., 1965). Simultaneous to the magmatic episodes, the Cenozoic extension event began and continued into the Oligocene, creating extensive normal faulting in the area (Janecke, et al., 1991). This region continues to be tectonically active today, as evidenced by the 1983 Borah Peak earthquake (Crone and Machette, 1984; Crone, 1988).

Doublespring Duplex

The Sevier-aged Doublespring duplex is a fault-related fold complex composed of a horse of massively bedded, flne-grained, cherty-silty limestones, of the Upper Mississippian Scott Peak Formation (Figure 4). The Doublespring duplex is located at the northern end of Doublespring Pass (Janecke, 1992b), and on the northeastern edge of Christian Gulch (Figure 2). The duplex is composed of the Scott Peak Formation, which has the most widespread exposure (an average of 400 meters in thickness) of all the Upper Paleozoic units in the Lost River Range. The fold axis of the duplex trends NW-SE , parallel to the Lost River Range, plunges 11 ° toward N23°W (Figure 5), and dips homoclinally 25° toward N700E. The fold axis was determined from poles to bedding that defme a great circle in lower hemisphere, equal area projection (Figure 5). Poles to bedding of the data in Figure 5 determined that the fold axis trends SE (15T, 11°), however this was calculated with only 7 measurements and may reflect variable dip within

11 'fif---~.

?"",'-...

Doriblespring Dnplex

N70E

'i'

Figure 4. Schematic diagram of Doublespring duplex. The middle fold of the duplex was sampled for this study; Closed symbols indicate samples collected from the top bed, open circles indicate samples from the shear zone, and grey symbols indicate samples from the bottom bed. Hand sample means froin the six samples in boxes were used to determine the postfolding direction. The shear zone is a highly fractured, clay-rich layer located between the top and bottom beds of the middle fold. Cleavage is orthogonal to bedding planes around the fold (modified from Hedlund, et al., 1994). Doublespring Duplex Top Bed Poles to Bedding

•

Equal Area • Poles to bedding N=7 • Fold Axis

Figure 5. Poles to bedding for 7 samples from the Doublespring duplex were used to detennine the trend of the fold axis (1ST, 11°). Fold axis calculations from an earlier study (Hedlund, 1992) detennined the fold axis at (33T, 11°), which is consistent with the regional trend of the Lost River Range folds. The fold axis hereafter referred to in this study was calculated with significantly more data, and thus, the discrepancy may be due to variable dip within the beds of the structure. The dip of the overall structure may not be adequately determined by measurement of a single bed.

13 the individual bed. The fold axis hereafter referred to was calculated during an earlier study of this structure that consisted ofsignificantly more data that detennined the fold axis trends NW (Hedlund, et al., 1994). The transport direction is therefore inferred to be N70oE, the horizontal projection of the dip direction, and is supported by regional fold orientation analyses (Hedlund, et al., 1994). The direction of shearing is north, toward the hinge of the duplex. This project concentrates on the middle of the three anticlinal folds that comprise the duplex (Figure 4), which resemble fault-bend fold geometries. The middle fold has a wavelength of 50 meters. The duplex is a thin-skinned feature, and is not characteristic of the large scale folds of this region. Although the fold axis of the duplex is analogous to the regional fold axis, the duplex is smaller scale than characteristic folds of the Lost River Range, which have wavelengths greater than 1 kIn. In addition, characteristic folds are a series ofconnected anticlines and synclines with similar fold wavelengths and amplitudes. In contrast, the duplex is a composite of three anticlinal folds disconnected and transported on top of one another. Between the massive beds and along the limbs of the fold are shear zones, composed ofa similar lithology to the massive beds of the structure, but enriched in AI, Ti,

K, Si, Mg, Fe, and P (Hedlund, et al., 1993). Initially, it was anticipated that there might be rock magnetic or paleomagnetic differences between either the top or bottom beds, and the shear zone, so each bed was sampled. Antitaxial fibrous overgrowths and veins were used for incremental strain analysis in order to constrain fold kinematics of the duplex

(Hedlund, et al., 1994). Two folding mechanisms affected the duplex: flexural flow toward pins in the axes ofthe shear zones, and rotation through a fixed extension direction for the massive layers (Hedlund, et al., 1994).

14 Willow Creek Anticline

The large scale (1.3 kIn wavelength and 1.5 kIn fold amplitude) Willow Creek anticline is located approximately 12 kIn south of the Doublespring duplex (Janecke and Wilson, 1992), at the southern end of Doublespring Pass (Figure 2). The Willow Creek anticline is characteristic of the folds of the Lost River Range. Unlike the duplex, this fold is composed of all formations ofthe upper Paleozoic stratigraphy of the Lost River Range (from McGowan Creek up to the Snaky Canyon Formation); however, to allow comparison to the Doublespring duplex results, samples were collected from one bed of the Scott Peak Formation around the anticline (Figure 6). During the Sevier orogeny, the angular hinged anticline was also fonned within the fold and thrust belt developmental event The anticline's geometry is similar to that of other regional folds: upright, parallel, asymmetrical, with a tight chevron fold at the core which broadens outward creating a conjugate box shape (Messina, 1993). A fault line (detachment surface) is evident along the base of the anticline with little lateral displacement, indicating that this is a decollement fold (Messina, 1993). Thus, depth to detachment calculations were made which located the detachment close to the base of the McGowan Creek Fonnation (Messina, 1993). This structure also has a NW trending fold axis (N3TW) with a shallow plunge of OT, and a fold amplitude of 1.5 kIn. The fold axis was detennined from poles to bedding that defme a great circle in lower hemisphere, equal area projection (Figure 7). Poles to bedding of the data in Figure 7 determined that the fold axis trends SE (143°, OT), however this was calculated with only 10 measurements and may reflect variable dip within the individual bed. The fold axis hereafter referred to was calculated during an earlier study of this structure that consisted of significantly more data that detennined the fold axis trends NW .~ (Messina, 1993). Thin, strongly cleaved deformation zones create distinct intervals among the massive beds of the anticline. Kinematic analyses were carried out on mineral fibers in

15 veins and pressure shadows to determine the magnitude and orientation of principal extension (Messina, 1993). These analyses indicate that flexural slip deformation with rigid rotation occurred during Sevier-age folding.

16 Willow Creek Anticline

.... -..l

SW NE 100 meters II (modified from Messina, 1993)

Figure 6. Schematic diagram ofWillow Creek anticline. The highlighted limestone bed of the anticline was sampled because it is composed of Scott J;>eak Formation, for comparison with duplex analyses. Hand sample means from the five circled hand samples were used to detennine the postfolding direction. Cleavage is orthogonal to bedding planes around the fold. ) Willow Creek Anticline Scott Peak Formation Poles to Bedding

Equal Area • Poles to bedding N=lO II Fold Axis

Figure 7. Poles to bedding for the Willow Creek anticline were used to determine the trend of the fold axis (143°,07°). Fold axis calculations from an earlier study (Messina, 1993) determined the fold axis at (337°, 11°), which is consistent with the regional trend of the Lost River Range folds. The fold axis hereafter referred to in this study was calculated with significantly more data, and thus, the discrepancy may be due to variable dip within the beds ofthe structure. The dip of the overall structure may not be adequately determined by the measurement of a single bed.

18 Methods

Thirty-five oriented hand samples were collected from the top and bottom beds of the horse in the duplex, as well as from the shear zone in between those beds (Figure 4).

In addition, ten oriented hand samples were collected from one bed around the anticline

(Figure 6). Between one and four 25 mm diameter cores were drilled from each of the oriented hand samples. The natural remanent magnetization (NRM) of each core was measured in a two-axis C1F, Inc. superconducting magnetometer.

One half ofthe cores from each hand sample were subjected to alternating field demagnetization and the remaining half to thermal demagnetization. Stepwise alternating field demagnetization (AP) was performed on each core in alternating magnetic fields up to

100 mT in a Schonstedt GSD-5 AC Geophysical Tumbling-Specimen Demagnetizer.

Specimens were AF demagnetized at 2.5,5, 10, 15 and 20 mT, and then at progressive 10 mT steps to 100 mT. At least one core per hand sample was thermally demagnetized.

Thermal demagnetization was done incrementally in 50·C steps up to 575 ·C, and because

AF demagnetization data was available from other cores within each hand sample, the results could be compared for the two methods.

Orthogonal vector endpoint demagnetization diagrams (Zijderveld, 1967), were used to illustrate successful isolation and removal of a magnetization component (evident by a linear trend into the origin). The characteristic magnetization (ChRM) of each sample was then isolated by principal component analysis ofdemagnetization results (Kirschvink,

1980). Fisher (1953) statistics were used to average specimen directions for hand sample means and to average hand sample means for site means. The three beds of the middle fold of the duplex and the bed sampled around the anticline constitute the two sites of this study.

The fold test (Graham, 1949) was applied incrementally at each site using mean hand sample directions. The statistical significance of the fold test was checked using the

19 techniques ofMcElhinny (1964). Although the McElhinny statistical signific~ce test has been proven incorrect (because of its assumption that the precision of the magnetization before and after unfolding is Fisherian), it is a more stringent test than other statistical tests (McFadden and Jones, 1981).

Three rock magnetic experiments were applied to samples from the Doublespring duplex and Willow Creek anticline: coercivity spectrum analysis, IRM acquisition, and thermal demagnetization of IRM. Thermal demagnetization of IRM allows for the determination ofpeak unblocking temperatures for different coercivity components. Coercivity spectrum analysis was performed by applying a partial anhysteretic remanent magnetization (pARM) in a 10 mT window, in incremental steps from °to 100 mT (which is the limit of the instrument). A sample from each bed of the duplex (top, shear, and bottom, Figure 4), as well as ~ee from around the anticline fold (Figure 6) were used in the analyses. Coercivity spectrum analysis indicates the coercivity spectrum, and hence magnetic grain size, and the relative concentration of ferromagnetic minerals per unit volume of a sample. Acquisition of isothermal remanent magnetization, IRM, was the second rock magnetic experiment applied to these rocks in order to identify the magnetic remanence carriers. The IRM acquisition procedure involves exposing each sample to a DC magnetic field (H), measuring the IRM acquired, exposing the sample to a progressively stronger H, and measuring again. The progressive steps for IRM acquisition are 50, 75, 100, 120, 150,200,400,600, 1000, and 1200 mT. IRM acquisition allows for the identification of magnetic minerals with different coercivities. IRM applied in two perpendicular directions to a sample followed by thermal demagnetization was used to identify and characterize the low and high coercivity fractions (Lowrie, 1990). A 200 mT field was applied in the MX direction, and perpendicular to that a 1200 mT field was applied in the MY direction. Following IRM acquisition in two perpendicular directions, the samples were thermally

20 demagnetized up to 675°C incrementally. IRM experiments were dOlle on samples from both structures for identification of the magnetic carrier in the Scott Peak Formation. A total of five cores (one from the top bed, two from the shear zone, and two cores from the bottom bed) were used. One core from each limb of the anticline was used in the IRM acquisition experiment. Anisotropy of magnetic susceptibility (AMS) measurements were made on a Kappabridge susceptibility meter at Colgate University, on forty-nine previously AF demagnetized cores from the two folds. AMS is a technique used to study the preferred orientation ofmagnetic grains and to examine the magnetic fabric of the magnetic grains (Jackson, 1991) within the carbonates. XRD of magnetic separates from the carbonates was employed to identify magnetic minerals. Shear zone material was crushed, and then the calcite matrix was dissolved away in buffered acetic acid, leaving insoluble residue that included the magnetic minerals (Hedlund, et al., 1993). The powder was sieved at 2 ~ grain size, and the coarse fraction was reserved for x-ray diffraction analysis. Six cores from the two folds were polished using 0.04 Jlm Si02 grit, cleaned in an alcohol sonic bath, and rinsed with ethanol, and then examined in reflected light to identify possible remanence-carrying minerals. A diamond scribe was used to circle minerals suspected to be remanence carriers. One ofthese polished cores from the shear zone of the duplex was analyzed by scanning electron microscopy on a JSM-6300 F field emission scanning microscope. Energy dispersive spectroscopy ~1O KeV) was used to identify the remanence-carrying grains within the carbonate matrix of the Scott Peak Formation.

21 Results

Data analysis indicates similar results from AF and thennal demagnetization (Figures 8 and 10; Appendices 1-5) of duplex and anticline samples, and reveals great internal consistency for each hand sample with typical precision parameters, k, of approximately 25 to 75 (Figures 9 and 11). Results of thermal demagnetization reveal intensity decreases at 100°, 300-350°, and 580°C for most duplex and anticline samples. AF demagnetization results indicated coercivities greater than 100 mT. Results yield a postfolding, steep, south and up (predominantly reversed) magnetization for both the duplex and the anticline, however there were also normal polarity hand samples at both the duplex and the anticline. The sample means for the duplex and anticline are plotted in g~ographic (in situ) and stratigraphic (tilt corrected) coordinates on equal-area projections (Figures 12 and 13). The average of the duplex site means is 1=-57", 0=245°, (N=6, a95=6.8°) (Figure 12). The best clustering of site means, as well as the highest k (precision parameter) is at 0% unfolding, and therefore, the duplex failed the fold test (Figure 12), which indicates that the age of magnetization postdates the deformation. The magnetization is significantly postfolding at the 99% confidence level

(McElhinny, 1964). The average of the anticline site means is 1=-82°, D=229°, (N=5, a95=18.2°) is plotted on the stereonet in Figure 13. The best clustering of site means is at 0% unfolding, and therefore, the anticline failed the fold test (Figure 13). The magnetization is significantly postfolding at the 99% confidence level (McElhinny, 1964).

Because the magnetization has been determined to be postdefonnational (best clustering of site means at 0% unfolding), then the nature of the secondary magnetic overprint could be investigated using rock magnetic experiments and SEM observations.

pARM coercivity data is plotted with mean step (mT) versus magnetization (J in

Aim). The pARM results also reveal that there is a higher concentration of ferromagnetic

22 Doublespring Duplex , T6-1 Thermal Demagnetization N, UP

Doublespring Duplex T6-2 Alternating Field Demagnetization N,UP

Figure 8. Zijderveld diagrams for Doublespring duplex. (a) Thennal demagnetization of duplex sample T6-1, with labeled temperature steps in ·C; (b) AF demagnetization of duplex sample T6-2, with labeled AF steps in mT. 23 Doublespring Duplex Site Mean Direction Sample T6

Equal Area o Measured demagnetization N=4 directions K=76.16 a95=8.02° iii Site Mean

Figure 9. Typical site mean directions for several cores from one hand sample (T6) shown on equal-area projection net The site mean is at (214.8°, -59.0°). Kappa =76.16 and a95 = 8.02° indicates good clustering of data for this sample.

24 Willow Creek Anticline R8-5 Thennal Demagnetization N,UP

100·

Willow Creek Anticline R8-1 Alternating Field Demagnetization N, UP

Figure 10. Zijderveld diagrams for Willow Creek anticline. (a) Thennal demagnetization ofanticline sample R8-5, with labeled temperature steps in °C; (b) AF demagnetization of anticline sample R8-1, with labeled AF steps in mT.

25 Willow Creek Anticline Site Mean Direction Sample R8

Equal Area o Measured demagnetization N=3 directions K=24.28 0:95=16.4° fi Site Mean

Figure 11. Typical site mean directions for several cores from one hand sample (R8) shown on equal-area projection net The site mean is at (221.7", -62.2°). Kappa = 24.28 and 0:95 = 16.4° indicates reasonably good clustering of data for this sample.

26 ...:' ..:;."",.,

Slritlgnplilc Coordinate"

Doublesprlng Duplex Fold Test '

N --.l 70.0 -1-11- Kappa I 60.0 -I' 50.0 ~ 99focr ~ 40.0 30.0 ~:c~~.~,.·. 20.0- 10.0

0.0 ~ III L:!::t=-=. • j o w ~ ~ W ~ " Unfoldin& Figure 12. Fold test for Doublespring duplex. Site means from six hand samples are plotted in geographic (in situ) and stratigraphic (corrected for bedding tilt) coordinates. Best clustering of site means in geographic coordinates, which indicates magnetization is .postfolding. The graph shows that the Kappa (precision parameter) decreaseswith increasing percent unfolding of sitemeans,thereby depicting the failure of the fold test' The magnetization is significantly postfolding at the 99% cbnfidencelevel (McElhinny, 1964).

i. Geographic Coordinates Stratigraphic Coordinates

12.0 tv 00 10.0 a- 8.0 .. ~ 6.0

4.0 ~~~;",.- ... ". 2.0

0.0 !•,, J,,, I•, ! I•,,I !!, j o 20 40 60 80 100 % Unfolding Figure 13. Fold test for Willow Creek anticline. Site means from five hand samples are plotted in geographic (in situ) and stratigraphic (corrected for bedding tilt) coordinates. Best clustering of site means in geographic coordinates, which indicates . magnetization is posffolding. The graph shows that the Kappa (precision parameter) decreases with increasing percent unfolding of site ~eans, therebydepicting the failure ofthe fold test. The magnetization is..significantlypostfolding at the 99% confidence level (McElhinny, 1964). ) minerals in the shear zone, relative to the surrounding beds, demonstrated by the greater pARM for the shear zone sample, SI-2 '(Figure 14). Three cores from around the Scott

Peak bed ofthe anticline were also used for coercivity spectrum analysis (Figure 15). It is interesting to note that although the pARM spectrum for the anticline has the same shape as the coercivity spectrum of the duplex, the anticline has a higher concentration of ferromagnetic minerals than the duplex (Figure 16).

In the IRM acquisition experiments, Doublespring duplex data from five cores around the fold retain the same basic shape (Figure 17), however the sample from the top bed (T3-1I) acquired the highest IRM relative to the other cores. The break in slope indicates that two coercivity fractions carry the remanence; the high coercivity fraction is between 200 and 1200 mT and the low coercivity fraction is below 200 mT. It is important to note that IRM does not saturate by 1200 mT, which is the limit of the impulse magnetizer. The two Willow Creek anticline samples display nearly identical behavior, which is similar to the behavior ofthe duplex samples (Figure 18). The top bed sample of the duplex has the highest IRM overall and the rocks all have similar IRM acquisition behavior (Figure 19). In order to best determine the minerals that carry the high and low coercivity fractions, subsequent thermal demagnetization was applied to these cores following application of an IRM in the MY direction (perpendicular to that acquired in the original experiment).

Thermal demagnetization of low coercivity ~oo mT) IRM showed that the low coercivity grains have unblocking temperatures less than 500·C (Figure 22). The high coercivity fraction is composed of two magnetic phases; one with unblocking temperatures near 350 ·C, and another with unblocking temperatures between 100-150 ·C (Figures 20 and 21). Although the duplex and anticline show similar pARM and IRM acquisition behavior, the anticline samples do not appear to contain the low unblocking temperature,

29 Coercivity Spectrum Doublespring Duplex 1.6 10-3

1.4 10-3 o 18-2 --0-- 51-2 3 1.2 10- 6 B4-1

1.0 10-3

~ 8.010-4

6.0 10-4

4.0 10-4

2.0 10-4

0.010° o 20 40 60 80 100 Mean Step (mT)

Figure 14. Coercivity spectrum ofDoublespring duplex. One core from each bed ofthe duplex was measured for this rock magnetic experiment Data is plotted with mean steps in mT versus J in SI units. The shear zone sample, SI-2, contains the highest concentration of ferromagnetic minerals relative to the top and bottom beds of the duplex. All three samples retain the same shape, which describes a Gaussian distribution of magnetic grain sizes with some skew toward fmes for the Scott Peak Fonnation. The high coercivity component is between 20 and 120 mT, and the low coercivity component is retained below 20mT. 30 Coercivity Spectrum Willow Creek Anticline 3.5 10-3 • RS-3a 3.0 10-3 • R3-1a

2.5 10-3 * Rl0-6

2.0 10-3 ~ 1.5 10-3

1.0 10-3

5.0 10-4

0.010° 0 20 40 60 80 100 Mean Step (mT)

Figure 15. Coercivity spectrum of Willow Creek anticline. Three cores from around the Scott Peak bed of the anticline were measured for this rock magnetic experiment. Data is plotted with mean steps in mT versus J in SI units. Sample RS-3a from the hinge of the fold contains the highest concentration of ferromagnetic minerals relative to the western and eastern samples of the bed. All three samples retain the same shape, which describes a Gaussian distribution of magnetic grain sizes with some skew toward fmes for the Scott Peak Fonnation. The high coercivity component is between 20 and 120 mT, and the low coercivity component is retained below 20 mT.

31 Coercivity Spectrum Willow Creek Anticline & Doublespring Duplex 3.5 10-3 RS-3a 3.0 10-3 • • R3-1a RI0-6 2.5 10-3 .. 0 1'8-2 2.0 10-3 0 51-2 ~ ts B4-1 1.5 10-3

1.0 10-3

5.0 10-4

0.010° 0 20 40 60 80 . 100 Mean Step (mT)

Figure 16. Combined coercivity spectrum for the Doublespring duplex and the Willow Creek anticline. The three duplex cores are plotted with open symbols, and the three anticline cores are plotted in closed symbols. Data is plotted with mean steps in mT versus J in 51 units. Because the plots all retain a similar shape, it can be determined that the rocks are magnetically similar, however, the anticline has a relatively higher concentration of ferromagnetic minerals than the duplex. 32 IRM Acquisition Doublesprings Duplex 8.0 10-4 7.0 10-4 o B12-21 6.0 10-4 o B4-31 8. S2-1I 5.0 10-4 ~S3-1I -0-13-11 ~ 4.0 10-4 3.0 10-4 2.0 10-4 1.0 10-4 0.0 100 ~~~===±::=t::~=:::::t:=~;=±:::==::!=:l=~==~ o 200 400 600 800 1000 1200 Field (mT)

Figure 17. IRM acquisition experiment for Doublespring duplex. One core from the top, two from the shear zone, and two from the bottom bed were measured for this rock magnetic experiment Data is plotted with the field in mT versus the NRM for each step of the experiment All five cores retain the same basic shape, however the top bed sample TI II acquired the highest IRM relative to the other cores in this experiment The break in slope indicates that two coercivity fractions retain the remanence: the IRM for the high coercivity fraction was acquired in a field from 200 to 1200 mT, and the low coercivity fraction was acquired below 200 mT.

33 IRM Acquisition Willow Creek Anticline 1.0 10-4

8.0 10-5

6.0 10-5 ~ 4.0 10-5

5 2.0 10- .. R3-lBI • RlO-21 0.0 100 0 200 400 600 800 1000 1200 Field (mT)

Figure 18. IRM acquisition experiment for Willow Creek anticline. One core from each limb of the Scott Peak bed of the anticline was measured for this rock magnetic experiment Data is plotted with the field in mT versus the NRM for each step of the experiment Both cores retain the same shape and acquired a similar IRM for each step, indicating that they are very similar magnetically. The break in slope indicates that two coercivity fractions retain the remanence: the IRM for the high coercivity fraction was acquired in a field from 200 to 1200 mT, and the low coercivity fraction was acquired below 200 mT.

34 IRM Acquisition Willow Creek Anticline & Doublespring Duplex 8.0 10-4

4 7.0 10- o B12-21 4 -0-B4-31 6.0 10- .& S2-1I --lSI- S3-1I 5.0 10-4 o TI-ll "" R3-lBI ~ 4.0 10-4 • RlO-21

3.0 10-4 2.0 10-4 1.0 10-4 0.0 100 ~~~=!=I=::I:::::&=±==l:=~=t==:::::!==::t:::itI>===:::itl. o 200 400 600 800 1000 1200 Field (mT)

Figure 19. Combined IRM acquisition data for the Doublespring duplex and Willow Creek anticline. All samples retained the same characteristic shape, however the top bed sample from the duplex acquired the highest IRM. Doublespring duplex samples are plotted with open circles, and Willow Creek anticline samples are plotted with closed circles. 35 IRM-Thermal Experiment Willow Creek Anticline & Doublespring Duplex High Coercivity 0.008000 ...l:"""rrr-T-rr"T"'"'"r""rr-T-rr-r-r-1r-r-T""T'"'T""-r-r-I--r-T'""""""'-"""""""""""""-'--'-' 0.007000 o MX-B4-3I o MX-B12-2I 0.006000 6: MX-S2-11 ---rsJ-- MX-S3-11 0.005000 ~MX-T3-l1 ~ 0.004000 • MX-RIQ-2I ... MX-R3-1BI 0.003000 0.002000 0.001000 0.000000 ~~~~~~~~~@IlD~i§,-.3 o 100 200 300 400 500 600 700 Temperature °c

Figure 20. IRM-Thermal experiment for Doublespring duplex and Willow Creek anticline. The high coercivity fraction is acquired in a 1200 mT field in the MX direction. The high coercivity fraction is composed of overlapping coercivity spectra of goethite and an iron sulfide. Duplex data is plotted with open symbols and anticline data is plotted with closed symbols. 36 IRM-Thermal Experiment Willow Creek Anticline & Doublespring Duplex High Coercivity 0.002000 o MX-B4-31 o MX-B12-21 0.001600 t:s. MX-S2-1I -{S}- MX-S3-1I -0-- MX-TI-ll 0.001200 • MX-RIG-21 ~ ... MX-R3-lBI 0.000800

0.000400

0.000000 o 100 200 300 400 500 600 700 Temperature ·C

Figure 21. IRM-Thennal experiment for Doublespring duplex and Willow Creek anticline. The high coercivity fraction is acquired in a 1200 rnT field in the MX direction. The first point was removed from the data in Figure 20 in order to reveal the decrease in SIRM at 325 ·C. The high coercivity fraction is composed of overlapping coercivity spectra of goethite and an iron sulfide. Duplex data is plotted with open symbols and anticline data is plotted with closed symbols. 37 IRM-Thermal Experiment Willow Creek Anticline & Doublespring Duplex Low Coercivity 0.002000 o MY-B4-31 0.001600 o MY-B12-21 & MY-S2-1I -iSl- MY-S3-1I 0.001200 --0- MY-TI-ll ~ • MY-R10-21 0.000800 .... MY-R3-1BI

0.000400

0.000000 o 100 200 300 400 500 600 700 Temperature °C

Figure 22. IRM-Thennal experiment for Doublespring duplex and Willow Creek anticline. Low coercivity fraction is retained below 200 mT in the MY direction. The steady decay to 525 °C indicates that the low coercivity fraction is composed of magnetite. Duplex data is plotted with open symbols and anticline data is plotted with closed symbols. 38 high coercivity component (Figure 20). Anisotropy of magnetic susceptibility (AMS) showed that the larger, multidomain magnetic grains exhibited no fabric (preferred orientation of multidomain grains) in either the duplex or anticline. Measurements of Kmax and Kmin in geographic and stratigraphic coordinates are plotted separately for the top, shear, and bottom beds of the duplex (Figures

23-25), and the anticline (Figure 26). Mainly, there is no preferred orientation of grains either in situ or with structural correction. However, the bottom'bed of the duplex seems to suggest a tectonic fabric in geographic coordinates, where the intermediates cluster parallel to the NW-SE trend ofthe regional fold axes (Figure 25). During crushing of a shear zone sample, a sulfur smell was emitted, providing more evidence for the presence of an iron sulfide as the remanence carrier. The powder sample residue that was analyzed by XRD revealed quartz, calcite and illite, but no defInitive identifIcation of the magnetic fraction. Scanning electron microscopy (SEM) was used to analyze a polished shear zone sample, S3-4, in order to conclusively identify the postfolding remanence carrier of the Scott Peak Formation. Energy dispersive spectrometry (EDS) was employed for the identifIcation of Fe and S interior to some Fe-O grains, individual Fe-O grains, as well as the presence of Cu veins in the x-rayed sample. The large (-10 JlIl1 in diameter), detrital iron oxides contained small regions (-1 ~m) within the grain that are iron sulfIdes. Small veins within the shear zone sample were x-rayed, and copper was identifIed by EDS. The copper veining is secondary like the iron sulfIdes, due to the fact that mineralization occurred in the veins subsequent to deformation and contemporaneously with the magmatic events of the region.

Complete results of this study are included in data tables in the appendix.

39 Doublespring Duplex Top Bed Doublespring Duplex Geographic Coordinates Top Bed Stratigraphic Coordinates

a . + • • \ ------. a • a + a • + a +• a• • a + a • • a ;:r-- • + • a • + T • • -jD + • • + +•. • + + +a +" • •+ • T• + ~ \ + + + a a • + • a+ .+ + • a • + + • I:'a • a a a a a .. ""- a Equal Area • + • 0=17 Kmax Equal Area 0=17 o Kmax ~~·i{in!:·· .Kmm

Figure 23. Anisotropy of Magnetic Susceptibility of the top bed of Doublespring duplex. Data for 17 measured samples is plotted with open boxes for Kmax, crosses for Kint, and closed circles for Kmin. The data is plotted in geographic (in sitU) and stratigraphic (corrected for bedding tilt) coordinates, however there is no preferr~ orientation or fabric with structural correction. Doublespring Duplex Doublespring Duplex Shear Zone Shear Zone Geographic Coordinates Stratigraphic Coordinates

Equal Area o Kmax Equal·Area D~k;Wc ....:..- .~ ,- n=5 + Kin~ n=5 Kmm + Kint e eKmin

Figure 24. Anisotropy of Magnetic Susceptibility of the shear zone of Doublespring duplex. Data for 5 measured samples is plotted with open boxes f~r Kmax, crosses for Kint, and closed circles for Kmin. The data is plotted in geographic (in situ) and stratigraphic (corrected for bedding tilt) coordinates, however Utere is no preferred orientation or fabric with structural correction. ~ -.._.... ~'

Doublespring Duplex Doublespring Duplex Bottom Bed Bottom Bed Geographic Coordinates Stratigraphic Coordinates

+ + + a D • • • • .J a + (. • a D • D + + + • a DD a + • a ++ t; + D + + + + • • + • + D a a + • + + '" • r:.D .f a a

Equal Area + Kmax Equal Area n=17 "+ • Kim n=17 D Kmin

Figure 25. Anisotropy of Magnetic Susceptibility of the bottom bed ofDoublespring duplex. Data for 17 measured samples is plotted with open boxes for Kmax, crosses for Kint, and closed circles for Kmin. The data is plotted in geographic (in situ) and stratigraphic . (co~ted for bedding tilt) coordinates, however there is no preferred orientation or fabric with structural correction. .,:," .

Willow Creek Anticline Willow Creek Anticline Geographic Coordinates Stratigraphic Coordinates

• a :I- • D • • • ",.... a c '+ '+ a +" • D + a + • • • D + ~ + + w \ a D + a + + + + • ;t

+ D o Kmax Equal Area D o Kmax Equal Area n=lO "- • + Kint.,n=lO . + Kint • Kmin '~"·.K.min

Figure 26. Anisotropy of Magnetic Susceptibility of Scott Peak Formation of the Willow Creek anticline. Data for 10 measu~ samples is plotted,with open boxes for Kroax, crosses for Kint, and closed circles for KInin. The data is plotted and stratigraphic (corrected for bedding tilt) coordinates, however thrre is no preferred orientation or fabric with structural correction. Discussion

Remanence Carriers

Remanence was originally thought to be carried by magnetite since this is typically the primary magnetic mineral in carbonate rocks, however, during thermal demagnetization, the signal dropped off between 300-350 DC which is not characteristic of magnetite, but could indicate the presence oftitanomagnetite or a sulfide, such as pyrrhotite (Fe(l_x)S); (Figures 8 and 10). With an unblocking temperature in the range of 300-350 DC and complete removal of the signal by 100 mT, an iron sulfide was determined to be the high coercivity component of magnetization from both demagnetization (thermal and AF) methods, and from thermal demagnetization ofIRM. Fe(l_x)S is a secondary mineral, as indicated by SEM analyses which identified small iron sulfides included within large iron oxide grains, and is probably associated with the Tertiary magmatism and Cu mineralization.

In nearly all cases of demagnetization of NRM, a large decrease in remanence was identified between 0 and 100 DC, the unblocking temperature range indicating the presence of goethite. Because goethite is typically a present-day weathering product, it was not considered to be a large contributor to the remanence, although it contributes minimally to the high coercivity fraction. Thermal demagnetization of NRM would remove the goethite component from our characteristic magnetization. Agreement between AF and thermal demagnetization data suggests that goethite has not contributed significantly to the signal.

During demagnetization of NRM of some cores, the signal was retained up to 580

DC, which is the characteristic unblocking temperature of magnetite. The low coercivit)r magnetite fraction is probably a primary (depositional) mineral that has been overprinted by the high coercivity component. This is supported by SEM observations. Some samples

44 ·continue to decay to 680 ·C, suggestinglhat either hematite developed as a secondary product from heating the goethite during thermal demagnetization or that some hematite is present in the rocks. The agreement between AF and thermal demagnetization results suggests it is not an important component. AMS results demonstrated that there is no fabric in these rocks. The fact that there is no preferred orientation ofmagnetic grains in both geographic and stratigraphic coordinates ts consistent with a postfo1ding remagnetization (Figures 23-26). IRM acquisition and thermal demagnetization of SIRM determined that magnetite is the low coercivity remanence carrier due to an unblocking temperature at 500· C. The high coercivity fraction is composed of overlapping coercivity spectra of iron sulfide, which has a characteristic unblocking temperature of 350· C, and goethite, which has a characteristic unblocking temperature near 100· C. Based on the results from the IRM acquisition and thermal demagnetization experiments it is suggested that the characteristic magnetization is carried by the high coercivity fraction, which was suspected to be a secondary iron sulfide, probably brought in by fluids associated with Tertiary magmatic activity and precipitated out as pyrrhotite which then acquired a CRM. The presence of a secondary iron sulfide is supported by SEM observations. The most likely source of the postfolding, Tertiary remagnetization is the Challis volcanics (Figures 1 and 2). The Challis magmatic event could bring in heat and/or drive hydrothermal fluids, thereby thermoviscously or chemically remagnetizing the Scott Peak carbonates. Although the Challis volcanics could have cooled quickly, the extensive magma chamber underlying much of south-central Idaho could cause fluid convection in the region (Figure 1; Janecke and Snee, 1993; Criss, et al., 1991). The Challis Volcanics are Eocene in age (Janecke and Snee, 1993; Norman and Mertzman, 1991; Lewis and Kiilsgaard, 1991; McIntyre, et al., 1982), and are coeval to the North American Eocene paleopole isolated by Diehl et al. (1983) in Montana volcanics. Both the

45 similarity of rock magnetic behavior as well as the postfolding, reversed directions supported the comparison of both folds' magnetization with the North American Eocene paleopole (Diehl, et al., 1983).

SEM combined with EDS analyses identified an iron sulfide, which was associated with magnetite. The documentation ofan iron sulfide included within a magnetite grain indicates that pyrrhotite is probably a secondary alteration product, thereby supporting a chemical remagnetization (Figures 27 and 28), and is most likely caused by magmatic fluids circulating during the Tertiary volcanic episodes at 48 and 46 Ma.

In addition, individual magnetite grains were identified (Figures 29 and 30) during

SEM analysis, which are believed to be primary detrital grains due to their average size (10

1JlD.) and scattered occurrence throughout the calcite matrix. These magnetites are probably the low coercivity fraction of the remanence which unblocks at 580 DC. EDS, or energy dispersive spectrometry, identified a Cu peak in a vein within the calcite matrix (Figure 31).

Copper-bearing veins have been documented throughout the Lost River Range (Staatz,

1972), particularly in Mackay, Idaho (Criss, et al., 1991), close to where these two folds are located. Several workers have reported the copper veins to be associated with the

Tertiary volcanics (Criss, et al., 1991). SEM observations indicate that iron sulfides are secondary, IRM indicates that they are high coercivity, and thermal demagnetization indicates a 350 DC blocking temperature. Thus, the iron sulfide fraction carries the characteristic magnetization. The characteristic magnetization is postfolding, and probably

Eocene in age. Copper veins appear to be secondary from SEM observations, hence, they are probably Eocene in age as well because the copper is associated with secondary Fe(l_ x)S, thereby relating the age of mineralization with the timing of chemical remagnetization in the Scott Peak Formation.

46 Figure 27. Scanning Electron Microscopy photographs of two iron sulfide minerals within magnetite grains from duplex shear zone sample S3-4. The bright, irregularly . shaped grains within the spherical grain are the iron sulfides, from EDS identification. The iron sulfide minerals average 1micron in size, and are believed to be secondary minerals associated with primary magnetite grains that range from 5 to 10 microns in size.

47 Figure 27. Scanning Electron Microscopy photographs of two iron sulfide minerals within magnetite grains from duplex shear zone sample S3-4. The bright, irregularly shaped grains within the spherical grain are the iron sulfides, from EDS identification. The iron sulfide minerals average I micron in size, and are believed to be secondary minerals associated with primary magnetite grains that range from 5 to 10 microns in size.

47 X-RAY; . 0 - 10 keU Live: 159 s Pre set: 1000 s Rema. i ni n9 : 8111s Rea.1 : 1755 9~ Dea.d

FS e I

o S

Lf.912 keU 10.0 > FS= 2K OS= Lf ch 501= 79 cts MEM1:S3-Lf MARCH 2q,199~

Figure 28. Energy Dispersive Spectroscopy graph of iron sulfide minerals x-rayed at 10 Kev. The corresponding Fe and S peaks conclusively identify the presence of iron sulfides as remanence carriers in the Scott Peak Fonnation. EDS graph was produced from x-ray of iron sulfide minerals in Figure 27. 48 Figure 29. Scanning Electron Microscopy photographs of two magnetite minerals within carbonate matrix from duplex shear zone sample S3-4. The magnetites are thought to be primary, depositional grains that range from 5 to 10 microns in size. 49 Figure 29. Scanning Electron Microscopy photographs of two magnetite minerals within carbonate matrix from duplex shear zone sample S3-4. The magnetites are thought to be primary, depositional grains that range from 5 to 10 microns in size. 49 X-RAY: o ~ 10 ke:V Live: 100 s Pres e: t : 1000s Rem.a i ni n9: 900s Rea.l: 108$ 7% Dea.d

.F e s o

F e

Lf.972 kelJ 10. 1 > FS= 1K OS= Lf ch 507= 1f8 cts MEM1:S3-Lf MARCH 2Lf,199Lf

Figure 30. Energy Dispersive Spectroscopy graph ofmagnetite minerals x-rayed at 10 KeV. The corresponding Fe and 0 peaks conclusively identify the grains as magnetite, the low coercivity remanence carriers in the Scott Peak: Formation. The Si peak: is attributed to the carbonate matrix, or perhaps residue of Si02 polish. EDS graph was produced from x ray of magnetite minerals in Figure 29.

50 X-RAY; o - 10 keU Live: ~02s Preset: 1000s Remaining: 598s Real: ~19s ~% Dead c u

2.292 keU ~.9 > FS= 2K OS= ~ ch 239= 136 cts MEM1:S3-~ MARCH 2q,199~

Figure 31. Energy Dispersive Spectroscopy graph of copper x-rayed at 10 KeV. The corresponding Cu and 0 peaks conclusively identify the material as a copper oxide. Copper mineralization during the Eocene magmatic event has been identified in Custer County, Idaho (Criss, et al., 1991), where the duplex is located. The Mg and AI peaks might also be products of mineralization in this region. The Si peak is attributed to the carbonate matrix, or perhaps residue of Si~ polish. EDS graph was produced from x-ray of what was thought to be a,quartz vein, but was most likely a copper oxide vein within the carbonate matrix. 51 Because the rock magnetic behavior of the Doublespring duplex and Willow Creek anticline is so similar and both are postfolding, it is possible that the two directions are

similar and that neither has averaged secular variation. However, a statistical test indicates that the two postfolding directions are statistically different at the 95% confidence level (McFadden and McElhinny, 1990). In a_ddition, the angular dispersion ofthe virtual

geomagnetic poles (VGP) for the hand sample directions at each site is close (12°) to the expected angular dispersion (16.5°; Butler, 1992) for the paleolatitude of the duplex

(Figure 32). The VGPs for the hand sample directions at each site is much higher (36°) '" than the expected angular dispersion (16.5°; Butler, 1992) for the paleolatitude of the anticline (Figure 32). Therefore, due to angular dispersion of the VGP and the dual polarity directions of the two folds, there is strong evidence that secular variation was averaged for both sites.

Age of Magnetization and Tectonic Implications

It is important to understand the influence of fluids in this system (Criss and Champion, 1984) and their relation to the origin of the documented chemical remagnetization of these rocks. Once the relative timing of deformation and acquisition of remanence sequence was established, it was necessary to constrain the age and source of

remagnetization. Fluids could be responsible for growing magnetic minerals, altering minerals such as magnetites to sulfides, or transporting in new magnetic grains (CRM),

thereby increasing the strength ofremanence by creating an overprint The higher concentration of ferromagnetics in the shear zone relative to the

surrounding beds of the duplex (documented by coercivity spectrum analysis) may be due

to hydrothermal fluids or mass transfer by fluids through the shear zone bringing in

52 ~-:-..__o.__-.:~_

Angular Dispersion of Virtual Geomagnetic Poles .~

Site N Angular Dispersion Paleolatitude Expected Angular Dispersion

VI duplex 6 W 11.92° 46° 16.5° anticline 5 35.73° 46° 16.5" ..

~~,c". ....

Figure 32. Angular dispersion of virtual geomagnetic poles (YGP) for the Doublespring duplex and Willow Creek anticline: The . angular dispersion of VGPs for the hand sample directions is close (12°) to the expectedangulardispersion(16;-SO; Butler,-1992) for-the paleolatitude ofthe duplex. However, the angular dispersion of VGPs for the hand sarnpledirections is muchhigh~r(3~)than the expected angular dispersion (16.5°; Butler, 1992) for the paleolatitude of the anticline. The large dispersion can be attributed to the .,' scatter ofthe anticline data. ferromagnetic material. Perhaps a more-reasonable explanation for the relatively higher ferromagnetic concentration ofthe shear zone is passive concentration due to removal of non-magnetic (Le., carbonate) material from between the top and bottom beds ofthe

Doublespring duplex. The geochemical analyses performed by Hedlund, et ala (1993) provide evidence for the presence of fluids in this tectonic system. illite crystallinity temperatures of220 DC and Ti enrichment of the shear zone ofthe duplex have been attributed to the irifluence of fluids (Hedlund, et al., 1993). Remagnetization of the duplex and anticline supports the idea offluids passing through the Scott Peak Fonnation as well.

The geochemical analyses indicated an enrichment in Ti by fluid infiltration or mass transfer through the shear zone. This could have been a pathway through which fluids migrated, and thereby caused the postfolding remagnetization.

The Cenozoic time scale indicates that there were several polarity reversals during the Tertiary (Figure 33). The two pulses of magmatic activity dated by 40Ar/39Ar thermochronology (Janecke, 1992) occur during a period ofreverse polarity according to this time scale and the demagnetization directions obtained by this study. During both episodes of volcanism (at 48 and 46 Ma) the geomagnetic field was reversed, labeled chrons 21 and 20, which further supports the hypothesized age ofremagnetization of the

Scott Peak Formation. Because the magnetization is postfolding, it thereby constrains both the age of folding and the age of volcanism. The Challis volcanics are the most likely source of the fluids and/or heat migrating through the system, and causing the remagnetization because of their widespread coverage of the Upper Mississippian rocks and the coincidence ofmagmatism and acquisition of a predominantly reversed, Eocene-aged CRM. The age of volcanism of the Tertiary magmatic event has been separated into two discrete pulses of activity at 48 and 46 Ma by 40Ar/39Ar thermochronology (Janecke,

54 eraSub- Epoch Ma Eon era Period 1

I- W Olr Holocene .... Pleistacenf

Pliocene PII 5

10 Neogene Nt .. Miocene 1-15 .

~ Mio

25-

Oligocene c.J >- 30 0 ~ N (12 0 '';:: c: ~ e) e) l- 0Ii 35 u I-

45 Paleogene Eocene PI

'-50 I-

Paleocene - I-- 1-65 '- Gulf '- 601

Figure 33. Geologic linear time scale for the Cenozoic. There were several magnetic polarity reversals throughout the Tertiary. The reversed, Eocene, postfolding directions of the two folds coincide with chrons 21 (fIrst pulse of magmatism at 48 Ma) and 20 (second episode of magmatism at 46 Ma), both of which were reyersed polarity (adapted from Harland, et aI., 1990).

55 1992). Because the directions are postfolding and predominantly reverse polarity which is consistent with the geomagnetic polarity time scale at 48 and 46 Ma, they were compared to the Eocene pole since this is the suspected age ofremagnetization. The duplex and anticline paleopoles plotted on the North American apparent polar wander path indicates they are close to the Eocene pole (DieW, et al., 1983) for western North America (Figure 34). Ifit is assumed that these folds were remagnetized during the extensive, regional Tertiary magmatic event, and their magnetizations are compared to Diehl, et al.'s (1983) Eocene paleopole for North America, it suggests 60° clockwise rotation for the duplex, while the anticline magnetization is statistically indistinguisha~le from the Eocene direction (Figure

34). Essentially the same results are obtained with removal of the shallow plunge ofthe fold axes (11 °from the duplex and OT from the anticline). The duplex 0=-63 0, D=231 0) continues to suggest 62° clockwise rotation while the anticline 0=-64°, D=169°) remains closely associated with the Eocene pole.

The implications of local block rotations on regional tectonics remains an important consideration, particularly with respect to the normal faults and block rotations associated with Cenozoic ~xtension (Janecke, 1992). A localized rotation of 60° for the duplex may be unreasonable considering that the duplex fold axis is consistent with the trend of the fold axes in the Paleozoic thrust sheets and there is no strong geological evidence for such a rotation. However, by untilting the duplex site mean direction for westward tilt, there is no need to require clockwise rotation. This model would allow the trend of the duplex fold axis to remain consistent with the trend of the fold axes of the rest ofthe Lost River Range.

The tilting must therefore have occurred subsequent to emplacement and cooling of the

Eocene volcanics, following acquisition of the postfolding, Tertiary remanence. Eas~ard tilting of the volcanics along normal faults has been documented in the Lost River Range

(Janecke, per. comm., 1994; Janecke, 1992). The nearest measured volcanics exposure is

56 Figure 34. Apparent Polar Wander Path for North America from the Early Triassic to the Late Cenozoic. The study area in south-central Idaho is marked with an asterisk. The' Eocene paleopole is labeled E. The calculated Eocene paleopole for the Willow Creek anticline (82°, 171 0) lies directly on the Diehl, et ai, 1983 pole (82.0° N, 170.2° E), marked with a white dot The Eocene paleopole for the Doublespring Duplex (54°, 318°) is marked with a black dot and labeled DD (modified from Butler, 1992). 57 the Spring Hill site that was corrected for 35° eastward tilt when compared to the Diehl, et

. al. (1983) paleopole (Janecke, et al., 1991). This same correction was applied to the

Doublespring duplex, however, with correction for 35° eastward tilt, the duplex direction

has a shallower inclination of (_20°), and the same declination (245°) as before untilting.

When the paleopole calculated from this corrected direction is compared with the APWP for

North America from the Late Cretaceous (postfolding) until the Cenozoic, there is no time during which such a shallow inclination is consistent with the polepath. Because of this, an

eastward tilt correction is not reasonable. With _20° correction for westward tilt, the

duplex direction comes directly in concordance with the Eocene direction. Although there are some measurements of westward tilt in the Lost River Range (Fisher, et al., 1992; Mapel, et al., 1965; Ross, 1947), they are not well documented, and the general consensus

is that tilting was predominantly to the east A third postulated model calls for reactivation of the thrust faults that surround the middle fold of the fault-bounded duplex. By

reactivating the thrust faults, it would be possible for the middle fold of the duplex to be

rotated relative to the upper and lower bounding folds.

The problem remains unresolved: Although 60° of clockwise rotation is

inconsistent with the general parallelism offold axes in the area and Tertiary tilting is

predominantly to the east, the Doublespring duplex magnetization direction is tightly

constrained. In addition, the angular dispersion of the VGP is close (12°) to the expected

(16.5°; Butler, 1992) for the paleolatitude of the duplex, and is much higher (36°) than the

expected (16.5°; Butler, 1992) for the paleolatitude of the anticline, and the presence of

two polarities indicates that secular variation has been averaged. The rock magnetic

experiments indicate similar magnetic mineralogies for the two structures, the only

difference is the two postfolding directions. There is strong support for either westward tilt

or clockwise rotation of the Doublespring duplex.

58 Perhaps the duplex has been subjected to a combination of both vertical axis rotation and tilting along a normal fault A large scale fault has been suggested along Doublespring

Pass (Ross, 1947) adjacent to the duplex (Figure 2). It could also be inferred that there is a fault through Christian Gulch, and through the small gulch to the north of the duplex, perhaps related to motion along the large scale Lost River Fault to the west of the duplex (Figure 2). The Doublespring duplex may be surrounded by these suspected faults, and the small, isolated block has been shallowly tilted to the west by _20·; or, the block was rotated 60· clockwise; or the duplex has been subjected to a component ofvertical and horizontal axis rotation. The trend of the duplex fold axis does not suggest rotation, and the anticline is not rotated, so there is most likely more credence to the tilting mod~l. In addition, there is no strong geological evidence for a fault along Doublespring Pass, so another proposed model involves differential tilting along a non-linear normal fault Variable down-dropping along a normal fault located to the east of the duplex and the anticline could account for the discrepancy between the two postfolding poles. The post volcanism tilting model is still viable, however. The Spring Hill volcanics locality analyzed by Janecke, et al. (1991) is east of the Doublespring duplex. The rocks were corrected for 35.1· of eastward tilt (Janecke, et al., 1991). The remanence directions corrected for tilt indicate significant counterclockwise rotation of 43· at this locality (Janecke, et al., 1991).

The sites sampled for the Janecke, et al. (1991) study outline a progression from south to north of no rotation to counterclockwise rotation to clockwise rotation (Janecke, et al., 1991) in an area southeast of Doublespring duplex and Spring Hill. This rotation model suggests a pattern of block rotations along normal faults throughout the Lost River Range that could be invoked to explain the discrepancy between the duplex and anticline directions.

59 Conclusions

The magnetization of the Scott Peak Fonnation at two (olds in the Lost River Range is postfolding, predominantly reversed polarity, Eocene in age. Rock magnetic experiments suggest the!emanence is carried by pyrrhotite and SEM analyses indicate iron sulfides are secondary alterations of iron oxides, so chemical remagnetization is indicated. The chemical remagnetization is attributed to Eocene fluids convected by heat from an extensive magma chamber underlying south-central Idaho (Janecke and Snee, 1993; Criss, et al., 1991), and is related to the two pulses of magmatic activity dated at 48 and 46 Ma Suggestions ofcopper veins associated with secondary iron sulfides in SEM observations suggests that copper mineralization is coeval with the age of the chemical remagnetization of the Scott Peak Fonnation.

The Willow Creek anticline direction is definitively Eocene, yet the Doublespring Duplex direction suggests 60° clockwise rotation around a vertical axis. The proposed alternatives to large-scale rotation include westward tilting along NE trending normal faults during Cenozoic extension following emplacement of the volcanics, and reactivation of the thrust faults that surround the middle fold of the fault-bounded duplex. To further understand the discrepancy between the duplex and anticline directions, the upper and lower fold surrounding the middle fold of the duplex could be sampled and subjected to the same paleomagnetic techniques applied in this study. It would also be important to measure the dip ofthe volcanic exposures to the north and east of Doublespring duplex, to thoroughly complete this investigation.

60 REFERENCES

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Criss, R. E., Ekren, E. B., Hardyman, R. F., 1984. Casto Ring Zone: A 4,500-km2 fossil hydrothermal system in the Challis Volcanic Field, central Idaho. Geology, Vol. 12, No.6, p. 331-334.

Criss, R. E., Fleck, R. J., Taylor, H. P. Jr., 1991. Tertiary Meteoric Hydrothermal Systems and their Relation to Ore Deposition, Northwestern United States and Southern British Columbia. Journal ofGeophysical Research, Vol. 96, No. B8, p. 13,335-13,356.

Crone, A. J., 1988. Field Guides to the Quaternary Geology of Central Idaho: Part D.

61 Surface Faulting and Groundwater Eruptions Associated With the 1983 Borah Peak Earthquake. Guidebook to the Geology of Central and Southern Idaho, Link, P. K., Hackett, W~ R., eds., p. 227-232.

Crone, A. J., Machette, M. N., 1984. Surface faulting accompanying the Borah Peak earthquake, central Idaho. Geology, Vol. 12, p. 664-667.

Diehl, J. F., Beck, M. E. Jr., Beske-Diehl, S., Jacobson, D., Hearn, B. C. Jr., 1983. Paleomagnetism of the Late Cretaceous-Early Tertiary North-Central Montana Alkalic Province. Journal of Geophysical Research, Vol. 88, No. B12, p. 10,593-10,609.

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Fisher, D. M., Anastasio, D. 1., 1994. Kinematic analysis of a large-scale leading edge fold, Lost River Range, Idaho. Journal ofStructural Geology, Vol. 16, No.3, p. 337-354.

Fisher, F. S., McIntyre, D. H., Johnson, K. M., 1992. Geologic Map of the Challis 10 x 2 0 Quadrangle, Idaho, 1:250,000. United States Geological Survey, Map 1 1819.

Gillett, S. L., Taylor, M. E., 1985. Triassic Remagnetization ofLower Paleozoic Rocks, Bear River Range, Utah-Idaho: A Possible Constraint on Thermal History. Orogenic Patterns and Stratigraphy ofNorth-central Utah and southeastern Idaho; Utah Geological Association. Publication 14. p. 249-260.

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Harland, W. B., Armstrong, R. L., Cox, A. V., Craig, L. E., Smith, A. G., Smith, D. G., 1990. A Geologic Time Scale 1989. Cambridge University Press, New York.

62 Hedlund, C. A., Anastasio, D. 1., Fisher, D. M., 1994. Kinematics of fault-related folding in a duplex, Lost River Range, Idaho, U.S.A. Journal of Structural Geology, Vol. 16, No.4, p. 571-584.

Hedlund, C. A., Bebout, G. E., Anastasio, D. J., 1993. Mass Transfer during Cleavage Formation in Carbonate Shear Zones, Double Springs Duplex, Idaho. EOS,AGU Abstracts with Programs, T32B-l1.

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Janecke, S. U., 1992. Kinematics and Timing of Three Superimposed Extensional Systems, East Central Idaho: Evidence for an Eocene Tectonic Transition. Tectonics, Vol. 11, No.6, p. 1121-1138.

Janecke, S. U., 1992b. Geologic Map of the Donkey Hills and Part of the Doublespring 15-Minute Quadrangles, Custer and Lemhi Counties, Idaho. Idaho Geological Survey, Technical Report 92-4.

Janecke, S. U., Geissman, J. W., Bruhn, R. L., 1991. Localized Rotation During Paleogene Extension in East Central Idaho: Paleomagnetic and Geologic Evidence. Tectonics, Vol. 10, No.2, p. 403-432.

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Janecke, S. U., Wilson, E., 1992. Geologic Map of the Borah Peak, Burnt Creek, Elkhorn Creek, and Leatherman Peak 7.5-Minute Quadrangles, Custer and Lemhi Counties, Idaho. Idaho Geological Survey, Technical Report 92-5.

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63 Kodama, K. P., 1988. Remanence Rotation Due To Rock Strain During Folding And The Stepwise Application Of The Fold Test. Journal ofGeophysical Research, Vol. 93, No. B4, p. 3357-3371.

Lewis, R. S., Kiilsgaard, T. H., 1991. Eocene Plutonic Rocks in South Central Idaho. Journal ofGeophysical Research, Vol. 96, No. B8, p. 13,295-13,311.

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i McCabe, C., Elmore, R. D., 1989. The Occurrence and Origin of Late Paleozoic Remagnetization in the Sedimentary Rocks of North America. Reviews of Geophysics, Vol. 27, No.4, p. 471-494. . McCabe, C., Jackson, M., Ellwood, B. B., 1985. Magnetic Anisotropy in the Trenton Limestone: Results of a New Technique, Anisotropy of Arlhysteretic Susceptibility. Geophysical Research Letters, Vol. 12, No.6, p. 333-336.

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McFadden, P. L., Jones, D. L., 1981. The fold test in paleomagnetism. Geophysical Journal ofResearch astr., Vol. 67, p. 53-58.

McFadden, P. L., McElhinny, M. W., 1990. Classification of the reversal test in palaeomagnetism. Geophysical Journal International, Vol. 103, p. 725-729.

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64 Framework of the Challis Volcanics in the Eastern Half of the Challis 1° x 2° Qua4rangle, Idaho; Cenozoic Geolol:Y of Idaho: Idaho Bureau of Mines and Geolol:Y Bulletin 26. Bonnichsen, B., and Breckenridge, R. M., eds., p. 3-22.

McWhinnie, S. T., Van Der Pluijm, B. A., Van der Voo, R., 1990. Remagnetizations and Thrusting in the Idaho-Wyoming Overthrust Belt. Journal ofGeophysical Research, Vol. 95, No. B4, p. 4551-4559.

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Rember, W. c., B~nnett, E. H., 1979. Geologic Map of the Dubois Quadrangle, Idaho. Idaho Bureau, of Mines and Geology.

Ross, C. P., 1947. Geology of Borah Peak Quadrangle, Idaho. Geological Society of America Bulletin, Vol. 58, p. 1085-1160.

Schwartz, S. Y., Van der Voo, R., 1984. Paleomagnetic Study of Thrust Sheet Rotation During Foreland Impingement in the Wyoming-Idaho Overthrust Belt. Journal of , , Geophysical Research, Vol. 89, No. B12, p. 10,077-10,086.

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Stamatakos,1., Kodama, K. P., 1991a. Flexural Flow Folding And The Paleomagnetic Fold Test: An Example Of Strain Reorientation Of Remanence In The Mauch Chunk Formation. Tectonics, Vol. 10, No.4, p. 807-819.

Stamatakos,1., Kodama, K. P., 1991b. The Effects of Grain-Scale Deformation on the Bloomsburg Formation Pole. Journal of Geophysical Research, Vol. 96, No. Bll, p. 17,919-17,933.

Zijderveld, J. D. A., 1967. A. C. Demagnetization of rocks: Analysis of Results.

65 Methods in Paleomacnetism. Collinson, D. W., Creer, K. M., Runcorn, S. K., eds., New York, Elsiever, p. 254-286.

66 ~.::~

.,..,.-'.~ .....J< - :.£..'~

....

Table ofPoles ~,:.,;::,>,;.-1<;.- ;

~:'~~'~-'" " 'r

~"'''. .~.:-,-

..::-.':,,:.,.;:.. t;-';....,.

Top Bed Data Table for DL!ElsX'

-,..-~- Site CIne CDac Glne GDac ,Alpha Beta strike dip polat polong , 1 13 35.39 276.08 27.3 334.2 130 60 130 30 53.19 111.2 2 12 42.73 234.56 53.2 327.2 150 60 150 30 62,71 145.72 3 11 71.94 339.61 53.2 22.3 126 75 126 15 69.94 359.61 4 10 64.9 239.11 68.2 321.3 130 72 130 18 63.27 186.23 0\ 146 00 5 8 -16.11 209.81 60.6 312.7 11 146 79 55.68 169.32 6 5 31.86 328.3 52.1 24.4 341 8 341 82 67:91 358.94 7 4 38.24 198.27 55.6 328.2) 84 8 84 82 64.61 149.46 t' 8 3 65.88 121.97 61.4 321.3 5 56 5 34 62.04 167.15

~,~..... , .. ...;' ',--,-".

- \ ."':""~::'-<;:'~ : Shear Zone Data Table

Site' Cine CDec Glne GDee - Alpha Beta strike dip polat polong 1 1 0 0 16.86 30.97 320 65 320 25 45.56 - 19.85 - .".-'~ 2 2 0 0 62.28 322.n 360 10 360 80 63.38 168.79 3 3 0 0 59.94 317.83 40 55 40 35 59.01 '. 165.46 I~ , 4 4 0 0 15.82 245.96 310 65 310 25 -11.09 179.32 5 6 0 0 46.81 232.9 350 75 350 15 -3.24 201.66. 0\ \0 6 7 0 0 62.3 124 334 20 334 70 10.82 284.18

~~C'2.'-~----

.1 ...,.:. "-'~

~-;:--J<::-.~'''~ -: '8ottomBed Data Table

••<. Site Cine CDec Glne GDee alpha . Beta strike dip polat polong 1 3 24.1 204.33 67.72 296.49 108 23 108 67 47.79 188.86 2 7 0 0 ' 46.9 65.7 334 49 334 41 36.05 330.33 3 4 35.28 178.14 58.3 341.57~ 68 4 68 86 75.38, 142.83 4 6 0 0 54.4 297.5' 106 7 196 83 42.07 168.07 5 9 0 0 78.13 143.16 62 24 62 66 '24.61 261.33 6 8 0 0 38.75 321.65 64 a 64 90 51.53 134.06 ~ 7 15 0 a 64.3 130.14 330 7 330 83 10.32 279.13 8 10 0 a 55.27 318.72 91 30 " 91 60 57.65 156.29 9 11 a a -44.91 274.52 40 40 40 50 1Cj! 14 a a 79.95 19.21 125 36 125 54 61.77 259.87 11 12 a a 56.22 323.92 23 40 23 50 61:81 1~4.17

~~~;;,~ -',~.- " ..,

r' "

t, ~-~-~o,~ ~-~-~'--'-~'"-,-'-; ....:' ".~~., i~

Duplex Qata Table (Best Data)

~'::-'.:' ...;:.~~ .' ".-r

. - , ~ Site Cine CDec Glne GDec alpha Beta strike dip polat polong 1 T13 35.39 276.08 27.3 334.2 130 60 130 30 53.19 111.2 2 T12 42.73 234.56 53.2 327.2 150 60 150 30 62.71 145.72 1- "'~ 3 Tl0 64.9 239.11 68.2 321·3. 130 72 130 18 63.27 186;23 4 T8 -16.11 209.81 60.6 312.7 146 11 146 79 55.68 169.32 5 T4 38.24 198.27 5~.6 328.2 84 8 84 82 64.&1 149.46 .. 6 T3 65.88 121.97 61.4 321.3 5 56 5 34 62.04 167.15 7 S2 62.28 322.n 360 10 31?0 80 63.38 168.79 ~ 8 S3 59.94 317.83 40 55 40 35 59.01 165.46 - 9 B3 24.1 204.33 67.72 296.49 108' 23 108 67 47.79 188.86 10 84 35.28 178.14 58.3 341.57' 68 4 68 86 75.38 142.83 11 86 54.4 297.5 106 7 106 83 42.07 168.07t' 12 88 38.75 321.65 64 o _ 64 90 51.53 134.06 13 810 55.27 318.72 91 30 91 60 ·57.65 156.29

14 812 56.22 323.92 23 40 23 50 61.81 154.1~ h,.. _. ~ . -..:..- ~~.~.

"f -~ Anticline Data Table ~

Core # Treatment Glnc GDec # points Steps into origin strike dip Alpha Beta 1 RH th 68.5 293.1 5 250-org 138 74 138 16 2 R1-2 th 17.2 41.20 12 100-org 138 74 138 16 3 R2-1 th 62.4 32.90 5 25D-org 130 70 130 20 4 R2-3 af 72.4 325.9 8 400-org 130 70 130 20 5 R3-1 af 48.2 168.3 6 150-600 148 72 148 18 6 R3-1b af 53.3 199.1 3 200-400 148 72 148 18

7 R3-2a af " 64.7 183.0 4 800-org 148 72 148 18 8 R3-2b af 53.6 191.2 8 400-org 148 72 148 18 9 R3-3a th 52.4 177.9 8 100-org 148 72 148 18 10 R4-1a th 46.5 184.3 8 100-org 132 58 132 32 11 R4-1b th 67.4 150.8 13 100-org 132 58 132 32 12 R4-2a th 38.2 173.3 10 100-org 132 58 132 32 13 R5-1 th 53.8 150.8 7 25D-org 132 30 132 60 14 R5-2a th 54.4 140.7 8 100-org 132 30 132 60 15 R5-3a af 67.4 187.5 9 200-org 132 30 132 60 16 R6-1a af 56.1 69.40 12 100-org 210 8 210 82 17 R6-2a th 42.4 99.20 6 100-325 210 8 210 82 18 R6-sa th 29.7 120.5 5 370-org 210 8 210 82 19 R7-1 th 67.5 160.6 6 100-350 42 10 42 80 20 R7-2a th 60.1 334.0 8 100-org 42 10 42 80 21 R7-3a th -53 332.1 3 425-org 42 10 42 80 22 R7-3b th -80.4 348.0 14 nnn-org 42 10 42 80 23 R8-1 af -44.6 225.3 3 100-200 332 45 332 45 24 R8-2a th -65.6 208.7 10 200-org 332 45 332 45 25 R8-3a th 60.9 184.7 3 500-org 332 45 332 45 26 R8-5a th -75.3 232.7 8 100-org 332 45 332 45 27 R9-1 th 35.6 2.600 3 560-org 332 70 332 20 28 R9-2a th 44.5 213.2 3 450-org 332 70 332 20 29 R9-sa th 32.7 213.4 5 250-org 332 70 332 20 30 R9-4a af 63.2 125.8 4 100-300 332 70 332 20 31 R10-1 th 67.8 154.6 6 150-350 330 58 330 32 32 R10-2 af 47 131.5 4 800-org 330 58 330 32 33 R10-3 th 48.7 197.9 3 500-org 330 58 330 32 34 R10-4 th 69.2 166.4 8 100-org 58 330 32 -~ 330 35 R10-5 af 63.3 154.1 6 600-org 330 58 330 32 36 R10-0 af 72.8 116.6 5 700-org 330 58 330 32

72 VITA ELIZABETH REBECCA SHERWOOD

PERSONAL Date of Birth: January 26, 1970; NY, NY Parents: Donald and Joan Sherwood I EDUCATION Master of Science, Lehigh University, Bethlehem, PA, 1994. Bachelor of Arts, Colgate University, Hamilton, NY, 1992.

EXPERIENCE .. Research Assistant, Lehigh University Geophysics Laboratory, January 1993-June 1994. Teaching Assistant, Environmental Geology, Optical Mineralogy, Lehigh University, Fall 1993-Spring 1994. Field Work, Lost River Range, Idaho, Summer 1992; Middletown, New York, Summer 1991. . Teaching Assistant, Physical Geology, Mineralogy, and Petrology, Colgate University, Fall 199G-Fa111991. . Colgate University Geology Off-Campus Study Group, Field work in New England, Summer 1990. . Research Assistant, Deformational and Metamorphic History of Taconic Flysch, Eastern New York and Western Vermont Summer and Fall 1990. Private Tutor, Physical Geology, Colgate University, Fall 1990.

PUBLICATIONS Sherwood, E. R., Kodama, K. P., Remagnetization Associated With Tertiary Igneous Activity, Lost Ri~er Range, Idaho. Abstract, EOS Transactions, Abstracts with Programs, Vol. 75, No. 16, p. 127, American Geophysical Union, 1994. Kodama, K. P., Cioppa, M. T., Sherwood, E., Warnock, A. C., Paleomagnetism of Baked Sedimentary Rocks, in the Newark and Culpeper Basins: Evidence for the JI Cusp and Significant Late Trias.sic Apparent Polar Wander from Mesozoic Basins of North America, Tectonics. in press. Sherwood, E. R., Paleomagnetic Investigation of Two Deformed Carbonate Structures, Lost River Range, Idaho. NE Paleomagnetism Workshop, research presentation, October 16, 1993. Sherwood, E. R., Preliminary Study of Strain and Cleavage Development in the Taconic Flysch of Southeastern New York. Colgate Journal of the Sciences, Vol XXIV, p. 137-144, 1992. Sherwood, E. R., Paleomagnetism of the Mid-Ordovician Taconic Flysch of Eastern New York. Col2ate Journal of the Sciences, Vol. xxm, p. 97-105, 1991. Schott, R., Meyer, W., Sherwood, E., Schulist, M., Goldstein, A., Deformational and Metamorphic History of Taconic Flysch, Eastern New York and Western Vermont. Abstracts with Programs, Geological Society of America Northeastern/Southeastern Section, p. 82, 1991.

HONORS Sigma Xi Scientific Research Society, Lehigh University Chapter, Inducted March 1993. • Palmer Reseach Grant, Department of Earth and Environmental Sciences, Lehigh University, June 1993. Paleontology Study Group, Colgate University, January 1992. Konosioni, Senior Honor Society, Colgate University, Spring 1991-Spring 1992. Hackett-Rathmel Research Scholarship, Colgate University, Summer 1991. National Science Foundation Research Grant, Summer 1990. Environmental Research Project, Awarded Honors, January 1989. ~