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Master's Theses and Capstones Student Scholarship
Spring 2011
Paleomagnetism of the Kittery Formation: A record of tectonism and rotation
Julianne Batchelder Boucher University of New Hampshire, Durham
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Recommended Citation Boucher, Julianne Batchelder, "Paleomagnetism of the Kittery Formation: A record of tectonism and rotation" (2011). Master's Theses and Capstones. 625. https://scholars.unh.edu/thesis/625
This Thesis is brought to you for free and open access by the Student Scholarship at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Master's Theses and Capstones by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. PALEOMAGNETISM OF THE KITTERY FORMATION: A RECORD OF TECTONISM AND ROTATION
BY
JULIANNE BATCHELDER BOUCHER
BS University of New Hampshire, 2008
THESIS
Submitted to the University of New Hampshire
In partial Fulfillment of
The Requirements for the Degree of
Master of Science
In
Earth Sciences: Geology
May, 2011 UMI Number: 1498946
All rights reserved
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In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMT Dissertation Publishing
UMI 1498946 Copyright 2011 by ProQuest LLC. All rights reserved. This edition of the work is protected against unauthorized copying under Title 17, United States Code.
ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 This thesis has been examined and approved. CfJM mJL Thesis Director, William C. Clydev Associate Professor of Geology
Wallace A. Bothner, Professor Emeritus of Geology
Laird, Associate Professor of Geology £ Joel E. JoMison, Assistant Professor of Geology ACKNOWLEDGEMENTS
I am very appreciative and thankful for the help, encouragement and constructive criticism of William Clyde, Wallace Bothner, and Jo Laird and Joel Johnson. I am also thankful to my husband for keeping me sane with his unusual sense of humor. Many thanks are due to my parents for their continual support. Also many thanks to William Clyde, Wallace Bothner, Andrew Lord, Daniel Jack,
Arthur Hussey II and my parents who helped in reconnaissance and field work.
Last but not least, many thanks to the UNH Earth Science Department for two years of financial support as a teaching assistant, and to the UNH Graduate
School for a summer 2010 Teaching Assistant Fellowship.
in TABLE OF CONTENTS:
ACKNOWLEDGEMENTS iii
LIST OF TABLES iv
LIST OF FIGURES v
ABSTRACT vii
CHAPTER PAGE
INTRODUCTION 1
I. REGIONAL GEOLOGY OF CENTRAL COASTAL NEW ENGLAND 8
II. STRATIGRAPHIC CORRELATIONS OF THE MERRIMACK GROUP 11
III. TECTONIC REGIME OF THE MERRIMACK GROUP 14
IV. THE KITTERY FORMATION 17
General lithologic descriptions 17
Stratigraphy 17
Folding 19
Faulting 20
V. PALEOMAGNETISM 22
Magnetic mineralogy and magnetizing rocks 25
Magnetic hysteresis 27
Kinds of natural remnant magnetism (NRM) 29
Tectonic uses of paleomagnetism 30
Anisotropy of magnetic susceptibility (AMS) 31
Isothermal remnant magnetism (IRM) 34
VI. FIELD TESTS AND MAGNETIZATION AGES 37
Fold test 37
iv Baked contact test 39
VII. X-RAY DIFFRACTION AND PETROGRAPHY 40
VIII. METHODS 41
Choosing field sites 41
Drilling procedures 46
Laboratory procedures 47
Data analysis 49
IX. RESULTS 51
Magnetic mineralogy 51
X-ray diffraction 57
Petrography 63
Natural remnant magnetism 64
Site and localities virtual geomagnetic poles 65
Fold tests 73
Baked contact tests 73
Anisotropy of magnetic Susceptibility (AMS) 80
X. DISSCUSIONS AND CONCLUSIONS 85
Magnetic mineralogy 85
Natural remnant magnetism (NRM) 89
Anisotropy of magnetic susceptibility 91
Tectonic and paleomagnetic history of the Kittery Formation 93
REFERENCES CITED 97
v LIST OF TABLES
l.a,b Demagnetization temperature steps 60
l.c AMS data in unfolded coordinates 60
l.d AMS data in folded coordinates 60
l.e Natural remnant magnetism data and virtual geomagnetic poles 60
LIST OF FIGURES
1. Paleogeography of the eastern margin of proto-North America during the Acadian orogeny- 2
2. Paleogeography of the eastern margin of proto-North America during the Acadian orogeny -2
3. Paleogeography of the assemblage of Pangea 3
4. Paleogeography of the rifting of Pangea 3
5. Geology of central coastal New England 7
6. Stratigraphic column of the Casco Bay Group and the Merrimack Group 12
7. Ordovician tectonic regime for the Central Maine Basin and the Merribuckfred Basin 13
8. Silurian tectonic regime for the Central Maine Basin and the Merrimuckfred Basin 13
9. Basics of Earth's magnetic field 20
10. Paleomagnetic poles and continental reconstructions 24
11. Aparent polar wander paths 24
12. Fold test figure 38
13. Baked contact test figure 38
14. Geologic map with drill sites 42
15. Portsmouth region geologic map 43
16. Wells region geologic map 44
17. Cape Elizabeth geologic map 45
18. Paleomagnetic drill 48
19. Core orienter 48
vi 20. SQUID spinner magnetometer 48
21a. IRM results at Cape Elizabeth 53
21b. IRM results at Pierce Island 53
22a. IRM results at Adams Point 54
22b. IRM results at Moody Point 54
23. XRD results 58
24. XRD results 59
25. Petrography results 60
26. Petrography results 60
27. Petrography results 61
28. Petrography results 61
29. Petrography results 62
30. Petrography results 62
31. Great circle demagnetization behavior 66
32. Unstable demagnetization behavior 66
33. Great circle demagnetization behavior 67
34. NRM results 69
35. NRM results 70
36. NRM results 71
37. VGP's and the APWP 72
38. Fold test results 74
39. Fold test results 75
40. Adams point baked contact test results 76
41. Moody Point baked contact test results 77
42. Ft. McClary baked contact test results 78
vii 43. AMS equal area projections unfolded coordinates 81
44. AMS equal area projections folded coordinates 82
45. Shape of the AMS ellipsoid 83
46. AMS plotted geographically 84
47. Chemical pathways for greigite formation 88
«
VIII ABSTRACT
PALEOMAGNETISM OF THE KITTERY FORMATION:
A RECORD OF TECTONISM AND ROTATION.
by
Julianne Batchelder Boucher
University of New Hampshire, May, 2011
The Kittery Formation is an early Silurian metaturbidite sequence that formed just before the Acadian Orogeny in central coastal New England. Despite a long history of tectonism and deformation, the Kittery Formation preserves primary sedimentary features suggesting that paleomagnetic data may further elucidate current tectonic and metamorphic interpretations of the Merribuckfred basin. A paleomagnetic study of the Kittery Formation was carried out to determine its original geographic location, to confirm its current age assignment, and to analyze its remagnetization history.
Seven or more cores were drilled from each of 17 different sites within the
Kittery Formation. All cores were demagnetized in thermal increments from 25 to
400°C and measured by a SQUID spinner magnetometer at the University of
New Hampshire. IRM, XRD, and reflected light microscopy confirm greigite as the dominant carrier of the ChRM. AMS indicates the percent anisotropy of Cape
Elizabeth and Ft. McClary is larger than 20%, while the rest were less than 16%.
ix To a first order, K1 at all sites follows the F2 fold directions of the Kittery
Formation in tectonic coordinates, suggesting a regional scale expression of the outcrop scale F2 folds with a wavelength of approximately 50 miles. At all localities the Kittery Formation fails the fold test because of tectonism and / or multiple generations of greigite growth. However, it does pass the baked contact test and therefore the magnetization age must be older than Jurassic, but younger than late Silurian/early Devonian. ChRM sample directions are well clustered within sites, but comparison of different sites do not cluster in either geographic or tilt adjusted coordinates. Some site VGPs cluster more closely with the middle Paleozoic of the North America APWP, and some are discordant.
This suggests rotation of fault bounded blocks and/ or magmatic shouldering during the Acadian and Alleghanian orogenies in central coastal New England.
These results also indicate that greigite can remain stable over hundreds of millions of years, which is significantly longer than previously documented. This thesis has been examined and approved. bJJZ nrj?JL Thesis Director, William C. Clyde> Associate Professor of Geology
Wallace A. Bothner, Professor Emeritus of Geology
aird, Associate Professor of Geology £ Joel E. Jonfnson, Assistant Professor of Geology INTRODUCTION
The geology of New England is made up of mostly accreted terranes, volcanic deposits, igneous intrusions, and lithotectonic sedimentary basins
(Keppie, 1989; Wintsch, 1997; Kent et al., 1978; Hussey et al., 2010 and
references therein). These units were formed and sutured together, during three
main orogenic events that affected the eastern margin of North America
throughout its geologic history (Keppie, 1989; Van der voo, 1990; Van der Pluijm
et al., 1993 and references therein). These orogenic events are known as the
Taconic orogeny from late Cambrian to middle Ordovician, the Acadian orogeny from late Silurian to middle Devonian, and the Alleghanian orogeny in the early
Carboniferous to late Permian. The Taconic orogeny involved the collision of an
island arc with the eastern margin of the continent Laurentia (proto North
America) beginning in the late Cambrian (Van der Voo, 1990; Keppie, 1989;
Thompson et al., 2007). Also at this time, two land masses called Baltica and
Avalonia were approaching Laurentia from a distance (Figure 1). Baltica was a
micro continent, and Avalonia was an island arc complex (Van Der Voo, 1990).
Collision of these land masses led to the Acadian orogeny from the late Silurian
to middle Devonian (Figure 2). This orogeny caused folding, regional
metamorphism and plutonic igneous activity (Fargo, 1995; Keppie, 1989; Hussey
et al., 2010; Escamilla-Casas, 2003; and references therein). The Alleghanian
orogeny was the last orogeny to contribute to the geologic history of
l fed
Laurent
Figure 1. Tectonic regime for the eastern margin of proto-North America (Laurentia). Figure after Miall, A.D. and Blakely, R.C. (2008).
Figure 2. Tectonic regime for the eastern margin of Proto-North America (Laurentia) in the early Devonian. Figure modified after Miall, AD. and Blakely, R.C. (2008).
2 **wa.
ray
feStujlffil^^ ^^y
s^^^fi
Figure 3. Tectonic regime for Proto-North America in the early Permian, showing the end of the Alleghanian orogeny in the early Permian and the assemblage of the super continent Pangea. Figure modified atter Miall, A.D. and Blakely, R.C. 2008.
Figure 4. Tectonic regime for Proto-North America in the eariy Jurassic, showing extension, the break up of Pangea, the beginning of the current Mid-Atlantic spreading ridge system and Atlantic ocean. Figure after Miall, A.D. and Blakely, R.C. 2008.
3 central coastal New England. This orogeny involved the collision of Laurentia and the continent Gondwanna to form the supercontinent Pangea in the early
Carboniferous to late Permian (Figure 3). This orogeny is inferred by many geoscientists to have caused additional regional metamorphism, strike-slip faulting and shear in some of the igneous intrusions and sedimentary basins in central coastal New England which formed during the Acadian orogeny. The
Norumbega fault system in central coastal New England and New Brunswick
Canada is the fault system that caused deformation and strain in this region at this time (Swanson, 1992,1999; Escamilla-Casas, 2003; Boeckeler, 1994;
Bothner and Hussey, 1999). During the Triassic through Jurassic, the current configuration of North America and the continents as we know them today began to form via the rifting of Pangea. This rifting opened the Atlantic Ocean and its current mid-ocean ridge spreading system, in addition to the intrusion of multiple dikes and volcanic complexes in central coastal New England and along the
Eastern Atlantic seaboard in North America (McHone, 1984; Swanson, 1992;
McEnroe, 1989; Hussey et al., 2008; Figure 4).
The geologic record left behind by this sequence of orogenic events is complex and sometimes enigmatic. In particular, the age, provenance, and correlative relationships of the lithotectonic sedimentary units within the same tectonic basin can be difficult to assign because they lack fossils and are fault bounded, folded (sometimes in multiple generations) and / or highly metamorphosed. Yet the sedimentary units within these lithotectonic basins make up a large portion of central coastal New England and thus can provide 4 great insight into the timing and tectonic evolution of central coastal Maine and
New Hampshire.
This thesis is based on a paleomagnetic study of the Kittery Formation within the Merrimack Group of the Merribuckfred lithotectonic Basin (Hussey et al., 2010). The Kittery Formation is unusual in that it has the potential to provide invaluable paleomagnetic data compared to other formations within the
Merribuckfred Basin. The Kittery Formation is an early Silurian metaturbidite sequence that has been multiply deformed, variably metamorphosed mostly to greenschist fades, intruded by igneous activity, and yet still retains well documented, primary sedimentary features (Fargo and Bothner, 1995). Other units in the Merribuckfred Basin have fewer primary stratigraphic features, and the features preserved are not completely diagnostic of stratigraphic up direction
(Tucker et al., 2001; Hussey et al., 1993). The existence of primary sedimentary features in the Kittery Formation makes it possible to apply paleomagnetic methods which could be valuable for regional tectonic reconstructions. The age of the Kittery Formation has been debated and reassigned several times from
Precambrian (Hussey et al., 1984) to Devonian (Bothner et al., 1993) and is currently assigned an age of late Ordovician to early Silurian based on U/Pb dating of two detrital zircon grains in southern Maine and cross cutting relationships with the 407 Ma Devonian Exeter Pluton (Hussey et al., 2010;
Wintschetal.,2007).
5 Paleomagnetic analysis of the Kittery Formation has the potential to test the current age assignment, correlative relationships, and geographic location of this unit during its tectonic evolution from deposition through deformation. The paleomagnetic information the Kittery Formation could provide is a paleomagnetic pole. Additionally, studying the magnetic mineralogy of this unit could help constrain the current age and tectonic model for the Acadian orogeny in central coastal New England. To date, the main methods used to understand the Kittery Formation have been geologic mapping, cross cutting relationships and isotopic dating. No widespread or detailed paleomagnetic studies have yet been performed on the Kittery Formation or in the Merrimack Group as a whole.
However, some previous magnetic studies has been completed in the area such as an aeromagnetic survey (Bothner and Hussey, 1999), a ground magnetic survey of Adams Point (Willard, 2000), and a passed dike test between the Cape
Neddick Complex and the Kittery Formation (McEnroe, 1988). These results are useful but do not provide detailed information of magnetic mineralogy or paleogeography for this region.
Because the Kittery Formation is one of the least metamorphosed sedimentary units in central coastal Maine and New Hampshire, it could still record primary magnetizations as well as other later remagnetizations associated with subsequent geologic events. Therefore, the goal of this research is to evaluate the paleomagnetism of the Kittery Formation from different metamorphic and tectonic regions of importance to compare with the apparent polar wander path (APWP) for North America to get an age and geographic location of the 6 Kittery Formation during different stages of its geological history (deposition, deformation, and metamorphism). Additionally, studies of the magnetic mineralogy in the Kittery Formation will also be undertaken to add insight to the virtual geomagnetic pole data and further constrain its tectonic history.
Figure 5. Geology of central coastal New England, delineating the different geologic units that encompass the Merribuckfred Basin. Figure after figure 2 in Hussey etal., (2010). 7 I. REGIONAL GEOLOGY OF CENTRAL COASTAL NEW ENGLAND
There are five main terranes that are relevant to this study, which make up central coastal Maine and New Hampshire: the Avalon terrane, the Merrimack terrane, the Putnam-Nashoba terrane, the Central Maine terrane, and the
Fredericton terrane. The Avalon terrane is composed of intrusive and extrusive igneous rocks, and it is thought to be part of the accreted island arc Avalonia which collided during the Acadian orogeny. The rocks of this terrane crop out from Long Island Sound to northeastern Massachusetts and in the northern most part of the Gulf of Maine and maritime Canada west of the Meguma terrane
(Wintsch et al., 2007). The Merrimack terrane is a fault-bounded slice of sandy, silty and calcareous metamorphic rocks extending from south central Connecticut to the Gulf of Maine (Wintsch et al., 2007). This terrane is in fault contact with the Putnam-Nashoba terrane in Connecticut and Massachusetts and the Rye
Complex in New Hampshire. Originally, the rocks of the Merrimack Group
(Berwick Formation, Eliot Formation, and Kittery Formation) were assigned to the
Merrimack terrane because of lithologic similarity. However, based on SHRIMP
U-Pb dating of detrital zircons, two distinct provenances were determined for the traditionally assigned Merrimack terrane in Connecticut and Massachusetts and the Merrimack group of New Hampshire (Wintsch et al., 2007). Therefore, the
Merrimack group which contains the Kittery Formation and the Eliot Formation studied here is now reassigned to a new tectonostratigraphic basin named the
8 Merribuckfred Basin by Hussey et al. (2010). Additionally, Wintsch et al. (2007) assigned the Merrimack group to the Fredericton terrane, thus extending the
Fredericton terrane into southern New Hampshire.
The Putnam-Nashoba terrane is a mix of medium-to-high grade paragneiss and orthogneiss, which is separated to the west and northwest from the Merrimack terrane by the Clinton Newbury Fault system. It is separated to the east and southeast by the Honey Hill-Lake Char-Bloody Bluff fault system
(Wintsch etal., 2007).
The Fredericton terrane encompasses the Merribuckfred Basin which consists of the Merrimack Group (late Ordovician to Early Silurian), Casco Bay group (middle to late Ordovician), Bucksport Formation (late Ordovician to early
Silurian), and East Harpswell group (late Ordovician to early Silurian, Hussey et al., 2010). The Merrimack group consists of the Eliot Formation stratigraphically underlying the Kittery Formation in conformable contact (Hussey et al., 2010).
The Casco Bay group consists of the Jewel Formation (phyllite), Spurwink
Formation (limestone), Scarboro Formation (phyllite), Diamond Island Formation
(slate), Spring Point Formation (greenstone), Cape Elizabeth Formation (slate), and the Cushing Formation (extrusive igneous, Hussey et al., 2010). The Eliot
Formation and the Jewel Formation are interbedded, which strongly suggests that the Casco Bay Group and the Merrimack Group are conformable (Figure 6).
The Bucksport Formation crops out in the Boothbay Harbor area and is composed of feldspathic and calcareous metawackes, with minor sulfidic shale
9 (Hussey et al., 2010). The Bucksport Formation is younger than the Casco Bay
Group, but is structurally underlying it, causing Hussey et al., (2010) to interpret the contact between the Casco Bay Group and the Bucksport Formation to be separated by a folded thrust fault or an overturned limb of a nappe fold. For more specific descriptions and structural data of the Merribuckfred basin and the stratigraphy of southwestern Maine, see Hussey et al., (2010) and Hussey,
(1968).
10 II. STRATIGRAPHIC CORRELATIONS OF THE MERRIMACK GROUP
The rocks of the Merrimack group can be difficult to correlate regionally due to folding, faulting, and gradational high-grade metamorphism. For example, the correlations of the oldest formation in the Merrimack group, the Eliot
Formation, is uncertain north of Portland, Maine because the Eliot Formation increases in metamorphic grade, becomes migmitized in places and becomes difficult to correlate with the Hitchens Corner Formation in the Central Maine
Basin (Hussey et al., 2010). Additionally, correlations of the Eliot Formation to the east and west are undetermined due to the fact that to the east it is bounded by the Falmouth-Brunswick sequence, and to the west it is fault bounded by the
Nonesuch River Fault (Hussey et al., 2010). The Kittery Formation crops out from south of Portsmouth, NH to its most northern
11 MERRIMACK GROUP
CASCO BAY i^^.^Jr^^AV^^*y'i,w^^^^^»^^t*i GROUP 5CAPE BUZABETH FORMATIONS
!^5SS5^ /iison Ccvo M -
-»MCUSH1NG FORMATIONX-X
Figure 6. Stratigraphic Column showing the relationship and conformable contact between the Casco Bay Group and the Merrimack Group and shows the interfayering of the
Jewell Formation and the Eliot Formation. Figure modified after figure 45 Hussey et aLt (2010).
12 point in Cape Elizabeth, Maine. The Kittery Formation in the Cape Elizabeth locality was correlated originally to the pelitic Cape Elizabeth Formation, however it has been reassigned to the Kittery Formation based on lithological similarity to the Kittery Formation in southern New Hampshire and Maine (Katz, 1917;
Hussey and Bothner, 1995). To the northwest, the Kittery Formation is bounded by the right lateral Broad Cove fault, which is part of the Norumbega fault system.
For other correlative relationships in the Merribuckfred Basin see Hussey et al.,
(2010).
13 III. TECTONIC REGIME OF THE MERRIMACK GROUP AS PRESENTLY
INTERPRETED
In the Ordovician, the Casco Bay Group and the Jewell Formation were deposited in the Casco Bay backarc basin, and the Eliot Formation of the
Merrimack Group was beginning to be deposited, allowing the interlayering of the
Casco Bay Jewell Formation and the Eliot Formation seen in stratigraphic sequence today (Hussey et al., 2010). The Falmouth Brunswick Casco Bay arc
(FBCB) forms the relief separating sedimentation between the Central Maine
Basin units in the forearc basin, and the Merribuckfred Basin in the backarc of this subduction zone setting (figure 7, Hussey et al., 2010).
By early Silurian, the FBCB had eroded sufficiently such that it was no longer separating the two basins. This is when the Kittery Formation began deposition in the Merribuckfred Basin (figure 8A). By late Silurian (420-425 Ma), sedimentation in the Merribuckfred Basin had ceased, and the first pulse of the
Acadian Orogeny caused uplift, deformation, metamorphism, initiation of the
Boothbay thrust, and plutonic igneous activity (figure 8B). This uplift in the late
Silurian through early Devonian in the Merribuckfred Basin began erosion of the
Merrimack group into the Central Maine Basin (figure 8B). This uplift, erosion and deposition of the Merrimack group into the Central Maine Basin was one of the primary source of material for the Berwick Formation, which supported the reassignment of the Berwick Formation to the Central Maine Basin (Hussey et
14 al., 2010). Deposition in the Central Maine Basin ended by a later main phase of the Acadian Orogeny (400-375 Ma). This main pulse of the Acadian Orogeny caused regional metamorphism and deformation of the Central Maine Basin, in addition to a second phase of deformation, metamorphism and intrusion of igneous rocks into the units in the Merribuckfred Basin (Hussey et al., 2010).
Subsequent movement along both ductile and brittle fault zones such as the
Great Commons Fault Zone (GCFZ), the Portsmouth Fault Zone (PFZ), and the
Nannie Island Fault Zone (NIFZ), which are most probably extensions of the
Norumbega fault system, caused additional shearing along with another potential generation of folding (Bothner and Hussey, 1999; Escamilla-Casas, 2003). Lastly, as Pangea rifted apart, the Merribuckfred Basin was cut by several extensional faults and intruded by basaltic and diabase dikes (McHone, 1984; Swanson,
1992).
15 CENTRAL MAJKg FAiMOUTMBRUNSWiC* . ME*Riauc«Fft£D BAStN BASIN CASCO DAY ARC
Figure 7, Late Ordovician tectonic egime for the Merribuckfred Basin and the Central Maine Basin. Dssj = Diamond L, Scarboro, Spurwink, and Jewell Fms Sp = Spring Point Formation, Ce = Cape Elizabeth Formation, Cu = Cushing Formation, Fb - Falmouth-Brunswick Volcaniclastics, Fbv = inferred Falmouth-Bruinswick Volcanics, Mb = inferred Miramtchi basement, Mg = Merrimack group. Figure Modified after figure 9, Hussey et aiM (2010),
ri = proposed site of Merrimack Group deposition according to Hussey et alM (2010).
(?$mM&t$ttfmm Cemm Ubim basin feast Harpswetf Group (KHGJ
ana aider sediments Hue**»cosmf Ocean hthosphete
A Earty SiJurian (tate Llandovery)
ManffticicfoHt <^*ermod bett Cmtim *6mm 8a*i« Te*e» ar* £ulV €>*«• Pew
Asthenosphere ***** f^, Appi&tm f?Kt§» and older saOimenis B SlSunan {Wenlock} through Earty Devonian em
LJ - location of the Kittery Formation and the Merribuckfred Basin Figure 8. General tectonic and sedimentation regime for the Central Maine and Merribuckfred Basins m the early Silurian and the early Devonian. A) Durring the early Silurian time, the Kittery Formation has already been deposited in the Merribuckfred Basin. B) Durfmg the late Silunan through early Devonian time, the Kittery Formation has already undergone folding, metamorphism. intrusion by igneous activity and uplift, it is also this time that the Kittery Formation was eroded and deposited into the Central Maine Basin, Figure modified after figure 10, Hussey et al., (2010).
16 IV. THE KITTERY FORMATION:
General Litholoqic Descriptions:
The Kittery Formation is an early Silurian low greenschist to amphibolite fades turbidite sequence with variably limy, sandy, and sulfidic phyllite beds
(Hussey et al., 2008). The primary sedimentary structures preserved in this unit are graded bedding, flute casts, flame structures, occasional rip-up mud clasts, small scale cross laminations, and channel cut and fill structures (Hussey et al.,
2010; Rickerich, 1983). This unit weathers grayish purple in quartz and feldspathic rich beds, and rusty brown in the pelitic units (Escamilla-Casas,
2003). Escamilla-Casas (2003) identified a few suspect biogenic structures in the Kittery Formation, but they are neither abundant nor definitive.
Stratigraphy:
Rickerich (1983) used the primary sedimentary structures and the westward directions of these structures to interpret the Kittery Formation as a lobe fades of a submarine fan in a continental rise environment. He also proposed that the primary sedimentary structures suggested an eastward depositional source in present day coordinates, interbedded with contourite deposits from a northwest flowing current. Rickerich (1983) identified four main kinds of laminae and several kinds of cross bedding, which he used to refine four subfacies: S1, S2, S3, S4. The subfacies S1 is characterized by thick bedded, medium to coarse-grained metasandstones. These beds have a very high
17 metasandstone to phyllite ratio, little to no change in grain size from the top of the metasandstone bed to the bottom, and are very poorly sorted (Rickerich, 1983).
S2 is a graded, fine to medium grained often laminated metasandstone. Bed thickness for this unit is variable and ranges from greater than one meter to fewer than ten centimeters. S3 is manifested by well-developed, extremely thin parallel laminations and small scale cross bedding throughout the metasandstone beds, and are frequently weakly graded. S4 is manifested by very thin phyllite layering with little to no metasandstone interlayering.
Escamilla-Casas (2003) subdivided the Kittery Formation into three subunits based on lithic composition in Southern New Hampshire to help identify the contact between the Eliot Formation and the Kittery Formation. These subunits are as follows: SOka, SOkb, and SOkc. SOka is characterized by light brown metasandstone interrupted by a dark brown weathering phyllite. This subunit usually has multiply preserved primary sedimentary structures. Quartz, feldspar and biotite are common mineral assemblages in this unit. SOkb is a light brown to light grey metasandstone interrupted by dark phyllite.
Determination of stratigraphic up direction can be difficult in this unit due to contacts with intermittent pelitic layers being very sharp. X-ray diffraction by
Escamilla-Casas (2003) determined common minerals in this unit are biotite, quartz, feldspar and chlorite. SOkc is characterized by light brown massive metasandstone beds, interrupted by very thin layers of dark phyllite. This unit is essentially void of primary stratigraphic structures, and Escamilla-Casas (2003)
18 interpreted this unit as the probable basal layer of the Kittery Formation between the conformable Eliot and Kittery Formation.
Folding:
Rickerich (1983) found evidence for three generations of folding in the
Kittery Formation: 1) Recumbent soft sediment slump folding, 2) recumbent folding, and 3) upright chevron and open folds that refold earlier recumbent folds.
In general, outcrop of the recumbent folding is scarce, but the chevron and open folds are common at outcrop scale in the Kittery Formation. Rickerich (1983) also assumed little to no vertical axis rotation (no more than 3 degrees) of the
Kittery Formation from calculated displacements of the PFZ and GCFC at the time of study.
Escamilla-Casas (2003) reinterpreted the folding style of the Kittery
Formation. His results were determined by field work, microstructural analysis,
3-dimensional computer analysis of folding, and finite element analysis of deformed pyrite crystals. He interprets that there was one main folding event in
both the Rye complex and the Merrimack group. He determined that the second apparent generation of folding was due to transpression which significantly deformed the first generation of folding to create a long-short-long fold geometry, where the short limb was usually very steep to overturned. Bothner per comm.
interprets the change of geometry of the first generation of folds due to transpression as a second generation of folding. Escamilla-Casas (2003) and
Willard (2000) also determined that it was differing lithology and thus different
19 rock competence during folding that caused different fold geometries in the
Kittery Formation, varying from chevron, to sinusoidal, to open folding. In areas near ductile shear bands, Escamilla-Casas (2003) did find two distinct fold generations, which he attributes to ductile shearing. Escamilla-Casas (2003) also found that the orientation of the axial planes of the F2 folds in the Kittery
Formation in the study area are deflected and different from each other, such that the relative deflection decreases with increasing distance from ductile shear zones in the Durham and Portsmouth Harbor region. In addition, he also found evidence for anticlastic bending of the fold hinge surfaces, suggesting that the fold hinge surfaces are irregular.
Fargo and Bothner (1995) describe evidence for two generations of folding in the Kittery Formation and evidence for rotation of the Kittery Formation in the
Great Bay region of Durham of up to 90 degrees due to emplacement of the large Devonian Exeter pluton. This rotation is due to magmatic shouldering, which is a vertical axis rotation caused by the extension in the host rock from the intrusion. Lastly, Fargo and Bothner (1995) suggested one generation of regional metamorphism instead of two because of the low grade metamorphism preserved in the Kittery Formation.
Faulting:
The major fault system in central coastal New England, and extending to central New Brunswick Canada, is the Norumbega fault zone (Escamilla-Casas,
2003; Swanson, 1995; Bothner and Hussey, 1999; and references therein).
20 Bothner and Hussey (1999) proposed a probable extension of this fault zone to southern Maine and New Hampshire, suggesting that the Portsmouth and Great
Commons fault zone were part of the Norumbega fault system. The Portsmouth fault zone is a 100-300 meter wide northeast trending and northwest dipping, ductile fault zone. After significant amounts of ductile deformation, this fault zone was uplifted such that the fault system transitioned to a brittle deformational structure (Escamilla-Casas, 2003; Swanson, 1995). The Portsmouth fault zone forms the contact between the Kittery Formation and the Rye complex. The ductile structure that is part of the Portsmouth fault zone has a mostly right lateral movement sense, whereas the brittle movement sense of this structure is mostly a dip slip motion with the northwest side down (Bothner and Hussey, 1999;
Escamilla-Casas, 2003). The Great Commons fault zone is approximately 50 meters wide within the Rye complex and separates less migmitized rocks in the southeast from more migmitized rocks in the northwest (Escamilla-Casas, 2003;
Carrigan,1984; Welsh, 1993). The last movement of this ductile zone is determined to be approximately 277+/-16 Ma, in the Carboniferous/Permian, by
Rb/Sr dating (Boeckeler, 1996). Lastly, the Nannie Island phyllonite is a narrow northeast trending shear zone approximately 200 m wide with a mostly right- lateral sense of shear (Escamilla-Casas, 2003; Bothner and Hussey, 1999).
21 V. PALEOMAGNETISM
Paleomagnetism is the study of the record of the earth's magnetic field preserved in various magnetic minerals throughout time (Butler, 1992). To a first approximation, the earth's magnetic field over long timescales can be viewed as a geocentric axial dipole (GAD). The main features of the GAD is that the center of the earth is modeled as a simple dipole (e.g. bar magnet) and magnetic field flux lines surround the earth, varying in intensity and direction by latitude. The magnetic field lines that form from a GAD have a direction such that near the surface projection of the positive magnetic pole (south geographic pole) the magnetic field lines point outwards from the earth, and near the negative magnetic pole (north geographic pole) the flux lines point into the Earth (Figure
8). Similar to any magnetic field, this field exerts a magnetic torque and aligning direction on magnetic substances within the field. The geocentric axial dipole model has another component to it: a magnetic pole, or magnetic pole projection. The position of this pole is the geographic location of the projection of the negative or positive end of the dipole onto the earth's surface. This feature of the geocentric axial dipole is called the geomagnetic pole and acts as a relative
"anchor" for observing past plate movements (i.e., continental drift reconstructions, supercontinent assemblages; Butler, 1992; Figure 9).
22 ijT&P^**mm*'^w^-^:*w*w »«c
Figure 9. a) Generalized representation of the geomagnetic field showing the elements of a Geocentric Axial Dipole. M is a dipole in the center of the earth aligned with the rotation axis, H is the magnetic field, and I is the angle from the horizontal, or inclination. Declination not shown. This configuration produces the magnetic field directions at the surface of the Earth, varying \n magnitude and direction depending on location. Figured modified after figure 1.3, Butler, (1992). b) Geocentric axial dipole showing the north geographic pole, south magnetic pole* south geographic pole, north magnetic pole. Also note the field lines surrounding the Earth and model dipole aligned with the Earth's axis. Figure copyrighted from Addison Wesley Longman inc 2009.
23 Fixed pole
Fixed continent Wandering continent (a) (b)
Figure 10. Two different possibilities with respect to differences in observed continental paleomagnetic poles through time and the geomagnetic pole, a) The continents remain stationary, and the paleomagnetic poles wander relative to the geomagnetic pole, b) The pole for the continent remains fixed relative to the geomagnetic pole, and the continent wanders. Figure modified after Marshak (2001)
Figure 11 . The Aparent Polar Wander Paths (APWP) for both North America and Europe. O = Ordovician, S - Silurian, D = Devonian, C - Carboniferous, P ~ Permian T = Triassic, J = Jurassic, L = Lower, M = Middle, U = Upper. Figure modified after figure 10.9, Butler, (1992).
24 If the earth's geomagnetic field is accurately described by a geocentric axial dipole model, the geomagnetic poles should project right on top of the earth's current geographic north and south pole, aligned with the earth's rotational axis (Butler, 1992). It has been observed that this is not the case, and that the magnetic north pole actually wanders around the geographic north pole
(Butler, 1992). Therefore, this suggests there are non-dipole components to earth's magnetic field. Despite these non-dipole components, the GAD model is still used because over geologic time scales (e.g., 2000 years or more), the wandering of the earth's geomagnetic pole averages to the GAD. For most paleomagnetic studies, the time scales are over millions of years; therefore the assumption of a GAD model for Earth's magnetic field is more than sufficient
(Butler, 1992; Tauxe 2005). Another important feature of the earth's magnetic field is that the magnetic poles have reversed polarity periodically throughout earth history. This change has been abundantly recorded in marine and terrestrial rocks and forms the basis of the Geomagnetic Polarity Timescale
(GPTS).
Magnetic Mineralogy and Magnetizing Rocks:
All minerals will respond to an applied magnetic field. What determines if the mineral 'records' the direction of the applied magnetic field depends on how the mineral responds to the applied field. The magnetic responses of minerals are categorized into three groups: diamagnetic minerals, paramagnetic minerals, or ferromagnetic minerals (Butler, 1992).
25 Diamagnetic minerals acquire a small induced magnetization opposite to the applied magnetic field. The induced magnetization of the sample is linearly dependent on the applied magnetic field and reduces to zero when the field is removed. The application of the magnetic field interferes with the orbital motion of the atoms electrons, creating a temporary induced magnetization opposite to the applied field. If the mineral does not have atoms that have a magnetic moment due to unpaired electron spins and/or unfilled orbitals, this is the only magnetization that the mineral will temporarily experience (Butler, 1992; Tauxe,
2005).
Paramagnetic minerals contain atomic magnetic moments, but they do not interact with each other. When a magnetic field is applied to a paramagnetic substance, the magnetic field aligns the individual magnetic moments in the direction of the applied field, so the sample obtains a magnetization in the direction of the applied field. Like the diamagnetic substance, once the applied field is removed, the magnetization reduces to zero (Butler, 1992; Tauxe, 2005).
Ferromagnetic substances have atomic magnetic moments that strongly interact with adjacent atomic magnetic moments. This causes an induced magnetization from an applied field much stronger than the paramagnetic case, and upon removal of the applied field, the magnetization does not return immediately to zero. It is these kinds of minerals that record and hold the direction of the earth's magnetic field over geological timescales. The magnetization in these materials is temperature dependent, where at a certain
26 temperature for each mineral, the thermal energy causes enough interatomic distance such that the interacting atomic moments no longer interact, resulting in a magnetization of zero. This temperature at which magnetization in ferromagnetic minerals reduces to zero is called the Curie temperature, and is different for different ferromagnetic mineral phases. Above the Curie temperature, the ferromagnetic substance becomes paramagnetic (Butler, 1992).
The previous discussion of magnetic minerals was for one mineral grain.
Each mineral grain does not rotate towards the magnetic field like a compass needle; instead, depending on the size of the mineral grain, individual magnetostatic zones form dipolar domains within the crystal that rotate towards the applied field within the crystal. Large grains break into many domains within one grain (multidomain grain), and small grains will not (single domain grains). In general, single domain grains have a higher magnetic moment than multidomain grains. In a rock as a whole, the sum of the different directions of each ferromagnetic mineral adds up to the net direction of magnetization in the rock as a whole (Butler, 1992; Tauxe, 1995).
Magnetic Hysteresis:
When a magnetic field of a particular strength is applied in a particular direction, the domain(s) of the ferromagnetic grains will begin to rotate in the direction of the applied field. When all the magnetic moments within the ferromagnetic particles in the rock are aligned with the applied field, this is called the saturation magnetization of the rock. However, if the field strength does not
27 reach saturation magnetization, some ferromagnetic particles can still be oriented randomly. When the magnetic field is removed, the magnetic domain(s) will rotate back to the direction that minimizes magnetostatic energy. The vector sum of all the magnetic domain(s) directions of all the mineral grains in the rock sums to the direction of the last applied field and is the remnant magnetization of the sample. This net direction is called the natural remnant magnetization of a rock (NRM), and may be the original magnetization of the rock when it formed
(Butler, 1992; Tauxe, 2005). If a magnetic field with the same magnitude but an opposite direction is then applied to the sample, the magnetic domain(s) will then begin to rotate in the new direction. Then, the magnetic domain(s) will again relax to the direction of minimum magnetostatic energy. The sum of all the domain(s) and grains of the sample will then add to a net magnetization of zero.
This is called hysteresis or a hysteresis loop and is the physical process
responsible for recording ancient directions in a rock (Butler, 1992; Tauxe 2005).
Due to the nature of hysteresis, long exposure to different orientations of the geomagnetic field can cause a Viscous' remnant magnetization in the sample, or an 'overprint direction'. Many times this direction is the same as the current geomagnetic field and can be isolated by demagnetization procedures; however the secondary component can be ancient as well. Additionally, rocks can be thermally reset by a heat source beyond the unblocking temperature for the ferromagnetic mineral, causing the grains to realign their magnetic domains with the direction of the applied geomagnetic field (Butler, 1992; Tauxe, 2005).
28 Kinds of natural remnant magnetization (NRM):
There are three main kinds of processes that can cause the acquisition of a natural remnant magnetization: TRM, CRM and DRM. TRM is thermoremnant magnetization, and it is common in the cooling of igneous rocks. In this process, rocks cool below their unblocking temperature, and the orientation of the magnetic field at that locality and time is locked in the ferromagnetic minerals
(Butler, 1992). CRM is a chemical remnant magnetization which is commonly secondary to the formation of the rock and forms by precipitation, or degradation of other ferromagnetic minerals to create a secondary magnetization. This kind of magnetization is commonly preserved in sedimentary red beds. Sometimes, the time of the CRM can be very close to the actual formation of the rock sample and can be counted as a primary signal to a first order (Butler, 1992). Finally,
DRM is called detrital remnant magnetization. In the case of DRM, the fine grained detrital ferromagnetic minerals in the sediment actually rotate towards the direction of the geomagnetic field at the time of deposition. The vector sum of the directions of these ferromagnetic particles represents the natural remnant magnetization in the samples. For a more in-depth and quantitative description of magnetic fields, magnetic domains, hysteresis, and kinds of NRM, see Butler
(1992) and Tauxe (2005).
To isolate the NRM in the lab, rock samples are demagnetized via stepwise thermal or alternating field demagnetization. At these different temperatures and/or magnetic fields, the rock samples slowly begin to
29 demagnetize. These demagnetization data forms a vector representing intensity and direction of the NRM. If the sample is characterized by more than one stage of remnant magnetization, then the different components can often be distinguished (Butler, 1992).
Tectonic Uses of Paleomagnetism:
The inclination and declination of the magnetic field varies on a continental scale, therefore continental scale paleomagnetic reconstructions are usually represented by a paleomagnetic pole (Van der Voo, 1993). A paleomagnetic pole is the surface projection of the negative end of a geocentric dipole that explains the observed declination and inclination of a particular locality or continent on the surface of the earth (Figure 10). If the continent has not moved from the present location, this paleomagnetic pole should fall directly on the time averaged GAD. If the pole does not fall directly on the GAD, there are two possible interpretations. One, the geocentric axial dipole is not an acceptable model for the earth's magnetic field. However, it is well accepted by paleomagnetists that this model is an acceptable assumption when secular variation is averaged over a few thousand years (Butler, 1992; and Tauxe, 2005).
The second interpretation is that the continents have moved in the past (Figure
10). To reconstruct the geographic location of a continent at a particular time of interest, the calculated paleomagnetic pole is rotated along a great circle to rest on top of the geomagnetic pole. The corresponding location of the continent after this rotation is the geographic location of the continent during this period in
30 geologic time. This is one simple way of constructing plate motions in the past.
However, there is no physical law that continents must follow a great circle when moving across the globe. Therefore, many paleomagnetists construct the path traveled by continents by an apparent polar wander path (APWP). An apparent polar wander path is the sequence of poles of a continent plotted through time on the globe (Figure 11). Usually, the poles of these paths converge towards the location of the present geomagnetic pole as the age approaches the present
(figure 11). The apparent polar wander path is the preferred method for constructing a continent's movement through time because of the ambiguity in longitude associated with the previously mentioned great circle method.
However, Mesozoic and Cenozoic paleolongitude and latitude are calculated and known reasonably well for well sampled continents because of relatively good additional geologic evidence such as the sea floor paleomagnetic record and inferred latitude based on depositional environment information (Butler, 1992;
Van der voo, 1993; Tauxe, 2005).
Anisotropy of Magnetic Susceptibility (AMS):
Many rocks show anisotropy of magnetic susceptibility. Magnetic susceptibility is a dimensionless measurement of how easily an applied magnetic field can induce a magnetization in a rock or mineral sample (Tauxe, 1995; Birch,
1978). Therefore, if a rock sample shows anisotropy of magnetic susceptibility, then it is easier to magnetize the sample or rock in some directions than others
(Tauxe, 1995). The AMS is a measure of all the minerals in a rock, and therefore
31 is not limited to just the minerals carrying the magnetization. When susceptibility is anisotropic, a full tensor (3x3 matrix) is required to describe the anisotropy completely (Tauxe, 1995). Results are shown as an ellipse with three axes
(eigenvalues of the tensor), of maximum anisotropy (k1), intermediate anisotropy
(k2), and minimum anisotropy (k3) directions. The magnetic lineation (L) in a sample is the ratio of k1/k2, and the magnetic foliation (F) is the ratio of k2/k3
(Hrouda et al., 1976). These directions can then be reoriented into geographic coordinates which gives a geologically significant interpretation of the directions of maximum, intermediate, minimum magnetic anisotropy, and magnetic lineation and foliation of the rock as a whole. AMS can be caused by the crystallography of the minerals present in the rock or the grain shape of the minerals in the rock
(Birch, 1978). Possible causes of AMS include flow direction of magmas and lavas (fluid flow orienting grains in a particular direction), direction of sedimentary transport in sedimentary rocks, magnetotactic microbial action, tectonic applications such as qualitative correlations of the AMS ellipsoid with the strain ellipsoid, initial shortening due to folding, and potential lineation and or foliations due to directional metamorphism, and shear (Tauxe, 1995; Birch, 1978; Martin-
Hernandez et al., 2004). Many times, if a rock has undergone some sort of tectonic stress, AMS studies can detect a tectonic petrofabric before it is obvious at the outcrop scale (Martin-Hernandez et al., 2004). Sometimes there is a combination of a 'primary' AMS fabric and a tectonic fabric, and this can take skill in deciphering. Many attempts have been made to quantitatively correlate the
AMS ellipsoid to the principle axes of incremental and finite strains, with or
32 without other strain markers. So far, this has not proved very successful quantitatively, but qualitatively, there is some relationship between the two
(Martin-Hernandez et al., 2004). Lastly, large percent anisotropy in rocks can cause a directional deflection of remnance directions at a particular site
(Borradaile, 1997) so AMS studies can help determine whether deflection could be a problem in a paleomagnetic data set. The greater the percent anisotropy, the more likely the direction of the ChRM at a site is changed due to the anisotropy (Martin-Hernandez et al., 2004). The goal of this study is to give a first order look at the varying amounts of anisotropy at each locality and see general trends and possible reasons for the directions of the AMS ellipsoid at each locality and for the Kittery Formation as a whole.
In general, AMS foliation in sedimentary rocks is a combination of depositional processes and diagenetic compaction (Tauxe, 1995). The magnetic lineation can result from currents in marine settings or wind in continental settings. When the rock has been strained, the magnetic lineation begins to record quickly an imprint of this strain (Hrouda et al., 1976). The magnetic lineation records beginning tectonic shortening or extension in the rock and is resistant to further deformation. The magnetic foliation is more resistant to early tectonic deformation but continues to record increases in deformation as the deformation proceeds (Hrouda et al., 1976; Martin-Hernandez et al., 2004). In the case of low grade metamorphic sedimentary rocks, the AMS is mostly carried by phyllosilicates, and the foliation in the rock is closely parallel to the microscopic cleavage of the rock. The magnetic lineation is often the result of 33 microfolding of phyllosilicates and thus reflects the fold axis of the rock, assuming the crenulation cleavage is axial planar. However, many times low grade metasedimentary rocks haven't experienced enough tectonic stresses to overprint the original anisotropy found from deposition (Martin-Hernandez et al.,
2004).
Isothermal Remnant Magnetism Studies (IRM):
Identifying the magnetic mineralogy that is carrying the magnetic remnance is important in paleomagnetic studies because it is possible that there are two different magnetic minerals in a rock, one corresponding to a weathering or diagenetic process and another to the stable magnetic remnance that was acquired at the time the rock was formed. Differentiating between the two is essential for accurate paleomagnetic reconstructions.
Frequently, the main remnance carrier is magnetite or hematite or a digenetic iron oxide such as goethite or limonite (Butler, 1992). Another potentially important class of magnetic minerals are sulfides, such as pyrrhotite and greigite. Pyrrhotite has been recognized as a magnetic mineral for some time, and greigite is a relatively new mineral discovered in 1964 (Skinner et al.,
1964, Roberts et al., 2011). These sulfide minerals are usually found in relatively deep marine or lacustrine settings in anoxic environments, although pyrrhotite can be found in contact aureoles (Roberts et al., 2011). These phases are metastable and usually convert to pyrite over short geologic time periods
(Roberts et al., 2011). Additionally, detrital greigite is most often cited as being
34 formed by magnetotactic bacteria, and both mineral phases have been associated with marine gas hydrates (Larrasoana et al., 2007). Sulfides can also be diagenetic, and can form at the expense of other previously existing iron oxides or iron bearing sheet silicates, recording a chemical remnant magnetization that could be millions years younger than the original magnetization (Roberts etal., 1994,2011; Kao et al., 2004).
Because there are multiple ways of forming magnetic minerals in a rock, it is imperative that the magnetic remnance carrier is identified. The most common and diagnostic way this is done is by Isothermal Remnant Magnetization studies, or IRM studies. What this entails is adding a small magnetic remnance to a 1 x 1 cm cube sample in increasing magnitude along one axis direction in the lab until the sample reaches its saturation magnetization, which can be diagnostic to particular minerals. Then the sample is stepwise thermally demagnetized. The temperature at which the sample completely demagnetizes is also diagnostic to particular minerals. Therefore, this process in most cases completely describes and identifies the carrier of the magnetic remnance. Because it is possible to have more than one magnetic mineral in a rock sample, the x and y axes are given a smaller remnance, therefore separating different minerals of different coercivities. The demagnetization of the different axes are plotted, and if different axes demagnetized at different temperatures, the sample is shown to have more than one magnetic phase present.
35 Different magnetic minerals have different unblocking temperatures and coercivities, therefore it is possible to use this type of IRM study to identify the minerals carrying the remnant magnetization.
36 VI. FIELD TESTS AND MAGNETIZATION AGE
Fold Test:
An essential requirement for paleomagnetic data to be used for plate reconstructions is that the age of the magnetization is known, and in the case of primary magnetic poles, this age should be the same as the age of the rock. To test this requirement, paleomagnetists use several field tests to determine the age of the magnetization and to test whether the rocks have been remagnetized since deposition/emplacement. One test used frequently is the fold test. The basic idea of the fold test is when a rock forms and acquires a magnetic direction and intensity, the magnetic vectors are essentially parallel to one another in the rock, because the magnetic field is generally uniform across short distances.
When this same rock layer is folded, assuming it has not been remagnetized, the direction of the magnetic field vectors should follow the shape and orientation of the fold. If the rock has been remagnetized since the rock has been folded, then the magnetic vectors should not follow the orientation and shape of the fold. One way this can be tested is plotting the magnetic vectors on an equal area stereonet and correcting these data back to horizontal. If the magnetic vectors are clustered more tightly on the stereonet, these data "pass" the fold test.
However, if the directions scatter, then the samples are considered to be remagnetized because the original parallel orientation is no longer preserved
37 Figure 12. Diagram shewing a passed fold and conglomerate test. The orientations of the magnetic directions in the fold follow the orientation of the fold. Therefore, when the bedding of the fold is corrected to horizontal, the directions of the magnetic vectors will be corrected to their original direction, therefore clustering better in tilt corrected coordinates than in geographic coordinates. The layer above the fold shows a conglomerate with magnetic field directions randomly oriented, suggesting that this layer has also not been remagnetized. Figure after figure 5.11, Butler, (1992).
Figure 13. Diagram shewing the basic idea of the baked contact test Directions of the magnetic field vectors of the undistrubed host rock show different directions than the Intrusion, showing that the host rock has not been completly remagnetized by the intrusion. Figure after figure 9.5 in Tauxe, (2005).
38 (Figure 12). Sometimes, a magnetization can be acquired during folding, especially in regions that have undergone tectonism. This is considered a synfolding magnetization (Tauxe, 1995, 2005).
The Baked contact test:
Another essential paleomagnetic field test used in this study is the baked contact test. The baked contact test involves a dike or other intrusion that represented a significant post depositional heat source. In this test, samples are taken progressively closer to the intrusion, with one sample in the baked contact and the last sample in the actual intrusion. If the rock in the region of the dike has not been remagnetized, the magnetic vectors of each sample moving progressively away from the dike should show progressively different orientations. If the rock has been remagnetized, then the magnetic vectors of each sample should be the same as the dike (Tauxe, 1995; Butler 1992; Figure
13).
39 VII. X-RAY DIFFRACTION AND REFLECTED LIGHT PETROGRAPHY
Two final methods for determining the overall composition and mineralogy of rocks are X-ray diffraction (XRD) and reflected light microscopy. X-ray diffraction bombards a powdered rock sample with X-rays of a particular wavelength and intensity at different angles of incidence. These X-rays are diffracted at different angles depending on the initial angle of incidence and the crystal lattice of the different minerals in the rock sample. When the diffracted X- rays satisfy Bragg's law, the interaction of the crystal lattice and the diffracted X- ray shows positive interference and a peak in diffraction intensity per a specific angle of incidence and crystal lattice spacing (d-spacing). The diffractometer measures these peaks of intensity as counts per second. These diffraction patterns are plotted as a function of 20 and compared to a standard, which can identify or confirm the presence of many minerals in a powdered sample from a particular locality. This method was used in this study to confirm the magnetic mineralogy. Additionally, reflected light thin section analysis was used to see if there were any particular textural relationships between any visible magnetic minerals and the rest of the rock. Both approaches add additional evidence to the IRM studies and can give more information on the timing of acquired magnetization in the Kittery Formation.
40 VIM. METHODS
Choosing Field Sites:
In accordance with the goals of this research, three basic criteria were used to choose field sampling sites. The first and most important criterion was the existence of ample primary stratigraphic structures, which could indicate stratigraphic up direction. Without this information, stratigraphically corrected natural remnant magnetic directions could not be calculated. Based on the metamorphic isograd map of the seacoast of New Hampshire and the more recent map of the state of New Hampshire, several areas of tectonic and metamorphic importance were identified, such as biotite versus chlorite grade at different localities (Novotny, 1969; Lyons et al., 1997). Some sites were chosen
41 Contact unoertafo
• HlgTr-angs* fautt (dashed where uncertain) / 70°W
| j = Location of AP, SB, PI, FM (JB0901-JB0914)
[ = Location of MP (JB0908-JB0911)
I I = Location of CE (JB0915-JB0917)
fcFalmoulhj
^Portland N| M
Major plutons
Ba. Barrington Bi Bidctelord Ei Exeter L: Lyman S. Saoo WA' Wefatianrw! and
We: Westbrook
Central Maine sequence (Esrfy S&mn to EtafyDwom*) PhyUonH© at Church Road (age uncwtiain} Berwick Formation (Lsto$i^nK>BvyO»«xw))
Bucksoort Formation
East Harpswell Group (Lama&OYtcm & Eafy Sikjitw) Merrimack Group fcato Onfcvtafer? «P &KV Srt«n*# »*j Casco Bay Group ~ " (Mf&tetoi*l&Qrtevlct*r\}
YPPx Fatmouth-Brunswicfc sequence
Rye complex
Figure 14. General geologic map of the study area of this thesis showing the units of the Merrimack Group, Casco Bay Group, fault zones and igneous intrusions from southern New Hampshire to the Casco Bay region, Maine. Figure modified after the Bath 1:100,000 (Hussey and Marvinney 2002), Portland 1:100,000 (Berry and Hussey 1998) and Kittery 1:100,000 (Hussey et al 2008) quadrangles, figure 2 in Hussey et al 2010, AP = Adams Point, SB = Scammel Bridge, PI = Pierce Island, FM = Ft. McClary
42 mzm
Mitet (n»I 3
Figure 15, location of sites in the Portsmouth (Pierce island), Durham (Adam's Point & Scammel Bridge) and Kittery Area (Ft McClary), New Hampshire and Maine. Notice the close proximity of each site to a mapped shear zone; Portsmouth Fault Zone (PFZ), or the Nannie Island Fault Zone (NIFZ). Rgure modified after Hussey, AM. II, Bothner, WA, and Thompson, PJ. 1:100,000 Kittery Quadrangle, Maine Geological Survey, 2008* SOk = Kittery Formation, see refemce for other map unit descriptions.
Q » Location of sites JB0901-JB0907,JK>912-iB0914
43 Miki imp E 10 II Figure 16. Location of sites JB0908-JB0911, Moody Point locality, Wells Maine. Figure modified d^»t Hussey, A.M. II, Bothner, WA, ami Thompson, RJL Maine Geological Survey 1:100,000 Kittery Quadrangle, 2008. SOk = Kittery Formation.
D = Location of sites JB0908-JB0911.
44 T
3
Figure 17. Location of JB0915, JB0916, and JB0917 showing the northern most mapped exposure of the Kittery Formation in Cape Elizabeth Maine, Two Lights State Park. Figure modified after the Portland 1*100,000 scale map by Henry N Berry IV and Arthur M. Hussey II, 1998 CE T^o Lights State Parle «t, Cape Elizabeth Maine
n Location of sites ^60916, JB0916, ana JB091 (
of lowest metamorphic grade to potentially isolate original magnetic components of the Kittery Formation during deposition. Third, sites were chosen that would represent potential remagnetization near important tectonic and contact metamorphic events. Finally, sites were chosen based on accessibility and the presence of folds and / or basaltic dikes for field tests of magnetic stability (see
Figure 14 for a map of the field area). The sites sampled which showed the three most important criteria are as follows: 1) Adam's Point in Durham, New
Hampshire (Figure 15), 2) rocks under the Scammel Bridge on Route 4 in
Durham, New Hampshire (Figure 15), 3) Pierce Island in Portsmouth, New
Hampshire (Figure 15), 4) Ft. McClary State Park in Kittery Point, Maine (Figure
45 15), 5) Moody Point in Wells, Maine (Figure 16), 6) Two Lights State Park in
Cape Elizabeth, Maine (Figure 17). Cape Elizabeth was sampled in an attempt to test the correlation of the Maine portion of the Merribuckfred basin with the southern portion of the Merribuckfred basin.
Drilling Procedures:
All subfacies were sampled with the exception of the phyllite bedding as long as stratigraphic up indicators were present such as cross-bedding or truncated laminations (Escamilla-Casas, 2003; Rickerich, 1987). Ideally, beds were sampled on either limb of a fairly tight fold so the fold test could be applied.
Fold tests were possible at all localities except under Scammel Bridge. In this case, a regional fold test was used. If no fold was present and a basaltic or diabase dike was, then a baked contact test was used to check for magnetic stability. However, frequently both a dike test and a fold test were taken at each site. Samples were drilled to approximately two inches depth by a water cooled, modified chainsaw drill with a diamond bit (Figure 18). Before the core was chiseled out of the drill hole, its orientation was measured by slipping a brass cylinder with an orienter stage over the core sample (Figure 19). Once the compass was leveled, a trend of the sample core was measured, followed by the plunge measured by the compass clinometer. The orientation of the samples in the outcrop was preserved by marking the orientation of the cylinder with a permanent marker. The sample was then chiseled out of the outcrop, given a label and down core orientation mark, and finally wrapped and placed in a
46 sample bag for that particular site. Once approximately seven samples were extracted, the strike and dip of the bed that the samples came from were measured, along with a GPS measurement of the site.
Laboratory Procedures:
Samples were cut to 25 mm by a rock saw specific for paleomagnetic cores. The label and down core direction marked in the field were reapplied on the core after cutting. Originally, the samples were demagnetized by alternating field methods (AF methods). However, alternating field demagnetization procedures were not able to remove the magnetization in most samples and yielded erratic demagnetization behavior. For steps that were demagnetized by
AF methods, the resulting demagnetization behavior on most samples was very erratic. Therefore, the samples were demagnetized thermally in increasing temperature steps. An initial pilot batch of samples were demagnetized in 25 degree steps until 400 degrees Celsius, and then in larger increments all the way to the unblocking temperature of the iron oxides magnetite (580 degrees Celsius) and hematite (690 degrees Celsius, table 1a).
After following this thermal demagnetizing protocol, it was found that most samples from the Kittery Formation would demagnetize between 275 and
350 degrees Celsius. Therefore smaller thermal steps to 400 degrees Celsius were used to demagnetize samples after the preliminarily run (table 1b). After each thermal step, the samples were put in a SQUID spinner magnetometer in six different positions (Figure 20). At each position, the magnetometer
47 Figure 18. Water cooled, portable diamond bit drill used to drill core samples.
Figure 19. Orienter and stage used to measure the azimuth and plunge erf the core in the outcrop.
Figure 20. HSM 2 SQUID based Spinner Magnetometer, used to measure the core samples at each demagnetization step. Figure from ASC scientific* measures the magnetization of each sample along two axes while the sample is spinning. After the sixth position, the computer calculates the magnetic inclination, declination, and intensity of the sample from the measured cartesian coordinates. The computer also calculates the error associated with the measurements. As the sample becomes subsequently demagnetized, the results are visible on a Zijderveld diagram and on an equal area stereonet.
Data Analysis:
After all the samples were demagnetized, the data were imported into another paleomagnetic computer program called Super IAPD (interactive analysis of paleomagnetic data), where paleomagnetic directions can be determined. The paleomagnetic directions were determined by principle component analysis. This entails making a trend line through demagnetization points that show a linear relationship in different segments. These trend lines represent the magnetic history of the sample, with the last trend line often being the primary, or characteristic magnetic direction (ChRM) vector of the sample when the rock was originally formed. These trend lines were described by a statistic called the maximum angle of deviation, or MAD. Principle component analysis was utilized on all samples at each site. However, it was quickly apparent that a great circle provided a better fit for demagnetization data from the
Kittery Formation. The great circle method fits a great circle to each sample in a site. Once all samples per site are fitted with a great circle, the intersection point of all the samples per site shows the true direction of the site. Therefore, the
49 clustered intersection of all the samples' great circles within a site should yield the true ChRM of the site. This was done for every site in the Kittery Formation, with the exception of the sites for dikes tests, since these sites' demagnetization
behavior is better characterized by a line. The great circle intersection between
all samples per site was determined (site mean calculation) and constrained by the three main statistics of alpha 95, R, and K (figures 38, 39, 40). Alpha 95 is
an angle of confidence that is a measure of the precision of the true mean of the data (Butler, 1992). K denotes how well clustered these data were to each other.
Higher k values indicate better clustering, whereas R is a value that determines the probability that these data are completely random (Tauxe, 1998). The higher the obtained R value compared with the minimum tabulated R value for
randomness, the more likely these data were not random. This is referred to as
Watson's Test of Randomness (Tauxe, 1995; table 1f).
Once site mean directions are calculated, magnetic stability is tested and
analyzed, and VGPs (virtual geomagnetic poles) are calculated for sites in either geographic coordinates, tilt corrected coordinates, or synfolding coordinates, depending on the outcome of the fold test. The VGP's are averaged together to
get a paleomagnetic pole for a particular locality and then combined (if possible) to calculate a total paleomagnetic pole for the Kittery Formation.
50 IX. RESULTS
Magnetic Mineralogy:
Samples of the Kittery Formation exhibit very intense magnetizations compared with typical sedimentary rocks and demagnetize at relatively low temperatures. Additionally, these samples were not successfully demagnetized by AF methods. The initial demagnetization of the core samples was not enough to identify a particular magnetic mineral phase; IRM was used to determine what minerals are carrying the magnetization.
Samples that broke during drilling but were large enough to cut a 1 cm cube were analyzed for IRM. A total of four samples were cut to this size and used. One was from Adam's Point (JB0903), one from Pierce Island (JB0922, same as site JB0906), another from Cape Elizabeth (JB0916), and one from a low grade rip-up mudclast (weakly metamorphosed) found in the Kittery
Formation at Moody Point (JB0910). In this study, the Kittery samples were so strongly magnetic that the magnetometer was modified for demagnetization of these intense cubes by moving the HSM 2 SQUID sensor farther away from the spinning sample, which enabled a complete demagnetization curve for each cube to be obtained. While the actual intensity of the sample was several orders of magnitude larger than the measured intensity, the demagnetization pattern and temperature is of greater importance, and this method proved sufficient for
51 proper identification purposes. Because the demagnetization curves were obtained, information about the coercivity of the samples was also obtained by magnetically partitioning the Y and Z axes, and subsequently plotting the demagnetization curves. This method identified the magnetic mineralogy of the
Kittery Formation, based on coercivities, unblocking temperatures, and hard, intermediate, and soft magnetic axes.
There are two known iron sulfide phases that are magnetic: greigite and pyrrhotite. Greigite has a Curie temperature that is approximated, due to the fact that the mineral phase becomes thermally unstable between 200 and 350° C, after which greigite subsequently breaks down to magnetite, pyrrhotite or other paramagnetic or non-magnetic phases at 500° C (Roberts et al., 2011). Roberts et al. (2011) suggests that the Curie temperature must be higher than 350° C.
Pyrrhotite has a curie temperature of approximately 325° C, above which it converts to magnetite. This conversion helps distinguish between the two different phases during demagnetization, but additional constraints by XRD and thin section analysis are required to identify the magnetic mineralogy completely.
Pyrrhotite does not show thermal instability between 200 and 325° C like greigite, but begins to show significant demagnetization after 325° C where it undergoes a phase transition to magnetite, which then completely demagnetizes at 580° C
(Torii et al., 1995; Roberts, 1995). Lastly, greigite is known to be ineffectively demagnetized by both spinning and stationary AF demagnetization methods due
52 a) 9O0O0 Cape Elizabeth: JB0916 80000
(axis 12T 4T ~&-Zaxis 1 IT
100 200 300 400 500 600 DEMAGNETIZATION STEP, IN DEGREES C
b) 25000 Pierce Island: JB0906
2O000
£ 15000
-Xaxis 12T -Y axis 4T -Zaxis 1 IT
100 200 300 400 soo 600
5000 DEMAGNETIZATION STEP, IN DEGREES C
Figure 21 a) IRM demagnetization pattern of sample JB0916, Cape Elizabeth The green line is 1 1 T IRM, the red line is 4 T IRM, and the blue line »s 12 T IRM Notice all components come close to complete demagnetization at 325 degrees Celsius, regain some magnetization at 350, and then completely demagnetize at 400 b) IRM demagnetization profile for a sample from Pierce Island All three components demagnetize by 325 degrees Celsius, with no obvtous phase transition to magnetite
53 a) 30000 Adams Point: JB0903
25000
—£»~XAxis 12T B Y axis 4T ^^F^Z axis 1 IT
600
-5000 DEMAGNETIZATION STEP, IN DEGREES C
b) 900 Moody Point: JB0910 800 I A •% X 700 ! ~~X _ .... _ -. --- -
5 500 z 1 ^m V *X axis 3 400 1 rar^ \ "1 J2T E I \ \ *Yaxis g 300 4T - Z ax*s < 1,1 T -h— - ^--~ S 200
100
0 0 100 200 300 400 500 600 -100 DEMAGNETIZATION STEP, IN DEGREES C
Figure 22, a) IRM demagnetization of a 1 cm cube of the Kittery Formation from Adam's Point site JB0903 The green line represents 1.1 T of IRM, the red Itne .4 T of IRM, and the blue line .12 T of IRM. All components completely demagnetize at 300 degrees Celsius, b) IRM demagnetization of the three components of a one cm cube of the Kittery Formation from Moody Point site JB0910. Notice the demagnetization of all components at 300 degrees Celsius. to the nature of the greigite crystallography which causes an acquired magnetization during the application of alternating fields (Roberts et al., 2011).
54 Cape Elizabeth Locality (JB0916) shows a gentle decline in magnetic intensity from 0 to 125° C and then begins to drop off exponentially from 125 to
250° C (Figure 21a). Next, the magnetization decreases again from 250 to 325°
C. Lastly, there is a small increase in intensity among all components from 325 to 400° C, where it completely demagnetizes at 400° C. Even though this sample seems to exhibit a higher unblocking temperature, this sample's main magnetic phase is attributed to the iron sulfide greigite as well because the sample completely demagnetizes at 400 degrees, while pyrrhotite would convert to magnetite and then completely demagnetize at 580° C. Additionally, the IRM profiles show that the magnetic mineralogy begins to significantly break down much before 325° C, which is characteristic of greigite (Roberts, 1995, 2011;
Figure 21a). Therefore the preliminary IRM results indicate greigite is the carrier of the magnetization at this locality. However, further studies such as SEM or more extensive XRD studies could also potentially identify a small amount of pyrrhotite in this sample.
The Pierce Island Locality (JB1022, same site as JB0906) is characterized by a steady linear decrease in magnetization from 0 to 125° C, and then an exponential decrease in magnetization from 125 to 250° C (Figure 21b). From
250 to 325° C, the magnetization decreases linearly to demagnetization at 325°
C. Once again, it is interpreted that greigite is the phase carrying the magnetization in this sample, due to the lack of a phase transition to magnetite
55 after 325° C, and a rapid loss in magnetization between 175 and 250° C (Figure
21b).
Adam's Point Locality (JB0903) has a steady and slow decline in magnetization from 0 to 150° C and then begins to decrease rapidly from 150 to
200° C (figure 20a). At 200° C, the intensity of magnetization on all axes increases sharply and then decreases very quickly until it is completely demagnetized between 225 and 300° C (Figure 22a). It is mainly iron sulfide minerals that display such low unblocking temperatures. The magnetic mineralogy in JB0903 is identified as greigite due to three factors. One reason is the significant decrease in magnetic intensity between 225 and 300 ° C. The second reason is the presence of the complete demagnetization at 300°C, with a lack of renewed intensity that demagnetizes at 580° C which would be indicative of pyrrhotite transitioning to magnetite, and lastly, the inability of these samples to be completely demagnetized by AF methods.
The low grade mud clast from Moody Point Locality (JB0910) has the strongest hard axis of magnetization decreasing linearly from 0 to 200° C and then exponentially decreasing until the magnetization becomes zero at 300° C.
The medium and intermediate components show an immediate increase in magnetization that peaks at 75° C for the medium component and 125° C for the weakest component. The medium component rapidly decreases from 75 to 125°
C, while the weakest component rapidly demagnetizes from 125 to 200° C. Then the magnetization decreases slowly, and becomes completely demagnetized
56 very rapidly from 275 to 300° C. Based on the above evidence and arguments, this site is also characterized by the iron sulfide greigite (Figure 22b).
X-Rav Diffraction Analysis:
The fine grained, limy mudclast from Moody Point (JB0910A, Figure 23 & 24) was X-rayed to further investigate the magnetic mineralogy of the Kittery
Formation. A small piece of JB0910A was dissolved in dilute HCL to concentrate mineral phases that would have been overshadowed by the larger concentrations of calcite in XRD profile. When the Eva software system attached to the XRD searched for likely magnetic minerals in the insolubles, greigite matches the pattern fairly well (Figure 24). Additionally, the paramagnetic phase Ulvospinal was also a good match to the dissolved XRD profile (Figure 24). When a match of iron oxide phase such as magnetite or hematite was plotted, neither was good matches for the observed XRD peaks and therefore was not plotted. Other phases in this mudclast are calcite, chlorite, quartz, and muscovite (Figure 23).
Therefore, these results are consistent with the IRM results in suggesting that the dominant magnetic phase present in these samples is greigite. XRD of magnetic separates could add additional evidence to the argument that greigite is the dominant magnetic phase in this sample, because it is possible that even though the calcite is dissolved, other non-magnetic phases of higher concentration could be overshadowing the magnetic phase(s) in the Kittery Formation.
57 2-TWa- Scale
Figure 23. XRD profile showing mudclast mineralogy before and after dissolution by dilute HCL, a) Profile for undissolved sample, showing a large peak of calcite, and several peaks of chlorite and quartz. b) Profile for insoluble material left after dissolution by dilute HCL. Notice the dissolution was sucessful, and calcite is no longer present in large quantities. Muscovite is also present in both profiles in smaller quantites.
Aj = Chlorite
#| = Quartz
= Calcite
^ = Moody Point mudclast, undissolved profile
A/V = Moody Point mudclast, insolubale material
58 >lj jilW \J u \*""i " 'I111 "i1" '| " a1""! ""•'»•"•"> "'^ T—,—r-H—i—f- 0 -*—i—i—i—«—i—i—r^r _^—J—t—,—,—,—r^r 2-Theta - Scale Rgure 24. XRD profile of the mudclast at Moody Point showing a plot of greigite and ulvospinel. Note that both greigite and ulvospinel are a reasonably good match to the profile. K/y = XRD profile of dissolved musclast at Moody point. = Greigite = Ulvospinel 59 Figure 25. Photo micrograph from site JB0910 showing an unidentified cubic grey isometric mineral with potential secondary growth of pyrite. Note also the large arcular region of iron staining right next to the mineral. This could be the potential source for the mobile iron to form greigite and pyrite in the sample. Figure 26. Photo micrograph from site JB0910 showing a cubic grey isomethc mineral with potential secondary growth of pyrite. 60 figure 27, Photo micrograph for site JB0910. Reflective isometric mineral, neither metalie gold nor grey, showing no transition to another mineral. This mineral seems to have more of a pink creamy color and therefore could be greigite. Note however that the laths co-exsist within a large matrix of sheet silicates. Rgure 28. Photo micrograph for site JB0910. This sample also showed small metallic gold-like laths of reflective material, most likely pyrite, or potentially greigite. Samples were too small to confirm the mineralogy, however note that the minerals co-exsist with sheet silicates (non-reflective grey matrix). 61 Figure 29. Photo micrograph from site JB0910. Small laths of reflective material within a larger matrix of sheet silicates and isometric grey iron oxide. Color and reflectivity seem indicative of greigite and/or pyrite* Figure 30. Photo micrograph from site J80910* Another example of the grey isometric mineral potentially being converted to pyrite. 62 Reflected Light Petrography: Reflected petrography was undertaken on samples from Moody Point (JB0910) to examine any potential textural relationships to further investigate the magnetic mineralogy and timing of the magnetization. A few circular spots of apparent iron staining were visible in transmitted and reflected light (Figures 25- 29). In reflected light, opaque mineral intergrowths suggest alteration or transition from a light grey isometric phase to a brassy yellow, isometric phase, but the direction of conversion was not clear based on the texture. One mineral had a reflective, metallic luster and a brassy yellow color (Figures 25-30). The other mineral was grey in color, and in some instances had a cubic form. There was one other mineral not associated with the conversion texture, which is a creamy color with a slightly metallic luster (Figure 28). All minerals were isometric, ruling out multi-domain pyrrhotite and hematite. The brassy yellow mineral is identified as pyrite based on its crystal form, luster, and color. The grey isometric mineral could be a titanomagnetite phase, or greigite. Titanomagnetites are grayish brown in reflected light, and when visible, greigite is a pink to creamy white color with a metallic luster in reflected light. Both greigite and ulvospinel/titanomagnetite have an inverse spinel crystal structure which could appear cubic in thin section. Without scanning electron microscopy or electron microprobe, it is difficult to identify with certainty the grey isometric phase, or the creamy isometric phase (Figures 25-30). 63 NRM: Many cores (122 cores from 15 sites) were demagnetized thermally in a magnetic shielded oven and measured after each thermal step. Initially, three samples from each site were thermally demagnetized up to 690° C in small temperature steps. Typically, samples were nearly demagnetized before 400° C, but even upon heating to 690° C the samples never fully demagnetized, which suggested that the original mineralogy had broken down long before 690° C and that the residual magnetism was due to minerals being formed in the oven after the original ChRM was demagnetized. Once the samples were fully demagnetized, paleomagnetic vectors were initially fit to linear portions of their demagnetization data to determine the directions of the different NRM components for each sample. However, it quickly became apparent that a line did not adequately fit the demagnetization data for most samples. After further inspection of the demagnetization behavior of the samples, it appeared that the stable portion of demagnetization was best fit by great circles (see Figures 31-33 for demagnetization behavior examples). A great circle was fit to each sample from every site except those that represented dike tests which could be described using best fit lines. The mean of all points of intersection in a hemisphere for all cores at a particular site was used as the site means. The site means makes the assumption that if there is a common direction for all samples within a particular site then these samples should 64 intersect at the direction, and thus point, along the plane that all the samples within the site share. The uncertainty of the mean point of intersection is described by a95 (95% angular confidence interval) and the precision parameter k. These statistics measure how close each great circle intersects with one another. This method was much more successful in that individual sites have much smaller (better constrained) a95 (less than 30) and higher precision parameters (greater than 5, some up to 600, see Figures 34-36). Site and Locality VGPs: In geographic coordinates, single sites are well constrained statistically (a95 less than 26 degrees for most sites, with some less than 15 degrees). When sites are compared within the same locality all sites are not statistically significant or well clustered in either geographic or tectonic coordinates (with a95 180 degrees for many sites). Data and corresponding statistics for site mean directions and VGPs are summarized in table 1. VGP's were calculated for individual sites at each locality, and were not calculated for the locality or Kittery Formation as a whole. Site VGPs have moderately low error (a95 less than 25 degrees in general, see figure 37). Comparing site VGPs in geographic coordinates to the APWP of North America shows that some sites fall within error of part of the path (Scammel Bridge (JB0904), Moody Point (JB0908), Adams Point (JB0905), and Moody Point (JB0909)), and others are statistically distinct from the path (Adams Point (JB0903), Pierce Island (JB0906), Pierce 65 lsland(JB0907), and Ft. McClary(JB0912)). Scammel Bridge (JB0904) falls within error of the upper Silurian/lower Devonian and Upper Triassic of the W,Up \ s,s JB0912A(Ticks=1O0.0mA/M) Figure 31. Example of one kind of demagnetization behavior shown by the Kittery Formation, sample JB0912A (Moody Point). The line bypasses the origin, suggesting another component unresolvable by demagnetization. This sample has a linear trend, but since the final component is not completly resolved, a great circle is fit to this data. W,Up S,S-^ JB0902D(Tick$=0.1 mA/M) Figure 32. Site JB0902 (Adams Point) yielded unreliable demagnetization behavior. Therefore, Site JB0902 was not used in this study. 66 W,Up s,s -+- JB0907A{Ticks=1O.OmA/M) Figure 33. Demagnetization behavior of sample J80907A (Pierce Island) shows a good example of a site that is best fitted by a great circle. The obvious two components of this sample show curved behavior that does not trend to the origin, therefore suggesting that demagnetization was unable to completly isolate the ChRM of this sample> The great circle method is particularly useful for this sample. 67 31 Step Temperature *C Step Temperature * C 1 25 1 25 2 SO 2 75 7\ . K ™» 125 4 IOCT " 4 175 s 125 5 200 6 ISO K 225 7 175 7 250 8 2°0L 8 275 9 250 % 300 10 275L 10^ 325 11 300* U 350 12 350 12*I 400 13 400 * 15* 450 #• ~~ 17 1 58cT * 18^ 600^ * _ 625 19* t 20* 690* Maximum Axis Intermediate Axis MtaimumAxte Silt AMS Pediwttw* i(Kii Table 1 a) Expenmental thermal demagnetization procedure, b) Thermal demagnetization procedure used for the majority of the study, notice the last temperature step only reaches 400 degrees Celsius, c) AMS data in tectonic coordinates (unfolded), d) AMS data in geographic coordinates (folded), e) Site mean directions, associated statistics, and VGP's associated with these sites. Notice site JB0925 does not have a corresponding VGPt because of the large error associated with the site mean Also notice that the R and N values show signrficantJy passed Watsons Test for Randomness. 68 North North Figure 34. Equal area projection of NRM great circles for sites a) JB0903 (Adams Point), b) JB0904 (Scammel Bridge), c) JB0905 (Adamds Point), d) JB0906 (Pierce Island), 69 North North C) North North Figure 35> Equal area projection of NRM great circles for sites a) JB0907 (Pierce Island), b) JB0908 (Moody Point), c) JB0909 (Moody Point), d) JB0912 (Ft. McClary). 70 Figure 36. Equal area projection of NRM great circles for site JB1025 (Ft. McClary). 71 UHP a a I = lower •—• = APWP poles LHP m m M = middle site/locality poles U = upper — — Great circle trend O = APWP 95% confidence O - VGP 95% confidence Figure 37. Site VGPs plotted against the APWP for North America. Notice that several localities overlap with the APWP, whereas others are discordant. Also note that many VGP's follow a great circle trend, intersecting with the APWP in the upper Carboniferious / lower Permian. UHP = upper hemeshperic projection, and LHP = lower hemipsheric projection, AP = Adams Point, MP = Moody Point, SB = scammel Bridge, FM = Ft. McClary, and PI = Pierce Island, Some locaities have multiple sites, which are shown as duplicate localities with different directions on the plot. 72 APWP. Moody Point (JB0908) overlaps with the upper Silurian/ lower Devonian and upper Devonian of the APWP. Adams Point (JB0905) only overlaps with the middle Ordovician of the APWP. Moody Point (JB0909) overlaps with both the upper Jurassic and lower Cretaceous of the APWP. For sites that are distinct from the APWP for North America, sites Pierce Island (JB0906, JB0907), and Ft. McClary (JB0912) fall fairly close to the path, while Adams Point (JB0903) falls significantly away from the APWP for North America. Lastly, these data follow a great circle path, which intersects the APWP in the upper Carboniferious / Lower Permian (Figure 37). Fold Tests: The characteristic remnant directions of the Kittery Formation do not cluster well in either geographic or tectonic coordinates. When progressively unfolded from 0 to 100%, the Kittery Formation shows the largest amount of clustering at 0 % unfolding at all sites except Pierce Island (figure 38 and 39). Pierce Island shows a maximum clustering at 28 % unfolding, however the 95% confidence interval includes 0% unfolding so a post folding magnetization cannot be ruled out for the Kittery Formation at this locality either (figures 38 and 39). Baked Contact Test: The Kittery Formation passes the dike test at most sites where a test was available. The classic result for a "passed" test is that there is a progressive change in magnetic vector directions the farther the sites are removed from the 73 a) % Dec Inc k Kmax 0 330.0 67.9 1.67 1.67 10 317,6 69.7 L42 20 302.3 69.9 1.20 30 286.5 67.8 1.03 40 273.2 62.8 0.89 50 263.8 54.2 0.79 60 258.2 40.6 0.71 70 255.7 19.9 0.66 80 256.1 -6.9 0.65 90 259.5 -32.0 0.67 K 100 266.4 -49.5 0.73 N=2 100 b) % Dec inc k Kmax 0 84.2 22.9 17.69 34.54 10 83.4 23.3 24.54 20 82.8 23.3 31.R3 30 82.4 23 J 34.43 A 40 82,3 22.5 29,73 SO 824 21.6 22.34 60 82.7 20.3 16.25 / 70 83.1 IU.6 12.10 80 83.6 16.5 9.39 K |L \ 90 84.2 14.1 7.63 I0O 84 .8 11.3 6.47 N=2 V \, 100 % Figure 38. a) Adams Point fold test showing a maximum clustering (k value) at 0 percent unfolding, and a k value of 1.67. b) Pierce Island fold test showing a maximum clustering (k value) at 28.3 percent unfolding with a corresponding k value of 34.54. 74 a) % Dec ktc k Kmax 0 1L9 15.1 139 5.63 10 143 18.5 1.15 20 17.7 21.9 0.98 30 22.9 25,4 0.84 40 3L2 28.6 0.74 50 45.2 30.5 0.67 60 68.3 27.6 0.62 70 97.5 14.4 0.61 80 120.5 -3.6 0.63 90 134 J -16.8 0.6S 100 1423 -25.5 0.75 N=2 100 % b) % Dec Inc k Kmax 0 20.4 30.4 2 58 5.52 10 25.7 34.2 2,0g 20 33.2 37.2 1,6ft 30 43.4 38.9 1.40 40 563 383 1.19 50 70,9 34.1 1,07 60 84.9 25.7 1.00 70 96.7 14.0 0.99 80 105.5 1.2 1.04 90 111.8 -10.9 1,16 N=2 100 Figure 39. a) Moody Point fold test, with a maximum percent unfolding at 0 percent, and a corresponding k value of 5.63. b) Ft McClary fold test, with a maximum percent unfolding at 0 percent unfolding, and a k value of 5.52. 75 North Oft. [j = Sample closest to the dike, in the baked contact Figure 40. Baked contact test at Adams Point. Note that the samples closest to the dike and within the baked contact show progressively different magnetic vector orientations, which cluster well nearby site JB0903. Diagram is a map view projection of the samples proximity to the dike. 76 North D Dike JB0911A O o A JB0911D c o E Oft. 6 ft. o Bedding JB0911E o • = Dike(JB0911D) IJB0911C Figure 41. Dike test for Moody Point site J80911 showing different vector directions for samples away from the dike. Map inset shows proximity of different samples to the dike. 77 Figure 42. Dike test for Ft. McClary, showing an inconclusive test. Both samples JB0914F and J80914F1 are from the same core. JB0914E and JB0914E1 are also from the same core. The presence of scatter between the samples from the same cores as proximity to the dike increases, while a site mean from an area far from the dike showing a different direction suggests a passing situation. There is too much error and scatter to say definitively whether this site is a passing' situation or a failing* situation. 78 dike, and the samples the farthest from the dike cluster with the characteristic magnetization of the host rock. Adams Point (JB0901) shows a progressive change in magnetic vector directions, with very different directions between the sample farthest away from the dike (JB0901A,B,C) and the samples closest to the dike (with JB0901G being closest to the baked contact, and JB0901FB in the actual baked contact next to the dike). Additionally, the site mean from nearby site JB0903 falls right within error of the samples that cluster farthest away from the dike (Figure 40). Moody Point (JB0911) also passes the dike test in that samples close to the dike (JB0911C, D) share directions to the dike, whereas samples farther from the dike (JB0911 A) has different vector directions. However, it is not the case in this site that the sample closest to the dike has the most similar magnetization to the dike, because JB0911C is the closest to the dike, but sample JB0911E which is the next closest to the dike has the most similar direction to the dike. Unfortunately, other sites within this locality are too far away to provide additional sample control. However, the dike at this site is very large (approximately 1.5 meters) compared with the others, and the subsurface geometry of the dike is not known and could cause areas of thermal heterogeneity in this local area disturbing different samples at different locations in the test area (Figure 41). Ft. McClary (JB0914) shows an inconclusive dike test. The sample in the baked contact and the actual dike were long enough to take two samples from 79 one core when cutting the samples in the lab. The demagnetization of these two different samples from the same core show significantly different directions (Figure 42). Another ambiguity is that site directions from nearby site JB1025 is not close to either the host Kittery Formation or the dike direction, albeit this site has a large amount of error associated with its direction. Therefore, the directions are too scattered and the results remain equivocal (figure 42). For all samples, the Kittery Formation failed the fold test, and, with the exception of one ambiguous site, passed the dike test. These results indicate the age of the magnetization in all sites except Ft.Mclary is constrained to older than Jurassic (age of the dike), and younger than late Silurian (maximum age of the folding). AMS: Anisotropy of magnetic susceptibility was measured on one sample from each locality. The goal of the AMS portion of this study is to use AMS as a first order tool to investigate the magnetic petrofabric of the Kittery Formation in hopes to inform other data sets in the study. The magnetic susceptibility in each sample was measured in 18 different positions, and these data were evaluated using the computer program MS-2. AMS directions are reported in both geographic and tectonic coordinates. K1 follows a great circle trajectory in geographic coordinates, and K3 clusters in a northerly direction, with a plunge slightly sub vertical. K1 and K3 in tectonic coordinates do not show any clear patterns (Figure 43 and 44). 80 When the magnetic lineation is plotted versus the magnetic foliation at each locality, Cape Elizabeth, Ft. McClary, and Pierce Island fall just beyond the line of unit slope into the field of constriction. The line of unit slope separates the field of flattening (oblate) from the field of constriction (Prolate) of the AMS ellipsoid. Adams Point, Moody Point, and Scammel Bridge show no lineation, and small amounts of foliation (Figure 45). Hrouda et al. (1976), and Martin- Hernandez et al. (2004) propose that magnetic lineation record earlier deformation in a rock, and the foliation continuously records progressive deformation. 81 j I = Maximum axes (k1) - Minimum axes (k3) Figure 43. Directions of the maximum (k1) and minimum (k3) axes of the AMS ellipsoid in tectonic (unfolded) coordinates. Notice that to a first order, k1 shows a great circle trajectory, k3 shows generally very shallow inclinations. 82 North JB0912 . n B JB09Q3 IJB0917 "\ Q J80906 JB0908 D J80908 D JB0904 DJB0903 JB091? D JB0904 [""] = Maximum axes (kl) = Minimum axes (k3) Figure 44. Directions of the maximum (k1) and minimum (k3) directions of the AMS ellipsoid in geographic (folded) coordinates. Notice that the overall directions of the maximum axes (k1) shows a great circle pattern, while the minimum (k3) axes show the most amount of clustering positioned north/northwest. 83 Magnetic Anisotropy Ramsay Diagram • Adams Point (JB0903) • Scammel Bridge (JB0904) A Pierce Island (JB0906) X Moody Point (JB0908) X Cape Elizabeth (JB0917) » Ft McClary (JB0912) — Increasing Anisotropy 0.1 0.2 03 0.4 Foliation (log (k2/k3) Figure 45. Magnetic anisotropy plot after Ramsay showing all localities in either the plane of flattening (oblate ellipsoid) or the fiefd of constriction (prolate ellipsoid). Note Adams Point plots m the same location as Scammel Bridge and Moody Point. 84 Figure 46. Trend and plunge of k1 of the AMS ellipsoids at each locality. Arrow direction corresponds to the azimuth and different lengths indicate the degree of the plunge. Note that Adams Point and Scammel Bridge show different directions than Ft McClary and Pierce Island. Also note that plunge changes from very shallow to steep to shallow again from Pierce Island to Cape Elizabeth, AP = Adams Point, SB = Scammel Bridge, FM = Ft McClary, PI = Pierce Island, MP = Moody Point, CE = Cape Elizabeth. Modified after figure 2 in Hussey et al., (2010). = Great Bay fault, approximated = Nannie Island fault, approximated —- = Portsmouth fault, approximated • = Paleozoic Plutons \ = k1 I I = Paleozoic metasedimentary rocks 0 = Merrimack Group 1 j = Rye Complex 85 When k1 in geographic coordinates are plotted on a map of the Portsmouth Harbor region, the directions are deflected relative to one another across the Portsmouth fault zone and the Nannie Island fault zone. K1 also shows varying dips from very shallow to steep at different localities with similar strikes (figure 46). X. DISCUSSION AND CONCLUSION Magnetic Mineralogy: IRM profiles, XRD, and reflected light microscopy suggest three possible magnetic phases within in the Kittery Formation: greigite, titanomagnetite or pyrrhotite. As mentioned previously, greigite is characterized by thermal instability between 200 and 300° C, and low unblocking temperatures. The unblocking temperature of titanomagnetite is dependent on the concentration of titanium in the B cation site of the titanomagnetite crystal. Therefore, a few possibilities for the the magnetic mineralogy of the Kittery Formation can be proposed. 1) The grayish phase in reflected light is greigite because it is isometric and cubic in form. 2) The grey phase is a titanomagnetite with a concentration of Ti 4+ .8 or larger in the B cation site, therefore reducing the titanomagnetite to a superparamagnetic phase. Additionally, greigite is present but not visible in thin section, or greigite is the phase that appears within the matrix of sheet silicates. 3) Greigite does not actually exist in this rock, instead there is a variable amount of Ti 4+ in concentrations .7 or less, changing the unblocking temperature of titanomagnetite and therefore causing the samples to 86 demagnetize like an iron sulfide. 4) There is both titanomagnetite and pyrrhotite in the Kittery Formation. Hypothesis three and four are very unlikely, because of the ineffectiveness of AF demagnetization on these samples which is characteristic of greigite, and not pyrrhotite (Roberts et al., 2011). Additionally, the thermal instability present on the IRM profiles is characteristic of greigite and not a titanomagnetite or pyrrhotite phase. Lastly, the XRD profile of insoluble material from Moody Point matches with greigite and ulvospinel enough to be considered significant. Therefore, hypothesis one is possible, but less likely than hypothesis two due to the grey color instead of pinkish white usually diagnostic of greigite in thin section. Therefore, it is taken that greigite is the dominant magnetic phase in the Kittery Formation, and ulvospinel is most likely the grey isometric mineral shown in reflected light. It is possible that small amounts of pyrrhotite are present in the Kittery Formation, but its presence does not exclude the possibility that greigite is present. Hypothesis two, as stated above, also seems most likely because of the very strong intensity of the magnetization which is usually carried by single domain grains that are very small and hard to distinguish in thin section. Scanning electron microscopy or microprobe could confirm or revise these interpretations. In summary the evidence that supports greigite as the main magnetic phase in the Kittery Formation is as follows: • Greigite is not demagnetized by alternating field methods. • Greigite shows thermal instability between 200°C and 300°C during demagnetization, which is shown in the demagnetization profiles. 87 • The demagnetization profiles do not show an increased intensity that demagnetizes at 580°C which is characteristic of pyrrhotite. • Greigite is a fairly good match to some peaks on the insoluble X-ray diffraction profile. Greigite may be formed in at least three common ways, at least one of which occurs long after a sedimentary rock has been deposited (Figure 47). Greigite can form from the partial or complete dissolution of previous detrital iron oxide phases during or after diagenesis (Roberts and Turner, 1992). Another possibility is that greigite can form from the partial decomposition of iron bearing sheet silicates over 100,000 year time scales, and it has been documented in particular to coexist frequently with chlorite (Roberts, 1995). Lastly, greigite can be produced by magnetotactic bacteria in marine environments with organic-rich detritus, abundant available iron, and sufficient depth such that the iron combines with available sulfur (Larrasoana et al., 2007). This is the reason that greigite is frequently associated with modern methane gas hydrate environments (Larrasoana et al., 2007; figure 50). The main mode of greigite formation in the Kittery Formation is taken to be diagenetic, given the post folding magnetization age, corresponding to a CRM. The small amounts of ulvospinel, iron straining, and the presence of sheet silicates in both thin section and XRD profile suggests 88 (a) Unresolved texture Spheres Framboids CO FeS FeS2 Fe3S4• 2S -**3FeSa Figure 47. a) Different pathways for forming sedimentary and diagenetic greigite. b) Crystal class and texture of different sufide phases, c) Chemical equations for forming pyrite from pyrrhotite and greigite. Red highlighting illustrates pathway proposed for greigite formation in this study. Modified after figure 11, Roberts and Turner, (1993). 89 that the available iron to form greigite in the Kittery Formation came from the near complete dissolution of detritial iron oxides and / or iron-bearing sheet silicates during folding and metamorphism. Greigite is reported in many rocks from the Cretaceous to the present that form in reducing marine and lacustrine environments e.g., Sagnotti et al., 2005. Greigite is a metastable phase that was assumed by many geologists to convert to pyrite over short periods of geologic time, and therefore was ignored in older rocks (Sagnotti et al., 2005). This study however documents that greigite can be a strong and potentially stable carrier of a magnetic remnance for hundreds of millions of years, even in tectonically disturbed rocks. NRM: NRM results show four site VGP's that overlap with the APWP of North America within error, and four that are discordant. Several causes for the discordance of site VGP's from the APWP and within localities are possible. 1) varying degrees of vertical axis rotation in the Kittery Formation since the Late Silurian through Jurassic Period has occurred, related to movement along the southern extension of the Norumbega fault system (PFZ and NIFZ), and magmatic shouldering due to the emplacement of Devonian plutons and Mesozoic dikes. 2) Widespread penetrative shear and deformation in the Kittery Formation caused the VGP's to be significantly deflected as reflected in high percent anisotropy. 3) The site and locality VGP's obtained do not adequately 90 average out secular variation. 4) There have been multiple periods of greigite growth in the Kittery Formation from the late Silurian through the Jurassic. A combination of hypothesis one (rotation) and four (multiple greigite growth) is the most likely interpretation for these data for several reasons. The site directions are well constrained statistically, and these data are not random (reasonably well constrained a95 and significantly passed Watson's Test for Randomness, see table 1 and 2). Hypothesis three (inadequately averaged secular variation) is possible, but less likely because the magnetic mineralogy likely formed over time scales of over 120,000 years, which is more than enough time to average out non-dipole components of the geomagnetic field (Roberts et al. 2011; Butler, 1992; Tauxe, 1998). The post-folding magnetization suggests a slow diagenetic origin, which would also average out secular variation.' Hypothesis two (widespread penetrative shear) is less likely because some sites that could have a significant angular deflection of the NRM data due to shear are closest to the APWP, while the site with the lowest percent anisotropy is actually farthest from the APWP (Figure 49). This suggests a different process has caused the discordance of some sites with the APWP instead of shear. Hypothesis one (vertical axis rotation) is a viable interpretation of the NRM data because AMS data indicate rotated fold axes in the Durham - Portsmouth region, and does not indicate penetrative shear in most localities. Also, hypothesis four (at least two generations of greigite growth) is consistent with several paleomagnetic studies in New England in different terranes which commonly record two main remagnetization events, one in the early to mid-Devonian and 91 one in the late Paleozoic. These approximately correspond to the Acadian and Alleghanian orogenies (Lombard et al., 1990; Thompson et al., 2007; Thompson, 2010; Seguin etal., 1986; Johnson etal., 1996). Thompson etal. (2007) found two secondary components of remagnetization in a Neoproterozoic Avalonian rock which are consistent with remagnetizations from the Ordovician to the Permian. A combination of hypothesis one and four is also consistent with previous work of Fargo and Bothner (1995), which suggested up to 90 degrees of rotation due to emplacement of the Exeter pluton, and observations of clockwise rotation at Adams Point by Willard (2000). Additionally, it is likely that there are at least two generations of greigite growth because of the multiple generations of deformation and magmatism cited by Fargo and Bothner (1995), Escamilla- Casas (2003), Hussey (1968), MacEnroe (1996), among many others. Finally, the site VGP's follow a great circle pattern, which interests in the upper Carboniferous / lower Permian. This adds additional evidence to the argument that the Kittery Formation has indeed been rotated, and the intersection age corresponds with the timing of the Alleghanian orogeny in central coastal New England. AMS: When a tectonic disturbance controls the petrofabric of a rock, the maximum axis (k1) is parallel to the elongation direction, the minimum axis (k3) is parallel to the shortening direction, and the shape of the AMS ellipsoid is either triaxial or prolate (Tauxe, 1998). In the case of the Kittery Formation, the 92 elongation directions are northeast/southwest, while the shortening directions are approximately northwest/southeast. The shortening direction showed by the minimum axis most likely parallels the direction of maximum shortening during the last episode of folding in the Kittery Formation. However, because there are three obvious oblate ellipsoid shapes in the magnetic anisotropy Ramsay diagram, it is not possible to distinguish an obscured depositional signal along with a tectonic signal. When k1 is plotted on a map in geographic coordinates, k1 directions are deflected relative to one another across the Great Bay and Nannie Island fault zone. Escamilla-Casas (2003) also indicates the rotation of average axial plane directions in the Portsmouth Harbor/ Durham NH region, adding further evidence that directions of k1 to a first order follow the fold axes of Kittery Formation (direction of maximum elongation). k1 also shows varying dips from very shallow to steep at different localities with similar strikes, suggesting that the smaller scale folds visible on an outcrop scale (10-20 ft fold wavelength) are also expressed regionally, with a wavelength on the order of 50 miles (Figure 46). The magnetic anisotropy Ramsay diagram suggests that Scammel Bridge, Adams Point, and Moody Point have undergone smaller amounts of strain throughout their geologic history because these localities show very little magnetic anisotropy, and show no magnetic lineation. Pierce Island, Ft. McClary, and Cape Elizabeth are more highly strained. Cape Elizabeth shows the greatest strain and is attributed to the proximity to the Norumbega restraining bend (Swanson, 1999). If anisotropy is high, then it is possible that the NRM 93 directions can have significant angular deflection. For 5% anisotropy within a TRM, the NRM directions are deflected approximately 2.7°. For 10% anisotropy within a TRM, the NRM is deflected approximately 5°, and for 20% anisotropy within a TRM, the deflection is 10° (McElhinny and McFadden, 2000). The angular deflection of NRM for sedimentary or metamorphic rocks is not necessarily a 1:1 correlation; for this AMR (anhysteresis of magnetic remnance) studies must be undertaken. However, given this general relationship, Ft. McClary (site JB0912) and Cape Elizabeth (JB0917) could have a significant deflection of the NRM which could be a potential cause for their VGP directions to fall statistically far from the APWP for North America. Cape Elizabeth is deemed completely unsuitable for NRM paleomagnetic studies because of 59% anisotropy of susceptibility (potential NRM deflection of more than 20°) so it is not possible to test the correlation of the Kittery Formation in Cape Elizabeth with the rest of the typical Kittery Formation in southern New Hampshire and southern Maine using NRM results. However, both localities show the same magnetic mineralogy which is consistent with the correlation of Bothner and Hussey (1999) that this unit is indeed part of the traditional Kittery Formation of southern New Hampshire and Maine. Paleomagnetic and Tectonic History of the Kittery Formation: This study provides additional tectonic constraints of the tectonic evolution of the Kittery Formation. Unfortunately, this history does not begin with deposition because of a post folding magnetization but aids in further tectonic 94 interpretations after folding. In the early Silurian, the Kittery Formation was deposited in a reducing backarc basin environment just before the Acadian Orogeny, in what is now termed the Merribuckfred basin of Hussey et al. (2010). The mix of slightly calcareous and pelitic sedimentation of this unit suggests general equatorial latitude during deposition, however it was not possible to test this by using paleomagnetic analysis. In previous tectonic interpretations, the depositional source direction for the Kittery Formation was to the east (Rickerich, 1984). However, paleomagnetic data presented here supplementing data from Fargo and Bothner (1995), suggest that significant amounts of rotation could have occurred since deposition and could change the original eastern source direction calculated by Rickerich (1984) from paleocurrent observations. Soon after depositon of the Kittery Formation the Acadian Orogeny folded the Kittery Formation into early recumbent folds, followed by upright, overturned F2 folds. k1 of the AMS ellipsoid follows the fold axes of these F2 folds, which for the Kittery as a whole trend northeast/southwest. The direction of maximum shortening of the F2 folds during this time is estimated to be northwest/southeast, as delineated by the direction of k3. It is most likely that this is the first stage of deformation that supplied the shear and metamorphism to cause the dissolution of previously existing iron oxide phases, and subsequently the first generation of greigite growth. Because the magnetization, and the interpretation of the AMS data is post folding, this study was unable to confirm the total generations of folding events in the Kittery Formation. Next, the Kittery Formation is intruded by the 407 + -1 Ma Devonian Exeter Diorite, which could possibly have caused up 95 to 90 degrees of rotation and or magmatic shouldering of the Kittery Formation (Fargo and Bothner, 1995). Also, as suggested by Kent et al. (1976), it is possible that at this time the dextral strike slip Norumbega fault system had begun, which would lead to at least a second generation of greigite growth at the maximum time of shear in the lower Carboniferous / upper Permian. The continued movement along this fault system, until the end of the Alleghanian Orogeny and the formation of the supercontinent Pangea could have caused further rotation of the Kittery Formation. These rotations and multiple generations of greigite growth are evidenced by discordant VGP's in relation to the APWP of North America, and the intersection of the great circle trend of the site VGP's in the upper Carboniferous lower Permian. Lastly, the heat due to multiple intrusions of basaltic dikes and other gabbroic intrusions in the Mesozoic during the break up of Pangea was insufficient to completely remagnetize the Kittery Formation in the area of study, as evidenced by mostly passed dike tests on basaltic dikes and on large gabbroic intrusions at Cape Neddick (MacEnroe, 1996). Conclusions: • Greigite is the dominant magnetic phase in the Kittery Formation and is interpreted to have formed by the dissolution of detrital iron oxides and iron bearing sheet silicates. 96 • More importantly, this study documents that greigite can remain stable in the geologic record for millions of years, even in tectonically disturbed rocks, which is longer than previously thought. • The AMS ellipsoid preserves a tectonic petrofabric. K1 suggests regional scale folding similar to outcrop scale F2 folds in the Kittery Formation with a wavelength of approximately 50 miles, rotation of the Kittery Formation across the Great Bay fault zone and Nannie Island fault zone, and magmatic shouldering due to Paleozoic and Mesozoic plutonism. k3 represents the direction of maximum shortening due to the last folding event in the Kittery Formation and is approximately northwest/southeast. • Cape Elizabeth is too anisotropic for NRM studies without AMR studies, but has the same magnetic mineralogy as the traditionally mapped 'Kittery Formation, and is consistent with the hypothesis that the exposures at Cape Elizabeth should be correlated with the Kittery Formation and Merrimack Group as defined by Hussey et al. (2010). • NRM directions are consistent within particular sites, but not for the Kittery Formation as a whole. 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