Bedrock Geology of the the Horseback Quadrangle, Maine Chunzeng Wang Date: September 2020

DEPARTMENT OF AGRICULTURE, CONSERVATION AND FORESTRY Maine Geological Survey Robert G. Marvinney, State Geologist

OPEN-FILE NO. 20-13

Title: Bedrock geology of the The Horseback quadrangle, Maine Chunzeng Wang Date: September 2020

Contents: 25 p. report and color map

Recommended Citation: Wang, Chunzeng, 2020, Bedrock geology of the The Horseback quadrangle, Maine: Maine Geological Survey, Open-File Report 20-13, 25 p. report and color map, scale 1:24,000.

Bedrock geology of the The Horseback quadrangle, Maine

TABLE OF CONTENTS Introduction ...... 1 Geologic Setting ...... 1 Stratigraphy ...... 2 County Road Formation (Scr) ...... 3 Flume Ridge Formation (Sf) ...... 3 Flume Ridge Formation – Hall Hill Member (Sfh)...... 5 Bucksport Formation (Sb) ...... 6 Great Pond Formation (Mgp)(new name) ...... 9 Igneous Rocks ...... 11 Lucerne Granite (Dl) ...... 11 Turner Mountain Syenite (Dtm) ...... 12 Saddleback Brook Leucogranite (Dsb) ...... 13 Structural Geology ...... 21 Deformation structures within metasedimentary formations ...... 21 The Norumbega fault system ...... 22 Geologic History ...... 22 Acknowledgments ...... 23 References Cited ...... 23

Bedrock Geology of the The Horseback 7.5′ Quadrangle, Maine

Chunzeng Wang, PhD College of Arts and Sciences University of Maine at Presque Isle Presque Isle, Maine 04769

Field bedrock mapping in the Horseback quadran- INTRODUCTION gle by the author started in summer 2004 with mapping The Horseback 7.5′ quadrangle lies mostly in the neighboring Great Pond quadrangle (Wang, 2012). Hancock County of eastern-central Maine between 44° In summer 2011, with financial assistance of a Universi- 52′30″ and 45°00′ north latitude and between 68°22′30″ ty of Maine Trustee Professorship, the author did and 68°30′ west longitude. The topography in the additional mapping in the Horseback quadrangle. A quadrangle is directly related to differential weathering USGS STATEMAP Program grant allowed completion and erosion of the bedrock. For example, igneous of fieldwork in 2013. A Zillman Family Professorship intrusions stand in high relief to form rounded hills and funded geochemical and geochronological analyses in prominent ridges in the southeast, whereas metasedi- 2014. mentary and sedimentary rocks stand low in relief and GEOLOGIC SETTING form low, rolling hills and lowlands with large swamps in the central and northern parts of the quadrangle. Due The region around the Horseback quadrangle is to considerable glaciation during the Pleistocene Epoch, underlain by three slightly metamorphosed Paleozoic the area is characterized by prominent glacial land- lithostratigraphic terranes (Osberg et al., 1985) and the forms, in particular by a well-developed esker, named Norumbega fault system (Plate 1). From the northwest The Horseback esker. The esker begins at Simmons Hill to the southeast, the terranes include: (1) the eastern in the northwest corner of the quadrangle and extends lobe of the post-Taconic Aroostook-Matapedia/ southeastward for nearly 12 kilometers (km) to the Waterville belt located to the west and northwest of the southwest side of Turner Mountain in the neighboring quadrangle; (2) the Ganderian Miramichi terrane which Great Pond quadrangle. is a Cambrian-Ordovician sedimentary and volcanic The Horseback quadrangle is sparsely populated assemblage exposed in the neighboring Greenfield with only several houses and seasonal camps scattered quadrangle in the northwest; and (3) the post-Taconic, mostly along Myra Road of Greenfield Township in the Silurian Fredericton Trough turbidite suite. The Horse- north. Most of the map area is covered by timber back quadrangle is entirely underlain by the Fredericton forests, and bedrock exposures comprise less than 2% of Trough. In the previously published maps and reports, the total area. Lumber roads such as Stud Mill Road in the metasedimentary rocks on the northwest side of the the north provide access to most of the map area. Norumbega fault system were called Vassalboro Bedrock geologic mapping, mostly reconnaissance Formation (Perkins and Smith, 1925; Osberg, 1968; mapping, was performed in the Horseback 7.5′ quadran- Osberg et al., 1985) which was later re-named Hutchins gle and neighboring quadrangles in the 1960s and 1970s Corner Formation (Osberg, 1988) or Vassalboro Group by geologists McGregor (1963), Stoeser (1966), Gilman - Brewer Formation (Pollock, 2011); and the metasedi- (1974), Griffin (1976a, 1976b), Wones (1977, 1980), mentary rocks on the southeast side of the fault zone and Wones and Ayuso (1993). Among them, the most were mapped as Bucksport Formation (Trefethen, 1950; valuable reconnaissance maps were made by Griffin Wing, 1957; Osberg et al., 1985). The metasedimentary (1976a) and Wones and Ayuso (1993). Early workers rocks on both sides of the fault zone are composed identified and described major rock types within the predominantly of thick piles of deep-water, sandy quadrangle such as metasedimentary rocks, intrusive turbidites that were tightly folded and metamorphosed igneous rocks, and unmetamorphosed redbeds. More to lower greenschist facies conditions (chlorite zone) recent workers focused on the Norumbega fault system during the Late Silurian to Early Devonian Acadian that is the most prominent geologic feature of the orogeny. quadrangle (Wang and Ludman, 2003, 2004, 2012, The geology of the Horseback area and vicinity is 2013; Wang et al., 2014) and the Lucerne Granite that is also characterized by emplacement of large granitic exposed in the southeast of the quadrangle (Wones, plutons that are members of the Coastal Maine Magmat- 1980; Wones and Ayuso, 1993). ic Province, for example, the Lucerne and Deblois Editor’s note: Technically, when using the name of the quadrangle the text should read ‘the The Horseback’. For readability the second ‘the’ is removed in the report.

Chunzeng Wang plutons. The Lucerne Granite is elongated in the redbeds. In the past, the metasedimentary package direction of 210°; it extends from Great Pond area northwest of the Norumbega fault system in the quad- southwestward to the town of Orland in the Penobscot rangle and vicinity was mapped as “Sangerville For- Bay area for at least 85 km with an exposed area of 625 mation” and “Vassalboro Formation” by Griffin (1976a) km2. The Deblois, with its exposed area of 1670 km2, is or “Vassalboro Formation” by Osberg et al. (1985), the largest pluton in the Coastal Maine Magmatic Wones and Ayuso (1993), and Wang (2012); the Province. Based on Wang (2012), both Lucerne and metasedimentary package on the southeast side of the Deblois plutons connect on the east side of Great Pond fault zone as “Bucksport Formation” by Osberg et al. and indeed occur as a single batholith. (1985), Wones and Ayuso (1993), and Wang (2012). The dominant structural feature in the region is the Field mapping and observations suggest that both Norumbega fault system. The system is one of the packages of the metamorphosed sedimentary rocks are largest and longest transcurrent fault zones in the very similar in lithology and in sedimentary features and northern Appalachian Mountains (Hubbard et al., 1995; that both could be correlated to the Flume Ridge Ludman et al., 1999). It extends for at least 450 km, Formation (Osberg et al., 1985; Ludman, 1991) that from the Casco Bay region in southwestern Maine to crops out in the area north and northeast of the Horse- central New Brunswick in Maritime Canada. The fault back quadrangle. Based on correlation with the Flume zone was initiated as an orogen-scale ductile shear Ridge Formation in the neighboring Greenfield quad- system approximately 380 million years ago (Ludman et rangle in the north and northeast (Ludman, 2020), this al., 1999; West, 1999) as a result of oblique collision report and the accompanying bedrock geologic map (Swanson, 1999b) during the Acadian orogeny, and (Plate 1) adopt the nomenclature of Flume Ridge followed by episodic, regional-scale brittle reactivation Formation for the metasedimentary package on the (Ludman, 1998; Ludman and Gibbons, 1999; Ludman northwest side of the Norumbega fault system and et al., 1999; Wang and Ludman, 2003, 2004). A Bucksport Formation for the metasedimentary package complex displacement history, possibly continuous for on the southeast side of the fault system in the Horse- almost 100 million years, has been inferred for the back quadrangle. deeper segment in south-central Maine by West and Previous workers assigned Silurian (Griffin, Hubbard (1997) and West and Roden-Tice (2003). Two 1976a), Silurian-Ordovician (Osberg et al., 1985), or ductile shearing events have been recognized along the Devonian-Silurian (Wones and Ayuso, 1993) ages for Norumbega fault system in south-central Maine and the metasedimentary rocks on the northwest side of the dated to ~380 Ma (at amphibolite facies) and ~290 Ma Norumbega fault system (the Vassalboro Group or (at greenschist facies), respectively (West and Lux, Vassalboro Formation, now in this report the Flume 1993; West and Hubbard, 1997; West, 1999). Swanson Ridge Formation), and Silurian (Griffin, 1976a), (1999a, 1999b) proposed that the regional dextral Devonian-Ordovician (Osberg et al., 1985) or Devonian shearing and accompanying upright folding, granitic -Silurian (Wones and Ayuso, 1993) ages for the Buck- emplacement, and metamorphism can be linked to a sport Formation on the southeast side. Based on recently restraining-bend geometry along the Norumbega fault published detrital zircon geochronological data (e.g. system in south-central Maine. Dokken et al., 2018; Ludman et al., 2018) and correla- The shallower segment of the Norumbega fault tion with the Greenfield quadrangle located to the system in eastern-central and eastern Maine, however, northwest (Ludman, 2020), this report and the accompa- has experienced a complex, episodic deformational nying map assign a Silurian age for both Flume Ridge history involving distinctive ductile and brittle defor- and Bucksport formations. The Silurian age for Buck- mation (Ludman, 1998; Wang and Ludman, 2003, 2004, sport Formation is confirmed by a detrital zircon 2012, 2013). The initial greenschist-facies dextral geochronological analysis performed during this project ductile shearing began at ~380 Ma and strain was and the analytical data is included in the report. largely partitioned into the Kellyland and Waite ductile Based on previous studies, the unmetamorphosed shear zone strands in eastern Maine (Ludman, 1998; redbeds distributed along the Norumbega fault system, Ludman et al., 1999). These shear strands, distinct from herein called the Great Pond Formation, are post- one another near the Maine-New Brunswick border, Acadian terrestrial molasse sediments deposited in pull- converge in the area just northeast of the neighboring apart basins that were produced by brittle reactivation of Great Pond quadrangle. the fault system (Wang and Ludman, 2003, 2004, 2012, 2013). Bradley (1982) used “Norumbega Basin” to STRATIGRAPHY name the belt of redbeds in the Chemo Pond - The Stratified rocks in the Horseback quadrangle Horseback - Great Pond area. Based on correlation with include slightly metamorphosed and folded submarine similar redbeds along the length of the Norumbega fault sedimentary rocks and unmetamorphosed terrestrial system on the Canadian side of the Maine-New Bruns-

2 Bedrock geology of the The Horseback quadrangle, Maine wick border where it is called “Shin Formation (of weathering medium to thick beds of quartzofeldspathic Mabou Group)” of Early Carboniferous age (Fyffe, graywacke sandstone interbedded with subordinate, thin 1988), the Great Pond Formation redbeds are assigned a to medium horizons of well-cleaved meta-claystone Mississippian age in this report. slate and with minor, medium layers of feldspathic siltstone (Figures 1A and 1B; see Plate 1 for figure County Road Formation (Scr) locations). Bed thickness is generally between 10 Based on the report by Ludman (2020), in the centimeters (cm) and 0.5 meters (m) for graywacke neighboring Greenfield quadrangle in the north, a new, sandstone beds (which could exceed 1 m), and between independent formation named County Road Formation 1 cm and 15 cm for meta-claystone layers (which exists on the west side of the Flume Ridge Formation. locally could exceed 35 cm or even occasionally 1 m). In the Horseback quadrangle, however, only three The graywacke is generally characterized by its hard- outcrops of the formation have been mapped along ness and poorly sorted angular clasts of quartz, feldspar, Pickerel Pond Road near the northwest corner of the and small lithic fragments set in a compact, clay-rich quadrangle. The formation is well exposed along the matrix (Figures 1C and 1D). Claystone layers are very County Road in the Otter Chain Ponds quadrangle to the fine grained, composed of clay minerals of predomi- west from which it was named (Ludman, 2020). nantly sericite, minor biotite, and opaque material, and Field observations and descriptions by Ludman generally present as dark slate or phyllite (Figures 1A (2020) indicate a slight change from the Flume Ridge and 1B). At several locations, claystone dominates and Formation. Generally, both Flume Ridge and County presents as thick and massive slate or phyllite. For Road formations consist dominantly of turbiditic example, at a gravel pit located on the south side of sandstones (wackes) and pelite with similar bedding Myra Road at Madden Hill in Greenfield Township, styles. Fresh surfaces of County Road sandstones are massive black shale-like slate and phyllite dominate and darker gray and weathered surfaces are medium gray contain abundant fine quartz veins. Calcareous siltstone (for quartz-rich sandstone) to chalky white (for layers are sporadically distributed throughout and quartzofeldspathic sandstone) in contrast to the buff- or locally weathered to a rusty color where sulfide is orange-brown-weathering Flume Ridge sandstone. abundant. Calc-silicate bands are relatively rare. County Road sandstones are non- to sparsely calcare- In the map area the Flume Ridge Formation is ous, lack ferroan carbonate, have few or no detrital interpreted as a typical turbidite suite. Primary sedimen- muscovite flakes and are, in general, coarser grained. tary structures are common, including parallel- County Road wacke layers can be thick. laminated and ripple-laminated turbidite intervals According to Ludman (2020) and Ludman et al. (Figures 1B and 1E), graded bedding (Figure 1F), and (2018), detrital zircon dating and spore ornamentation soft-sediment deformation structures (Figure 1G). A dating point toward a late Wenlock to early Pridoli general northeasterly strike of bedding at 30°–60° is range for the County Road Formation. prevalent throughout the area – however, bedding Flume Ridge Formation (Sf) striking northwest (or southeast) was measured in places where the hinge of folded strata probably exists. Dips The Flume Ridge Formation is composed predomi- are medium to steep at an angle ranging from 65° to 85° nantly of dark gray, grayish-black, and brown- or rusty- to either northwest or southeast.

A B

Figure 1. Metasedimentary rocks of the Flume Ridge Formation. (A) Alternating thick graywacke and thin claystone on pavement outcrop, viewer facing north. (B) Thick graywacke and laminated claystone on pavement outcrop, viewer facing north. 3

Chunzeng Wang

C D

E F

G H

Figure 1 (continued). Photomicrographs (C) graywacke and (D) foliated graywacke; both use cross-polarized light. (E) Laminat- ed claystone on pavement outcrop, pen pointing to north. (F) Graded bedding on pavement outcrop. (G) Mud chips showing soft- sediment deformation or disturbance on pavement outcrop. (H) Slaty cleaved graywacke on vertical ledge face. See the text for detailed interpretation.

The Flume Ridge Formation was folded during the plane foliation or cleavage associated with the tight Acadian orogeny. Small-scale tight and isoclinal folds folding is penetrative throughout the formation. Cleav- are observed throughout the area but individual large- age is parallel or nearly parallel to the bedding at most scale folds are hardly shown on the map even though outcrops (Figures 1A and 1B). systematic measurement of strike and dip of the bedding The Flume Ridge Formation was metamorphosed and foliation patterns do show their existence. Axial- to lower greenschist facies during Acadian folding and 4 Bedrock geology of the The Horseback quadrangle, Maine occurs predominantly as meta-graywacke, slate (meta- 1:62,500) by Griffin (1976a, 1976b) and as “Olamon claystone), and phyllite. Meta-claystone usually dis- Pond Member” in partially mapped Saponac quadrangle plays more closely spaced cleavage compared to meta- (at scale 1:62,500) by Olson (1972). This unique belt of graywacke that shows wide-spaced cleavage (Figure sedimentary rocks is well exposed along Madden Hill 1H). Microscopically, the slightly metamorphosed (in the Horseback quadrangle) and Hall Hill (in Green- graywacke-sandstone show typical relict clastic textures field quadrangle) in the north. To be consistent with and (Figure 1C), with some more foliated showing shape- following the Greenfield 7.5′ quadrangle bedrock preferred fabrics defined by elongated quartz and geologic map (Ludman, 2020), this belt of slate and feldspar clasts and muscovite flakes (Figure 1D). phyllite is also named Hall Hill Member of the Flume Ridge Formation in this report. Flume Ridge Formation – Hall Hill Member (Sfh) The estimated width of this slate and phyllite belt is An extraordinary, northeast-striking belt of red about 140 to 295 m. It is predominantly red (maroon) in (maroon) and green, very fine or fine-grained, thinly color but locally may alternate with green, light green, layered slate and phyllite occurs within the Flume Ridge and/or white subordinate layers (Figure 2A). Layers Formation in the northwestern part of the Horseback could be as thin as sub-centimeter. It is generally quadrangle. It is well exposed around the border with foliated and the foliation is parallel or sub-parallel to the neighboring Otter Chain Ponds quadrangle, on the bedding. It is locally contorted and contains white thin southwest side of Titcomb Brook. A similar belt of quartz veins that either fill in foliations or cross-cut rocks was shown as “maroon and green member” in the foliation/bedding. Locally it also contains pyrite. The Great Pond and Orono reconnaissance maps (at scale predominant lithology of the red slate member is very

A B

C D

Figure 2. Flume Ridge Formation – Hall Hill Member of maroon slate and phyllite. Photo (A) shows alternating maroon and light -green or white layers of fine-grained, siliceous, and tuffaceous slate (in the adjacent Otter Chain Ponds quadrangle), on pavement, pen pointing to north. Photomicrographs (B) clay-rich tuffite. (C) siliceous tuffite with augen quartz aggregates which may relate to devitrification, both in the adjacent Otter Chain Ponds quadrangle, and (D) siliceous tuffite with angular quartz; cross- polarized light. See the text for detailed interpretation.

Chunzeng Wang fine to fine-grained, siliceous, and tuffaceous slate and intrusions from the Lucerne pluton (see later section for phyllite characterized by alternating dark (red-maroon) details). Because the septum of the metasedimentary and light (light-green or white) thin bands (layers). Thin rocks is located on the southeast side of the Norumbega sections of the light-colored, claystone-like samples fault system, it is mapped as Bucksport Formation. show abundant, extremely fine grained sericite, chlorite, The Bucksport Formation generally consists quartz, and elongated (or augen-like) dark particles predominantly of dark-gray, thick-layered feldspathic (Figure 2B). Thin sections of the dark-colored, siliceous graywacke and meta-siltstone beds, alternating with samples show extremely fine grained texture as well, in medium-thin layers of dark claystone (Figures 3A and addition to interesting features such as ovoid augen-like 3B). Some interbedded medium to thin siltstones are silicified aggregates (lapilli spherules?) that form a locally calcareous and weathered to a rusty color shape-preferred fabric within an even finer matrix (Figure 3A). Lithologically the Bucksport Formation is composed probably of hematite and other opaque so similar to the Flume Ridge Formation that it would minerals (Figures 2C and 2D). The augen-like silicified be impossible to separate them were it not for the aggregates (Figure 2C) could be the result of devitrifica- presence of the Norumbega fault system. The Bucksport tion of glass fragments. Quartz clasts in the dark- Formation was also tightly folded and metamorphosed colored, siliceous samples are mostly angular in shape to lower greenschist facies during Acadian deformation. (Figure 2D). These characteristics suggest that the red Like the Flume Ridge Formation, both bedding and slate member most likely has a tuffaceous, clay-rich or axial-plane foliation/cleavage generally strike northeast silica-rich (felsic) protolith of distal volcanic origin. The and steeply dip to either the northwest or southeast. alternating clay-rich and silica-rich layers suggests that The metasedimentary rocks of the Bucksport its protolith was a tuffite. Formation next to the Lucerne Granite were subjected to thermal contact metamorphism from emplacement of Bucksport Formation (Sb) the pluton. The claystone and fine-grained siltstone Bucksport Formation occurs only as a narrow became purplish-black hornfels (Figure 3B). The dark septum between the unmetamorphosed redbeds and the color of the hornfels is due to presence of numerous Lucerne Granite in the Horseback quadrangle. Several small flakes of biotite produced as a result of the contact exposures of the metasedimentary rocks on the north- metamorphism (Figure 3D). Locally, hornblende co- west side of the Lucerne Granite were mapped as exists with biotite as a hornfels mineral. The contact “country-rock xenoliths within Lucerne pluton” in the zone is at least 30 meters wide. The metasedimentary Great Pond quadrangle (Wang, 2012). With more rocks next to the leucogranite were also affected by the outcrops of the similar metasedimentary rocks mapped contact metamorphism, as were the metasedimentary along the northwest margin of the Lucerne pluton in the rock xenoliths within the leucogranite. Horseback quadrangle, it is now believed that these Most of the metasedimentary rocks of the septum outcrops are a continuation of a septum between the are ductilely sheared and strongly foliated due to their Lucerne pluton and the redbeds (or the mylonitic involvement in Norumbega ductile shearing, the early leucogranitic rocks next to the redbeds). The mylonitic deformation phase of the fault system. As such, these granitic rocks indeed occur as independent leucogranite rocks became phyllonitic, schistose, or mylonitic

A B

Figure 3. Metasedimentary rocks of Bucksport Formation. (A) Thinned and shortened alternating graywacke, siltstone, and claystone on pavement outcrop, viewer facing north. (B) Thinned and shortened alternating sandstone, siltstone, and claystone on pavement outcrop, viewer facing north. 6 Bedrock geology of the The Horseback quadrangle, Maine

C D

E F

G H

Figure 3 (continued). (C) Spangled muscovite-quartz schist on pavement outcrop, pen pointing to north. Photomicrographs (D) foliated and sheared hornfelsed silty claystone, (E) micro-schist, (F) phyllonite; cross-polarized light. (G) spangled muscovite- quartz schist with mica-fish; cross-polarized light. (H) spangled muscovite-quartz schist with garnet porphyroblasts; plane- polarized light.

(Figures 3C, 3D, 3E, 3F, 3G, and 3H). Closer to the spangled muscovite-quartz schist even contains garnet mylonitic leucogranite, they present as a spangled porphyroblasts (Figure 3H). Some graywacke sandstone muscovite-quartz schist (Figures 3C, 3G, and 3H). Meta changed to quartzite. -siltstone and meta-claystone were ductilely sheared to A sample was collected at Location A (Plate 1) in become very fine grained muscovite-quartz schist November 2013 with an initial intention to apply zircon (Figures 3E and 3G) or phyllonite (Figure 3F). Some U-Pb method to date the leucogranite. Zircon grains

Chunzeng Wang

Figure 4. CL (cathodoluminescence) images of 38 detrital zircon grains selected from a Bucksport Formation xenolith within the leucogranite. Each grain is labeled with 206Pb/238U age. White circles show laser analytic targets. were first separated from the sample at Overburden zircon grains should be excluded from consideration. Drilling Management Limited (ODM) laboratory Zircon SG-5 gives a 206Pb/238U age of 462±4 Ma from (Canada) and later analyzed by using LA-ICP-MS U-Pb its core but a much younger age of 412±7 Ma on its method at University of New Brunswick, Canada. margin (Figure 4). If this younger age and three other However, CL (cathodoluminescence) images of the young ages of 414±5 Ma (zircon grain SG-31), 415±5 zircon grains show them to be detrital zircons as they Ma (zircon grain SG-15), and 418±4 Ma (zircon grain are all worn and rounded (Figure 4). Based on field SG-3) are considered to be reliable, it would suggest observations, the leucogranite contains sedimentary that the earliest sedimentation timing of this part of the rock xenoliths that originated from the surrounding Bucksport Formation was in Silurian Pridoli Epoch. country rock, the Bucksport Formation. The Bucksport Formation metagraywacke and metapelite next to the leucogranite locally also experienced in situ melting. Therefore, it is believed that the sample with the detrital zircon grains belongs to Bucksport Formation and the detrital zircon grains could be used to reveal provenance and maximum deposition age of the Bucksport For- mation. Table 1 contains the geochronological analytical data of 38 detrital zircon grains (with 40 analyses). The detrital zircon grains are predominantly prismatic in shape and the majority clearly show oscillatory zoning (Figure 4), indicative of a magmatic origin. Figure 5 shows their concordia spectra with a prominent concordia age at 463 Ma. The majority of the zircon grains have 206Pb/238U ages between 441±7 Ma and 476±4 Ma with one (sample SG-26) showing a 706±10 Ma age of its core, indicating a provenance in peri-Gondwana terranes – probably the collided Ordovi- cian arcs or back-arcs of Ganderia. Among the youngest 207 235 206 238 6 grains, zircon grain SG-22 gives a 206Pb/238U age of Figure 5. Pb/ U – Pb/ U concordia spectra of all the 410±4 Ma, but this zircon grain is extensively cracked analyzed detrital zircon grains selected from a Bucksport Formation xenolith within the leucogranite. and the laser analytic spot is poorly located on the margin (Figure 4). Zircon grain SG-32 (412±4 Ma) is also cracked. Therefore, the ages from both of these

8 Bedrock geology of the The Horseback quadrangle, Maine Table 1. LA-ICP-MS U-Pb analytical data of detrital zircon grains selected from a Bucksport Formation xenolith within the leucogranite.

Isotopic Ratios Ages (Ma) Sample 207Pb/235U 2σ 206Pb/238U 2σ 207Pb/206Pb 2σ 207Pb/235U 2σ 206Pb/238U 2σ 207Pb/206Pb 2σ SG-38 0.577 0.015 0.0737 0.0007 0.0561 0.0015 462 10 458 4 456 36 SG-37 0.586 0.014 0.0746 0.0009 0.0568 0.0011 467 9 465 5 489 27 SG-36 0.573 0.010 0.0743 0.0008 0.0556 0.00029 460 6 462 5 436 12 SG-35 0.591 0.014 0.0744 0.0009 0.0573 0.0012 471 9 463 5 544 31 SG-34 0.572 0.010 0.0740 0.0009 0.05598 0.00018 459 6 460 6 452 7 SG-33 0.539 0.015 0.0707 0.0012 0.056 0.0015 438 10 441 7 448 35 SG-32 0.506 0.009 0.0660 0.0007 0.05574 0.00097 416 6 412 4 449 20 SG-31 0.504 0.013 0.0663 0.0008 0.0559 0.0014 418 9 414 5 445 28 SG-30 0.590 0.015 0.0748 0.0007 0.0574 0.0013 470 10 465 4 503 33 SG-29 0.582 0.011 0.0746 0.0007 0.0563 0.001 467 7 464 4 473 22 SG-28 0.574 0.009 0.0741 0.0006 0.05631 0.00076 461 6 461 4 465 19 SG-27 0.578 0.014 0.0746 0.0007 0.0561 0.0013 463 9 464 5 473 29 SG-26-1 1.008 0.021 0.1158 0.0018 0.06304 0.0003 707 11 706 10 709 10 SG-26-2 0.578 0.014 0.0750 0.0012 0.05632 0.00025 463 9 466 7 465 10 SG-25 0.580 0.010 0.0745 0.0006 0.05602 0.00096 465 7 463 4 464 19 SG-24 0.584 0.013 0.0750 0.0007 0.0563 0.0013 468 8 466 4 478 30 SG-23 0.548 0.019 0.0712 0.0013 0.0554 0.0014 443 13 444 8 441 32 SG-22 0.498 0.006 0.0657 0.0007 0.05502 0.00011 410 4 410 4 413 4 SG-21 0.570 0.012 0.0733 0.0007 0.0567 0.001 457 8 456 4 487 23 SG-20 0.585 0.010 0.0747 0.0006 0.05648 0.00093 467 6 465 3 468 23 SG-19 0.607 0.012 0.0746 0.0006 0.0587 0.0011 483 7 464 4 552 23 SG-18 0.593 0.015 0.0737 0.0006 0.058 0.0013 472 10 459 4 534 30 SG-17 0.533 0.024 0.0709 0.0014 0.0562 0.0029 433 16 442 9 469 64 SG-16 0.547 0.013 0.0716 0.0008 0.056 0.0012 442 9 446 5 449 25 SG-15 0.493 0.012 0.0666 0.0009 0.0542 0.0015 406 9 415 5 394 29 SG-14 0.588 0.014 0.0759 0.0009 0.0563 0.0013 469 9 472 6 475 28 SG-13 0.560 0.011 0.0727 0.0007 0.05529 0.00086 451 7 452 4 454 19 SG-12 0.592 0.017 0.0766 0.0007 0.0565 0.0016 471 11 476 4 469 26 SG-11 0.571 0.009 0.0740 0.0006 0.05578 0.00076 458 6 460 3 452 17 SG-10 0.573 0.009 0.0743 0.0006 0.05614 0.00077 460 6 462 4 454 18 SG-9 0.583 0.015 0.0758 0.0008 0.0558 0.0015 466 10 471 5 450 28 SG-8 0.575 0.010 0.0744 0.0007 0.05601 0.00098 460 7 463 4 454 21 SG-7 0.575 0.012 0.0738 0.0007 0.05671 0.00098 461 8 459 4 456 25 SG-6 0.584 0.011 0.0723 0.0006 0.05836 0.00098 466 7 450 4 540 19 SG-5-1 0.581 0.013 0.0743 0.0007 0.0559 0.0012 464 9 462 4 459 28 SG-5-2 0.505 0.017 0.0660 0.0011 0.0554 0.0015 416 11 412 7 446 33 SG-4 0.592 0.019 0.0753 0.0008 0.0563 0.0015 473 12 468 5 472 29 SG-3 0.511 0.010 0.0670 0.0006 0.05543 0.00093 418 7 418 4 437 21 SG-2 0.580 0.011 0.0754 0.0007 0.05606 0.00083 465 7 469 4 467 19 G-1 0.599 0.011 0.0761 0.0008 0.05679 0.00091 476 7 473 5 496 21

Great Pond Formation (Mgp)(new name) the southeast side. The redbeds occur today as steeply A narrow, northeast-striking sliver of unmetamor- dipping beds of variable thickness that strike northeast phosed redbeds occurs between the Flume Ridge (locally northwest). The present steep dip of the redbeds Formation and the mylonitic leucogranite/Bucksport indicate subsequent dip-slip motion (likely in reverse Formation septum. A new formation name is proposed sense) along the fault zone. for the redbeds in this report. It is called “Great Pond Lithologically the redbeds can be classified into Formation” due to its excellent exposure on the north- two major categories: one is composed predominantly west side (in Main Stream) and southwest side (at of pebble to cobble conglomerate (Figure 6A) and the Turner Mountain) of Great Pond in the neighboring other is a combination of maroon sandstone, arkose, Great Pond quadrangle. This redbed sliver is one of nine siltstone, and mudstone (Figures 6B, 6C, 6D, and 6E). that occur along the length of the Norumbega fault The conglomerate occurs mostly near the northwest system in eastern and eastern-central Maine, all of boundary of the redbeds sliver. It is massive and can be which are interpreted as having been deposited in several meters thick. The conglomerate is polymictic sedimentary pull-apart basins generated by Late Devo- and composed mostly of red (maroon) or gray (light nian–Early Mississippian dextral strike-slip faulting red) sandstone and siltstone pebbles with some quartz along the length of the Norumbega fault system (Wang clasts (Figure 6A). Most clasts (pebbles) are rounded or and Ludman, 2003). They are in fault contact with the sub-rounded but poorly sorted. The clasts vary in size Flume Ridge Formation on the northwest side and the and can be up to 25 cm long. The matrix is composed of mylonitic leucogranite/Bucksport Formation septum on detrital quartz, hematite, plagioclase, potassic feldspar,

Chunzeng Wang muscovite, chlorite, and opaque minerals. The red are mostly angular or sub-angular in shape (Figure 6F). sandstone and siltstone consist predominantly of detrital Finely laminated mudstone is deep red in color and quartz and feldspar with a fine-grained hematite and composed of extremely fine grained muscovite, quartz, sericite matrix. The detrital quartz and feldspar clasts and plagioclase.

A B

C D

E F

Figure 6. Photos showing lithologies of the redbeds and their sedimentary features of Great Pond Formation. (A) Poorly sorted pebble conglomerate on pavement outcrop, pen pointing to north. (B) Arkose and red mudstone with load and flame structure on pavement outcrop, viewer facing north. (C) Sandstone fill in a channel (showing only half of the channel) on pavement outcrop, pencil pointing to north. (D) Arkose with graded bedding on pavement outcrop, pen pointing to north. (E) Cross-bedding in arkose on pavement outcrop, viewer facing north. (F) Photomicrograph of sandy siltstone of polymictic, angular-subangular quartz and feldspar clasts, cross-polarized light. 10 Bedrock geology of the The Horseback quadrangle, Maine A distinctive lithology of the redbeds is the coarse- and pink potassic feldspar megacrysts (Figures 7A and grained arkose (Figures 6B and 6D). The arkose is 7B). The granite is composed predominantly of white- composed predominantly of fragmental and angular pink perthitic microcline and white sodic plagioclase pink potassic feldspar clasts sized up to 5–6 cm in megacrysts up to 8 cm in length set in a coarse-grained length and fragmental quartz and plagioclase clasts. The matrix of subhedral albite and anhedral quartz, biotite, red-pink, coarse-grained arkose occurs as thin to and minor hornblende (Figures 7A and 7B), with a medium beds interbedded within finer red sandstone typical seriate texture (Figure 7A) (Wones, 1980). and mudstone horizons (Figure 6B). Rapakivi textures of albite rims on alkali feldspar Primary sedimentary structures of graded bedding megacrysts are observed but not common (Figures 7A (Figure 6D) and cross-bedding (Figure 6E) are common. and 7B). In addition to the main-phase megacrystic Soft-sediment deformation structures such as load and granite (Figure 7A), local variations also include areas flame structures are observed around contacts between characterized by porphyritic texture (Figure 7B). coarse-grained beds such as arkose and fine-grained Phenocrysts in the porphyritic variety include predomi- beds of siltstone and mudstone (Figure 6B). Primary nantly sub-euhedral and anhedral potassic feldspar and structures also include channel fills at different sizes quartz. Feldspar phenocrysts can be as large as 5 cm. (Figure 6C). The matrix is medium or fine grained (Figures 7B, 7C, The arkosic nature of the redbeds demonstrates that and 7D). Figure 7C shows medium-grained matrix of their sediments were extremely immature, suggesting a subhedral feldspar, anhedral quartz, and biotite in source region proximal to coarse-grained, potassic contact with feldspar megacrysts; and Figure 7D shows feldspar rich, felsic plutons. Two possible local sources medium-grained matrix with myrmekitic quartz. of potassic feldspars are the Lucerne Granite pluton and Contacts between the porphyritic and coarser grained the Turner Mountain Syenite pluton because both the megacrystic varieties appear to be gradational. Two granite and syenite are largely composed of megacrystic large areas of porphyritic granite are located on the potassic feldspars (see later sections for details). The southeast side of Bald Bluff Mountain ridge and in the poor sorting and angular shape of the detrital clasts and southeast corner area of the quadrangle. pebbles suggest that the redbeds were near-source Outcrop-scale, medium-grained granite dikes or intermontane molasse deposits. aplite dikes are relatively common within both the megacrystic and the porphyritic varieties within the IGNEOUS ROCKS Lucerne pluton (Figures 7E and 7F). Figure 7E shows a Igneous rocks mapped in the Horseback quadrangle small medium-grained granite dike intruded within the include the Lucerne Granite that occurs in the southeast main-phase megacrystic granite and Figure 7F shows a of the quadrangle, the Turner Mountain Syenite that thicker aplite dike intruded within the porphyritic only shows its southwest “tail” at the middle-east border granite. The width of dikes ranges from several centi- of the quadrangle, and the elongated, ductilely sheared meters to 2 m. They are composed predominantly of leucogranite, herein named Saddleback Brook Leu- white sodic plagioclase, white potassic feldspar, and cogranite, next to the Great Pond Formation redbeds. quartz. Ferromagnesian minerals such as biotite are Lucerne Granite (Dl) scarce. Primary flow foliation defined by alignment of The Lucerne Granite within the Horseback quad- euhedral and subhedral feldspars has been locally rangle is characterized by a massive and extremely observed near the margin of the pluton. For example, in coarse grained appearance and distinctive pale-white the area around the southeast corner of the quadrangle,

A B

Figure 7. Lucerne Granite. (A) Lucerne main-phase megacrystic granite with seriate texture and with rapakivi feldspar (in the adjacent Great Pond quadrangle), on pavement. (B) Lucerne minor-phase porphyritic granite on pavement outcrop.

Chunzeng Wang

C D

E F

Figure 7 (continued). Photomicrographs (C) and (D) showing matrix of porphyritic granite variety under cross-polarized light. (E) A medium-grained granite dike within megacrystic granite on pavement outcrop. (F) An aplite dike (upper) within porphyritic granite on pavement outcrop, pen indicating location of the contact. at several outcrops, the granite shows clearly defined the neighboring Great Pond quadrangle and partly in the flow foliation that strikes at 055°–077°, nearly parallel Horseback quadrangle. In the Horseback quadrangle, it to the southeastern contact of the pluton, and dips near shows only its southwest “tail” (about 10% of the entire vertically. stock) at the middle-east border of the quadrangle where According to Loiselle and Ayuso (1980), Wones the best exposure is on a small, southeast-facing cliff. (1980), Hogan and Sinha (1989), and Wones and Ayuso The syenite stock has long been identified by previous (1993), the Lucerne Granite is a calc-alkaline granite workers (Stoeser, 1966; Gilman, 1974; Griffin, 1976a; and chemically metaluminous to mildly peraluminous, Wones, 1977, 1980; Wones and Ayuso, 1993) as an indicated by a mean ACNK of 1.05±0.02, with a range independent intrusion and the only syenite found in of 1.0 to 1.1. They have a mean SiO2 content of central-eastern and eastern Maine. On the Great Pond 71.9±2.0 wt% (with a range of 68.4 to 75.1 wt%), a 7.5′ quadrangle bedrock geologic map (Wang, 2012), 2 mean K2O content of 5.55±0.30 wt%, and a mean Rb the syenite intrusion, a stock of at least 2 km exposed, content of 322.00±68.52 ppm. is tabular in shape (vertically) and extends about 2.75 Geochronological studies on the Lucerne pluton by km along the Norumbega fault system. The syenite previous workers have yielded a zircon 207Pb/206Pb age stock is sandwiched between the Great Pond Formation of 380±4 Ma (Zartman and Gallego, 1979) and a redbeds to the northwest and the mylonitic leucogranite 207Pb/206Pb age of 380 Ma (Wones and Ayuso, 1993). A to the southeast within the fault system. Because it is recent zircon LA-ICP-MS geochronological analysis of more resistant to weathering than other surrounding a granite sample collected from the neighboring Hop- rocks, it stands in high relief and forms Turner Moun- kins Pond quadrangle yielded a U-Pb concordia age of tain and Little Turner Mountain. 386.1±2.3 Ma (Wang, unpublished data). The Turner Mountain Syenite is texturally and mineralogically homogenous. It is a deeply weathered Turner Mountain Syenite (Dtm) and altered dark brown to dark gray porphyritic horn- The Turner Mountain Syenite is well exposed blende-biotite syenite. Its weathering surfaces are a around Turner Mountain and Little Turner Mountain in lighter, pinkish color. The syenite is characterized by

12 Bedrock geology of the The Horseback quadrangle, Maine

A B

C D

Figure 8. Turner Mountain Syenite. (A) Porphyritic syenite dominated by pink potassic feldspar phenocrysts on pavement outcrop. Photomicrographs (B) cataclasized syenite and (C) calcite veins within fractured potassic feldspar crystals (in the adjacent Great Pond quadrangle), and (D) chlorite veins within fractured potassic feldspar crystals (also in the adjacent Great Pond quadrangle); cross-polarized light. large pink euhedral potassic feldspar phenocrysts calcite veins and Figure 8D showing chlorite veins). commonly 2–6 cm long (Figure 8A). Potassic feldspar Substantial alteration of hornblende and biotite to phenocrysts are mostly homogenous with only a small chlorite is observed throughout the entire syenite stock, percentage showing perthitic intergrowths. Its medium- in particular along its fault-contact margins. to coarse-grained matrix is composed predominantly of According to whole-rock geochemical analysis subhedral orthoclase, plagioclase feldspars, biotite, and (Wang et al., 2014), the Turner Mountain Syenite is hornblende. Fine-grained interstitial anhedral quartz in largely intermediate-felsic in SiO2 content (58.68 – the matrix makes up less than 5% of the rock. Small and 65.11 wt%), ultrapotassic (6.41 - 7.93 wt% of K2O and dark inclusions of medium- to fine-grained alkaline and K2O/Na2O ratios of 2.75 - 4.15), and yet relatively more mafic rocks have been observed. Small xenoliths primitive in terms of MgO, Ni, and Cr contents. The of metasedimentary rocks were also observed within the syenite is enriched in large ion lithophile elements (Rb, syenite. K, Th, U, Ba, etc.) relative to high field strength The entire syenite stock is in fault contact with its elements, has elevated abundance of light rare earth country rocks. The syenite next to the fault contact is elements (relative to heavy rare earth elements), and has substantially cataclasized. For example, feldspar high 87Sr/86Sr initial ratios (0.703843 - 0.706818). A phenocrysts are cracked or fractured into smaller zircon U-Pb geochronological analysis with LA-ICP- fragments (Figure 8B). Hydrothermal secondary MS method yielded a weighted mean 206Pb/238U age of minerals such as chlorite, calcite, and sericite are 410.5±2.4 Ma for the syenite (Wang et al., 2014). common and chlorite and calcite can occur as small Saddleback Brook Leucogranite (Dsb) veins. At microscopic scale, the veins fill in cracks or fractures within feldspar crystals (Figure 8C showing A narrow belt of northeast-elongated granite occurs 13

Chunzeng Wang between the Great Pond Formation redbeds fault sliver and very few biotite (Figures 9C, 9D, 9E, and 9F). Low- and the septum of the ductilely sheared Bucksport strain domains showing granitic texture and composi- Formation metasedimentary rocks, within the Norumbe- tion are distinguishable in the field and microscopically ga fault system. The latter separates it from the Lucerne (Figures 9C and 9D). The lack of ferromagnesian granite pluton, clearly indicating that this belt of granitic silicates makes this belt of granite a leucogranite. Due to rocks cannot be part of the Lucerne granite pluton. The its excellent exposure along the ridge on the north side granite is entirely ductilely sheared to be mylonitic and of Saddleback Brook located in the southwest corner of ultramylonitic. In previous studies this belt of mylonitic the quadrangle, this leucogranite belt is referred to as and ultramylonitic granite was mapped as either the Saddleback Brook Leucogranite in this report and on “mylonitized granitic gneiss and/or volcanics” (Griffin, the accompanying map (Plate 1). 1976a) or “Mixer Pond Member of Passagassawakeag Microscopically, the grain-size reduction was Gneiss” (Wones, 1980; Osberg et al., 1985; Wones and achieved predominantly by dynamic recrystallization, Ayuso, 1993) or part of the Lucerne pluton in the dislocation, and sub-grain rotation of quartz crystals, neighboring Great Pond 7.5′ quadrangle (Wang, 2012). and quartz crystals have been sheared/smeared into Compared to the megacrystic, coarse-grained, and quartz ribbons (Figures 9D, 9E, and 9F). Feldspar seriate Lucerne Granite, although it is entirely sheared crystals, however, show no plastic deformation but do and mylonitized (Figure 9A) or ultramylonitized (Figure show cataclasis, suggesting that the deformation 9B) within the Norumbega ductile shear zone, this temperature was below 450°C (Simpson, 1985; Tullis granite is generally finer grained (than the Lucerne and Yund, 1985). Granite) and composed predominantly of quartz, Metasedimentary xenoliths occur in the leucogran- plagioclase, and potassic feldspar with minor muscovite ite, in particular in places near the contact with the

A B

C D

Figure 9. The Saddleback Brook Leucogranite. (A) Mylonitic leucogranite on pavement outcrop, viewer facing north. (B) Ultra- mylonitic leucogranite on pavement outcrop, viewer facing north. Photomicrographs (C) showing granitic texture, (D) showing granitic texture and quartz ribbons.

14 Bedrock geology of the The Horseback quadrangle, Maine

E F

Figure 9 (continued). Photomicrographs (E) showing muscovite fish and quartz ribbons, and (F) showing quartz ribbons and aligned biotite flakes. Cross-polarized light.

Bucksport Formation metasedimentary rocks. Although been observed within the leucogranite. The thickness of two pieces of xenolith are large enough to be shown on the veins ranges from several centimeters to 2 m. Based the accompanying geologic map, most of them are too on cross-cutting relationships, coarser grained or small to be shown on the map (Figure 10A). Like the pegmatitic veins are generally younger than the finer hosting leucogranite, the xenoliths are also ductilely grained ones; all of them are mylonitized and foliated to sheared into phyllonite or spangled muscovite-quartz some extent. The veins may present in a diffusive (or schist. penetrative) pattern in places next to the contact with Multiple phases of outcrop-scale leucogranitic or the metasedimentary country rocks. This pattern pegmatitic veins (Figures 10B, 10C, and 10D) have resembles typical migmatite because it is presented as

A B

C D

Figure 10. Geologic features of the Saddleback Brook Leucogranite. (A) A country-rock xenolith of spangled muscovite-quartz schist (right) within the leucogranite on pavement outcrop. (B) A pegmatite dike (white) within the leucogranite - all are sheared/ mylonitized, on pavement outcrop, viewer facing north. (C) Folded diffusive leucogranite veins showing gneissic appearance on pavement outcrop, pen pointing to north. (D) Sheared and mylonitized leucogranite veins and metasedimentary rock xenoliths (schist) on pavement outcrop, viewer facing north.

Chunzeng Wang

E F

Figure 10 (continued). (E) Ferromagnesian-silicate-rich leucogranite due to assimilation with country rocks, on pavement outcrop, viewer facing north. (F) Cataclasized leucogranite mylonite due to subsequent brittle fault reactivation, on pavement outcrop, pen pointing to north. Table 2. Geochemical analytic results of the leucogranite samples. 2011062 2011030-2 2013060 H04 H11 H19 H28 H29

SiO2 72.72 65.72 68.7 74.84 74.22 67.66 74.22 70.88 Al2O3 13.68 16.69 13.86 12.71 12.86 15.38 11.47 14.55 Fe2O3(T) 1.13 3.76 5.95 1.35 1.58 3.63 3.09 3.41 MnO 0.044 0.067 0.09 0.019 0.013 0.092 0.054 0.057 MgO 0.26 1.7 1.97 0.16 0.22 1.07 1.02 1.16 CaO 1.25 3.01 0.89 0.4 0.5 0.43 0.44 0.38

Na2O 3.41 4.12 4.02 3.31 3.8 3.4 1.81 2.34 K2O 4.86 2.15 1.53 5.21 4.24 4.73 3.91 3.72 TiO2 0.116 0.695 0.642 0.126 0.187 0.567 0.426 0.598 P2O5 0.08 0.13 0.03 0.05 0.05 0.1 0.09 0.15 LOI 0.48 1.55 2.12 0.64 0.67 1.64 1.5 2.07 Total 98.05 99.6 99.81 98.81 98.33 98.71 98.02 99.31 Sc 3 11 17 4 5 9 6 8 Be 3 4 2 2 3 2 2 3 V 7 78 84 9 13 52 53 65 Cr <20 <20 30 <20 <20 30 <20 <20 Ni <20 <20 <20 <20 <20 <20 <20 <20 Ga 16 23 23 19 18 19 15 22 Ge 2 1.9 1.8 2.4 2.2 1.4 1.1 1.2 Rb 104 113 74 174 139 185 143 181 Sr 186 377 203 57 81 142 157 140 Y 21.2 23.6 33.4 54.1 50.6 34.3 7.9 16.8 Zr 70 155 370 119 136 208 137 211 Nb 10.3 15.5 28.7 12.6 15 13.4 6.4 7.2 Cs 1.4 2.9 1.3 0.9 1.3 3.2 2.8 5 Ba 432 407 337 192 266 686 746 497 La 19.7 38.3 23.6 31.6 34.8 43.8 14.9 29.7 Ce 40 68.3 52.8 66.9 70.5 88.9 37.8 60.5 Pr 4.51 7.46 6.09 8.11 8.21 9.94 3.67 7.03 Nd 15.7 26.7 23.5 28.9 30.9 34.9 12.6 24.6 Sm 3.62 5.24 5.25 7.18 6.86 7.13 2.46 4.46 Eu 0.765 1.3 1.02 0.321 0.477 1.21 0.442 0.887 Gd 3.3 4.28 4.89 6.94 6.79 5.89 1.75 3.46 Tb 0.59 0.75 0.88 1.37 1.32 1.01 0.29 0.56 Dy 3.56 4.33 5.45 8.66 8.32 5.87 1.63 3.05 Ho 0.74 0.85 1.11 1.77 1.71 1.18 0.31 0.59 Er 2.09 2.4 3.59 5.1 5.06 3.51 0.8 1.55 Tm 0.322 0.354 0.62 0.826 0.798 0.603 0.122 0.227 Yb 2.1 2.21 4 5.43 5.46 3.98 0.79 1.39 Lu 0.293 0.308 0.561 0.784 0.825 0.563 0.112 0.192 Hf 2.1 3.3 4.9 4.1 4 4.9 3.1 4.2 Ta 1.21 1.51 1.28 0.67 1.53 1.02 0.4 0.58 Tl 0.78 0.78 0.6 0.9 0.85 1.34 1.08 1.26 Pb 33 15 12 29 25 20 8 9 Th 8.62 13.6 11.1 18.5 24.4 23.3 10.8 10.1 U 1.96 2.27 2.21 2.93 5.54 3.57 1.28 1.72 16 Bedrock geology of the The Horseback quadrangle, Maine alternating light-colored quartzofeldspathic mylonite West, 1999), this report assigns a Devonian age for the bands (which are derived from the leucogranite or leucogranite. pegmatite veins) with dark-colored phyllonite or schist The leucogranite is in brittle-fault contact with the bands (which are derived from the metasedimentary redbeds to the northwest. This is indicated by considera- rocks) (Figures 10B and 10C), even though the rock is ble cataclasis of the mylonitic leucogranite along the genetically not a migmatite. The diffusive pattern or the boundary with the redbeds. As shown in Figure 10F, migmatitic appearance most likely resulted from due to brittle faulting and cataclasis, the original repeated, diffusive emplacement of leucogranitic leucogranitic mylonite changes to banded cataclasite. magmas along the bedding or foliation of the metasedi- Eight samples of the leucogranite were collected for mentary rocks. As shown in Figure 10C, the alternating whole-rock major, trace, and REE analyses. The bands may be folded due to subsequent ductile defor- samples were crushed and powdered in agate ball mills mation. in the University of New Brunswick sample preparation Because this diffusive pattern resembles gneissic laboratory. The prepared samples were analyzed at texture, it was presumably the reason for mapping these ActLabs in Canada: ME–ICP method was used for rocks as “Passagassawakeag Gneiss” by previous major elements and ICP–MS method was employed for workers. REE and trace elements. The analytic results are The widespread existence of metasedimentary included in Table 2. xenoliths within the leucogranite and the diffusive Harker diagrams of the eight samples clearly show “migmatitic” appearance suggest considerable assimila- a magmatic evolution trend (Figure 11), confirming that tion between the leucogranitic magmas and the country they are magmatic rocks. The samples have high rocks of the Bucksport Formation metagraywacke, meta contents of SiO2 (average 71 wt%) and Al2O3 (average -siltstone, and meta-claystone. Due to the assimilation, 13.90 wt%) and low contents of Fe2O3(T) (average 2.99 the leucogranite may locally become more mafic as wt%), MgO (average 0.95 wt%), Cr (≤30 ppm), and Ni evidenced by increased amount of biotite and horn- (<20 ppm), showing typical geochemical characteristics blende (Figure 10E); and the boundary (or the contact) of leucogranite. In the Na2O+K2O vs. SiO2 classification between the leucogranite unit and the metasedimentary diagram (Figure 12A), the samples fall in the granite country rocks is gradational and characterized by the field with only one sample (sample 2011030-2) plotted development of such an assimilation zone. near the boundary between granite and granodiorite. Because the Saddleback Brook Leucogranite Geochemically, the samples have an average aluminum contains the Silurian Bucksport Formation metasedi- saturation index (ASI) greater than 1.1 and are peralu- mentary rock xenoliths and is ductilely sheared by the minous (Figure 12B); and they belong to calc-alkaline initial Norumbega shearing which was dated at circa to high K calc-alkaline series (Figure 12C). In the 380 Ma (West and Lux, 1993; West and Hubbard, 1997; (Na2O)+K2O)/CaO vs. Zr+Nb+Ce+Y diagram (Figure

A B

Figure 11. Harker diagrams of the leucogranite samples showing magmatic evolution trend.

Chunzeng Wang

C D

Figure 11 (continued). Harker diagrams of the leucogranite samples showing magmatic evolution trend.

A B

Figure 12. (A) Na2O+K2O vs. SiO2 igneous classification diagram. (B) A/NK vs. A/CNK diagram for aluminum saturation. (C) K2O vs. SiO2 diagram for alkalinity.

18 Bedrock geology of the The Horseback quadrangle, Maine In regard to the genesis and emplacement mechanism of the leucogranite, because the leucogranite is entirely ductilely sheared, there exist two possibilities: (1) The leucogranite was pre-Norumbega and emplaced as dikes probably coeval with the Lucerne Granite; and (2) the leucogranite was syn-tectonic and emplaced during the Norumbega ductile shearing process. In the first mechanism, the question is: why is the leucogranite texturally and mineralogically so different from the neighboring Lucerne Granite? What is their genetic and temporal relationship? Or was there no relationship at all? Why was the leucogranite emplaced in an elongated form within the Norumbega fault system? If these Figure 13. (Na2O)+K2O)/CaO vs. Zr+Nb+Ce+Y granite classi- questions cannot be easily answered, the second fication diagram (after Whalen et al., 1987). A – A-type granite; FG – fractionated granite; OTG – unfractionated (M-, I-, mechanism may become more favorable. In the second and S-type granites). mechanism, the ductile shearing could either facilitate ascent of leucogranitic magmas produced at depth or generate in situ leucogranitic magmas with “shear 13), the samples fall in the FG (fractionated felsic heating.” Localized anatexis of the meta-pelite of the granites) and OTG (unfractionated M-, I-, and S-type Bucksport or Flume Ridge formations due to elevated granites) fields (and only one in A-type granite field but geotherms caused by “shear heating” at deeper levels of it is near the boundary with FG+OTG field), suggesting the upper crust along the ductile shear zone may address that the leucogranite is not an A-type granite. The the genesis and emplacement mechanism of the mylo- leucogranite contains abundant muscovite and locally nitized leucogranite. This argument that the leucogranite some biotite; with it geochemically being peraluminous was derived from a source enriched in clay minerals or and non-A-type affinity, it is suggested that the leu- it was a pelite-derived melt is supported by the CaO/ cogranite is an S-type granite. Na2O vs. Al2O3/TiO2 diagram (Figure 15A). The Zr/Nb The chondrite-normalized spider diagram of trace vs. Zr diagram (Figure 15B) shows a partial melting elements (Figure 14A) shows prominently elevated Rb, trend. Positive anomalies of Th, Rb, K, and Nd (Figure Th, K, and Nd, which supports the leucogranite being an 14A) also suggest partial melting of source rocks and S-type granite. The depletion of Ba, Nb, Ta, and Sr assimilation processes involved in the evolution of the (Figure 14A) is indicative of a continental crust source leucogranite. This suggestion is supported by wide- for the magmas. The chondrite-normalized REE spread assimilation features observed in the field. patterns (Figure 14B) demonstrate enrichment of light Four whole-rock samples collected from the REEs relative to heavy REEs, which is normally leucogranite went through Nd isotopic analysis at indicative of partial melting of the source rocks. The Isotopic Ratio Mass Spectrometry Laboratory of the 143 144 REE patterns show a negative Eu anomaly. Stony Brook University. Final Nd/ Nd and εNd

A B

Figure 14. (A) Chondrite-normalized trace element spider diagram (after Thompson, 1982). (B) Chondrite-normalized REE patterns (after Nakamura, 1974). See the text for interpretation.

Chunzeng Wang

A B

Figure 15. (A) CaO/Na2O vs. Al2O3/TiO2 discrimination diagram (after Sylvester, 1998) for source of leucogranite melts. (B) Zr/ Nb vs. Zr diagram for discriminating partial melting trend from fractional crystallization trend.

Table 3. Whole-rock Nd isotopic analysis result of the leucogranite Sample 143Nd/144Nd 2 s.d. εNd H29 0.512238 0.000004 -7.8 2013060 0.512446 0.000063 -3.7 H19-1 0.512130 0.000033 -9.9 H19-2 0.512155 0.000024 -9.4 determinations are shown in Table 3. εNd values were discrimination diagram (Figure 16B). In the Rb vs. calculated with a CHUR value of 0.512638, and with a Y+Nb diagram most of the samples plot in the VAG 146Nd/144Nd = 0.7219. (volcanic arc granite) field with three samples plotting The analytical result (Table 3) shows εNd values in the WPG (within plate granite) field but near the ranging from -3.7 to -9.9, strongly confirming a conti- boundary with the VAG field (Figure 16C). In the Nb nental crust source for the leucogranitic magmas (e.g., vs. Y diagram most of the samples fall in the VAG+syn- DePaolo and Wasserburg, 1976). COLG (syn-collisional granite) field with the same Regarding the tectonic setting for magma genera- three samples plotting in the WPG field but near the tion and emplacement, the leucogranite samples fall in boundary with the VAG+syn-COLG field (Figure 16D). non-WIP (within-plate) field in the Zr vs. Y tectonic These tectonic discrimination results suggest that the discrimination diagram (Figure 16A) and in CAP tectonic setting was not within-plate but in an active (continental arc potassic) and PAP (post-collisional arc mobile zone. This mobile zone was coincident with the potassic) fields in the Zr/Al2O3 vs. TiO2/Al2O3 tectonic Norumbega fault system. Because the leucogranite is

A B

Figure 16. (A) Y vs Zr and (B) Zr/Al2O3 vs. TiO2/Al2O3 tectonic discrimination diagrams of potassic rocks (Muller et al., 1992). WIP – within plate; CAP – continental arc potassic rocks; PAP – post-collisional arc potassic rocks; IOP – initial oceanic arc potassic; LOP – late oceanic arc potassic.

20 Bedrock geology of the The Horseback quadrangle, Maine

C D

Figure 16 (continued). (C) Rb vs. Y+Nb and (D) Nb vs. Y tectonic discrimination diagrams for granitoids (Pearce et al., 1984). WPG – within-plate granite; ORG – oceanic ridge granite; VAG – volcanic arc granite; syn-COLG – syn-collisional granite.

strongly ductilely sheared, it is likely that the initial dip and is parallel to primary bedding (S0) at most of the Norumbega ductile shearing was localized along a pre- mapped outcrops. However, in places the foliation is not existing rheologically weak zone with elevated heat, at a coincident with the bedding which in turn suggests the relatively deeper level of the upper crust. The ductile existence of folds. For example, at stop 2011016 on shearing probably also facilitated the generation, Stud Mill Road, southwest of Myra, the outcrop shows assimilation, and ascent of melts derived from Buck- thick-bedded meta-sandstone and thinly layered meta- sport Formation metagraywacke and pelites rich in clay claystone with bedding dipping 85° toward the north- minerals. west and foliation dipping 85° toward the west (Figure The Eddington Leucogranite that occurs within the 17). Norumbega fault system in the neighboring Chemo Where the metasedimentary rocks, in particular Pond quadrangle shares the same geologic and geo- those of the Bucksport Formation, were involved in the chemical features and is thought to be generated by the Norumbega ductile shearing, a mylonitic or phyllonitic same mechanism and emplaced in the same tectonic foliation (S2) was developed. This is observed in the setting (Wang, in press). A zircon LA-ICP-MS U-Pb field, for example, in the schistose foliation in the dating of the Eddington Leucogranite gives a U-Pb spangled muscovite-quartz schist. This mylonitic concordia age of 380.1±2.0 Ma (Wang, in press). It is foliation could be parallel to S1 or even to S0 due to the suggested that both Eddington and Saddleback Brook leucogranites were coeval and genetically related. STRUCTURAL GEOLOGY

Deformation structures within metasedimentary formations Rocks of both Flume Ridge and Bucksport formations were folded, foliated, and metamorphosed during Acadian orogeny. The regional metamorphic grade is lower greenschist facies and primary bedding (S0) is generally preserved. The bedding generally strikes northeast and dips steeply toward either northwest or southeast due to repeated Acadian tight folds. Locally, bedding may instead strike east-southeast/west- northwest, suggesting the hinge of folds. Due to poor exposure, tightness of folds, and lithological similarity, large folds within both formations are not recognized on Figure 17. Angular relationship between bedding (S0) and the geologic map. foliation (S1) in Flume Ridge Formation. Compass points to north. On pavement outcrop, Stud Mill Rd. Axial-plane cleavage (S1) is penetrative throughout both formations; it strikes northeast with a general steep 21

Chunzeng Wang fact that the ductile shear zone also strikes northeast. with the mylonitic leucogranite unit, the motion along the boundary fault must have been remarkable. As The Norumbega fault system shown in the studies performed in the Great Pond The most remarkable deformational structural quadrangle by Wang and Ludman (2012, 2013), this feature in the Horseback quadrangle is the Norumbega was a compressional, high-angle, southeast-over- fault system. The northeast-striking fault system spans northwest reverse faulting event with significant vertical the entire quadrangle and extends northeast into the and horizontal displacement. Great Pond quadrangle and southwest into the Chemo Pond quadrangle. Based on previous studies, the fault GEOLOGIC HISTORY system has a prolonged history involving early ductile The geologic history of the Horseback quadrangle deformation that produced a ductile shear zone and begins in the Silurian with the deposition of the deep- subsequent brittle reactivation that produced the pull- water turbidite suites of the Flume Ridge and Bucksport apart redbed basins and brittle faults. The total width of formations in the Fredericton Trough. These turbidite the Norumbega fault system in the Horseback quadran- suites were soon metamorphosed at lower greenschist gle is about 2.5 km. facies and folded during the early stage of the Acadian The ductile shear zone in the southern half of the orogeny near the end of Silurian or the beginning of the fault system in this area is about 1.25 km wide. As Devonian time. In the Horseback area and vicinity, the described previously, the Saddleback Brook Leucogran- low-grade, metamorphosed sedimentary units were ite and part of the Bucksport Formation in the quadran- shortly intruded by the 415.7±1.4 Ma Parks Pond gle were ductilely sheared to become mylonite or monzodiorite pluton located in the neighboring Chemo phyllonite or spangled muscovite-quartz schist. Shear- Pond and Hopkins Pond quadrangles (Wang, in press), sense indicators such as mica-fish shown in both the the 410.5±2.4 Ma Turner Mountain Syenite (Wang et spangled muscovite-quartz schist (Figure 3G) and the al., 2014), and subsequently by the 386.1±2.3 Ma mylonitic leucogranite (Figure 9E) indicate a dextral Lucerne-Deblois granite batholith (Wang, unpublished strike-slip motion, which is consistent with its coeval data). Slow cooling and crystallization of the granitic eastern Maine and south-central Maine ductile shear magmas produced an impressive megacrystic coarse- zone extensions (Ludman, et al., 1999; Swanson, 1999a; grained texture as seen today within the Lucerne pluton. Wang and Ludman, 2004). The metasedimentary rocks around the pluton experi- Geologic features produced by subsequent brittle enced thermal contact metamorphism which changed fault reactivation have been observed along the length them to hornfels. of the Norumbega fault system in eastern-central and The Saddleback Brook Leucogranite was later eastern Maine by previous studies (Ludman, 1998; emplaced at 380.1±2.0 Ma (assuming it was coeval with Ludman et al., 1999; Wang and Ludman, 2003). Wang the Eddington Leucogranite in the Chemo Pond quad- and Ludman (2003) identified three episodes of subse- rangle; Wang, in press), during the Norumbega ductile quent brittle fault reactivation that were superimposed shearing process. Localized anatexis or partial melting on the early ductile shear zones. In the Horseback of the meta-pelite of the Bucksport Formation due to quadrangle, the direct evidence of the brittle faulting is elevated geotherms (which could be partially caused by from the redbeds that occur as a fault sliver between its “shear heating”) at deeper level of the upper crust along fault contact with the Flume Ridge Formation to the the ductile shear zone may address the genesis and northwest and with the mylonitic leucogranite unit to emplacement mechanism of the syn-tectonic, mylo- the southeast. According to previous studies (e.g. nitized leucogranite. This is supported by the strong Wones and Ayuso, 1993; Wang and Ludman, 2003, peraluminous nature, high ASI index, negative εNd 2012), the Great Pond Formation occurs in a pull-apart values, and S-type category of the leucogranite. basin that resulted from brittle dextral strike-slip The Norumbega ductile shearing produced a ductile faulting. The 1.25-km-wide redbeds unit in the quadran- shear zone in the metasedimentary rocks and the gle is part of a pull-apart basin that extends southwest- leucogranite (the northwest margin of both Lucerne and ward to the town of Eddington (on the southwest side of Deblois plutons in the vicinity were also sheared) that is Chemo Pond) and northeastward to the area around Elm more than a kilometer wide. This shearing was coeval Brook (near the northeast corner of Great Pond quadran- with others observed throughout the entire Norumbega gle), for about 40 km. fault system in Maine. Within the ductile shear zone, the The redbeds, which were originally deposited as metasedimentary rocks of the Bucksport Formation flat or nearly flat layers, are steeply tilted at 75-85°, were ductilely sheared into phyllonite or spangled suggesting a post-depositional brittle faulting event. As quartz-muscovite schist, and the leucogranite into a indicated by significant cataclasis shown in Figure 10F leucogranitic mylonite or ultramylonite. which was observed at a stop near the boundary fault Subsequent brittle faulting reactivation events along

22 Bedrock geology of the The Horseback quadrangle, Maine the length of the ductile shear zone have made the DePaolo, D.J. and Wasserburg, G.J., 1976, Inferences Norumbega fault system structurally more complicated. about magma sources and mantle structure from 143 144 For example, a dextral strike-slip faulting produced a variations of Nd/ Nd: Geophysical Research transtensional pull-apart basin in the Great Pond - The Letters, v. 3, no.12, p. 743–746. Horseback - Chemo Pond area. Gravels, sand, silt, and Dokken, R.J., Waldron, J.W.F., and Dufrane, S.A., clay from nearby sources were quickly transported into 2018, Detrital zircon geochronology of the Freder- the pull-apart basin, forming an immature suite of icton Trough, New Brunswick, Canada: constraints poorly sorted pebble conglomerate and arkosic granule on the Silurian closure of remnant Iapetus Ocean: conglomerate, as well as arkose, sandstone, siltstone, American Journal of Science, v. 318, p. 684–725. and mudstone. The pull-apart basin did not survive doi 10.2475/06.2018.03. unscathed because another large-scale, high-angle brittle Fyffe, L.R., 1988, Geology of Beaconsfield area (NTS faulting event reactivated the faults with significant 21 G/6e), Charlotte County, New Brunswick: New reverse motion, which tilted and displaced the redbeds Brunswick Department of Natural Resources and vertically as seen today (Wang et al., 2014). Energy, Minerals and Energy Division. Plate 88- 189 (revised 2002), scale 1:20,000. ACKNOWLEDGMENTS Gilman, R.A., 1974, Progress report of geologic The Horseback 7.5′ quadrangle bedrock geologic mapping in the Ellsworth, Great Pond, Lead mapping project has been funded by two USGS Mountain, Tug Mountain, and Wesley quadrangles, STATEMAP grants (2004 and 2013) through Maine Maine: Maine Geological Survey, Progress Report, Geological Survey, a University of Maine Trustee https://digitalmaine.com/geo_docs/70. Professorship (2011), and a Zillman Family Professor- Griffin, J.R., 1976a, Reconnaissance bedrock geology ship (2013-2014). I am grateful to Drs. Robert of the Great Pond [15-minute] quadrangle, Maine: Marvinney and Henry Berry IV of Maine Geological Maine Geological Survey, Open-File Map 76-22, Survey for their many years of great support and scale 1:62,500. guidance, to Dr. Chris McFarlane of the University of Griffin, J.R., 1976b, Reconnaissance bedrock geology New Brunswick for helping with geochronological and of the Orono [15-minute] quadrangle, Maine: geochemical analyses, to Dr. Marty Yates for assisting Maine Geological Survey, Open-File Map 76-21, with zircon cathodoluminescence imaging, to Dr. map, scale 1:62,500. Stephen Pollock for many constructive discussions, and to Amber Whittaker for carefully reviewing and editing Hogan, J.P., and Sinha, A.K., 1989, Compositional variation of plutonism in the coastal Maine mag- both the report and the map. I give special thanks to my matic province; mode of origin and tectonic setting: field assistant Jared Dickinson for his hard fieldwork in Tucker, R.D., and Marvinney, R.G. (editors), with me in mosquito-infested woods and swamps; we Studies in Maine geology: Volume 4 - igneous and worked seven days a week without any weekend offs, metamorphic geology: Maine Geological Survey, rain or shine. I also thank undergraduate students Hollis p. 1–33. Seamans, Gary Parent, Dayton Maxcy, Ray Kohutka, Hubbard, M.S., West, D.P., Jr., Ludman, A., Guidotti, Andy Hunt, Mike Henderson, Chris Staples, Angelique C.V., and Lux, D.R., 1995, The Norumbega Fault Paul, and Jared Dickinson for their hard work in the Zone, Maine; a mid- to shallow-level crustal field looking for outcrops during a 3-day field camp in section within a transcurrent shear zone: Atlantic fall 2013; Carol Ann Naro served as a great “camp Geology, v. 31, no. 2, p. 109–116. mother” which is much appreciated. I owe many thanks Loiselle, M.C., and Ayuso, R.A., 1980, Geochemical to Dr. Allan Ludman for his many years of encourage- characteristics of granitoids across the Merrimack ment and mentoring. synclinorium, eastern and central Maine: in Wones, During my field trips to the area in 2011–2014, my D. R. (editor), Proceedings of 'The Caledonides in three young daughters, Angela (now age 23), Dora (now the USA': Virginia Polytechnic Institute, Depart- age 20), and Joy (now age 18) joined me several times ment of Geological Sciences, Memoir no. 2, p. 117 as my “special field assistants”. In the field, they were –121. always complaining about mosquitos and bugs, but in Ludman, A., 1991, The Fredericton trough and No- the end they were my best field companions. Those rumbega fault zone in eastern Maine: in Ludman, great days are so much missed. A. (editor), Geology of the coastal lithotectonic REFERENCES CITED block and neighboring terranes, eastern Maine and southern New Brunswick: New England Intercolle- Bradley, D.C., 1982, Subsidence in late Paleozoic giate Geological Conference, 83rd Annual Meeting, basins in the Northern Appalachians: Tectonics, v. September 27-29, 1991, Princeton, Maine, p. 186– 1, no. 1, p.107–123. 208.

Chunzeng Wang Ludman, A., 1998, Evolution of a transcurrent fault Maine Geological Survey, scale 1:500,000. system in shallow crustal metasedimentary rocks; the Norumbega fault zone, eastern Maine: Journal Pearce, J.A., Harris, N.B.W., and Tindle, A.G., 1984, of Structural Geology, v. 20, no. 1, p. 93–107. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks: Journal of Ludman, A., 2020, Bedrock geology of the Greenfield Petrology, v. 25, no. 4, p. 956–983. quadrangle, Maine: Maine Geological Survey, Open-File Report 20-10, 43 p. report and color Perkins, E.H., and Smith, E.S.C., 1925, Contributions to map, scale 1:24,000. the geology of Maine, No. 1; A geological section from the Kennebec River to Penobscot Bay: Ludman, A., and Gibbons, S., 1999, Multistage shearing American Journal of Science, 5th series, v. 9, no. of the Deblois Granite in the Kellyland fault zone, 51, p. 204–228. eastern Maine: in Ludman, A., and West, D.P., Jr. (editors), Norumbega fault system of the Northern Pollock, S.G., 2011, Bedrock geology of the Veazie Appalachians: Geological Society of America, quadrangle, Maine: Maine Geological Survey, Special Paper 331, p. 41–57. Open-file Map 11-58, scale 1:24,000. Ludman, A., Aleinikoff, J., Berry, H.N., IV, and Simpson, C., 1985, Deformation of granitic rocks across Hopeck, J.T., 2018, SHRIMP U–Pb zircon evi- the brittle-ductile transition: Journal of Structural dence for age, provenance, and tectonic history of Geology, v. 7, no. 5, p. 503–511. early Paleozoic Ganderian rocks, east-central Stoeser, D., 1966, Geology of a portion of the Great Maine: Atlantic Geology, v. 54, p. 335–387. Pond quadrangle, Maine: M.S. thesis, University of Ludman, A., Lanzirotti, A., Lux, D., and Wang, C., Maine, Orono, Maine, 88 p. 1999, Constraints on timing and displacement Swanson, M.T., 1999a, Kinematic indicators for multistage shearing in the Norumbega fault system, regional dextral shear along the Norumbega fault eastern Maine: in Ludman, A., and West, D.P., Jr. system in the Casco Bay area, coastal Maine: in (editors), Norumbega fault system of the Northern Ludman, A., and West, D.P., Jr. (editors), No- Appalachians: Geological Society of America, rumbega fault system of the Northern Appalachi- Special Paper 331, p. 179–194. ans: Geological Society of America, Special Paper McGregor, J., 1963, Geology of the southeast part of the 331, p. 1–23. Great Pond quadrangle, Maine: Maine Geological Swanson, M.T., 1999b, Dextral transpression at the Survey, Progress Report, 9 p., map, scale 1:62,500. Casco Bay restraining bend, Norumbega fault zone, Muller, D., Rock, N.M.S., and Groves, D.I., 1992, coastal Maine: in Ludman, A., and West, D.P., Jr. Geochemical discrimination between shoshonitic (editors), Norumbega fault system of the Northern and potassic volcanic rocks in different tectonic Appalachians: Geological Society of America, settings: a pilot study: Mineralogy and Petrology, v. Special Paper 331, p. 85–104. 46, p. 259–289. Sylvester, P.J., 1998, Post-collisional strongly peralumi- Nakamura, N., 1974, Determination of REE, Ba, Fe, nous granites: Lithos, v. 45, p. 29-44. Mg, Na and K in carbonaceous and ordinary Thompson, R.N., 1982, Magmatism of the British chondrites: Geochimica et Cosmochimica Acta, v. Tertiary Volcanic Province: Scottish Journal of 38, no. 5, p. 757–775. Geology, v. 18, p. 49–107. Olson, R.K., 1972, Bedrock geology of the southwest Trefethen, J.M., 1950, Bucksport - Orland Map area: one sixth of the Saponac quadrangle, Penobscot and New England Intercollegiate Geological Confer- Hancock Counties, Maine: M. S. thesis, University ence, 42nd Annual Meeting, Bangor, Maine, 3 p., of Maine at Orono, Orono, Maine, 61 p., map. map scale 1:62,500. Osberg, P.H., 1968, Stratigraphy, structural geology, Tullis, J.A., and Yund, R.A., 1985, Dynamic recrystalli- and metamorphism of the Waterville-Vassalboro zation of feldspar: a mechanism for ductile shear area, Maine: Maine Geological Survey (Department zone formation: Geology, v. 13, no. 4, p. 238–241. of Economic Development), Bulletin 20, 64 p., scale 1:62,500. Wang, C., 2012, Bedrock geology of the Great Pond quadrangle, Maine: Maine Geological Survey, Osberg, P.H., 1988, Geologic relations within the shale- Open-File Map 12-33, scale 1:24,000. wacke sequence in south-central Maine: in Tucker, R.D., and Marvinney, R.G. (editors), Studies in Wang, C., in press, Bedrock Geology of the Chemo Maine geology: Volume 1 - Structure and stratigra- Pond quadrangle, Maine: Maine Geological Survey, phy: Maine Geological Survey, p. 51–73. scale 1:24,000. Osberg, P.H., Hussey, A.M., II, and Boone, G.M. Wang, C., and Ludman, A., 2003, Evidence for post- (editors), 1985, Bedrock geologic map of Maine: Acadian through Alleghanian deformation in eastern Maine: multiple brittle reactivation of the

24 Bedrock geology of the The Horseback quadrangle, Maine Norumbega Fault system: Atlantic Geology, v.38, Wones, D.R., 1977, Bedrock geologic map of part of the p. 37–52. Great Pond quadrangle, Maine: Maine Geological Survey, Progress Map, scale 1:62,500. Wang, C., and Ludman, A., 2004, Deformation conditions, kinematics, and displacement history of Wones, D.R., 1980, Contributions of crystallography, shallow crustal ductile shearing in the Norumbega mineralogy, and petrology to the geology of the fault system in the Northern Appalachians, eastern Lucerne pluton, Hancock County, Maine: American Maine: Tectonophysics, v. 384, no. 1-4, p. 129– Mineralogist, v. 65, nos. 5-6, p. 411–437. 148. Wones, D.R., and Ayuso, R.A., 1993, Geologic map of Wang, C., and Ludman, A., 2012, Exhumation of the the Lucerne Granite, Hancock and Penobscot Turner Mountain syenite fault sliver in the No- Counties, Maine: U.S. Geological Survey, Miscel- rumbega Fault Zone of Maine: implications for laneous Investigations Series I-2360, map, scale kinematics of orogen-parallel fault reactivation: 1:125,000. Geological Society of America Abstracts with Programs, v. 44, no. 2, p. 106. Zartman, R.E., and Gallego, M.D., 1979, USGS(D)- BUB-8 (Sample 139), USGS(D)-BUB-9 (Sample Wang, C., and Ludman, A., 2013, Complexities of 140), USGS(D)-BUBIO (Sample 141), and USUS orogen-parallel faults: an example from the No- (D)-ORA-3D1 (Sample 142): in Marvin, R.F., and rumbega Fault Zone in central-eastern Maine: Dobson, S.W., (editors), Radiometric ages: Geological Society of America Abstracts with Compilation B, U. S. Geological Survey: Isochron Programs, v. 45, no.7, p. 809. West, The Bulletin of Isotopic Geochronology, no. 26, p. 16–19. Wang, C., Ludman, A., and Wiao, L.X., 2014, The Turner Mountain syenite, Maine, USA: geology, geochemistry, geochronology, petrogenesis, and post-orogenic exhumation: Atlantic Geology, v. 50, p. 233–248. West, D.P., Jr., 1999, Timing of displacements along the Norumbega fault system, south-central and south-coastal Maine: in Ludman, A., and West, D.P., Jr. (editors), Norumbega fault system of the Northern Appalachians: Geological Society of America, Special Paper 331, p. 167–178. West, D.P., Jr., and Hubbard, M.S., 1997, Progressive localization of deformation during exhumation of a major strike-slip shear zone; Norumbega fault zone, south-central Maine, USA: Tectonophysics, v. 273, nos. 3-4, p. 185–201. West, D.P., Jr., and Lux, D.R., 1993, Dating mylonitic deformation by the 40Ar-39Ar method; an example from the Norumbega Fault Zone, Maine: Earth and Planetary Science Letters, v. 120, nos. 3-4, p. 221– 237. West, D.P., and Roden-Tice, M.K., 2003, Late Creta- ceous reactivation of the Norumbega fault zone, Maine; evidence from apatite fission-track ages: Geology, v. 31, no. 7, p. 649–652. Whalen, J.B., Currie, K.L., and Chappell, B.W., 1987, A-type granites: geochemical characteristics, discrimination and petrogenesis: Contributions to Mineralogy and Petrology, v. 95, p. 407–419. Wing, L.A., 1957, Aeromagnetic and geologic reconnaissance survey of portions of Hancock and Penobscot Counties, Maine: Maine Geological Survey (Department of Economic Development), GP. and G. Survey No. 1, Feb. 13, 1957, [1958], 10 sheets, scale 1:62,500.

25 EXPLANATION OF UNITS

68°30'00"W 68°27'30"W 68°25'00"W 68°22'30"W

540000m E 41 42 43 44 45 46 47 48 549000m E INTRUSIVE ROCKS

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!  78 Bedrock Geology of the !

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! euhedral and subhedral feldspars occurs near margin of the pluton. It is parallel or near parallel to the

n a

! Amber T. H. Whittaker k !

! Hill

! h

a !

z ! p ! e S w

T d

t ! !

! re field contact.

a ! ! n

m ! ree

! G ! Henry N. Berry IV

! P

! P 0 ! B

! D 5 ! !

! 2 M

! 3

! T !

! !

! Turner Mountain Syenite. Deeply weathered, dark brown to dark gray porphyritic hornblende-biotite !

! Dtm

! !

! syenite. Characterized by large, pink, euhedral potassic feldspar phenocrysts commonly 2-6 centimeters !

! Robert G. Marvinney

! !

! long. T he medium-grained to coarse-grained groundmass is composed of mostly subhedral orthoclase and

! !

! plagioclase feldspars, biotite, and hornblende. Substantial alteration of hornblende and biotite to chlorite is State Geologist !

! !

! common. Fine-grained interstitial quartz makes up less than 5% of the rock. Weathered surfaces are !

! Crock er !

! !

! ! 3

Pond 0 ! pinkish-gray, a lighter color than the fresh rock. T he pluton is tex turally and mineralogically homogenous.

! 0 W Sf

81 !

! i !

! le Funding for the preparation of this map was provided in part by the U.S. Geological Survey

! y

! 81 !

! 0 T he syenite is significantly cataclasized adjacent to the faults. Z ircon U -Pb dating yielded a weighted mean

! 0 ! 3 B

! roo !

! 3 k 206 238

0 ! STATEMAP Program, Cooperative Agreement No. G13AC00117. !

CO 0 !

! T !

CO ! Pb/ U age of 410.5±2.4 Ma for the syenite (Wang and others, 2014). S !

B !

O !

N !

E ! !

P C! O

K ! !

OC !

! C !

AN ! Myra

! P

H ! !

! ic ! !

! k 62

! !

! r  DEFORMED INTRUSIVE ROCKS

! a

! l !

! 0

! P 40 ! !

! o

n !

! d

! !

! R

oo ! ! D

Br k  Devonian [ ]

n ! d

! ! o Sf

ns 

h ! !

Jo ! 85

! 

! 85 Maine Geological Survey

! 00

 Open-File No. 20-13

! 3 85

! Saddleback Brook Leucogranite (new name). Foliated to mylonitic, white, fine-grained to medium- !

!  ! Dsb !  17

! 85 ! grained leucogranite composed predominantly of alkali feldspar, plagioclase, and quartz, with minor

! 85 Address: 93 State House Station, Augusta, Maine 04333 !

! 2020

! !

! Sf

! muscovite and sparse biotite. T he leucogranite is entirely sheared to mylonite or ultramylonite within the

! 300 Telephone: 207-287-2801 E-mail: [email protected]

! !

80 ! Norumbega ductile shear zone. In low-strain domains, granitic tex ture and composition are preserved

! P

! In

! Home page: www.maine.gov/dacf/mgs/ ! i d

c 3 i ! a 80 Plate 1

! k 0 0 n Brook ! 0 0

! P e 3 locally, distinguishable in the field and microscopically. T he leucogranite intrudes as dikes into !

! o r

! n e !

! d l T d metasedimentary country rock and contains metasedimentary x enoliths throughout. T he leucogranite is !

! ll R ! i

! M !

! ud !

! St intruded by multiple phases of leucogranite or pegmatite, all mylonitic and foliated to some ex tent.

! H !

! ! 3

0 !

! 0 Alternating thin bands of light quartzo-feldspathic mylonite and dark phyllonite or schist, which locally !

! O !

! E

! a !

! k produce a gneissic structure, are interpreted to represent strongly deformed thin dikes of leucogranite !

! !

! R !

! intruded along bedding or foliation of the metasedimentary rocks. Ex cellent ex posures are found along the !

! id

! g ! ! 4 EXPLANATION OF LINES

! 00 e ridge on the north side of Saddleback Brook located in the southwest corner of the quadrangle. Based on !

! !

! field observations and major, trace, and εNd elemental analyses, it is suggested that the leucogranite was !

! !

! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

! derived locally from clay-mineral-rich pelite and metagraywacke of the Bucksport Formation through partial !

! Sf Dollar !

! Pond melting. Early ductile shearing facilitated the generation, assimilation, and ascent of the melts.

79 !

! 79 !

! B Contact between rock units, of stratigraphic or intrusive origin !

! !

! i

! STRATIFIED ROCKS

! r 1B (well located, approx imately located, poorly located). ! ! S t 

T h ream

! B c c

! i r Sf

! 85

3 ! h

 

2 !

M ! ! 85 M

Mississippian(?) (Early Carboniferous) [ ] M !

! 85

i ! !

l ! H D U

f ! 300

o ! !

r B ! 3 ! 0 d

! 0 Great Pond Formation (new name). T hin to thick beds of red sedimentary rock, including conglomerate,

! O

! !

P ! 00 Mgp D

! 3 !

! arkose, quartz sandstone, and finely laminated mudstone. Massive pebble to cobble conglomerate up to !

! R !

! High-angle fault, interpreted from truncation of units on the map

! !

! several meters thick occurs mostly near the northwest boundary of the mapped unit. Its poorly sorted clasts

! !

! S U D

! or from disruption of stratigraphic sequence. (up) and (down) indicate sense of dip-slip motion.

! S

44°57'30"N ! 44°57'30"N

! are predominantly sandstone and siltstone pebbles with some quartz clasts. A distinctive rock type is red to

! t

! ! r



! E (well located, approx imately located, poorly located).

! e !

! a pink coarse-grained arkose, which occurs in thin to medium beds interbedded with red sandstone and !

! Sfh ! m

! B !

! Sf

! mudstone. Primary sedimentary structures such as cross-bedding and graded bedding are common.

78 !

! !

! A 4

! 0 78

! 0 Ex cellent ex posures are found on the northwest side (in Main Stream) and southwest side (at T urner ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ !

! 62

! C Mountain) of Great Pond in the neighboring Great Pond quadrangle. !

! 70 !

!  ! 

!  !

! K Boundary of mylonitic shear zone. May represent a fault or a high strain gradient. Arrows indicate sense of shear.

! !

! Fredericton Belt !

Sf !

! !

! Silurian [S] !

! 

! 2 !

0 !

! 75

! ! 85 

! Southeast of the Norumbega fault system

! EXPLANATION OF SYMBOLS !

! 85

! !

! Sf

! ! H

! Bucksport Formation. Predominantly dark gray, thick beds of feldspathic graywacke and medium to thin

! o

! ! r

! s Sb

! Sf e

! b Note: Structural symbols are drawn parallel to strike or trend of measured structural feature. Barb or tick indicates direction of dip, if known.

! beds of pelite. Interbedded medium-bedded to thinly bedded siltstone is locally calcareous and weathers to a

! a ! c

! k

77  !

! R ! Annotation gives dip or plunge angle, if known. For most planar features, symbol is centered at observation point; for joints, observation point is at end

! d rusty color. Lithologically indistinguishable from the Flume Ridge Formation. Nex t to the Lucerne Granite,

! 65 77

! !

!  1E,F,G of strike line opposite dip tick. For linear features, tail of symbol is at observation point. Multiple measurements at a site are represented by combined

! contact metamorphism has converted the rock to purplish-black hornfels, containing small flakes of biotite

! ! 75

! 

! symbols. Symbols on the map are graphical representations of information stored in a bedrock database at the Maine Geological Survey. T he database

! and locally hornblende. X enoliths of various sizes are present within the Lucerne Granite. Where the !

! 64 !

! !

! Bucksport Formation was affected by ductile shearing associated with the Norumbega fault system, the rocks contains additional information that is not displayed on this map. !

! !

! rd o !

! Milf  !

! are strongly foliated and include phyllonite, schist, or mylonite. Some muscovite-quartz schist contains !

y d 300 le!

rad R B !

d garnet porphyroblasts. U -Pb dating of detrital zircon grains in a x enolith of Bucksport Formation within the !

! Outcrop of mapped unit.

o !

 ! Saddleback Brook Leucogranite (Location A) indicated a provenance in peri-Gondwana terranes and yielded 

! b 2D !  m B

! o a Silurian Pridoli age for the earliest sedimentation of the formation.

! c e 75 t

m 75 ! i a Occurrence of medium-grained granitic dike.

! T e

! r

30 t !  0 s

! D Northwest of the Norumbega fault system !

e y !

3 s ! 00 n   

76  Bedding, inclined (upright, top direction unknown), vertical (top direction unknown). D t l 20 20 H 76

85 u Flume Ridge Formation. Medium to thick bedded meta-graywacke interbedded with subordinate slate, il U

l a Sf f

phyllite, and minor meta-siltstone. T he brown-weathering to rusty-weathering dark gray meta-graywacke

A 8A   a Primary flow foliation in plutonic rock, defined by feldspar alignment (vertical).

g contains angular clasts of feldspar, quartz, and lithic fragments. Beds are generally between 10 and 50 1C  3  e 0  0  b centimeters, but up to a meter in thickness. Primary sedimentary structures are common, including parallel- Sf Dtm   ill Rd m Metamorphic foliation or cleavage (inclined, vertical). n H laminated and ripple-laminated turbidite intervals, graded bedding, and soft-sediment deformation features. De u 20 ar r Be 85 D

35 o Penetrative foliation or cleavage is widely spaced to absent in the more massive meta-graywacke beds, some  d U  N  85 00 n 30 3 o of which preserve sedimentary grain tex tures. Cleavage is well developed and closely spaced in the slate and Schistosity (inclined). Titcomb Bro 0 P 20 ok b mudstone. T he foliation or cleavage is parallel to the ax ial planes of tight folds. om D

65 tc Mgp

 Ti U   Mylonitic foliation (inclined, vertical).

 20 85  Hall Hill Member. Fine-grained to very fine grained, siliceous, and tuffaceous slate and phyllite 75 80 Sfh

0 characterized by alternating, dark, reddish-maroon layers and subordinate light-colored layers of

Pa 30 75 1 Photo location. Numbers refer to figure numbers in the report. re 6C

 ntRd  green to light green or white. Layers may be less than a centimeter in thickness. Its protolith may  !

 !

85 ! have a distal volcanic origin, such as a tuffite with alternating clay-rich or silica-rich layers. Some P ! H 80

80 ! Geochronology location. Refer to report T able 1 and tex t for detailed discussion.

E A 75 !

A Sf ! ex tremely fine grained mineral aggregates are suggestive of lapilli or devitrified glass fragments.

N ! N

O 4 !

0 !

C 0 ! Pyrite is present in some places. T he rock is generally foliated and the foliation is parallel or sub- B

O ! S !

C !

C ! parallel to bedding. T hin white quartz veins either follow the foliation or cross-cut foliation and

O K !

! !   T Dsb

! bedding. T he layering is locally contorted. T his distinctive unit continues north into the !

C O

85 ! 85 ! O  Greenfield quadrangle (Ludman, 2020).

71 D ! !

3 !

0 3 ! 0 !

0 0 ! !

U ! !

3 ! 0 !

0 ! ~ County Road Formation (Ludman, 2020). Medium gray weathering to chalky white weathering, dark gray, ! !

 !

! Sb ~

 ! Sc r ! ~

 ! !

74   10E ! ~ non- to weakly calcareous turbiditic sandstone (wacke) and pelite. T he formation is well ex posed along the !

   ! ~ !

 !

! 80 78 ! ~ !

 ! 74 80 ! !

85 85 ! ~ ! !

! County Road in the Otter Chain Ponds quadrangle to the west from which it was named (Ludman, 2020).

! 1H ! ! ~

! ~

70 ! !

  ~

! 0 82 ! T  0

75 Sb ! 4 ~

3 ~  85 10F ~ 85 2 B ~ 85  M ! 85  ~

r ! ! 0 a

! ~ 0 1D ! 5 D

4 d 78 ! ! ~

4°55'00"N  ! 44°55'00"N

l ! !

! ~

! ! e ! 0 

B ! ~ y  0 ! 5 ~ 0 Sf P Sf ~ 60 EXPLANATION OF PATTERNS

P ~

 ~  4 ~ 700

0 85  75 Mgp 0 ~

 ~  Ductile shear zone of the Norumbega fault system. ~ 00  8 75 ~ ~ 85 ~  ~ 900 75 ~

~ ~

 85 ~  85 ~   73 ~ ~ Springy Brook 6B,D,E,F ~ ~ 73 ~ ~ Mtn INTERPRETIVE CROSS SECTION

  ~ ! !

! ~ ! !

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! ! Dsb ~  85 !

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! 70

85  ! 

! Norum be ga fault syste m

! 65

U 88  ! 80

! Bald Bluff Mtn

75  !

! ~

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! ~

! ! A A′

85 ~ ) !

! Duc tile sh e ar zone

! ! ~

! Sb s

! !

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trea ~ A T

m E  9B  ~   ~ 85 ~ ~ ~ Be d d ing (sc h e m atic ) R e gional foliation (Ac ad ian) Be d d ing (sc h e m atic ) Mylonitic foliation Inferred motion on faults is indicated by arrows  ~ Dsb ~ 54 Sb ~  or by A (away) and T (towards). 52 ~

85 70 PP~ No vertical ex aggeration. ! B ~

! MD

! T 32 ~ !

s ! 3B,D ~

k ! ~erst B

r ! mh

o ! A ~ a W !

! ~ l

! d

! ~

! ~ B

! reat Works S

! G trea ~ ! m l

! ~ u t !

! ~ f ! f

a !

71 ! ~ ! M

e !  ~

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! 0

! 0 ! ~

! ~

! 40  !

! ~

! ~ 9

! 0

! ~

! ~ !

! !

! ~  ~ ~ 3F ~ ~ 0 REFERENCES Sf  ~ 0

6 ! GEOLOGIC TIME SCALE ! ! ~ !

! 75 ! Dl !

! ! ~ ! ! !

! ! Geologic Age Absolute Age* D ! 78 ~ ! Ludman, Allan, 2020, Bedrock geology of the Greenfield quadrangle, Maine: Maine Geological Survey, Open -File Report 20-10, 43 p. report, map scale !  Sb ! !  3A,E ~

! A ! ! ! ~ B ! U ! 65 Cenozoic Era () 0-66 m 85  ~ 1:24,000. r Mgp ! ~   7C,D

a h ! ~ ! d

! Mesozoic Era () e 

~ !  ! l Wang, Chunzeng, Ludman, Allan, and X iao, Long, 2014, T urner Mountain syenite of Maine: geochemistry, geochronology, petrogene sis, and post-

r 73 !

e ~ s ! 7B !

y t ! ! A′

! ! ~ K

!  ___Cretaceous Period ( ) 66-145 !

70 ! !

~ ! orogenic ex humation: Atlantic Geology, v. 50, p. 233–248.

! ! !

! ~ ! 49 000 ! !

! ~ ! J ! ! 70 m N ___Jurassic Period ( ) 145-201

! 

! 9A,C;10C !

! 78 ~ Wones, David R., 1980, Contribution of crystallography, mineralogy, and petrology to the geology of the Lucerne pluton, Hancock County, Maine: !

! !

! ~ T ro

! ut Pond ! !

! ! ~

! ___T riassic Period () 201-252 ! 9F !



! 9 American Mineralogist, v. 65, no. 5-6, p. 411–437.

! ~ ! ! 7F ! East Great Works 0

! 0 ~ ! Mtn !

! ! !

~ ! ! ! Paleozoic Era ()

!  Pond !

 !

! A ~ 0 !

! 0 ! ~

 Dl 8 !

! 7 Dl ! P

0 

~ 0 ___Permian Period ( ) 252-299 !

10B ! 0

! ~ 7 ! Trout

! d

Dsb ! ~

! !

~ R 0 C ! 0   ___Carboniferous Period ( )

80 ~ d Pond 7

79 !

~ ! 7E

o ~ ! P ______Pennsylvanian Subperiod () 299-323

0 ~ ! 0 t

2  ~ ! u

Saddl e ! ~ 44 o M b r ______Mississippian Subperiod ( ) 323-359

a ! 

ck ~ T

 ! Br ~ ook 80 ~ ! ___Devonian Period (D) 359-419 ACKNOWLEDGMENTS

 ! Grassy 4 ~ I 0 n 

 80  ! d

0 ~ ia 7 ! n

 Sb ~ Pond C 00 S ! a ___Silurian Period ( ) 419-444  m 6 0 ~ p 0 0 75 ! B 600  ~ 0 80 3  ! ro  T he mapping project was funded by U SGS ST AT EMAP Program and Maine Geological Survey, as well as a U niversity of Maine T rustee Professorship

49 000 ~ o ! O 69 80 ~ k 60 ___Ordovician Period ( ) 444-485

m N 3C,G,H ! 80 ~ 0  (2011) and a Z illman Family Professorship (2013-2014). I am grateful to Drs. Robert Marvinney and Henry Berry IV of the Maine Geological Survey 44°52'30"N ~ 44°52'30"N ___Cambrian Period () 485-541 540000m E 41 42 43 44 45 46 47 48 549000m E for their many years of support and guidance, to Dr. Chris McFarlane of the U niversity of New Brunswick for helping with geochronological and 68°30'00"W 68°27'30"W 68°25'00"W 68°22'30"W Precambrian time (p) Older than 541 geochemical analyses, to Dr. Marty Y ates for assisting with zircon cathodoluminescence imaging, and to Dr. Stephen Pollock for sharing field trips and Duc tile sh e ar zone * In millions of years before present. (Walker, J.D., Geissman, J.W., discussions. I owe many thanks to Dr. Allan Ludman for his many years of encouragement and mentoring – we both made our first stops at outcrops in Bowring, S.A., and Babcock, L.E., compilers, 2012 Geologic T ime Scale v. the quadrangle in 1998. I give special thanks to my field assistant Jared Dickinson who worked hard with me in the woods. I thank Amber Whittaker for 4.0: Geological Society of America, doi: 10.1130/2012.CT S004R3C.)

d editing and making this beautiful map. l ¼ Base map features from Maine Office of GIS - 1:24,000 U SGS contour e  i SCALE 1:24,000 M T

SOURCE OF GEOLOGIC INFORMATION f

Brandy r n

a u

Olamon e lines, E911 roads, 1:24,000 National Hydrography Dataset, U SGS GNIS g e e

Pond n

r 1 0.5 0 1 Mile e N

G t Field work by Chunzeng Wang, 2004, 2011, and 2013. o i placenames and 1:24,000 political boundaries. Map projection c r k t

N h c

Assisted by Jared Dickinson, 2013. Otter a o U niversal T ransverse Mercator, North American Datum, 1927. e b 1000 0 1000 2000 3000 4000 5000 6000 7000 Feet r

h Great e t h Maine s

Chain T r Pond Ponds o H 1 0.5 0 1 K ilometer T he use of industry, firm, or local government names on this map is for t s

s Approx imate Mean n r i d e k Chemo n location purposes only and does not impute responsibility for any h Declination, 2011 p o

o o m Pond P

H 17 W A present or potential effects on the natural resources. CONT OU R INT ERVAL 10 FEET