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Bedrock Geologic Map of the Hanover 7.5' Quadrangle, New Hampshire N

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Bedrock Geologic Map of the Hanover 7.5' Quadrangle, New Hampshire N Bedrock Geologic Map of the Hanover 7.5' Quadrangle, New Hampshire N " 72°22'30"W 72°20'0"W 72°17'30"W 72°15'0"W 0 ' N 5 " 4 0 ° ' 3 5 4 4 ° 3 B' 4 DESCRIPTION OF MAP UNITS EXPLANATION OF INT RU SIVE AND FAU L T ROCKS MAP SYMBOLS Kjd Mafic dikes (Mesozoic) — No Mesozoic diab ase dikes were foun d, Con tac t Beddin g So although L yon s (1958) reported on e on Crafts Hill an d several in trudin g the L eb an on gran ite. (c ertain ) Foliation Sn Con tac t md Metadiabase sills and dikes (unknown age) — A few m etadiab ase dikes of un kn own age (m d) c on sistin g of fin e- to m edium -grain ed horn b len de gn eiss (in ferred) in trude the Partridge Form ation . T heir exten t is lim ited to on e or a few Foliation S1 Con tac t outc rops. (c on c ealed) 35 In tersec tion 35 Amphibolite (unknown age) — Am phib olite, likely m etagab b ro, c rops out Oo9B lin eation 38 as sills within the m etavolc an ic s west of Bald Hill an d in a larger b ody alon g Fault the c rest of Crafts Hill. T he m assive, b loc ky- an d b rown -weatherin g roc k Min eral Min eral lin eation 37 seem s to b e in terc alated with quartz diorite alon g the east side of Crafts Hill. isograd T his b ody c on tin ues south all the way to a n ear-outc rop at an old dam site on 36 the Masc om a River upstream from the Route 4 b ridge n orth of the airport. (in ferred) Fold axis Rum b le (pers. c om m ., 2015) reported that L yon s had suggested to a t c on trac tor that the am phib olite m ight serve as road m etal, b ut the roc k was 29 s g 38 so tough that it apparen tly b roke the testin g equipm en t. 39 27 ORDOVICIAN OL IVERIAN PL U T ONIC ROCKS 34 Granite (Ordovician) — T he gran ite (Oo1b ) in the c en ter of the L eb an on Oo1b Dom e is a pin kish gray, m edium -grain ed, weakly to n on -foliated b iotite Oo9B gran ite, whic h has b een quarried for dim en sion ston e. 49 27 29 Oo3A Tonalite/quartz diorite (Ordovician) — Quartz diorite or ton alite (Oo3A) 23 m an tles the gran ite an d is well exposed on Starr Hill in L eb an on an d in the 23 Masc om a River b etween old m ills n orth an d south of Route 4. T he quartz diorite is a dark to m edium gray, m edium -grain ed b iotite roc k, m ore stron gly Oo1b N " foliated alon g its c on tac ts with the Partridge Form ation . Valley et al. (2015) 0 3 N ' " 2 0 4 reported a U /Pb age on zirc on s from the gran ite in the En field Quadran gle as 3 ° ' 3 2 4 4 ° 448+/-5 Ma, an d from the quartz diorite n ear the Poverty L an e/Route 4 40 3 4 39 in tersec tion in Han over Quadran gle as 445+/-7 Ma. Field relation s suggest 44 that the gran ite is youn ger. T he Route 4 road c ut also c on tain s a xen olith of Partridge felsic volc an ic s parallel to foliation within the quartz diorite. At 39 Ops the I-89/Route 12A in tersec tion , n orth of the Verizon W ireless b uildin g, a white-weatherin g ton alite that in trudes the Am m on oosuc Volc an ic s was 20 dated at 466+/-8 Ma (Valley et al., 2015). T his is part of the sm all pluton ) shown b y L yon s (1955) as a b ody of L eb an on gran ite, b ut it is c learly older n o i than the dom e roc ks, an d together with ton alite in Plain field (U /Pb 475+/-5 t Oo6 a Ma, Valley et al., 2015), provides som e c on strain ts on the m in im um age of T r L the Am m on oosuc . e U g A g F Oo6 Quartz Diorite a x E l MET ASEDIMENT ARY AND MET AVOL CANIC ROCKS C Oa a U c i S Op Partridge formation undifferentiated (Ordovician) — T he Partridge t O Form ation in this quadran gle c on sists of sc hist (Ops) with felsic r 30 e O 40 V m etavolc an ic len ses an d layers (Opf). N O o M Ops Sulfidic schist member — Sc hists in the Partridge are rusty-weatherin g, N ( M b lac k to dark gray, graphitic an d sulfidic fin e- to c oarse-grain ed sc hist. T hey ' A are c oarser away from the L eb an on Dom e, for exam ple on the west slopes of B - Oak Hill, where c lum ps of b iotite (pseudom orphs after staurolite?) an d Oo1b B loc ally staurolite itself join tin y garn ets as porphyrob lasts. Closer to the dom e the Partridge is overall fin er-grain ed b iotite sc hist, loc ally with garn et. n o i T he staurolite isograd tren ds n ortheast toward a well defin ed c on tin uation in t the L ym e Quadran gle (T hom pson , 2008). (A study of feldspar c om position s c e S in the m afic roc ks would c on trib ute to loc atin g the c om parab le am phib olite s fac ies lim its.) s 47 o r Opf Felsic volcanics member — Felsic m etavolc an ic s of the Partridge ran ge LEBANON C from rusty weatherin g, light gray fin e-grain ed sulfidic felsite to rusty, e 31 DOME m edium -grain ed b iotite feldspar-studded gn eiss. Sulfide prospec ts are v 53 i c om m on in this un it, espec ially n ear Farn um Hill in the North Hartlan d t e Quadran gle, where a series of tren c hes an d pits were dug in the 1880’s r 42 42 50 p r N " (L yon s, 1958) in m etavolc an ic roc ks an d what appears to b e a quartz diorite 0 ' e N 0 " t 4 0 ° sill. Material in spoils piles c on sists of vein quartz an d gossan -like m aterial. 65 ' 3 0 4 n 4 ° 3 I Ab out 1500 m eters n orth, in the Han over Quadran gle n orth of the Old Kin gs 4 t s Highway, an other tren c h was foun d durin g this study, where the roc ks are so 49 g ric h in pyrrhotite that c om pass b earin gs were disturb ed. 48 52 40 Oa Ammonoosuc Volcanics undifferentiated (Ordovician) — Ran ge from Opf 49 dark green -b lac k fin e- to m edium -grain ed horn b len de gn eisses to b lac k an d Oo9B white m etavolc an ic s with distin c t altern atin g horn b len de-ric h an d feldspathic layers in the Han over quadran gle. T he un it is well exposed on the 56 60 Dartm outh College c am pus, where a sill of white-weatherin g feldspar-garn et 45 64 gn eiss with horn b len de fasc ic les lies parallel to m ore typic al m afic roc ks. A Som e layers c on tain epidote-ric h len ses up to 30 c en tim eters lon g, som e of Opf 52 57 whic h have pillow-like shapes. T he Am m on oosuc is also exposed in a sm all quarry east of Route 10 n ear Cam p Brook, on Cham b ers Road just south of 73 the Han over lin e, an d from W ilder Dam south alon g a ridge east of Route 10 to the outskirts of W est L eb an on , where it disappears b en eath Quatern ary c over. T he on ly exposures south of there are at the I-89/Route 12A 59 in tersec tion (disc ussed further b elow) an d on Poverty L an e at the south b order of the quadran gle, where it is a well foliated, c oarse-grain ed Oo9B am phib ole-epidote-c hlorite gn eiss. Dg/Dgm Gile Mountain Formation/ Meetinghouse Slate Member (Devon ian) — No outc rop presen t in study area, un derlies youn ger un its. Oa Ops Oa 82 51 40 52 75 Oo3A Opf Oo6 Ops 67 N " 68 57 55 0 3 N ' " 7 B 71 md 87 0 3 77 3 ° ' 3 7 4 A' 3 ° 3 4 72°22'30"W 72°20'0"W 72°17'30"W 72°15'0"W Scale 1:24,000 Topographic basemap from the USGS 1998 Hanover 7.5' quadrangle Projection: North American Datum 1983 New Hampshire State Plane Feet.
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