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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 " 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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  • Petrochemistry and Tectonic Origin of the Ammonoosuc Volcanics, New Hampshire—Vermont

    Petrochemistry and Tectonic Origin of the Ammonoosuc Volcanics, New Hampshire—Vermont

    Petrochemistry and tectonic origin of the Ammonoosuc Volcanics, New Hampshire—Vermont JOHN N. ALEINIKOFF Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire 03755 ABSTRACT The volcanic rocks are mapped over a fairly large area in western New Hampshire, generally occurring in the form of bedded am- The Middle Ordovician Ammonoosuc Volcanics of the Branson phibolite or greenstone and locally as pillows. Billings (1937) dis- Hill anticlinorium in the upper Connecticut River valley, New tinguished several facies within the Ammonoosuc Volcanics, in- Hampshire—Vermont, is composed of amphibolite, greenstone, cluding soda-rhyolite, volcanic conglomerate, greenstone, and and felsic schists. Major-element analyses of rocks believed to have meta-andesite. Rocks of basaltic composition constitute 50% of the been basaltic flows, such as pillowed greenstones and dense ara- formation. Lyons (1955) mapped the Post Pond Volcanic member phibolites, reveal that they are tholeiitic in composition. The felsic as chlorite and hornblende schists that were probably originally schists do not have igneous compositions, therefore indicating con- basalt flows but later were reworked with admixtures of sedimen- tamination by sedimentary detritus. Regional metamorphism ap- tary detritus. In this study, only pillowed metabasalts or thick, pears to have been isochemical. However, sea-floor alteration prior dense amphibolites that suggested flows were sampled. Rocks with to regional metamorphism probably depleted the basalts in MgO well-preserved pillow structure, most with a dark rind representing and slightly enriched them in Si02 and P205. On the basis of the original glassy chill at the pillow margin, were collected at three trace-element discrimination diagrams (Ti-Zr, Ti-Zr-Y, Ti-Zr-Sr), localities in the Hanover (Lyons, 1955) and Mt.