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Mineral Resources > Online Spatial Data > Geology > by state > New Hampshire Geology

Geologic units in Rockingham county, New Hampshire

[Additional scientific data in this geographic area]

Merrimack Group, Eliot Formation, Calef Member (Ordovician? - Silurian?) at surface, covers 0.9 % of this area

Merrimack Group, Eliot Formation, Calef Member - Black phyllite at western contact of the Eliot Formation.

Lithology: phyllite

Merrimack Group, Berwick Formation, Unnamed member (Ordovician? - Silurian?) at surface, covers 10 % of this area

Merrimack Group, Berwick Formation, Unnamed member - Contains more calc-silicate (15 percent) than does the remainder of the formation (5 percent).

Lithology: granofels; quartz-feldspar schist; meta-argillite

Mesoperthitic biotite granite (Early Cretaceous) at surface, covers < 0.1 % of this area

Mesoperthitic biotite granite - Pink Conway-type granite of Kingsley (1931).

Lithology: granite

Newburyport Complex (early Late Silurian) at surface, covers 0.8 % of this area

Newburyport Complex - Gray, medium-grained tonalite and granodiorite.

Lithology: tonalite; granodiorite

Rye Complex, Breakfast Hill Granite of Novotny (1964). (Ordovician? - Late Proterozoic? ) at surface, covers 1 % of this area

Breakfast Hill Granite of Novotny (1964) - Blastomylonitic quartz-feldspar granitic gneiss and pegmatite intruded the Rye Complex and formed a migmatite.

Lithology: granitic gneiss; pegmatite; migmatite

Merrimack Group, Berwick Formation, Gove Member (Ordovician? - Silurian?) at surface, covers 1 % of this area

Merrimack Group, Berwick Formation, Gove Member - White muscovite schist. Equivalent to the Gonic Formation of Hussey (1962).

Lithology: mica schist

Newburyport Complex (Silurian) at surface, covers < 0.1 % of this area

Newburyport Complex - Gray, medium-grained porphyritic granite with microcline phenocrysts; intrudes SOk. Newburyport Complex was divided into two facies, tonalitic granodiorite and granite, by Shride (1971). Tonalitic facies was originally termed Newburyport Quartz Diorite and included dioritic rocks north of Clinton-Newbury fault zone that are now called Sharpners Pond Diorite in Nashoba zone, and Topsfield Granodiorite in Milford-Dedham zone. These correlations are no longer tenable due to differences in age and composition. Therefore, Newburyport Complex is restricted to the two facies present in Newburyport area. Rocks formerly mapped as Newburyport Quartz Diorite and Salem Gabbro-Diorite, except for gabbros at Salem Neck, MA, are included in undifferentiated diorite and gabbro unit (Zdigb) on MA State Geologic Map (Zen and others, 1983), largely because they could not be mapped separately at 1:250,000 scale. Unit Zdigb also includes mafic dikes and sills that are probably younger or contemporaneous. Most of the dioritic rocks northeast of Boston previously assigned to Newburyport Quartz Diorite are now assigned to an undifferentiated diorite unit (Zdi) on MA State Geologic Map. Newburyport Complex forms a large mass near Newburyport and a small one to its west, both truncated by Clinton-Newbury fault. Tonalite and granodiorite facies occupies core of Newburyport Complex at Newburyport and is intruded to the north by granite facies; described as medium to dark gray in fresh rock, weathering to both green and red, fine to medium grained, and highly variable in mineralogy. A U-Pb zircon age of 455 +/-15 Ma was determined by Zartman and Naylor (1984) for the tonalite. Granite facies intrudes both the Kittery Formation and the tonalite and granodiorite facies and covers an area of about 45 sq km. Described as light gray to dark gray, buff weathering, and porphyritic. No radiometric ages available for granite facies, but it is conceivable that the two facies are different in age. [Papers presented as chapters in U.S. Geological Survey Professional Paper 1366 are intended as explanations and (or) revisions to MA State bedrock geologic map of Zen and others (1983) at scale of 1:250,000.] (Wones and Goldsmith, 1991).

Lithology: granite

Pink equigranular biotite granite (Late Devonian) at surface, covers 0.4 % of this area

Pink equigranular biotite granite - Found in Woodsville and Whitefield quadrangles and in small intrusive units in northern and southeastern New Hampshire.

Lithology: granite

Augite-hornblende diorite and gabbro (Cretaceous ) at surface, covers 0.2 % of this area

Augite-hornblende diorite and gabbro - Gray to black, coarse-grained, porphyritic. Found in Mt. Pawtuckaway quadrangle.

Lithology: diorite; gabbro

Concord Granite (Late Devonian ) at surface, covers 7 % of this area

Concord Granite - Gray two-mica granite, locally grading to tonalite.

Lithology: granite; tonalite

Rye Complex (Ordovician? - Late Proterozoic?) at surface, covers 4 % of this area

Rye Complex - Migmatite of gray, foliated, sheared or mylonitized two-mica granite and pegmatite, minor hornblende-biotite diorite, intruding metapelites and metavolcanic rocks in southeastern New Hampshire.

Lithology: migmatite; granite; pegmatite; diorite; meta-argillite; metavolcanic rock

Augite-hornblende-biotite gabbro (Cretaceous) at surface, covers < 0.1 % of this area

Augite-hornblende-biotite gabbro - Fine- to coarse-grained.

Lithology: gabbro

Berwick Formation (Silurian) at surface, covers < 0.1 % of this area

Berwick Formation - Thin- to thick-bedded metamorphosed calcareous sandstone, siltstone, and minor muscovite schist. In New Hampshire: Used as Berwick Formation of Merrimack Group. Consists of purple biotite-feldspar granofels or schist. Contains interbeds of calcsilicate granofels and minor metapelites. Includes Gove Member, mapped separately. Stratigraphic sequence with respect to Eliot Formation is uncertain. Age of all formations in Merrimack Group changed to Ordovician(?) to Silurian(?) based on isotopic age determinations of approx 440 and 420 Ma from detrital zircons from Berwick by J.N. Aleinikoff (oral commun., 1994) (Lyons and others, 1997).

Lithology: metasedimentary rock; mica schist

Smalls Falls Formation, undivided (Upper to Middle Silurian (Ludlovian and Wenlockian)) at surface, covers 0.7 % of this area

Smalls Falls Formation, undivided -Very rusty weathering, thinly bedded sulfidic-graphitic schist and pyrrhotitic calc-silicate granofels. Eastern facies equivalent to lower part of the Fitch Formation. Locally mapped as Francestown Formation of Nielson (1981) in southern New Hampshire.

Lithology: schist; granofels

Mesoperthitic granite (Jurassic) at surface, covers < 0.1 % of this area

Mesoperthitic granite - Contains riebeckite and (or) hastingsite.

Lithology: granite

Littleton Formation, undivided (Lower Devonian; Siegenian) at surface, covers 0.4 % of this area

Littleton Formation undivided - Gray metapelite and metawacke and subordinate metavolcanic rocks; generally, but not everywhere, conformable with underlying Fitch or Madrid Formations. Fossiliferous in western New Hampshire.

Lithology: metasedimentary rock; metavolcanic rock

Newburyport Complex (Late Silurian) at surface, covers 0.4 % of this area

Newburyport Complex - Medium-grained porphyritic granite.

Lithology: granite

Merrimack Group, Eliot Formation (Ordovician? - Silurian?) at surface, covers 17 % of this area

Merrimack Group, Eliot Formation - Gray to green phyllite, calcareous quartzite, quartz-mica schist, and well-bedded calc-silicate.

Lithology: phyllite; quartzite; mica schist; calc-silicate rock

Newburyport Complex (Silurian or Ordovician) at surface, covers < 0.1 % of this area

Newburyport Complex - Gray, medium-grained tonalite and granodiorite. Newburyport Complex was divided into two facies, tonalitic granodiorite and granite, by Shride (1971). Tonalitic facies was originally termed Newburyport Quartz Diorite and included dioritic rocks north of Clinton-Newbury fault zone that are now called Sharpners Pond Diorite in Nashoba zone, and Topsfield Granodiorite in Milford-Dedham zone. These correlations are no longer tenable due to differences in age and composition. Therefore, Newburyport Complex is restricted to the two facies present in Newburyport area. Rocks formerly mapped as Newburyport Quartz Diorite and Salem Gabbro-Diorite, except for gabbros at Salem Neck, MA, are included in undifferentiated diorite and gabbro unit (Zdigb) on MA State Geologic Map (Zen and others, 1983), largely because they could not be mapped separately at 1:250,000 scale. Unit Zdigb also includes mafic dikes and sills that are probably younger or contemporaneous. Most of the dioritic rocks northeast of Boston previously assigned to Newburyport Quartz Diorite are now assigned to an undifferentiated diorite unit (Zdi) on MA State Geologic Map. Newburyport Complex forms a large mass near Newburyport and a small one to its west, both truncated by Clinton-Newbury fault. Tonalite and granodiorite facies occupies core of Newburyport Complex at Newburyport and is intruded to the north by granite facies; described as medium to dark gray in fresh rock, weathering to both green and red, fine to medium grained, and highly variable in mineralogy. A U-Pb zircon age of 455 +/-15 Ma was determined by Zartman and Naylor (1984) for the tonalite. Granite facies intrudes both the Kittery Formation and the tonalite and granodiorite facies and covers an area of about 45 sq km. Described as light gray to dark gray, buff weathering, and porphyritic. No radiometric ages available for granite facies, but it is conceivable that the two facies are different in age. [Papers presented as chapters in U.S. Geological Survey Professional Paper 1366 are intended as explanations and (or) revisions to MA State bedrock geologic map of Zen and others (1983) at scale of 1:250,000.] (Wones and Goldsmith, 1991).

Lithology: tonalite; granodiorite

Berwick Formation (Silurian) at surface, covers < 0.1 % of this area

Berwick Formation - Mica schist. In New Hampshire: Used as Berwick Formation of Merrimack Group. Consists of purple biotite-feldspar granofels or schist. Contains interbeds of calcsilicate granofels and minor metapelites. Includes Gove Member, mapped separately. Stratigraphic sequence with respect to Eliot Formation is uncertain. Age of all formations in Merrimack Group changed to Ordovician(?) to Silurian(?) based on isotopic age determinations of approx 440 and 420 Ma from detrital zircons from Berwick by J.N. Aleinikoff (oral commun., 1994) (Lyons and others, 1997).

Lithology: mica schist

Eliot Formation (Silurian) at surface, covers < 0.1 % of this area

Eliot Formation - Phyllite and calcareous phyllite. In New Hampshire: Used as Eliot Formation of Merrimack Group. Consists of gray to green phyllite, calcareous quartzite, quartz-mica schist, and well-bedded calc-silicate. Includes Calef Member, mapped separately. Age of all formations in Merrimack Group changed to Ordovician(?) to Silurian(?) based on isotopic age determinations of approx 440 and 420 Ma from detrital zircons from Berwick Formation (of Merrimack Group) by J.N. Aleinikoff (oral commun., 1994) (Lyons and others, 1997).

Lithology: phyllite

Massabesic Gneiss Complex (Late Proterozoic) at surface, covers 13 % of this area

Massabesic Gneiss Complex - Migmatite consisting of pink, foliated biotite granite intruding gneissic and granulose metasedimentary and metavolcanic rocks in southeastern New Hampshire.

Lithology: migmatite; granite; metasedimentary rock; metavolcanic rock

Two-mica granite of northern and southeastern New Hampshire (Early - Late Devonian) at surface, covers 2 % of this area

Two-mica granite of northern and southeastern New Hampshire - Similar to Concord Granite.

Lithology: granite

Perry Mountain Formation, undivided (Lower? - Middle? Silurian) at surface, covers 3 % of this area

Perry Mountain Formation, undivided - Sharply interbedded quartzites, light-gray nongraphitic metapelite, and "fast-graded" meta-turbidites. Coticule layers common.

Lithology: quartzite; meta-argillite; metasedimentary rock

Merrimack Group, Kittery Formation (Ordovician? - Silurian?) at surface, covers 7 % of this area

Merrimack Group, Kittery Formation - Tan, graded-bedded, calcareous metasandstone and purple and green phyllite. Grades into the Eliot formation but facing direction is uncertain.

Lithology: metasedimentary rock; phyllite

Exeter Diorite (Early Devonian) at surface, covers 4 % of this area

Exeter Diorite - Includes associated intrusive rocks of southeastern New Hampshire; pyroxene and pyroxene-hornblende diorite and gabbro, along with minor granodiorite and granite.

Lithology: diorite; gabbro; granodiorite; granite

Gray augite-hornblende-biotite monzonite (Cretaceous) at surface, covers 0.1 % of this area

Gray augite-hornblende-biotite monzonite.

Lithology: monzonite

Merrimack Group, Berwick Formation (Ordovician? - Silurian?) at surface, covers 27 % of this area

Merrimack Group, Berwick Formation - Purple biotite-quartz-feldspar granofels or schist and interbeds of calc-silicate granofels and minor metapelites. Stratigraphic sequence with respect to Eliot Formation uncertain

Lithology: granofels; quartz-feldspar schist; meta-argillite

Ayer Granodiorite (Early Silurian) at surface, covers 0.2 % of this area

Ayer Granodiorite - Gneissic granite to tonalite, locally coarsely porphyritic and muscovitic, southeastern New Hampshire.

Lithology: granodiorite; granite; tonalite