bedrock geologic map of the reading quadrangle, … · 2008-02-14 · sd sap ssb soqt sap sab soqd...
Post on 21-Apr-2020
9 Views
Preview:
TRANSCRIPT
DRAFT IN REVIEW
A
A'
Dp
Ssbh
Ssd
Zwb
Sab
Si
Dp
SOqd
Sm
ls
Zwb
Ssb
SOqd
COg
Ssbh
Zw
Ssbh
Oba
Si
Zwp
Zwb
Sap
Zw
Ssbh
Si
Sab
SOqt
Ssb
Sap
Zwba
Dp
SOqt
Sab
Sab
Ssbh
Ssd
Ssd
Ssbh
Ssbh
Ssbh
Zwba
Jrd
Obb
Ssd
SOqd
Zwba
Ssd
Zwba
Zwa
DSn
SOqd
Jrd
Sab
Obb
Sap
Ssd
Ssbh
JrTrm
Sap
Sab
Ssd
Sap
Ssb
SOqt
Sap
Sab
SOqd
Zmu
Zwa
Dp
Zw
Sm
SOqd
Ssb
Ssd
Ssbh
Sab
COg
Sab
Zwba
DSn
Zwba
Sab
Sm
COga
Ssd
Zw
DtSsb
Ssd
Ssbh
Ssbh
Sm
Ssb
Ssbh
Sab
Ssd
Ssb
Zmu
Ssd
Dp
Ssb
Ssbh
SOqd
Ssd
SOqd
Sab
Ssb
COgaSsbh
Sap
Ssbh
Sap
Sm
Sap
Ssb
Sap
Zwba
Sab
Ssd
Zwba
Zwa
Jrd
Sap
Sap
Ssb
Ssb
Ssbh
Ssbh
Sap
Zw
Ssd
SOqd
Sap
Sab
Sap
Ssb
Sab
Zwba
Sap
Ssd
Ssd
Ssd
SabSap
SOqt
Dp
Sap
Sap
Ssbh
Oba
Oba
Sap
Sab
Ssd
Ssd
56
41
60
28 78
80
80
85
85
75
75
76
70 82
20
80
80
7070
68
78
87
5
45
68
22
30
4522
70
62
66
61
55
44
30
50
45
47
23
70
82
75
87
18
76
20
65
76
6557
55
60
72
62
85
72
60
82
84
70
60
65
50
45
80
70
56
80
5550
76
57
80
74
80
7058
65
80
70
70
65
8075
80
60
80
75
302325
65
70
85
55
72
55
52
85
70
80
72
85
50
27
30
40
30
65
72
39
80
83
75
80
65
64
25
BLOODY BLUFF FAULT ZONE
Oba
Ssbh COg
Ssd
Ssd
Sm
Sab
Si
ls
Ssbh
Location approximate
Lithologic Contacts
Bedrock Exposure
Individual Outcrop Areas of abundant outcrops or shallow bedrock
(within 10 ft (3 m) of surface)
Faults
Contact, location generally approximate
32
32
50
50
Structural Symbols
Strike and dip of dominant foliation / vertical foliation (includes mylonitic foliation). Compositional layering generally parallels foliation in stratified rocks
Planar Features
Linear Features
Trend and plunge of mineral lineation
Trend and plunge of minor fold axis
EXPLANATION OF MAP SYMBOLS
Only faults traceable at map-scale and on surface are shown
Strike and dip of bedding32
Approximate strike and dip of heavily deformedfoliation / vertical deformed foliation
Mine or bedrock quarry
DESCRIPTION OF LITHOLOGIC UNITS
NASHOBA TERRANE
Metasedimentary and Metavolcanic Rocks Boxford Formation (Ordovician)--Reduced in rank and included as Boxford "Member" of
Nashoba Formation by Bell and Alvord (1976) B member--Chiefly fine-grained, distinctly foliated, very thinly Obb layered, light-gray to black schist and gneiss. Composed of rocks of widely differing
mineralogical composition, including amphibolite, calc-silicate rock, andalusite-sillimanite-sericite schist, quartz-feldspar gneiss, and others transitional between these extremes. Contains a few thin beds of white quartzite along flanks of formation
A member--Chiefly fine- to medium-grained schist, gneiss and Oba amphibolite. Schist commonly bluish-gray and composed mainly of muscovite, biotite
and quartz with minor amounts of andalusite and fibrolitic sillimanite. Gneissic rocks composed of quartz and plagioclase with varietal amounts of actinolite. Amphibolites in part coarser-grained than those of B member of Boxford Formation. Poorly exposed
COg Gneiss (Cambrian to Ordovician)--Confined to northern part of Reading quadrangle.
Chiefly medium-grained, contorted, light-gray gneiss. Composed mainly of quartz, plagioclase and biotite with accessory amounts of apatite, magnetite and zircon
Amphibolite facies--Chiefly fine-grained, foliated and locally layered COga dark-gray amphibolite. Composed mainly of hornblende, plagioclase, quartz and biotite
Intrusive Rocks Monzogranite at Middleton Pond (Probably Silurian)--Medium- to fine Sm grained, massive, pink to red monzogranite. Composed chiefly of microcline, plagioclase and
quartz with varietal amounts of biotite almost completely altered to chlorite. Contains abundant xenoliths
Andover Granite (Silurian )--Age about 450 ± 25 (Rb-Sr) to 412 ± 2 (U-Pb) Pegmatitic granite facies--Chiefly medium- to extremely coarse-grained, Sap massive, pearly-white to light-bluish-gray monzogranite and pegmatite. Composed
mainly of microcline, plagioclase, quartz and muscovite. Biotite occurs locally and garnet is a common accessory. Broad areas underlain entirely by pegmatite
Binary granite facies--Chiefly medium-grained, massive to faintly foliated,
pearly-white to light-gray monzogranite. Composed mainly of microcline, plagioclase, quartz, muscovite and biotite with accessory garnet. Pegmatite prominent locally
Sharpners Pond Diorite (Silurian )--Age about 430 ± 5 (U-Pb)
Biotite tonalite facies--Chiefly medium- to fine-grained, massive to Ssb distinctly foliated, light- to medium-gray tonalite. Granodiorite and monzogranite occur
locally. Composed mainly of plagioclase, quartz and biotite, together with lesser amounts of microcline and hornblende. Contains accessory amounts of magnetite, apatite and sphene
Biotite-hornblende tonalite facies--Chiefly medium-grained, massive Ssbh to vaguely foliated, medium to dark-gray tonalite. Composed mainly of plagioclase,
hornblende, quartz and biotite, together with accessory amounts of sphene, apatite and magnetite
Hornblende diorite facies--Chiefly medium- to coarse-grained, massive, Ssd medium-gray to black diorite and tonalite. Composed mainly of plagioclase and
hornblende, together with variable but generally small amounts of quartz. Biotite locally composes as much as 10 percent of the rock. Main accessories include magnetite, sphene and apatite
MILFORD-DEDHAM (AVALONIAN) ZONE
Metasedimentary and Metavolcanic Rocks
Middleton basin red beds (Late Triassic to Early Jurassic)--Conglomerate, JrTm arkose and sandy shale, light to dark red. Confined to Middleton basin of Kaye (1983)
Newbury Volcanic Complex (Early Devonian and Late Silurian)--Fine grained DSn to aphanitic, locally porphyritic, massive to thinly layered metavolcanic rocks. Dark greenish
gray and flesh-colored to white varieties predominate. Dark rocks composed chiefly of plagioclase, quartz and epidote; lighter colored rocks composed chiefly of feldspar and quartz. (Interbedded sediments unexposed in this area)
Waltham Tectonic Melange (Late Proterozoic to Silurian(?))--Modified from LaForge (1932)
B member--Chiefly fine-grained, foliated and locally layered, Zwb greenish-gray to black biotite-quartz-hornblende-plagioclase schists locally interlayered
with ultra-fine-grained siliceous schists. The siliceous schists commonly are chloritic and epidotitic and crop out most conspicuously along the flanks of the Waltham Melange. Commonly mylonitic or sheared. Interlayered quartzite and quartz-feldspar gneiss occur locally. Transitional with A member
Amphibolite facies of B member--Chiefly fine-grained, distinctly Zwba foliated and locally thinly layered, gray to black amphibolite and plagioclase amphibolite.
Composed mainly of hornblende and plagioclase with lesser amounts of magnetite, chlorite and calcite. Epidote conspicuous locally. Mapped separately where amphibolite or plagioclase amphibolite is the predominant rock type
Porphyroblastic gneiss member--Chiefly interlayered plagioclase Zwp amphibolite and porphyroblastic biotite-feldspar-quartz gneiss. Porphyroblasts are
chiefly microcline and range from 3 to 10 mm in diameter. Poorly exposed in this area
A member--Chiefly medium- to coarse-grained foliated and Zwa layered, very light- to dark-gray gneiss. Commonly possesses an augen- or flaser-like
texture. Composed mainly of varying amounts of quartz, plagioclase, microcline and biotite. Hornblende, muscovite, epidote and chlorite commonly present in small amounts. Contains some amphibolite and thin quartzite layers. Transitional with B member
Metamorphic rocks, undifferentiated (Late Proterozoic?)--Fine-grained and Zmu locally porphyroblastic, foliated and locally layered, dark- to light-gray metamorphic rocks.
Lithologic varieties include hornfels, calc-silicate rock and quartzitic gneiss. Confined to area adjacent to Hawkes Pond
Westboro Formation (Late Proterozoic)--Chiefly fine-grained, massive to Zw faintly foliated, light-greenish-gray to white quartzite. Composed mainly of quartz with minor
amounts of feldspar, chlorite and amphibole. Poorly exposed Serpentinite at Lynnfield (age uncertain)--Chiefly ultra-fine-grained, ls massive and slickensided, very dark bluish- to greenish-gray serpentinite. Composed chiefly
of antigorite. Colorless amphibole, olivine, magnetite and chlorite present locally. Poorly exposed
Intrusive Rocks
Diabase (Early Jurassic)--Fine- to medium-grained, massive, dark-gray Jrd to black. Commonly porphyritic with tabular plagioclase phenocrysts up to 3 cm in diameter.
Composed chiefly of plagioclase and pyroxene. Confined to Wilmington, Woburn, Reading, Lynnfield and Peabody areas
Trachyte at Middleton (Devonian?)--Fine-grained, generally massive, Dt light-gray trachyte or keratophyre. Composed chiefly of sodic plagioclase, potassium feldspar
and pyroxene. Highly altered. Localized within small area about 2.2 km south of Middleton center
Peabody Granite (Late and Middle Devonian)--Age about 360 ± 24 (Rb-Sr) Dp to 395 ± 20 (U-Pb). Coarse-grained, massive, light-gray granite. Composed chiefly of
microperthite, quartz, hornblende and plagioclase. Biotite occurs mainly in peripheral rocks. Included with "alkalic" intrusive series of Toulmin (1964)
Tonalite athwart Ipswich River at Middleton-Peabody town boundary Si (Silurian?)--Chiefly medium-grained, massive and locally foliated medium- to dark-
greenish-gray tonalite. Composed mainly of plagioclase and quartz together with minor amounts of microcline. Abundant secondary chlorite and epidote. Intensely sheared and brecciated locally. Continuous with Newburyport (?) Quartz Diorite of Toulmin (1964)
Diorite at Lake Quannapowitt and vicinity (Silurian or Ordovician)--Age about 444
± 3 (U-Pb) Biotite-hornblende tonalite facies--Chiefly massive, medium-grained SOqt dark-gray, alkali-rich tonalite. Composed largely of plagioclase, hornblende, quartz and
biotite Hornblende diorite facies--Chiefly massive, medium grained, gray to black, SOqd alkali-rich diorite. Composed mainly of plagioclase and hornblende, together with variable but generally small amounts of quartz and biotite. Accessories
chiefly magnetite and sphene
Sab
ls
DSn
JrTrm
Sab
Ssb
Ssbh
Ssd
Zmu
Zw
Zwa
Zwb
Zwba
Zwp
Dp
Dt
Jrd
SOqd
SOqt
Si
COg
COga
Oba
Obb
Sap
Sm
SsbhSm
ZwbSsb
COg
SsdSsdSsbh Ssb
Ssbh
SapSab
Sab
Sap
Ssbh Ssbh
COg SsbhSsbh
500 ft
sea level
-500 ft
-1000 ft
-1500 ft
-2000 ft
A'
NA
SHO
BA
TER
RA
NE
MIL
FOR
D-D
EHA
MZO
NE
BLOODY BLUFFFAULT ZONE
200 m
-200 m
-400 m
-600 m
sea level
A
Ipsw
ich
Riv
er
Nor
th A
ndov
erN
orth
Rea
ding
Ste
arns
Pon
d
OFFICE OF THE MASSACHUSETTS STATE GEOLOGISTUNIVERSITY OF MASSACHUSETTS
Topographic base scanned from U.S. Geological Survey, 1966 Polyconic projection. 1927 North American DatumDigitally reprojected to 1983 North American Datum, 1:24,000 scale10,000 foot grid ticks based on Massachusetts state plane coordinate system, mainland zone1000-meter Universal Transverse Mercator grid ticks, zone19
Bedrock geology by R.O. Castle (1951-1952, 1992).Updated and revised by J.C. Hepburn and J.P. Kopera (2004). Digitized by J.P. Kopera (2005).
Prepared in cooperation with the COMMONWEALTH OF MASSACHUSETTS
STATE GEOLOGISTBEDROCK GEOLOGIC MAP
READING QUADRANGLE, MASSACHUSETTSv. 1.0
Stratigraphic correlation chart accompanies map
This manuscript is submitted for publication with the understanding that the United States Government is authorized to reproduce and distribute reprints for government use.
This research was supported by U.S. Geological Survey, National Cooperative Geologic Mapping Program, under assistance Award No. 04HQAG0028. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.
Citation:Castle, R.O, Hepburn, J.C., and Kopera, J.P., Bedrock geologic map of the Reading quadrangle, Massachusetts, v 1.0, Massachusetts Geologic Survey (4th), (in review, April 2005)
Note: This manuscript is currently undergoing peer review, and is not a final
Affiliations:
1United States Geological Survey Menlo Park, CA2Department of Geology and Geophysics Boston College Chestnut Hill, MA, 02467
3Corresponding Author: Office of the Massachusetts State Geologist Department of Geosciences University of Massachusetts, Amherst, MA 01003 jkopera@geo.umass.edu
�MA
GN
ET
IC N
OR
TH
AP P R O X IMAT E ME ANDE C L IN AT IO N , 1999
TR
UE
NO
RT
H
15 / 1 2
QUADRANGLE LOCATION
BEDROCK GEOLOGIC MAP OF THE READING QUADRANGLE, MASSACHUSETTSBy
Robert O. Castle1, J. Christopher Hepburn2, and Joseph P. Kopera3
2005 (in review)
top related