Bedrock Geology of Rhode Island o 5. GEOLOGICAL SURVEY BULLETIN 1295 I 09 i Prepared in cooperation with the State 8 of Rhode Island Development Council * Ci PI iO o TJ i i I toM & Ol I C.to Bedrock Geology of Rhode Island By ALONZO W. QUINN GEOLOGICAL SURVEY BULLETIN 1295 Prepared in cooperation with the State of Rhode Island Development Council Lithology, structure, and metamorphism of Narragansett basin sedimentary rocks of Pennsylvanian age, younger Westerly Granite, and underlying igneous and metamorphic rocks of early Paleozoic or Precambrian age UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1971 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 76-610762 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.G. 20402 CONTENTS Page Abstract---__---___---_____-___---------------------.-_---------_ 1 Introduction. _______-_-__________---__---___--_____--___---'____.-_ 1 Earlier geological studies in Rhode Island____._.________.-__.-_-____. 5 Position of Rhode Island in the Appalachian Mountain system..________ 6 Stratigraphic units________________________________________________ 6 Age relationships-___-__-____---_-----__-__-________----_------ 6 Older metamorphic rocks.-__-_--____--_____-----------_-__----_ 8 Blackstone Series, Precambrian(?)___________________________ 8 General features...--..______-_____-____--____-___---._ 8 Mussey Brook Schi8t_-------_-__---_-__-----_--__-_--- 12 Marble. _--_-._-____--_---_-_-_---_-_-----_----_._--- 12 Quinnville Quartzite___-_-__-__._---__----___-_-__----- 12 Sneech Pond Schist___---_--_-____--__--_-_----_-_----_ 13 Hunting Hill Greenstone_______________________________ 13 Blackstone Series, undivided_--___--___----___---____--_ 13 Migmatite of Blackstone Series_________---__-__-___--_- 14 Older gneissic rocks of northwestern Rhode Island.____________ 14 Nipsachuck Gneiss------------------------------------ 15 Absalona Formation_---_-___-_____--__---____--___-_-_ 18 Woonasquatucket Formation___-__-_____-_____-____--_ 19 Light-colored gneiss.._--________-__--_-__----__-___---- 19 Metamorphic rocks of western and southwestern Rhode Island. _ 19 Metavolcanic rocks of western Rhode Island.___-_.___--._ 20 Cambrian(?) Plainfield Formation.. ------------------- 20 Ordovician(?) rocks.----.---------------.-------------- 21 Metamorphic rocks of southeastern Rhode Island_____-._--__ 21 Older plutonic rocks.___.-_____-__---__________-___--__---.---_ 23 West of the Narragansett basin.______-_-_________---_-_--_- 23 Metadiorite. ___-_.____-_-_____._________-_____.___._-_ 24 Ponaganset Gneiss:.__--_---_-_-_---_---__---__---_---- 24 Porphyritic granite gneiss.._._-______.__---____-------_- 25 Scituate Granite Gneis8-___-_--____--_-__-__--.-_------ 26 Hope Valley Alaskite Gneiss...-----.-._---_-----_------ 26 Ten Rod Granite Gneiss...._____---____---__-_-_--_--- 27 Fine-grained granite related to Scituate Granite Gneiss and Ten Rod Granite Gneiss...-__-_--_-___-.....-.....-_ 27 Potter Hill Granite Gneiss...-._-__________.-_ 28 Quartz diorite, several types.--------------------.------ 28 Grant Mills Granodiorite.------------.-.--------------- 28 in IV CONTENTS Stratigraphic units Continued Older plutonic rocks Continued West of the Narragansett basin Continued Page Esmond Granite-__-_-__-.-_-________________.__-___-__ 29 Fine-grained granite related to Esmond Granite__---__-.__ 30 Gabbro, probably of several ages-_--_-____---__--_______ 30 Cumberlandite ________________________________________ 31 Southeastern Rhode Island_____-___--_______.______________ 32 Metacom Granite Gneiss.-_____________________________ 32 Porphyritic granite at Newport and Conanicut Island_______ 32 Bulgarmarsh Granite-_________________________________ 33 Igneous rocks of Mississippian(?) or older age_____________________ 33 Quincy Granite and granite porphyry._______________________ 33 East Greenwich Group...----___--_--_-_.-_-_-_____________ 34 Spencer Hill Volcanics__-__-_--__-____--_-___-_-_-.-_ 35 Maskerchugg Granite.____--____-_________-______-_--__ 35 Granite porphyry associated with Cowesett Granite.______ 36 Cowesett Granite____________________________________ 36 Perthitic Cowesett Granite_____-____--____--__--_______ 36 Fine-grained granite related to Cowesett Granite __________ 37 Pennsylvanian rocks ___________________________________________ 37 Narragansett basin_______________________-____.__-____--__ 37 Pondville Conglomerate________________________________ 38 Wamsutta Forniation------_---_-__----__---_-_-----_-_ 39 Rhode Island Formation_______________________________ 39 Dighton Conglqmerate_______________--__-__________-_- 41 Felsite at Diamond Hill______.__._--___--_-_-______ 41 North Scituate and Woonsocket basins.______________________ 42 Bellingham Conglomerate____--__--__-___--__-----_---_ 42 Pennsylvanian or post-Pennsylvanian granitic rocks______-___--__ 42 Narragansett Pier Granite-_-__-_-__-__------_---_--------_- 42 Westerly Granite___-_________-____---__-__-_-__---_------- 43 Mafic dikes and sills._________-____________-_____---__--------_ 44 Vein quartz..--___-____---_______--_-_-_--_----_-------------- 45 Upper Cretaceous Raritan Formation(?) of Block Island-__________ 46 Structural geology--..----------.----------- _-____--__-----_---- 46 Older metamorphic rocks.._-______-__-____._--___--_-_---_----- 46 Older plutonic rocks._________--__----__--._--___-------------- 47 Igneous rocks of Mississippian(?) or older age_______--___.-------- 47 Narragansett basin._____-_____-___-___-____-__---------_-----_ 47 Pennsylvanian or post-Pennsylvanian granitic rocks________-_-_--- 48 Metamorphism. -_-_-___.________________---_-___-_---_------------ 49 Pre-Pennsylvanian metamorphism__--___-____-____-------------- 49 Pennsylvanian or post-Pennsylvanian metamorphism__________---- 50 Radiometric ages._____________-_----_----_---_----_--------------- 51 Geological history___-______-__-_---------_---------.-------------- 53 CONTENTS Page Economic geology. 56 Carbonate rocks. __. 56 Dimension stone 57 Granite. ______ 57 Other rocks. _.. 58 Crushed stone.. 58 Metal deposits._-.. 58 Cumberland! te. 59 Meta-anthracite. _ _. 59 Quartz ____________ 60 References cited. ___.__. 60 Index----...._.--__... 65 ILLUSTKATIONS Page PLATE 1. Bedrock geologic map of Rhode Island.___________.-___ In pocket FIGURE 1. Index map of Rhode Island____________ 2. Generalized geologic map of Rhode Island. TABLES Page TABLE 1. Typical modes of Rhode Island rocks______-_-___--__--___. 15 2. Radiometric ages of rocks in Rhode Island and nearby Massachusetts.___-_____._-_-__._.__-__---__--__---_-- 51 BEDROCK GEOLOGY OF RHODE ISLAND By ALONZO W. QUINN ABSTRACT Probably the oldest rocks in Rhode Island are the Blackstone Series of Pre- cambrian(?) age. These and several other groups of metamorphic rocks in the State include quartzite, quartz-mica schist, greenstone, amphibolite, marble, and several types of gneiss. All were folded and metamorphosed one or more times before the Pennsylvanian Period. Intrusive into these older metamorphic rocks are varied plutonic rocks that range from metadiorite through quartz diorite and granodiorite to granite, and from strongly gneissic syntectonic granitic rocks to almost massive granites. These plutonic rocks probably are of Paleozoic age, and they may belong to one series or to more than one. After solidifying at depth, they were exposed at the surface by erosion before the formation of the volcanic, hypabyssal, and plutonic rocks of the East Greenwich Group. This group and the Quincy Granite of northern Rhode Island were exposed by erosion before Penn­ sylvanian time when the Narragansett basin rocks were deposited. The Narragansett basin contains several thousand feet of coarse clastic non- marine rocks, which contain plant fossils and some meta-anthracite. These rocks were folded, faulted, and progressively metamorphosed in Pennsylvanian or post-Pennsylvanian time. They were also intruded by the Narragansett Pier Granite, which in turn was intruded by the Westerly Granite. Two masses of vein quartz and several mafic dikes have also been mapped. The Raritan Forma­ tion ( ?) of Late Cretaceous age is exposed on Block Island. INTRODUCTION Various aspects of the geology of Khode Island have been treated in many reports published over a long period of time. Since 1944, almost all the bedrock of the State has been mapped in a series of quadrangle maps on scales of 1:31,680 and 1:24,000. These were done under a cooperative project between the U.S. Geological Survey and the Khode Island Development Council and predecessor State agencies. Ehode Island probably is the first State to be geologically mapped on a scale of 1:31,680 (2 inches to 1 mile) or larger. On the basis of these maps, a geologic map of the whole State has been compiled on a scale of 1:125,000 (pi. 1). 2 BEDROCK GEOLOGY OF RHODE ISLAND The present report, which is the descriptive text to accompany this map, is based mainly on the quadrangle reports; unpublished maps have also been made available by H. E. Dixon, U.S. Geological Survey, and G. E. Moore, Jr., Ohio State University and U.S. Geological Survey. Most of the information on Block Island has been provided by C. A. Kaye, U.S. Geological Survey. This help is gratefully acknowledged. I mapped several other areas, chiefly in quadrangles that are mostly in Massachusetts or Connecticut. Officers in the co­ operating State agencies who worked