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Geology topics

R. E. Zartman

Publications and source records attributed to R. E. Zartman.

At least 37 records · Page 2Linked to original sources
USGS1990

Trace-element and Sr, Nd, Pb, and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America

The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups. The "cratonic" basalts erupted in areas of Cenozoic plateau volcanism and continental sedimentation and show considerable variation in 87Sr/86Sr (0.70316 to 0.70512), 143Nd/144Nd (e{open}Nd) and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (18.26 to 19.38, 15.53 to 15.68, and 38.30 to 39.23, respectively). These isotopic values are within the range of oceanic island basalts, as are the Ba/La, Ba/Nb, La/Nb, K/Rb, and Cs/Rb ratios of the "cratonic" basalts. In contrast, the "transitional" basalts, erupted along the western edge of the outcrop belt of the Pliocene and Quaternary plateau lavas in areas that were the locus of earlier Cenozoic Andean orogenic arc colcanism, have a much more restricted range of isotopic composition which can be approximated by 87Sr/86Sr=0.7039??0.0004, e{open}Nd, 206Pb/204Pb=18.60??0.08, 207Pb/204Pb=15.60??0.01, and 208Pb/204Pb=38.50??0.10. These isotopic values are similar to those of Andean orogenic are basalts and, compared to the "cratonic" basalts, are displaced to higher 87Sr/86Sr at a given 143Nd/144Nd and to higher 207Pb/204Pb at a given 208Pb/204Pb. The "transitional" basalts also have Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios higher than the "cratonic" and oceanic island basalts, although not as high as Andean orogenic are basalts. In contrast to the radiogenic isotopes, ??18O values for both groups of the Patagonian alkali basalts are indistinguishable and are more restricted than the range reported for Andean orogenic are basalts. Whole rock ??18O values calculated from mineral separates for both groups range from 5.3 to 6.5, while measured whole rock ??18O values range from 5.1 to 7.8. The trace element and isotopic data suggest that decreasing degrees of partial melting in association with lessened significance of subducted slabderived components are fundamental factors in the west to east transition from arc to back-arc volcanism in southern South America. The "cratonic" basalts do not contain the slab-derived components that impart the higher Ba/La, Ba/Nb, La/Nb, Cs/Rb, 87Sr/86Sr at a given 143Nd/144Nd, 207Pb/204Pb at a given 208Pb/204Pb, and ??18O to Andean orogenic arc basalts. Instead, these basalts are formed by relatively low degrees of partial melting of heterogeneous lower continental lithosphere and/or asthenosphere, probably due to thermal and mechanical pertubation of the mantle in response to subduction of oceanic lithosphere below the western margin of the continent. The "transitional" basalts do contain components added to their source region by either (1) active input of slab-derived components in amounts smaller than the contribution to the mantle below the arc and/or with lower Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios than below the arc due to progressive downdip dehydration of the subducted slab; or (2) subarc source region contamination processes which affected the mantle source of the "transitional" basalts earlier in the Cenozoic. ?? 1990 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1988

The plumbotectonic model for Pb isotopic systematics among major terrestrial reservoirs: A case for bi-directional transport

Version IV of plumbotectonics expands and refines the original model of Doe and Zartman (1979) and Zartman and Doe (1981) for explaining Pb (Sr, and Nd) isotopic systematics among major terrestrial reservoirs. A case for bi-directional transport among reservoirs is based on the observed isotopic compositions for different tectonic settings, and finds a rationale in the kinetics of plate tectonics. Chemical fractionation and radioactive decay create isotopic differences during periods of isolation of one reservoir from another, whereas dynamic processes allowing mixing between reservoirs tend to reduce these differences. Observed isotopic characteristics reflect a balance between these opposing tendencies and provide constraints on the extent and timing of fractionation and mixing processes. Plumbotectonics does not require interaction with a lower mantle or core reservoir over most of the Earth's lifetime, and, in fact, achieves a material balance consistent with no such exchange of material. Important evidence of the amount and timing of crustal recycling, and of the residence times of mantle heterogeneities lies in the coupled 207 Pb 204 Pb- 206 Pb 204 Pb "> 207 Pb 204 Pb- 206 Pb 204 Pb systematics. We believe that examination of the published data base fully supports our contention of significant bi-directional transport of material among terrestrial reservoirs. Plumbotectonics allows us to explore many aspects of reservoir interaction, and to identify parameters that provide meaningful constraints on mantle-crust differentiation. We put forth a compromise fit to many of the model variables in version IV, which can serve as a reference for future work.

Geochimica et Cosmochimica Acta↗
USGS1988

Three decades of geochronologic studies in the New England Appalachians

Over the past 30 years, both isotope geochronology and plate tectonics grew from infancy into authoritative disciplines in the geological sciences. Previously, mountain systems like the Appalachians had been viewed almost entirely in the context of the classical geosyncline, implying a gradualism in stratigraphic and structural change throughout the orogen. Age control, determined largely from distant fossiliferous strata, was unabashedly carried to high-grade metamorphic rocks based only on lithological correlations. With the new concepts in tectonics came the realization that abrupt breaks in stratigraphy and structure occur in many cases at the boundaries of lithotectonic zones. Fortunately, the new techniques of isotope geochronology could be brought to bear directly on the rocks of the immediate study area. This paper chronicles some of the major contributions to the geology of the New England Appalachians that resulted from these efforts during the past three decades. In tracing the history of geochronologic research, one encounters an increasingly sophisticated approach to the analytical and interpretive aspects of the discipline. Today, the geochronologist can, under optimum conditions, constrain the age of stratigraphic units, igneous activity, deformation, and metamorphism with accuracy that is capable of resolving fine structure within individual orogenic pulses. He participates in full partnership with other colleagues of the science in unravelling the mysteries of mountain building. Several of the topical problems of New England geology in which geochronology played a key role include (1) the recognition and delineation of Avalonia as a Late Proterozoic eastern basement distinct from more western terranes, (2) the dating of the White Mountain Plutonic-Volcanic Suite, a Mesozoic igneous event spanning 100 m.y., and (3) the temporal and spatial separation of structural and metamorphic features imprinted by the Taconic and Acadian orogenies. The existing geochronology is summarized into a map and table emphasizing the temporal construction of the New England Appalachians. By using lithotectonic zones as the building blocks of the orogen, seven such zones are defined in terms of pre-, syn-, and post-assembly geologic history. From west to east, these lithotectonic zones are (1) Berkshire-Green Mountain, (2) Rowe-Hawley, (3) Connecticut Valley, (4) Bronson Hill, (5) Kearsarge-Central Maine, (6) Tatnic Hill-Nashoba, and (7) Avalonia. Avalonia is further divided into three subzones, Hope Valley, Esmond-Dedham, and Penobscot Bay, which themselves may have had distinct origins and assembly histories. The boundaries between these zones are faults in most cases, some of which may have had recurring movement to further complicate any plate-tectonic scenario. A delineation of underlying Grenvillian, Chain Lakes, and Avalonian basement is also attempted, which now can make use of isotopes in igneous rocks as petrogenetic indicators to supplement the rare occurrences of basement outcrop within mobile zones of the orogen. The belt of Permian thermal disturbance within the Kearsarge-Central Maine zone is hypothesized to reflect rapid rebound following compressional thickening of underlying Avalonian basement during the Alleghanian orogeny.

Geological Society of America Bulletin↗
USGS1987

Archean inheritance in zircon from late Paleozoic granites from the Avalon zone of southeastern New England: An African connection

In southeastern New England the Narragansett Pier Granite locally intrudes Carboniferous metasedimentary rocks of the Narragansett basin, and yields a monazite U Pb Permian emplacement age of 273 ± 2Ma. Zircon from the Narragansett Pier Granite contains a minor but detectable amount of an older, inherited component, and shows modern loss of lead. Zircon from the late-stage, aplitic Westerly Granite exhibits a more pronounced lead inheritance —permitting the inherited component to be identified as Late Archean. Such old relict zircon has not been previously recognized in Proterozoic to Paleozoic igneous rocks in New England, and may be restricted to late Paleozoic rocks of the Avalon zone. We suggest that the Archean crustal component reflects an African connection, in which old Archean crust was underplated to the Avalon zone microplate in the late Paleozoic during collision of Gondwanaland with Avalonia.

Earth and Planetary Science Letters↗
USGS1987

Geologic map of the Chelan 30-minute by 60-minute quadrangle, Washington

Summary -- The Chelan quadrangle hosts a wide variety of rocks and deposits and display a long geologic history ranging from possible Precambrian to Recent. Two major structures, the Leavenworth and Entiat faults divide cross the quadrangle from southeast to northwest and bound the Chiwaukum 'graben', a structural low preserving Tertiary sedimentary rocks between blocks of older, metamorphic and igneous rocks. Pre-Tertiary metamorphic rocks in the quadrangle are subdivided into five major tectonostratigraphic terranes: (1) the Ingalls terrane, equivalent to the Jurassic Ingalls Tectonic Complex of probable mantle and deep oceanic rocks origin, (2) the Nason terrane, composed of the Chiwaukum Schist and related gneiss, (3) the Swakane terrane, made up entirely of the Swakane Biotite Gneiss, a metamorphosed, possibly Precambrian, sedimentary and/or volcanic rock, (4) the Mad River terrane composed mostly of the rocks of the Napeequa River area (Napeequa Schist), a unit of oceanic protolith now considered part of the Chelan Mountains terrane (the Mad River terrane has been abandoned, 2001), and (5) the Chelan Mountains terrane, dominated by the Chelan Complex of Hopson and Mattinson (1971) which is composed of migmatite and gneissic to tonalite of deep-seated igneous and metamorphic origin.During an episode of Late Cretaceous regional metamorphism, all the terranes were intruded by deepseated tonalite to granodiorite plutons, including the Mount Stuart batholith, Ten Peak and Dirty Face plutons, and the Entiat pluton and massive granitoid rocks of the Chelan Complex. The Duncan Hill pluton intruded rocks of the Chelan Mountains terrane in the Middle Eocene. At about the same time fluvial arkosic sediment of the Chumstick Formation was deposited in a depression. The outpouring of basalt lavas to the southeast of the quadrangle during the Miocene built up the Columbia River Basalt Group. These now slightly warped lavas lapped onto the uplifted older rocks. Deformation, uplift, and erosion recorded in the rocks and deposits of the quadrangle continued into post-Miocene time. Quaternary deposits reflect advances of glaciers down the major valleys, a complicated history of catastrophic glacial floods down the Columbia River, the formation of lakes in the Columbia and Wenatchee river valleys by landslides and flood backwaters, and hillslope erosion by large and small landslides and debris flows.

IMAP↗
USGS1986

Pb-, Sr- and Nd-Isotopic systematics and chemical characteristics of cenozoic basalts, Eastern China

Forty-eight Paleogene, Neogene and Quaternary basaltic rocks from northeastern and east-central China have been analyzed for major-element composition, selected trace-element contents, and Pb, Sr and Nd isotopic systematics. The study area lies entirely within the marginal Pacific tectonic domain. Proceeding east to west from the continental margin to the interior, the basalts reveal an isotopic transition in mantle source material and/or degree of crustal interaction. In the east, many of the rocks are found to merge both chemically and isotopically with those previously reported from the Japanese and Taiwan island-arc terrains. In the west, clear evidence exists for component(s) of Late Archean continental lithosphere to be present in some samples. A major crustal structure, the Tan-Lu fault, marks the approximate boundary between continental margin and interior isotopic behaviors. Although the isotopic signature of the western basalts has characteristics of lower-crustal contamination, a subcrustal lithosphere, i.e. an attached mantle keel, is probably more likely to be the major contributor of their continental “flavor”. The transition from continental margin to interior is very pronounced for Pb isotopes, although Sr and Nd isotopes also combine to yield correlated patterns that deviate strikingly from the mid-ocean ridge basalt (MORB) and oceanic-island trends. The most distinctive chemical attribute of this continental lithosphere component is its diminished U/Pb as reflected in the Pb isotopic composition when compared to sources of MORB, oceanic-island and island-arc volcanic rocks. Somewhat diminished Sm/Nd and elevated Rb/Sr, especially in comparison to the depleted asthenospheric mantle, are also apparent from the Nd- and Sr-isotopic ratios.

Chemical Geology↗
USGS1985

A reconnaissance Rb-Sr, Sm-Nd, U-Pb, and K-Ar study of some host rocks and ore minerals in the West Shasta Cu- Zn district, California

The Copley Greenstone, Balaklala Rhyolite, and Mule Mountain stock in the West Shasta Cu-Zn district, California, have Rb-Sr, Sm-Nd, U-Pb, and K-Ar systematics that indicate they are a cogenetic suite of ensimatic island-arc rocks about 400 m.y. Pervasive alteration and mineralization of these rocks, for the most part, was syngenetic and the major component of the mineralizing fluid was Devonian seawater. K-Ar ages of quartz-sericite concentrates from ore horizons and Rb-Sr systematics of a few rock and ore specimens record a later thermal and mineralizing event in the district of about 260 m.y. Contamination of some rocks with pelagic sediments is indicated by the Sm-Nd data.

Economic Geology↗
USGS1985

K-Ar ages and Pb, Sr isotopic characteristics of Cenozoic volcanic rocks in Shandong Province, China

28 samples of Cenozoic volcanic rocks collected from Shandong Province have been dated by K-Ar method. They are mainly Neogene with an age range of 4-19 m. y. The basalts from Linqu and Yishui in west Shandong Province are Miocene and those from Penglai and Qixia in east Shandong Province are Miocene and Pliocene in age. The basalts from Wudi in north Shandong Province are Middle-Early Pleistocene in age. In each area the duration of volcanic eruption was estimated at about 2-3 m. y. Pb and Sr isotopic compositions and U, Th, Pb, Rb, Sr, and major elements in most of the samples were determined. The isotopic compositions are:206Pb/204Pb-16.92-18.48,207Pb/204Pb-15.30-15.59,208Pb/204Pb-37.83-38.54, and (87Sr/86Sr)i-0.70327-0.70632. There are some positive or negative linear correlations between206Pb/204Pb and207Pb/204Pb, Pb isotopes and Pb content, Pb isotopes and Sr isotopes, and Sr isotopes and other elements. The basaltic rocks from east and west Shandong Province have somewhat differences in isotopic composition and element content. The basalts probably are products of multi-stage evolution of the mantle. They have preserved the primary features of the source, although they were influenced, to some extent, by the contamination of crustal materials. ?? 1985 Institute of Geochemistry, Chinese Academy of Sciences.

Chinese Journal of Geochemistry↗
USGS1985

Geology and geochronology of granitoid and metamorphic rocks of late Archean age in northwestern Wisconsin

Granitoid rocks of the Puritan Quartz Monzonite and associated biotite gneiss and amphibolite in northwestern Wisconsin compose the southwestern part of the Puritan batholith of Late Archean age. They differ from rocks in the Michigan segment of the batholith in having been deformed by brittle-ductile deformation and partly recrystallized during shearing accompanying development of the midcontinent rift system of Keweenawan (Middle Proterozoic) age. Granitoid rocks ranging in composition from granite to tonalite are dominant in the Wisconsin part of the batholith. To the north of the Mineral Lake fault zone, they are massive to weakly foliated and dominantly of granite composition, whereas south of the fault zone they are more strongly foliated and mainly of tonalite composition. Massive granite, leucogranite, and granite pegmatite cut the dominant granitoid rocks. Intercalated with the granitoid rocks in small to large conformable bodies are biotite gneiss, amphibolite, and local tonalite gneiss. Metagabbro dikes of probable Early Proterozoic age as much as 15 m thick cut the Archean rocks. Rubidium-strontium whole-rock data indicate a Late Archean age for the granitoids and gneisses, but data points are scattered and do not define a single isochron. Zircon from two samples of tonalitic gneiss for uranium-thorium-Iead dating define a single chord on a concordia diagram, establishing an age of 2,735?16 m.y. The lower intercept age of 1,052?70 m.y. is in close agreement with rubidium-strontium and potassium-argon biotite ages from the gneisses. Two episodes of deformation and metamorphism are recorded in the Archean rocks. Deformation during the Late Archean produced a steep west-northwest-oriented foliation and gently plunging fold axes and was accompanied by low amphibolite-facies metamorphism of the bedded rocks. A younger deformation resulting from largely brittle fracture was accompanied by retrogressive metamorphism; this deformation is most evident adjacent to the Mineral Lake fault and took place during Keweenawan rifting about 1,050 m.y. ago. The Mineral Lake fault is one of several northwest-trending faults in the Lake Superior region that originated in the Late Archean and were reactivated intermittently during the Proterozoic, including Keweenawan time. The faults dominantly have right-lateral displacements. The Archean rocks of the Puritan batholith exposed in northwestern Wisconsin compose part of the greenstone-granite terrane, as defined in the Lake Superior region. These rocks were formed 2,7502,600 m.y. ago. The long dimension of the Puritan batholith as well as that of several batholiths in adjacent Minnesota are oriented sub parallel to the boundary between the greenstone-granite terrane and the older gneiss terrane, to the south. This conformity in trend is interpreted as indicating that the granite probably was emplaced after the two basement crustal segments had been joined.

Professional Paper↗
USGS1984

Geochronometric and lead isotope data on samples from the Wallace 1 degree by 2 degrees Quadrangle, Montana and Idaho

Most of the bedrock in the Wallace quadrangle belongs to the Belt Supergroup, a thick (about 18,000 m) sequence of generally fine-grained clastic and carbonate rocks of Middle Proterozoic age. Regional metamorphism prior to Cambrian time prograded the Belt rocks to greenschist facies, and some metal-bearing veins were emplaced in fractures. The Belt rocks were intruded in Late Proterozoic time by basic dikes and sills.

Idaho, Montana↗
USGS1984

Glastonbury Gneiss and mantling rocks (a modified Oliverian dome) in south-central Massachusetts and north-central Connecticut: Geochemistry, petrogenesis, and isotopic age

The Glastonbury dome is a long, narrow structure trending approximately 70 km north-northeast through Connecticut and Massachusetts along the west side of the Bronson Hill anticlinorium. Structurally and stratigraphically the dome is analogous to the Oliverian domes of New Hampshire. It is cored by Glastonbury Gneiss and is mantled by Ammonoosuc Volcanics and Partridge Formation (or their equivalents) of Ordovician age. The Glastonbury Gneiss intrudes the Ammonoosuc and, thereby, establishes the relative age of the two units. Monson Gneiss, which unconformably underlies the Ammonoosuc Volcanics in the Monson anticline to the east, is not in contact with Glastonbury Gneiss except near Stafford Springs, Conn., where the contact may be gradational. In some places, Monson Gneiss shows evidence of plastic flow and potential anatexis. The northern part of the Glastonbury Gneiss typically is leucocratic, granoblastic, relatively potassium-poor gneiss that appears homogeneous in outcrop, but proves to be chemically and modally inhomogeneous over short distances, as shown by variation diagrams and REE plots. The gneiss straddles the compositional fields of trondhjemite, tonalite, and granodiorite, and partly overlaps that of Monson Gneiss. The southern part of the Glastonbury Gneiss is consistently more potassic than the northern, having compositions ranging from granite to granodiorite. All of the Glastonbury Gneiss show pervasive, strong foliation, deformation, and local shearing related to the Acadian orogeny. Field relations, textures, and chemistry of the northern part of the Glastonbury suggest an origin by anatexis of the premetamorphic Monson sequence at temperatures of about 690 DC to 750 DC and pressures of <3kbars. The southern part of the Glastonbury appears to have been generated contemporaneously but not comagmatically from calcalkaline crust. U-Pb zircon ages for both the northern and southern bodies are slightly discordant with 207PbfosPb ages of 445 to 467 m.y. At first these results seem to contradict the known stratigraphic position of the Glastonbury relative to the Monson, which yields distinctly younger zircon 207PbfosPb ages of 428 to 440 m.y. However, this apparent discrepancy in the radiometric ages-younger Monson, older Glastonbury-could be resolved by postulating either (1) a small component of old inherited zircon in the Glastonbury or (2) preferential metamorphic overprinting of the zircon in the Monson. In any case, the isotopic age discrepancy is not so large as to render the proposed Monson anatectic model implausible. Rb-Sr whole-rock data show a large amount of scatter on an isochron diagram and hence do not permit a reliable estimate of age. This condition may reflect inhomogeneities in the initial 87S r /8SS r ratio or may have been also induced by later Acadian or Alleghanian metamorphism. An early Silurian to Middle Ordovician age of the Glastonbury Gneiss gives evidence of higher heat flow and more extensive plutonism in the Taconic than has generally been recognized. With certain qualifications, the Glastonbury and associated volcanic rocks are compatible with recent plate-tectonic models involving the Bronson Hill anticlinorium.

Connecticut, Massachusetts↗
USGS1983

Early Tertiary age of pitchstone in the northern Black Hills, South Dakota

A block of pitchstone in the northern Black Hills, South Dakota, is Paleocene in age, according to potassium-argon dating of biotite and fission-track dating of zircon in the sample. These data invalidate published suggestions that the age is much younger. The pitchstone is not extrusive in its present position but instead is in a volcanic pipe with other fragments that came downward from as much as 1100 meters above the modern surface.

South Dakota↗
USGS1981

Plumbotectonics-the model

Plumbotectonics is an attempt to model the geochemical behaviour of U, Th and Pb, among major terrestrial reservoirs in agreement with observational data. By recycling rock through the orogenic environment, a dynamically communicating upper crust, lower crust, and mantle can produce the required patterns of lead-isotope evolution.

Tectonophysics↗