Relative Age Data Research Articles

Diagenetic and Epigenetic Mineralizing Events in the Kalahari Copperbelt, Botswana: Evidence from Re-Os Sulfide Dating and U-Th-Pb Xenotime Geochronology

Abstract The ages of sedimentation and copper-silver mineralization in the late Meso- to Neoproterozoic Kalahari Copperbelt in Botswana, an economically significant copper province, have previously been poorly constrained within an ~600 m.y. period that spans the Neoproterozoic from the assembly and breakup of Rodinia to the assembly of Gondwana. Rhenium-osmium geochronology of molybdenite and copper sulfide minerals and U-Th-Pb laser ablation split-stream inductively coupled plasma-mass spectrometry (LASS ICP-MS) analysis of xenotime grains are utilized to provide absolute and relative age data on the host rocks and mineralizing events within the Ghanzi Ridge region of the Kalahari Copperbelt. The data reveal a prolonged history of events, which is partially comparable with depositional and mineralizing events in the neighboring Central African Copperbelt. Abundant disseminated molybdenite is located within a shale layer near the base of the Proterozoic D’Kar Formation at the Northeast Mango Two deposit. Unusual molybdenite textures suggest organic matter may have been a precursor. Two molybdenite separates from a small calcite-molybdenite stringer in a wall-rock fragment that is enclosed within an epigenetic quartz-calcite-chalcopyrite vein with ill-defined and mismatched margins yielded Re-Os ages of 981 ± 3 and 981 ± 7 Ma. These ages indicate an early hydrothermal mineralizing event in the basin. A xenotime inclusion intergrown with molybdenite and chalcopyrite within the epigenetic vein yielded a younger U-Th-Pb age of 538 ± 8 Ma, suggesting two mineralizing events are preserved in a complex 6-cm-wide vein. Based on vein texture and alteration, the ages represent an ~981 Ma calcite-molybdenite mineralization event overprinted by an ~538 Ma quartz-chalcopyrite-molybdenite mineralization event, perhaps during reopening of the vein. Re-Os and U-Th-Pb geochronology were utilized at the Zone 6 deposit on minerals associated with a hydrothermal quartz-calcite-chalcocite-idaite-bornite vein. Several authigenic xenotime grains that occur along the margin of the vein yielded three concordant U-Th-Pb ages that indicate xenotime growth at ~950 to 925 Ma while other xenotime grains in a similar position yielded mostly discordant data, suggesting disturbance of the isotopic system in the xenotime grains. A coprecipitated chalcocite-idaite mixture within the hydrothermal vein produced an Re-Os age of 549.0 ± 11.2 Ma. Re-Os analysis obtained from a coprecipitated molybdenite-bornite mixture at the Northeast Fold deposit yielded an age of 515.9 ± 2 Ma. Together, the earliest Neoproterozoic Re-Os molybdenite and U-Th-Pb xenotime ages provide both a minimum depositional age constraint for the lowermost D’Kar Formation and clear evidence that diagenetic hydrothermal mineralizing events took place within the Ghanzi basin. The timing of this mineralizing event corresponds with a poorly documented regional thermal event that affected the northern margin of the Kalahari craton during the final stages of the assembly of Rodinia at ~980 Ma. The lower to middle Ghanzi Group of the Kalahari Copperbelt is at least 100 m.y. older than the host rocks within the neighboring Central African Copperbelt, which are associated with the breakup of Rodinia. The latest Neoproterozoic to Cambrian Re-Os and U-Th-Pb ages indicate that hydrothermal copper-silver mineralizing events occurred during the Pan-African (~600–480 Ma) fold-thrust evolution of the Ghanzi-Chobe zone and were broadly synchronous with widespread epigenetic hydrothermal copper-cobalt mineralizing events in the adjacent Central African Copperbelt.

Analysis of a blockstream in the northern Lesotho Drakensberg, southern Africa

Blockstreams are found in many mountain ranges worldwide and can be considered as an expression of the interplay between upslope sediment supply and transport-limited capacity of slope sediment systems. In mountain settings, blockstreams have been most commonly described as periglacial landforms, whose development and internal morphology reflect active layer processes, and where the landforms are not active under present climatic conditions. In the Maloti–Drakensberg mountain range of eastern Lesotho, southern Africa, several blockstreams have been identified but their age, evolution and relationships to climatic conditions are largely not known. This study maps and analyses the properties of one large blockstream in the Maloti–Drakensberg using field measurement techniques including Schmidt hammer relative exposure age dating of blockstream boulders. Results show that the blockstream is a relict feature but debris may have been derived from several sources including from periglacial slope activity. The presence of arcuate flow lobes within the main body of the studied blockstream attests to phases of slope-driven boulder movement possibly controlled by active-layer processes and cryoturbation, or by slip at the base of the sediment body driven by seasonal water availability. Relative age data from Schmidt hammer analysis suggest that different parts of the blockstream may have different ages and/or sources. By comparison with blockstreams elsewhere in the Maloti–Drakensberg, it is likely that it is of late Quaternary and probably of local last glacial maximum age, but younger Holocene phases of activity cannot be excluded.

Use of 10Be exposure ages and Schmidt hammer data for correlation of moraines in the Krkonoše Mountains, Poland/Czech Republic

Exposure ages and relative-age data are presented from eight sites in the Łomnica and Łomniczka valleys to provide essential information for reconstructing local glaciation chronology. A combination of 10Be exposure ages and Schmidt hammer data obtained for moraines indicate relatively short period of glacier accumulation lasting from 17.0 0.4 ka to 13.6 0.9 ka. Exposure age of 8.4 0.3 ka measured on the lowermost section of the Łomnica cirque headwall further confirms the view of glacier preservation in favourable sites until the beginning of the Holocene. A comparison of the obtained chronological data with timing of mountain glaciation in the nearby Upa Valley is used to propose the first correlative model of Late Quaternary glaciation in the eastern part of the Krkonose Mountains. The correlation implies that the lowermost preserved moraines originated during the local maximum of the last glaciation whereas recessional moraines were deposited until the Lateglacial period. A subsequent melting of glaciers terminated at the beginning of the Holocene. The implications of the model are discussed and further investigations are suggested to extend its validity to the whole mountain area.

Age of Rotational Landslides in the Cypress Hills, Alberta-Saskatchewan

The topography of the west block of the Cypress Hills indicates that fluvial dissection of the plateaux and subsequent rotational landsliding of valley sides have been the dominant Quaternary geomorphic processes. This paper presents a preliminary chronology of rotational landslides based on the relative ages of 17 landslides and on 3 absolute dates. Four indices of relative age were used: organic content in Ah and B soil horizons, the size and coverage of lichens and weathering rind thickness on boulders exposed by landsliding, and the concavity and gradient of gullies in landslide debris, One landslide occurred in 1965. Organic materials collected from buried soil horizons beneath depressions on 3 other landslides were radiocarbon dated at 1235 ± 105, 1635 ± 105 and 7259 ± 165 yrs. BP. Microscopic analysis of the organic material revealed that the oldest sample was contaminated with older carbon. Cluster analysis of the relative age data in conjunction with 3 acceptable absolute dates suggests that the landslides under study have occurred during late Holocene time.

Holocene Glacier Fluctuations in the Torngat Mountains, Northern Labrador

Lichen measurements and other relative-age data were collected from deposits of several cirque glaciers in the Torngat Mountains of northern Labrador. Lichen growth stations were established, but no lichen-growth curve has yet been determined for the local area. However, moraines can be correlated between valleys on the basis of the largest diameter thallus of Rhizocarpon geographicum sensu lato combined with other relative-age data. These data suggest several discrete periods of Holocene glacier recession. If the R. geographicum s. I. growth curve established for the northern Cumberland Peninsula of Baffin Island (MILLER, 1975) is valid for similar environments in the Torngat Mountains, then glacier recession occurred < 150, 400, 550-750, 950, ≥ 1850, > 1850, ≥ 2800, > 2800, ≥ 4000, and > > 4000 yr BP. The latest three periods of glacier recession may correlate with periods of glacier recession on the Cumberland Peninsula of Baffin Island.

Pleistocene glacial history of the southern Ahklun Mountains, southwestern Alaska: Soil-development, morphometric, and radiocarbon constraints

Four new AMS 14 C ages, glacial mapping, and measurements of soil development, loess thickness, and moraine morphology constrain the age and extent of at least three Quaternary advances by outlet lobes of an ice cap over the Ahklun Mountains of southwestern Alaska. The relative-age data are from 107 sites correlated to 25 ice-marginal positions in the Kanektok, Goodnews, Togiak, and Kulukak River valleys and along the southeastern flank of the range. Radiocarbon ages provide minimum ages for six — and a maximum age for one — of the former ice margins. Soil and morphometric parameters subdivide the ice limits into three relative-age groups. One to three pre-Wisconsin advances, probably middle Pleistocene in age, are represented by drift with relatively thick B horizons (60±5 cm, with Bt horizons), thick loess caps (80±12 cm), and broad moraines (135±134 m) with gentle side slopes (7±5°). An extensive early Wisconsin (sensu lato, s.l.) advance, >39.9 ka, and three associated stillstands or readvances are characterized by intermediate soil and morphometric parameters (Bw and weak Bt horizons with thicknesses of 40±11 cm; loess thicknesses of 69±46 cm; crest widths of 38±13 m; and slope angles of 14±4°). The maximum late Wisconsin advance, >16.9 ka, and two readvances or stillstands are associated with thin (20±5 cm), weakly to moderately developed Bw horizons, thin loess caps (28±8 cm), narrow crest widths (28±9 m), and steep slope angles (18±3°). The data confirm that early-Wisconsin glaciers in southeast Beringia were much more extensive than late Wisconsin glaciers, which were apparently limited by availability of moisture.

Analysis of small-scale erosional data and a sequence of late Pleistocene flow reversal, northern New England

Research Article| January 01, 1990 Analysis of small-scale erosional data and a sequence of late Pleistocene flow reversal, northern New England THOMAS V. LOWELL; THOMAS V. LOWELL 1Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221 Search for other works by this author on: GSW Google Scholar J. STEVEN KITE; J. STEVEN KITE 2Department of Geology and Geography, West Virginia University, Morgantown, West Virginia 26506 Search for other works by this author on: GSW Google Scholar PARKER E. CALKIN; PARKER E. CALKIN 3Department of Geology, State University of New York at Buffalo, Buffalo, New York 14260 Search for other works by this author on: GSW Google Scholar ERIC F. HALTER ERIC F. HALTER 3Department of Geology, State University of New York at Buffalo, Buffalo, New York 14260 Search for other works by this author on: GSW Google Scholar Author and Article Information THOMAS V. LOWELL 1Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221 J. STEVEN KITE 2Department of Geology and Geography, West Virginia University, Morgantown, West Virginia 26506 PARKER E. CALKIN 3Department of Geology, State University of New York at Buffalo, Buffalo, New York 14260 ERIC F. HALTER 3Department of Geology, State University of New York at Buffalo, Buffalo, New York 14260 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1990) 102 (1): 74–85. https://doi.org/10.1130/0016-7606(1990)102<0074:AOSSED>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation THOMAS V. LOWELL, J. STEVEN KITE, PARKER E. CALKIN, ERIC F. HALTER; Analysis of small-scale erosional data and a sequence of late Pleistocene flow reversal, northern New England. GSA Bulletin 1990;; 102 (1): 74–85. doi: https://doi.org/10.1130/0016-7606(1990)102<0074:AOSSED>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A sequence of latest Pleistocene ice-flow reversal, principally based on analysis of small-scale erosional features, has been reconstructed for northernmost New England. Single and crossing striations, together with small-scale stoss and lee or other erosional forms, provided more than 1,200 widely dispersed striation sets along with relative age data. The striations were grouped into grids from which vector-mean data were extracted and in turn five zones delineated, each characterized by similarities in ice flow. A sequence of six flow direction shifts between and within zones (for example, east-south-east flow gives way to north flow) was determined using a transition matrix of 159 striation sets. Nondirectional striation data, till-fabric measurements, and glacial-dispersal studies further complement the striation information.All these data were integrated to produce a sequence of ice flow that began with (interval A) east-southeast flow of the Laurentide ice sheet through Maine. Interval B involved a reversal of flow direction from eastward to northwestward in northern Maine, with development of an ice divide. During interval C, this divide strengthened and migrated southeastward, so that by interval D it occurred nearly 120 km southeast of the Québec-Maine border. Interval E encompassed a final northward flow from the northern flank of the Boundary Mountains and the start of rapid, large-scale stagnation of the last glacier of northern New England. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Morphometric Analysis of Pleistocene Glacial Deposits in the Kigluaik Mountains, Northwestern Alaska, U.S.A.

Since the earliest studies of alpine glacial geology, descriptive evaluation of moraine morphology has remained an important relative-age criterion. However, the development of moraine morphology as a quantitative relative-dating tool has lagged considerably behind other techniques. Morphometric and other relative-age data were collected on early- to latePleistocene end moraines located in the Kigluaik Mountains of Seward Peninsula, Alaska. Slope-frequency, Fourier, and linear regression analyses of topographic profiles measured along and normal to moraine axial-crests were used to generate nine indices of surface irregularity. Discriminant analysis indicates that average slope, calculated from the slope-frequency distribution, is the best single distinguishing criterion, and that even a few simple field measurements of morphometry provide a viable basis for subdividing and correlating moraines. Morphometric and other relative-age data constrain the timing of glaciations in the Kigluaik Mountains, and suggest that successively older advances are separated by intervals of increasing duration. In addition, morphometric study of moraines can offer insights into processes controlling landscape degradation.

Holocene glacier fluctuations in the American Cordillera

In many areas of the American Rocky Mountains (Colorado, Wyoming, Utah, Idaho, Montana), Cascade Range (Washington, Oregon), and the Sierra Nevada (California), radiocarbon ages suggest that ice receded to near present limits before 10 ka BP. A pre-Altithermal readvance or stillstand left moraines ca. 1–3 km beyond and ca. 50–300 m below present glacier margins. At one locality on Glacier Peak in Washington, these deposits are perhaps dated to the early Holocene, but in general these deposits are probably at least 10 ka old. Glacial advances during the Altithermal (ca. 8 to 5 ka BP) elsewhere are rare; radiocarbon evidence for Altithermal glacial advances in the Colorado Front Range is questionable. The earliest radiocarbon-dated Neoglacial advances occurred about 5 ka BP in the Washington Cascades; moraines and related deposits believed to be of early Neoglacial age (i.e. 5 to 3 ka BP) elsewhere are poorly dated. For example, moraines believed to date to the early Neoglacial in Colorado (Triple Lakes) and Wyoming (Temple Lake) are actually late Pleistocene age, based on radiocarbon ages derived from lake sediments at the type localities. Although relative-age data (i.e. lichens, rock weathering, soils) from many areas suggest a three-fold Neoglacial sequence, little supporting radiocarbon evidence is available. However, tephrochronology distinguishes three Neoglacial advances near Mount Rainier in Washington. In most mountain ranges of the western United States, fresh, unweathered, sharp-crested moraines usually adjacent to present ice margins, or near headwalls in empty cirques, date to the Little Ice Age of the last several centuries. However, detailed photographic or other historical records of glacial fluctuations during the last century are rare, and detailed mass balance studies rarer still. Whether or not pre-Little Ice Age glacial fluctuations in the American Cordillera are synchronous must await better radiometric dating of local moraine sequences.

A comment on certain multivariate techniques used in the analysis of late Quaternary relative age data

A comment on certain multivariate techniques used in the analysis of late Quaternary relative age data

Stratigraphy and correlation of glacial deposits from Indiana to New York and New Jersey

The Quaternary glacial history of part of the region from Indiana to New York and New Jersey (Fig. 1) was outlined in three summaries prepared for the VII Congress of the International Union for Quaternary Research (Wayne and Zumberge, 1965; Goldthwait et al., 1965; Muller, 1965). Subsequent regional summaries by White (1969, 1982), White et al. (1969), Ray (1974) and Coates (1976) reviewed the entire succession of tills in parts of Kentucky, northeastern Ohio, Pennsylvania, and New York. Other syntheses and discussions by Dreimanis and Goldthwait (1973), Evenson and Dreimanis (1976), Dreimanis (1977), Fullerton (1980), Mayewski etal. (1981) and Mickelson et al. (1983) were concerned only with late Wisconsin tills. The glacial history of the region (Fig. 2 and Chart 1) is much more complex than was assumed in 1965. Much of the new information is in unpublished theses and dissertations and other publications of limited distribution, and it has not been summarized. Correlations in Chart 1 are based primarily on stratigraphic relationships of tills and paleosols, and secondarily on radiometric ages, paleomagnetic polarity data, and relativeage data. This summary serves as an expanded explanation of Chart 1. Glacial events are discussed within a framework of time divisions, from older to younger, and by glacial lobes, as shown in Chart 1. Paleomagnetic polarity data in Chart 1 are from Harrison and Terasmae (1961), Bleuer (1976, and pers. commun.), Johnson (1976, this volume and pers. commun.), Hoyer (1977,1983, and pers. commun.), Bonnett et al. (1978) and Teller and Last (1981). Sources of data related to named tills in Indiana, Ohio, Pennsylvania, New York and New Jersey are listed in Appendix 1. The term 'glacial lobe' here is applied both to a regional, physiographically-controlled pattern of ice dispersal and to the geographic region influenced by such movement. Huron-Erie lobe glaciation includes ice movement from the Georgian Bay region, Ontario, into the Lake Erie basin, as well as ice movement through the Lake Huron basin into the Lake Erie basin (Fig. 3). Illinoian and pre-Illinoian tills throughout the region have not been well studied and they have no radio-

Multivariate statistical approaches to the analysis of late Quaternary relative age data

Multivariate statistical approaches to the analysis of late Quaternary relative age data

Volcanism on Mars

More than 15 years of planetary exploration of Mars have given insight into the geologic processes that have shaped its surface. The newly acquired Viking data have shown that volcanism is one of the most important geologic processes operating on Mars throughout its history. In situ chemical analyses of Martian soil by the Viking lander spacecraft indicate mafic to ultramafic source rocks. This is consistent both with available remote sensing data, which indicate the presence of mafic minerals such as pyroxene and olivine, and with petrologic modeling, based on available geophysical data which suggest that Martian lavas are probably iron rich and ultramafic. These data strongly suggest that basaltic volcanism is widespread on Mars, and much of the photogeological data may be studied in this context. Photogeological analysis of the Martian surface has shown two main types of volcanic morphologies: the first type is central volcanoes, which are volcanic landforms developed by continued and prolonged eruption from a point source vent. This category includes (1) shields, the classic low‐profile volcanic mountains of which Olympus Mons is the most spectacular example, (2) domes, steep‐sided constructs, such as Tharsis Tholus, that may represent lower rates of eruption than the shields or, possibly, more silicic lava compositions, (3) highland patera, radially textured low‐profile volcanoes that occur in the cratered terrain and are interpreted as ash shields, (4) Alba Patera, an apparently unique volcanic landform consisting of a vast volcanic center over 1500 km across with flank slopes of less than a tenth of a degree, and (5) various small features such as cinder cones. The second major category is volcanic plains, which are units recognized by several criteria, of which the presence of mare ridges and flow lobes are the most useful. Volcanic plains are subdivided into four main groups: (1) simple flows, broad, smooth to rolling plains that contain numerous mare‐type ridges but no flow lobes, interpreted as being composed of thick, single‐cooling units, (2) complex flows, displaying multiple overlapping flow lobes interpreted to be indicative of thin, multiple‐cooling units, (3) undifierentiated flows, plains that typically lack any morphologic identifying feature but are considered to be volcanic partly on the basis of their association with large volcanic centers, and (4) questionable plains, volcanic(?) units heavily modified by other processes (erosion, tectonism, etc.) so that their origins are uncertain. When these categories of volcanic morphologies are combined with relative age data provided by crater statistics, a volcanic history for Mars can be derived as follows: Early heavy bombardment of Mars was accompanied and followed by small‐scale fluvial channeling, extensive flood volcanism (the plateau plains), and ash shield volcanism in the cratered terrain. Shortly after this time, less extensive flood volcanism continued to resurface the planet during formation of the northern/southern hemisphere dichotomy. Central volcanism became more prominent with the development of the Alba Patera center as well as the older shields and domes of the northern hemisphere (early Tharsis and Elysium regions). The development of the Tharsis and Elysium uplifts may have triggered the release of large‐scale catastrophic floods, producing large channels. Continued uplift and lithospheric thinning concentrated volcanic activity in the Tharsis region, producing large shield volcanoes and extensive lava plains. Both central vent and plains volcanism have been active throughout Martian history, but the volumes of extrusion have gradually decreased with time. This is consistent with a moonlike thermal history involving a lithosphere of increasing thickness with time, gradually ‘turning off’ the volcanism. Although many questions remain regarding Martian volcanism, the Viking data have provided a remarkable, detailed overview of the probable nature of the volcanic history of Mars.