Petrogenesis of the Railroad Mountain Alkali Olivine Diabase Dike: Intrusion at the Edge of the Stable Craton in Eastern New Mexico

Early Aphebian Gowganda sedimentary rocks and intruding Nipissing diabase sills were sampled for paleomagnetic study at 88 sites (~500 cores, ~1000 specimens) along two ~42 km long profiles extending north from the Grenville Front into the Cobalt Plate of the Southern Structural Province in the River Valley – Lake Temagami area of Ontario. After AF demagnetization a postfolding pre-Nipissing ~2200 Ma remanence was found in eight of the 37 Gowganda sediment sites that were > 2 km north of the front, giving a pole at 109°W, 63°N (dp = 10°, dm = 19°). The Nippissing diabase from > 2 km north of the front retains a stable antiparallel prefolding N1 remanence direction in 22 of 40 sites, giving a pole position of 85°W, 17°S (dp = 6°, dm = 10°). These "south and down" remanence directions found in the southern portion of the plate contrast with the antiparallel "north and up" directions found in the northern portion, thereby indicating the occurrence of either two nearly cogenetic Nipissing intrusive events or the sequential emplacement of the Nipissing during an Earth's magnetic field reversal across the plate. At two sites a Nipissing remagnetized remanence was found in Gowganda sediments with a pole of 115°W, 18°S. Also three "Nipissing" sites give a pole at 164°W, 3°N, which is close to the known pole for the later ~1.25 Ga Sudbury olivine diabase dikes. One site is adjacent to a large dike and two were found on thin-section examination to be olivine diabase. The eight sites in Gowganda sediment matrix and conglomerate clasts and in Nipissing diabase from within < 2 km from the front were found to have a postfolding metamorphic remanence with a Grenville orogenic pole at 45°W, 51°N (dp = 19°, dm = 21°). Finally, the results lead to a suggested revision in the APW path for the ~2300–~1650 Ma interval for North America.

Formations of the "original Huronian" occur in a 200-km.-long belt along the north shore of Lake Huron. The Huronian formations lie unconformably upon an Archean basement complex of granite, gneiss, and metasedimentary and metavolcanic rocks. Previous age determinations on this basement complex indicate that it is about 2,500 m.y. old. Several igneous formations are intrusive into the Huronian formations. The oldest of these is the Nipissing diabase, which forms a complex of sills and dikes throughout the area studied; granophyric differentiates occur at several localities. In the southeastern part of the area two granitic intrusive bodies occur, the Cutler granite, previously dated at 1,750 m.y. by Wetherill, Davis, and Tilton, and the Eagle granite. An olivine diabase dike which cross-cuts the Cutler granite and adjacent Huronian formations is the youngest intrusive rock in the area. Age determinations were carried out by the Rb-Sr method on mineral and whole-rock samples from the crystalline rocks of the area. A plot of whole-rock analyses from granophyre and diabase of the Nipissing diabase on an isochron diagram yields an age of . A similar plot of mineral separates from one locality yields an isochron age of These results are interpreted as showing that the Nipissing diabase was intruded about 2,155 m.y. ago and that it was metamorphosed about 1,700 m.y. ago. This age of intrusion of the Nipissing diabase limits the age of the Proterozoic Huronian formations to greater than 2,100 m.y. and younger than the 2,500-m.y.-old Archean basement. The other intrusive units were dated at for the Eagle granite and for the olivine diabase dike. Several age determinations from the Archean basement indicate that, for the most part, the Archean rocks in the area studied have undergone alteration during some later event. As a result of this work, the Precambrian history of this area may be related to the regional Precambrian history of the northern Great Lakes area. The age of the Nipissing diabase indicates that it is unrelated to any other major event in the area. However, the metamorphism of the Nipissing diabase, the alteration of the basement minerals as shown by younger measured ages, and the age of the Cutler granite show that the 1,700-1,800-m.y.-old Penokean orogeny extended eastward from Minnesota, Wisconsin, and Michigan. The Eagle granite appears to be unrelated to any major event in the area, but the olivine diabase may be considered to represent Keweenawan igneous activity.

Research Article| November 01, 1967 AGES OF MAFIC DIKES NEAR GRANITE FALLS, MINNESOTA G. N HANSON; G. N HANSON MINNESOTA GEOLOGICAL SURVEY, MINNEAPOLIS, MINNESOTA (HANSON AND HIMMELBERG) PRESENT ADDRESS, DEPT. OF EARTH AND SPACE SCIENCES, UNIV. NEW YORK, STONYBROOK, NEW YORK (HANSON) Search for other works by this author on: GSW Google Scholar G. R HIMMELBERG G. R HIMMELBERG MINNESOTA GEOLOGICAL SURVEY, MINNEAPOLIS, MINNESOTA (HANSON AND HIMMELBERG) PRESENT ADDRESS, U. S. GEOL. SURVEY, MENLO PARK, CALIFORNIA (HIMMELBERG) Search for other works by this author on: GSW Google Scholar Author and Article Information G. N HANSON MINNESOTA GEOLOGICAL SURVEY, MINNEAPOLIS, MINNESOTA (HANSON AND HIMMELBERG) PRESENT ADDRESS, DEPT. OF EARTH AND SPACE SCIENCES, UNIV. NEW YORK, STONYBROOK, NEW YORK (HANSON) G. R HIMMELBERG MINNESOTA GEOLOGICAL SURVEY, MINNEAPOLIS, MINNESOTA (HANSON AND HIMMELBERG) PRESENT ADDRESS, U. S. GEOL. SURVEY, MENLO PARK, CALIFORNIA (HIMMELBERG) Publisher: Geological Society of America Received: 17 Feb 1967 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1967, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1967) 78 (11): 1429–1432. https://doi.org/10.1130/0016-7606(1967)78[1429:AOMDNG]2.0.CO;2 Article history Received: 17 Feb 1967 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation G. N HANSON, G. R HIMMELBERG; AGES OF MAFIC DIKES NEAR GRANITE FALLS, MINNESOTA. GSA Bulletin 1967;; 78 (11): 1429–1432. doi: https://doi.org/10.1130/0016-7606(1967)78[1429:AOMDNG]2.0.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 Tholeiitic diabase, hornblende andesite, and olivine diabase dikes cut Precambrian gneissic rocks in the Minnesota River Valley near Granite Falls, Minnesota. K-Ar ages on hornblende from the dikes show that the tholeiitic diabase dikes were intruded more than 2000 m.y. ago and that the hornblende andesite dikes were intruded approximately 1800 m.y. ago. 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.

The Harp olivine diabase dikes, of Neohelikian age, form an east-northeast trending swarm that cuts rocks of the Harp Lake Complex in central Labrador. The petrography, and rock and mineral chemistry of the dikes indicate that they are transitional in character between tholeiitic and alkalic compositions. The major element chemistry of the dikes is similar to basaltic magmas from other comparable continental settings and in particular closely resembles basalts and diabase sills of the Neohelikian Seal Lake Group.Correlation of the Seal Lake – Harp dikes magmatism is suggested with two other groups of hypabyssal intrusions of olivine gabbro east and southeast of the Seal Lake synclinorium (Michael gabbros and diabase dikes in the Mealy Mountains complex). All of this basic magmatism may have been related to a Neohelikian zone of continental rifting or incipient rifting. Intrusion and extrusion of basic magma under conditions indicative of crustal extension closely follows, or is associated with, uplift and erosion of anorogenic anorthosite–'granite' complexes in other places in the world and is inferred to be a consequence of a continuing evolving process of mantle–crust interactions; in Labrador, the process began in the Paleohelikian with intrusion of major anorthosite–adamellite complexes.

A sequence of semi-brittle deformational tectonic events in gently dipping middle Precambrian argillite and graywacke, and late Precambrian sandstone and volcanic rocks on the northwest coast of Lake Superior is interpreted from detailed geologic mapping in the Pigeon Point, Cook County, Minnesota area. The earliest tectonic event was broad, open folding in the middle Precambrian Rove Formation along N 35 °E axes and the development of two sets of joints (North and N 70° E). The second event was eastward trending, high-angle faulting in the Rove Formation and the disconformably overlying late Precambrian Puckwunge sandstone and North Shore Volcanic Group; the south sides moved upward relative to the north sides. These faults and associated joints were the loci of emplacement of 'early mafic' dikes of ilmenite-bearing diabase, which probably correlate with the 'Logan intrusions'. Subsequently, east-northeastward trending olivine diabase sills and dikes were emplaced in the Rove Formation and the North Shore Volcanic Group, and they cross-cut the early mafic dikes and sills. The third event occurred after cessation of igneous activity; two sets of regional joints (N 14 °W and N 53 °E) were formed, apparently as a result of fracturing accompanying initial subsidence of the so-called 'Lake Superior syncline' to the southeast. The fourth event was the development of a zone of cataclastic rock trending N 65 °E from the Pigeon Point area northeastward at least 60 km. To the north of this fracture zone, bedding in the Rove Formation dips 15–25 °SE. Copper and silver mineralization was subsequently emplaced within this fracture zone.The first three tectonic events appear to represent reactivation of structures of early Precambrian age, and appear to control the general outcrop pattern. The fourth event is an entirely Keweenawan feature, and marks the beginning of subsidence of the 'Lake Superior syncline'. It may correlate in time with the deposition of the Copper Harbor Conglomerate, and other late middle Keweenawan events.

The study is a result of a continuing surface-mapping program that was begun in 1953, with additional data provided by the drilling and underground activities of mining companies. The Archean rocks are Keewatin greenstones intruded by Algoman granites, for which the geological age has been determined as about 2,500 million years. These granitic rocks consist of gneissic granodiorites and massive, slightly radioactive quartz monzonite. The Archean complex was eroded to a peneplain with valleys in the less resistant rock types. The Lower Huronian formations are a sequence containing a great variety of sedimentary rocks such as conglomerate, arenites, argillite, siltstone, greywacke, limestone, and quartzite. Thickness and facies changes indicate a northwesterly source, nort erly overlap, and deposition in shallow water controlled by basement topography. The Lower Huronian formations unconformably overlie the Archean rocks and in turn are unconformably overlain by the Middle Huronian formations. The Middle Huronian rocks consist of the Gowganda and Lorrain formations of conglomerate, greywacke, quartzite, and arkose. Age-dating methods give the age of the Nipissing diabase as 1,950 million years and of the granite at Cutler as 1,750 million years (Penokean orogeny). A few dikes of Keweenawan olivine diabase have been tentatively dated at 1,000 million years. Copper mineralization is associated with the Nipissing diabase. Uranium ores in oligomictic conglomerates are post-Archean placers modified at a later date. Uranium production to the end of 1962 consisted of 44,937,871 tons of ore grading approximately 0.1% U3O8, valued at $944,373,250. End_of_Article - Last_Page 544------------

Specimens were collected at 19 sites from Precambrian anorthosites in the French River region of the Grenville Province. AF and thermal step demagnetization analyses indicate the presence of four components: A, B, C, and D. After bulk AF and thermal demagnetization at 550, 650, and 670 °C, conventional two-tiered statistical analysis reveals only the presence of the B component for the collection. Point density contour plots isolate objectively all four components. Vector subtraction shows that the A component survives up to ~40 ± 10 mT or 300 ± 100 °C and resides in magnetite. Its pole position of 45°W, 26°N, δp = 9°, δm = 10° is consistent with it being a Grenvillian orogenic metamorphic overprint acquired 975 Ma ago at the same time as the K–Ar dates were reset. The B component survives up to 100 mT and resides both in magnetite up to 585° C and in hematite up to 670 °C. Its pole position of 26°W, 13°S, δp = 1°, δm = 2° is ~30° off the pre-1000 Ma portions of the APW path, but falls directly on the 1725 Ma portion. This fits the known whole-rock Rb–Sr and zircon U–Pb ages of 1700 ± 100 Ma found for these rocks, which date the Hudsonian Orogeny. The C component is found only at 650 °C or above. Its pole of 57°W, 27°S, δp = 4°, δm = 7° is 60° away from 1000–1400 Ma portion of the APW path but falls directly on the 1800 Ma path. The D component is isolated only after the 670 °C treatment. Its pole of 1°W, 6°N, δp = 4°, δm = 7° falls on the 1250 Ma segment of the APW path. It is attributed to alteration associated with the Sudbury olivine diabase dikes of this age, which are adjacent to some sites. Thus the Grenville Orogeny is essentially only a thermal event in the anorthosites, and the B and C components were acquired during cooling after the more intense Hudsonian Orogeny. Also population level screening provides a more efficient and objective way of isolating multicomponents than conventional tiered statistics after bulk AF or thermal cleaning of a collection.

Research Article| April 01, 1939 Geology and Mineralization of the Northeastern Humboldt Range, Nevada EUGENE N. CAMERON EUGENE N. CAMERON Search for other works by this author on: GSW Google Scholar GSA Bulletin (1939) 50 (4): 563–634. https://doi.org/10.1130/GSAB-50-563 Article history received: 14 Nov 1938 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation EUGENE N. CAMERON; Geology and Mineralization of the Northeastern Humboldt Range, Nevada. GSA Bulletin 1939;; 50 (4): 563–634. doi: https://doi.org/10.1130/GSAB-50-563 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract This paper presents the results of an investigation of the geology and mineralization of the northeastern portion of the Humboldt Range, Nevada. The principal rock units of this area are keratophyric and rhyolitic volcanics overlain with apparent conformity by the Middle and Upper Triassic Star Peak limestones and associated clastic strata. These strata have been folded, faulted, and intruded by Late Jurassic or Early Cretaceous diabase, gabbro, syenite, and granite porphyry. Extensive mineralization and hydrothermal alteration have also taken place. Later deformation and igneous activity, which probably accompanied uplift of the present Humboldt Range by Pliocene “Basin Range” block faulting, are shown by olivine diabase dikes, by post-mineral faulting (in part), and by basalt, trachyte porphyry, and trachytic ash.The hypogene ore deposits of silver, antimony, and gold are sulphide-bearing quartz fissure veins, bed veins, and stockworks in rhyolite, in granite porphyry, and in the lower Star Peak strata. Hypogene fissure filling and replacement have been accompanied by extensive wall-rock alteration. Supergene deposits comprise portions of the hypogene silver deposits enriched by supergene argentite and native silver. The ore deposits are grouped along major fault zones which trend roughly parallel to Jura-Cretaceous (?) folds and apparently were initiated during Jura-Cretaceous (?) orogeny. The forms of the hypogene deposits and the distribution of the hypogene vein minerals within them show a close control by structural features produced by deformation prior to and during mineralization. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

Chapter 23 - Chemical and physical constraints on petrogenesis and emplacement of ENA olivine diabase magma types