Accreted forearc, continental, and oceanic rocks of Maryland’s Eastern Piedmont: The Potomac terrane, Baltimore terrane, and Baltimore Mafic Complex

2020 ◽  
pp. 21-41
Keyword(s):  
Mafic Complex ◽  
Oceanic Rocks

Zircon geochronology and paleomagnetism of an Archean harzburgite intrusion, eastern Bighorn Mountains, Wyoming

2020 ◽  
Vol 57 (1) ◽  
pp. 21-40
Author(s):  
Alexandra Wallenberg ◽  
Michelle Dafov ◽  
David Malone ◽  
John Craddock
Keyword(s):  
Hanging Wall ◽  
Vertical Axis ◽  
Shear Zones ◽  
Strike Slip ◽  
Zircon Geochronology ◽  
Weighted Mean ◽  
Mafic Complex ◽  
Laramide Orogeny ◽  
Axis Rotation ◽  
Bighorn Mountains

A harzburgite intrusion, which is part of the trailside mafic complex) intrudes ~2900-2950 Ma gneisses in the hanging wall of the Laramide Bighorn uplift west of Buffalo, Wyoming. The harzburgite is composed of pristine orthopyroxene (bronzite), clinopyroxene, serpentine after olivine and accessory magnetite-serpentinite seams, and strike-slip striated shear zones. The harzburgite is crosscut by a hydrothermally altered wehrlite dike (N20°E, 90°, 1 meter wide) with no zircons recovered. Zircons from the harzburgite reveal two ages: 1) a younger set that has a concordia upper intercept age of 2908±6 Ma and a weighted mean age of 2909.5±6.1 Ma; and 2) an older set that has a concordia upper intercept age of 2934.1±8.9 Ma and a weighted mean age 2940.5±5.8 Ma. Anisotropy of magnetic susceptibility (AMS) was used as a proxy for magmatic intrusion and the harzburgite preserves a sub-horizontal Kmax fabric (n=18) suggesting lateral intrusion. Alternating Field (AF) demagnetization for the harzburgite yielded a paleopole of 177.7 longitude, -14.4 latitude. The AF paleopole for the wehrlite dike has a vertical (90°) inclination suggesting intrusion at high latitude. The wehrlite dike preserves a Kmax fabric (n=19) that plots along the great circle of the dike and is difficult to interpret. The harzburgite has a two-component magnetization preserved that indicates a younger Cretaceous chemical overprint that may indicate a 90° clockwise vertical axis rotation of the Clear Creek thrust hanging wall, a range-bounding east-directed thrust fault that accommodated uplift of Bighorn Mountains during the Eocene Laramide Orogeny.

scholarly journals Metasediments Covering Ophiolites in the HP Internal Belt of the Western Alps: Review of Tectono-Stratigraphic Successions and Constraints for the Alpine Evolution

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 411
Author(s):  
Paola Tartarotti ◽  
Silvana Martin ◽  
Andrea Festa ◽  
Gianni Balestro
Keyword(s):  
High Pressure ◽  
Western Alps ◽  
Metamorphic Evolution ◽  
Alpine Orogeny ◽  
Sedimentary Evolution ◽  
Hp Metamorphism ◽  
Tethys Ocean ◽  
Depositional Setting ◽  
Oceanic Rocks ◽  
Outer Band

Ophiolites of the Alpine belt derive from the closure of the Mesozoic Tethys Ocean that was interposed between the palaeo-Europe and palaeo-Adria continental plates. The Alpine orogeny has intensely reworked the oceanic rocks into metaophiolites with various metamorphic imprints. In the Western Alps, metaophiolites and continental-derived units are distributed within two paired bands: An inner band where Alpine subduction-related high-pressure (HP) metamorphism is preserved, and an outer band where blueschist to greenschist facies recrystallisation due to the decompression path prevails. The metaophiolites of the inner band are hugely important not just because they provide records of the prograde tectonic and metamorphic evolution of the Western Alps, but also because they retain the signature of the intra-oceanic tectono-sedimentary evolution. Lithostratigraphic and petrographic criteria applied to metasediments associated with HP metaophiolites reveal the occurrence of distinct tectono-stratigraphic successions including quartzites with marbles, chaotic rock units, and layered calc schists. These successions, although sliced, deformed, and superposed in complex ways during the orogenic stage, preserve remnants of their primary depositional setting constraining the pre-orogenic evolution of the Jurassic Tethys Ocean.

I.—Observations on Some of the Foraminifera of the Oceanic Rocks of Trinidad

1904 ◽  
Vol 1 (6) ◽  
pp. 241-250
Author(s):  
R. J. Lechmere Guppy
Keyword(s):  
Geological Society ◽  
Zoological Society ◽  
Oceanic Rocks ◽  
Geological Magazine

The Oceanic beds of Naparima, in Trinidad, contain numerous forms of Foraminifera of great interest, and I propose to make some observations on a few of them These rocks and their contents were described by me in the Journal of the Geological Society of London, 1892 (vol. Xlvii, p. 519). Messrs. Jukes-Browne and Harrison treated of the same subject in the same journal in 1899 (vol. lv, p. 177), and I have given further particulars in the Proceedings of the Zoological Society, 1894 (p. 647), in the Proceedings of the Trinidad Field-Naturalists Club, 1893, and in the GEOLOGICAL MAGAZINE, 1900, p. 322. A few further observations are published in the Proceedings of the Victoria Institue.

scholarly journals ERRATUM: Suprasubduction zone ophiolite fragments in the central Appalachian orogen: Evidence for mantle and Moho in the Baltimore Mafic Complex (Maryland, USA)

Geosphere ◽  
2021 ◽  
Author(s):  
George L. Guice ◽  
Michael R. Ackerson ◽  
Robert M. Holder ◽  
Freya R. George ◽  
Joseph F. Browning-Hanson ◽  
...  
Keyword(s):  
Suprasubduction Zone ◽  
Mafic Complex ◽  
Appalachian Orogen

In the Table 3 note and captions of Figures 8 and 9, the equation Fe2+# = molar Fe2+/[Mg+Fe2++Fe3+] is incorrect. It should instead be Fe2+# = molar Fe2+/[Mg+Fe2+].

Crystallisation of fine- and coarse-grained A-type granite sheets of the Southern Oklahoma Aulacogen, U.S.A.

2000 ◽  
Vol 91 (1-2) ◽  
pp. 139-150 ◽  
Author(s):  
John P. Hogan ◽  
M. Charles Gilbert ◽  
Jon D. Price
Keyword(s):  
Solidus Temperature ◽  
Direct Consequence ◽  
Progressive Increase ◽  
Coarse Grained ◽  
Fine Grained ◽  
Mafic Complex ◽  
Southern Oklahoma ◽  
History Of ◽  
Volcanic Pile ◽  
Crustal Magma

A-type felsic magmatism associated with the Cambrian Southern Oklahoma Aulacogen began with eruption of voluminous rhyolite to form a thick volcanic carapace on top of an eroded layered mafic complex. This angular unconformity became a crustal magma trap and was the locus for emplacement of later subvolcanic plutons. Rising felsic magma batches ponding along this crustal magma trap crystallised first as fine-grained granite sheets and then subsequently as coarser-grained granite sheets. Aplite dykes, pegmatite dykes and porphyries are common within the younger coarser-grained granite sheets but rare to absent within the older fine-grained granite sheets. The older fine-grained granite sheets typically contain abundant granophyre.The differences between fine-grained and coarse-grained granite sheets can largely be attributed to a progressive increase in the depth of the crustal magma trap as the aulacogen evolved. At low pressures (<200MPa) a small increase in the depth of emplacement results in a dramatic increase in the solubility of H2O in felsic magmas. This is a direct consequence of the shape of the H2O-saturated granite solidus. The effect of this slight increase in total pressure on the crystallisation of felsic magmas is to delay vapour saturation, increase the H2O content of the residual melt fractions and further depress the solidus temperature. Higher melt H2O contents, and an extended temperature range over which crystallisation can proceed, both favour crystallisation of coarser-grained granites. In addition, the potential for the development of late, H2O-rich, melt fractions is significantly enhanced. Upon reaching vapour saturation, these late melt fractions are likely to form porphyries, aplite dykes and pegmatite dykes.For the Southern Oklahoma Aulacogen, the progressive increase in the depth of the crustal magma trap at the base of the volcanic pile appears to reflect thickening of the volcanic pile during rifting, but may also reflect emplacement of earlier granite sheets. Thus, the change in textural characteristics of granite sheets of the Wichita Granite Group may hold considerable promise as an avenue for further investigation in interpreting the history of this rifting event.

The Orocopia Schist in southwest Arizona: Early Tertiary oceanic rocks trapped or transported far inland

2002 ◽  
Author(s):  
Gordon B. Haxel ◽  
Carl E. Jacobson ◽  
Stephen M. Richard ◽  
Richard M. Tosdal ◽  
Michael J. Grubensky
Keyword(s):  
Early Tertiary ◽  
Oceanic Rocks

scholarly journals Contrasting magma types and timing of intrusion in the Permian layered mafic complex of Mont Collon (Western Alps, Valais, Switzerland): evidence from U/Pb zircon and 40Ar/39Ar amphibole dating

2007 ◽  
Vol 100 (1) ◽  
pp. 125-135 ◽  
Author(s):  
Philippe Monjoie ◽  
François Bussy ◽  
Urs Schaltegger ◽  
Andreas Mulch ◽  
Henriette Lapierre ◽  
...  
Keyword(s):  
Western Alps ◽  
Mafic Complex

The geology of the oceanic crust: Compressional wave velocities of oceanic rocks

1973 ◽  
Vol 78 (23) ◽  
pp. 5155-5172 ◽  
Author(s):  
Paul J. Fox ◽  
Edward Schreiber ◽  
J. J. Peterson
Keyword(s):  
Oceanic Crust ◽  
Compressional Wave ◽  
Wave Velocities ◽  
Oceanic Rocks

Timing of events in an Early Cretaceous island arc–marginal basin system on South Georgia

1979 ◽  
Vol 116 (3) ◽  
pp. 167-179 ◽  
Author(s):  
P. W. G. Tanner ◽  
D. C. Rex
Keyword(s):  
Continental Crust ◽  
Island Arc ◽  
Magmatic Arc ◽  
South Georgia ◽  
Marginal Basin ◽  
Early Mesozoic ◽  
Mafic Complex ◽  
Minimum Age ◽  
Radiometric Ages ◽  
Basin System

Summary19 new K–Ar mineral ages of 78-201 Ma and 3 Rb–Sr whole rock isochron ages of 81 ± 10, 127±4 and 181±30 Ma are presented from units of continental crust, mafic complex and island arc assemblage on South Georgia. The Drygalski Fjord Complex, part of the possible floor of the marginal basin in the southern part of the island, includes granodiorite and gabbro plutons of minimum age 180–200 Ma. Together with older metasediments they have been affected by a major thermal event at about 140 Ma, thought to have resulted from the emplacement of a mafic complex (Larsen Harbour Formation) during the initial opening of the marginal basin. Rocks of the Larsen Harbour Formation are cut by the Smaaland Cove intrusion dated by Rb–Sr whole rock isochron at 127±4 Ma. An island arc assemblage exposed to the SW of South Georgia consists of pyroclastic rocks cut by monzodiorite and andesite intrusions, which give radiometric ages of 81–103 Ma. These data suggest that the marginal basin opened during the late Jurassic (pre-140 Ma); that part of an earlier (early Mesozoic) magmatic arc is preserved in continental crust making up part of the floor of the basin; and that subduction continued beneath the island arc until at least the Senonian time. The younger plutons in the arc were emplaced at roughly the same time as turbidite facies rocks at deep levels in the marginal basin were being affected by penetrative deformation and metamorphism. The timing of events on South Georgia agrees closely with that deduced for the continuation of the same island arc–marginal basin system in South America. The 180–200 Ma plutons correlate with an older suite of plutonic rocks reported from the Antarctic Peninsula and southern Andes; they are part of a once-continuous magmatic arc related to subduction of the Pacific plate beneath Gondwanaland during the early Mesozoic.

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