New paleomagnetic results from Middle and Late Proterozoic intrusive rocks of the central and southern Rocky Mountains

Conference · Thu Apr 01 00:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5127679

Harlan, S S ^[1]

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1. Geological Survey, Denver, CO (United States)

Paleomagnetic results from Proterozoic intrusive rocks from the central and southern Rocky Mountains yield data that provide definition to the North American APW path. Results from the ca. 1420 Ma Laramie anorthosite (LA) and Sherman Granite (SG) yield dual polarity magnetizations; a combined pole (7[degree]S, 215[degree]E, A[sub 95] = 4[degree]) is essentially identical to 1400 Ma poles from elsewhere in North America. Group A dikes from the Tobacco Root (TR) Mtns, MT, along the southern margin of the Belt Basin, have a dual-polarity remanence with a pole at 10[degree]N, 222[degree]E (A[sub 95] = 11[degree]) that plots slightly north of the LA/SG and other poles of ca. 1450 Ma. Comparison of Belt Supergroup poles, assuming coherence of the Belt terrane and interior Laurentia, with 1400 Ma poles and those of the well-defined western arm of the Logan Loop of the N. American APW path, would seem to indicate that the age of most Belt poles are in the range of 1300--1400 Ma, although this age assignment conflicts with available geochronologic data. Results from 1100 Ma diabase sheets from central AZ yield two distinct, normal and reverse polarity magnetizations: ADn and ADr. ADn gives a pole at 23[degree]N, 181[degree]E (A[sub 95] = 8[degree]) that overlaps poles of ca. 1100 Ma from the midcontinent rift (MR). Pole ADr is located at 38[degree]N, 248[degree]E (A[sub 95] = 39[degree]); the large uncertainty of this pole precludes its use in defining the APW path. All dikes are of WNW trend and several from the TR Mtns and the Christmas Lake dike from the Beartooth uplift give hornblende [sup 40]Ar/[sup 39]Ar ages of 760--770 Ma. The data are interpreted to provide evidence for Late Proterozoic mafic magmatism along the W and SW margin of the Wyoming Province, possibly related to crustal extension accompanying deposition of the Windermere Group in the northern part of the Cordillera and volcanism and sedimentation in SE Idaho and NE Washington.

• OSTI ID: 5127679
• Report Number(s): CONF-9305259-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GEOLOGIC DEPOSITS
ISOTOPE DATING
PALEOMAGNETISM
PLUTONIC ROCKS
ROCKY MOUNTAINS
ALBERTA
ARGON 39
ARGON 40
BRITISH COLUMBIA
GEOLOGIC HISTORY
IDAHO
MONTANA
PRECAMBRIAN ERA
WYOMING
AGE ESTIMATION
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CANADA
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
IGNEOUS ROCKS
ISOTOPES
LIGHT NUCLEI
MAGNETISM
MOUNTAINS
NORTH AMERICA
NUCLEI
RADIOISOTOPES
ROCKS
STABLE ISOTOPES
USA
YEARS LIVING RADIOISOTOPES
580000* - Geosciences