DOI: 10.5593/sgem2011/s01.131


AUTHOR/S: H. Cao, C. Fletcher
Monday 1 August 2011 by Libadmin2011

11th International Multidisciplinary Scientific GeoConference SGEM2011, www.sgem.org, SGEM2011 Conference Proceedings/ ISSN 1314-2704, June 20-25, 2011, Vol. 1, 229-236 pp


A similar succession of Foliation Inflection/Intersection Axis trends preserved within
porphyroblasts (FIAs) is present in two areas separated by 200 km along the Rocky
Mountains. PreCambrian rocks in Central Colorado and Northern New Mexico were
affected by deformation and metamorphism from approximately 1506 to 1370 Ma. A
succession of five FIAs trending W-E, SSW-NNE, NNW-SSE, NW-SE and WSW-ENE
has been distinguished in Central Colorado that have been dated at 1506±15 Ma,
1467±23 Ma, 1425±18 Ma, not dated and 1366±20 Ma, respectively. To the south in
Northern New Mexico, a succession of five FIAs trending SSW-NNE, WNW-ESE,
NNW-SSE, NW-SE and WSW-ENE have been distinguished dated at 1482±48 Ma,
1448±12 Ma, 1422±35 Ma, not dated and 1394±22 Ma. The excellent correlation of the
sequence of FIA trends and their ages between regions reveals a six fold FIA succession
across the region with the first developed FIA not being present in Northern New
Mexico and the third not being present in Central Colorado. Preferential partitioning of
W-E trending deformation into the Central Colorado region around 1506±15 Ma was
followed by SSW-NNE trending deformation that affected both regions at 1470±20 Ma.
However, preferential partitioning of WNW-ESE trending deformation into Northern
New Mexico at 1448±12 Ma left Central Colorado unaffected. Both regions were then
affected by the three remaining periods of orogenesis, the first trending NNW-SSE at
1424±15 Ma followed by one trending NW-SE that has not yet been dated, and then one
trending WSW-ENE at 1390±19 Ma. This suggests that the Yavapai terrain was
tectonized at approximately 1506 Ma, prior to amalgamation with the Mazatzal terrain
around 1470 Ma. Subsequent orogenesis was initially partitioned preferentially into the
Mazatzal terrain, but the following three periods of tectonism affected both terrains in a
similar manner.

Keywords: Deformation partitioning, Foliation Inflection/Intersection Axis (FIA),
porphyroblast, Colorado, New Mexico

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