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  • Newly discovered stromatolites and bimodal magmatism at ~1.23 Ga in the Burro Mountains of New Mexico: Mesoproterozoic rifting formed a shallow ocean basin in southwestern Laurentia
Title: Newly discovered stromatolites and bimodal magmatism at ~1.23 Ga in the Burro Mountains of New Mexico: Mesoproterozoic rifting formed a shallow ocean basin in southwestern Laurentia
We interpret a newly discovered laminated limestone associated with Middle Proterozoic rocks in the Redrock and Brushy Mountain quadrangles of southwestern New Mexico as representing stromatolites, possibly Conophyton. This locality is geographically aligned with other outcrops of ~1.2 Ga stromatolites documented in the southwest U.S., such as those in the Bass Formation (Grand Canyon, AZ), the Mescal Limestone (Salt River Canyon, AZ), the Castner Marble (Franklin Mountains, TX), and the Allamoore Formation (Van Horn, TX). These stromatolites have similar morphologies to those found in Texas and represent the first instance of Proterozoic fossils identified within the state of New Mexico. The stromatolite-bearing unit, termed here the Ash Creek Limestone, is exposed along with a marble unit surrounded by the ~1225 Ma Redrock Granite (Williams, 2015). Mapping at 1:6,000 scale shows that the carbonates are also associated with a unit consisting of serpentinite interbedded with talc (forming a rock informally referred to as ricolite), meaning they share a similar depositional setting. The carbonates are only found surrounded by granite, whereas ricolite outcrops are typically in contact with a metabasalt. The metabasalt yielded a U-Pb zircon weighted mean 207Pb/206Pb age of 1229 ± 12 Ma (n= 35; MSWD= 0.8). This represents the first direct dating of ~1.2 Ga mafic volcanism in the area, and these racks are similar in age to anorthosite dated at 1223 ± 6 Ma and 1231 ± 4 Ma (Ramo et al., 2003). Together, the ~1.2 Ga bimodal magmatism and shallow marine limestone units indicate that the tectonic setting of southwest Laurentia at this time involved a NW-SE-trending Mesoproterozoic seaway that formed as a result of coeval regional extension during the early stages of the Grenville orogeny.  more » « less
Award ID(s):
1826758
PAR ID:
10514690
Author(s) / Creator(s):
; ;
Publisher / Repository:
New Mexico Geological Society
Date Published:
Journal Name:
New Mexico Geological Society Annual Spring Meeting
ISSN:
2834-5800
Subject(s) / Keyword(s):
Proterozoic Grenville New Mexico Stromatolite Bimodal Laurentia
Format(s):
Medium: X
Location:
Macey Center, Socorro, NM
Sponsoring Org:
National Science Foundation
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