New Mexico Geological Society Annual Spring Meeting — Abstracts

The Turkey Mountains, a laccolith that was likely produced by a Tertiary intrusion, contains numerous north to northeasterly trending steeply dipping to vertical mafic dikes. The dikes intrude Mesozoic strata and range in size from 0.30 to 1.0 meter in thickness and up to 1200 meters length. We examined field relations and hand specimen features to assess the dikes’ genesis and relation to magmatism in northeastern New Mexico. We have two working hypotheses for the origin of the dikes: 1) the dikes relate to the granite intrusion that formed the laccolith structure; and 2) the dikes relate to extrusions of the Ocate Volcanic field. All dike rocks are gray to dark black in color and display aphanitic to porphyritic textures. One dike contains augite phenocrysts, one contains quartz phenocrysts, and one contains quartz plus olivine phenocrysts. A sample of the Baldy Mountain cinder cone, representing Ocate volcanism, contains quartz plus olivine phenocrysts. All phenocrysts are subhedral to anhedral and relatively small, averaging 0.2 mm in diameter. Most dikes contain vesicles and some contain amygdaloidal fillings. The Turkey Mountain dikes, together with dikes from the Las Vegas and adjacent quadrangles, show a mean orientation of N20ºE on a rose diagram (n = 26). This trend parallels that of the Jemez Lineament, a weakness in the earth's crust that is thought to give surface expression to the 1.65 billion year old suture between the Southern Yavapai and Mazatzal Provinces of the southern Laurentian supercontinent. The concordance of the Turkey Mountain dikes with the Jemez Lineament suggests that Turkey Mountain magmatism may be related to this regional magmatic event. We are currently studying the dikes petrographically and geochemically to characterize their source magmas, assess correlations among samples, and test petrogenetic models.