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Abstracts Are from M.S. Theses and Ph.D. Dissertations Completed in the Last 12 Months That Pertain to the Geology of New Mexico and Neighboring States

Abstracts Are from M.S. Theses and Ph.D. Dissertations Completed in the Last 12 Months That Pertain to the Geology of New Mexico and Neighboring States

Graduate Student Abstracts New Mexico Geology recognizes the important research of graduate students working in M.S. and Ph.D. programs. The following abstracts are from M.S. theses and Ph.D. dissertations completed in the last 12 months that pertain to the and neighboring states.

New Mexico Institute of shelf to basin sandy turbidites and as the Nitt Monzonite. The Nitt Monzonite is mass-transport deposits sourced from the north pervasively potassically and phyllically altered Mining and Technology and northeastern shelf margins during Leonard- with local late-stage vein-controlled propylitic ian time (275 Ma). Compositional heterogeneity alteration assemblages. Carbonate-phyllic alter- TWO-STAGE EMPLACEMENT within this unit is poorly understood but strongly ation observed in the Nitt Monzonite consists ON THE ALLUVIAL APRON OF AN impacts the spatial and temporal distribution of of sericite + carbonate + + chlorite ± STRATOVOLCANO reservoir forming elements. Substantial research pyrite. This alteration style is atypical of the Chirigos, Michael G., M.S. has focused on the , but classic quartz-sericite-pyrite (QSP) type phyllic little work has been undertaken to understand alteration of porphyry copper deposits. The Sawtooth Mountains, western New Mex- the depositional controls on intramember min- The Nitt Monzonite exhibits an inherently ico, comprise erosionally isolated klippen of eralogy and compositional heterogeneity of the low permeability (<<1% volume), yet hydrother- an initially contiguous landslide complex that formation within a chemostratigraphic frame- mal fluid has pervasively permeated and altered developed on the alluvial apron of an Eocene work. The aim of our research is to characterize this intrusion. Petrographic observations imply stratovolcano during late Laramide volcanic-tec- the bulk geochemical and lithologic heterogene- that mineral replacement reactions from the tonic activity. Volcanogenic siltstone, alluvial ity within the Bone Spring Formation to better interaction of a hydrothermal fluid produced and conglomerate of the lower Spears understand the depositional controls effecting net-zero to negative volume changes in the Nitt Group were deposited on mainly fine-grained stratigraphic hierarchy. Monzonite. This creation of space during miner- Baca Formation (fluvial flood-plain facies). The Element data is presented from 837 feet al-fluid reactions facilitated the infiltration of the klippen are underlain by a locally exposed, (255 meters) of Bone Spring Formation core hydrothermal fluid through the Nitt Monzonite, low-angle fault within fine-grained, laminated from Eddy and Lea county of New Mexico and resulting in the precipitation of secondary quartz basal Spears strata (distal fan). The lower fault identify compositional changes at the foot scale. in voids as phyllic alteration was developed and is overlain by a sheet 7–100 m thick of sandy Bulk element data collected via handheld XRF evolved in this hydrothermal system. volcanogenic sandstone (Volcaniclastic Unit of analyses conducted at an unbiased 6 inch spacing Electron microprobe data shows secondary Largo Creek, mid-fan facies) that is strongly in the cores. XRF bulk composition was analyzed phengites are of an intermediate composition, deformed by large-scale soft- structures. statistically using principal component analysis known as aluminoceladonite, with a range of Another low-angle fault caps this sheet, and car- (PCA) and hierarchical cluster (HCA) analysis 2+ (K0.69-0.96Na0-0.26Ca0-0.03)Al1.641.94Mg0-0.25Fe ries less-deformed conglomerates (Dog Springs to determine stratigraphic heterogeneity from a )(Si A )O (OH F ). chemofacies standpoint. Distinct changes in min- 0-0.18 3.08-3.41 l0.59-0.92 10 1.88-1.96, 0-0.12 Formation, proximal fan facies). Secondary chlorite is Mg dominant, representing The lower fault, where exposed, has a poorly eralogy describe chemostratigraphic units that a clinochore end-member species, with a range of developed fault core, locally comprised of floury relate to depositional trends and the evolution of (Mg Fe2+ Mn Ti Al ) or foliated gouge, and surrounded by a thin, in the Leonardian. 4.936.26 3.19-3.92 0.12-0.37 0-0.02, 2.14-2.64 poorly developed fractured damage zone. The Understanding the compositional hetero- (Si5.51-6.06Al1.94-2.49)O20(O16H15.61-15.85F0.11-0.26). upper fault has a well-developed cataclasite core, geneity of the Bone Spring Formation has is the exclusive carbonate mineral in the 0.12– ~0.40 m thick, with 1–3 primary slip sur- implications for petroleum system analysis in phyllic alteration assemblage. faces, rare pseudotachylyte, and local cataclastic the Delaware Basin and overlying hydrocarbon Microthermometric analyses of primary fluid injections into the upper plate. Striations on both reservoirs such as the Brushy Canyon Formation. inclusions in secondary quartz associated with faults are widely dispersed but cluster in two Our results help to define mechanical properties the phyllic alteration styles indicate the trapping directions, NNE and ESE. The main structure in intrinsic to the compositional architecture of the of a high-density fluid during quartz deposition. the upper plate is an E-vergent monocline. Bone Spring Formation and will help to improve Homogenization temperatures range from 172– We conclude that the landslide complex was future well development in the Delaware Basin. 427°C; with an average of 296°C. -bearing emplaced in two events, first N-directed sliding Furthermore, our work demonstrates the suit- fluid inclusions are common within this second- down the alluvial apron, while the ability of handheld XRF as a tool to quickly ary quartz and the measured salinities range were poorly consolidated. Most soft-sediment generate and assess large geochemical datasets from 43–54 wt.% NaCl equivalent, implying deformation probably occurred in this event, to describe stratigraphic changes in deep-water that some of the trapped fluid was hypersaline. due to loading and shear transmitted down deposits and in their relation to sequence strati- Primary liquid-dominant and vapor-dominant from the upper plate, causing liquefaction. The graphic evolution. fluid inclusions are locally present within some second event was likely due to W-side-up uplift individual hydrothermal quartz crystals, suggest- on the Laramide Hickman Fault, located west of CARBONATE-WHITE PHYLLOSILICATE ing the trapping of a boiling fluid occurred in the field area, likely was triggered by an earth- ALTERATION OF INTRUSIVE ROCK IN THE quartz, at least locally, during the history of the quake, and occurred at seismogenic slip rates, NORTHERN KELLY MINING DISTRICT, phyllic alteration. forming pseudotachylyte on the upper detach- NEW MEXICO Short-wave infrared spectroscopic analyses ment and injections, after the sediments were Herman, Colton Tate, M.S. (SWIR) performed on phyllically altered partially lithified. samples show Al-OH absorption wavelengths The polymetallic Kelly mining district is located between 2198–2214 nm with an average of CHEMOSTRATIGRAPHY OF THE BONE in the northern Magdalena Mountains, Socorro 2209 nm, consistent with other studies reporting SPRING FORMATION, DELAWARE BASIN, County, New Mexico approximately 170 kilo- aluminoceladonite. Shorter average Al-OH SE NEW MEXICO. meters south-southwest of Albuquerque. Miner- wavelengths (2203–2205 nm) of samples in the Foli, Isaac David, M.S. alization mainly occurs as manto-like carbonate south-central area of Hardscrabble Valley are replacement deposits (CRD) and locally minor characteristic of a more muscovitic composition, The Bone Spring Formation is a middle skarn, both of which primarily replacedMis- which may imply proximity to the hydrothermal mixed carbonate and clastic turbidite petro- sissippian-age . Hardscrabble Valley, fluid source. leum reservoir in the Delaware Basin of west located in the northern extent of the district, con- The geologic features of Hardscrabble Valley and southern New Mexico. It consists of tains the -age (28 Ma) intrusion known are inferred to have formed as a result of

Spring 2021, Volume 43, Number 1 10 New Mexico Geology initial development of a graben associated with of 81.9 ka, the calculated intra-dome eruptive vanadium and arsenic are released under collapse of the Magdalena caldera during the frequency is 1 eruption event per 5.5 ka for when oxidizing, alkaline conditions. mid-Tertiary. This study infers that, although Valles caldera enters periods of sustained dome leaching experiments showed appreciable release not exposed at present erosion levels, a magma emplacement. Volume estimations, along with of uranium and vanadium, but not arsenic. The intruded the fault zone associated with the published volumes of the youngest eruptions, third study investigates the leachability of redis- graben and generated a magmatic hydrothermal indicate that the post-caldera dome and vent tributed-type ores from the Westwater Canyon fluid which interacted with indigenous carbonate complexes range in volume from 0.8 km3 to Member, and primary-type ores of the Jackpile strata in the subsurface. The dissolution of car- 14.1 km3 and have both increased and decreased Sandstone and Brushy Basin members. Here, bonate resulted in modification of the magmatic throughout post-caldera evolution. In contrast, leaching tests using alkaline lixiviants and ambient fluid which rose to upper structural levels and eruptive flux following caldera collapse has sys- groundwater showed that gangue mineralogy and reacted with the Nitt Monzonite, producing the tematically increased between each post-caldera the non-mineral hosts of uranium produce leach- carbonate phyllic alteration. This process may volcanic complex from 0.09 to 2.56 km3/ka ing trends entirely discordant to those of stoichio- be related to underlying calcsilicate alteration in during post-caldera evolution. Using new ages of metric minerals previously identified as important the subsurface rock units, with the potential for the caldera-forming ignimbrite, a syn-resurgent components in these deposits (meta-tyuyamunite, accompanying base metal mineralization. lava, and the oldest post-resurgent ring-fracture meta-autunite, uraninite). eruption, the resurgence durations at Valles QUANTIFYING THE TIMESCALES OF caldera are constrained to be between 74.4 ± RAINFALL-RUNOFF RELATIONSHIPS IN ERUPTIONS AND RESURGENCE FOL- 3.3 ka and 41.8 ± 6.7 ka. The average magmatic THE ARROYO DE LOS PINOS, SOCORRO, LOWING CALDERA COLLAPSE: 40AR/39AR flux during resurgence is between 0.52 and 0.92 NEW MEXICO DATING AND VOLUME ESTIMATIONS OF km3/ka, which is similar to pluton-filling rates, Richards, Madeline A., Ph.D. POST-CALDERA VOLCANISM AT VALLES suggesting that resurgence is partially explained CALDERA, by a significant decrease in magmatic flux follow- The Arroyo de los Pinos is an ephemeral tribu- Nasholds, Morgan Wade Maynard, Ph.D. ing the large fluxes that sustain caldera-forming tary to the located in central New magma bodies. Establishing an accurate timing Mexico, draining an area of 32 km2. In 2018 the Despite recognition as one of the greatest of rapid events during post-caldera evolution is US Bureau of Reclamation funded a sediment volcanic hazards in the southwestern United possible due to the combination of dating only transport study at the confluence of the arroyo States, many aspects of the post-caldera history sanidine grains without melt inclusion-hosted and the Rio Grande, with the goal of monitoring of Valles caldera are poorly constrained. This excess 40Ar and the ability of ARGUS VI mass sediment influx to the mainstream channel study provides 49 new high-precision 40Ar/39Ar spectrometer to identify problematic grains that in order to better inform sediment transport sanidine ages and surface volume estimations to skew the weighted mean ages. The eruptive fre- models. To supplement this study and to enable reveal insights into lifespans of dome emplace- quency during dome activity and increasing flux generalization to other ephemeral tributaries, ment as well as resurgence. Caldera collapse has important implications should Valles caldera more information was needed on up-basin flow and deposition of the Tshirege Member of the enter a new phase of volcanic activity. Likewise, generating processes. This thesis focuses on these Bandelier Tuff at 1231.6 ± 1.0 ka was followed developing similar comprehensive age and efforts to characterize the runoff generating by emplacement of 34 volcanic units erupted volume datasets is necessary to assess hazards at mechanisms. from vents on the resurgent dome and along the other Quaternary volcanic systems. A network of eighteen pressure transducers caldera-ring fracture. New ages indicate vent and and five rain gauges were installed throughout dome complexes that followed collapse were IMPLICATIONS OF CRYPTIC, NONSTOI- the arroyo’s watershed in various subbasin trib- emplaced during polygenetic and monogenetic CHIOMETRIC URANIUM MINERAL- utaries. Pressure transducers monitored water eruptive events. The Deer Canyon rhyolite IZATION ON THE FORMATION AND stage data, and these were converted to discharge eruptions began immediately following caldera LEACHABILITY OF SANDSTONE-HOSTED hydrographs for each flow event. The runoff formation and lasted until 1220.5 ± 3.6 ka for a URANIUM ORES, GRANTS DISTRICT, events monitored this way were all small, close total lifespan of 11.4 ka. Similarly, the Redondo NEW MEXICO to the threshold of runoff generation, and did Creek Member erupted between 1199.0 ± 5.9 Pearce, Alexandra Rose, Ph.D. not fully activate the channel network. Tipping ka and 1186.3 ± 2.9 ka for a lifespan of 12.7 bucket rain gauges monitored rainfall. Data ka. Cerro del Medio, the oldest post-resurgent This dissertation consists of three studies exam- collected from this network show that rainfall dome, is also the longest-lived ring-fracture ining sandstone-hosted uranium ores from the intensity, subbasin lithology and antecedent soil complex, erupting seven units in 25.2 ka between Grants uranium district in northwestern New moisture conditions are the primary factors that 1157.2 ± 3.1 and 1132.0 ± 4.7 ka. Following Mexico. The first investigates the mineralogy control runoff initiation, while total rainfall Cerro del Medio, Cerros del Abrigo erupted at of primary-type uranium ores from the Jackpile depth and lithology are the main controls on run- least twice between 1009.8 ± 1.7 and 997.0 ± Sandstone and Brushy Basin members of the off ratio, and subbasin area is the main control 1.6 ka. These longer-lived dome complexes are . These ores are on lag time. located within structurally-complex zones of the characterized by cryptic mineral and mineraloid Prior to transducer installation, a particularly caldera suggesting the dense network of faults mixtures, and uranium hosted by “uraniferous large flood on 7/26/2018 left behind high-water promote magma transport to the surface, pro- organic matter.” The host organic matter and the marks at several locations throughout the water- ducing long-lived eruptions. Conversely, the six uranium mineralization is interpreted as having shed. These high-watermarks were surveyed and dome and vent complexes that erupted between been fixed within the sediments during multistage used as a proxy for maximum flood stage at 804.7 ± 1.9 ka and 68.7 ± 1.0 ka have shorter groundwater mixing episodes involving one each location. Peak stage comparisons show that eruptive lifespans than the early post-caldera or more and humic acid-bearing fluid(s) maximum infiltration occurs in the lower third of eruptions. Three of the complexes— that resulted in humate flocculation. The second the watershed that is dominated by alluvial cover Mountain, South Mountain, and the East Fork study evaluates the environmental geochemistry and where the channel develops a multi-threaded Member—are polygenetic with lifespans between of ores of the Jackpile Sandstone sampled from planform. Results from a relative gravity survey 5.2 and 5.5 ka. The Cerro Santa Rosa 2, Cerro the St. Anthony Mine in Cibola County, NM. conducted in 2018 confirm that maximum San Luis, and Cerro Seco domes are either mono- The site, slated for remediation, was assessed infiltration occurs in the lower elevations of the genetic or polygenetic with lifespans less than by its responsible party using a geochemical watershed, where the channel is multi-threaded the associated age uncertainties.The mapped model which used the uranylsilicate mineral and flows over alluvium. post-caldera units are grouped into a total of 15 uranophane to determine alternate abatement eruptive events, bracketed by measurable intra- standards for uranium in groundwater. In our and inter-dome repose periods. Combined with examination, we did not find uranophane. Batch the total duration of dome and vent lifespans leaching tests showed that significant uranium,

Spring 2021, Volume 43, Number 1 11 New Mexico Geology -PERMIAN EVOLUTION gene and Quaternary Puysegur Zone arc zircons (92–223 Ma). Isolated, secondary OF THE DARWIN BASIN OF EASTERN of New Zealand. The formation of a subduction peak ages occur at the 2.0 Ma strati- CALIFORNIA: BASIN DEVELOPMENT zone on the southwestern margin of graphic horizon in the Mesilla basin and 3.1 Ma IN THE BACK-ARC OF THE INCIPIENT would end the transmission of transpressional stratigraphic horizon in the Socorro basin and CORDILLERAN SUBDUCTION ZONE. stress from the California-Coahuila Transform overlap in age with Cambrian intrusions that Vaughn, Lochlan Wright, Ph.D. Fault that drove Ancestral have been reported from parts of New Mexico uplift. Our timeline for the onset of Cordilleran and southern (519–516 Ma). All strati- The Pennsylvanian-Permian Darwin Basin of Subduction is independently supported by detailed graphic horizons record contributions derived Eastern California records the abrupt onset of studies of ARM basins which indicate that the slip from basement sources that were large-magnitude subsidence of the southwestern on high-angle faults that drove ARM uplift ended being exhumed during –Miocene rifting. margin of Laurentia. The basin formed in the at the Pennsylvanian-Permian boundary. Mixing models were determined from the Rio late Pennsylvanian but continuously expanded Grande rift corridor in southern Colorado and during the early Permian as subsidence and throughout New Mexico and used with detrital extensional faulting allowed calciclastic base-of- New Mexico State zircon provenance trends to better understand slope apron depositional systems to retrograde University the timing and nature of drainage development. on to the subsided slope and shelf. Areal expan- Inputs for mixing models required grouping sion of the Darwin Basin propagated east and source areas into three primary provinces that PROVENANCE AND SEDIMENT MIXING southeast through time and is marked by the first included detritus from (1) late volcanic TRENDS OF THE PLIO– deposition of deep-water facies in areas that had fields primarily associated with the San Juan ANCESTRAL RIO GRANDE FLUVIAL been carbonate shelves since the Ordovician. A and Mogollon Datil volcanic fields, (2) recycled SYSTEM, RIO GRANDE RIFT, NEW MEXICO nearly identical stratigraphic and structural evo- strata (reflecting previously determined Parker Ridl, Shay, M.S. lution is present in the Pennsylvanian-Permian Mesozoic eolianite provenance signatures); and of southern California, indicating that the driver (3) recycled and Precambrian basement of subsidence in the Darwin Basin was able to –Pleistocene strata that record axial-flu- that crop out along the Rio Grande rift flanks. affect a large swath of the southwestern margin vial sedimentation of the ancestral Rio Grande The earliest phase of drainage development of Laurentia at once. Furthermore, subsidence in fluvial system crop out in New Mexico and (~5.0–4.5 Ma) in northern New Mexico was the Pennsylvanian-Permian of California coin- southern Colorado, and they preserve the history characterized by elevated detrital contributions cides with a significant change in deformation of drainage evolution and late-stage exhumation from recycled Mesozoic stratigraphy likely style of Ancestral Rocky Mountains basins and of the Rio Grande rift. Presented here are new derived from the , whereas uplifts, suggesting that the driver of subsidence U-Pb detrital zircon data (N=8 samples; n=2382 basins in central and southern New Mexico were in California may have affected tectonics across analyses) from the Camp Rice and Palomas receiving detritus largely from rift flanks (i.e., southwestern Laurentia. Speculative basin formations collected at two to three stratigraphic Paleozoic and Precambrian sources) and late evolution models invoke tectonism associated intervals in the Socorro, Hatch-Rincon, Jornada Cenozoic volcanic-field sources. The late Pliocene with the Late Paleozoic continent-truncating del Muerto, and Mesilla basins. U-Pb ages were (3.1–2.6 Ma) phase of drainage development in California-Coahuila transform fault as the then integrated with similar, previous studies northern New Mexico was marked by a relative principal driver of subsidence in the Darwin from age-equivalent strata that are exposed in decrease in detrital contributions from recycled Basin and southern California. However, the southern Colorado and northern New Mexico to Mesozoic strata. The model shows nearly equal onset of large-magnitude subsidence in southern develop sedimentary mixing models for the entire detrital contributions from recycled Mesozoic and eastern California is spatially and tempo- Rio Grande rift corridor in this region. strata, rift flank, and volcanic field sources at the rally associated with the first appearance of New U-Pb detrital zircon data from the central 3.1–2.6 Ma stratigraphic horizon in central and magmatism and volcaniclastic sedimentation in and southern portion of the Rio Grande fluvial southern New Mexico. The Pleistocene (2.0–1.6 the Late Paleozoic of the southwestern U.S. The system record peak ages at 34, 167, 519, 1442, Ma) phase of drainage development records a geochemistry of these early to middle Permian and 1686 Ma, suggesting that the ancestral Rio shift in provenance in the southern rift basins igneous rocks, which include plutons and lavas Grande was receiving detritus from late Ceno- and models suggest decreased contributions in southern California and newly identified tuffs zoic volcanic fields (e.g., San Juan and Mogollon from late Cenozoic volcanic field and rift flank in eastern California, demonstrates that these Datil volcanic fields), recycled Mesozoic stra- sources, and increased contributions from recy- rocks formed in a continental subduction zone. tigraphy (Mesozoic eolianites), and Proterozoic cled Mesozoic stratigraphy. The presence of continental arc-derived igneous basement provinces (e.g., A-Type granitoids and Provenance data and mixing trends that rocks in the early Permian of California is inter- the Mazatzal and Yavapai provinces). Although demonstrate increased detrital contributions preted to indicate that the onset of Cordilleran peak ages across the southern Rio Grande rift from recycled Mesozoic strata of the Colorado Subduction occurred earlier than has previously are similar across all basins and stratigraphic Plateau support a model of headward erosion been recognized. horizons in this study, there are distinct spatial of the Rio Puerco into the Jemez Lineament and We present 15 new measured sections, facies and temporal, up-section changes in provenance southwestern margin of the Colorado Plateau analysis, clast and point counts, and new cono- recorded across the southern Rio Grande fluvial during the Plio–Pleistocene. Headward erosion dont biostratigraphy that document the Pennsyl- system in central and southern New Mexico. and possibly minor exhumation along the west- vanian-Permian evolution of the Darwin Basin. Basal strata (~5.0–4.5 Ma) record the largest ern margin of the rift resulted in increased detrital We also report on whole-rock geochemistry and contributions of detritus derived from the San contributions from the oldest and deepest parts XRD analysis of five previously unknown tuffs Juan and Mogollon Datil volcanic fields (34–29 of caldera sources between the Pliocene and late identified in the Darwin Basin. We propose that Ma) and lesser occurrences of recycled Cordille- Pliocene. These same caldera source areas were subsidence in the Darwin Basin and southern ran arc zircons derived from recycled Mesozoic less of a source for the system by the Pleistocene. California was caused by extension and dynamic stratigraphy from the Colorado Plateau. The topography above the incipient Cordilleran Sub- late Pliocene phase (3.1–2.6 Ma) marks similar ERUPTIVE VOLUME AND EXPLOSION duction Zone. We further suggest that the first contributions of detritus derived from late Ceno- ENERGY ESTIMATES FROM KILBOURNE appearance of this subsidence dates the onset of zoic volcanic fields and marks the emergence of HOLE MAAR, SOUTH-CENTRAL subduction, which appears to have begun shortly peaks that overlap with recycled Cordilleran arc NEW MEXICO before the Pennsylvanian-Permian boundary. Arc sources (217–82 Ma). Pleistocene (2.0–1.6 Ma) Vitarelli, Daniela C., M.S magmatism may have begun as early as 290 Ma, stratigraphic horizons show a relative decrease but was likely low-volume and confined to small of zircons that overlap in age with the San Juan portions of the southwestern plate margin during and Mogollon Datil volcanic field sources and an Maar-diatremes are a common type of mono- the Permian, as is the case for the nascent Neo- increase in contributions of recycled Cordilleran genetic volcano defined by ascending magma

Spring 2021, Volume 43, Number 1 12 New Mexico Geology interacting explosively with an external water ern Grand Canyon. This study refines the timing FLUVIAL GEOMORPHIC AND HYDRO- source, or phreatomagmatic activity. In terms of of this drainage reversal in the River area LOGIC EVOLUTION AND CLIMATE area, Kilbourne Hole is an unusually large and by constraining the ages of paleoriver sediments CHANGE RESILIENCE IN YOUNG VOLCA- irregularly shaped, young (~20 ka) maar with deposited during the time of northeast-flowing NIC LANDSCAPES: RHYOLITE PLATEAU well exposed and accessible deposits. Traditional rivers, internal drainage and southwest-flowing AND LAMAR VALLEY, YELLOWSTONE field methods and complementary remote sensing rivers. These results provide insights into the NATIONAL PARK methods were used to investigate the potential evolution of the southern Colorado Plateau. Burnett, Benjamin Newell, Ph.D. eruptive volume, explosion energy, and eruption U-Pb dating of detrital zircon is used for maxi- progression of Kilbourne Hole maar to shed mum depositional ages and provenance analyses. Quaternary volcanism associated with the last light on large maar-forming eruptions. With a 40Ar/39Ar dating of detrital sanidine is used for caldera cycle in Yellowstone National Park minimum total eruptive volume of 0.23 km3, higher precision maximum depositional ages. included emplacement of ash-flow tuffs, massive Kilbourne is the largest known single maar by The majority of paleoriver samples that were rhyolite flows ranging from 79 to 484 ka, and eruptive volume. The deposits around the maar analyzed with both detrital zircon and sanidine valley-filling basalts. This study examines (1) the crater rim range in thickness from ~1 to ≥60 m. show similar maximum depositional ages. Mini- evolution of spring hydrology with flow age on The thickness of individual beds also varies, with mum or direct depositional ages are determined the Rhyolite Plateau, (2) initial development and beds generally increasing in thickness towards by overlying or interbedded volcanic units. evolution of stream networks on the rhyolite the north-northeast particularly up-section, The Mogollon Rim Formation is composed flows, and (3) the impact of the 630 ka caldera suggesting vent migration potentially occurred of river gravel, sandstone and mudstone on the formation and volcanic flow emplacement on at Kilbourne or that the vent was located north- southern rim of the Colorado Plateau that were Lamar Valley incision rates. ward towards the later stages of the eruption. deposited by northeast-flowing rivers. Results Integrated stream networks formed within 79 The deposits themselves lack a later magmatic indicate deposition began after 59.38 Ma in the kyr on the Rhyolite Plateau. Incision is focused phase and are dominated by fine ash and - Flying V Canyon area and from 37–33.55 Ma on steep flow margins and knickpoints and is waves, indicating emplacement largely by dilute in the Trout Creek section. The Whitetail Con- dependent on local stream power. Plugging of density currents (surges), suggesting that the glomerate represents the transition from north- fractures causes hydraulic conductivity of the water-magma ratio remained constant through- east-flowing rivers to internal drainage in the Salt flows to decline over time. Snowmelt infiltrates out the eruption and that explosions occurred River paleocanyon. Whitetail Conglomerate is as rapidly into younger flows, leaving ephemeral dominantly at greater-than-optimal scaled depths old as the interbedded 37.6 Ma dacite in Canyon surface streams, but many flow-margin springs (OSD), which produce abundant surges. The Creek fault side drainages, but deposition in experience a delayed snowmelt response and total explosion energy predicted by crater dimen- the axis of the Salt River paleocanyon occurred enhanced discharge during late-summer periods sions ranges from 5.21 x 1016 to 1.45 x 1017 J, between 30 and 21.8 Ma. The transition from of water stress, providing important refugia for which when compared to the explosion energies northeast-flowing rivers to internal drainage aquatic organisms threatened by climate change. derived from individual events, suggests a range occurred between 33.55–30 Ma, marking the age Incision rates over the past 630 kyr in the of 54 to 209 explosions of 6.94 x 1014 J would be of initial development of the southern edge of the Lamar Valley are greatest (≤ 0.55 mm/yr) where required to form Kilbourne Hole maar. Although Colorado Plateau. Apache Leap tuff flowed NE the greatest thickness of Quaternary volcanic the individual explosion energies predicted at down the Salt River paleocanyon nearly to Can- material was emplaced, where they are higher Kilbourne are not necessarily more energetic than yon Creek fault at 18.6 Ma. Internal drainage is than most rivers in the region. Incision rates are those predicted by previous maar studies, the documented by the 14.67 Ma Black Mesa basalt lowest (≤ 0.15 mm/yr) above a knickpoint caused thick deposits and large eruptive volume suggest that flowed onto underlying lake beds. The first by erosion resistant crystalline bedrock, and a prolonged eruption is likely responsible for the southwest-flowing river system in the Salt River in the upper reaches of two tributaries, where large maar-forming eruption and that in some paleocanyon deposited the Dagger Canyon con- I infer that faulting associated with caldera special circumstances, maar eruptions dominated glomerate after incising at least 200 m deep into formation led to stream capture of portions of by greater-than-OSD explosions may produce the Whitetail Conglomerate. The lower Dagger the headwater areas. large volumes. While further work is needed to Canyon conglomerate is present in tilted fault investigate the lateral changes in the deposits at blocks on the eastern side of Tonto Basin and the BASAL OF THE BOUSE Kilbourne, particularly in the west, and further western portion of the Salt River paleocanyon. FORMATION: GEOCHEMISTRY, DIA- assess the potential for vent migration at this The dip of bedding increases down-section from GENESIS AND IMPLICATIONS FOR THE location, this study has demonstrated that pro- 0 to 27o providing evidence that deposition INTEGRATION OF THE longed activity, consistent water-magma ratios, occurred while the faults were active. Lower Ferguson, Christina, M.S. and greater-than-OSD dominated explosions can Dagger Canyon conglomerate deposition began result in large maar-forming eruptions and result after 12.49 Ma, presumably due to base level fall The Pliocene Bouse Formation is discontinuously in immense eruptive volumes. associated with Basin and Range extension. The exposed in the lower Colorado River region and is upper Dagger Canyon conglomerate is composed a record of the first arrival of the Colorado River of flat-lying river gravels and sandstone located to the Gulf of California 5 million years ago. It University of New Mexico at higher elevations than the lower Dagger consists broadly of a lower carbonate member Canyon conglomerate in Tonto Basin and the (travertine, marl, and bioclastic units) and an NEOGENE DRAINAGE REVERSAL AND Salt River paleocanyon. Deposition of the upper upper siliciclastic member (claystone, mudstone, COLORADO PLATEAU UPLIFT IN THE SALT Dagger Canyon conglomerate began after 7.34 and Colorado River ). This paper focuses RIVER AREA Ma and a possible lag in fluvial deposition on the basal travertine (synonymous with “tufa”) Anderson, Jordan Curtis, M.S. occurred between the two facies. If a lag in flu- unit of the lower carbonate member. Because of vial deposition occurred then the upper Dagger its basal position and its chemical encrustation The modern Salt River flows southwest from the Canyon conglomerate represents a rejuvenation of pre-Bouse topography, the travertine can offer Colorado Plateau, through the Transition of the southwest-flowing river system in the Salt insight into the earliest depositional settings and Zone and into to the Basin and Range. Rivers in River paleocanyon after Basin and Range fault- may be a proxy for the composition of the waters this area flowed northeast during the ing waned. A likely driver for this rejuvenation that deposited the first Bouse . Hence from the Laramide Mogollon Highlands into would be southern Colorado Plateau uplift by the the travertine unit, if it can be shown to preserve structural basins of the topographically lower building of Mount Baldy volcanic field 12–8 Ma. a primary geochemical signal, offers the potential southern Colorado Plateau area. One of these to discriminate between alternative hypotheses rivers carved the Salt River paleocanyon through for marine versus non-marine deposition of the a portion of the Mogollon Highlands known as Bouse carbonates of the Blythe Basin. This paper the Apache Uplift to similar depths as the mod- examines the geochemistry of the travertine unit

Spring 2021, Volume 43, Number 1 13 New Mexico Geology using stable isotopes of carbon and , travertine suggest influences from deeply circu- in a (possibly active) zone of inboard transtension. 87Sr/86Sr, petrographic examinations of thin lated geothermal . We do not rule The remaining chapters focus on Late sections, and microprobe traverses. Testing for out mixing of marine and non-marine waters in and younger tectonism within the diagenesis included subsampling techniques and an estuarine environment to explain marine fos- Laramide foreland region, a world class study textural studies using thin section examinations sils and reported sequence stratigraphic and tidal area that is still vigorously debated after over and SEM investigations. sedimentary evidence, but the geochemical data 100 years. Chapter 2 utilizes apatite thermochro- The travertine unit forms an encrustation are more consistent with the interpretation that nology to addresses the timing of Cretaceous that drapes and mantles pre-Bouse topography, the initial travertine deposition in multiple Bouse (Laramide) and Miocene–Recent tectonism including volcanic bedrock and fanglomerates. basins (and the travertine depositing waters) recorded in distinctly situated samples within the The travertine unit is generally thin, often less were dominantly non-marine. of west-. than several meters thick although it can reach Chapter 3, through integrated apatite thermo- thicknesses of tens of meters. It is intermittent INTERPRETING AMALGAMATION chronology and basin stratigraphy, interprets a but fairly widespread in the Blythe Basin, the PROCESSES OF A FLUVIAL SANDSTONE OF ca. 95–70 Ma eastward sweep of Laramide onset southernmost of the Bouse basins, and also THE IN THE of deformation (when it began) across northern is present in scattered locations in the more , NEW MEXICO Arizona–New Mexico. Chapter 4 scales up the northern basins. Its facies include: porous tufa, Miltenberger, Keely Elizabeth, M.S. methodology of Chapter 3 with a regional scale microbialite domes (bioherms), vegetation-casts compilation effort to interpret an east-northeast (charophytes of marsh and probable non-marine Outcrop studies of fluvial sand bodies are directed sweep of time transgressive onset of origin), and botryoidal travertine, all onlapped important for the study of fluid transport Laramide deformation from Montana–South by and interfingered with marl and high energy and storage capabilities because the deposits Dakota to Arizona–New Mexico during the Late bedforms of bioclastic sandstone that were are heterogeneous. 3-D photogrammetry was Cretaceous–Paleogene. deposited before the first arriving Colorado used to evaluate the amalgamation processes These studies contribute to our understanding River sands. This Walther’s Law relationship of a multi-storey sheet sandstone in the San of plate tectonics and the role that intracon- suggests that the are broadly coeval Juan Basin, NM. The Angel Peak Member was tinental deformation plays. Inboard plate with the other facies in the basal carbonate unit deposited in the proximal-medial transition of a margin deformation and its role on river system of the Bouse Formation. Stable isotope data for distributive fluvial system by a meandering river integration and potential ongoing deformation travertine reveal a covariation of δ13C with δ18O during the . Within the study area, are described. Likewise, the timing and spatio- and a spread of values between (+4, +2‰) and amalgamation occurred by avulsion and reoc- temporal patterns of deformation shed light on (-16, -9‰) for the southern Blythe Basin and a cupation of channel-belts to produce five storeys the tectonic processes that operated during the regression line with R2 = 0.63. Northern basin of the multi-storey sheet sandstone. Within each Laramide , as well as additional Ceno- travertines have a similar covariation trend (R2 = storey is evidence of processes that are internal zoic exhumation related to epeirogenic uplift of 0.73). Travertines show multiple carbonate gener- to a channel-belt, such as bar migrations, small the western and southwestern United States. ations in thin section, but stable isotope analyses scour surfaces, and chute deposits. Vertical trun- did not show continuous or regular differences in cation by subsequent channel-belts has occurred LANDSCAPE EVOLUTION OF THE composition of subsamples. Silica diagenesis was to each storey. Miocene to present erosion has SOUTHERN COLORADO PLATEAU USING observed in the Buzzard’s Peak area where the also removed portions of the uppermost storeys LOW-TEMPERATURE APATITE THERMO- 4.834 Ma Lawlor Peak tuff is interbedded with within the detailed study area. The multi-storey CHRONOLOGY AND DETRITAL ZIRCON carbonates, but this area showed overlapping sheet sandstone of the Angel Peak Member was AND SANIDINE PROVENANCE STUDIES carbonate chemistry to other areas, although deposited as the San Juan Basin was almost full, Winn, Carmen L., Ph.D. somewhat more positive along the regression thus has many characteristics of amalgamation line. Compiled and new 87Sr/86Sr analyses show during low accommodation space. Chapter 1: Westernmost Grand Canyon that the basal Bouse carbonates have non-marine Conflicting hypotheses about the timing of values of ~ 0.711 (as opposed to 0.709 for sea- INTEGRATED STUDIES OF INTRACON- carving of the Grand Canyon involve either a 70 water) in all carbonate facies (marls, bioclastic TINENTAL DEFORMATION IN THE Ma (“old”) or < 6 Ma (“young”) Grand Canyon. unit, travertine, and numerous types). Dou- INTERIOR WESTERN USA, CRETACEOUS This paper evaluates the controversial western- ble dissolution tests for 87Sr/86Sr values were per- TO RECENT most segment of the Grand Canyon where the formed in travertine and marl to evaluate potential Thacker, Jacob Oliver, Ph.D. following lines of published evidence firmly favor diagenetic changes: these revealed little change in a “young” Canyon. 1) North-derived Paleocene values (from 0.71051 to 0.71081; from 0.71056 The advent of plate tectonic theory satisfactorily Hindu Fanglomerate was deposited across the to 0.71074; and from 0.71088 to 0.71088). Plots explained a number of deformation belts around present track of the westernmost Grand Canyon, of δ18O versus 87Sr/86Sr and versus latitude show the world. However intracontinental deforma- which therefore was not present at ~55 Ma. 2) no covariation in 87Sr/86Sr over a wide range of tion (deformation inboard of a plate margin) The 19 Ma Separation Point basalt is stranded δ18O and facies types. remains poorly understood in plate tectonic between high relief side canyons feeding the main The combined data are interpreted as showing models. In order to further our understanding of stem of the Colorado River and was emplaced only limited carbonate diagenesis within the intracontinental tectonics and its effects, this dis- before these tributaries and the main canyon were basal travertine of the Bouse Formation such that sertation examines paleotectonic and neotectonic incised. 3) Geomorphic constraints indicate that carbonate geochemistry can be used as a proxy settings within the interior western USA. relief generation in tributaries and on plateaus for the waters that deposited them. Two possi- Chapter 1 focuses on late Miocene–Recent adjacent to the westernmost Grand Canyon took bilities are examined to explain the covariation deformation inboard of the San Andreas plate place after 17 Ma. 4) The late Miocene-Pliocene of δ18O with δ13C: 1) mixing of sea water (0, 0) margin fault and its role on the integration Muddy Creek Formation constraint shows that and meteoric water (-16, -7); or 2) evaporation history of the lower Colorado River. The neotec- no river carrying far-traveled materials exited at of basin water. We favor evaporation as the tonic analysis included geometric and kinematic the mouth of the Grand Canyon until after 6 Ma. dominant explanation based on the similarity fault data collected in key geologic units to Interpretations of previously-published low-tem- of travertine variation in northern (lacustrine) characterize the timing and style of deformation perature thermochronologic data conflict with and southern (debated marine versus lacustrine) in an area that has commonly been considered these lines of evidence, but are reconciled in basins, the presence of non-marine charophytes in to lack young deformation. It is found that post- this paper via the integration of three methods travertines, and absence of covariation between 12 Ma deformation in the region is cumulatively of analyses on the same sample: apatite (U-Th)/ δ18O and 87Sr/86Sr, consistent with evaporation significant and persisted before, during, and after He ages (AHe), 4He/3He thermochronometry but not mixing. Radiogenic 87Sr/86Sr and the deposition of the Bouse Formation—a unit that (4He/3He), and apatite fission-track ages and presence of localized zones of large volumes of represents the first arrival of the Colorado River— lengths (AFT). “HeFTy” software was used

Spring 2021, Volume 43, Number 1 14 New Mexico Geology to generate time-temperature (t-T) paths that The 35-15 Ma ignimbrite flare-up, initiation and thus is preferred as a hypothesized sink for predict all new and published 4He/3He, AHe, and of Basin and Range extension, and incision of the Music Mountain fluvial system. The maxi- AFT data to within assumed uncertainties. These the East Kaibab paleocanyon is associated with mum depositional age via both detrital sanidine t-T paths show cooling from ~100°C to 40–60°C 37,000 cubic kilometers of volume loss above the and detrital zircon is ~73 Ma, several tens of in the Laramide (70–50 Ma), long-term residence Kaibab datum. Post-6-Ma river integration of the million years older than the best age estimates of at 40-60°C in the mid-Tertiary (50–10 Ma), and Colorado River system through Grand Canyon 50-60 Ma and provides little new information. cooling to near-surface temperatures after 10 and probable young uplift is driving ongoing Detrital zircon age populations for the Buck Ma, and thus support a “young” westernmost deep incision and is associated with a minimum and Doe Conglomerate are also dominated by Grand Canyon. of 15,500 cubic kilometers of volume loss above peaks at ~1680 Ma and 1390 Ma, although A subset of AHe data, when interpreted the Kaibab datum, with at least 4,166 additional the 1390 Ma peak is significantly stronger in alone (i.e., without 4He/3He or AFT data), are cubic kilometers of volume loss from the Grand comparison with the older Music Mountain better predicted by t-T paths that cool to surface Canyon alone. Cliff retreat rates are highly lithol- Formation. There are very minor peaks of temperatures during the Laramide, consistent ogy dependent and range between 1.8 km/Ma for Mesozoic-aged zircons and a sharp peak at ~20 with an “old” Canyon. This inconsistency, which the Chocolate Cliffs, 2.4 km/Ma for the Jurassic Ma sourced from local volcanism, although this mimics the overall controversy, is reconciled (Vermillion) Cliffs, and 1.8 km/Ma for the Grey is only present in two of the 6 samples. These age by optimizing cooling paths so they are most Cliffs. We conclude that three periods of acceler- populations suggest continued unroofing of the consistent with multiple thermochronometers ated denudation of the southwestern Colorado Kingman uplift with increased contribution from from the same rocks and adjusting parameters Plateau, most likely driven by epeirogenic uplift, the 1390 Ma Peacock Mountain and to account for model uncertainties. We adjusted represent punctuated periods of broad-scale cliff reworking of the Music Mountain Formation. model parameters to account for uncertainty in retreat that are coeval with evidence for signifi- Contemporaneous deposits include the lower the rate of radiation damage annealing during cant fluvial systems. The Colorado Plateau region portion of the Brown’s Park Formation from sedimentary burial in these apatites and thus is thus a type example of epeirogenic controls on northern and the Rainbow Gardens Forma- possible changes in He retentivity. In the west- geomorphic re-shaping of plateau landscapes. tion in the Lake Meade region of eastern Nevada, ernmost Grand Canyon, peak burial conditions and a sample from the Table Cliffs Basin that (temperature and duration) during the Laramide Chapter 3: Provenance and Pathways of the unexpectedly yielded a population of ~20 Ma were likely insufficient to fully anneal radiation Music Mountain and Buck and Doe Paleorivers zircon U-Pb ages. Comparison of age spectra for damage that accumulated during prolonged, Scattered remnants of “Rim Gravels” on the these units with the Buck and Doe ages indicate near-surface residence since the Proterozoic. southern margin of the Colorado Plateau preserve that a relationship with the Rainbow Gardens The combined AFT, AHe, and 4He/3He analysis a direct record of its fluvial and erosional history. or the Brown’s Park Formation are unlikely, but of a key sample from Separation Canyon can Two paleoriver deposits containing well-de- that there is a high likelihood of a connection only be reconciled by a ‘young’ Canyon, but scribed gravels occur on the far southwestern with the “White Claron” sample from the Table thermochronologic uncertainties remain large corner of the plateau, the Paleocene (55–50 Cliffs Basin. Maximum depositional ages from for this geologic scenario. Additional new AFT Ma) Music Mountain Formation and the Oligo- detrital sanidine for three samples from the Buck (5 samples) and AHe (3 samples) data in several cene-early Miocene (24–18 Ma) Buck and Doe and Doe Conglomerate are 18.065 ± 0.017 Ma, locations along the canyon corridor also support Conglomerates (Young, 1999). Detrital zircon 25.52 ± 0.10 Ma, and 30.2 ± 0.2; the youngest of a “young” Canyon and suggest the possibility of analysis can provide clues to potential sources these is slightly younger than the Peach Springs variable mid-Tertiary thermal histories beneath and sinks of these deposits and more recently, Tuff (18.78 ± 0.02 Ma), which caps the type north-retreating cliffs. We conclude that appli- high-precision detrital sanidine studies have been section of the Buck and Doe Formation. cation of multiple thermochronometers from developed to tightly constrain the maximum The erosional history of the southern Colo- common rocks reconciles conflicting thermo- depositional ages and provenance of Cenozoic rado Plateau has been a topic of scientific debate chronologic interpretations and is best explained deposits. In this study, we use a combination of for over 150 years. Key conclusions include 1) by a “young” westernmost Grand Canyon. new and published detrital zircon and detrital both of these fluvial systems were sourced from sanidine data to determine provenance and the Kingman uplift to the south as shown by the Chapter 2: Formation of the Grand Staircase potential sinks of the Music Mountain Forma- 1390 Ma age population, 2) a potential connec- Dutton’s (1882) “Great Denudation” involved tion (n = 1090 U-Pb zircon ages and n = 5 detrital tion is proposed between the Music Mountain. the lateral erosion of Mesozoic strata northwards sanidine ages used for maximum depositional Formation and the San Juan Basin, which is also from the rim of Grand Canyon via cliff retreat. ages) and the Buck and Doe Conglomerates (n = based on this 1390 Ma population, and 3) we He described a “great stairway” of alternating 1028 U-Pb zircon ages and n = 6 detrital sanidine also propose a ca. 18 Ma connection between benches of erodible strata and cliffs of resistant ages used for maximum depositional ages). In the westernmost Buck and Doe sample and the strata now known as the Grand Staircase. We addition, we collected 4 samples (n = 670 U-Pb Miocene “White Claron” of the Table Cliffs Basin, analyze 52 samples from across the southwestern zircon ages) from formations in the Table Cliffs indicating there was no paleo Grand Canyon at Colorado Plateau and use linear inverse modeling Basin (e.g. Markagunt and Paunsaugunt Plateau that time. The timing of these fluvial systems is of apatite thermochronometric data in HeFTy regions) to evaluate it as a potential sink for the consistent with the major periods of denudation to determine continuous thermal histories for Music Mountain Formation. found in Chapter 2 and these paleorivers provide each sample. Results from these histories were Detrital zircon age populations for the Music potential pathways for the removal of this material. then passed through a MATLAB code to extract Mountain Formation are dominated by a 1691 temperatures of the weighted mean paths every 5 Ma age peak with a smaller 1390 Ma peak and TRIPLE OXYGEN ISOTOPE COMPOSITION Ma, combined with geologic constraints on dated a small portion of Mesozoic ages. Grenville-aged OF CARBONATES paleosurfaces, and interpolated across the study grains (~1100 Ma) are conspicuously absent. Wostbrock, Jordan A.G., Ph.D. area. These interpolations show reconstructed This age distribution indicates that the Music cooling patterns of the top contact of the Kaibab Mountain fluvial system is sourced from the This dissertation presents a method of analyzing the Limestone through time since 70 Ma and can be nearby Kingman uplift, where basement rocks triple oxygen isotope compositions of carbonates, used to estimate the geometry and rates of lateral of these ages occur. Comparison of this age presents an empirical calibration of the carbonate-wa- cliff retreat and resulting erosional volumetric distribution with coeval Laramide deposits from ter equilibrium fractionation line, presents a triple loss through time. We find three main times of the Uinta Basin, San Juan Basin, and Table Cliffs oxygen isotope equipped fluid-rock mixing model denudational cooling, each associated with major Basin reveal that while none of these basins are for carbonates to see through diagenesis, and applies through-going river systems. The Laramide orog- ideal matches, connections with the Table Cliffs all these findings to ancient carbonate samples. Using eny (70–50 Ma) and incision of Paleocene fluvial or Uinta Basins are unlikely. The San Juan Basin modern carbonates and associate water, the following valleys is associated with 55,750 cubic kilome- provides a potential match for age populations, equations are calculated to describe equilibrium triple ters of volume loss above the Kaibab datum. particularly the significant ~1390 Ma age peak, oxygen isotope fractionation of carbonates:

Spring 2021, Volume 43, Number 1 15 New Mexico Geology ( ) 6 and 1.5–1.45 Ga Trampas groups of the Picuris Pecos volcanic complex. Juxtaposition of amphi- 18 _2.84______​± 0.02 ​ × ​10​ ​ ( ) ( ) ​1000lnα ​ ​ Ο​ ​ = ​ 2 ​ − 2.96​± 0.19 ​ ​1 ​,​ cc−wt ​T​ ​ Mountains and Rio Mora areas of northern New bolite-grade upper plate rocks against 1.48–1.45

− 1.39​(​ ± 0.01​)​ Mexico combined with new geochronologic Ga metasedimentary lower plate rocks are the ​ θ​ ​ = _​ ​ + 0.5305 (​2)​.​ ​ c c−wt​ T and thermochronologic constraints. These data product of progressive thrusting from 1.50 to Using these fractionation equations provides suggest the following tectonic evolution. An 1.40 Ga, synchronous with development of an extremely useful tool to determine whether early bedding-parallel S1 fabric is present only syntectonic foreland basins. The 1.45 Ga granite a carbonate sample is altered or preserves its in pre-Trampas Group rocks and is interpreted and pegmatites show only minor penetrative original isotopic composition. In samples that to be related to early isoclinal folds and thrusts. strain but are considered broadly syntectonic are altered, a fluid-rock mixing model is used to All groups were folded by F2 and F3 fold genera- with waning deformation at 1.45–1.40 Ga. A see through the diagenesis. Applying these tools tions during the Picuris orogeny. New U-Pb dates modern analog is the Tien Shan–Tarim basin to ancient carbonate rocks shows that many from monazite cores of about 1.5 Ga in alumi- region of the interior Tibetan Plateau inferred samples thought to be pristine are altered and are nous gneisses from the Vadito–Hondo group for the Picuris tectonism. New 40Ar/39Ar dates confusing paleoenvironmental interpretations. aluminous contact zone within the Pecos thrust on hornblende and muscovite constrain cooling This work shows that temperature sheet are interpreted as onset of Picuris orogeny through ~500°C and ~350–400°C respectively and isotopic composition is unchanged over the prograde tectonism. This onset of heating/ and provide insight into cooling rates following Phanerozoic, an important consideration when deformation is thus close in age, and apparently the Picuris orogeny, and hence the nature and reconstructing paleoenvironments. pre-dates deposition of the Trampas Group at timing of demise of Picuris orogenic uplifts. ~1488 ± 6 Ma in the footwall of the Pecos and Hondo and Trampas group rocks cooled through STRUCTURAL AND GEOCHRONOLOGIC Plomo thrusts. Growth of metamorphic garnets 500°C 1420–1381 Ma and through 350°C from CONSTRAINTS ON THE DURATION OF at 1.45- 1.40 Ga from previous studies and new 1378–1359 Ma. This is similar to new data with THE PICURIS OROGENY AND DEMISE OF monazite rim dates of ~1.45 Ga may record 40Ar/39Ar cooling data from muscovite from the AN OROGENIC PLATEAU, NORTHERN NM metamorphism close in age to deposition of the Petaca pegmatite district (mean cooling age of Young, Daniel J., M.S. thrust-bound 1.453 ± 10 Ga Marqueñas Forma- 1375 ± 10 Ma), and similar ages in basement tion. Regional cross sections show that the mod- exposures from neighboring mountain ranges. Metasedimentary and igneous basement rocks ern surface exposure represents an exhumed ~15 Slow cooling from >500 to <350°C from ~1420 in northern New Mexico record episodic pulses km middle crustal duplex system that juxtaposes, to ~1360 Ma suggests cooling rates of ~3°C/Ma of tectonism during cratonic growth from 1.8 to from north to south: 1) 1.45 Ga triple point over 60 Ma following peak triple point meta- 1.38 Ga. Continued challenges involve parsing (>550 C, 3.5 kbars) polyphase metamorphic morphism. To explain this protracted cooling the deformational features attributable to the tectonites in the Copper Hill anticline-Hondo we propose that an orogenic plateau was built Yavapai Orogeny (1.71–1.68 Ga), Mazatzal syncline thrust sheet made between the Pilar and by thrust duplexing and penetrative folding orogeny (1.66–1.60 Ga), and Picuris orogeny Plomo thrusts, 2) a similar grade thrust-bound in northern New Mexico during the Picuris (1.5–1.38 Ga) in this region and understanding Marqueñas tectonite that makes up the Plomo orogeny followed by relatively slow erosional how older structures may have been overprinted shear zone, 3) the 1.45 Ga Peñasco granite that removal. Erosion of much of the region initiated and reactivated to explain the observed strain. intrudes Vadito Group rocks between the Plomo by 1.1–1.3 Ga, resulting in deposition of the De This paper presents regional cross-sections of shear zone and the Pecos master thrust, and 4) Baca Group and correlative strata. the 1.7 Ga Vadito, 1.68 to 1.50 Ga Hondo, overriding volcanic rocks of the ~1.72–1.65 Ga

Spring 2021, Volume 43, Number 1 16 New Mexico Geology

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