Joshua Schwartz

California State University, Northridge

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Keith A. Klepeis

University of Vermont

Harold H. Stowell

University of Alabama

Elena A. Miranda

California State University, Northridge

Joseph L. Wooden

Stanford University

M. J. Cheadle

University of Wisconsin–Madison

Rose Turnbull

GNS Science

A. J. Tulloch

GNS Science

Barbara E. John

University of Wyoming

Kenneth Johnson

University of Houston - Downtown

C. B. Grimes

Mississippi State University

Cooperative Institutions

United States Geological Survey

California State University, Northridge

University of Wisconsin–Madison

University of Alabama

Stanford University

University of Wyoming

China University of Geosciences (Beijing)

Geological Survey of Alabama

GNS Science

Consejo Nacional de Investigaciones Científicas y Técnicas

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GEON 14 OROGENESIS IN SOUTHERN LAURENTIA: A PERSPECTIVE FROM THE MIDCONTINENTAL BARABOO OROGENY

Abstracts with programs - Geological Society of America (2020)

L. Gordon Medaris Brad S. Singer Brian R. Jicha David H. Malone Joshua Schwartz

Laurentia

Orogeny

10.1130/abs/2020am-355032

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Emplacement and Paleozoic and Cretaceous recrystallisation of the Broughton Arm Peridotite in Western Fiordland, New Zealand

Figshare (2018)

T. Dwight James M. Scott Joshua Schwartz

Ultramafic rocks are rare on Earth’s surface but can provide important insights into crust and mantle evolution. The recently discovered Broughton Arm Peridotite in the mountains of central Fiordland is exposed as two 75–150 m wide by several hundred metres-long harzburgite-dunite lobes encased sequentially in hornblendite, amphibolite and then quartzofeldspathic gneiss. On the basis of the refractory harzburgitic-dunitic composition and the bulk rock Mg# (86–87) lower than most mantle peridotites, the peridotite is interpreted to have an igneous cumulate rather than an exhumed mantle peridotite origin. The marginal hornblendite and amphibolite and internal pods of edenite-diopside rock may represent metasomatised peridotite. The Broughton Arm Peridotite has been metamorphosed twice. The first event generated an anhydrous assemblage comprising olivine (Mg# = 79.4–92.8), enstatite and Cr-magnetite. This assemblage has been overprinted by an anastomosing weak to pervasive mylonitic foliation of Mg-chlorite, tremolite ± serpentinite ± talc. The age of the anhydrous assemblage is unknown but suspected from regional data to be Early Carboniferous. A titanite ²⁰⁸Pb/²³⁸U lower intercept age of 105.6 ± 6.8 Ma in the host Deep Cove Gneiss is correlated with the peridotite hydration-deformation event. The proximity of the Early Cretaceous (≥ 114 Ma) Western Fiordland Orthogneiss to the east, west and north means that the Broughton Arm Peridotite and surrounding rocks may have recrystallised within the extensional Doubtful Sound Shear Zone, which elsewhere is an up to several hundred meter-wide shear zone active at c. 110–100 Ma separating Western Fiordland Orthogneiss from Deep Cove Gneiss. The Broughton Arm Peridotite therefore preserves a history that involves emplacement in the Early Paleozoic, penetrative anhydrous metamorphism in the Early Carboniferous, and hydration and recrystallisation during regional extensional tectonism in the Early Cretaceous.

Peridotite

10.6084/m9.figshare.7181180

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Supplemental Material: Tectonic and magmatic construction of lower crust in the Southern California Batholith

Joshua Schwartz et al.

<p>The supplemental material contains U-Pb isotope data for zircons from the Cucamonga and San Antonio terranes.</p>

Batholith

10.1130/gsab.s.26218589

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INTEGRATING MICROKINEMATIC CRYSTALLOGRAPHIC VORTICITY AXIS (CVA) ANALYSIS AND PETROCHRONOLOGY TO INVESTIGATE THE TEMPORAL DEVELOPMENT OF FABRIC IN AN INTRA-ARC SHEAR ZONE, FIORDLAND, NEW ZEALAND

Abstracts with programs - Geological Society of America (2022)

Virginia Brown Elena Miranda Joshua Schwartz Keith A. Klepeis

10.1130/abs/2022cd-374359

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Linking the Pinware, Baraboo, and Picuris orogens: Recognition of a trans-Laurentian ca. 1520–1340 Ma orogenic belt

Geological Society of America eBooks (2022)

Christopher G. Daniel Aphrodite Indares L. Gordon Medaris Ruth F. Aronoff David H. Malone

ABSTRACT It is proposed that the Pinware orogen of eastern Canada, the Baraboo orogen of the midcontinent, and the Picuris orogen of the southwestern United States delineate a previously unrecognized, ~5000-km-long, ca. 1520–1340 Ma trans-Laurentian orogenic belt. All three orogenic provinces are characterized by Mesoproterozoic sedimentation, magmatism, metamorphism, and deformation—the hallmarks of a tectonically active plate margin. Tectonism was diachronous, with the earliest stages beginning ca. 1520 Ma in eastern Canada and ca. 1500 Ma in the southwest United States. Magmatic zircon age distributions are dominated by Mesoproterozoic, unimodal to multimodal age peaks between ca. 1500 and 1340 Ma. The onset of magmatism in the Pinware and Baraboo orogens was ca. 1520 Ma, and onset for the Picuris orogen was ca. 1485 Ma. Detrital zircon age distributions within each orogenic province yield maximum depositional ages between ca. 1570 and 1450 Ma. Minimum depositional ages generally fall between ca. 1500 and 1435 Ma, as constrained by crosscutting intrusions, metatuff layers, or the age of subsequent metamorphism. Metamorphic mineral growth ages from zircon, garnet, and monazite yield peak ages between ca. 1500 and 1350 Ma and tend to be older in the Pinware and Baraboo orogens than in the Picuris orogen. The 40Ar/39Ar cooling ages for hornblende, muscovite, and biotite yield significant peak ages between ca. 1500 and 1350 Ma in the Baraboo and Picuris orogens. We propose that the Pinware-Baraboo-Picuris orogen formed in a complex, diachronous, convergent margin setting along the southern edge of Laurentia from ca. 1520 to 1340 Ma.

Diachronous

Laurentia

Orogeny

Rodinia

Baltica

10.1130/2022.1220(11)

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SPATIOTEMPORAL EVOLUTION OF A MAGMA FEEDER ZONE BETWEEN THE LOWER AND UPPER CRUST IN THE FIORDLAND CONTINENTAL ARC OF SW NEW ZEALAND

Abstracts with programs - Geological Society of America (2020)

Keith A. Klepeis Joshua Schwartz Elena A. Miranda Rose Turnbull Harold H. Stowell

Upper crust

Island arc

10.1130/abs/2020cd-347238

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FORMATION, DOCKING, AND OROGEN-PARALLEL TRANSPORT OF A TACONIAN ARC AND BACK-ARC BASIN: THE DADEVILLE COMPLEX IN THE SOUTHERNMOST APPALACHIAN OROGEN

Abstracts with programs - Geological Society of America (2019)

Chong Ma Dane S. VanDervoort Mark G. Steltenpohl Joshua Schwartz

The Taconian orogeny in the southern Appalachian orogen has not been well understood due to lack of recognized Taconian arc(s) and modern geochronology data. U-Pb LA-SF-ICPMS (laser ablation-sector field-inductively coupled plasma-mass spectrometry) dates of zircons from the arc-related meta-igneous units of the Dadeville Complex in the Alabama Inner Piedmont indicates peak magmatism at ca. 467‒457 Ma following an earlier phase at ca. 479 Ma. These meta-igneous rocks are interpreted to represent the remnant of a Taconian arc, the Dadeville arc. Metamorphic overgrowths on zircons from the meta-igneous rocks and a strongly sheared schist at the uppermost Emuckfaw Group, along with zircons from a felsic boudin of the metasedimentary cover of the Dadeville arc (the Agricola Schist), reveal a regional metamorphism at about 403‒398 Ma. The time of this metamorphism and the youngest detrital zircons of the Agricola Schist in the combined data from the current study and literature constrains that the Agricola Schist was likely deposited between ~440 Ma and ~400 Ma. Presence of dominant Grenville-aged zircons in the Agricola Schist suggests that the Dadeville arc possibly accreted onto Laurentia by ~440 Ma. The similarities of Early Devonian metamorphism and magmatism, common provenances of detrital zircons between rocks in the Dadeville Complex and those in the Carolina Appalachians, the distribution of the Taconian Blount clastic wedge, the location of Taconian volcano vents indicated by thickness distribution patterns of bentonites, and the channel flow structures in the Inner Piedmont, jointly suggest that the Dadeville arc was originally formed and docked in the Tennessee Embayment and was subsequently transported to the Alabama Promontory along orogen-parallel strike-slip shear zones likely associated with Acadian-Neoacadian transpressional convergence.

Orogeny

Geochronology

Laurentia

Devonian

Island arc

10.1130/abs/2019se-326413

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DISTINGUISHING MULTIPHASE AND NON-STEADY DEFORMATION HISTORIES IN LARGE SEISMOGENIC FAULTS AND SHEAR ZONES

Abstracts with programs - Geological Society of America (2022)

Keith A. Klepeis Laura E. Webb Elena Miranda Joshua Schwartz

10.1130/abs/2022am-379838

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A hidden Rodinian lithospheric keel beneath Zealandia, Earth’s newly recognized continent

Geology (2021)

Rose Turnbull Joshua Schwartz Marco L. Fiorentini Richard Jongens Noreen J. Evans

We present a data set of >1500 in situ O-Hf-U-Pb zircon isotope analyses that document the existence of a concealed Rodinian lithospheric keel beneath continental Zealandia. The new data reveal the presence of a distinct isotopic domain of Paleozoic–Mesozoic plutonic rocks that contain zircon characterized by anomalously low δ18O values (median = +4.1‰) and radiogenic εHf(t) (median = +6.1). The scale (>10,000 km2) and time span (>>250 m.y.) over which plutonic rocks with this anomalously low-δ18O signature were emplaced appear unique in a global context, especially for magmas generated and emplaced along a continental margin. Calculated crustal-residence ages (depleted mantle model, TDM) for this low-δ18O isotope domain range from 1300 to 500 Ma and are interpreted to represent melting of a Precambrian lithospheric keel that was formed and subsequently hydrothermally altered during Rodinian assembly and rifting. Recognition of a concealed Precambrian lithosphere beneath Zealandia and the uniqueness of the pervasive low-δ18O isotope domain link Zealandia to South China, providing a novel test of specific hypotheses of continental block arrangements within Rodinia.

Supercontinent

10.1130/g48711.1

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Citations (16)

Heavy mineral provenance and paleomagnetic studies of Mesozoic rocks in the Gold Beach terrane, southwestern Oregon, USA

Geological Society of America Bulletin (2025)

Ericka Boudreau Richard M. Gaschnig Jeffrey D. Vervoort Joshua Schwartz Bernard Housen

We present detrital mineral and paleomagnetic data from the Gold Beach terrane of southwestern Oregon, USA, that supports its large-magnitude northward translation along the North American margin in the Late Cretaceous. Detrital zircon and titanite were gathered from Late Jurassic−Late Cretaceous aged sandstones and indicate a shift in sediment sources over time. Zircon Hf isotopes in Jurassic grains (200−144 Ma) yield positive εHf(i) values (+15 to +6), whereas Late Cretaceous grains (100−90 Ma) have a wide range of values spanning 20 epsilon units (+11 to −12). Trace-element abundances in detrital zircons show increasing U/Yb and Eu/Eu* with decreasing age. Detrital titanite Nd isotopes mimic zircon Hf isotopes and show εNd(i) values ranging from +8 to +1 in Jurassic aged grains and +5 to −9 in Late Cretaceous grains. Gold Beach titanites are primarily of magmatic origin and are derived from felsic sources, while others have trace element chemistry revealing metamorphic sources. Paleomagnetic results from the Late Cretaceous Houstenaden Creek Formation pass fold tests with a tilt-corrected mean of D = 130°, I = 70°, n = 12, k = 10, and α95 = 14.4°. The directions have a widely streaked distribution along a small-circle path due to local rotations of blocks between sites. The tilt-corrected, inclination-only mean is I = 59°, n = 12, k = 58, α95 = 4.4°, which yields a Late Cretaceous paleolatitude of 41° ± 4°N. Comparing these results with a Late Cretaceous reference for North America shows an expected paleolatitude of 47°N, resulting in an estimate of 750 ± 500 km of displacement and ∼100° of clockwise rotation. This estimate is consistent with detrital mineral results that indicate continentally derived sources in southern California, as well as a western source offshore of the Late Cretaceous North American margin. We conclude that northward translation of the Gold Beach terrane from southernmost California occurred during the Late Cretaceous and that it was near its present location in southwestern Oregon by the Eocene.

Heavy mineral

10.1130/b37293.1

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