The thermo-tectonic evolution of the Suckling-Dayman metamorphic core complex, southeastern Papua New Guinea

<p>The Suckling-Dayman metamorphic core complex (SDMCC) in the Woodlark Rift of southeastern Papua New Guinea is being exhumed along the Mai’iu Fault, an active low-angle normal fault dipping ~20-22° northwards at the surface. The spectacularly smooth topography of the Mai’iu Fault footwall clearly is expressive of geologically recent uplift. The precise timing and rates of the exhumation of this continental metamorphic core complex (MCC) have, however, never been studied in detail. This thesis provides the first systematic set of U-Pb, fission track (FT), (U-Th[-Sm])/He and ²⁶Al/¹⁰Be ages from metaigneous and metasedimentary rocks of the footwall of the SDMCC, clasts and a tephra deposit contained within syn-tectonic conglomerates (the Gwoira Conglomerate) in a rider block, and modern stream sediments in the footwall and hanging wall of the Mai’iu Fault. The ages are complemented by whole-rock compositional and thermobarometric data (Al-in-amphibole, Al-in-biotite, Raman spectroscopy of carbonaceous material). Based on these data, the timing of the onset of extension along the Mai’iu Fault, its long-term dip-slip rate and its initial dip were constrained. These data are presented in the context of the evolution of the SDMCC from the Cretaceous to the present. The dominant lithology of the SDMCC, the Goropu Metabasalt, formed in a marginal basin to the northeast of the Australian continent. Two zircon U-Pb ages of 103.0 ± 5.7 and 71.6 ± 3.3 Ma, indicative of maximum depositional ages, from metasedimentary intercalations (the Bonenau Schist) in the Goropu Metabasalt, suggest formation of the oceanic protolith in the Late Cretaceous. Between 60.4 ± 2.5 and 56.6 ± 2.3 Ma (zircon U-Pb), tholeiitic to mildly calc-alkaline gabbroic to tonalitic rocks of the Yau Igneous Complex intruded the Goropu Metabasalt. The age of the Yau Igneous Complex overlaps with the known timing of north-directed subduction of the oceanic lithosphere along the Owen Stanley Fault (OSF) beneath the Cape Vogel Arc and provides a minimum age for the oceanic protolith. A second phase of magmatism, consisting of peraluminous-metaluminous calc-alkaline (Suckling Granite) and high-K (Mai’iu Monzonite, Bonua Porphyry) granitoids and basaltic andesite dikes that were cut by the Mai’iu Fault, was associated with the tectonic inversion of the OSF. Zircons from these syn-extensional intrusions suggest crystallization between 3.8 ± 0.2 and 2.0 ± 0.1 Ma. The oldest age of this range is inferred to mark the time by which the OSF had been re-activated as an extensional structure, the Mai’iu Fault. Al-in-amphibole and -biotite thermobarometry suggests crystallization of the Suckling Granite and Mai’iu Monzonite in a relatively shallow crust (~2-8 km depth) at pressures of ~0.4-2.3 kbar. Inherited zircons in the Plio-Pleistocene granitoids indicate that the Goropu Metabasalt carapace of the SDMCC is underlain by Australian-derived Cretaceous crustal material that is inferred to be the continuation of the Kagi Metamorphics in the central Papuan Peninsula. Further constraints of the timing of unroofing of the SDMCC were determined from three quartz clasts in the Gwoira Conglomerate. ²⁶Al/¹⁰Be burial ages of these samples indicate deposition in the Pliocene between 4.6 ± 2.9 and 3.4 ± 2.1 Ma. A tephra in the upper section of the exposed conglomerates was dated employing U-Pb methods on zircon, combined with apatite, zircon and magnetite (U-Th[-Sm])/He chronometers, yielding a complex age spectrum. An eruption age of 0.6 ± 0.4 Ma was extrapolated for this tephra. FT and (U-Th[-Sm])/He low-temperature thermochronometry details a young (≤3 Ma) and rapid exhumation history. Based on the crystallization ages of the syn-extensional granitoids, the depositional age of the Gwoira Conglomerate, the extensional cooling recorded by low-temperature thermochronometry, and the backwards projection of the published Holocene dip-slip rate of the Mai’iu Fault, the timing of the onset of extension is estimated at ~4 Ma. A minimum dip-slip rate of 8.1 ± 1.3 km/myr has been calculated from the inverse slope of zircon (U-Th)/He (ZHe) ages with slip-parallel distance from Mai’iu Fault trace. This is slightly lower than the >12 km/myr required to restore the intrusion depths (2-8 km) of the syn-extensional granitoids, now exposed 20-25 km south of the Mai’iu Fault trace at elevations up to 3.4 km. Collectively, these constraints suggest that the Mai’iu Fault has moved at cm-per-year rates since ~3 Ma. Evidence for both a fossil zircon FT (ZFT) partial annealing zone (PAZ) and a ZHe partial retention zone (PRZ) on the footwall of the SDMCC is presented. Combining paleo-temperature estimates from the inferred bases of the zircon PAZ and PRZ, peak-metamorphic temperatures inferred from Raman spectroscopy of carbonaceous material (RSCM), and published peak-metamorphic temperature constraints on the extensional shear zone mylonites near the Mai’iu Fault trace, a minimum slip-parallel, down-dip paleo-temperature gradient of 9.7 ± 2.2°C/km has been estimated for the exhumed Mai’iu Fault plane. Assuming that the modern regional geothermal gradient in the Woodlark Rift is a maximum estimate of that which existed prior to extensional exhumation of the SDMCC, the paleo-temperature gradient was used to estimate an average initial dip of the Mai’iu Fault of ~44° for pre-extensional geothermal gradients ranging between 10 to 20°C/km. Presently dipping 20-22° at the surface, the constraints on the initial dip suggest that the Mai’iu Fault may have been back-rotated by >20° since the onset of extension, consistent with a rolling hinge-style evolution of this continental MCC.</p>

The thermo-tectonic evolution of the Suckling-Dayman metamorphic core complex, southeastern Papua New Guinea

<p>The Suckling-Dayman metamorphic core complex (SDMCC) in the Woodlark Rift of southeastern Papua New Guinea is being exhumed along the Mai’iu Fault, an active low-angle normal fault dipping ~20-22° northwards at the surface. The spectacularly smooth topography of the Mai’iu Fault footwall clearly is expressive of geologically recent uplift. The precise timing and rates of the exhumation of this continental metamorphic core complex (MCC) have, however, never been studied in detail. This thesis provides the first systematic set of U-Pb, fission track (FT), (U-Th[-Sm])/He and ²⁶Al/¹⁰Be ages from metaigneous and metasedimentary rocks of the footwall of the SDMCC, clasts and a tephra deposit contained within syn-tectonic conglomerates (the Gwoira Conglomerate) in a rider block, and modern stream sediments in the footwall and hanging wall of the Mai’iu Fault. The ages are complemented by whole-rock compositional and thermobarometric data (Al-in-amphibole, Al-in-biotite, Raman spectroscopy of carbonaceous material). Based on these data, the timing of the onset of extension along the Mai’iu Fault, its long-term dip-slip rate and its initial dip were constrained. These data are presented in the context of the evolution of the SDMCC from the Cretaceous to the present. The dominant lithology of the SDMCC, the Goropu Metabasalt, formed in a marginal basin to the northeast of the Australian continent. Two zircon U-Pb ages of 103.0 ± 5.7 and 71.6 ± 3.3 Ma, indicative of maximum depositional ages, from metasedimentary intercalations (the Bonenau Schist) in the Goropu Metabasalt, suggest formation of the oceanic protolith in the Late Cretaceous. Between 60.4 ± 2.5 and 56.6 ± 2.3 Ma (zircon U-Pb), tholeiitic to mildly calc-alkaline gabbroic to tonalitic rocks of the Yau Igneous Complex intruded the Goropu Metabasalt. The age of the Yau Igneous Complex overlaps with the known timing of north-directed subduction of the oceanic lithosphere along the Owen Stanley Fault (OSF) beneath the Cape Vogel Arc and provides a minimum age for the oceanic protolith. A second phase of magmatism, consisting of peraluminous-metaluminous calc-alkaline (Suckling Granite) and high-K (Mai’iu Monzonite, Bonua Porphyry) granitoids and basaltic andesite dikes that were cut by the Mai’iu Fault, was associated with the tectonic inversion of the OSF. Zircons from these syn-extensional intrusions suggest crystallization between 3.8 ± 0.2 and 2.0 ± 0.1 Ma. The oldest age of this range is inferred to mark the time by which the OSF had been re-activated as an extensional structure, the Mai’iu Fault. Al-in-amphibole and -biotite thermobarometry suggests crystallization of the Suckling Granite and Mai’iu Monzonite in a relatively shallow crust (~2-8 km depth) at pressures of ~0.4-2.3 kbar. Inherited zircons in the Plio-Pleistocene granitoids indicate that the Goropu Metabasalt carapace of the SDMCC is underlain by Australian-derived Cretaceous crustal material that is inferred to be the continuation of the Kagi Metamorphics in the central Papuan Peninsula. Further constraints of the timing of unroofing of the SDMCC were determined from three quartz clasts in the Gwoira Conglomerate. ²⁶Al/¹⁰Be burial ages of these samples indicate deposition in the Pliocene between 4.6 ± 2.9 and 3.4 ± 2.1 Ma. A tephra in the upper section of the exposed conglomerates was dated employing U-Pb methods on zircon, combined with apatite, zircon and magnetite (U-Th[-Sm])/He chronometers, yielding a complex age spectrum. An eruption age of 0.6 ± 0.4 Ma was extrapolated for this tephra. FT and (U-Th[-Sm])/He low-temperature thermochronometry details a young (≤3 Ma) and rapid exhumation history. Based on the crystallization ages of the syn-extensional granitoids, the depositional age of the Gwoira Conglomerate, the extensional cooling recorded by low-temperature thermochronometry, and the backwards projection of the published Holocene dip-slip rate of the Mai’iu Fault, the timing of the onset of extension is estimated at ~4 Ma. A minimum dip-slip rate of 8.1 ± 1.3 km/myr has been calculated from the inverse slope of zircon (U-Th)/He (ZHe) ages with slip-parallel distance from Mai’iu Fault trace. This is slightly lower than the >12 km/myr required to restore the intrusion depths (2-8 km) of the syn-extensional granitoids, now exposed 20-25 km south of the Mai’iu Fault trace at elevations up to 3.4 km. Collectively, these constraints suggest that the Mai’iu Fault has moved at cm-per-year rates since ~3 Ma. Evidence for both a fossil zircon FT (ZFT) partial annealing zone (PAZ) and a ZHe partial retention zone (PRZ) on the footwall of the SDMCC is presented. Combining paleo-temperature estimates from the inferred bases of the zircon PAZ and PRZ, peak-metamorphic temperatures inferred from Raman spectroscopy of carbonaceous material (RSCM), and published peak-metamorphic temperature constraints on the extensional shear zone mylonites near the Mai’iu Fault trace, a minimum slip-parallel, down-dip paleo-temperature gradient of 9.7 ± 2.2°C/km has been estimated for the exhumed Mai’iu Fault plane. Assuming that the modern regional geothermal gradient in the Woodlark Rift is a maximum estimate of that which existed prior to extensional exhumation of the SDMCC, the paleo-temperature gradient was used to estimate an average initial dip of the Mai’iu Fault of ~44° for pre-extensional geothermal gradients ranging between 10 to 20°C/km. Presently dipping 20-22° at the surface, the constraints on the initial dip suggest that the Mai’iu Fault may have been back-rotated by >20° since the onset of extension, consistent with a rolling hinge-style evolution of this continental MCC.</p>

Geology of Zagros metamorphosed volcaniclastic sandstones: a key for changing the Mawat Ophiolite Complex to a metamorphic core complex, Kurdistan Region, NE-Iraq

Mawat Ophiolite Complex is located about 36 km to the northeast of Sulaimani city and directly to the east-northeast of Mawat town near the border of Iran in the northeastern Iraq. The complex has about 600-km2 surface area and consists of high mountain terrains that subjected to intense geological investigations from the fiftieth of previous century till now. According to previous studies, the complex contains tens of igneous rocks such as basalt, metabasalt, tuff, diabase, metadiabase, diorite dykes, periodotite, serpentinite, serpentinite-matrix mélange, gabbro, metagabbro, harzbergite, pyroxenite, plagiogranite, pegmatite, granitiod rocks and dunite. They added occurrences of the volcanic and subvolcanic rocks in the form of dykes or basaltic flows. The present study tries to change the petrology and tectonics of whole complex from Ophiolite Complex to Metamorphic Core Complex. The revision includes refusal of all the above igneous rocks, instead they considered as medium grade regional metamorphism of different types of volcaniclastic sandstones (volcanic wackes), arenites and greywackes (impure sandstones) which sourced predominantly from remote volcanic source area inside Iran. The revision depended on several conjugate field and laboratory evidences inside the complex. These evidences such as absence of pillow basalt, volcanic flows, glass shards, volcanic cones, dykes, sills, contact metamorphism, dilatational structures and flow structures. Other evidences are presence of cross beddings, erosional surfaces, lensoidal channel fills, metamorphosed conglomerate, exposures of thousands of laminated planar beds and transition from fresh volcaniclastic sandstones to its medium grade metamorphosed counterparts, which previously considered as igneous rocks of ophiolite types. Another, evidence, in contrast to ophiolite section, the basalt location is at the base of the claimed ophiolite section while plutonic (dunite and peridotite) rocks located at its top. These locations of the two rocks contradict the definition of ophiolites. Accordingly, the present study changed the geological map of the whole Mawat area from igneous outcrops to metamorphosed volcaniclastic sandstones, arenites and greywackes that belong to Walash-Naoperdan Series. The parent rocks of the series transformed to different types of regionally metamorphosed rocks by deep burial during Eocene. During the burial, diageneses and metamorphisms enhanced by complex mixture of materials from different source areas and seawaters environments. Later, they uplifted, unroofed and exhumed during Pliocene as a core complex.

Jurassic–Cenozoic tectonics of the Pequop Mountains, NE Nevada, in the North American Cordillera hinterland

The Ruby Mountains–East Humboldt Range–Wood Hills–Pequop Mountains (REWP) metamorphic core complex, northeast Nevada, exposes a record of Mesozoic contraction and Cenozoic extension in the hinterland of the North American Cordillera. The timing, magnitude, and style of crustal thickening and succeeding crustal thinning have long been debated. The Pequop Mountains, comprising Neoproterozoic through Triassic strata, are the least deformed part of this composite metamorphic core complex, compared to the migmatitic and mylonitized ranges to the west, and provide the clearest field relationships for the Mesozoic–Cenozoic tectonic evolution. New field, structural, geochronologic, and thermochronological observations based on 1:24,000-scale geologic mapping of the northern Pequop Mountains provide insights into the multi-stage tectonic history of the REWP. Polyphase cooling and reheating of the middle-upper crust was tracked over the range of &lt;100 °C to 450 °C via novel 40Ar/39Ar multi-diffusion domain modeling of muscovite and K-feldspar and apatite fission-track dating. Important new observations and interpretations include: (1) crosscutting field relationships show that most of the contractional deformation in this region occurred just prior to, or during, the Middle-Late Jurassic Elko orogeny (ca. 170–157 Ma), with negligible Cretaceous shortening; (2) temperature-depth data rule out deep burial of Paleozoic stratigraphy, thus refuting models that incorporate large cryptic overthrust sheets; (3) Jurassic, Cretaceous, and Eocene intrusions and associated thermal pulses metamorphosed the lower Paleozoic–Proterozoic rocks, and various thermochronometers record conductive cooling near original stratigraphic depths; (4) east-draining paleovalleys with ~1–1.5 km relief incised the region before ca. 41 Ma and were filled by 41–39.5 Ma volcanic rocks; and (5) low-angle normal faulting initiated after the Eocene, possibly as early as the late Oligocene, although basin-generating extension from high-angle normal faulting began in the middle Miocene. Observed Jurassic shortening is coeval with structures in the Luning-Fencemaker thrust belt to the west, and other strain documented across central-east Nevada and Utah, suggesting ~100 km Middle-Late Jurassic shortening across the Sierra Nevada retroarc. This phase of deformation correlates with terrane accretion in the Sierran forearc, increased North American–Farallon convergence rates, and enhanced Jurassic Sierran arc magmatism. Although spatially variable, the Cordilleran hinterland and the high plateau that developed across it (i.e., the hypothesized Nevadaplano) involved a dynamic pulsed evolution with significant phases of both Middle-Late Jurassic and Late Cretaceous contractional deformation. Collapse long postdated all of this contraction. This complex geologic history set the stage for the Carlin-type gold deposit at Long Canyon, located along the eastern flank of the Pequop Mountains, and may provide important clues for future exploration.

Supplemental Material: Cenozoic structural evolution of the Catalina metamorphic core complex and reassembly of Laramide reverse faults, southeastern Arizona, USA

<div>Spot map data for geochronology samples discussed in Appendix A.<br></div>