Pressure-temperature evolution of andalusite-kyanite-sillimanite-bearing pelitic schists from Nishidohira, southern Abukuma Mountains, Northeast Japan: Implications for Cretaceous rapid burial and exhumation in the Northeast Asian continental margin

Abstract. The Mesozoic sequences of the Oman Mountains experienced only weak post-obduction overprint and deformation, thus they offer a unique natural laboratory to study obduction. We present a study of the pressure and temperature evolution in the passive continental margin under the Oman Ophiolite, using numerical basin models calibrated with thermal maturity data, fluid inclusion thermometry and low-temperature thermochronology. Thermal maturity data from the Adam Foothills constrain burial in the foredeep moving in front of the advancing nappes to be at least 4 km. Peak temperature evolution in the carbonate platform under the ophiolite is only weakly dependent on the temperature of the overriding nappes which have cooled during transport from the oceanic subduction zone to emplacement. Fluid-inclusion thermometry yields pressure-corrected homogenization temperatures of 225 to 266 °C for veins formed during progressing burial, 296–364 °C for veins related to peak burial and 184 to 213 °C for veins associated with late-stage strike-slip faulting. In contrast, the overlying Hawasina nappes have not been heated above c. 170 ºC, as witnessed by only partial resetting of the zircon (U-Th)/He thermochronometer. In combination with independently determined temperatures from solid bitumen reflectance, we infer that the fluid inclusions of peak-burial-related veins formed at minimum pressures of 225–285 MPa. This implies that the rocks of the future Jebel Akhdar Dome were buried under 8–10 km of ophiolite on top of 2 km of sedimentary nappes, which is in agreement with thermal maturity data of solid bitumen reflectance and Raman spectroscopy. Burial of the passive margin under the ophiolite results in sub-lithostatic pore pressures, in agreement with observations on veins formed in dilatant fractures in the carbonates. We infer that overpressure is induced by rapid burial under the ophiolite nappes. Obduction-related tilt of the passive margin in combination with overpressure in the passive margin caused fluid migration towards the south in front of the nappes. Exhumation of the Jebel Akhdar as indicated by our zircon (U-Th)/He data, integrated with existing data, started as early as the late Cretaceous to early Cenozoic, linked with extension along a major listric shear zone with top-to-NNE shear sense, together with an early phase of extensional dome formation. The carbonate platform and obducted nappes of the whole Jebel Akhdar cooled together below c. 170 °C between 50 and 40 Ma, before the final stage of anticline formation.

Download Full-text

Izanagi-Pacific ridge subduction revealed by a 56 to 46 Ma magmatic gap along the northeast Asian margin

Geology ◽

10.1130/g46778.1 ◽

2019 ◽

Vol 47 (10) ◽

pp. 953-957 ◽

Cited By ~ 9

Author(s):

Jeremy Tsung-Jui Wu ◽

Jonny Wu

Keyword(s):

Continental Margin ◽

Spatial Configuration ◽

Russian Far East ◽

Far East ◽

Late Eocene ◽

Spreading Ridge ◽

Geological Evidence ◽

Ridge Subduction ◽

Northeast Asian ◽

Early Cenozoic

Abstract Recent studies have debated the timing and spatial configuration of a possible intersection between the Pacific-Izanagi spreading ridge and the northeast Asian continental margin during Cretaceous or early Cenozoic times. Here we examine a newly compiled magmatic catalog of ∼900 published Cretaceous to Miocene igneous rock radioisotopic values and ages from the northeast Asian margin for ridge subduction evidence. Our synthesis reveals that a near-synchronous 56–46 Ma magmatic gap occurred across ∼1500 km of the Eurasian continental margin between Japan and Sikhote-Alin, Russian Far East. The magmatic gap separated two distinct phases of igneous activity: (1) an older, Cretaceous to Paleocene pre–56 Ma episode that had relatively lower εNd(t) (−15 to + 2), elevated (87Sr/86Sr)0 (initial ratio, 0.704–0.714), and relatively higher magmatic fluxes (∼1090 km2/m.y.); and (2) a younger, late Eocene to Miocene post–46 Ma phase that had relatively elevated εNd(t) (−2 to + 10), lower (87Sr/86Sr)0 (0.702–0.707), and a lower 390 km2/m.y. magmatic flux. The 56–46 Ma magmatic gap links other geological evidence across northeast Asia to constrain an early Cenozoic, low-angle ridge-trench intersection that had profound consequences for the Eurasian continental margin, and possibly led to the ca. 53–47 Ma Pacific plate reorganization.

Download Full-text

Tectono-thermal evolution of Oman's Mesozoic passive continental margin under the obducting Semail Ophiolite: a case study of Jebel Akhdar, Oman

Solid Earth ◽

10.5194/se-10-149-2019 ◽

2019 ◽

Vol 10 (1) ◽

pp. 149-175 ◽

Cited By ~ 12

Author(s):

Arne Grobe ◽

Christoph von Hagke ◽

Ralf Littke ◽

István Dunkl ◽

Franziska Wübbeler ◽

...

Keyword(s):

Fluid Inclusion ◽

Continental Margin ◽

Tectonic Evolution ◽

Carbonate Platform ◽

Passive Continental Margin ◽

Passive Margin ◽

Temperature Evolution ◽

Burial Depth ◽

Thermal Maturity ◽

Solid Bitumen

Abstract. We present a study of pressure and temperature evolution in the passive continental margin under the Oman Ophiolite using numerical basin models calibrated with thermal maturity data, fluid-inclusion thermometry, and low-temperature thermochronometry and building on the results of recent work on the tectonic evolution. Because the Oman mountains experienced only weak post-obduction overprint, they offer a unique natural laboratory for this study. Thermal maturity data from the Adam Foothills constrain burial in the basin in front of the advancing nappes to at least 4 km. Peak temperature evolution in the carbonate platform under the ophiolite depends on the burial depth and only weakly on the temperature of the overriding nappes, which have cooled during transport from the oceanic subduction zone to emplacement. Fluid-inclusion thermometry yields pressure-corrected homogenization temperatures of 225 to 266 ∘C for veins formed during progressive burial, 296–364 ∘C for veins related to peak burial, and 184 to 213 ∘C for veins associated with late-stage strike-slip faulting. In contrast, the overlying Hawasina nappes have not been heated above 130–170 ∘C, as witnessed by only partial resetting of the zircon (U-Th)/He thermochronometer. In combination with independently determined temperatures from solid bitumen reflectance, we infer that the fluid inclusions of peak-burial-related veins formed at minimum pressures of 225–285 MPa. This implies that the rocks of the future Jebel Akhdar Dome were buried under 8–10 km of ophiolite on top of 2 km of sedimentary nappes, in agreement with thermal maturity data from solid bitumen reflectance and Raman spectroscopy. Rapid burial of the passive margin under the ophiolite results in sub-lithostatic pore pressures, as indicated by veins formed in dilatant fractures in the carbonates. We infer that overpressure is induced by rapid burial under the ophiolite. Tilting of the carbonate platform in combination with overpressure in the passive margin caused fluid migration towards the south in front of the advancing nappes. Exhumation of the Jebel Akhdar, as indicated by our zircon (U-Th)/He data and in agreement with existing work on the tectonic evolution, started as early as the Late Cretaceous to early Cenozoic, linked with extension above a major listric shear zone with top-to-NNE shear sense. In a second exhumation phase the carbonate platform and obducted nappes of the Jebel Akhdar Dome cooled together below ca. 170 ∘C between 50 and 40 Ma before the final stage of anticline formation.

Download Full-text