Tectonic Unroofing Research Articles

Late Cenozoic extension in northeastern Greece: Strymon Valley detachment system and Rhodope metamorphic core complex

The Strymon Valley detachment system accommodated at least 25 km of extension at the northern margin of the Aegean extensional province from middle Miocene through early Pliocene time. The primary detachment surface is exposed as a gently southwest-dipping low-angle normal fault—similar to those widely known in core complex settings of the U.S. Basin and Range province—for more than 150 km along strike, from the Aegean Sea coast in northeastern Greece northward into the Struma Valley of southern Bulgaria. Hanging-wall rocks in the Strymon Valley detachment system moved in a S53°W direction relative to the footwall, resulting ultimately in the tectonic unroofing of the Rhodope metamorphic core complex. Several segments of the Strymon Valley detachment have previously been interpreted as thrust faults formed during a Miocene compressional event. Our results negate the principal evidence for this event and imply instead that extensional deformation has characterized the northern Aegean region since at least middle Miocene time. Displacement ceased on the Strymon Valley detachment with the late Pliocene development of the Strymon and Drama basins. We propose that those basins, together with the other principal basins of the northern Aegean region, are subsiding above an active northeast-dipping, extensional detachment zone that forms a unified kinematic system with the western offshore continuation of the dextral North Anatolian strike-slip fault, the North Aegean trough. If this hypothesis is correct, then the North Aegean trough, the western strands of the North Anatolian fault, and the principal modern depocenters of the northern Aegean region may all have originated no earlier than late Pliocene time.

An Archean metamorphic core complex in the southern Slave Province: basement–cover structural relations between the Sleepy Dragon Complex and the Yellowknife Supergroup

Archean rocks in the Fenton Lake – Brown Lake area, southern Slave Province, are subdivided into two lithotectonic domains: a supracrustal domain, which consists mainly of the Archean Yellowknife Supergroup, and a gneiss–granite domain. The latter is composed of gneissic and metaigneous rocks of the Sleepy Dragon Complex, determined to be basement to the Yellowknife Supergroup, and granite plutons, including the 2641 ± 3.5 Ma Suse Lake granite and the 2583.5 ± 1 Ma Morose Granite. Volcanic rocks of the Cameron River Belt and greywacke–mudstone turbiditic metasedimentary rocks of the Burwash Formation constitute the supracrustal domain.A late Archean, amphibolite- to greenschist-facies, ductile to local brittle, high-strain zone separates the domains. Kinematic indicators demonstrate that the zone experienced two kinematically opposed episodes of displacement. The older episode involved pre- to synthermal peak thrusting of the supracrustal rocks over the gneiss–granite domain. Thrusting is kinematically and temporally consistent with late Archean, pre- to synthermal peak, regional contractional deformation. Structural and metamorphic relations and kinematic indicators suggest that thrusting and regional contraction were followed shortly by intrusion of the peraluminous Morose Granite and thereafter by a late syn- to post-thermal peak episode of extension, resulting in tectonic unroofing of the gneiss–granite domain.The sequential history of contraction and attendant regional metamorphism, granite intrusion, and, ultimately, extensional collapse, which is documented in the Archean rocks in the area, is a common feature of Phanerozoic collisional orogens. Moreover, the tectonic history of the gneiss–granite domain is broadly similar to the evolution of metamorphic core complexes in the North American Cordillera.

Very high rates of cooling and uplift in the Alpine belt of the Betic Cordilleras, southern Spain

Cooling-rate estimates of 150-350 °C/m.y., suggesting magnitudes of uplift and exhumation of ∼15-20 km at rates of 5-10 km/m.y., are proposed for the final stage of the orogenic development in a major part of the Betic Cordilleras. The results are based on a combination of radiometric and paleontological dates. Six isotopic chronometers (muscovite and biotite whole-rock Rb-Sr, muscovite and biotite 40 Ar/ 39 Ar, biotite K-Ar, and whole-rock Rb-Sr) yield analytical ages between 23 and 18.5 Ma for rocks from Alpine nappe complexes. Nappe-sealing marine sedimentary rocks contain early Miocene foraminifera and nannoplankton indicating minimum ages of 18-15.5 Ma. The very high estimates of cooling and uplift-exhumation rates suggest tectonic unroofing, which is tentatively connected geodynamically to lithospheric slab detachment and concomitant diapirism in the upper mantle, and extensional tectonics in the crustal section.

Major Late Miocene cooling of the middle crust associated with extensional orogenesis in the Funeral Mountains, California

The Funeral Mountains of the Death Valley region consist of a metamorphic core complex that underlies the Miocene Boundary Canyon detachment fault. Fissiontrack age determinations on sphene, zircon, and apatite from the highest grade portions of the Funeral Mountains (collected in Monarch Canyon) indicate rapid cooling from above ∼285°C at 9–10 Ma. The steep dT/dt slope implied by the cooling path envelope as well as its synchroneity with development of the Boundary Canyon detachment suggests tectonic unroofing of between 9.5 and 17 km since ∼10 Ma (assuming typical geothermal gradients prior to detachment development of between ∼20–30°C/km). Previous studies report muscovite 40Ar/39Ar plateau ages from the same area indicating that the Funeral Mountains core may have cooled below ∼350°C between 110‐55 Ma. These data, when combined with the fission track ages, suggest residence of the metamorphic terrain at 285–350°C from Late Cretaceous to late Miocene time. Recent studies, using petrologic constraints, have suggested that much of the unroofing of the Funeral Mountains, as well as development of tectonite fabrics, occurred during Mesozoic extension. Recognition of temperatures in the 300°C range during Miocene time suggests some of the ductile extensional fabrics may be late Miocene in age.

Decompressional coronas and symplectites in granulites of the Musgrave Complex, central Australia

Abstract In granulite facies metapelitic rocks in the Musgrave Complex, central Australia, reaction between S1 garnet and sillimanite involves the development in S2 of both garnet + cordierite + hercynitic spinel + biotite and hercynitic spinel + cordierite + sillimanite + biotite. The S2 assemblages occur either in coronas and symplectites, mainly around garnet, or, in rocks in which S2 is more strongly developed, as recrystallized assemblages. Ignoring the presence of biotite and ilmenite, the mineral textures can be accounted for qualitatively by a consideration of the model system FeO‐MgO‐Al2O3‐SiO2 (FMAS); the textural relationships accord with decompression accompanying the change from S1 to S2. However, since biotite and ilmenite are involved in the assemblages, the parageneses are better accounted for in terms of equilibria in the expanded model system K2O‐FeO‐MgO‐Al2O3‐SiO2‐H2‐TiO2‐Fe2O3 (KFMASHTO), i.e. AFM + TiO2+ Fe2O3. The coronas reflect the tectonic unroofing of at least part of the Musgrave Complex from peak S1 conditions of about 8 kbar to S2 conditions of about 4 kbar.

Nature and origin of seismic reflection fabric, Ruby‐East Humboldt Metamorphic Core Complex, Nevada

Seismic reflection profiling across exposed upper and middle crustal rocks of the Ruby‐East Humboldt metamorphic core complex delineates important characteristics of the crustal structure developed during Tertiary extensional deformation. The goals of this study were to trace a Tertiary extensional shear zone from mylonitic surface outcrops into a seismic section and to characterize the deeper crustal fabric associated with the polyphase deformational history of the complex. Reflections in the shallow surface correlate with a plastic to brittle shear zone that formed during the tectonic unroofing of the middle crustal rocks. Constructive interference from strong planar layering in the mylonitic shear zone is considered chiefly responsible for generating the reflections. East and southwest dipping reflectors in the seismic section appear to correlate with exposed, opposing dipping mylonitic foliation domains. The opposing dips of the mylonitic layering may reflect warping of the normal‐sense shear zone during tectonic exhumation coupled with an overall anastomosing character. Deeper in the section, a heterogeneous reflection character correlates with increases in velocity shown from wide‐angle measurements in this region and is interpreted as penetrative fabric originating from extensional flow facilitated by broad‐scale pure shear and localized simple shear. Lower crustal rocks apparently achieved granulite facies metamorphism during extension. A maximum of 6–8 km of mafic material could have been added to the crust during Cenozoic extension. The Moho reflection has such a high amplitude that it may be caused by partially molten rocks interleaved with peridotite. Reflections from the Moho show no significant upwarping of the base of the crust beneath the core complex. This suggests that the lower‐crustal configuration is at least as young as the period of extensional activity that lasted from approximately 40 to 20 Ma which was responsible for the exhumation of the metamorphic core complex.

Mid-crustal Cretaceous roots of Cordilleran metamorphic core complexes

Research Article| April 01, 1988 Mid-crustal Cretaceous roots of Cordilleran metamorphic core complexes J. Lawford Anderson; J. Lawford Anderson 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741 Search for other works by this author on: GSW Google Scholar Andrew P. Barth; Andrew P. Barth 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741 Search for other works by this author on: GSW Google Scholar Edward D. Young Edward D. Young 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741 Search for other works by this author on: GSW Google Scholar Author and Article Information J. Lawford Anderson 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741 Andrew P. Barth 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741 Edward D. Young 1Department of Geological Sciences, University of Southern California, Los Angeles, California 90089-0741 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (4): 366–369. https://doi.org/10.1130/0091-7613(1988)016<0366:MCCROC>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation J. Lawford Anderson, Andrew P. Barth, Edward D. Young; Mid-crustal Cretaceous roots of Cordilleran metamorphic core complexes. Geology 1988;; 16 (4): 366–369. doi: https://doi.org/10.1130/0091-7613(1988)016<0366:MCCROC>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Thermobarometry for Cretaceous to mid-Tertiary plutonism and deformation in the lower plate of Whipple and Santa Catalina metamorphic core complexes shows that both crystalline terranes originated in the middle crust. Moreover, they are characterized by a striking acceleration of tectonic decompression coincident with middle Tertiary, low-angle detachment faulting leading to erosional and tectonic unroofing by mid-Miocene time.Depth estimates for emplacement of five intrusive suites within the Whipple complex include (1) 33 ±4 km for the peraluminous, 89 Ma Whipple Wash plutonic suite; (2) 29 ±1 km for the 73 Ma Axtel quartz diorite; (3) 16 ±5 km for mylonitization and synkinematic plutonism at 26 Ma; (4) 6.2 ±1.9 km for the postkinematic, 19 Ma War Eagle gabbro-quartz diorite complex; and (5) 5.2 ±2.3 km for a 17 Ma postkinematic granodiorite. Decompression initially occurred at a low rate of 0.3 mm/yr from 89 to 26 Ma and increased to approximately 2 mm/yr during the late Oligocene to middle Miocene. Estimated depths for four pluton emplacement or deformational events in the Santa Catalina Mountains include (1) 21 ±1 km for the magmatic epidote-bearing, 68 Ma Leatherwood quartz diorite; (2) 15 ±3 km for the garnet, two-mica, 47 Ma Wilderness granite; (3) 9.3 ±1.9 km for post-Wilderness mylonitzation; and (4) 6.3 ±2.6 km for the 27 Ma Catalina monzogranite. Post-Laramide decompression, estimated at 0.3 mm/yr, accelerated to 1.3 mm/yr prior to the cessation of detachment faulting.Whereas most batholithic terranes of the North American Cordillera are representative of an upper crustal setting, core complexes provide, as a consequence of their tectonic evolution, a petrological and structural view into middle crustal processes. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Crustal-scale extension in a convergent orogen : the Sterzing-Steinach mylomte zone in the Eastern Alps

The western margin of the Tauera Window (Eastern Alps) is defined by a low angle westward dipping fault zone of potently We disp lacement. Ductile deformation of the fault rocks results in a carpet of mylonites up to 400 metres thick. Evidence from shear criteria and the excision of part of the Cretaceous-Tertiary metamorphic edifice both indicate normal displacements, and relative movement of Austroalpine nappe complex towards the west. The Sterzing-Steinach mylonite zone overprints the Alpine nappe edifice. Movements occurred on the cooling path of the Tauern metamorphism, and may be as recent as Middle Miocene. The Kinematics and geometry of the mylonite zone constrain two likely t ectonic explanations that are both compatible with secondary thining of a thick orogenic wedge. (1) Ute the Austroalpine nappe pile due to tectonic unroofing of the Tauern window. (2) Continental escape by east-west stretching of the Alpine orogenic wedge in response to continental collision.

In search for a relationship between harmonic resolutions of the geoid, convective stress patterns and tectonics in the lithosphere: a possible explanation for the Betic-Rif orocline

Convective stress fields implied by the Runcorn model have been integrated with geological structures in the overlying lithosphere. This is dangerous since small-scale convection patterns in the mantle might have remained stationary for at least 50 Ma while particular parts of the lithosphere are likely to have passed over distinct convective stress regimes in such periods. The mantle component of the stress history of lithospheric structures younger than 32 Ma is potentially tractable if a mean plate velocity of 5 cm y −1 is assumed. This is because the satellite gravity data used here allow the detection of convection cells with horizontal length scales of the order of 1600 km (which the lithosphere may cross in 32 Ma). For example, the sublithospheric stress field might have accounted for the uplift and subsequent subsidence of the Alboran Sea basin (W. Mediterranean), between 25 and 20 Ma ago. An immature diapiric rise of the mantle due to upwelling is likely to have occurred beneath this region between 25 and 20 Ma ago. The resulting lithospheric swell caused extensive tectonic unroofing by nappe spreading with or without some sliding. The subsidence of the Alboran Sea after the rise of the dome seems an excellent example of the combined effects of lithospheric cooling connected with ceasing mantle diapirism and mechanical thinning of the lithosphere by nappe translations.