Removal Of Lithospheric Mantle Research Articles

Topographic response to mantle lithosphere removal in the southern Sierra Nevada region, California

Geological studies of mantle xenoliths entrained in late Neogene‐Quaternary lavas from the southern Sierra Nevada region and regional geophysical studies suggest that the highdensity mantle lithosphere that formed beneath the Sierra Nevada batholith in conjunction with arc magmatism is being convectively removed as a ‘‘drip’’ structure. This structure, as imaged seismically, is roughly cylindrical in shape with a diameter of ;100 km, and extends to ;225 km depth. Centered above this structure is a region ;120 km in diameter that is undergoing active subsidence relative to adjacent regions. Such subsidence is seen in the active fluvial-alluvial sediment flooding of mountainous topography of the southwestern Sierra and in the development of the adjacent Tulare Lake basin of the San Joaquin Valley. Dynamic modeling of such upper-mantle drip structures predicts a phase of overlying surface subsidence during the most vigorous phase of drip formation. The southern Sierra upper mantle drip and the overlying crust appear to be in this phase of their dynamically coupled evolution.

A review of the geodynamic setting of large-scale Late Mesozoic gold mineralization in the North China Craton: an association with lithospheric thinning

Abundant gold deposits are distributed along the margins of the North China Craton (NCC). Occurring throughout the Precambrian basement and located in or proximal to Mesozoic granitoids, these deposits show a consistent spatial–temporal association with Late Jurassic–Early Cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock. Their ages are mainly Early Cretaceous (130–110 Ma) and constrain a very short period of metallogenesis. Sr–Nd–Pb isotopic tracers of ores, minerals and associated rocks indicate that gold and associated metals mainly were derived from multi-sources, i.e., the wall rocks (Precambrian basement and Mesozoic granites) and associated mafic rocks. Previous studies, including high surface heat flow, uplift and later basin development, slow seismic wave speeds in the upper mantle, and a change in the character of mantle xenoliths sampled by Paleozoic to Cenozoic magmas, have been used to suggest that ancient, cratonic mantle lithosphere was removed from the base of the NCC some time after the Ordovician, and replaced by younger, less refractory lithospheric mantle. The geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization (130–110 Ma) indicate that they were derived from an ancient enriched lithospheric mantle source; whereas, the mafic dikes and volcanic rocks younger than 110 Ma were derived from a relatively depleted mantle source, i.e., asthenospheric mantle. According to their age and sources, relation to magmatism and geodynamic framework, the gold deposits were formed during lithospheric thinning. The removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature. The fluids derived from the lower crust were mixed with magmatic and meteoric waters, and resulted in the deposition of gold and associated metals.

Lithospheric roots beneath western Laurentia: the geochemical signal in mantle garnets

This study presents major and trace element data for 243 mantle garnet xenocrysts from six kimberlites in parts of western North America. The geochemical data for the garnet xenocrysts are used to infer the composition, thickness, and tectonothermal affinity of the mantle lithosphere beneath western Laurentia at the time of kimberlite eruption. The garnets record temperatures between 800 and 1450°C using Ni-in-garnet thermometry and represent mainly lherzolitic mantle lithosphere sampled over an interval from about 110–260 km depth. Garnets with sinuous rare-earth element patterns, high Sr, and high Sc/V occur mainly at shallow depths and occur almost exclusively in kimberlites interpreted to have sampled Archean mantle lithosphere beneath the Wyoming Province in Laurentia, and are notably absent in garnets from kimberlites erupting through the Proterozoic Yavapai Mazatzal and Trans-Hudson provinces. The similarities in depths of equilibration, but differing geochemical patterns in garnets from the Cross kimberlite (southeastern British Columbia) compared to kimberlites in the Wyoming Province argue for post-Archean replacement and (or) modification of mantle beneath the Archean Hearne Province. Convective removal of mantle lithosphere beneath the Archean Hearne Province in a "tectonic vise" during the Proterozoic terminal collisions that formed Laurentia either did not occur, or was followed by replacement of thick mantle lithosphere that was sampled by kimberlite in the Triassic, and is still observed there seismically today.

Seismic evidence for catastrophic slab loss beneath Kamchatka.

In the northwest Pacific Ocean, a sharp corner in the boundary between the Pacific plate and the North American plate joins a subduction zone running along the southern half of the Kamchatka peninsula with a region of transcurrent motion along the western Aleutian arc. Here we present images of the seismic structure beneath the Aleutian-Kamchatka junction and the surrounding region, indicating that: the subducting Pacific lithosphere terminates at the Aleutian-Kamchatka junction; no relict slab underlies the extinct northern Kamchatka volcanic arc; and the upper mantle beneath northern Kamchatka has unusually slow shear wavespeeds. From the tectonic and volcanic evolution of Kamchatka over the past 10 Myr (refs 3-5) we infer that at least two episodes of catastrophic slab loss have occurred. About 5 to 10 Myr ago, catastrophic slab loss shut down island-arc volcanic activity north of the Aleutian-Kamchatka junction. A later episode of slab loss, since about 2 Myr ago, seems to be related to the activity of the world's most productive island-arc volcano, Klyuchevskoy. Removal of lithospheric mantle is commonly discussed in the context of a continental collision, but our findings imply that episodes of slab detachment and loss are also important agents in the evolution of oceanic convergent margins.

The Recrystallization Front of the Ronda Peridotite: Evidence for Melting and Thermal Erosion of Subcontinental Lithospheric Mantle beneath the Alboran Basin

with a process involving partial melting, kilometre-scale migration of Evidence for a major heating event accompanied by decompression melts by diffuse porous flow and limited melt extraction (2·5–6·5%). was recently reported from crustal rocks drilled in the Alboran basin. Hence, the Ronda recrystallization front is interpreted as the The metamorphic evolution recorded by these rocks implies complete narrow boundary of a partial-melting domain (the coarse-granular removal of lithospheric mantle during the Cenozoic, a process that peridotites) formed at the expense of subcontinental lithospheric is confirmed by geophysical modelling indicating thin lithosphere mantle (the spinel tectonites). The existence of melt-consuming beneath the Alboran domain. In this region, the Ronda lherzolite reactions in the transitional peridotites, a few hundred metres ahead massif (Betic Cordillera, southern Spain) provides a unique opof the melting front, demonstrates that the front was thermally portunity for the observation of mantle processes associated with controlled. This implies that a smooth thermal gradient existed across lithospheric thinning. A striking feature of the Ronda peridotite is the Ronda massif during the development of the recrystallization front. a narrow recrystallization front, which has been ascribed to kilometreDifferences in pyroxene compositions on either side of the front may scale porous melt flow through the massif. The front separates the be explained by a transient heating event at [1200°C (>1·5 spinel tectonite domain, interpreted as old, veined lithospheric mantle, GPa) coeval with partial melting. Consistent with the geodynamic from the granular domain where the lithospheric microstructures, scenario proposed for the Alboran domain during the Cenozoic, the mineralogical assemblages and geochemical signatures were obevolution of the Ronda recrystallization front is considered as an literated by grain growth coeval with pervasive infiltration of basaltic example of thermal erosion and partial melting of lithospheric mantle melts. On the basis of trace-element abundances in peridotites above upwelling asthenosphere. collected over a distance of 12 km along the recrystallization front, our study confirms that the front is a relatively sharp (Ζ400 m) geochemical discontinuity at the scale of the Ronda massif. Compared with the spinel tectonites, the coarse-granular peridotites are more homogeneous, more refractory in terms of major elements and more

Osmium isotopic evidence for mesozoic removal of lithospheric mantle beneath the sierra nevada, california

Thermobarometric and Os isotopic data for peridotite xenoliths from late Miocene and younger lavas in the Sierra Nevada reveal that the lithospheric mantle is vertically stratified: the shallowest portions (<45 to 60 kilometers) are cold (670 degrees to 740 degrees C) and show evidence for heating and yield Proterozoic Os model ages, whereas the deeper portions (45 to 100 kilometers) yield Phanerozoic Os model ages and show evidence for extensive cooling from temperatures >1100 degrees C to 750 degrees C. Because a variety of isotopic evidence suggests that the Sierran batholith formed on preexisting Proterozoic lithosphere, most of the original lithospheric mantle appears to have been removed before the late Miocene, leaving only a sliver of ancient mantle beneath the crust.

Magmatism Associated with Orogenic Collapse of the Betic-Alboran Domain, SE Spain

lithospheric mantle. Overall, the magmatic succession is more Extensional collapse of the Betic–Alboran Domain in the Miocene consistent with a geodynamic model involving convective removal of was accompanied by several discrete episodes of magmatism which the majority of the lithospheric mantle than with models invoking provide insights into the relationships between the thermal and wholesale delamination at the Moho, slab detachment or slab rollmechanical state of the lithosphere during late orogenesis. The back. tholeiitic Malaga dykes, emplaced at ~30–27 Ma, have flat rare earth element (REE) patterns and low Sr/Sr and high Nd/ Nd indicative of shallow decompression melting (5–15%) within the asthenosphere following removal of lithospheric mantle. Calcalkaline magmas, erupted between 15 and 6 Ma, have negative

Petrological and Structural Evolution of High-Grade Metamorphic Rocks from the Floor of the Alboran Sea Basin, Western Mediterranean

The metamorphic basement beneath the Alboran Sea, a Neogene extensional basin drilled during Ocean Drilling Program (ODP) Leg 161 (Site 976), consists of high-grade pelitic schist overlying migmatitic pelitic gneiss. Inferred assemblages in the high-grade schist evolved from garnet + staurolite + biotite + muscovite + plagioclase (Assemblage 1) to biotite + sillimanite + K-feldspar + plagioclase ± garnet (Assemblage 2) to andalusite + biotite + K-feldspar + plagioclase (Assemblage 3). In the gneiss, which shows abundant migmatitic textures, the present assemblage is biotite + andalusite + sillimanite + muscovite + cordierite + K-feldspar + plagioclase ± garnet. Phase relations and thermobarometric calculations suggest that the high-grade schist experienced decompression accompanied by heating from ∼500°C at 10.5 kbar through 600 ± 30°C at 6–7 kbar (Assemblage 1), and thence to 650–700°C at 3–4 kbar (Assemblage 2), followed by cooling through 500–600°C at 2 kbar or less (Assemblage 3). Peak temperature and melting occurred under low-pressure conditions. The widespread disequilibrium and overstepping of metamorphic reactions suggests that decompression was rapid. The P–T evolution is consistent with metamorphism in a late orogenic extensional basin, and suggests the existence of an external source of heat, probably indicating the complete removal of lithospheric mantle beneath the extending region.

Thermal evolution, rate of exhumation, and tectonic significance of metamorphic rocks from the floor of the Alboran extensional basin, western Mediterranean

High‐grade metamorphic rocks drilled at Ocean Drilling Program Site 976 in the Alboran Sea show a PT path characterized by decompression from about 1050 MPa (40 km depth) to 350 MPa (13 km depth) accompanied by an increase in temperature from about 550°±50°C to 675°±25°C. The Ar/Ar dating on muscovite and apatite fission track analysis indicate that the final stage of exhumation and cooling occurred very rapidly in the interval 20.5–18 Ma, which coincides with the initiation of sedimentation in the Alboran Sea basin. The Alboran Sea formed by Miocene extension on the site of a Late Cretaceous? to Paleogene contractional orogen, and extension coincided with thrusting in the peripheral parts of the Betic‐Rif arc, which surrounds the basin on three sides. Thermal modeling of the PT path was carried out with the aim of constraining geodynamic models for the formation of the basin. Variables considered in the modeling included (1) the thickness and thermal gradient of the postorogenic lithosphere; (2) the radiogenic heat production in the thickened crust; (3) the time gap (pause) between the end of contractional tectonics and the start of extension; (4) removal of lithospheric mantle below 125, 75, or 62.5 km; and (5) the rate of extension. The only combinations of variables that produce modeled PT paths with the observed characteristics involve high radiogenic heat production combined with a significant postcontractional pause (to produce high temperatures in rocks initially at 40 km depth), removal of lithosphere below 62.5 km (to produce further heating during decompression), extension by a factor of 3 in 6 m.y. (to delay the attainment of the maximum temperature until the rocks reached shallow depths), and final exhumation and cooling in about 3.3 m.y. (to satisfy radiometric and petrological constraints). This gives a maximum of about 9 m.y. for exhumation from 40 km depth to the surface. Lithospheric stretching in response to plate‐boundary forces such as trench rollback, without removal of lithosphere, cannot explain the late onset of heating and the high temperatures reached by these rocks. Removal of lithosphere at depths significantly greater than 62.5 km cannot explain the combination of high temperatures reached by these rocks and the shallow depth at which they attained the maximum temperature. Only a combination of significant postcollisional radiogenic heating, then wholesale removal of lithospheric mantle below the orogenic crust, followed by rapid stretching can explain the observed PT path. These results appear to support some form of lithospheric delamination as the primary cause for the formation of the Alboran Sea basin.

Decompression and high-temperature–low-pressure metamorphism in the exhumed floor of an extensional basin, Alboran Sea, western Mediterranean

Leg 161 of the Ocean Drilling Program (ODP) has made a major contribution to our understanding of the origin of the Alboran Basin by demonstrating that it is underlain by rocks of continental origin that have undergone high-temperature metamorphism and melting at exceptionally low pressure after exhumation and decompression. Basement rocks recovered from Site 976 consist of high-grade schist and gneiss derived from aluminous sediments, and minor amounts of marble, granitic dikes, and migmatitic segregations of granitic material. Mineral assemblages and textural relations show that an early assemblage including biotite, garnet, staurolite, plagioclase, and rutile is overprinted by a second assemblage of biotite, sillimanite, plagioclase, potassium feldspar, and ilmenite. Both assemblages are overprinted by andalusite, potassium feldspar, and minor garnet. Migmatitic gneiss contains relict andalusite, overprinted by sillimanite and cordierite coexisting with granitic leucosome. Preliminary pressure-temperature estimates suggest that the metamorphic evolution followed an approximately isothermal decompression path from 7 to 3 kbar at temperatures in the range 580 to 630 °C. After decompression, granitic melts formed at 670 °C, after andalusite breakdown and within the sillimanite stability field. The cored rocks closely resemble high-grade metamorphic rocks in the adjacent Betic Cordillera of southern Spain, which yield early Miocene radiometric dates. At ODP Site 976 they are overlain by middle Miocene marine sediments. The combination of exhumation in an extensional tectonic environment and the evidence for high and increasing temperature during exhumation provide support for and new constraints on current models for the basin that involve the removal of lithospheric mantle below a zone of continental collision, accompanied or followed by extension.

Source of the Lachlan fold belt flysch linked to convective removal of the lithospheric mantle and rapid exhumation of the Delamerian-Ross fold belt

Research Article| October 01, 1996 Source of the Lachlan fold belt flysch linked to convective removal of the lithospheric mantle and rapid exhumation of the Delamerian-Ross fold belt S. P. Turner; S. P. Turner 1Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, United Kingdom Search for other works by this author on: GSW Google Scholar S. P. Kelley; S. P. Kelley 1Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, United Kingdom Search for other works by this author on: GSW Google Scholar A. H. M. VandenBerg; A. H. M. VandenBerg 2Department of Energy and Minerals, Victoria 3065, Australia Search for other works by this author on: GSW Google Scholar J. D. Foden; J. D. Foden 3Department of Geology and Geophysics, University of Adelaide, South Australia 5005, Australia Search for other works by this author on: GSW Google Scholar M. Sandiford; M. Sandiford 3Department of Geology and Geophysics, University of Adelaide, South Australia 5005, Australia Search for other works by this author on: GSW Google Scholar T. Flöttmann T. Flöttmann 3Department of Geology and Geophysics, University of Adelaide, South Australia 5005, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information S. P. Turner 1Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, United Kingdom S. P. Kelley 1Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, United Kingdom A. H. M. VandenBerg 2Department of Energy and Minerals, Victoria 3065, Australia J. D. Foden 3Department of Geology and Geophysics, University of Adelaide, South Australia 5005, Australia M. Sandiford 3Department of Geology and Geophysics, University of Adelaide, South Australia 5005, Australia T. Flöttmann 3Department of Geology and Geophysics, University of Adelaide, South Australia 5005, Australia Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1996) 24 (10): 941–944. https://doi.org/10.1130/0091-7613(1996)024<0941:SOTLFB>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 S. P. Turner, S. P. Kelley, A. H. M. VandenBerg, J. D. Foden, M. Sandiford, T. Flöttmann; Source of the Lachlan fold belt flysch linked to convective removal of the lithospheric mantle and rapid exhumation of the Delamerian-Ross fold belt. Geology 1996;; 24 (10): 941–944. doi: https://doi.org/10.1130/0091-7613(1996)024<0941:SOTLFB>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 During the Cambrian-Ordovician the paleo–Pacific margin of Gondwana underwent a rapid transition from a site of convergent deformation (Delamerian-Ross orogeny) to one of sedimentation during which the thick turbiditic sequences of the adjacent basal Lachlan fold belt were deposited. Laser-probe 40Ar-39Ar data show that the synkinematic (523–486 Ma), mid-crustal I- and S-type granites and metamorphic country rocks of the Delamerian fold belt were rapidly cooled at 490–485 Ma, coincident with the intrusion of a suite of high-level, postkinematic A-type granites and gabbros (ca. 497–481 Ma). 40Ar-39Ar data on detrital muscovites from the basal sections of the Lachlan fold belt provide information on exhumation rather than cooling but yield an age pattern (507–480 Ma) identical to that of the Delamerian fold belt, demonstrating that this was the source of the sediments. The combined data require that some 15 km of exhumation occurred very rapidly (∼ 5–15 mm ·yr−1), coincident (as implied by overlapping ages) with the cessation of convergent deformation and partial melting to form the postkinematic magmas. This scenario implies a causative link, which we infer to have been convective removal of lithospheric mantle following orogenic thickening. The model is analogous to the Tertiary uplift of the India-Asia orogen, which provided the sediment source for the Bengal fan. Our results suggest that similar processes were important in the evolution of mountain belts at least as far back as the early Phanerozoic. 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.