Timescales of partial melting in the Himalayan middle crust: insight from the Leo Pargil dome, northwest India

2013 ◽  
Vol 166 (5) ◽  
pp. 1415-1441 ◽  
Author(s):  
Graham W. Lederer ◽  
John M. Cottle ◽  
Micah J. Jessup ◽  
Jackie M. Langille ◽  
Talat Ahmad
Keyword(s):  
Partial Melting ◽  
Middle Crust ◽  
Northwest India

scholarly journals Thermal conditions during deformation of partially molten crust from TitaniQ geothermometry: rheological implications for the anatectic domain of the Araçuaí belt, eastern Brazil

Solid Earth ◽  
2014 ◽  
Vol 5 (2) ◽  
pp. 1223-1242 ◽  
Author(s):  
G. C. G. Cavalcante ◽  
A. Vauchez ◽  
C. Merlet ◽  
M. Egydio-Silva ◽  
M. H. Bezerra de Holanda ◽  
...  
Keyword(s):  
Partial Melting ◽  
Flow Direction ◽  
Regional Scale ◽  
Thermal Conditions ◽  
Middle Crust ◽  
Low Viscosity ◽  
Lateral Extrusion ◽  
Eastern Brazil ◽  
Gravity Driven ◽  
Gravity Driven Flow

Abstract. During the Neoproterozoic orogeny, the middle crust of the Araçuaí belt underwent widespread partial melting. At the regional scale, this anatectic domain is characterized by a progressive rotation of the flow direction from south to north, suggesting a 3-D deformation of the anatectic middle crust. To better determine whether melt volumes present in the anatectic middle crust of the Araçuaí orogen were large enough to allow a combination of gravity-driven and convergence-driven deformation, we used the titanium-in-quartz (TitaniQ) geothermometer to estimate the crystallization temperatures of quartz grains in the anatectic rocks. When possible, we compared these estimates with thermobarometric estimates from traditional exchange geothermobarometers applied to neighboring migmatitic kinzigites. TitaniQ temperatures range from 750 to 900 °C, suggesting that quartz starts crystallizing at minimum temperatures of ≥ 800 °C. These results, combined with the bulk-rock chemical composition of diatexites, allows the estimation of a minimum of ~ 30% melt and a corresponding viscosity of ~ 109–1010 Pa s. Such a minimum melt content and low viscosity are in agreement with interconnected melt networks observed in the field. Considering that these characteristics are homogeneous over a wide area, this supports the finding that the strength of the middle crust was severely weakened by extensive partial melting, making it prone to gravity-driven flow and lateral extrusion.

Archean granitoids of the Aravalli Craton, northwest India

2020 ◽  
Vol 489 (1) ◽  
pp. 215-234 ◽  
Author(s):  
Iftikhar Ahmad ◽  
M. E. A. Mondal ◽  
Md Sayad Rahaman ◽  
Rajneesh Bhutani ◽  
M. Satyanarayanan
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Mantle Wedge ◽  
Nd Isotope ◽  
Oceanic Plateau ◽  
Slab Breakoff ◽  
Northwest India ◽  
Aravalli Craton ◽  
Metasomatized Mantle ◽  
Asthenospheric Upwelling

AbstractThe Archean granitoids of the Aravalli Craton (NW India) are represented by orthogneisses (3.3–2.6 Ga) and undeformed granitoids (c. 2.5 Ga). Here we present whole-rock geochemical (elemental and Nd-isotope) data of the granitoids from the Aravalli Craton with an aim of understanding the evolution of the continental crust during the Archean. These Archean granitoids have been classified into three compositional groups: (1) TTG – tonalite–trondhjemite–granodiorite; (2) t-TTG – transitional TTG; and (3) sanukitoids. Based on the geochemical characteristics, it is proposed that the TTGs have formed from the partial melting of subducting oceanic plateau. The t-TTG formed owing to reworking of an older continental crust (approximately heterogeneous) in response to tectonothermal events in the craton. For the formation of the sanukitoids, a two-stage petrogenetic model is invoked which involves metasomatization of the mantle wedge, followed by slab breakoff and asthenospheric upwelling, which leads to the melting of asthenosphere and the metasomatized mantle wedge. It is also proposed that subducted sediments contributed to the genesis of sanukitoid magma.

Crustal melt granites and migmatites along the Himalaya: melt source, segregation, transport and granite emplacement mechanisms

2009 ◽  
Vol 100 (1-2) ◽  
pp. 219-233 ◽  
Author(s):  
M. P. Searle ◽  
J. M. Cottle ◽  
M. J. Streule ◽  
D. J. Waters
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Internal Heat ◽  
Shear Zones ◽  
Source Rocks ◽  
Crustal Thickening ◽  
Main Central Thrust ◽  
Crustal Layer ◽  
Middle Crust ◽  
The Himalaya

ABSTRACTIndia–Asia collision resulted in crustal thickening and shortening, metamorphism and partial melting along the 2200 km-long Himalayan range. In the core of the Greater Himalaya, widespread in situ partial melting in sillimanite+K-feldspar gneisses resulted in formation of migmatites and Ms+Bt+Grt+Tur±Crd±Sil leucogranites, mainly by muscovite dehydration melting. Melting occurred at shallow depths (4–6 kbar; 15–20 km depth) in the middle crust, but not in the lower crust. 87Sr/86Sr ratios of leucogranites are very high (0·74–0·79) and heterogeneous, indicating a 100 crustal protolith. Melts were sourced from fertile muscovite-bearing pelites and quartzo-feldspathic gneisses of the Neo-Proterozoic Haimanta–Cheka Formations. Melting was induced through a combination of thermal relaxation due to crustal thickening and from high internal heat production rates within the Proterozoic source rocks in the middle crust. Himalayan granites have highly radiogenic Pb isotopes and extremely high uranium concentrations. Little or no heat was derived either from the mantle or from shear heating along thrust faults. Mid-crustal melting triggered southward ductile extrusion (channel flow) of a mid-crustal layer bounded by a crustal-scale thrust fault and shear zone (Main Central Thrust; MCT) along the base, and a low-angle ductile shear zone and normal fault (South Tibetan Detachment; STD) along the top. Multi-system thermochronology (U–Pb, Sm–Nd, 40Ar–39Ar and fission track dating) show that partial melting spanned ̃24–15 Ma and triggered mid-crustal flow between the simultaneously active shear zones of the MCT and STD. Granite melting was restricted in both time (Early Miocene) and space (middle crust) along the entire length of the Himalaya. Melts were channelled up via hydraulic fracturing into sheeted sill complexes from the underthrust Indian plate source beneath southern Tibet, and intruded for up to 100 km parallel to the foliation in the host sillimanite gneisses. Crystallisation of the leucogranites was immediately followed by rapid exhumation, cooling and enhanced erosion during the Early–Middle Miocene.

scholarly journals Petrogenesis of Secondary Diatexites and the Melt Budget for Crustal Reworking

2020 ◽  
Vol 61 (3) ◽  
Author(s):  
E W Sawyer
Keyword(s):  
Mass Balance ◽  
Partial Melting ◽  
Rock Type ◽  
Granulite Facies ◽  
Initial Amount ◽  
Middle Crust ◽  
Rock Types ◽  
Mass Balance Models ◽  
Crustal Reworking

Abstract This study investigates the petrogenesis of diatexite migmatites and leucogranites in a granulite facies terrain and quantifies the melt budget for it. The anatectic rock types in the Ashuanipi Subprovince are: (1) melt-depleted orthopyroxene metatexite migmatite, (2) secondary diatexite migmatite formed where anatectic melt intruded, entrained and accumulated in the metatexite, and (3) leucogranite. The FeO, MgO, TiO2, Cr, Co and Sc contents of the diatexites are controlled by the fraction of entrained metatextite. However, most diatexites and many leucogranites are richer in (Na2O+CaO) but depleted in K2O relative to an anatectic melt + metatexite mixture. This, and the predominance of plagioclase + orthopyroxene frameworks in the diatexites, indicates loss of fractionated melt. Mass-balance models using the metatexite and compositions of fractionated melts and crystallised solids obtained from simulated crystallisation of the anatectic melt indicate that ‘typical’ diatexite formed by mixing ∼40% metatexite with ∼60% anatectic melt, and then when 8 to 30% crystallised, most (>73%) of the remaining melt was expelled, likely by shear-enhanced compaction. The processes making the diatexites and leucogranites expelled ∼50% of the initial amount of melt; some formed the K2O-rich leucodiatexites and leucogranites in the terrain, but most escaped. A melt budget for the present Ashuanipi surface made by combining mass-balance calculations and the area of each rock type reveals that it once held 3.05 times more melt than was generated there. The adjacent Opinaca Subprovince contains 10 times more leucogranite than partial melting there produced; moreover, its leucogranites are compositionally similar to fractionated melts expelled from the Ashuanipi. Combining these crustal levels and assuming a gradient of 30oC km-1, then ∼400 000 km3 of melt representing >68% of the total generated during crustal reworking in the Ashuanipi remained in the middle crust where temperatures were above the solidus.

U–Pb geochronology, Nd–Sm geochemistry, structural setting, and tectonic significance of Late Devonian and Paleogene intrusions in northern Yukon and northeastern Alaska

2019 ◽  
Vol 56 (6) ◽  
pp. 585-606
Author(s):  
Larry S. Lane ◽  
James K. Mortensen
Keyword(s):  
Partial Melting ◽  
Ocean Basin ◽  
Volcanic Edifice ◽  
Late Devonian ◽  
Upper Crust ◽  
Upward Migration ◽  
Middle Crust ◽  
Structural Setting ◽  
Magmatic Underplating ◽  
Tectonic Significance

A suite of six Devonian granites and one syenite were emplaced into the upper crust of northern Yukon between 364.8 ± 2.7 and 371.2 ± 1.4 Ma. The Bear Mountain syenite and related rhyolite porphyry in adjacent Alaska intruded at 52.3 ± 0.4 and 53.5 ± 0.2 Ma, respectively. A felsic volcaniclastic unit and quartz-phyric sill are newly documented adjacent to the Mount Sedgwick granite. The volcaniclastic unit may indicate the presence of a related volcanic edifice. The presence of xenocrystic zircon grains in most of the intrusions suggests initial emplacement of magmas began 10–20 Myr before final emplacement into the upper crust. A Famennian final intrusion age coincides with Late Devonian encroachment of Ellesmerian deformation into the region. Attendant crustal flexure, or evolving foreland structures, may have facilitated upward migration of the magmas. Geochemistry of the intrusions indicates that the Devonian magmatism was largely derived from partial melting of lower and middle crust, implying widespread mafic magmatic underplating in Middle to Late Devonian time. Only Dave Lord syenite retains evidence of an original mantle geochemical signature. Mantle underplating may have played a role in localizing extension, volcanism, and rifting that led to the Late Devonian opening of the Angayucham ocean basin. The Eocene Bear Mountain pluton is inferred to be a northerly example of widespread Cenozoic within-plate magmatism in Alaska.

Multiphase melting, magma emplacement and P-T-time path in late-collisional context: the Velay example (Massif Central, France)

2015 ◽  
Vol 186 (2-3) ◽  
pp. 93-116 ◽  
Author(s):  
Pierre Barbey ◽  
Arnaud Villaros ◽  
Christian Marignac ◽  
Jean-Marc Montel
Keyword(s):  
Partial Melting ◽  
Temperature Drop ◽  
Path Following ◽  
Thermal Anomaly ◽  
Stability Field ◽  
Complete Disappearance ◽  
Massif Central ◽  
Radiogenic Heat ◽  
Middle Crust ◽  
Magma Emplacement

AbstractThe West European Variscan chain is a remarkable illustration of how partial melting marks out the geodynamic evolution of mountain belt through time. Here, we focus on the Late Carboniferous melting events reported in the southeastern French Massif Central (Velay dome), with emphasis on the modes of partial melting, relationships between partial melting and magma emplacement, transition between the melting episodes and related P-T-t path. Following nappe stacking events under medium pressure/temperature conditions (M1 and M2 events), three melting events are identified in the southern envelope of the Velay dome. A first melting episode (M3 event) occurred within the biotite stability field at 325–315 Ma (T ≈ 720°C and P = 0.5–0.6 GPa). It led to the complete disappearance of muscovite and to the formation of migmatites consisting of biotite ± sillimanite melanosome and of granitic/tonalitic leucosomes depending on protolith composition. It is interpreted as the result of internal heating mainly linked to decay of heat producing elements accumulated in a thickened crust. It resulted in the formation of a partially molten middle crust with decoupling between the lower and upper crust, late-collisional extension and crustal thinning.The second episode of melting (M4 event) occurred at ca. 304 Ma (T 800°C and P 0.4 GPa), synchronously with emplacement of the Velay granites and growth of the dome. It led to the breakdown of biotite and growth of cordierite (locally garnet or tourmaline), with formation of diatexites and heterogeneous granites. This high-T event synchronous with crustal extension is considered to result from intrusion of hot mantle-derived and lower crustal magmas triggering catastrophic melting in the middle crust. This event ends with local retrograde hydrous melting within the stability field of biotite close to the solidus in response to local input of water during temperature drop in the late stage of emplacement of the Velay dome.The last evidence of melting in this area (M5 event) corresponds to emplacement of late granites generated under conditions estimated at ≈850°C and 0.4–0.6 GPa. They may have been generated from melting of specific lithologies triggered by injection of mafic magmas. These granites emplaced in a partly cooled crust (medium-grade conditions). The emplacement age of these granites is not well constrained (305–295 Ma) though they clearly post-date the Velay granites.The melting episodes in the Velay area and generation of granites appear to correspond to the conjunction between (i) the effects of collision-related crust thickening and (ii) those related to slab break off and asthenospheric mantle decompression melting. The driving process is mainly the internal radiogenic heat in a first stage, relayed by the propagation of a thermal anomaly initially located in the lower crust (M3 event), but which subsequently rose to the middle and upper crustal levels through magma transfer (M4 event). Overall, the Velay example is a remarkable illustration of the progressive dehydration and sterilisation of a thickened crustal segment. It documents how large amounts of granitic magmas can be produced at shallow crustal levels in relation to the injection of mantle-derived magmas.

scholarly journals Thermal conditions during deformation of partially molten crust from TitaniQ geothermometry: rheological implications for the anatectic domain of the Araçuaí belt, Eastern Brazil

2014 ◽  
Vol 6 (1) ◽  
pp. 1299-1333 ◽  
Author(s):  
G. C. G. Cavalcante ◽  
A. Vauchez ◽  
C. Merlet ◽  
M. Egydio-Silva ◽  
M. H. Bezerra de Holanda ◽  
...  
Keyword(s):  
Partial Melting ◽  
Flow Direction ◽  
Regional Scale ◽  
Thermal Conditions ◽  
Rock Composition ◽  
Middle Crust ◽  
Low Viscosity ◽  
Lateral Extrusion ◽  
Eastern Brazil ◽  
Gravity Driven

Abstract. During the Neoproterozoic orogeny, the middle crust of the Araçuaí belt underwent widespread partial melting. At the regional scale, this anatectic domain is characterized by a progressive rotation of the flow direction from South to North, suggesting a 3-D deformation of the anatectic middle crust. To better constrain whether melt volumes present in the anatectic middle crust of the Araçuaí orogen were large enough to allow a combination of gravity-driven and convergence-driven deformation, we used the titanium-in-quartz geothermometer (TitaniQ) to estimate the crystallization temperatures of quartz grains in the anatectic rocks. When possible, we compared these estimates with thermobarometric estimates from traditional exchange geothermobarometers applied to neighboring migmatitic kinzigites. TitaniQ temperatures range from 750 to 800 °C, suggesting that quartz start crystallizing at a minimum temperatures ≥800 °C. These results, combined with the bulk-rock composition of isolated leucosomes allow to estimate a minimum of ∼30% melt in the anatectic leucossomes and a corresponding viscosity of ∼109–110 Pa s. Such a minimum melt content and low viscosity are in agreement with interconnected melt networks observed in the field. Considering that these characteristics are homogeneous over a wide area, this supports that the strength of the middle crust was severely weaken by extensive partial melting turning it prone to gravity-driven channel flow and lateral extrusion.

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