scholarly journals Large-Scale Partial Melting of Deeply Subducted Continental Slab during Continental Collision: An Example from the Sulu Orogen

2020 ◽  
Author(s):  
He-Zhi Ma ◽  
Yi-Xiang Chen ◽  
Yong-Fei Zheng
Keyword(s):  
Partial Melting ◽  
Large Scale ◽  
Continental Collision

scholarly journals An anticlockwise metamorphic P-T path and nappe stacking in the Reisa Nappe Complex in the Scandinavian Caledonides, northern Norway: evidence for weakening of lower continental crust before and during continental collision

2018 ◽  
Author(s):  
Carly Faber ◽  
Holger Stünitz ◽  
Deta Gasser ◽  
Petr Jeřábek ◽  
Katrin Kraus ◽  
...  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Large Scale ◽  
Structural Data ◽  
Geothermal Gradient ◽  
Continental Collision ◽  
Crustal Thickening ◽  
Northern Norway ◽  
Nappe Complex ◽  
T Path

Abstract. This study investigates the Caledonian metamorphic and tectonic evolution in northern Norway, examining the structure and tectonostratigraphy of the Reisa Nappe Complex (RNC; from bottom to top, Vaddas, Kåfjord and Nordmannvik nappes). Structural data, phase equilibrium modelling, and U-Pb zircon and titanite geochronology are used to constrain the timing and P-T conditions of deformation and metamorphism that formed the nappes and facilitated crustal thickening during continental collision. Five samples taken from different parts of the RNC reveal an anticlockwise P-T path attributed to the effects of early Silurian heating followed by thrusting. An early Caledonian S1 foliation in the Nordmannvik Nappe records kyanite-grade partial melting at ~ 760–790 °C and ~ 9.4–11 kbar. Leucosomes formed at 439 ± 2 Ma (U-Pb zircon) in fold axial planes in the Nordmannvik Nappe indicate that compressional deformation initiated while the rocks were still partially molten. This stage was followed by pervasive solid-state shearing as the rocks cooled and solidified, forming the S2 foliation at 680–730 °C and 9.5–10.9 kbar. Multistage titanite growth in the Nordmannvik Nappe records this extended metamorphism between 444 and 427 Ma. In the underlying Kåfjord Nappe, garnet cores record lower P-T (590–610 °C and 5.5–6.8 kbar) but a similar geothermal gradient as the S1 migmatitic event in the Nordmannvik Nappe, indicating formation at a higher relative position in the crust. S2 shearing in the Kåfjord Nappe occurred at 580–605 °C and 9.2–10.1 kbar, indicating a considerable pressure increase during nappe stacking. Gabbro intruded in the Vaddas Nappe at 439 ± 1 Ma, synchronously with migmatization in the Nordmannvik Nappe. In the Vaddas Nappe S2 shearing occurred at 630–640 ºC and 11.7–13 kbar. Titanite growth along the lower RNC boundary records S2-shearing at 432 ± 6 Ma. It emerges that early Silurian heating (~ 440 Ma), probably resulting from large-scale magma underplating, initiated partial melting that weakened the lower crust, which facilitated dismembering of the crust into individual nappe units. This tectonic style contrasts subduction of mechanically strong continental crust to great depths.

scholarly journals Anticlockwise metamorphic pressure–temperature paths and nappe stacking in the Reisa Nappe Complex in the Scandinavian Caledonides, northern Norway: evidence for weakening of lower continental crust before and during continental collision

Solid Earth ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 117-148 ◽  
Author(s):  
Carly Faber ◽  
Holger Stünitz ◽  
Deta Gasser ◽  
Petr Jeřábek ◽  
Katrin Kraus ◽  
...  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Large Scale ◽  
Structural Data ◽  
Continental Collision ◽  
Crustal Thickening ◽  
Western Gneiss Region ◽  
Nappe Complex ◽  
T Path ◽  
Tectonic Style

Abstract. This study investigates the tectonostratigraphy and metamorphic and tectonic evolution of the Caledonian Reisa Nappe Complex (RNC; from bottom to top: Vaddas, Kåfjord, and Nordmannvik nappes) in northern Troms, Norway. Structural data, phase equilibrium modelling, and U-Pb zircon and titanite geochronology are used to constrain the timing and pressure–temperature (P–T) conditions of deformation and metamorphism during nappe stacking that facilitated crustal thickening during continental collision. Five samples taken from different parts of the RNC reveal an anticlockwise P–T path attributed to the effects of early Silurian heating (D1) followed by thrusting (D2). At ca. 439 Ma during D1 the Nordmannvik Nappe reached the highest metamorphic conditions at ca. 780 ∘C and ∼9–11 kbar inducing kyanite-grade partial melting. At the same time the Kåfjord Nappe was at higher, colder, levels of the crust ca. 600 ∘C, 6–7 kbar and the Vaddas Nappe was intruded by gabbro at > 650 ∘C and ca. 6–9 kbar. The subsequent D2 shearing occurred at increasing pressure and decreasing temperatures ca. 700 ∘C and 9–11 kbar in the partially molten Nordmannvik Nappe, ca. 600 ∘C and 9–10 kbar in the Kåfjord Nappe, and ca. 640 ∘C and 12–13 kbar in the Vaddas Nappe. Multistage titanite growth in the Nordmannvik Nappe records this evolution through D1 and D2 between ca. 440 and 427 Ma, while titanite growth along the lower RNC boundary records D2 shearing at 432±6 Ma. It emerges that early Silurian heating (ca. 440 Ma) probably resulted from large-scale magma underplating and initiated partial melting that weakened the lower crust, which facilitated dismembering of the crust into individual thrust slices (nappe units). This tectonic style contrasts with subduction of mechanically strong continental crust to great depths as seen in, for example, the Western Gneiss Region further south.

Origin of syn-collisional granitoids in the Gangdese orogen: Reworking of the juvenile arc crust and the ancient continental crust

2021 ◽  
Author(s):  
Yu-Wei Tang ◽  
Long Chen ◽  
Zi-Fu Zhao ◽  
Yong-Fei Zheng
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Continental Collision ◽  
Late Eocene ◽  
Igneous Rocks ◽  
Early Eocene ◽  
Southern Tibet ◽  
Crustal Rocks ◽  
Mafic Magmas ◽  
T Values

Granitoids at convergent plate boundaries can be produced either by partial melting of crustal rocks (either continental or oceanic) or by fractional crystallization of mantle-derived mafic magmas. Whereas granitoid formation through partial melting of the continental crust results in reworking of the pre-existing continental crust, granitoid formation through either partial melting of the oceanic crust or fractional crystallization of the mafic magmas leads to growth of the continental crust. This category is primarily based on the radiogenic Nd isotope compositions of crustal rocks; positive εNd(t) values indicate juvenile crust whereas negative εNd(t) values indicate ancient crust. Positive εNd(t) values are common for syn-collisional granitoids in southern Tibet, which leads to the hypothesis that continental collision zones are important sites for the net growth of continental crust. This hypothesis is examined through an integrated study of in situ zircon U-Pb ages and Hf isotopes, whole-rock major trace elements, and Sr-Nd-Hf isotopes as well as mineral O isotopes for felsic igneous rocks of Eocene ages from the Gangdese orogen in southern Tibet. The results show that these rocks can be divided into two groups according to their emplacement ages and geochemical features. The first group is less granitic with lower SiO2 contents of 59.82−64.41 wt%, and it was emplaced at 50−48 Ma in the early Eocene. The second group is more granitic with higher SiO2 contents of 63.93−68.81 wt%, and it was emplaced at 42 Ma in the late Eocene. The early Eocene granitoids exhibit relatively depleted whole-rock Sr-Nd-Hf isotope compositions with low (87Sr/86Sr)i ratios of 0.7044−0.7048, positive εNd(t) values of 0.6−3.9, εHf(t) values of 6.5−10.5, zircon εHf(t) values of 1.6−12.1, and zircon δ18O values of 5.28−6.26‰. These isotopic characteristics are quite similar to those of Late Cretaceous mafic arc igneous rocks in the Gangdese orogen, which indicates their derivation from partial melting of the juvenile mafic arc crust. In comparison, the late Eocene granitoids have relatively lower MgO, Fe2O3, Al2O3, and heavy rare earth element (HREE) contents but higher K2O, Rb, Sr, Th, U, Pb contents, Sr/Y, and (La/Yb)N ratios. They also exhibit more enriched whole-rock Sr-Nd-Hf isotope compositions with high (87Sr/86Sr)i ratios of 0.7070−0.7085, negative εNd(t) values of −5.2 to −3.9 and neutral εHf(t) values of 0.9−2.3, and relatively lower zircon εHf(t) values of −2.8−8.0 and slightly higher zircon δ18O values of 6.25−6.68‰. An integrated interpretation of these geochemical features is that both the juvenile arc crust and the ancient continental crust partially melted to produce the late Eocene granitoids. In this regard, the compositional evolution of syn-collisional granitoids from the early to late Eocene indicates a temporal change of their magma sources from the complete juvenile arc crust to a mixture of the juvenile and ancient crust. In either case, the syn-collisional granitoids in the Gangdese orogen are the reworking products of the pre-existing continental crust. Therefore, they do not contribute to crustal growth in the continental collision zone.

scholarly journals Volatile-rich melts as markers of the asthenospheric influx prior to rifting events: the case of the alkaline-carbonatitic lamprophyres of the Dolomitic Area (Southern Alps, Italy)

2020 ◽  
Author(s):  
Federico Casetta ◽  
Ryan B. Ickert ◽  
Darren F. Mark ◽  
Costanza Bonadiman ◽  
Pier Paolo Giacomoni ◽  
...  
Keyword(s):  
Partial Melting ◽  
Large Scale ◽  
Southern Alps ◽  
Ne Italy ◽  
Enriched Mantle ◽  
New Findings ◽  
Geodynamic Processes ◽  
Alkaline Magmas ◽  
And Behavior

<p>The appearance of alkali- and volatile-rich melts often marks the opening of major magmatic cycles, always reflecting the partial melting of heterogeneously enriched mantle domains. In these cases the study of highly alkaline, H<sub>2</sub>O-CO<sub>2</sub>-rich magmatic pulses provide important insights on the composition and behavior of the sub-continental lithospheric mantle (SCLM) prior to rift initiation. The camptonitic dykes cropping out at Predazzo (Dolomitic Area, NE Italy) are among the oldest examples of lamprophyric rocks in Italy, and were historically related to the orogenic-like Middle Triassic magmatism of the Southern Alps. A detailed petrological, geochemical and geochronological characterization of these rocks was developed to frame them inside the articulated geodynamic evolution of the Southern Alps domain during Triassic. Whole-rock and mineral phase geochemistry, together with <sup>40</sup>Ar/<sup>39</sup>Ar data showed that Predazzo lamprophyres represent an alkaline-carbonatitic magmatic event temporally isolated (~220 Ma) from the major Ladinian orogenic-like magmatism of the Southern Alps (~238 Ma). Lamprophyres can thus be attributed to the volumetrically limited alkaline magmatic phase that infiltrated several portions of the Southern Alps lithosphere between 225 and 190 Ma. Partial melting models and Sr-Nd isotopes demonstrate that Predazzo lamprophyres were produced by low partial melting degree of a garnet-amphibole-bearing mantle source interacting with a significant asthenospheric contribution. In the light of these new findings, they are interpreted as the geochemical/geochronological bridge between the orogenic-like Ladinian magmatism and the rifting phase related to the opening of the Alpine Tethys. This study highlights the paramount importance of alkaline magmas for tracking the volatiles cycle in the SCLM and the potential lithosphere-asthenosphere interactions during large-scale geodynamic processes.</p>

The Kamusite A2-type granites in the Karamaili tectonic belt, Xinjiang (NW China): tracing staged postcollisional delamination in the eastern Junggar

2020 ◽  
pp. 1-26
Author(s):  
Bowen Zhang ◽  
Chuan Chen ◽  
Xiaoping Gong ◽  
Yaxiaer Yalikun ◽  
Kadeliya Kaheman
Keyword(s):  
Partial Melting ◽  
Large Scale ◽  
Late Carboniferous ◽  
Zircon Geochronology ◽  
High Field Strength ◽  
Original Source ◽  
Type Granite ◽  
Juvenile Crust ◽  
Tectonic Belt ◽  
Extensional Setting

Abstract The Kamusite pluton is located in the eastern Junggar area, the westernmost segment of the Karamaili structural belt, and is predominantly composed of medium granite and microgranite with an exposure area of 30 km2. The U–Pb zircon geochronology of the Kamusite granites indicates that they crystallized in the late Carboniferous period (328–321 Ma). These granites exhibit high contents of SiO2 (76.09–77.85 wt %) and K2O + Na2O (8.01–9.06 wt %), but low MgO (0.01–0.14 wt %), CaO (0.07–0.32 wt %) and TiO2 (0.01–0.13 wt %) contents, showing alkalic–calcic, weakly peraluminous and ferroan features. They are depleted in Ba, Sr, Ti and P and enriched in Rb and some high-field-strength elements (Hf, Nd, Ta and Y); their rare earth element patterns are slightly right-leaning with strongly negative Eu anomalies, high 10 000 * Ga/Al (3.4–5.36, >2.6) and especially high Y/Nb ratios (1.61–10.33, >1.2), showing the geochemical characteristics of A2-type granite. These granites were produced by partial melting in a high-temperature, low-pressure, reduced and anhydrous environment and experienced extensive fractional crystallization, which concomitantly resulted in tin mineralization. Combining the high positive zircon ϵHf(t) values of +10.9 to +15.76 with young Hf (TDM2) model ages (638–330 Ma), it can be suggested that underplating-related mantle-derived materials were the original source of the Kamusite A2-type granites; namely, these granites formed by the partial melting of juvenile crust. The record of large-scale magmatism indicates that the whole tectonic belt was in a postcollisional extensional setting induced by staged delamination from west to east during the late Carboniferous to early Permian periods.

scholarly journals Petrogenesis and Tectonic Implications of the Early Cretaceous Granitic Pluton in the Sulu Orogenic Belt: The Caochang Granitic Pluton as an Example

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 432
Author(s):  
Yuanku Meng ◽  
Zhongbo Wang ◽  
Baoping Gan ◽  
Jinqing Liu
Keyword(s):  
Partial Melting ◽  
Early Cretaceous ◽  
Large Scale ◽  
Eastern China ◽  
Orogenic Belt ◽  
Crustal Material ◽  
Granitic Pluton ◽  
Tectonic Implications ◽  
Type Granite ◽  
Sulu Orogenic Belt

The Sulu orogenic belt is the source of information on important magmatic events associated with the collision of the Yangtze craton and North China craton (NCC) and the destruction of the NCC during the Mesozoic in eastern China. In this study, we have, for the first time, identified a monzonitic granitic pluton. We hereby present petrological, geochemical, and zircon U-Pb-Hf-O isotopic data, shedding new light on the petrogenesis and tectonic implications for the granitic pluton in the Sulu belt. LA-ICP-MS and SHRIMP II analyses of zircon grains suggest that the monzonitic granitic pluton was crystallized in the Early Cretaceous (ca. 120 Ma). Geochemically, the granitic pluton shows sub-alkaline, high-K calc-alkaline, and metaluminous signatures, and is genetically of I-type granite, excluding the possibility of S-type granite, as evidenced by mantle-like zircon oxygen isotopic features. In addition, the pluton is enriched in light REE and large-ion lithophile elements (LILE) (e.g., La, Cs, Ba, K, and Pb), but depleted in high-field-strength elements (HFSE) (e.g., Nb, Ta, P, and Ti), suggesting an arc-related affinity. Zircon Hf isotopes (εHf(t) = −27.51~−32.35; TDM2 = 2979~3175 Ma) and mantle-like δ18O values (5.12–6.24‰) together indicate that the identified granitic pluton is derived from the partial melting (reworking) of the ancient mafic lower crustal material, with no supra-crustal material participation. Moreover, high Magnesium number (Mg# = 42–49) values and mafic micro-granular enclaves suggest that mantle-derived magma participated in the evolution of the granitic pluton in this study. Integrating the findings of this study and previous work, we propose that the Caochang granitic pluton is derived from the partial melting of the deep Yangtze basaltic lower crust during the Early Cretaceous, and that the large-scale thinning of the lithospheric mantle was the main factor that led to Early Cretaceous magmatic flare-up in the Sulu orogenic belt.

The Early Cretaceous tectonic evolution of the southern Great Xing'an Range, NE China: New constraints from A2-type granite and monzodiorite

2021 ◽  
Author(s):  
Chenghan Xu ◽  
Fengyue Sun ◽  
Xingzhu Fan ◽  
Liang Huo ◽  
Depeng Yang ◽  
...  
Keyword(s):  
Partial Melting ◽  
Early Cretaceous ◽  
Tectonic Evolution ◽  
Large Scale ◽  
Crustal Contamination ◽  
Stress Regime ◽  
Slab Breakoff ◽  
Significant Addition ◽  
Cretaceous Magmatism ◽  
Great Xing’An Range

The widespread Early Cretaceous plutons intruding along the southern Great Xing’an Range (SGXR) provide evidence for tectonic evolution of the region. Petrological, geochemical, zircon U–Pb geochronology and zircon Hf isotopic studies are conducted on intrusions from Bianjiadayuan and Hongling areas. These suites classify as A2-type granites and monzodiorites, respectively. The 138–133 Ma A2-type granites originated from partial melting of continental crustal materials at high temperatures and shallow depths with significant addition of juvenile mafic lower crust sourced from a metasomatized mantle. The 136–134 Ma monzodiorites originated from the partial melting of an enriched mantle that was modified by melts of a previously subducted slab coupled with crustal contamination. The Early Cretaceous magmatism in the SGXR occurred in two periods: ∼145–136 Ma (peak at ∼139 Ma; εHf (t) = 5 to 10) and ∼136–130 Ma (peak at ∼131 Ma; εHf (t) = −10 to 15). The Early Cretaceous granite–monzodiorite suite in the SGXR suggests a bimodal magmatism in an extensional setting. The ∼145–130 Ma magmatism may have been triggered by asthenospheric upwelling induced by the Mongol–Okhotsk oceanic slab breakoff and large-scale lithospheric delamination resulting from post-orogenic extension. The variation of subduction direction of the Paleo-Pacific Ocean likely triggered a change in stress regime at ca. 136 Ma and likely promoted the lithospheric delamination beneath the SGXR resulting in intense magmatism originating from various sources. As such, the Paleo-Pacific Oceanic subduction likely played an important role in the Early Cretaceous magmatism in the SGXR.

Trench Advance in Collisional settings: insights from large scale 2D and 3D models

2021 ◽  
Author(s):  
Arijit Laik ◽  
Wouter P. Schellart ◽  
Vincent Strak
Keyword(s):  
Large Scale ◽  
Driving Forces ◽  
3D Models ◽  
Continental Collision ◽  
Mantle Flow ◽  
Natural Systems ◽  
Mantle Reservoir ◽  
Spatio Temporal ◽  
Mountain Belts ◽  
2D And 3D

<p>Continental collision, which leads to mountain building (e.g. Himalayas, Alps), has been under the geodynamic modelling lenses for the last few decades. Such processes subjected to physical and numerical investigations, in conjunction with observational studies, enrich knowledge on mountain belts and have worked out the general architectural large-scale structure and crustal shortening in such regions. The intent to understand the driving forces of long term (~50 Ma) and consistent convergence at the India-Eurasia collisional zone is the goal of the dynamic self-consistent buoyancy-driven whole-mantle scale 2D and 3D models presented in this contribution. The maximum post-collisional convergence rate (~0.362 cm/year) in 2D models, is less than 2 cm/year convergence of India considering it advanced ~1000 km in about 50 Ma.  Additionally, the 2D models are inadequate in exploring the spatio-temporal evolution and dynamics of natural systems, thus necessitating modelling large scale subduction and subsequent continental collision resolving the 3D components of mantle flow.  With a whole mantle reservoir and buoyancy-driven 2D models, the observed trench advance rate, with a large and fixed overriding plate, is relatively novel and higher than previous studies and the high resolution in 2D models also shows crustal-scale localisation in conjunction with large scale mantle flow. The computationally intensive simulations have significantly large (11520 km) trench-perpendicular (in 2D and 3D) and parallel (in 3D) lengths, include two sets of modelled depths: whole mantle (2880 km) and, upper mantle + partial lower mantle (960 km) and use the Underworld2 framework. In 3D, the interaction of an adjacent subducting oceanic plate(s) significantly aids the indentation and trench advance in the collisional margin. These would help understand the dynamics of analogues system(s) in nature such as the Sunda subduction zone and the India-Eurasia collision zone.</p>

Geochronology, isotopic and Platinum-group elemental geochemistry of lavas and dykes from the western Guangxi in outer zone of Emeishan mantle plume, SW China

2021 ◽  
Author(s):  
Bing Zhao ◽  
Xijun Liu ◽  
Zhenglin Li ◽  
Wenmin Huang ◽  
Chuan Zhao
Keyword(s):  
Partial Melting ◽  
Mantle Source ◽  
Large Scale ◽  
Outer Zone ◽  
Large Igneous Province ◽  
Yangtze Block ◽  
Mafic Rocks ◽  
Emeishan Large Igneous Province ◽  
Low Degree ◽  
Igneous Province

<p>The Emeishan flood basalts are part of an important large igneous province along the western margin of the Yangtze Block, Southwest China. The western Guangxi region in southwestern China is geologically a part of the Yangtze Block. Mafic rocks, comprising mainly lavas and dykes in western Guangxi belong to the outer part of the ~260 Ma Emeishan Large Igneous Province (ELIP). Here we present a systematic study of platinum-group elements (PGEs) combined with the LA-ICP-MS zircon U–Pb age, whole-rock geochemical and isotopic data of the lavas and dykes in the Longlin area of outer zone of ELIP to constraints on their origin. On the basis of petrography and major elements characteristics, mafic lavas and dykes display an enrichment of LREE, LILE, HFSE, high (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub> ratios (0.704227~0.705754), low ε<sub>Nd</sub><sub>(t)</sub> values(0.42~0.99), high ε<sub>Hf</sub><sub>(t)</sub> values(5.19~6.04), they are similar to those of Permian Emeishan high-Ti basalts and Ocean island basalts (OIB) features. The Longlin mafic rocks was formed in the Late Permian with the zircon U-Pb dated age of 256.3± 1.7 Ma. The age of the Longlin mafic rocks is close to the formation age of the ELIP large-scale magmatism, suggesting that these lavas and dykes probably belongs to part of the ELIP large-scale magmatism. The Longlin mafic rocks have low total PGE contents ranging from 1.56×10<sup>-9 </sup>to 2.28×10<sup>-9</sup>, with Os, Ir, Ru, Rh, Pt and Pd contents of 0.040~0.076, 0.046~0.076, 0.027~0.079, 0.037~0.056, 0.6374~1.053 and 0.715~1.021ppb, respectively. They show left-leaning primitive mantle-normalized PGE patterns with depletion in Iridium group(IPGE) and enrichment in Palladium group, which also have lower contents than mafic rocks from the inner zone of the ELIP, suggesting that a low degree of partial melting of the mantle source plays an important role. The Longlin mafic rocks exhibit a marked increase in Cu/Pd ratios (>10<sup>5</sup>,84655 to 174785) albeit with a narrow range of lower Pd/Ir ratios (<50,13.4 to 18.7), different from the PGE-enriched basalts of the Siberian Traps, Emeishan Large Igneous Province (ELIP), East Greenland CFBs and Deccan Traps, indicating that their parent magmas was significantly depleted in chalcophile elements. Calculations based on the available trace element geochemistry reveal that the basalts were originated by low degree of partial melting(<5%)，with sulfides remain in the mantle during partial melting. Sulfide segregation could not happen during the evolution of the Longlin mafic rocks, due to the fact that neither significant fractional crystallization nor crustal contamination has been involved in their formation. Overall, mafic rocks from the outer zone of the ELIP show lower PGE contents than those in the inner zones, we find that the PGE contents in igneous rocks are related with the degrees of partial melting in the mantle source and the removal of sulfides before their emplacement.</p><p>This study was financially supported by the Guangxi Natural Science Foundation for Distinguished Young Scholars (2018GXNSFFA281009) and the Fifth Bagui Scholar Innovation Project of Guangxi Province (to XU Ji-feng).</p>

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