Petrology of the Chilliwack batholith, North Cascades, Washington: generation of calc-alkaline granitoids by melting of mafic lower crust with variable water fugacity

1993 ◽  
Vol 113 (3) ◽  
pp. 333-351 ◽  
Author(s):  
Jeffrey H. Tepper ◽  
Bruce K. Nelson ◽  
George W. Bergantz ◽  
Anthony J. Irving
Keyword(s):  
Lower Crust ◽  
Calc Alkaline ◽  
North Cascades ◽  
Water Fugacity ◽  
Variable Water ◽  
Mafic Lower Crust

Latest Cretaceous “A2-type” granites in the Sakarya Zone, NE Turkey: Partial melting of mafic lower crust in response to roll-back of Neo-Tethyan oceanic lithosphere

Lithos ◽  
2018 ◽  
Vol 302-303 ◽  
pp. 312-328 ◽  
Author(s):  
Orhan Karsli ◽  
Faruk Aydin ◽  
Ibrahim Uysal ◽  
Abdurrahman Dokuz ◽  
Mustafa Kumral ◽  
...  
Keyword(s):  
Partial Melting ◽  
Lower Crust ◽  
Oceanic Lithosphere ◽  
Sakarya Zone ◽  
Roll Back ◽  
Mafic Lower Crust

Tectonic and magmatic evolution of the Aqishan-Yamansu belt: A Paleozoic arc-related basin in the Eastern Tianshan (NW China)

2020 ◽  
Author(s):  
Shuanliang Zhang ◽  
Huayong Chen ◽  
Pete Hollings ◽  
Liandang Zhao ◽  
Lin Gong
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Lower Crust ◽  
Early Carboniferous ◽  
Late Carboniferous ◽  
Igneous Rocks ◽  
Calc Alkaline ◽  
Eastern Tianshan ◽  
Depleted Mantle ◽  
T Values

The Aqishan-Yamansu belt in the Chinese Eastern Tianshan represents a Paleozoic arc-related basin generally accompanied by accretionary magmatism and Fe-Cu mineralization. To characterize the tectonic evolution of such an arc-related basin and related magmatism and metallogenesis, we present a systematic study of the geochronology, whole-rock geochemistry, and Sr-Nd isotopes of igneous rocks from the belt. New zircon U-Pb ages, in combination with published data, reveal three phases of igneous activity in the Aqishan-Yamansu belt: early Carboniferous felsic igneous rocks (ca. 350−330 Ma), late Carboniferous intermediate to felsic igneous rocks (ca. 320−305 Ma), and Permian quartz diorite and diorite porphyry dikes (ca. 280−265 Ma). The early Carboniferous felsic rocks are enriched in large ion lithophile elements (LILEs) and depleted in Nb, Ta, and Ti, showing arc-related magma affinities. Their positive εNd(t) values (3.3−5.9) and corresponding depleted mantle model ages (TDM) of 0.83−0.61 Ga, as well as high MgO contents, Mg# values, and Nb/Ta ratios, suggest that they were derived from lower crust with involvement of mantle-derived magmas. The late Carboniferous intermediate igneous rocks show calc-alkaline affinities, exhibiting LILE enrichment and high field strength element (HFSE) depletion, with negative Nb and Ta anomalies. They have high MgO contents and Mg# values with positive εNd(t) values (3.9−7.9), and high Ba/La and Th/Yb ratios, implying a depleted mantle source metasomatized by slab-derived fluids and sediment or sediment-derived melts. The late Carboniferous felsic igneous rocks are metaluminous to peraluminous with characteristics of medium-K calc-alkaline I-type granites. Given the positive εNd(t) values (6.3−6.6) and TDM ages (0.56−0.53 Ga), we suggest the late Carboniferous felsic igneous rocks were produced by partial melting of a juvenile lower crust. The Permian dikes show characteristics of adakite rocks. They have relatively high MgO contents and Mg# values, and positive εNd(t) values (7.2−8.5), which suggest an origin from partial melting of a residual basaltic oceanic crust. We propose that the Aqishan-Yamansu belt was an extensional arc−related basin from ca. 350 to 330 Ma; this was followed by a relatively stable carbonate formation stage at ca. 330−320 Ma, when the Kangguer oceanic slab subducted beneath the Central Tianshan block. As the subduction continued, the Aqishan-Yamansu basin closed due to slab breakoff and rebound during ca. 320−305 Ma, which resulted in basin inversion and the emplacement of granitoids with contemporary Fe-Cu mineralization. During the Permian, the Aqishan-Yamansu belt was in postcollision extension stage, with Permian adakitic dikes formed by partial melting of a residual oceanic crust.

Seismic imaging of the upper mantle beneath the Rocky Mountain foreland, southwestern Alberta

2000 ◽  
Vol 37 (11) ◽  
pp. 1493-1507 ◽  
Author(s):  
David W Eaton ◽  
Gerald M Ross ◽  
Frederick A Cook ◽  
A VanderVelden
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Rocky Mountain ◽  
Seismic Signal ◽  
Ductile Deformation ◽  
Crust And Upper Mantle ◽  
Western Canada Sedimentary Basin ◽  
Tectonic Belt ◽  
Canada Sedimentary Basin ◽  
Mafic Lower Crust

The Vibroseis Augmented Listen Time (VAuLT) experiment is a special seismic-reflection survey designed to image the fine-scale structure of the continental upper mantle of the Rocky Mountain foreland in southwestern Alberta to depths of 200 km or more. Two mutually perpendicular profiles were acquired across and within the Vulcan structure, a roughly east-west-trending tectonic belt in the crystalline basement beneath the Western Canada Sedimentary Basin that separates the Medicine Hat block from the Loverna block. Relative-amplitude-preserving processing procedures were developed to estimate the seismic-signal-penetration limit, which varies between 100 and 220 km depth. Amplitude-decay analysis and Q estimation show that a seismically unreflective zone within the Vulcan structure is not caused by inadequate signal penetration. This blank zone is interpreted as part of an intrusive complex that has overprinted the preexisting structural fabric. Unlike most other parts of Alberta, the reflection Moho is indistinct and the uppermost mantle (45–60 km depth) is reflective, particularly for source–receiver offsets >10 km. South-dipping reflectivity in the lower crust and upper mantle beneath the Loverna block and northern Vulcan structure gives way to subhorizontal reflectivity beneath the Medicine Hat block. We interpret this reflectivity as compositional layering and (or) zones of ductile deformation that were previously part of the mafic lower crust, but that have now undergone metamorphic transformation to eclogite. The deepest observed reflection is an isolated, gently north-dipping event at ~120 km depth.

Petrogenesis of the Ulungur Intrusive Complex, NW China, and Implications for Crustal Generation and Reworking in Accretionary Orogens

2020 ◽  
Vol 61 (2) ◽  
Author(s):  
Gong-Jian Tang ◽  
Qiang Wang ◽  
Derek A Wyman ◽  
Wei Dan ◽  
Lin Ma ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Lower Crust ◽  
Mineral Chemistry ◽  
Isotopic Signature ◽  
Source Rocks ◽  
Intrusive Complex ◽  
Calc Alkaline ◽  
Depleted Mantle ◽  
Heavy Rare Earth Elements ◽  
Pressure Crystallization

Abstract Accretionary orogens are characterized by voluminous juvenile components (recently derived from the mantle) and knowing the origin(s) of such components is vital for understanding crustal generation. Here we present field and petrological observations, along with mineral chemistry, zircon U–Pb age and Hf–O isotope data, and whole rock geochemical and Sr–Nd isotopic data for the c.320 Ma Ulungur intrusive complex from the Central Asian Orogenic Belt. The complex consists of two different magmatic series: one is characterized by medium- to high-K calc-alkaline gabbro to monzogranite; the other is defined by peralkaline aegirine–arfvedsonite granitoids. The calc-alkaline and peralkaline series granitoids have similar depleted mantle-like Sr–Nd–Hf isotopic compositions, but they have different zircon δ18O values: the calc-alkaline series have mantle-like δ18O values with mean compositions ranging from 5·2 ± 0·5‰ to 6·0 ± 0·9‰ (2SD), and the peralkaline granitoids have low δ18O values ranging from 3·3 ± 0·5‰ to 3·9 ± 0·4‰ (2SD). The calc-alkaline series were derived from a hydrous sub-arc mantle wedge, based on the isotope and geochemical compositions, under garnet peridotite facies conditions. This study suggests that the magmas underwent substantial differentiation, ranging from high pressure crystallization of ultramafic cumulates in the lower crust to lower pressure crystallization dominated by amphibole, plagioclase and minor biotite in the upper crust. The peralkaline series rocks are characterized by δ18O values lower than the mantle and enrichment of high field strength elements (HFSEs) and heavy rare earth elements (HREEs). They likely originated from melting of preexisting hydrothermally altered residual oceanic crust in the lower crust of the Junggar intra-oceanic arc. Early crystallization of clinopyroxene and amphibole was inhibited owing to their low melting temperature, leading to HFSEs and HREEs enrichment in residual peralkaline melts during crystallization of a feldspar-dominated mineral assemblage. Thus, the calc-alkaline and peralkaline series represent episodes of crust generation and reworking, respectively, demonstrating that the juvenile isotopic signature in accretionary orogens can be derived from diverse source rocks. Our results show that reworking of residual oceanic crust also plays an important role in continental crust formation for accretionary orogens, which has not previously been widely recognized.

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