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Triassic lithospheric modification of the northern North China Craton: Evidences from the composite Kalaqin Batholith and ultramafic-mafic Heilihe Intrusive Complex in Inner Mongolia
- Source :
- Lithos. :105501
- Publication Year :
- 2020
- Publisher :
- Elsevier BV, 2020.
-
Abstract
- Whole rock major and trace elements and Sr-Nd-Hf isotopes and zircon in situ U Pb ages and Hf O isotopes have been determined for the Kalaqin granitic batholith and Heilihe Intrusive Complex (HIC) on the northern margin of the North China Craton (NCC), to investigate their magmatic sources and petrogenesis and further to reveal the lithospheric evolution of the craton. Zircon U Pb dating, combined with the field observations and petrographic features, shows that at least 5 episodes of granites can be identified in the Kalaqin Batholith, i.e., 246 Ma monzogranite in the north, 234–227 Ma medium-grained monzogranite in the southwest, 224–221 Ma syenogranites in the north, 211 Ma granites in the south-central part and 206 Ma coarse-grained to megacrystic monzogranites intruding into the early batholith, and 238–231 Ma for the HIC ultramafic to mafic rocks. The 246 Ma granites have high SiO2 contents, negative whole rock eNd(t) and eHf(t) values, and negative zircon eHf(t) values and high δ18O values (up to 6.55‰), with ancient Nd and Hf model ages, indicating that they were derived from an ancient continental crustal source. However, the 234–221 Ma granites have positive whole rock eNd(t) and eHf(t) values and zircon eHf(t) values, indicating that they were derived from a relatively young crustal source. The granites of later episodes own some transitional isotopic feature and are suggested to be derived from a mixed source. The 238–231 Ma HIC rocks have high MgO contents, primitive mantle-like whole rock eNd(t) and eHf(t) values and zircon eHf(t) values and slightly higher zircon δ18O values than mantle. Zircon Hf O isotopic constraints have further pointed to a mixed origin by depleted mantle and enriched lithospheric mantle for the HIC rocks. Calculation of the two-pyroxene thermobarometer yields crystallizing conditions of gabbronorites at around 1080 °C and 5 kbar, suggesting the emplacement of hot mantle-derived magmas into mid-crustal depth. All of the observations show that the lower continental crust beneath the northern margin of the NCC had been modified from ancient to relatively young by mantle-derived magma underplating during 246–221 Ma, although no solid evidences supporting the direct magmatic linkage were found between the batholith and the HIC. It is suggested that the lithosphere of the northern NCC had been modified and became weakened during 246–221 Ma, which makes the NCC easy to be destructed during late Mesozoic.
- Subjects :
- geography
Underplating
geography.geographical_feature_category
010504 meteorology & atmospheric sciences
Continental crust
Geochemistry
Geology
010502 geochemistry & geophysics
01 natural sciences
Craton
Geochemistry and Petrology
Batholith
Ultramafic rock
Mafic
0105 earth and related environmental sciences
Petrogenesis
Zircon
Subjects
Details
- ISSN :
- 00244937
- Database :
- OpenAIRE
- Journal :
- Lithos
- Accession number :
- edsair.doi...........a0c40327e9dccb2cf86507dc9facf395