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Discovery of a Miocene Mafic Dyke from the Western Hills of Beijing and its Geological Implications
Author(s) -
ZHANG Zhicheng,
HAN Baofu,
WU Tairan
Publication year - 2009
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2009.00060.x
Subject(s) - geology , mafic , basalt , geochemistry , asthenosphere , mantle (geology) , fractional crystallization (geology) , lithophile , olivine , pyroxene , lithosphere , partial melting , paleontology , tectonics
The present study is the first report of a Miocene mafic dyke from the Dahuichang, in the Western Hills of Beijing. The dyke cuts the fossil‐dated Changxindian Formation of Eocene sequences and yields K‐Ar ages of 14–15 Ma. The dyke is fine‐grained diabase and has 49.84%–50.81% SiO 2 and 3.56–3.97% Na 2 O+K 2 O, high TiO 2 (1.65%–1.93%) and MgO (7.36%–9.85%), and low K 2 O (<1.22%) contents, with Na 2 O>K 2 O and slightly varied magnesium numbers (Mg#=55.54–62.74). In trace elements geochemistry, the dyke is very similar to the Miocene basalts from Jining and Hanuoba. The enrichment of light rare earth elements ([La/Yb] N =5.03–6.12) and large ion lithophile elements (LILEs), no negative Eu anomalies, relatively high Cr (265–326 ppm) and Ni (155–262 ppm), and almost constant V concentrations (194–213 ppm) reveal that the composition close to the primary basaltic magma from an enriched‐mantle source, with little crustal contamination and fractional crystallization. The basaltic magma was possibly derived from the upwelling asthenosphere mantle beneath eastern China during the Miocene lithospheric thinning.