TY - JOUR
T1 - Geochemistry and Os-Nd-Sr isotopes of the Gaositai Alaskan-type ultramafic complex from the northern North China craton
T2 - Implications for mantle-crust interaction
AU - Chen, Bin
AU - Suzuki, K.
AU - Tian, W.
AU - Jahn, B. M.
AU - Ireland, T.
PY - 2009
Y1 - 2009
N2 - We report petrological, chemical and Os-Nd-Sr isotopic data for the Gaositai ultramafic complex from northern North China craton (NCC) to reveal its petrogenesis. The complex shows features of Alaskan-type intrusions, including (1) the concentric zoning from dunite core, to clinopyroxenite and hornblendite in the rim, and the common cumulative textures; (2) the abundance of olivine, clinopyroxene and hornblende, and the scarcity of orthopyroxene and plagioclase, and (3) the systematic decrease in Mg# of ferromagnesian phases from core to rim, accompanied by the Fe-enrichment trend of accessory spinel. The different rock types show highly varied, radiogenic Os isotopic ratios (0.129-5.2), and unradiogenic Nd isotopic composition (ε Nd(t) = -8 to -15), but are homogeneous in I Sr ratios (0.7054-0.7066). The ( 187Os/ 188Os) i ratios are found to be anti-correlated with ε Nd(t) values and whole-rock Mg# as well. These data suggest significant crustal contamination during magma evolution. The crustal contaminants are dominantly Archean mafic rocks in the lower crust, and subordinate TTG gneisses at shallower crustal levels. The parental magma was hydrous picritic in composition, derived from an enriched lithospheric mantle source above a subduction zone. The zoned pattern of the complex formed probably through "flow differentiation" of a rapidly rising crystal mush along a fracture zone that was developed as a result of lithospheric extension in a back-arc setting in the northern margin of the NCC at ca. 280 Ma.
AB - We report petrological, chemical and Os-Nd-Sr isotopic data for the Gaositai ultramafic complex from northern North China craton (NCC) to reveal its petrogenesis. The complex shows features of Alaskan-type intrusions, including (1) the concentric zoning from dunite core, to clinopyroxenite and hornblendite in the rim, and the common cumulative textures; (2) the abundance of olivine, clinopyroxene and hornblende, and the scarcity of orthopyroxene and plagioclase, and (3) the systematic decrease in Mg# of ferromagnesian phases from core to rim, accompanied by the Fe-enrichment trend of accessory spinel. The different rock types show highly varied, radiogenic Os isotopic ratios (0.129-5.2), and unradiogenic Nd isotopic composition (ε Nd(t) = -8 to -15), but are homogeneous in I Sr ratios (0.7054-0.7066). The ( 187Os/ 188Os) i ratios are found to be anti-correlated with ε Nd(t) values and whole-rock Mg# as well. These data suggest significant crustal contamination during magma evolution. The crustal contaminants are dominantly Archean mafic rocks in the lower crust, and subordinate TTG gneisses at shallower crustal levels. The parental magma was hydrous picritic in composition, derived from an enriched lithospheric mantle source above a subduction zone. The zoned pattern of the complex formed probably through "flow differentiation" of a rapidly rising crystal mush along a fracture zone that was developed as a result of lithospheric extension in a back-arc setting in the northern margin of the NCC at ca. 280 Ma.
KW - Alaskan-type
KW - North China craton
KW - Os-Nd-Srisotopes
KW - Ultramafic rocks
UR - http://www.scopus.com/inward/record.url?scp=70349224334&partnerID=8YFLogxK
U2 - 10.1007/s00410-009-0404-7
DO - 10.1007/s00410-009-0404-7
M3 - Article
SN - 0010-7999
VL - 158
SP - 683
EP - 702
JO - Contributions to Mineralogy and Petrology
JF - Contributions to Mineralogy and Petrology
IS - 5
ER -