TITLE:
Chronology, Geochemistry and Geological Significance of Haizi Bimodal Intrusive Bodies in Wuding District, Central Yunnan
AUTHORS:
Bin Yang, Weiqing Wang, Guochen Dong, Yang Guo, Zizheng Wang, Lin Hou
KEYWORDS:
Hai Zi, Bimodal Intrusions, Geochemistry and Geochronology, Geological Significance, Central Yunnan
JOURNAL NAME:
Open Journal of Geology,
Vol.5 No.5,
May
8,
2015
ABSTRACT: The Haizi diabase-granite
porphyry composite rock mass is located in the Wuding-Yanjing taphrogenic
trough within the Paleoproterozoic Kangdian fault-uplift zone. According to
field observations, the diabase is divided into two types: central facies and
marginal facies; the granite porphyry directly contacts the central facies of
diabase without transitional intermediate rock. In order to disclose its geological
and petrological significances, this paper carried out the LA-ICP-MS zircon
U-Pb dating and geochemical investigation on both masses of Haizi diabase and
granite porphyry. The results showed that the207Pb/206Pb
weighted average age of granite porphyry is 1764 ± 18 Ma and diabase 1765 ± 5.4
Ma. The geochemical investigations revealed that the Haizi diabase is a kind of
high-potassium alkaline basalt and the granite porphyry a kind of low-potassium
rhyolite, both enriched with high field intensity elements and depleted in
large-ion lithophile elements; there is obvious component intermittence between
the diabase and the granite porphyry, both being bimodal and showing
characteristics of continental rift valley magmatite. Thein situHf isotope of dating zircon showed
that mantle materials participated in the formation and emplacement of Haizi
granite porphyry and crust materials participated in the formation of diabase.
This meant that crustal remelting and accretion of new crust occurred in this region
in the 1.7 Ga period. It can be therefore inferred that the Haizi bimodal
intrusive rock came into being due to the breakup of Kunyang rift valley and
rapid ascent of mantle materials in the 1.7 Ga period, which echoed the global
Columbia supercontinent breakup and was the first petrological record of that
breakup found at the southwest margin of Yangtze platform.