Baddeleyite U-Pb Geochronology and Tectonic Significance of the Gabbro in Kalamaili, Eastern Junggar

Man YU; Pengfei DI

doi:10.11872/j.issn.1005-2518.2019.05.678

Highlights

The Kalamaili ophiolite belt is an important component of East Junggar.It extends along the Kalamaili Mountains in NWW direction, extending about 400 km.It is an important tectonic unit in the region. The opening and closing of oceanic separation represented by the ophiolite belt is of great significance to the tectonic evolution of the whole east Junggar region.Previous studies on the age of ophiolite have mainly come from the fossil age of siliceous rocks and the zircon U-Pb age of diabase, gabbro and baddeleyite granite. However,there are few reports on the age of baddeleyite in ophiolite.The Kalamaili ophiolite is mainly composed of peridotite,gabbro,plagiogranite and a small amount of siliceous rock, controlled by the Kalamaili fault, which makes gabbro appear as tectonic block and accompanied by peridotite.Gabbro belongs to the large class of silica-unsaturated rocks. Baddeleyite coexists steadily with pyroxene and olivine, while zircon belongs to silica-saturated, supersaturated minerals and gabbro. The crystallization of baddeleyitee is earlier than that of zircon, which is more representative of the true age of formation of rocks. Therefore, in this study, more than 200 baddeleyite were selected from fresh gabbro exposed in massive form in the western part of ophiolite belt, and 80 of them were selected to make targets and take transparent, reflective and cathodoluminescent photographs.Since baddeleyites are black in the cathodoluminescent photographs, LA-ICP-MS U-Pb dating was carried out at the selected testing sites of the transparent and reflective photographs, and 16 years of good harmony were obtained.Age data ranged from 431 Ma to 444 Ma. The harmonic age of rock ²⁰⁷Pb/²³⁵U-²⁰⁶Pb/²³⁸U is （434.4+2.7）Ma (MSWD=0.87) and the weighted average age of ²⁰⁶Pb/²³⁸U is （436.4+2.5）Ma (MSWD=0.59) calculated by ISOPLOT software. The two ages are consistent within the error range, indicating that the gabbro was formed in early Silurian.Up to now, this age is the earliest one found in the Karamari ophiolitic melange, which indicates that the Karamari oceanic basin began to stretch and form in the early Silurian.That is, the Karamari oceanic basin existed before the closure of the oceanic basin represented by the Zhaheba-Aermantai ophiolite in the north of the basin.

Cite this article

Man YU , Pengfei DI . Baddeleyite U-Pb Geochronology and Tectonic Significance of the Gabbro in Kalamaili, Eastern Junggar[J]. Gold Science and Technology, 2019 , 27(5) : 678 -686 . DOI: 10.11872/j.issn.1005-2518.2019.05.678

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