科研之友
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摘要
Madagascar is a complex, composite geological terrane that occupies an important location in Late Proterozoic plate reconstructions. The recognition in one of the Madagascan terranes of a Stenian to Tonian-aged arc magmatic suite (the Dabolava Suite) demonstrates that its host terrane resided at a plate boundary from c. 1080 to 980 Ma. Gabbroic and granitoid intrusions of the Dabolava Suite are recognized only in the Ikalamavony Domain in west-central Madagascar. The oxygen isotopic compositions of zircon indicate that the parental magmas involved crustal contributions that were fractionated by a hydrological cycle, whereas hafnium isotopic compositions reflect near depleted-mantle signatures with only minor deflection to more crustal values. Together, these trends suggest mantle derivation of parental magmas coupled with upper-crustal assimilation of Stenian-aged pre-existing plutonic and volcanic rocks. These magmatic rocks, together with the coeval sedimentary rocks of the Ikalamavony Group, are taken to represent a subduction-related magmatic arc that formed in an oceanic-arc tectonic setting in the Mozambique Ocean outboard of the Archaean to early Palaeoproterozoic shield of Madagascar. The arc accreted to the older craton before the initiation of the Imorona-Itsindro Suite magmatism at c. 850 Ma that intruded both domains.
- 出版日期2018-1
