Two major types of passive margins are recognized, i.e. volcanic and non-volcanic, without proposing distinctive mechanisms for their formation. Volcanic passive margins are associated with the extrusion and intrusion of large volumes of magma, predominantly mafic, and represent distinctive features of Larges Igneous Provinces, in which regional fissural volcanism predates localized syn-magmati...

Hornblende occurs in some andesitic and basaltic rocks of calc-alkaline affini1y, where it is commonly associated with olivine. The texture, eruption history, and composition are interpreted to indicate that hornblende commonly forms as a product of reaction between olivine and basaltic and andesitic liquids. The natural hornblendes probably formed within the crust at temperatures between 960o ...

Identification by Bhattacharya et al. (1994) of seafloor spreading type magnetic anomalies in the basin lying between Laxmi Ridge in the Arabian Sea and the Indian continent necessitates a change in plate tectonic reconstruction. Naini and Talwani (1982) named this basin the Eastern Basin and we will continue to use this term in this paper. Others, in the literature, have called this the Laxmi ...

T h e problem of the origin of the cont inental crust can be resolved into two fundamenta l quest ions: (1) the lo­ cation and mechani sms of init ial m a n t l e extract ion of the primitive crust and (2) the processes by which this primitive crust is converted into the cont inental crust that presently exists . W e know that Archean cont inen­ tal crust is compos i t iona l ly dist inct from ...

GSA Today: v. 16, no. 2, doi: 10.1130/1052-5173(2006)016<4:TIAACM>2.0.CO;2 INTRODUCTION Forty years ago, the eastern margin of North America inspired Tuzo Wilson (1966) to ask, “Did the Atlantic close and then re-open?” The Wilson cycle of closing and opening of ocean basins incorporates the cyclic assembly and breakup of supercontinents. Alternate processes of extension and compression of cont...

tertiary intrusive granitoids within the lut block in the khorasan razavi and south khorasan provinces are mainly sub-volcanic with porphyry texture and their composition varies from granite to diorite but monzonite is dominant. with the exception of hired, these are classified as belonging to the magnetite-series of i-type granitoids. chemically, these rocks are meta-aluminous. those with mine...