Site 1162 is located in Zone A ~90 km east of the ~127°E fracture zone and 40 km south of Site 1161. The seafloor magnetic age in this area is ~18 Ma. The site is located in a deep, wide, sediment-filled basin associated with an extinct westward-directed propagating rift. Site 1162 was selected as a complement to Site 1161 for two reasons: (1) it constrains the duration of the incursion of Indian-type mantle into Zone A that is recorded at Site 1161, and (2) it is located within the propagating rift valley, complementing the transferred lithosphere location of Site 1161. In both respects, the site is important to our understanding of the temporal and spatial limits of Indian-type mantle beneath the western part of Zone A.
Hole 1162A was spudded in 5464 m water depth and was washed through ~333 m of sediment, recovering a single wash barrel containing siliceous clay with a short interval containing tube casts and black chert clasts. Rotary drilling continued 31.4 m into volcanic basement, recovering 2.6 m (~8%) of mixed igneous clasts overlying a polymict fault breccia containing an array of clasts that can be divided into two metamorphic types. The first type is characterized by greenschist facies mineral assemblages (actinolite, chlorite, quartz, and epidote). Primary rock types include basalt, diabase, gabbro, and cataclasite. The second type is characterized by pervasive low-temperature alteration. A variety of basalts are more or less completely replaced by clay, and basaltic glass is extensively palagonitized. The distinctive mottled red and green breccia matrix is made up of finely divided, extensively altered igneous material and cemented by rhombohedral dolomite. Because it was unlikely to yield fresh volcanic samples suitable for analysis, Hole 1162A was abandoned.
Hole 1162B was spudded 200 m north of Hole 1162A and was washed through ~348 m of sediment, recovering 3.8 m of greenish gray clay and an unconsolidated breccia with abundant altered basaltic clasts. Rotary drilling continued 58.9 m into basement, recovering 9.9 m (~17%) of dolomite (Unit 1) overlying dolomite-cemented basalt breccia (Unit 2). Basaltic clasts range from aphyric to highly plagioclase ± olivine phyric and are extensively altered, with groundmass replaced by clay throughout the hole.
A single glass sample from Hole 1162B was analyzed on board by inductively coupled plasma-atomic emission spectrometry (ICP-AES). As no fresh clean glass was recovered at this site, the analyzed sample contains 25%-30% spherulites. Its Ba content is at the high end and Zr/Ba is just outside the low end of the 0- to 7-Ma Pacific-type array. We interpret this as demonstrating a Pacific-type mantle affinity for this site. This confines the incursion of Indian-type mantle beneath Site 1161 to an ~80-km-wide region between Sites 1158 and 1162. Indian mantle was, therefore, present beneath this part of western Zone A for no more than 2-3 m.y., suggesting that the arrival of the propagating rift reintroduced Pacific-type mantle beneath the spreading axis.
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