Question 3 of 10: Question 3, Part 1: Plate Boundaries on a World Map

Question 3, Part 1: Plate Boundaries on a World Map (5 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Given. World map (source page 4, Pacific-centred: Africa and Europe at the left edge, the Americas at the right): region "1" covers northern Eurasia (Siberia/Europe); region "2" covers Australia and the adjoining southern ocean floor; region "3" covers the broad central-to-western Pacific basin. Boundary "A" sits on the northern Pacific rim between region 3 (Pacific) and the North American Plate (the Aleutian arc/trench, just SW of Alaska); boundary "B" sits in the South Atlantic between South America (west) and Africa (east).

Find. (a) The identity of plates 1, 2, 3; (b) the tectonic-boundary type at A and B.

Approach. Match each numbered region's continental/oceanic content and each lettered boundary's plate-tectonic setting (trench vs. ridge) to the standard present-day plate map.

(a) Plate identification. Plate 1 = Eurasian Plate (carries Europe and northern/central Asia; the label sits over Siberia, west of the Kamchatka–Japan trenches). Plate 2 = Indo-Australian (Australian) Plate (carries Australia and the surrounding Indian/Southern Ocean floor). Plate 3 = Pacific Plate (the large, almost entirely oceanic plate occupying the central and western Pacific basin – the largest plate on Earth).

(b) Boundary types. Boundary A (convergent/subduction). This lies along the Aleutian arc-trench system, where the oceanic Pacific Plate (3) is subducting beneath the North American Plate (to the north) – a convergent (destructive) boundary, marked by a deep oceanic trench and an associated volcanic arc. Boundary B (divergent). This lies on the Mid-Atlantic Ridge between South America and Africa – a divergent (constructive) boundary where seafloor spreading creates new oceanic crust and pushes the South American and African Plates apart.