Gravity Anomalies and Inferred Crustal Structure in the Eastern Mediterranean Sea

Abstract

Gravity data in the eastern Mediterranean area have been compiled from Woods Hole Oceanographic cruises of the R/V Chain in 1964 and 1966, and supplemented by other shipboard and land measurements. Over most of the area, free-air anomalies are negative and Bouguer anomalies are consistently lower, by 50 to 100 mgal, than in the western Mediterranean. Broad negative free-air anomalies (−80 to −240 mgal) and low positive Bouguer anomalies (0 to 80 mgal) follow an arcuate zone, concave northward, south of Crete from western Greece to the Rhodes abyssal plain. Relatively high anomalies (free-air anomaly as high as −60 mgal and Bouguer anomaly of +100 to +140 mgal) centered over the Anaximander seamounts separate the arcuate low south of Crete from a similar trend south of Cyprus that gradually becomes less distinct toward northern Syria. Cyprus is characterized by free-air anomalies greater than 100 mgal, Bouguer anomalies of from +100 to +250 mgal, and some of the world9s largest positive isostatic anomalies (as great as +173 mgal). A crustal-structure model was constructed for a profile south from Turkey, approximately along long. 31°E., toward Egypt. The simulated structure showed a range in depth to the top of the mantle from 23 km beneath the outer margin of the Nile Cone to 34 km beneath the axis of the Mediterranean Ridge. A free-air anomaly gradient of about −1.2 mgal/km to the north over the southern margin of the Mediterranean Ridge corresponds to a downward slope on the crust-mantle interface of about 7° to the north. The thickening of the crust by almost 50 percent north of 34°N. is interpreted as largely due to underthrusting of Mediterranean crust beneath Cyprus, the Anaximander Mountains, and Turkey. A concomitant thick accumulation of sediment may have further downwarped the crust beneath the Mediterranean Ridge.