Abstract
Abstract New rock dredge samples supply key information to establish the tectonic and geological framework of the northern two‐thirds of the 95% submerged Zealandia continent. The R/V Investigator voyage IN2016T01 to the Fairway Ridge, Coral Sea, obtained poorly sorted poly‐lithologic pebbly to cobbly sandstones, well sorted fine grained sandstones, mudstones, bioclastic limestones, and basaltic lavas. Post‐cruise analytical work comprised petrography, whole rock geochemical and Sr and Nd isotopic analyses, and U‐Pb zircon, Rb‐Sr, and Ar‐Ar geochronology. A Fairway Ridge cobbly sandstone has a ∼95 Ma (early Late Cretaceous) depositional age; two biotite granite cobbles are 111 ± 1 and 128 ± 1 Ma in age, and some volcanic pebbles are also likely Early Cretaceous. Fairway Ridge basalts have intraplate alkaline chemistry and are of Late Eocene age (∼40–36 Ma). By analogy with South Zealandia, we interpret strong positive continental magnetic anomalies of North Zealandia to mainly result from Late Cretaceous to Cenozoic intraplate basalts, many of them rift‐related lavas. A new basement geological map of North Zealandia shows the position of the Mesozoic Gondwana magmatic arc axis (Median Batholith) and other major geological units. This study completes onland and offshore reconnaissance geological mapping of the entire 5 Mkm 2 Zealandia continent.
Plain Language Summary To support investigations of the Zealandia continent, we dredged rock samples from the seabed of the Fairway Ridge, Coral Sea. Basalts, sandstones, and pebbles from the sandstones were analyzed and dated. The sandstones are Late Cretaceous (∼95 million years old) and contain Early Cretaceous (130–110‐million‐year‐old) granite and volcanic pebbles. The basalts are Eocene (∼40 million years old). We have used these results, along with regional magnetic anomaly data, and information from other studies to make a map of the undersea geology of North Zealandia. Onland and offshore reconnaissance geological mapping of the entire 5 Mkm 2 Zealandia continent is now complete.
Key Points Basalts and pebbly to cobbly sandstones have been dredged from the Fairway Ridge, Coral Sea Dating of the rocks and interpretation of magnetic anomalies allow mapping of major geological units across North Zealandia This work completes offshore reconnaissance geological mapping of the entire 5 million square km Zealandia continent