SPATIAL AND TEMPORAL RELATIONS BETWEEN CORONAE AND EXTENSIONAL BELTS,NORTHERN LADA-TERRA, VENUS

Preliminary studies of the distribution of coronae and volcanic rises on Venus show that many of these features tend to cluster along zones of rifting and extension. The plains north of Lada Terra are crossed b y two such extensional belts. Each belt is composed of grabens, ridges , faults, volcanic flows, coronae, and coronalike features. The longer and more prominent belt is the NW trending Alpha-Lada extensional bel t, which is over 6000 km long and 50-200 km wide, and includes the cor onae Eve, Tamfana, Carpo, Selu, Derceto, Otygen, and an unnamed corona south of Otygen. The second belt is the NNE trending Derceto-Quetzalp etlatl extensional belt, which is about 2000 lan long and in places ov er 300 km wide, and includes the coronae Sarpanitum, Eithinoha, and Qu etzalpetlatl. The two belts intersect at the 1600 x 600 km wide Dercet o volcanic plateau. It is apparent that deformation along the two belt s overlapped in time, though deformation along the Alpha-Lada extensio nal belt probably continued after the deformation along the Derceto-Qu etzalpetlatl extensional belt terminated. In certain areas, volcanism originated in grabens within the extensional belts, whereas in other a reas, such as in Eve, Selu, Derceto, and Quetzalpetlatl, volcanism ori ginated in the coronae and flowed into the lower parts of the extensio nal belts. Regional extension has affected the evolution of all the co ronae at some stage of their development. Regional deformation occurre d before the initiation of Derceto and Eithinoha and after the initiat ion of Carpo, Tamfana, Otygen, and Sarpanitum. It is thus unlikely tha t coronae formation along the belts is solely a consequence of the reg ional extension, and it is also unlikely that regional extension has b een caused solely by the coronae. No corona along the belts was formed subsequent to the cessation of the regional extension. We therefore s uggest that the regional extension and the coronae are interrelated. S ome of the coronae may have determined the location of the surface exp ression of the regional extension, whereas the locations of other coro nae may have been influenced by the concentration of regional extensio nal stresses.