The evolution of rifting on the volcanic margin of the Pelotas Basin and the contextualization of the Paran谩-Etendeka LIP in the separation of Gondwana in the South Atlantic

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• 作者：Juliano Magalh茫es Stica ; Pedro Victor Zal谩n ; Andr茅 Luiz Ferrari
• 关键词：Pelotas Basin ; Paraná ; &ndash ; Etendeka LIP ; Volcanic margin ; Rifting evolution ; SDR ; Breakup unconformity ; Post-rift unconformity ; Magnetic anomaly
• 刊名：Marine and Petroleum Geology
• 出版年：February, 2014
• 年：2014
• 卷：50
• 期：Complete
• 页码：1-21
• 全文大小：10553 K

文摘

The Pelotas Basin is the classical example of a volcanic passive margin displaying large wedges of seaward-dipping reflectors (SDR). The SDR fill entirely its rifts throughout the basin, characterizing the abundant syn-rift magmatism (133-113聽Ma). The Paran谩-Etendeka Large Igneous Province (LIP), adjacent to west, constituted the pre-rift magmatism (134-132聽Ma). The interpretation of ultra-deep seismic lines showed a very different geology from the adjacent Santos, Campos and Esp铆rito Santo Basins, which constitute examples of magma-poor passive margins. Besides displaying rifts totally filled by volcanic rocks, diverse continental crustal domains were defined in the Pelotas Basin, such as an outer domain, probably constituted by highly stretched and permeated continental igneous crust, and a highly reflective lower crust probably reflecting underplating.

The analysis of rifting in this portion of the South Atlantic is based on seismic interpretation and on the distribution of regional linear magnetic anomalies. The lateral accretion of SDR to the east towards the future site of the breakup and the temporal relationship between their rift and sag geometries allows the reconstitution of the evolution of rifting in the basin. Breakup propagated from south to north in three stages (130-127.5; 127.5-125; 125-113聽Ma) physically separated by oceanic fracture zones (FZ). The width of the stretched, thinned and heavily intruded continental crust also showed a three-stage increase in the same direction and at the same FZ. Consequently, the Continental-Oceanic Boundary (COB) shows three marked shifts, from west to east, from south to north, resulting into rift to margin segmentation. Rifting also propagated from west to east, in the direction of the final breakup, in each of the three segments defined. The importance of the Paran谩-Etendeka LIP upon the overall history of rupturing and breakup of Western Gondwanaland seems to have been restricted in time and in space only to the Pelotas Basin.