Shares in Credit Suisse, one of the world’s largest investment banks, tumbled by 30 percent Wednesday morning, reigniting fears triggered last week by the failure of Silicon Valley Bank that the global financial system could be on the verge of a broader meltdown. The nosedive sent shockwaves through European markets, with other major banks on the continent seeing their share prices get hammered. The collapse in Credit Suisse shares came after the chairman of the Saudi National Bank, which has a 10 percent stake in Credit Suisse, ruled out providing the bank with any further financial assistance. Some analysts say that the latest banking crisis has been triggered by rising interest rates.